Two Subwoofers... Comb Effect

Duke,

Thanks - that we hear frequencies or cycles and NOT transients in the bass makes sense - you have convinced me that John Watkinson may be barking up the wrong tree. Your contention that integration is better with a sub close to the mains when using only 12 db/octave cut-off makes sense (because of higher frequencies above sub cut off).

However, there must be a limit to what extreme phase shifts can be allowed and not mess things up. Perhaps a full cycle is too much? This would be 30 feet of distance at 40 HZ - and so many small ported speakers have a 3 db point at 55 Hz and a port at 40 Hz and will therefore achieve this!

While I can't say for such large 360 phase shifts (are they really audible at all) However, my impression is that an EXTRA cycle is certainly audible/perceptible. In fact, I suspect the overdamped response of a low Q system is so pleasant and "tight" in the bass precisely BECAUSE you get absolutely no extra cycles as you would from an underdamped ported resonant design (the better in room roll off response may certainly be part of it too). So John may be right but for the WRONG reasons?

This thread is interesting to me because I've spent the last 10 days with a room analyzer, a PEq, 2 subs and 2 ears. There seems to be a lot of theory being argued here and I wonder how many people have worked through this process in their room. I only say this because my experience 'till now has been one of near total unpredictability: What works best for one combo of sub/main fails miserably for the next.

I understand that my experience is limited, and I do not want to overstate my expertise, but so far, trial and error appears to be the only way to a good answer. To date, being wed to one philosophy of phase coherence, crossover slope, etc would seem to be a recipe for disaster. I know this is not a satisfying conclusion, but it's the one I've reached thus far.

Marty

Thanks, Aldavis. Just so you know, I don't mean to discount your personal experiences and observations, such as regarding 4th order crossovers, but it's possible that the problems you heard could be traced to a frequency response issue arising from poor driver integration. For example, in a typical 6" two-way speaker, an abrupt change in power response is more likely with a steep crossover than with a gentle one, and in my experience that's likely to be audible. In fact, that's why I pattern-match in the crossover region in my two-way speakers.

Shadorne, I know it seems insane for me to make excuses for a phase rotation equal to 30 feet of distance or so... but, that's my understanding of how the ear processes deep bass information. I could be wrong.

I concede that a sealed box comes to a full stop (and a full start) faster, which is beneficial for impact but perhaps not for pitch recognition, assuming the vented box doesn't sound boomy. This post by Earl Geddes has some quite interesting thoughts on the subject of low frequency reverberation towards the end:

http://www.audioasylum.com/audio/speakers/messages/208728.html

Several months ago I performed an unscientific experiment, comparing equal-size, equal-efficiency small subwoofer boxes. The contestants were a 6.5" room-complimentary-tuned vented box, and a 10", Qtc = .5 sealed box. The 10" woofer was nearly three times the price of the 6.5" woofer.

On kick-drum, the sealed woofer sounded more tight and solid. On literally every other bass instrument I could come up with, the RGC-tuned vented woofer had a more natural-sounding tonal characteristic. On deep synthesized bass ("Tiger" by Paula Cole), the sealed woofer went into severe audible distortion at levels where the little vented woofer still sounded solid, and the little vented woofer was making the room shudder which the sealed woofer utterly failed to do. I think the ideal would have been an equalized sealed woofer with several times the displacement capability of the one I was using, but that would have been many times the price of the little vented woofer, not counting the equalizer and greater amplification required to get there. On the other hand, a subsequent vented box with a more expensive woofer (still considerably cheaper than the sealed box woofer) also had better solidity on kick-drum. Unfortunately, I've sold the sealed-box woofers so can't make that comparison to see if the better vented woofer evens things up in that area. I suspect the sealed box would still win out on kickdrum by a small margin, but would be even more outclassed elsewhere.

Duke

Duke,

Thanks. I read all your posts with great interest.