Top notch speakers with their own sub

Thanks for the kind words, Jax2.

The distributed multisub concept is something I learned from Earl Geddes. Here's a brief synopsis in his words:

"The modal response of rooms at low frequencies causes large peaks and dips in the overall response of a system...

"By using multiple subs distributed around the room, low frequency response can be smoothed out. Placing multiple subs in multiple locations, each sub will excite the room’s modes in a different way. While the response of each would still have the anomalies suggested above, the total combined response is much smoother than any of the individual responses. In essence, they balance each other out, resulting in a much smoother overall response."

Todd Welti of Harmon International has published multiple technical papers on the subject, as well as a non-technical paper which is posted on Harmon's website. Welti did not investigate asymmetrical sub placement, but this paper is still excellent information for anyone interested in a high quality subwoofer system:

http://www.harman.com/wp/pdf/multsubs.pdf

There are of course other issues, but a configuration that is conducive to relatively smooth in-room response is a good starting point.

One primary requirement for a distributed multisub system is a steep-slope lowpass filter (at least for those subs which are positioned away from the main speakers) so that you don't have subs reproducing lower midrange energy loud enough to betray their locations.

Duke
dealer/manufacturer

Equalizing peaks and nulls becomes more practical with a distributed multisub system. Before equalization the peaks are less peaky, the nulls are less nully, and there is less spatial variation (meaning that the response doesn't change as much from one location within the room to another). That being said, I'd still be hesitant about putting a lot of boost into a null unless you had plenty of headroom available - which apparently was the case in Marty's situation.

Jax2, in my opinion fairly flat in-room response is the goal in the bass region, and above the bass region, I prefer a gently downward-sloping curve. If I have to choose between too much and too little bass energy, I'll choose too little because that's less likely to be distracting.

Which brings up something else that most rooms do at low frequencies: Boundary reinforcement, sometimes called "room gain". Breifly, as we go down in frequency and the wavelengths become progressively longer relative to the distance to room boundaries, the first reflections become more in-phase rather than random-phase, so the net result is a roughly 3 dB per octave rise in bass energy as we go down below 100 Hz. This of course varies from room to room and with speaker positioning within a room, but since subs are usually placed close to the intersection of at least two room boundaries (on the floor and up against a wall) it's worth taking into account.

Without going off on a long semi-technical tangent, I'll just say that in my opinion a worthy "target curve" for a subwoofer system would be the approximate inverse of this 3-dB-per-octave typical room gain. If the subs are "flat" all by themselves, by the time room gain is factored in they will be bass-heavy. But if we have to err, imho best to err on the side of too much bass rolloff rather than not enough, so I'd rather have 6 dB per octave of rolloff (before room gain) below 100 Hz instead of none at all.

Duke

"PS Duke - is there pricing info on the Swarm and Planetarium systems? I didn't see any on your web site. Not that I'm thinking....." - Martykl

Yeah my website is a bit out of date. I have a forum on audiocircle.com that has more up to date info.

The two Planetarium systems are 6.5 grand and 10 grand, and the vented Swarm (as used in the Planetariums) is 2.5 grand including amp. I also have a sealed Swarm that's a bit less expensive.

Not that I'm holding my breath.....

You could probably roll your own without too much trouble, just be sure and use an amp that has a 4th order lowpass filter. Or better yet, add a couple more of whatever you're using now (Rhythmics??).

Now Earl Geddes would probably say you only need 3 subs, as long as you elevate one so that it's above the centerline of the room (closer to the ceiling than to the floor) so that your low frequency sources are scattered in all three dimensions. Neither Earl's approach nor my variation is particularly high in WAF, as Spatine obviously figured out!

Duke