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If Xmax shouldn't be exceeded, why have a Xlim?

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Topic: If Xmax shouldn't be exceeded, why have a Xlim?
Posted By: rich_gale
Subject: If Xmax shouldn't be exceeded, why have a Xlim?
Date Posted: 10 January 2011 at 10:17pm
why do manufacturers publish a xlim/xmech figure alongside an xmax figure, often the xlim/xmech is 4 times the travel of the xmax.  if you shouldnt drive a speaker past its xmax, why can they cater for further excursion?

what % excursion over the published xmax is considered too much?  i have had a pd186 sounding twice as loud with about 1" excursion than when it was within its 9mm xmax limit.  and it sounded no less defined than when keeping within xmax.  why in real life terms (not boring theoretical paperwork crap) should i not drive a speaker past its xmax???    


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REFLEX ALL THE WAY.... (however, im playing with horns again...) That ok Mister Valiant? :)



Replies:
Posted By: daywalk3r
Date Posted: 10 January 2011 at 10:24pm
Originally posted by rich_gale rich_gale wrote:

.. why in real life terms (not boring theoretical paperwork crap) should i not drive a speaker past its xmax???


One word:
DISTORTION

If a more "boring theoretical paperwork crap" answer is needed, willing to elaborate Smile


Posted By: MunkeyQ
Date Posted: 10 January 2011 at 10:30pm
Originally posted by daywalk3r daywalk3r wrote:

Originally posted by rich_gale rich_gale wrote:

.. why in real life terms (not boring theoretical paperwork crap) should i not drive a speaker past its xmax???


One word:
DISTORTION

If a more "boring theoretical paperwork crap" answer is needed, willing to elaborate Smile

Yep...

Xmax is the excursion keeping the voice coil immersed in its magnetic field, where the drive is linear. Over xmax, the voice coil leaves the field and is no longer controlled by the magnet, meaning distortion increases immensely.

Xmech/Xlim is when the suspension mechanically reaches its limits and is damaged.


Posted By: JR.junior
Date Posted: 10 January 2011 at 10:37pm
Originally posted by rich_gale rich_gale wrote:

why do manufacturers publish a xlim/xmech figure alongside an xmax figure, often the xlim/xmech is 4 times the travel of the xmax.  if you shouldnt drive a speaker past its xmax, why can they cater for further excursion?

what % excursion over the published xmax is considered too much?  i have had a pd186 sounding twice as loud with about 1" excursion than when it was within its 9mm xmax limit.  and it sounded no less defined than when keeping within xmax.  why in real life terms (not boring theoretical paperwork crap) should i not drive a speaker past its xmax???    
 
because you'll have too much coil windings out of the magnet gap x time, that can looks like that...than.
 


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Support the scoop technology, larger mouth plays louder!


Posted By: S DeXter
Date Posted: 10 January 2011 at 10:41pm
Drivers are often driven out of their Xmax. The magnetic fields can extend much further than xmax. Motor design alters the rate of distortion outside the gap (underhung designs for example suffer badly from this).

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Enjoy your self...... It's later than you think.......


Posted By: daywalk3r
Date Posted: 10 January 2011 at 10:56pm
Originally posted by MunkeyQ MunkeyQ wrote:

Xmech/Xlim is when the suspension mechanically reaches its limits and is damaged.

.. or when the voice coil slams into the back plate, which is also a thing you would normaly NOT want it to do Smile


Posted By: Pasi
Date Posted: 10 January 2011 at 10:58pm
Originally posted by S DeXter S DeXter wrote:

Drivers are often driven out of their Xmax. The magnetic fields can extend much further than xmax. Motor design alters the rate of distortion outside the gap (underhung designs for example suffer badly from this).


Magnetic fields do extend outside gap of course and it also moves a bit along with voice coil. Here is model from my latest 8" plateset design. Flux profile, magnet stength isn't right since i don't have specs for right magnet type. And i was anyway more interested about profile at this point. Goal is to make it as symmetrical as possible to reduce distortion.




Posted By: airbell
Date Posted: 10 January 2011 at 10:58pm
If the voicecoil is out of the xmax, its not like you lose the total control, its just that you lose the more control the more you are out of the xmax, what means distortion.
a good example why there is a xlim is the ciare 12sw.
it has a very big true xmax about 11,5mm, but unfortunately xlim is just slightly biggerOuch
the proof is my blown ciare, the voicecoil hit the magnet as i pushed it too far in the wrong enclosure,
now its damaged, but the wire in the coil is still fine -.-

I also think, but i have no proofs, its just my personal opinion, that
some manufactures are not exactly about there xmax specs,
coz some speakers with lower xmax seem to push more air than other speakers with a higher rated xmax,
even if they are in the same type of enclosure with the same tuning.


Posted By: airbell
Date Posted: 10 January 2011 at 11:01pm
btw the irony about it is that the ciare 12sw has no rated xlim in its specs sheedClown


Posted By: rich_gale
Date Posted: 10 January 2011 at 11:09pm
nice to see not everyone is blasting on about distortion.  going out of xmax does not add distortion from what i have heard in real life situations, using well engineered woofers.  running out of amp headroom makes this distortion, not exceeding xmax.  exceeding xlim will produce distortion.   going 3-5mm over a 9mm xmax still means a cabinet will go lower or louder or both, and i dont think the negative effects are anywhere near what most people go on about.  

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REFLEX ALL THE WAY.... (however, im playing with horns again...) That ok Mister Valiant? :)


Posted By: rich_gale
Date Posted: 10 January 2011 at 11:11pm
Originally posted by JR.junior JR.junior wrote:

Originally posted by rich_gale rich_gale wrote:

why do manufacturers publish a xlim/xmech figure alongside an xmax figure, often the xlim/xmech is 4 times the travel of the xmax.  if you shouldnt drive a speaker past its xmax, why can they cater for further excursion?

what % excursion over the published xmax is considered too much?  i have had a pd186 sounding twice as loud with about 1" excursion than when it was within its 9mm xmax limit.  and it sounded no less defined than when keeping within xmax.  why in real life terms (not boring theoretical paperwork crap) should i not drive a speaker past its xmax???    
 
because you'll have too much coil windings out of the magnet gap x time, that can looks like that...than.
 
come on man...:)  we all know that coil fried because of a continued clipping amp or a huge peak.  that woofer looks like a toy.  very rarely do you see a 186 or 1850 coil in this state


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REFLEX ALL THE WAY.... (however, im playing with horns again...) That ok Mister Valiant? :)


Posted By: Pasi
Date Posted: 10 January 2011 at 11:14pm
When going over Xmax, harmonic distortion increases significantly, no matter what you say. Completely different matter wheter you can hear it or do care about it. Of course you can do that, it doesn't cause any damage to speaker, or at least to well designed speaker. But sound quality does suffer.


Posted By: rich_gale
Date Posted: 10 January 2011 at 11:20pm
Originally posted by Pasi Pasi wrote:

When going over Xmax, harmonic distortion increases significantly, no matter what you say. Completely different matter wheter you can hear it or do care about it. Of course you can do that, it doesn't cause any damage to speaker, or at least to well designed speaker. But sound quality does suffer.

maybe my question should be "in real life situations do the negative effects caused by the increased harmonic distortion created by going over xmax outweight the positives such as being able to play lower and louder, shifting more air, etc, when playing in a room where the listeners' hearing has reached his dynamic limit anyway and will be unable to notice the difference?"  

id rather take 4 boxes and run them hard (within their mechanical and thermal capability) than take 6 boxes and run them carefully (especially when considering how vastly over engineered modern 18" woofers are.)


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REFLEX ALL THE WAY.... (however, im playing with horns again...) That ok Mister Valiant? :)


Posted By: JR.junior
Date Posted: 10 January 2011 at 11:23pm
Don't take it so serious, Rich.  You know what's about.. the coil part, with black burned wire, was out of the gap. 

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Support the scoop technology, larger mouth plays louder!


Posted By: Pasi
Date Posted: 10 January 2011 at 11:34pm
Originally posted by rich_gale rich_gale wrote:


maybe my question should be "in real life situations do the negative effects caused by the increased harmonic distortion created by going over xmax outweight the positives such as being able to play lower and louder, shifting more air, etc, when playing in a room where the listeners' hearing has reached his dynamic limit anyway and will be unable to notice the difference?"  

id rather take 4 boxes and run them hard (within their mechanical and thermal capability) than take 6 boxes and run them carefully (especially when considering how vastly over engineered modern 18" woofers are.)


You don't happen to be DJ?

Dynamic range for human hearing is about 140dB. I guess nobody cares about distortion anymore if you are playing louder than that, there is no-one left in the room.

Taking more off-topic, but why is it that it has to be so loud? Is loudness only way to measure how good system is because I always tought that it's more like comparing who has larger... "male organ". Wink


Posted By: airbell
Date Posted: 10 January 2011 at 11:45pm
arrr...i think its an interestic topic, and he didnt want to start sth like "loudness is all that counts"...
i can understand, if you have limited transport space, limited money, limited location space, and the audience expect a certain level of loudness, i wouldnt care about 3-4% or even more distortion too, instead of driving 2 times the way to get another 2 speakers and amplifiers...

well, a lot people quote rog, that distortion will increase dramatically when hitting the xmax,
but, it would be very interesting to know how much it really is, when lets say, hitting it 20% for example...!


Posted By: rich_gale
Date Posted: 10 January 2011 at 11:56pm
Originally posted by airbell airbell wrote:

arrr...i think its an interestic topic, and he didnt want to start sth like "loudness is all that counts"...
i can understand, if you have limited transport space, limited money, limited location space, and the audience expect a certain level of loudness, i wouldnt care about 3-4% or even more distortion too, instead of driving 2 times the way to get another 2 speakers and amplifiers...

well, a lot people quote rog, that distortion will increase dramatically when hitting the xmax,
but, it would be very interesting to know how much it really is, when lets say, hitting it 20% for example...!

/\ exactly.  i have never owned a rig where it could be run with more than 3db headroom in the situations they were used in.  usually the DDT compression is saving me from clipping on every kickdrum.  and most on here im sure will agree.  it was only when i joined sp that i started to worry so much about staying within xmax and i just realised all the computer predictions go out the window when the crowd want it louder.


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REFLEX ALL THE WAY.... (however, im playing with horns again...) That ok Mister Valiant? :)


Posted By: Pasi
Date Posted: 10 January 2011 at 11:57pm
Originally posted by airbell airbell wrote:

arrr...i think its an interestic topic, and he didnt want to start sth like "loudness is all that counts"...
i can understand, if you have limited transport space, limited money, limited location space, and the audience expect a certain level of loudness, i wouldnt care about 3-4% or even more distortion too, instead of driving 2 times the way to get another 2 speakers and amplifiers...

well, a lot people quote rog, that distortion will increase dramatically when hitting the xmax,
but, it would be very interesting to know how much it really is, when lets say, hitting it 20% for example...!


Or Rog quotes well known truth Wink

I'm doing some measurements with subs tomorrow anyway, i'll try to demonstrate this also. Not promising anything, only very strict maybe.


Posted By: S DeXter
Date Posted: 11 January 2011 at 12:00am
When dealing with subwoofers, distortion isn't such an issue. Group delay can be more objectionable (bandpass subwoofers) than distortion.

If you are pushing the boundaries, SPL is always very important when dealing with subwoofers.

SPL and extension are the keys of subwoofery. Distortion is often masked by natural harmonics (within reason).


Posted By: Centauri
Date Posted: 11 January 2011 at 12:23am
Originally posted by S DeXter S DeXter wrote:

When dealing with subwoofers, distortion isn't such an issue.


I beg to differ on that.  Distortion in subs isn't perceived as a harsh sound like mid/hi distortion, but rather as additional "meat" in the low mid area, and many people believe that's what it should sound like as they have never heard any different.  This extra "meat" adds to the real sound in this low mid area, prompting the pulling down of graphics sliders, which only serves to reduce the real sound and leave indistinct mud.  With things like vocals and bass guitar now being not as distinct, the tendency then is to increase the top end to get it "clearer".  An increase in top end is then perceived as an overall volume increase, so the low end is pushed up further to try and match it, resulting in more generated harmonic distortion.  The whole thing can then end up being a loud, harsh, muddy, unpleasant  experience which could have been avoided by using low distortion subs.  I hear this result far too often.

However, pushing past Xmax a small amount on transients shouldn't be too much of an issue.


Posted By: S DeXter
Date Posted: 11 January 2011 at 12:59am
Originally posted by Centauri Centauri wrote:

Originally posted by S DeXter S DeXter wrote:

When dealing with subwoofers, distortion isn't such an issue.


I beg to differ on that.  Distortion in subs isn't perceived as a harsh sound like mid/hi distortion, but rather as additional "meat" in the low mid area, and many people believe that's what it should sound like as they have never heard any different.  This extra "meat" adds to the real sound in this low mid area, prompting the pulling down of graphics sliders, which only serves to reduce the real sound and leave indistinct mud.  With things like vocals and bass guitar now being not as distinct, the tendency then is to increase the top end to get it "clearer".  An increase in top end is then perceived as an overall volume increase, so the low end is pushed up further to try and match it, resulting in more generated harmonic distortion.  The whole thing can then end up being a loud, harsh, muddy, unpleasant  experience which could have been avoided by using low distortion subs.  I hear this result far too often.

However, pushing past Xmax a small amount on transients shouldn't be too much of an issue.


I think its a bit of an extreme scenario... I thought the end of the world was coming half way through that post...!

Yes, lets not forget driving out of xmax will have more of a compressive effect than noticeable distortion to begin with.

The majority of 2x18" boxes are driven out of their xmax.... but they don't sound bad.

Also, I don't think distortion raises as drastically as people say out of xmax, there must be an experiment some where on the web.....


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Enjoy your self...... It's later than you think.......


Posted By: Centauri
Date Posted: 11 January 2011 at 1:10am
Originally posted by S DeXter S DeXter wrote:


The majority of 2x18" boxes are driven out of their xmax.... but they don't sound bad.


I think they do.  It's all about what you are used to - when you have experienced clean bass, you want more and will not be satisfied with harmonic distortion.

Originally posted by S DeXter S DeXter wrote:

Also, I don't think distortion raises as drastically as people say out of xmax, there must be an experiment some where on the web.....


Try setting up a measuring mic and RTA, and feed a 40Hz sine wave into a variety of boxes - it is very surprising the levels of 80Hz and 120Hz that show up at even moderate volume levels.


Posted By: audiomik
Date Posted: 11 January 2011 at 1:49am
Re: "Try setting up a measuring mic and RTA, and feed a 40Hz sine wave into a variety of boxes - it is very surprising the levels of 80Hz and 120Hz that show up at even moderate volume levels."

Fully agree with this approach, however non-linearity due to the changing magnetic field as the voice-coil moves through it can be a cause of additional third order inter-modulation effects; which as they are not directly 'related' to fundamental input frequencies are often perceived by listeners as harshness.....
Unfortunately these tend not to show up so well with 1/3 octave analysis.
Some more info better explained here:
http://www.libinst.com/close3rd.htm - http://www.libinst.com/close3rd.htm
and no doubt much more elsewhere.....

This partly explains the rationale of specifying Xmax against a Total Harmonic Distortion figure and not simply as a physical limit.....

Mik

-------------
Warning! May contain Nuts
plus springs, washers, screws, etc, etc.


Posted By: _djk_
Date Posted: 11 January 2011 at 2:30am
.

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djk


Posted By: Elliot Thompson
Date Posted: 11 January 2011 at 1:06pm
Those who are constantly concerning them selves about xmax don’t have enough loudspeakers to begin with. These individuals are trying to extract every bit of SPL using 1 – 4 bins in a large environment long-term. If you are toting 8 bins and above, xmax is not a big concern for you have enough surface area to get the job done with very little cone movement.

I am not concerned about xmax for I use more than enough bass bins to ensure I have enough headroom. Id rather have a 9 mm xmax driver with high efficency, than a 15 mm xmax driver with low efficency.

X-mechanical Limit relates to the spider, and surround than the voice coil. If anyone had the pleasure to destroy a speaker based on exceeding the x-mechanical limit, you will discover the cone, spider, and/or surround is the root of the failure. The coil is not damaged due to not exceeding the long-term thermal limit but the short-term mechanical limit.   

Best Regards,


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Elliot Thompson


Posted By: audiomik
Date Posted: 11 January 2011 at 1:51pm
Here are a couple of results I obtained this morning using a two tone sine wave signal source and then looking at the current frequency spectrum feeding a 'speaker which was driven a little over it's Xmax:
1) Twin input Frequency spectrum for reference purposes, 75Hz at +15dB and 330Hz at -5dB, cursor on the 330Hz fundamental signal:

2) (above) showing the spectrum of the Amplifier Output Current into the test 'speaker with 25volts RMS output which is well below any Amplifier clipping but exceeds the rated power of the test 'speaker and thus it's Xmax..Note the 'massive' amount of spurious current components which are both harmonic distortion products of the two input sine waves as well as numerous Intermodulation products; since the current drawn from the Amplifier by the 'speaker is not linear when Xmax is exceeded due to the change in impedance when the coil leaves the magnet gap....... sounded 'nasty'!

3) A 'reference' spectrum with 10volts RMS output from the Amplifier is below, cursor over the first Harmonic of the 75Hz sine wave (Edit: due to Amplifier crossover distortion) but noticeably reduced other distortion products. (please be aware of the scaling of this result)


Anyway, interesting results as to what happens when Xmax is exceeded in terms of high levels of distortion appearing in the current being delivered to or reflected back by the 'speaker's voice coil. It should be remembered that the Current is the actual 'driving force' for the coil and that this is directly proportional to the distortion of the sound output from the 'speaker.

Now to try and answer the point regarding having Xlim as well as Xmax; this could be obvious from the above as the tested 'speaker shows substantial increase in distortion above Xmax which might be taken as 'acceptable' up to a limit of Xlim.
IE: the acceptable (??) distortion limit is Xlim whereas the onset of distortion should be considered best as Xmax.
A useful link in fairly simple terms at: http://www.subwoofer-builder.com/xmax.htm - Xmax and Xlim

So there you are - with spectrum analysis pics to demonstrate what happens
Mik

-------------
Warning! May contain Nuts
plus springs, washers, screws, etc, etc.


Posted By: Elliot Thompson
Date Posted: 11 January 2011 at 2:20pm
Your test is nice.

However, the variabilities are endless when we are talking x-mechanical limits. Unless we are all using the same loudspeakers and cabinets your results are more of an estimate and not guaranteed.

Best Regards,

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Elliot Thompson


Posted By: rich_gale
Date Posted: 11 January 2011 at 2:20pm
thanks for all the good replies:)  and cheers MIK for doing the analysis.  I'll properly look at it when im out of work later on.  

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REFLEX ALL THE WAY.... (however, im playing with horns again...) That ok Mister Valiant? :)


Posted By: audiomik
Date Posted: 11 January 2011 at 2:41pm
Originally posted by Elliot Thompson Elliot Thompson wrote:

Your test is nice. However, the variabilities are endless when we are talking x-mechanical limits. Unless we are all using the same loudspeakers and cabinets your results are more of an estimate and not guaranteed. Best Regards,

Elliot
fully agree with what you state; but for the purpose of demonstration the results have value as they are restricted to well below any X-mechanical limits yet show substantial issues which occur.
Incidentally the 10volt test returns a current distortion near to 2% which is not bad for the 'speaker used!

I also agree with your post earlier on using sufficient hardware for the 'job in hand' instead of trying to squeeze the last ounce of SPL, with disregard to distortion, from a system and then expecting it to perform reliably again!

Mik



-------------
Warning! May contain Nuts
plus springs, washers, screws, etc, etc.


Posted By: airbell
Date Posted: 11 January 2011 at 3:06pm
someone in another forum wrote that its written in aes 2 standard 1984, that xmax is if the speaker still has so much cone control, that the distortion is not more than 10%...
dont know if its reliable, but wanted to let you know.


Posted By: S DeXter
Date Posted: 12 January 2011 at 9:22pm
Originally posted by Elliot Thompson Elliot Thompson wrote:

Those who are constantly concerning them selves about xmax don’t have enough loudspeakers to begin with. These individuals are trying to extract every bit of SPL using 1 – 4 bins in a large environment long-term. If you are toting 8 bins and above, xmax is not a big concern for you have enough surface area to get the job done with very little cone movement.

I am not concerned about xmax for I use more than enough bass bins to ensure I have enough headroom. Id rather have a 9 mm xmax driver with high efficency, than a 15 mm xmax driver with low efficency.

Best Regards,


In an ideal world more is better. Alot of time, space is limited. Both at venues and transportation. Why take 2 vans full, when you can take 1?

If you can 'extract' another 3dbs, you can take half the amount of bins which means alot less backwork! Thats why....

My point is, the majority of people are driving past xmax without even knowing it (i.e. its not percievable).

Especially with modern high power drivers - (Look at the newer beymas for example) you will run out of xmax before you hit their rated power.

In a closed box or open baffle (1/2 space 1m), a driver such as a PD 1850 will achieve

111.6db @ 40Hz
118.6db @ 60Hz
123.6db @ 80Hz

before reaching xmax.

Now I know drivers are seldom loaded in infinite baffle or cb, but it is still quite easily possible to drive a reflex out of its xmax while staying well within the power rating of a driver.




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Enjoy your self...... It's later than you think.......


Posted By: S DeXter
Date Posted: 12 January 2011 at 9:40pm
Also, if you trust hornresp for displacement (which I think should be fairly accurate for BR).

A Beyma 18SW1600 has an xmax of 5.5mm (regular measurement (Lvc - Hag)/2).

In a 185 litre 31Hz box hornresp has the beyma hitting its xmax @ 170W 45Hz

Even at Beymas 10mm quoted figure (Lvc - Hag)/2 + Hag/3.5), it will reach its xmax @ 600W 45Hz.

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Enjoy your self...... It's later than you think.......


Posted By: daywalk3r
Date Posted: 12 January 2011 at 11:49pm
Originally posted by S DeXter S DeXter wrote:

Also, if you trust hornresp for displacement (which I think should be fairly accurate for BR).

A Beyma 18SW1600 has an xmax of 5.5mm (regular measurement (Lvc - Hag)/2).

In a 185 litre 31Hz box hornresp has the beyma hitting its xmax @ 170W 45Hz

Even at Beymas 10mm quoted figure (Lvc - Hag)/2 + Hag/3.5), it will reach its xmax @ 600W 45Hz.

So, lets dissect those things one after another..

Found those numbers a bit odd so simmed it myself (185L/31Hz reflex) and I'm getting 5.5mm@260W and 10mm@860W for that particular driver, which is somewhat higher than what you got, but nothing excessively signifficant.. Nothing excessively surprising either though, as explained bellow..

What I found more odd is - why did you sim that driver in a box with a volume almost equaling its VAS, tuned it below its free air resonance (Fs), and then wonder what the heck is up with the power/excursion figures? Smile Could work if you added some mass to the cone, but otherwise those reflex enclosure parameters just seem not very ideal for that particular driver. You either need to reduce the box volume or tune it higher to make it work "as intended"..

But back to topic:
I believe the specified (some also call it "bloated") X-max figures, which most of the respected brands publish for their drivers nowadays are not necessarily just about marketing. Some of the brands (Beyma including) are not just getting those numbers out of thin air or by inventing random X-max formula (+Hag/x), but from measurements following certain AES standards, which set an upper limit on the allowed distortion of the reproduced signal (5 or 10%), and also a limit on the BL figure (=>70%).

What I wanted to point out with this is, that the X-max figures usually seen on driver spec-sheets nowadays are allready taking into account that "extra headroom before bad things happen", so it's usually a good idea to stick to them when designing enclosures..

Howgh Smile


Posted By: audiomik
Date Posted: 12 January 2011 at 11:55pm
Re: "Now I know drivers are seldom loaded in infinite baffle or cb, but it is still quite easily possible to drive a reflex out of its xmax while staying well within the power rating of a driver."

thought I'd shown this rather conclusively in the current spectra displays above.

Suggest you look at getting some current sensing circuitry which differences the Amplifier input signal to drive a limiter using it's external side-chain input.
Problem solved....
Mik

-------------
Warning! May contain Nuts
plus springs, washers, screws, etc, etc.


Posted By: S DeXter
Date Posted: 13 January 2011 at 9:38am

Originally posted by daywalk3r daywalk3r wrote:


So, lets dissect those things one after another..

Found those numbers a bit odd so simmed it myself (185L/31Hz reflex) and I'm getting mailto:5.5mm@260W - and mailto:10mm@860W - for that particular driver, which is somewhat higher than what you got, but nothing excessively signifficant.. Nothing excessively surprising either though, as explained bellow..

What I found more odd is - why did you sim that driver in a box with a volume almost equaling its VAS, tuned it below its free air resonance (Fs), and then wonder what the heck is up with the power/excursion figures?  Could work if you added some mass to the cone, but otherwise those reflex enclosure parameters just seem not very ideal for that particular driver. You either need to reduce the box volume or tune it higher to make it work "as intended"..

But back to topic:
I believe the specified (some also call it "bloated") X-max figures, which most of the respected brands publish for their drivers nowadays are not necessarily just about marketing. Some of the brands (Beyma including) are not just getting those numbers out of thin air or by inventing random X-max formula (+Hag/x), but from measurements following certain AES standards, which set an upper limit on the allowed distortion of the reproduced signal (5 or 10%), and also a limit on the BL figure (=>70%).

What I wanted to point out with this is, that the X-max figures usually seen on driver spec-sheets nowadays are allready taking into account that "extra headroom before bad things happen", so it's usually a good idea to stick to them when designing enclosures..

Howgh

OK, i forgot that everything in speakerplans is disected with a tooth comb.... Yes that box is a bit low tuned, you are correct. However the power figures are correct for the sim....

Anyway the first point to mention from your post is that at Beymas quoted xmax, the driver is already distorting, you said it yourself - dont forget this is the point I am making and that is why I chose not to use the stated figure.

 I also read somewhere, but do not quote me, (i will try to find it) that 70% BL requires double  power for same SPL....

The example I simmed was a worst case scenario but not totally unrealistic. So I have simmed the B & C Sub 18 with a 18NW100.

Now there can be alot of dispute as to where we should draw the power figures for this. Again B & C appear to quote the xmax to the 'bloated' figures. (Lvc-Hag)/2 = 6.5mm in this case - this is what I would term as linear travel.....

Hornresp comes up with these figures
 
At 700W has 10.6mm @ 48Hz
At 1200W has 13.9mm @ 48Hz
 
Even at these powers, you can see you are definitely out of the linear travel. This driver will take an amplifier substansially bigger thermally.... at 2000W (on peaks) you will be nearer 19mm.
 
 


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Enjoy your self...... It's later than you think.......


Posted By: IanD
Date Posted: 15 January 2011 at 3:15pm
Once you exceed the real linear Xmax where the coil starts to leave the gap there's less force so the cone moves less additional distance for each amp of current -- of course this is why the distortion increases.

So if you take an example of a 24mm coil in a 12mm gap, the real linear Xmax is 6mm, the quoted Xmax from manufacturers could be 9mm (added Hg/4) or 10mm (added Hg/3), or something else if they use measured distortion.

Hornresp might say you need 60V (450W) to reach 6mm, 90V (1000W) to reach 9mm, 100V (1250W) to reach 10mm, 120V (1800W) to reach 12mm, but only the first one of these is likely to be true. The further you go past the linear Xmax travel, the bigger the difference between the actual travel and that predicted by Hornresp.

It's still not a good idea to drive beyond the rated Xmax if you want decent sound...

Ian


Originally posted by S DeXter S DeXter wrote:

Originally posted by daywalk3r daywalk3r wrote:


So, lets dissect those things one after another..

Found those numbers a bit odd so simmed it myself (185L/31Hz reflex) and I'm getting mailto:5.5mm@260W - and mailto:10mm@860W - for that particular driver, which is somewhat higher than what you got, but nothing excessively signifficant.. Nothing excessively surprising either though, as explained bellow..

What I found more odd is - why did you sim that driver in a box with a volume almost equaling its VAS, tuned it below its free air resonance (Fs), and then wonder what the heck is up with the power/excursion figures?  Could work if you added some mass to the cone, but otherwise those reflex enclosure parameters just seem not very ideal for that particular driver. You either need to reduce the box volume or tune it higher to make it work "as intended"..

But back to topic:
I believe the specified (some also call it "bloated") X-max figures, which most of the respected brands publish for their drivers nowadays are not necessarily just about marketing. Some of the brands (Beyma including) are not just getting those numbers out of thin air or by inventing random X-max formula (+Hag/x), but from measurements following certain AES standards, which set an upper limit on the allowed distortion of the reproduced signal (5 or 10%), and also a limit on the BL figure (=>70%).

What I wanted to point out with this is, that the X-max figures usually seen on driver spec-sheets nowadays are allready taking into account that "extra headroom before bad things happen", so it's usually a good idea to stick to them when designing enclosures..

Howgh

OK, i forgot that everything in speakerplans is disected with a tooth comb.... Yes that box is a bit low tuned, you are correct. However the power figures are correct for the sim....

Anyway the first point to mention from your post is that at Beymas quoted xmax, the driver is already distorting, you said it yourself - dont forget this is the point I am making and that is why I chose not to use the stated figure.

 I also read somewhere, but do not quote me, (i will try to find it) that 70% BL requires double  power for same SPL....

The example I simmed was a worst case scenario but not totally unrealistic. So I have simmed the B & C Sub 18 with a 18NW100.

Now there can be alot of dispute as to where we should draw the power figures for this. Again B & C appear to quote the xmax to the 'bloated' figures. (Lvc-Hag)/2 = 6.5mm in this case - this is what I would term as linear travel.....

Hornresp comes up with these figures
 
At 700W has 10.6mm @ 48Hz
At 1200W has 13.9mm @ 48Hz
 
Even at these powers, you can see you are definitely out of the linear travel. This driver will take an amplifier substansially bigger thermally.... at 2000W (on peaks) you will be nearer 19mm.
 
 


Posted By: S DeXter
Date Posted: 15 January 2011 at 8:16pm
Originally posted by IanD IanD wrote:

Once you exceed the real linear Xmax where the coil starts to leave the gap there's less force so the cone moves less additional distance for each amp of current -- of course this is why the distortion increases.


I am aware of that Ian.

Originally posted by IanD IanD wrote:



It's still not a good idea to drive beyond the rated Xmax if you want decent sound...

Ian



For tops, I have to agree 100%.

For sub, I agree to differ.


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Enjoy your self...... It's later than you think.......


Posted By: greeef
Date Posted: 25 January 2011 at 9:36pm
I'm going to throw in my baseless opinion here.

As you drive air harder, it's elasticity and thermal compliance and all the physics stuff becomes relevant. An absolutely perfect pistonal speaker is still going to distort at high volume because it's going to get mounted in a real space, not a theoretical anechoic one, and cos that's the nature of air and ultimately, eardrums.

Yes it's distortion, but it's not hard high order clipping, it bears more similarity to power compression. I'd much rather hear a dynamic system that exceeds xmax on the transients than one that used outboard processing to bring everything below xmax at the same rms level.

EDIT - like above poster, i mean this applies to subs. Sounds rough on top where linearity properly matters.


Posted By: IanD
Date Posted: 26 January 2011 at 8:43pm
Originally posted by greeef greeef wrote:

I'm going to throw in my baseless opinion here.

As you drive air harder, it's elasticity and thermal compliance and all the physics stuff becomes relevant. An absolutely perfect pistonal speaker is still going to distort at high volume because it's going to get mounted in a real space, not a theoretical anechoic one, and cos that's the nature of air and ultimately, eardrums.

Yes it's distortion, but it's not hard high order clipping, it bears more similarity to power compression. I'd much rather hear a dynamic system that exceeds xmax on the transients than one that used outboard processing to bring everything below xmax at the same rms level.

EDIT - like above poster, i mean this applies to subs. Sounds rough on top where linearity properly matters.


Nonlinearity due to air heating/compression is only ever an issue for compression drivers with huge power density in the throat, not in bass horns even at very high levels -- look up the numbers if you don't believe me.


Posted By: TechnoChef
Date Posted: 07 February 2011 at 10:38am
From what I understand from all the above, driving a sub past xmax has more of a compression than distortion effect - like an analog tape deck. Obviously within reasonable power levels!
I've produced/written dance music for a good few years now and the best method I've found for making basslines sound Phat (with the capital P!) Is by adding a little soft tube compression. In planning for and designing subs I have always worked within xmax figures but now I think my mind has changed, maybe an extra couple of mm will add some warmth without necessarily destroying equipment???
^^^^all for sub and nowt else though!

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I think I'm in love with your mum.


Posted By: Matthias
Date Posted: 07 February 2011 at 11:08am
http://www.youtube.com/watch?v=JhYtHH5JdCA

DC - displacement kills a lot of speakers. It depends on the driver, tho. It will be generated when the coil leaves the gap and the cones 0 point will shift


Posted By: Rotorbar
Date Posted: 12 February 2011 at 7:25am
This all comes down to how much you want to hear distortion and how much equipment you want to cook.  Good judgment comes from experience, and experience comes from bad judgment.  You can exceed your xmax at the expense of some driver distortion during the musical transients.  Since they're transients, you can musically get away with considerable driver distortion, so long as the amplifiers don't clip.  That's another kettle of fish.  Eventually, exceeding xmax far enough, for long enough, will rip apart the surround or burn the voice coil, and after a recone job, you will have a new feeling for how much you can exceed those limits.  Since I go entirely with vented bass cabinets, the mechanical limits in that 1/3rd octave above Fb get to me first.  I try to stay in the 6-10dB-down range for running power at the amplifiers.  It seems to be a good trade-off between ruined voice coils and torn surrounds.  As a side note, I have never had a spider fail.  In the mids/tops, I see thermal limits first.  Got another lesson on that recently.  The photo's I see of burned voice coils mostly show that some part of the coil was out of the gap.  Some of them suggest poor reconing techniques, meaning the voice coil wasn't centered magnetically during the recone job.

The nice thing about a large xlim is having the ability to survive some monstrous transient, like when a mike gets dropped or a signal processor gets accidentally turned off.  If the driver can take that transient physical abuse, great.  You made it through another day.


Posted By: snowflake
Date Posted: 13 February 2011 at 7:55pm
if you read up an the psycho-acoustics of the missing fundamental this suggests that if the 2nd and 3rd harmonic distortion is in the right proportion the distortion will be indistinguishable from the fundamental and make it sound a lot louder. if a driver were designed with this in mind it will have slight asymetry in the suspension or motor field to introduce 2nd order distortion at high excursion and to keep it higher than the 3rd order distortion. as below 200Hz the human ear rapidly loses sensitivity (at 24dB/octave I think) a couple of percent distortion will make the perceived sound twice as loud.

amp clipping will not introduce the right sort of distortion to sound good so generally if you have to choose a big amp overpowering fewer speakers will sound better than a small amp clipping into a greater number of speakers.

other than for subs distortion does sound terrible, especially on human voices


Posted By: S DeXter
Date Posted: 15 February 2011 at 7:12pm
+1 snowflake and rotorbar!

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Enjoy your self...... It's later than you think.......


Posted By: cooky1257
Date Posted: 18 February 2011 at 11:59am
There's two halves to a waveform, if the coil is out of the gap on the upstroke then isn't the downstroke dependent on the surround and spider returning the coil to a driven position in time?. The pistonic behaviour is only guaranteed within xmax limits as I understand it. Start approaching xmech and you'll bottom your drivers, quite possibly wrecking them.


Posted By: S DeXter
Date Posted: 18 February 2011 at 12:45pm
Originally posted by cooky1257 cooky1257 wrote:

There's two halves to a waveform, if the coil is out of the gap on the upstroke then isn't the downstroke dependent on the surround and spider returning the coil to a driven position in time?.


Do you mean there will be an assymetry of motion? The surround and spider are always responsible for driver position, not just out of xmax...?

Originally posted by cooky1257 cooky1257 wrote:

The pistonic behaviour is only guaranteed within xmax limits as I understand it. Start approaching xmech and you'll bottom your drivers, quite possibly wrecking them.


Pistonic behaviour relates to cone breakup modes (cone flexing and resonating) rather than xmax effects . Loudspeaker modellers assume the driver to act like a perfect 'piston' (unless you are using FEA!).

Alot of newer drivers have quite large Xmechs....



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Enjoy your self...... It's later than you think.......


Posted By: cooky1257
Date Posted: 18 February 2011 at 2:57pm
Originally posted by S DeXter S DeXter wrote:

Originally posted by cooky1257 cooky1257 wrote:

There's two halves to a waveform, if the coil is out of the gap on the upstroke then isn't the downstroke dependent on the surround and spider returning the coil to a driven position in time?.


Do you mean there will be an assymetry of motion? The surround and spider are always responsible for driver position, not just out of xmax...?

Originally posted by cooky1257 cooky1257 wrote:

The pistonic behaviour is only guaranteed within xmax limits as I understand it. Start approaching xmech and you'll bottom your drivers, quite possibly wrecking them.


Pistonic behaviour relates to cone breakup modes (cone flexing and resonating) rather than xmax effects . Loudspeaker modellers assume the driver to act like a perfect 'piston' (unless you are using FEA!).

Alot of newer drivers have quite large Xmechs....

 Mr Flemings rule only applies if the coil is in the magnetic field, so yes if hit with a huge sine wave say, it wouldn't be producing that sine wave correctly. 

Of course the surround and spider's job is to position the vc correctly about the 0 position with applied signal creating the +/-'movement', they are not responsible for playing the undriven parts of a tune;-)




Posted By: snowflake
Date Posted: 01 March 2011 at 2:31pm
there is also the possibility with horn loaded subs of using the front chamber to roll-off the HF at right frequency to drastically reduce the amount of third harmonic. if the third harmonic is kept to about a third of the level of the second harmonic the distortion will sound a lot more musical. so if the horn has a low cut-off of 40 Hz it will have high excursion around 60Hz. Second harmonics of this will be 120Hz and third will be 180Hz. so if the front chamber can be sized to begin HF roll-off after 120Hz and to be at least 6dB down (in addition to the mass roll-off of the driver) at 180Hz there could be some improvement to the sound. this is all in theory BTW but will try it in my next prototype


Posted By: audiomik
Date Posted: 01 March 2011 at 10:44pm
Interesting idea - but it will do nothing much in terms of addressing IMD products!
Mik

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Warning! May contain Nuts
plus springs, washers, screws, etc, etc.


Posted By: wayward91
Date Posted: 01 March 2011 at 11:21pm

Well. Interesting reading. all I can add it that in my opinion a speaker is (usualy) designed or should be designed to reproduce a sound and not alter it. I kinda destroyed a speaker quite badly (shown below) so i wouldn’t purposely aim to over extend a driver on a regular basis. To me it seems to be asking for trouble.  Smile









Posted By: S DeXter
Date Posted: 02 March 2011 at 12:36am
Originally posted by wayward91 wayward91 wrote:

Well. Interesting reading. all I can add it that in my opinion a speaker is (usualy) designed or should be designed to reproduce a sound and not alter it. I kinda destroyed a speaker quite badly (shown below) so i wouldn’t purposely aim to over extend a driver on a regular basis. To me it seems to be asking for trouble.  Smile



A case of exceeding Xmech... not xmax...! Smile


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Enjoy your self...... It's later than you think.......


Posted By: audiomik
Date Posted: 02 March 2011 at 1:26am
Think there could be something here worth considering which comes from early mathematical models of the 'ideal' Horn loading for a cone loudspeaker and still holds true today.

This is that the ideal loading for a driver occurs with zero cone movement as it models as the ideal drive condition since the throat coupling volumes remain constant.

Now we know that in the real world this isn't very practical; but to best match our driver to our horn loading then the cone displacement should be as small as possible to achieve a result closest to the theoretical ideal....

For greater deviation from this ideal, distortion rises whilst when exceeding Xmax, distortion rises substantially more.

So rather than trying to extract the 'maximum' from a single driver/cabinet design; the use of multiple under-driven cabinets are the better solution in terms of the system being capable overall of reproducing the original program source whilst minimising 'colouration' of the original program material it is reproducing....

Ok - other factors apply but the principle is valid as posted by others in this thread earlier
Mik

-------------
Warning! May contain Nuts
plus springs, washers, screws, etc, etc.


Posted By: greeef
Date Posted: 02 March 2011 at 3:38am
Originally posted by snowflake snowflake wrote:

as below 200Hz the human ear rapidly loses sensitivity (at 24dB/octave I think) a couple of percent distortion will make the perceived sound twice as loud.


The rate of sensitivity loss varies with loudness. At home listening/conversation levels your figure is probably accurate, but as the system gets louder, the response flattens out. 

http://www.customanalogue.com/elsinore/elsinore_images/Fletcher-Munson_700W.gif">fltcher munson contour

I wouldn't trust this to the letter, there are a lot of different equal loudness contours out there, but they all show the same theme, a (erm...) less reduced sensitivity to bass notes as a sound becomes louder.

In my view, distorted bass usually sounds quite brash and undynamic (compressed). I prefer a subtle, understated bass tone that you feel rather than hear, but i listen to poncey music a lot.


Posted By: Centauri
Date Posted: 02 March 2011 at 5:48am
Originally posted by greeef greeef wrote:

I wouldn't trust this to the letter, there are a lot of different equal loudness contours out there,


That old Fletcher-Munson chart is extremely inaccurate, with the current standard being ISO 225:2003 - see http://en.wikipedia.org/wiki/Equal-loudness_contours - here and http://www.independentrecording.net/irn/resources/freqchart/ear_sensitivity.htm - here .


Posted By: Keen
Date Posted: 26 April 2014 at 11:23am
this thread was interesting to read : )



Posted By: fourway hornloaded
Date Posted: 28 April 2014 at 8:34pm
(a bit of a trhead hack, but it's on Xmax and i thought it appropriate to post this here)

The other day I replaced one of my beloved PD186 that had started scratching (for whatever reason?) and put in an 18Nd9300, which is a neo version of 18LW1400. Similar T/S, checked for plausible response and mech. movement using hornresp. I'm used to giving my bass bins 500 Watts each whole night long, so they should move about 8...10 mm in each direction which has proven totaly fine. Not too much power here.

Now what happens: that particular bin with the neo driver beats like it's hitting something. But only on high excursion, on loud drum beats. It was in parallel to a PD186 that had no problems. Turning down that particular amp by ~6dB cured the problem.

Do I just have a bad one? It's second hand, but I tested it with a tone generator, no scratching even at large displacement wo I thought it should be fine.

The 18Nd9300 is one of those 'new' drivers with 15mm gap and 24mm coil winding height. PD186 is one of those 'old' drivers with 8mm gap and 24mm vc. But then they promise similar Xmax figures and some say that having a less steep BL-curve leads to a larger controlled displacement anyway. There's also the DDS spider, where the PD has an 'old fashioned' double spider.

Has anyone had similar experience with 'modern' drivers?

Thanks in advance,
Robert







Posted By: Pasi
Date Posted: 28 April 2014 at 8:45pm
Yup. It's the cooling air noise when it exits from the plateset.


Posted By: Elliot Thompson
Date Posted: 28 April 2014 at 9:44pm
If you really want to know the answer, measure the TS Parameters of both drivers in question. You are overlooking many things that play a factor on how the loudspeaker is reacting in the box. Measure the TS Parameters of both drivers.

Best Regards,


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Elliot Thompson


Posted By: Mark James
Date Posted: 28 April 2014 at 9:49pm
also i may be well off here but if you sim in horn response say for example a stack of four identical cabs versus say 8 identical cabs same power per driver the 8 stack suld have lower excursion at same power input and acoustic output levels???? what im suggesting is with te stack feauturing alot of pd186 tat you are comparing to a single 18sound wich may not be coupling up with the oter bins maybey thats causing te driver to go over xmax? JUST a thought though can you say load four 18 sound and compare to 4 pd?????

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me so horny me love you long throw
horn loaded for her pleasure


Posted By: fourway hornloaded
Date Posted: 28 April 2014 at 10:53pm
thanks!

@Pasi: Maybe that's why they discontinued a seemingly sound driver? 15"ers and a 12"er are still available with the same magnet structure that the 18Nd9300 has, but no 18"er.

@Elliot: Point taken, i did not measure T/S. Still, such entirely different behaviour is a little bit unexpected, judging the datasheets, isn't it? 500W in any enclosure that properly loads the driver should be ok with this type of driver (35Hz HPF was set, just plain-old techno beats on and on). In the end of the day, the Nd9300 is quite high-tech compared to PD186 and you wouldn't expect 18sound to totally screw up the datasheet, would you? (I admit that PD kind-of did exactly that).

@Mark: They were in 3 stacks of 2 bins each, with only half a meter between stacks. So that shouldn't have been the problem. I'm going to have to do what you suggested though: have a direct stacked comparison between drivers. Because if this behaviour is structural, I can't use such drivers. Hopefully just one bad driver.

I must say I do like this forum for the type of discussion you can get here. Thanks again. This might also be interesting regarding the recent change of T/S on the much-used PD186.

Is there anyone else who can comment on 'new-fashioned' drivers, say 'P300 or 'LW1400 against PD186?

regards, robert


Posted By: Elliot Thompson
Date Posted: 29 April 2014 at 1:23am

Originally posted by fourway hornloaded fourway hornloaded wrote:

thanks!


@Elliot: Point taken, i did not measure T/S. Still, such entirely different behaviour is a little bit unexpected, judging the datasheets, isn't it? 500W in any enclosure that properly loads the driver should be ok with this type of driver (35Hz HPF was set, just plain-old techno beats on and on). In the end of the day, the Nd9300 is quite high-tech compared to PD186 and you wouldn't expect 18sound to totally screw up the datasheet, would you? (I admit that PD kind-of did exactly that).



regards, robert


Manufactures can change their parameters based on what they feel is best to sustain the longevity of the driver as time progress.

Once a loudspeaker is housed in an enclosure, the TS Parameters are going to change.

You cannot expect two drivers offering different model numbers from different manufactures to react the same.

The xmax is only there to help the driver when it is need of help. Obviously, the Nd9300 relies more on xmax than the PD 186 based on the music material involved in addition to the enclosure it is housed in.

This is why you must measure the drivers in free air to find out how the TS Parameters differs amongst the two. You may be startled to find out how great the figures differ between the Nd9300 & PD 186.

Best Regards,


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Elliot Thompson


Posted By: b grade
Date Posted: 29 April 2014 at 1:49am
That 18 sound is listed as much more sensitive (nominally speaking) than the 186. 98 to 95. The 18 sound also has higher impedence, so I would expect that it is pulling more of the power when run in parallel and reacting more dramatically with the power it is getting.


Posted By: DMorison
Date Posted: 29 April 2014 at 12:56pm
Originally posted by b grade b grade wrote:

That 18 sound is listed as much more sensitive (nominally speaking) than the 186. 98 to 95. The 18 sound also has higher impedence, so I would expect that it is pulling more of the power when run in parallel and reacting more dramatically with the power it is getting.
 
Sorry, that's the wrong way round.
Higher impedance means less current will flow for a given applied voltage, hence less power, not more.
Say the PD had Zmin of 5.5Ω in-band and the 18Sound had Zmin of 7.5Ω in-band, then for an input voltage of 62V (resulting in nominal power dissipation at that frequency of 700W for the PD), the 18Sound would only dissipate 512W.
HTH,
David.


Posted By: snowflake
Date Posted: 29 April 2014 at 3:52pm
Originally posted by Centauri Centauri wrote:

Originally posted by greeef greeef wrote:

I wouldn't trust this to the letter, there are a lot of different equal loudness contours out there,


That old Fletcher-Munson chart is extremely inaccurate, with the current standard being ISO 225:2003 - see http://en.wikipedia.org/wiki/Equal-loudness_contours" rel="nofollow - here and http://www.independentrecording.net/irn/resources/freqchart/ear_sensitivity.htm" rel="nofollow - here .

those new charts show that below 100Hz perceived loudness falls at 20dB/octave at low volumes and 10dB/octave at high volumes. as xmax is defined as as 10% distortion we can conclude that for subs operated at xmax we are hearing the distortion as much as the fundamental.


Posted By: b grade
Date Posted: 29 April 2014 at 4:23pm
Originally posted by DMorison DMorison wrote:

Originally posted by b grade b grade wrote:

That 18 sound is listed as much more sensitive (nominally speaking) than the 186. 98 to 95. The 18 sound also has higher impedence, so I would expect that it is pulling more of the power when run in parallel and reacting more dramatically with the power it is getting.
 
Sorry, that's the wrong way round.
Higher impedance means less current will flow for a given applied voltage, hence less power, not more.
Say the PD had Zmin of 5.5Ω in-band and the 18Sound had Zmin of 7.5Ω in-band, then for an input voltage of 62V (resulting in nominal power dissipation at that frequency of 700W for the PD), the 18Sound would only dissipate 512W.
HTH,
David.

D'oh. I know that, I was just stupid yesterday.



Posted By: fourway hornloaded
Date Posted: 02 May 2014 at 4:06pm
@bgrade: What you say might have been part of the problem. The Nd9300 does have a lower vc resistance so more current at the same voltage - more cone movement than the PD186 it is in parallel to.

"The xmax is only there to help the driver when it is need of help. Obviously, the Nd9300 relies more on xmax than the PD 186 based on the music material involved in addition to the enclosure it is housed in."

@Elliot: I reckon you mean extension when saying xmax? For example a BL>30 driver in a scoop won't hardly move at all and still be loud, so one could say it does not rely on extension.

Now putting aside the fact that I did not measure T/S, I must say I thought it would be exactly the other way round, really.

I'd have thought that the PD186, with its low BL ~ 20 and its high Qts ~ 0,5 would overexcurse rather than the Nd9300, sister to 18LW1400, with a published BL of 24 and a Qts of 0,28.

Is there anyone who can say where I'm getting this wrong? Is the PD186 some kind of a magic driver? Having the T/S you'd expect from a foam surround car woofer. It has even been put in horns! Do I have to revisit my understanding I thought I had about T/S?

Prodance PD186 T/S measurement:http://www.prodance.cz/files/dl/1/1979/TS_PD186.pdf
Prodance PD186 Mark II measurement:http://www.prodance.cz/files/dl/8/15605/PD186_2.pdf


Posted By: Elliot Thompson
Date Posted: 02 May 2014 at 9:47pm
Originally posted by fourway hornloaded fourway hornloaded wrote:

@bgrade: What you say might have been part of the problem. The Nd9300 does have a lower vc resistance so more current at the same voltage - more cone movement than the PD186 it is in parallel to.

"The xmax is only there to help the driver when it is need of help. Obviously, the Nd9300 relies more on xmax than the PD 186 based on the music material involved in addition to the enclosure it is housed in."

@Elliot: I reckon you mean extension when saying xmax? For example a BL>30 driver in a scoop won't hardly move at all and still be loud, so one could say it does not rely on extension.

Now putting aside the fact that I did not measure T/S, I must say I thought it would be exactly the other way round, really.

I'd have thought that the PD186, with its low BL ~ 20 and its high Qts ~ 0,5 would overexcurse rather than the Nd9300, sister to 18LW1400, with a published BL of 24 and a Qts of 0,28.

Is there anyone who can say where I'm getting this wrong? Is the PD186 some kind of a magic driver? Having the T/S you'd expect from a foam surround car woofer. It has even been put in horns! Do I have to revisit my understanding I thought I had about T/S?

Prodance PD186 T/S measurement:http://www.prodance.cz/files/dl/1/1979/TS_PD186.pdf
Prodance PD186 Mark II measurement:http://www.prodance.cz/files/dl/8/15605/PD186_2.pdf


You are not getting it wrong your real world analysis is correct in regards to the QTS. As a matter of fact, you may have learned more on those two drivers offering different parameters than many who post on the forum.

 

The PD 186 is not a magic driver. Precision Devices just designed it for a reflex cabinet in mind as the years progressed whereas the Nd9300 is designed for a folded horn. 

 

This is why it is essential to have a good understanding of the TS Parameters in regards to what kind of bass response you are aiming for.

 

In regards to car woofers, the ones many seek after are so inefficient they require dual 4, 2, or 1-ohm voice coils in order to attain a significant amount of SPL.  They too fall in the same category of relying heavily on xmax to achieve low frequency extension based on the TS Parameters they provide.

 

Study the TS Parameters. All the answers can be found once you have a good understanding what all the emblems mean.

 

Best Regards,


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Elliot Thompson


Posted By: beer_n_chips
Date Posted: 03 May 2014 at 1:05pm
Going past xmax not just increases harmonic distortion a bit favoured by guitar players and also reggae sound systems seem to like to push their drivers quite a bit.
But TOO far out the magnetic gap also reduces the cooling abilities.

Something I never understand from speaker manufactures is the xmax rating.
 Is it one way or both ways given?  And how that makes a difference?



Posted By: b grade
Date Posted: 03 May 2014 at 4:10pm
x max is one way. I have seen drivers with the full two way excursion listed though. It was not labelled x max though.


Posted By: fourway hornloaded
Date Posted: 08 May 2014 at 10:58pm
To get back to the original question: drivers react differently when driven over Xmax.

Those with stiff suspension will just not move any further at a point not far beyond Xmax. These are the ones that will eat kilowatts. Of course, as the output/input curve flattens, some compression occurs, but that might still sound (very) good.

Those with loose suspension will eventually hit the back plate (been there, done that as you might have read) but before doing so, they will reach quite high excursion, which gives high output (if the cone is loaded by the box).

In both cases, beyond Xmax, the BL decreases. That's the way both phenomena are defined. Electromagnetic force is not the same anymore beyond Xmax and when moving further, the cone is more controlled by the suspension than it is by the amplifier.

So if you use hornresp to simulate cone excursion at 1000 Watts into your bassbin, you might get something around 15mm; and using a driver with 8mm Xmax, the question may arise, how far can I drive that driver beyond Xmax. It might very well never get passt 10 mm, because after that point there's too little voice coil height left in the gap for the amplifier to have any influence, while at the same time, the suspension is stretching so far that it just stops the cone from moving. In the end of the day, drivers with larger Xmax do go louder.


Posted By: Elliot Thompson
Date Posted: 09 May 2014 at 3:12am
A lot of what you are saying is not based on testing the driver in free air. You cannot reach to a decision on a Manufactures driver’s excursion level in a box (more so the suspension) in which the driver will react differently once it is housed in a different box other than yours. Have you measured the TS Parameters of the drivers in question yet?

No matter what you do, if you do not literally measure the TS Parameters of your drivers, you will not get the answers you are seeking.

Horn Response’s prediction (Note: prediction not guarantee) can only give you an estimate providing you enter the correct parameters of the driver in question for Horn Response to calculate.

Best Regards,


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Elliot Thompson


Posted By: bitSmasher
Date Posted: 09 May 2014 at 4:22am
On that... I'm really surprised there aren't more forum members testing drivers and reporting back on this
As a total n00b, before I jumped in to design a few reflex boxes, I bought a Dayton DATS to verify my drivers
Why aren't the enthusiasts and almost-professional speaker nerds doing this? Too much emphasis on spec sheets, sims and anecdotes. Not much raw data and facts.
This rant also crosses over in to the discussion about a speaker brand "revising" their spec sheets
it baffles me.



Posted By: fourway hornloaded
Date Posted: 09 May 2014 at 1:14pm
Ok, again got your point Elliot. Intertechnik just called to confirm that a Dayton DATS will arrive at my doorstep in 8 weeks. So I'll be back on here in august, hopefully with some gained knowledge! Thanks for the replies again. Keep up the good work.
Regards,
Robert


Posted By: Elliot Thompson
Date Posted: 09 May 2014 at 11:03pm
You can use the fully functional demonstration version of LIMP until Dayton DATS arives.

http://www.artalabs.hr/" rel="nofollow - http://www.artalabs.hr/

Best Regards,

-------------
Elliot Thompson


Posted By: fourway hornloaded
Date Posted: 30 May 2014 at 12:41pm
For those interested, some kind of 'rectification': after a day of swapping and testing it has turned out that there was a tiny little air gap between basket and baffle. Only at 165 Hz, this leak would make an agressive, loud rattling sound. At all other frequencies it was silent. So on techno, it sounded very much like if the coil were hitting the plate on every beat. The Nd9300 that I got don't have a back gasket. So that's why the problem never arose with PD186, which has a back gasket. Without an air leak, there's hardly any difference noticable, which is what I'd expect with two similar drivers in horns.

So the 18sound was not reaching it's Xlim at all.

Another problem discovered in the process: the chassis holes on the 18sound driver are just about big enough to pass the head of a DIN912 M6 allen screw, if you don't use washers!

The original cardboard box contains a sheet of air tight plastic foam that looks just perfect for cutting out some gaskets ;-).


Posted By: b grade
Date Posted: 30 May 2014 at 5:12pm
Gasket tape is pretty cheap too. I love that stuff. I try to always own some for problem solving.


Posted By: Andre Vergison
Date Posted: 30 May 2021 at 8:12pm
In a closed box the cone excursion at low frequencies often exceeds Xmax when feeding the driver with its rated max. power.

We could make the box smaller, down to the point that Xmax is always safe for all low frequencies. WinISD nicely shows that. A Linkwitz transform can compensate for the worsened transfer magnitude at low frequencies.

The max SPL of such smaller box would not decrease at all, as max SPL depends on frequency, cone surface and Xmax only.

A disadvantage I see is that (much) more power is required to obtain the same SPL in the low regions. The driver has to pump more, so to speak. More power also leads to more coil heating.

But the big advantage is that it would not be possible anymore to overdrive and destroy the speaker by a too large excursion. In addition, the box is smaller and less heavy as well.

What would be against it? I haven't met many such alignments in practice yet...

Andre


Posted By: MarjanM
Date Posted: 31 May 2021 at 9:38am
Compensating 3db loss in the low end with more power means twice the power applied to the driver.
You will reach power compression threshold way faster and wont gain anything at the end and risk blowing up the driver because it will start overheating. 


-------------
Marjan Milosevic
MM-Acoustics
www.mm-acoustics.com
https://www.facebook.com/pages/MM-Acoustics/608901282527713


Posted By: toastyghost
Date Posted: 31 May 2021 at 10:27am
Conversely, this is entirely possible if you’re very smart about designing the cabinet and the driver together for a desired non-linear response. However, it requires the use of a very accurate lumped element model of the entire loudspeaker, including non-linear and linear distortions plus thermal compression and such.

You also have to be willing to use ‘wrong’ drivers and work with the non-linearities. For example, you can use over-damped suspension or even very low Bl motors to ensure there’s a large resonant peak at your desired cutoff frequency.

It works better for sealed and bandpass enclosures due to the nature of those cabinets’ effect on loading.

The model can then be used alongside measurements of a prototype to develop mirror filter sets which can be applied in real-time via DSP and relatively inexpensive current or pressure sensors to dynamically correct the response of the cabinet. It’s possible to work towards a pre-configured target, while reducing distortion and having an adaptable filter set as level increases.

You might be surprised how many consumer and automotive audio products use a variation of this method, obviously some better than others. Although since Klippel has been publishing papers on how to do it for over 20 years, maybe not. Plenty of those are available to read on the Klippel site, but be warned there’s a lot of equations ahead.

Typically it’s a method applied to small speakers. IPAL and M-Force use a similar method for large drivers and higher output.


Posted By: Andre Vergison
Date Posted: 31 May 2021 at 5:47pm
Marjan what you wrote makes sense, we don't want power compression at all.

The exercise I made was with a Beyma 18LEX1600Nd (which I own) in a 80 liter box. Qtc is then 0,841 and while cone excursion never exceeds 14,5 mm down to 20 Hz.
A box of 140 liter (Qtc 0,709) lets the cone excursion at max power raise up to almost 20 mm at 30 Hz, which still is within Xlim. Throughput increases with 3 db at 30 Hz, from -14 dB up to -11. Max power at 30 Hz is 850 W.

Not too bad, there's at least some degree of protection.

So better pick the 140 liter box?




Posted By: bob4
Date Posted: 03 June 2021 at 8:41am
Andre, a friend of mine has a pair of  Beyma loaded 18" DIY subs, they must be close to 30 years old by now. They are very compact CB, with a roughly 50x 50 cm baffle and about 30 cm depth if memory serves me well. 
They work surprisingly well, and have survived decades of abuse. 


Posted By: toastyghost
Date Posted: 03 June 2021 at 12:42pm
Originally posted by Andre Vergison Andre Vergison wrote:

Marjan what you wrote makes sense, we don't want power compression at all.

The exercise I made was with a Beyma 18LEX1600Nd (which I own) in a 80 liter box. Qtc is then 0,841 and while cone excursion never exceeds 14,5 mm down to 20 Hz.
A box of 140 liter (Qtc 0,709) lets the cone excursion at max power raise up to almost 20 mm at 30 Hz, which still is within Xlim. Throughput increases with 3 db at 30 Hz, from -14 dB up to -11. Max power at 30 Hz is 850 W.

Not too bad, there's at least some degree of protection.

So better pick the 140 liter box?






There are quite a few papers and documented lumped element models to calculate the onset of thermal compression for a proposed design, if you're so inclined:
https://www.klippel.de/fileadmin/klippel/Files/Know_How/Literature/Papers/Nonlinear_Modeling_of_Heat_Transfer_03.pdf" rel="nofollow - https://www.klippel.de/fileadmin/klippel/Files/Know_How/Literature/Papers/Nonlinear_Modeling_of_Heat_Transfer_03.pdf

If you're not, then pages 16 and 17 are still a good read as to why this is useful. Especially if you have access to a driver to measure a couple of parameters. Sadly I don't think any of the software has implemented this model yet.


Posted By: VECTORDJ
Date Posted: 04 June 2021 at 2:42pm
Please keep Us Reconers busy by grossly overdriving  Your woofers.......Thanx, Troy Bernard  VECTORSONICS



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