2 10" subs equals 1 12" or 15" sub?

Each sub will add around 6 db SPL. All things equal, which is rarely the case (same excursion, box size, placement, amp power etc).

A 12" sub is around 40% more surface area than a 10" and a 15" is just over 100% more or double. So more or less two 10's is sort of like one 15. Four 8" is like one 15". Six 6 inch woofers is like one 15".

Box volume is a big factor too so a box which is half the size of another with the same size woofer will have 3 db less SPL for the same bandwidth (bear in mind, a bigger box will of course use a more efficient driver!).

Ports are also a factor - a port can add 3 dB SPL but at the expense of making the subwoofer have a high group delay and poor transient response.

Amplifier is also a factor - doubling the power can add 3 db SPL (provided the driver can take that power - very long throw!!). So a 200 watt sub with 15" woofer is kind of like an 800 watt sub with a 10" woofer or a 3200 watt sub with an 8" woofer.

The worst part about all this is that for each octave you go lower in frequency you need EIGHT times the efficiency to maintain the same SPL output - so you are on the right track - ignore those 1 foot cube aesthetic looking subs as a foot rest is really all they are actually good for!

So you can see that SPL does not come easy...in some cases big really is better!

The only trick you have is that corner placement will give you an extra 6 db compared to wall placement...often this is at the expense of problematic modal problems.

Finally these are all generalizations...

Agreed-
(2) 10" subs are equal to (1) 15"
(4) 8" subs are equal to (1) 15"

I prefer 2 smaller subs vs. 1 larger sub.

Like Shadorne says, there are too many variables to equate the sonic performance of subwoofers based on driver size. The best thing is to listen to some and draw your own conclusions.

>A 12" sub is around 40% more surface area than a 10" and a 15" is just over 100% more or double. So more or less two 10's is sort of like one 15. Four 8" is like one 15". Six 6 inch woofers is like one 15".

But only if they have the same motor.

Long-throw sub-woofer motors have xmax exceeding 20mm one-way; while 6-8" woofers often go only 5mm so it can be more like one 15" sub matches the output of 24 6" woofers.

>The only trick you have is that corner placement will give you an extra 6 db compared to wall placement...often this is at the expense of problematic modal problems.

Sure, although you can equalize that back to flat in the frequency domain.

But only if they have the same motor. Long-throw sub-woofer motors have xmax exceeding 20mm one-way; while 6-8" woofers often go only 5mm so it can be more like one 15" sub matches the output of 24 6" woofers.

Absolutely agree...big is better! big is beautiful! Queen were right about fat bottomed speakers making the rockin' world go round! Although extremely long throw (overhung)designs often use small diameter but lengthy voice coils (increase EMF)..... in these designs you quickly get heat and thermal compression issues from voice coil heating up...you may also run into linear Xmax issues (many designers do not clarify what they mean by Xmax - is it VC geometry of is "linear operating range to within 10% field strength") so you may win in one aspect (extreme excursion) but may lose some SPL capability due to thermal compression and added harmonic distortion (due to lack of linearity). The only thing that always makes sense is the absolutely biggest most powerful honking magnets you can lay your hands on (increases EMF with no downsides but expensive).

Sure, although you can equalize that back to flat in the frequency domain.

Yes you can and I agree that this can work very well, however , I tend to think it is best to avoid exciting strong modes in the first place....because we are then talking long reverb issues. So it may be ok to EQ it out in terms of an extended test signal to get flat response but then what about short lived transients that hang around in the room? Just a thought.

Anyway, we have barely begun to penetrate the subject of big box ultra LF subwoofers on this thread...some people have DIY designed tube towers that run all the way to the ceiling and produce tremendous ultra LF.

Since the intellectual heavy lifting has mostly been covered, I thought I would ask if anyone else watched and enjoyed the episode of Mythbusters where they build a 52-inch aluminum bass driver into a diesel Mercedes, and powered it from the driveshaft?

I loved that episode.

And then there is the discussion of 2 subs operating in phase and the likelihood of getting that right.