Confused...what is Xmax?

[CanadianDream 10+ year member]

Okay guys, looked at a few threads like this.

http://www.caraudio.com/forum/showthread.php?t=123325&highlight=explain+xmax

Trying to figure out how much clearance I will need in front of a sub and a plexiglass panel covering it so it does not rub on hard bass notes. How do I determine the maximum the cone and surround will extrude? Is this Xmax?

If it is, how much clearance beyond Xmax do you leave as a safety factor.

Thanks.

Also if there are any good threads describing (even better with pictures) all the parameters I would really appreciate any links.

Click to read more...

 

[CBFryman2 5,000+ posts]

Xmag is more important than Xmax whne deciding how much clearance. XMax is the point at which Bl falls off to 70%.

 

[CanadianDream 10+ year member]

Never heard of Xmag - what is it?

So is Xmag then a measurment from the mounting ring outwards? I am looking at a mounting option with only 3 mm of clearance beyond Xmax. Theoretically then it should be enough, is it in practice?

 

[CBFryman2 5,000+ posts]

Xmag is as far as the motor is capeable of pushing the woofer in one direction...linear and non linear excursion.

 

[CanadianDream 10+ year member]

thanks, found this post.

http://www.caraudio.com/forum/showthread.php?t=154563&highlight=xmag+xmax

It says Xmax should be the limiting factor of Xsus and Xmag. So what about using Xmech?

The question remains how do you translate excursion into a value of clearance above the mounting ring - if you can of course.

 

[Immacomputer 10+ year member]

Use Xmech or Xsus when calculating clearance. Xsus or Xmech are as far as the suspension will allow the sub to travel before cause damage (coil against back plate or spider landing into the basket, etc..). Don't forget to measure this from where the cone meets the surround and not from the end of the surround.

Well, you will be even more in the clear if you measure from the peak of the surround.

 

[creyc 10+ year member]

It seems with most woofers you want to double the Xmax to get the mechanical limit the cone and surround will ever move. In practice, you'd be better off giving as much space as you can. It's never wise to block off either the front or the back of a driver too close.

 

[NDMstang65 10+ year member]

Here's a good general reference point..

http://www.the12volt.com/caraudio/thiele.asp

 

[Calikid 5,000+ posts]

Xmax = christmas //content.invisioncic.com/y282845/emoticons/fyi.gif.9f1f679348da7204ce960cfc74bca8e0.gif

 

[ngsm13 5,000+ posts]

Here's a good general reference point..
http://www.the12volt.com/caraudio/thiele.asp

Excellent choice.

nG

 

[CanadianDream 10+ year member]

thanks, really appreciate the link. Still confused as to where exactly the measurements are taken from. But a great start.

Also I read that some manufactures quote forward and backward movement combined. So there Xmax would be doubled. Is there a way to tell when this number is quoted? (ie. only certain manufacturers, or common sense if the Xmax value is way too high)

Here's a good general reference point..
http://www.the12volt.com/caraudio/thiele.asp

 

[CanadianDream 10+ year member]

Agree man...but unfortunately there are always those pesky space constraints in a car. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

Trying to figure out if my plan will work or interfere with the movement. Also I figured I could build a wood baffle with a sunken inner lip equal to the Xsus/Xmech value. That way i would ensure adequate clearance. Anyone think that is a bad idea...lol.

It seems with most woofers you want to double the Xmax to get the mechanical limit the cone and surround will ever move. In practice, you'd be better off giving as much space as you can. It's never wise to block off either the front or the back of a driver too close.

 

[Immacomputer 10+ year member]

Example:

My sub has 23mm of xmax and about 30.1mm of Xmech. I would then exaggerate this number to be about 1.5", which is actually 38mm, and then I would measure from the peak of the rubber surround and make sure I had at least 1.5" from whatever I'm concerned about.

Actually, I would just install these grills and let them come within about .25" from the edge:

http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=260-443

That's what I do right now and it works fine.

 

[Relax 10+ year member]

First off, Xmax, Xmech, and Xsus are all measured one way from the subs natural resting point. Xmech is usually limited in how far back the subwoofer's cone will travel, there happens to be large metal plates in the way- going forward however, there is little other then a spider and surround, which usually allow for more then Xmech travel anyways.

Next- anytime you are worring about mm of clearnace infront of a sub you have a bad design for several reasons. First among those reasons is the loading effect the subwoofer will experience when played. The loading of the cone will alter the performance of the sub enough that its predicted response in any enclosure you design will be altered. Next is the possiblity anything goes wrong. As soon as the subwoofer travels past the the clearance you ahve set aside, it will hit a ver solid object and it will die. The voicecoil will jam into the gap it rides in normally, and the sub will be broken. Why even risk it.

If you do have your heart set on slamming your sub up against some plexi glass- go with Xmech measured from the forward most part of your sub (probably the surround's apex).

 

[audioholic 5,000+ posts]

Next- anytime you are worring about mm of clearnace infront of a sub you have a bad design for several reasons. First among those reasons is the loading effect the subwoofer will experience when played. The loading of the cone will alter the performance of the sub enough that its predicted response in any enclosure you design will be altered. Next is the possiblity anything goes wrong. As soon as the subwoofer travels past the the clearance you ahve set aside, it will hit a ver solid object and it will die. The voicecoil will jam into the gap it rides in normally, and the sub will be broken. Why even risk it.

Loading the sub would be a problem I agree, if he wasn't talking about a speaker grill cover. If you are capable of calculating the sound anomolies encountered when adding a speaker grill, you are a better man than me. //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif

Also, people are describing a situation where he calculates physically how far the cone is capable of travelling... what's gonna go wrong to alter that? If the cone moves further than its physically capable of (while remaining in one piece), then the surround kissing your grill is the least of your concerns. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif