Determining The XMAX

[OMNIFEX]

Got my hands on this woofer, and, the paperwork
is partially destroyed.

However, I do have the coil winding length, and,
magnet gap depth.

Coil Winding Length = 16 mm

Magnet Gap Length = 9.5 mm


So, what is the xmax???

 

[kelticwizard]

Xmax = (length of coil - magnet gap)/2

= (16 - 9.5)/2

= 3.25 mm

 

[KevinLee]

Hello,

I believe electrical x-max and mechanical x-max are two different things. They may not be the same.

Any opinions?

KevinLee

 

[noodle_snacks]

I believe that mechanical Xmax (or XMech i think) is the furthest that the suspension of the driver will travel physically travel without bottoming out etc

 

[kelticwizard]

Noodle Snacks is correct. The mechanical Xmax is frequently given as Xmech, but sometimes also as Xmax (mechanical).

In hifi speakers it generally is 1.5 to 2 times the Xmax. In PA speakers it is more than that. The Eminence Kilowatt driver, for instance, has an Xmax of 10 mm, and Xmech of 25 mm.

 

[Centauri]

Hello,

I believe electrical x-max and mechanical x-max are two different things. They may not be the same.

Any opinions?

KevinLee

Xmax is usually linear excursion, and can be measured in different ways. From a mechanical viewpoint, once the amount of wire within the magnetic gap decreases, the movement becomes non linear - so the equation given by kelticwizard applies, and is commonly specified by speaker manufacturers. However, if due to design of the magnetic gap, the magnetic flux extends slightly further than the physical gap height, the electrical Xmax can be slightly higher. This is usually measured dynamically with a signal increased until a certain distortion figure is reached. I believe Beyma use this method.

Personally, I don't think the small differences mean much sound wise.

Cheers

 

[kelticwizard]

However, if due to design of the magnetic gap, the magnetic flux extends slightly further than the physical gap height, the electrical Xmax can be slightly higher. This is usually measured dynamically with a signal increased until a certain distortion figure is reached. I believe Beyma use this method.

Personally, I don't think the small differences mean much sound wise.

Cheers

Yes, I think when measured dynamically, figures 15% higher or so emerge than with the formula. So if the formula produces an Xmax of 6 mm, the dynamic might produce an Xmax of 6.9 mm.

I agree, not too much difference there. Most people just want an idea about how much output they can expect from a particular speaker.

 

[OMNIFEX]

Thanks!


One more question


Can I assume the 16 mm, is the Xmech?

 

[kelticwizard]

I wouldn't.

If it's a home speaker, I would assum e the Xmech is probably 50% more. That would make it about 5 mm.

If it's a PA speaker-then maybe I would assume an Xmech of 16 mm.

Which one is it? Does it have an accordian surround?

 

[OMNIFEX]

Its a PA Driver.

I've noticed that many companies don't offer the
mathematical xmax, but, add 1 - 2 mm more.

 

[kelticwizard]

It's pretty well understood that PA drivers are meant to be driven past Xmax.

I would think you have the length of the voice coil for your Xmech. Most PA drivers seem to do that. Don't hold me to that.

 

[kelticwizard]

Oops! Just took a quick look around at the Xmech of some PA speakers.

They are still designed to be driven pst the linear Xmax, to be sure, but perhaps not as far as the end of the voice coil

Instead of 16 mm for your Xmech, I would suggest a 12 mm would be safer.