Axiom Home Page Forums General Discussion Home Theater My four sub independant system .....Alan will it w

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While it is true that low bass is in theory non directional, the way that bass mixes in the room is not. An example - suppose that you have a group of performers on a stage and they are being recorded by two or three omni directional microphones in front about 15 feet away, which is a common technique. Now say you have someone playing a bass drum or string bass on the extreme left of the stage. The sound of that instrument will reach the left microphone earlier than the right microphone. Considering the frequency of the instruments will be be around 30 Hz in the case of the bass drum and 40 Hz in the case of the bass, the delay in the sound reaching the left and right microphones will be as much as half a wavelength. If you were to play this with a single subwoofer, or two subs with the bass between the channels electronically summed by the crossover as it is when you use the "sub/LFE" output on your pre/pro, this acoustic delay would simply cause peaks and dips in the response of the bass from that instrument. However, if you use stereo subs and are hearing ture stereo bass, this delay between the sound reaching the left and right microphones is heard as natural acoustic mixing of the bass frequencies from those instruments in the listening room, just as it did in the original recording venue. The way the bass mixes in the room is natural, acoustic, and dynamic over time.

As an example of another real-world benefit of stereo subs located next to the main left and right speakers, consider the following example. You have your single subwoofer connected to the "subwoofer/LFE output of your pre/pro, and the sub is located next to your couch, and you have it crossed over at 80Hz (in other words, a pretty conventional arrangement). The distance from your listening position to the mains is 10 feet (the sub is 10 feet from your mains). You play a studio recording that has a bass player coming from the right speaker. He plays an open "E" string. Guess what? The fundamental frequency of that string (about 40Hz) will come from the subwoofer next to you. The second harmonic at around 80Hz will come from both your sub and your main speakers. The 3rd harmonic (and above) of the bass will come exclusively from your mains. As you can imagine, this plays absolute havoc with the harmonic presentation and structure and of the instrument! The effect is of the same type, if not to the same degree, of taking the tweeter out of your speaker cabinets and relocating them a couple feet away. Fundamental frequencies coming from one place, and the harmonics coming from another. The closer the notes being played are to the bass crossover frequency, the worse this disembodiment of the fundamental from it's harmonics will be, as the phase difference between the two will be greater due to the higher frequency. Adjusting the "phase" control of your subwoofer will not correct this: it only corrects for one specific frequency, that of the crossover, and musicians hate being restricted to playing only one note (at least good ones!).

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Getting the stereo subs in phase and blended with the mains can be timeconsuming and then there are phase tradeoffs between the centre and the other subs. If you attempt it be sure to set aside the better part of a Saturday and try to do it with a RTA display as well as an SPL metre.

But lets step back and look at your equipment and what I think you are trying to accomplish. You have a great pair of deep floorstanders in the M80s so wouldn't it be better as was suggested already to put them to use by crossing them as low as possible at 60hz or perhaps 50hz. The M80s will give you lots of stereo bass at those crossover points and preserve more of the harmonic structure since more of the mid bass fundamental will originate in the M80s. Do you really need to run stereo subs with those deep M80s?

Now if you run the rest of the subs mono you will be able to concentrate on placement and proper phase between the subs to smooth response across the room. With dual subs while they look very cool up front the Harman papers on optimal sub placement recommend midsidewall placement for best frequency response across most seats. I like the idea of a pair of 500s and a pair of 350s because they allow you to lower gain on all subs and with it keep distortion components and other non-linearities to a minimum. If you get them working in phase the resulting bass will be very clean and detailed. Its well worth the effort but I would suggest running them all in mono for the best overall acoustical improvement.

I ran a pair of 600s and a pair of 500s like that for many months and the bass was absolutely spectacular. However my family had to get used to hearing bass sweeps running through the house for several weekends in a row.

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A 60Hz crossover would make this even more certain, but that would be a little low for your VP150 and QS8s(and you can set only a uniform crossover frequency on your 3803).

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