Will Sd x Xmax Always Tell You The Loudest Sub?

10+ year member

Hebrew Israelite
I keep reading that Sd times Xmax gives you the amount of air a sub can displace. And since BASS is, from what I understand, all about moving air, then will the numbers ALWAYS tell you the loudest sub(s) before you even have to hear them?

Because if that's the case then all the "SQL" fans just need to find a sub that sounds good with the longest throw possible.

And again, if that is true than these (below) are in a class by themselves.

The Untouchables:

1) JL Audio 13W7

2) Elemental Designs A Series 15"

3) Resonant Engineering XXX 15"

Is that ALWAYS the case?


10+ year member

Senior VIP Member
In terms of LINEAR displacement, which matters in terms of musical reproduction(not SPL burping) Yes, those subs(in contrast to lower linear displacement subs) will be able to move more air, more cleanly. The more air you move cleanly, the louder you will get while still maintaining very low distortion. Add in BL flattening technologies, like the XXX's or the W7, coupled with huge linear excursion and you have a sub that that is ideal for musical reproduction(that is if you like the lowest possible distortion at any given volume level)

Of course, you need to use an appropriate enclosure, with the right amount of power to use the linear displacement a driver like that affords you, and use it effectively. You wouldn't want to pull a 'Below 30' and waste the huge potential of the driver //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif :p


5,000+ posts

Kilroy was Here
Is that ALWAYS the case?
Nothing is ALWAYS the case. Larger Sd and Xmax point toward the POTENTIAL to get louder, but that does not mean that they will. Getting a sub to it's Xmax (especially the modern super subs) at all but the lowest of the low frequencies or with less than several kilowatts of power is nearly impossible. Add in a ported enclosure and the extra damping it provides and the task becomes even more difficult. There is so much more to the equation than merely theoretical displacement. It comes down to actual achievable displacement which includes motor strength at the extremes of excursion, power, enclosure, frequency, etc...


Premium Member

Master of all things loud
Southern WV
Sd x xmax will tell you the loudest sub if:

1. talking sealed enclosures

2. no limit on power availible

3. no limit on distortion level

otherwise.. it won't //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

Loyd L.

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