Sub output: Is it the woofer size or the rated RMS

Kijanki: Membrane of 18" speaker should be 10.5 times heavier because it should be 3.24 times thicker and the area is 3.24 times larger. That is probably why definition is getting poor (too heavy).

Drew_eckhardt: It's entirely about extended frequency response, which only matters when you're using the driver at high frequencies as in a musical instrument amp. It's not an issue for sub-bass drivers in multi-way audio playback systems.

Drew -- doesn't your response overlook bass damping, inertia of the cone and the other parts of the moving assembly, and the ability of the cone to stop quickly when the input signal stops? All of which I think support what Kijanki was saying.

Regards,
-- Al

Interesting debate. IMHO, there is no question that a larger well built subwoofer will sound better than than ten small cheap ones sharing a box. The issue is that the single large woofer may cost up to $2K! Most high quality 15" subs are expensive and most will use 3 or 4 inch voice coils - not your regular 1 inch VC found in most WAF friendly speakers. This all makes the amplifiers tough job as easy as possible which is what it is all about ....effortless clean dynamic sound with little or no compression is generally why a single large driver matched to an amplifier works well.

I do agree that 10 inch woofers with a whizzer cone tend to work well for a bass player (as in Zu) because there is a slap sound to the bass which is up around 3 to 5 K HZ. But this is not a valid reason to say that a 10 inch for a subwoofer is ideal. Certainly a 10" sub is likely far better than a 6 inch but likewise a 15" will be a lot better than a 10" (assuming good quality in both drivers).

IMHO, ideal is a super big sealed box with low Q (0.5 or so) and a large woofer. The very large woofer and super big box allow for the very poor efficiency of a low Q design.

the ability of the cone to stop quickly when the input signal stops?

That would be system Q or damping. An overdamped design would be extremely inefficient (low SPL output at 20 Hz) with a small woofer in a small box.

Compare a WAF friendly product with an ugly DIY brute. (Source HT Shack subwoofer tests)

Both probably sound equally as good but the brute is going to play a whole lot louder cleanly and effortlessly.

Shadorne - I wasn't thinking of slap and 5kHz when I mentioned 10" woofer's bass definition - for that bass enclosures have tweeters. I was thinking of low frequencies. 10" woofer arrays have better controlled/damped (shorter) bass while 18" woofers tend to produce "woolly" bass. The question is what is cheaper - 18" woofer or 3 x 10" woofers (to obtain the same surface area).

>Drew -- doesn't your response overlook bass damping, inertia of the cone and the other parts of the moving assembly, and the ability of the cone to stop quickly when the input signal stops? All of which I think support what Kijanki was saying.

Bass damping is a separate issue which also isn't related to driver size.

It's determined entirely by the transfer function.

How you get to a given Q (the ratio of stored to dissipated energy) isn't relevant to decay. Even convolving the input to a sealed or open baffle enclosure with a Linkwitz-Transform or shelving low-pass filters works (although with a small box the distortion from air-spring non linearities and power required make a large box more desirable).

Resonant devices (ports and passive radiators) rely on stored energy and may cause audible problems when within the musical power spectrum, but work fine to gain infrasonic extension.

Stored energy in the room is a much bigger problem than in sub-woofers built for flat response, with decay and the resulting amplitude response being very frequency dependant.

The relative significance of time and amplitude aberations is not well understood here. Stimulating fewer room resonances through directional bass works well (this implies dipoles which are dumping most of their power into an acoustic short circuit). Equalizing for flat steady state amplitude response seems to work. Sub-woofers at a null or two sub-woofers centered on the null work according to literature. Catch-throw arrays look real interesting.

Two sets of two (mounted push-pull to cancel even order harmonics) dipole sub-woofers equalized to a second order roll-off with poles at 20Hz (Q=.5) did produce the most natural bass I've heard from any room-loud speaker system in spite of having only 13x19x8' to work with and no acoustic treatments.