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-   -   xmax rating question. (http://www.diyaudio.com/forums/subwoofers/221078-xmax-rating-question.html)

shmb 7th October 2012 03:15 AM

xmax rating question.
 
Hi all, I have a quick possibly dumb question just out of curiosity.

This is the data sheet for the peerless 835017 XXLS http://www.parts-express.com/pdf/264-1114s.pdf

It states the max linear excursion as +/- 12.5mm.

Does this mean the xmax figure is 12.5mm or 25mm? :confused:

Thanks

Cokewithlime 7th October 2012 03:49 AM

12.5mm one way, total is 25mm.

If your using modeling software the one way amount is generally used as the default in most of those software packages.

shmb 8th October 2012 02:19 AM

Ok, so does this mean effectively, the typical max linear excursion of any woofer is double the xmax rating?

Cokewithlime 8th October 2012 05:06 AM

xmax(maximum linear excursion) that you see in almost all spec sheets is shown as a one way rating and that is the figure you would plug into your sim/modeling software.

Yes, total travel of the VC is double the xmax figure and accounted for in the sim/modeling software.

tvrgeek 8th October 2012 11:40 AM

Also note, Xmax is for the approximate linear range, not when the VC smashes into the back of the motor or rips the cone from the surround. Max excursion is sometimes listed separately and may be well more than twice Xmax. Don't go there. I tend to model at half Xmax as that is as far as I would ever intend to use a driver without distortion getting too bad. If the driver can't produce the level I need at that level, I have picked the wrong driver.

shmb 11th October 2012 03:32 AM

Ok, thanks guys. :)

Shadydave 11th October 2012 12:46 PM

push it to the limit
 
Quote:

Originally Posted by tvrgeek (Post 3193625)
SNIP... I tend to model at half Xmax as that is as far as I would ever intend to use a driver without distortion getting too bad. If the driver can't produce the level I need at that level, I have picked the wrong driver.

.
This is one point that I think allot of people tend to overlook.
Distortion may go way up at advertised Xmax as non-linearities in the motor come into play.
I wouldn't ride my 2 stroke at redline continuously, it is the same with a speaker.
But hitting redline, or Xmax in a transient situation can be exciting.
.
When I set an SPL meter on long time constant in my HT environment, at my listening position
(4 M from speaker stack) I rarely see more than 90 dBa.
But the occasional 120 dB transient makes things exciting.

IMHO,
Dave

forr 11th October 2012 01:06 PM

Expressing cone travelling as +/- x mm is unambiguous.
Il reminds the two ways of motion, forward and backward.

Remember that, for a sine signal, amplitude describes the motion one way. For instance, a electrical sine signal of 1 Vrms, the amplitude is 1.414 V, sometimes written 1.414 Vpk (pk = peak). It is very handy to say that the signal is +/- 1.414 V.

I agree that sometimes the specified Xmax of some driver datasheets can be puzzling.


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