[chadh]

The various subwoofer-related threads bouncing around right now have me wondering about the appropriate way to use my new swarm.

I'm using a swarm and enjoying the effect.  But I'm operating it in stereo (two per channel).  I'm actively crossing over between the subs and main drivers (Omega single drivers, with little 4.5" drivers) at 100 Hz, with 24dB/octave slopes on both filters.

What difference would I experience running the subs in mono? 

I understand that most recordings give you the same mono bass track in each channel everywhere below around 80Hz anyway.  Wouldn't that mean that my stereo set-up will be identical to a mono set-up in the majority of cases?  In the remaining cases, do I suffer in stereo because I don't get the same level of "dip/peak smoothing" as I would get in mono?  I initially imagined that I might gain something by preserving whatever separation that was intended to be part of the music, and not dealing with trying to sum two different signals.

I must admit, I haven't experimented much.  For example, I haven't tried running one of the subs out of phase with the others.  But would the effectiveness of that kind of approach be influenced by the choice to run the subs in  stereo or mono?

Thanks.

Chad

[Duke]

Hi chadh,

If the crossover point ends up being fairly high, then running the subs in stereo can be beneficial.  But I don't think it makes any difference on signals below about 100 Hz or so, as those are virtually always summed to mono to the best of my knowledge.  So in your case I don't think there would be a significant difference either way, but if you try it both ways and find otherwise please let us know!

Also, feel free to experiment with connecting one or more of the subs in reverse polarity. 

Duke

[Russell Dawkins]

I tried to use a mono sub (singular) placed in the middle between my monitors. The factory crossover was 90 Hz and I could clearly hear the basses in orchestral recordings, which should usually be fairly hard right, move halfway towards the center. Bass fiddles nominally go down to 42 Hz, but most of their output even on the low string, open, is around 84 Hz. Even so, the audible distortion of the soundfield was a deal breaker, even though in other respects the sound was much better.

Now I am making my own subs based on the multiple source concept, but H baffles with Goldwood 18s. I am starting with two but may go to four. I have to say, though, that Dukes set up with the subs being so small is attractive - I am afraid 4 18's may occupy too much space and be too hard to integrate visually.

They used to say bass below 100 Hz might as well be mono - and that may be true for 99.5% of popular music - but not, I think, for classical. Also it was said that the sub could be placed wherever it sounded best or was convenient since you could not localize a source under 100 Hz, but I would guess the correct figure would be more like 60 Hz in the typical room.

In vinyl days, bass was typically made mono under a certain frequency to minimize the vertical component of the groove motion to avoid kicking the needle out of the groove on bass transients, like bass drum hits and cannons (Telarc's Tchaikovksy 1812 Overture comes to mind!), but with digital this sort of thing is no longer done and bass can be stereo.

[Duke]

Russell, the steepness of the lowpass filter is a very significant factor.  I suspect that your sub was passing a considerably amount of energy north of the crossover point, or possibly was producing significant harmonic distortion.  Chadh's crossover slopes are quite steep, and if I did my homework right the subs should have low distortion until the get pushed pretty hard.

As for localizing the source(s) of low frequency energy in a room, here's one of the key mechanisms a play:  It takes the ear more than one cycle to even detect the presence of bass energy, and several cycles to tell what its pitch is.  If you stop and think about how long bass wavelengths are, you'll see that by the time multiple cycles have reached the ear the bass energy has bounced off the walls multiple times and so is literally coming from all around. 

I don't know what the considerations are from the recording industry's perspective, but sharing the low bass load between two speakers (rather than routing it all to just one) increases the playback system's headroom by probably 4 or 5 dB (we'd get a 3 dB increase with random-phase summing and a 6 dB increase with in-phase summing, and my guess is that the effective  increase lies somewhere in between). 

[Russell Dawkins]

The low pass slope was 24 dB/octave. I presume that's the high pass, too.

http://tinyurl.com/yl24soj

I was listening in the nearfield - about 4 feet from any of the speakers, including sub, so perhaps that removed the room somewhat from the equation.

[Russell Dawkins]

I tried to modify the above message, but kept getting a message saying the body of the message was empty  , so this is what I added:

I think it is pretty much a convention to share bass energy between channels for reasons you cite, where maximum loudness is the aim - and that often is the aim - but I have heard stand up bass panned hard left or right on jazz recordings. Actually I have heard a lot of hard panning (sounds placed all in one speaker and nothing of it in the other speaker) on older jazz recordings, now that I think of it.

... and after the link I said "click on 'Technical data' to the right of page."

[Duke]

Hmmm.... well maybe you're right about listening nearfield.  I've never tried that with subs.  There certainly is no reason to expect anything was less than stellar about that sub. 

[chadh]

Thanks for the feedback Duke.  I'll experiment away, and let you know if anything notable emerges.

Chad