Quote:
Originally Posted by
Jens Eklund
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Once you lose these beliefs; you´ll also accept that it doesn’t matter if the sub 80 Hz or so frequency range, comes from one side or both sides of a speaker system in a room; the sound of a kick (or whatever) will still appear to come from the side that also reproduces the harmonics of the instrument recorded, and as long as the two sets of low frequency drivers are working together constructively (and not spaced too far apart and sweet spot is near the center line between the two woofer sets) and there´s no major modal problems in the room; the “attack” of the low frequency sound wave won´t degrade when being produced by two sets of woofers instead of one. As stated previously; there are only positives by letting more woofers (at least two sets, L & R) share the burden of low frequency reproduction since this results in less distortion (less cone travel per woofer needed) and a better modal situation due to the directivity accomplished by this arrangement (minimizing the excitation of modes related to width).
Am currently using 2 homemade 12" sealed coax mains and one 18" sealed sub on the floor. The sub is directly under the right main, at the same distance to the sweet spot as the two mains.
I want to add another 18" sealed floor sub under the left main.
While experimenting with various crossover settings, the "best so far" lowpasses the subwoofer 24 dB Linkwitz Riley at 500 Hz, with no highpass on the Mains 12" speakers. An earlier "good" sweet spot was symmetrical Linkwitz Riley 24 dB crossover of mains and sub at 80 Hz.
I was afraid that letting the single subwoofer extend so far into the mids would ruin the stereo imaging, but if so my ears are not good enough to know. I'm not real concerned with stereo imaging, but even rolling off the sub at 500 Hz, directionality is easily perceivable on mid-bass and low-mid instruments.
The 18" sealed sub acoustically begins rolling off above about 200 Hz but still has significant output at higher frequencies.
The 12" sealed mains begin acoustically rolling off below about 60 or 80 Hz but are strong enough to make some SPL below 40 Hz even if un-equalized. In a bigger room and louder listening level they would be strained in the bass. But at 90 dB nominal SPL, point-blank range in a small room, can be equalized flat down below 40 Hz easy enough even without the subwoofer.
Apologies the tedious description. Just saying, with low frequencies primarily coming from the sub but also helped by the two 12" sealed mains, it behaves SOMEWHAT like a 3-sub system. The bass EQ is relatively flat so that at low frequencies the sub is naturally louder than the two 12" mains, but the lesser amount of bass from the two additional speaker locations seems to help flatten the room bass frequency response. The low bass frequency response gets poorer if I highpass the 12" mains and rely only on the single subwoofer.
The reason I eventually adjusted the subwoofer lowpass as high as 500 Hz-- I have some ceiling absorption and such but had a fairly big null-peak pair around 400 Hz probably the fault of floor-ceiling bounce. Though the sub is not very loud up that high, careful placement of the sub lowpass frequency fixes that 400 Hz problem, probably by adding some extra energy from a different room location. Probably the same as the "multiple sub" bass effect, except at higher frequency.
Maybe this winter will find time to build the other sub under the left main. That along with the overlapping-frequency mains would be like a four-sub system, but dunno if it will significantly affect my most problematic 37.5 Hz null.
I had read about people overlapping frequency ranges between mains and subs and was earlier skeptical of the procedure. For one thing, it would require mains strong enough not to rattle and distort if driven with low bass. But maybe one of the reasons it could be beneficial in bass and even low mids, would be the "multiple speaker" smoothing of room modes?