[mcgsxr]

I now have 2 DIY subs that are very similar with one major difference.

The first is a Nakamichi 12 inch driver, in a 3 foot box (roughly) tuned to 23Hz.  I use it with a 300w BASH amp in my main floor 3.1 setup.  I have used this sub on and off for 10 years now.

The second is a pair of MAW-12 woofers, in a 4 foot box tuned to 22Hz.  I use it with a 370w Dayton amp in my 5.1 basement HT.  It is new this year.

WOW does the larger sub with the pair of woofers with roughly the same power do it better.

No replacement for swept area for subs I guess.

I am assuming it is also that sharing the power across 2 subs puts the distortion in 1/2.

[medium jim]

Pretty cool, but how about some pic's!  I can easily see having less distortion by using two subs vs just one.

Jim

[*Scotty*]

Have you had both subs in the same room at the same time and heard the difference between the two? I could see the same the same sub used in two different rooms sounding considerably different in one room than it does in the other room. It is very hard to separate the sound of the sub from the effects that the room has on the bass you hear.
 In a basement you really don't loose bass energy into the walls and the floor as you do in an above ground room. The biggest loss of bass energy in a basement occurs through the ceiling. With double the cone area the sub in the basement could have lower distortion than the sub with the single twelve inch driver. To be sure, you would have to take distortion measurements of both subs operating at the same SPL.
In my opinion more cone area is a good thing.
Scotty

[James Romeyn]

Talked (voice, on the phone) with someone who's name readers might recognize named Bob Carver.  IIRC he is the first one to mention that AES and/or other studies indicate human hearing can barely differentiate differences in bass THD from 1% to about 30%.  Yes, in God's infinite wisdom He apparently designed us with extremely high tolerance to HD in the bass range.  If true, and I believe it is, the promises for low THD in subs are generally vain marketing gimmicks and nothing else except profits for speaker companies and advertisers.   

Per speaker designer/engineer John Krutke of Zaph Audio, we also have similarly high tolerance to FR aberrations in the top octave (possibly low tolerance to THD in the treble...he described high tolerance to FR aberrations).

Then there's that old story about how accurately your ear/brain mechanism can follow, while blindfolded, the arc of a coin as it turns on the pavement or concrete in a person's proximity.  All about distortion and phase sensitivity in the critical mid band for wavelengths similar to the 8" between our two stereoscopic ears. 

I got to hear Brian Cheney's humongous bass towers when I visited and they were set up in his sound room for whatever reason, demo, crossover tuning, etc.  I used to think the startlingly fantastic bass performance was a function of lower bass THD.  Now I instead think it was mostly a function of less floor-ceiling bounce resulting from the almost floor to ceiling array of active bass drivers, and less THD in the mid/treble array. 

The most audible frequent source of bass disturbance is the timing distortion caused by modes.  Lowering THD to zero has sum total zero effect on bass mode issues, which IMO can equal hundreds of percent of distortion because we're talking about wrong disharmonious notes playing when they should not.   

Thinking about this further though: it is definitely possible to exceed even 30% THD @ high output in the first octave.  So maybe doubling the woofers could lower THD enough to make audible upgrade. 
 

[SteveFord]

I'm pretty sure I couldn't hear distortion in the bass regions unless it was really high.
The OP hit the nail on the head with the no replacement for displacement, I believe.

[*Scotty*]

Let's look at this a little closer. One of the more common errors in bass reproduction is frequency doubling, a 40Hz note is played and an almost equal SPL at 80Hz is also produced. While we may be able to tolerate this level of inaccuracy, bass reproduction with this kind of error can't be considered High Fidelity.
 We have all heard "muddy" sounding bass at one time or another, one wonders what we are actually hearing? Distortion from the sub-woofer or the room resonating in the bass frequencies. I have certainly heard a substantial change in the definition of the bass produced from my sub-woofers when I swapped out a cheap no-name interconnect for one of the type I use to routinely connect the rest of the components in my system to my preamp. It sounds for all the world like I have less overhang on the notes.
 I don't know if I buy the idea of a "special" type of IC dedicated to only the bass regions as being a necessity but a case could be made for sticking to the same type and quality of IC for sub-woofer connections that is used in connecting the rest of the system together.
Scotty

[medium jim]

As noted by Bob Carver, the human is incapable of hearing distortion in the bass or lower frequency region.  I suspect that by adding another sub that the cone excursion is lowered and this makes for a faster resolve of individual notes.  Bass is energy which is unlike midrange and highs.   While bass is supposed to be omnidirectional, it isn't and there are overtones, note decay and harmonics that can be heard. Again, multiple subs typically mean that each bass driver has to work less to achieve that of one driver/sub.

Jim

[mcgsxr]

To answer one of the good questions posed, yes I have heard the single 12 sub in the basement.  It did very well for movies, but was not that musical.

The double 12 sub is really good for movies, and OK for music. 

We watched our first family movie last night, Rise of the Guardians.  It is a TrueHD soundtrack, and there were moments of tremendous bass.  There is a moment when a large dino steps down, that shook the room.

I guess it is not reduced distortion, but increased swept area that makes it more satisfying for movies.

[mcgsxr]

I don't think I have pics of each sub complete, and fully visible. 

Here is the 3 foot single 12.  I wrapped it with grill cloth to hide the nasty mdf build!


Here is the 4 foot double 12.  I buried it inside a cavity in the wall of my basement HT, again behind grill cloth so you cannot see it totally either!