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

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rich_gale View Drop Down
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    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???    
REFLEX ALL THE WAY.... (however, im playing with horns again...) That ok Mister Valiant? :)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote daywalk3r Quote  Post ReplyReply Direct Link To This Post 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
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MunkeyQ Quote  Post ReplyReply Direct Link To This Post 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.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JR.junior Quote  Post ReplyReply Direct Link To This Post 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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Post Options Post Options   Thanks (0) Thanks(0)   Quote S DeXter Quote  Post ReplyReply Direct Link To This Post 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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Post Options Post Options   Thanks (0) Thanks(0)   Quote daywalk3r Quote  Post ReplyReply Direct Link To This Post 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
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Pasi Quote  Post ReplyReply Direct Link To This Post 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.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote airbell Quote  Post ReplyReply Direct Link To This Post 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.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote airbell Quote  Post ReplyReply Direct Link To This Post 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
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rich_gale Quote  Post ReplyReply Direct Link To This Post 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.  
REFLEX ALL THE WAY.... (however, im playing with horns again...) That ok Mister Valiant? :)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rich_gale Quote  Post ReplyReply Direct Link To This Post 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
REFLEX ALL THE WAY.... (however, im playing with horns again...) That ok Mister Valiant? :)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Pasi Quote  Post ReplyReply Direct Link To This Post 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.
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