What exactly does a higher Xmax on a sub provide?

[txdog27 10+ year member]

I am at a crossroads right now with my subwoofer selection for my new truck install.

I am wondering what exactly a higher xmax does for you......does it hit lower frequencies, move more air, make it louder.........what........can someone please explain this in detail to me.....

I am inbetween these two subwoofers....

SSA Zcon 15" DVC2 - 32mm Xmax

RE Audio XXX 15" DVC2 - 54mm Xmax

Either will have 2500 clean watts to them and crossed and cleaned up with a RF 3sixty.2

Click to read more...

 

[LosIsATool 5,000+ posts]

From what I have experianced, high excursion gives the sub more authority on the bottom end

 

[The_Grimy_One 10+ year member]

Out of those, I am assuming that is the new xxx, so I would deff take the zcon... Not to mention the xxx is gonna need a huge box. I really can't explain the xmax theory tho...

 

[akheathen Premium Member]

theory? well x-max is total maximum movement(from a new sub) all will depend on how you tune the enclosure and the motor controll it will have, but plain an simple, more X-MECH is going to move more air for a given cone area, being allowed to do so. generally, the more x-mech, the lower the fs may be. the reason i am accentuating "x-mech" is that you can see x-max all over, usually having an x-mech 2x what the x-max is (x-max is the movement from dead rest to max excursion, where x-mech is total movement peak-to-peak) sometimes, you will find a sub sneak a deceptive x-max, where you will have as much as 3-4x as much forward movement from rest as bottoming movement. many times i've seen something like "15mmx-max, 21mm x-mech" also, make sure that the x-max, is not actually representing x-mech. i am actually seeing that more common nowadays. it's one cheat to sell you on the better sounding figure. for instance, sub "a" has an x-max of 17mm, and sub "b" has an x-max of 22.... while 22 does sound alot better than 17, manufacturer "a" advertises correct x-max, and manufacturer "b" is representing x-mech, usually with a astrix, or foot-note of "p-p", and the real comparison is 34mm vs 22mm. now, there are also more factors. lloking at the qts, bl, and other parameters may allow you to push the 2 subs in different ways, and the lower x-max sub might be able to be run harder in a restricted enclosure option, where the larger movement could simply allow you to gain a little efficiency off a lower power level without exceeding the suspension limits

 

[RAM_Designs 5,000+ posts]

Xmax is commonly measured as the amount of 1-way excursion while staying within 70% of the Bl value(motor strength). As the coil moves outside of the magnetic gap of the motor, the woofer looses strength, and as a result, control over the cone. You can't simply look at xmax to determine what will be louder, there are too many other variables.

On a side note, I like high xmax woofers, but the new XXX is sort of ridiculous and makes too many sacrifices in order to achieve the large xmax that it boasts.

 

[audioholic 5,000+ posts]

theory? well x-max is total maximum movement(from a new sub) all will depend on how you tune the enclosure and the motor controll it will have, but plain an simple, more X-MECH is going to move more air for a given cone area, being allowed to do so. generally, the more x-mech, the lower the fs may be. the reason i am accentuating "x-mech" is that you can see x-max all over, usually having an x-mech 2x what the x-max is (x-max is the movement from dead rest to max excursion, where x-mech is total movement peak-to-peak) sometimes, you will find a sub sneak a deceptive x-max, where you will have as much as 3-4x as much forward movement from rest as bottoming movement. many times i've seen something like "15mmx-max, 21mm x-mech" also, make sure that the x-max, is not actually representing x-mech. i am actually seeing that more common nowadays. it's one cheat to sell you on the better sounding figure. for instance, sub "a" has an x-max of 17mm, and sub "b" has an x-max of 22.... while 22 does sound alot better than 17, manufacturer "a" advertises correct x-max, and manufacturer "b" is representing x-mech, usually with a astrix, or foot-note of "p-p", and the real comparison is 34mm vs 22mm. now, there are also more factors. lloking at the qts, bl, and other parameters may allow you to push the 2 subs in different ways, and the lower x-max sub might be able to be run harder in a restricted enclosure option, where the larger movement could simply allow you to gain a little efficiency off a lower power level without exceeding the suspension limits

xmech is not peak to peak, it is also (suppose to be) measured one-way. xmech is the maximum movement allowed mechanically (hence the 'mech'). As RAM said, xmax is (usually) derived from 70% BL. xmech ignores BL (or distortion output), and simply describes how far the sub can move (one-way) without the coil bottoming out against the backplate (in a motor limited design) or the suspension bottoming against the cone or frame, or the spiders/surround tearing (suspension limited design). In some cases, cone strength also affects xmech. This is why you will often see something like xmax = 18mm and xmech = 22mm... the sub reaches 70% BL before the suspension or motor bottoms out. Most designers do this intentionally to avoid users damaging the speaker before realizing they are getting close to its failure point. Its easier to bottom a sub out and damage it if it doesn't display any audible distortion before reaching this point.

xmax is also sometimes derived from a simple equation by measuring the coil length and subtracting the height of the gap/2. Divide by 2 because it is one-way. This is a (slightly) less accurate way to measure xmax, as you really dont know if this will be a 70% BL point or not, but it is a much easier way to measure xmax, and so usually smaller companies with less testing equipment use this method instead of actually measuring BL (with a DUMAX machine).

Sometimes xmag is greater than xmech (rarely), so its also correct to say that xmax is simply which ever spec is less, xmag or xmech.

xmag = 70% BL ("mag" refers to magnetic potential, which is what creates BL)

xmech = maximum physical excursion potential of the speaker ("mech" refers to mechanical movement potential, which is limited by the things I mentioned previously)

In a sealed enclosure application, xmax is very important, because cone excursion is the only thing that factors into the amount of air moved. In vented setups, xmax is less important because the enclosure's vent and tuning also affects total air displacement. For example, when playing a note at or very near enclosure tuning, cone excursion is minimized, but enclosure efficiency is maximized, so obviously how far the cone can move linearly is not as important as in the sealed system where only cone movement affects air displaced. In a vented system, other factors such as heat dissipation become more important, because again at or near tuning you have peak output, but minimized excursion (and thus, minimized cooling capabilities).

Even in vented system, xmax is important however. For one reason, when playing music, your sub is not always playing at or near tuning, so excursion is not always minimized. Dip below tuning where the sub unloads, or play higher freqs well above enclosure tuning, and cone excursion becomes more and more important.

xmech is most important in SPL situations, where the sub is burped at one, and only one, frequency. SPL competitors do not care if their sub is distorting when burping, so the loss of BL (and thus the loss of cone control which leads to distortion) is of little importance. At that point, its basically just an air pump. xmech is important to an SPL competitor because they dont want their sub(s) to bottom out and become damaged while burping. Ideally, an SPL setup will burp the sub, with excursion reaching something just less than xmech. At that point, the sub/enclosure combo is displaying its maximum air displacement potential. That is where power handling/cooling capability comes into play, as most setups will melt the coil from passing that much current through the coil, before the sub reaches xmech (again because they are burping at or near tuning where excursion is minimized by the enclosure).

xmax is just like any other t/s spec, when looked at in a vacuum, it is/can be misleading. Never focus on just one spec, such as xmech, xmax, power handling, etc and expect to derive very useful conclusions about the speaker's performance.

 

[audioholic 5,000+ posts]

The new XXX suffers from the issue of having such a high xmax, that the coil is much more likely to fail from heat build up before that 54mm xmax is even close to being reached. That is why it is traditionally considered a large enclosure sub (plus it has a pretty large Vas iirc). But in a sealed application, with the right power and enclosure, the XXX is in a league of its own. No other production sub really even comes close. The next closest production sub that I know is the LMS Ultra, with an xmax in the mid to high 40's. The problem is, most people who go with such a large box simply opt for a vented system, again (from my previous post) where xmax isn't as important as it is with sealed setups, so that amazing xmax spec becomes less important. That is not to say that the new XXX cant be very potent in a vented system, it can, its just going to require an even larger vented box than its sealed counterpart. At some point, the box becomes so large that it tends to make it less of a 'car audio' subwoofer, and more of a 'home audio' sub, because we rarely care how large we need to make the enclosure for a home sub like we do with car audio setups where we are trying to cram this enclosure into a Honda's trunk.

Hope that clears up the confusion in this thread.

 

[Danometal 10+ year member]

Unfortunately, I've discovered the importance of Xmax in large, low tuned enclosures. My box is 2.5 cubes @ 25 hz, and my JBL P1224 can bottom out at full power from exceeding Xmax and Xmech down low, but yet above tuning where the excursion is reduced. But, 20 hz test tones don't bottom it out, as it's not unloading too much by that point. Maybe 14 mm Xmax isn't quite enough.

 

[dipitydoo 10+ year member]

good info, thanks, audioholic.

 

[zako 10+ year member]

On a related note, I often wonder how much xmax is enough for an SQ system playing in midsize car. I have a preference for rock music and some instrumental stuff, and that's 95% of what I listen. I assume the sub throw there is very low. However, I like to play occasionally play hip hop/rap and prefer the lows to be played effortlessly with authority. For example, Peerless XXLS and Dayton Reference (some models) have only 12.5mm of xmax. I have spent a while wondering if this was enough and eventually went for Infinity Kappa 120.9w, with 17.5mm xmax (the former figure had been measured and confirmed, but I take the manufacturer's word for the later). I know that may be this was a dumb way of making decision. I do like the Kappa sub though. I wouldn't be surprised if it was up there with Daytons or ID subs.

 

[Papermaker85 5,000+ posts]

wrong box, wrong tune..

try 2 tunes to 33..

 

[THATpurpleKUSH 5,000+ posts]

Unfortunately, I've discovered the importance of Xmax in large, low tuned enclosures. My box is 2.5 cubes @ 25 hz, and my JBL P1224 can bottom out at full power from exceeding Xmax and Xmech down low, but yet above tuning where the excursion is reduced. But, 20 hz test tones don't bottom if out, as it's not unloading too much by that point. Maybe 14 mm Xmax isn't quite enough.

whats your ssf set to?

 

[Danometal 10+ year member]

whats your ssf set to?

All the way down to like 10 hz. There only a small range in which my sub suffers over excursion, and above and below that is fine. For example (just a ballpark generalization), 20 - 28 hz is golden >>> 29 - 40 hz is risky for bottoming out >>> 41 - 100 hz is golden.

My thinking is the box's net volume is too big by about a .25 - .5 cubes margin.

 

[Buck 5,000+ posts]

All the way down to like 10 hz. There only a small range in which my sub suffers over excursion, and above and below that is fine. For example (just a ballpark generalization), 20 - 28 hz is golden >>> 29 - 40 hz is risky for bottoming out >>> 41 - 100 hz is golden.
My thinking is the box's net volume is too big by about a .25 - .5 cubes margin.

I think you may be right.

 

[Danometal 10+ year member]

I think you may be right.

I could very well attach blocks to the inside to reduce the net volume to 2.0 cubes, and that will increase my tuning to 28 hz. Or, I may just leave it, as regular music doesn't cause this problem. Not sure yet. At least it won't be much trouble to test out a smaller box by using the same box.