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

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Elliot Thompson View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post 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,
Elliot Thompson
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b grade View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote b grade Quote  Post ReplyReply Direct Link To This Post 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.

Edited by b grade - 29 April 2014 at 1:49am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DMorison Quote  Post ReplyReply Direct Link To This Post 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.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post 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 here and 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.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote b grade Quote  Post ReplyReply Direct Link To This Post 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.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote fourway hornloaded Quote  Post ReplyReply Direct Link To This Post 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
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Elliot Thompson View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post 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,
Elliot Thompson
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Post Options Post Options   Thanks (0) Thanks(0)   Quote beer_n_chips Quote  Post ReplyReply Direct Link To This Post 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?

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Post Options Post Options   Thanks (0) Thanks(0)   Quote b grade Quote  Post ReplyReply Direct Link To This Post 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.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote fourway hornloaded Quote  Post ReplyReply Direct Link To This Post 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.
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Elliot Thompson View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post 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,
Elliot Thompson
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bitSmasher Quote  Post ReplyReply Direct Link To This Post 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.

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