Raul:
"According to scientific studies four subs are optimal in a home audio system."
As a user of the 4 sub approach for the past year, I can attest to the validity of these scientific studies. I've found the 4 sub approach has been an excellent solution for bass performance in my 23' x 16' living room. My system is used about equally for 2-ch music and 5.1 surround HT.
I use an Audio Kinesis Debra distributed bass array system that consists of 4 non-amplified subs (each sub is ported, has a 10" driver, weighs 67 lbs. and measures 23.75″ x 14.5″ x 10.375″) and a 950 watt class A/B amp with variable crossover and phase controls. Total price for the system is $2,990 and there is a choice of woods.
I was originally considering getting 2 high quality powered subs like JL, REL or Vandersteen but discovered the Debra 4 sub system while reading about the scientific studies that Raul references above.
These were studies by Acoustical Engineers Dr. Geddes and Dr. O'Toole that were concerned with bass wave propagation in residential and commercial spaces. Here's a summary of their key conclusions:
Sound waves behave differently in typical rooms below and above about 200 hz.
Low frequency sound waves are so long ( a 20hz sound wave is 56.5 ft. long) that they'll bounce off room boundaries until they run out of energy.
These initial and subsequent long bass waves eventually overlap and meet which creates standing waves at various points in a room.
These standing waves result in bass peaks (perceived bass overemphasis) bass dips (perceived bass under-emphasis) and even bass cancellations (no perceived bass) at various points in a room.
They were able to mathematically predict and plot precisely where standing waves, and their corresponding peaks, nulls and cancellations, would exist in a room based on the location and number of bass sources (subs), bass frequency, room dimensions and boundary materials,
They found a relationship between the number of bass sources(subs) in a given room and the resulting number of standing waves in the room; Basically, the more subs in a given room the fewer bass standing waves are created and the better the bass.
They note that there is, of course, a practical limit to the number of subs users will deem acceptable.
As a result and perhaps the most crucial conclusion they reached
concerning the use of subs for residential and commercial spaces, was that the use of 4 subs in a given space resulted in the elimination of the vast majority of bass standing waves in that space. Each additional sub beyond 4 only resulted in marginal improvements.
The DEBRA and SWARM distributed bass array systems are both based on the Geddes and O'Toole studies and conclusions and they both, unsurprisingly, utilize 4 subs.
I honestly believe it would be almost impossible to overstate how well the DEBRA system has improved the bass performance in my room for both music and HT. I use Magnepans for my L/C/R channels and, as many of you know, they have been notoriously difficult to integrate with subs. The bass is solid and tuneful for music and powerful, impactful and even startling on HT.
With so many people using bass traps, microphones, room analysis and correction software, equalizers and digital signal processing to improve low bass performance in their rooms, I find it ironic and a touch humorous that the best solution available thus far is adding more subs.
I don't want to leave the wrong impression, I am not wealthy and $2,990 for a sub system is expensive to me, too. I rationalized the cost as being less than the cost of 2 high quality powered subs and that it's likely the last bass system I'll need to buy.
The progressive and precise setup procedure is fairly elaborate and took me most of an afternoon to complete. The subs are wired in parallel and it's recommended that 1 sub have its phase inverted.
Thanks,
Tim
