Dual Subwoofers, what's better, dual mono or stereo?

[frenchyfranky]

I'm just changing my 16 years old beast SVS PB12-plus/2 for two SVS SB-3000, I got one and the second ordered is on the way. As per many pro audio critics it might be better for dual Sub to be setting in stereo instead of dual mono, especially in music listening, that's what I think it's logically better. But in movie there's any advantage to running in mono? For dual subs owners what do you prefer?

[AudioHTIT]

I do what you describe, for my two channel preset / system I set my subs to stereo. For my HT preset / system I set them to dual mono. So I can only vote for one, but it would depend if I was voting for music or theatre. I’m about to swap out the XMC for an RMC so I’ll lose the stereo option 🙁 I guess I’ll vote for mono. Edit, I stuck with stereo in hopes they’d add the option back.

[frenchyfranky]

Aug 25, 2019 19:02:07 GMT -5 AudioHTIT said:

I do what you describe, for my two channel preset / system I set my subs to stereo. For my HT preset / system I set them to dual mono. So I can only vote for one, but it would depend if I was voting for music or theatre. I’m about to swap out the XMC for an RMC so I’ll lose the stereo option 🙁 I guess I’ll vote for mono.

I wait too for the XMC-2 upgrade program and I also be disappointed to see that in the XMC-2 bass management there's no more stereo setting like in the XMC-1, especially since now the XMC-2 having 3 subwoofer outputs. I think that is a mistake.

[AudioHTIT]

Aug 25, 2019 20:06:07 GMT -5 frenchyfranky said:

Aug 25, 2019 19:02:07 GMT -5 AudioHTIT said:

I do what you describe, for my two channel preset / system I set my subs to stereo. For my HT preset / system I set them to dual mono. So I can only vote for one, but it would depend if I was voting for music or theatre. I’m about to swap out the XMC for an RMC so I’ll lose the stereo option 🙁 I guess I’ll vote for mono.

I wait too for the XMC-2 upgrade program and I also be disappointed to see that in the XMC-2 bass management there's no more stereo setting like in the XMC-1, especially since now the XMC-2 having 3 subwoofer outputs. I think that is a mistake.

Keith said there was a possibility they’d add a stereo option for the new processors, so we can hope for that.

[frenchyfranky]

I hope too

[frenchyfranky]

As per the XMC-1 manual the stereo setting must be the ideal choice:

Bass Management

The XMC-1 is a full 7.2 channel surround sound processor, which means that it supports two
independent stereo subwoofers.
If you have two subwoofers, and configure the XMC-1 for Stereo subs, then both subs will be
configured separately, and will operate in full stereo mode. Both subs will receive content from
the LFE (low frequency effects) channel and, in modes where bass management is active, the Left
Subwoofer will receive audio content at frequencies below the configured crossover points for
the Left Front, Left Surround, and Left Back Surround Speakers; the Right Subwoofer will receive
audio content at frequencies below the configured crossover point for the Right Front, Right
Surround, and Right Back Surround Speakers; both subwoofers will receive audio content below
the crossover frequency for the Center Channel.

[donh50]

I have tried various configurations over the years and have gone back and forth on stereo subs. Long story short, not worth the effort for the extremely few times it matters, if it ever does in a consumer situation (i.e. not in a ballroom). I currently have two pairs of subs and each pair is driven dual-mono just to let the XMC-1 handle the timing and levels. Each pair is symmetric so that scheme works out well. I still had to tweak; never have quite figured out how Emo and DL play together (not all that well in the sub region, and least not for me). I did try stereo, mono, and piddling with various schemes in between (such as full-range mains to the AVR or processor and external crossover to main and sub power amps). It's a good way to feed your OCD.

Sub frequencies are so low and thus wavelengths so long they are essentially non-directional even for the very few recordings with stereo LF content (not this does not apply to movies as LFE is a single, mono, channel). The directional cues come from frequencies above the sub's crossover unless you have it set really high.

IME/IMO - Don

[repeetavx]

So, why does the discussion about multiple subs defeating room modes not apply to this discussion?

[donh50]

Aug 26, 2019 8:41:19 GMT -5 repeetavx said:

So, why does the discussion about multiple subs defeating room modes not apply to this discussion?

I am not sure to whom this was directed? If you really want stereo subs, then you'd have to place them symmetrically about the MLP and in the same relative position on each side (e.g. not one in a rear corner and one in front, etc.) That does not eliminate but severely constrains your ability to place them independently and cancel room modes. Mono or dual-mono lets you place them where they work best with the fewest constraints on placement.

IME/IMO - Don

[AudioHTIT]

Aug 26, 2019 8:41:19 GMT -5 repeetavx said:

So, why does the discussion about multiple subs defeating room modes not apply to this discussion?

I don’t think there’s any reason not to talk about it, but the OP asked whether you preferred the mono or stereo setting on your processor. My subs are symmetrically placed outside my Magnepan’s, and I just prefer them in stereo for stereo music. But (as donh50 points out), if my subs weren’t symmetrical I’d most certainly leave them in mono all the time.

[frenchyfranky]

Aug 26, 2019 14:02:47 GMT -5 donh50 said:

Aug 26, 2019 8:41:19 GMT -5 repeetavx said:

So, why does the discussion about multiple subs defeating room modes not apply to this discussion?

I am not sure to whom this was directed? If you really want stereo subs, then you'd have to place them symmetrically about the MLP and in the same relative position on each side (e.g. not one in a rear corner and one in front, etc.) That does not eliminate but severely constrains your ability to place them independently and cancel room modes. Mono or dual-mono lets you place them where they work best with the fewest constraints on placement.

IME/IMO - Don

You're right about this, my concern is about stereo recording, here's the article explaining the situation:

kenrockwell.com/audio/stereo-subwoofers.htm

While low frequencies are less directional, and the direction of a low-frequency sine-wave point-source may be less perceptible, critical to fine music reproduction are low-frequency interchannel phase differences present in true stereo recordings. When reproduced properly with stereo subwoofers (or two full-range speakers), these phase differences are critical to reproducing the sound space of the original concert hall.

Critical even to casual listeners is that if you sum the low frequencies of true stereo recordings into mono by using only one subwoofer, low-frequency interchannel phase differences partially or completely cancel each other, reducing or eliminating low-frequency output levels!

Try jamming a stereo bass signal through one mono subwoofer and you lose a lot of hall ambience as well as bass level.

True stereo recordings are usually classical and other proper acoustic recordings made with pairs of microphones. Most "stereo" pop and jazz recordings are really just multi-miked mono, with each mono mic "panned" someplace between left and right. Pop recordings rarely have low-frequency interchannel phase differences, although they usually have bass information panned one way or another that also should be reproduced through stereo subwoofers if you demand the most accurate reproduction.

[frenchyfranky]

Aug 26, 2019 8:41:19 GMT -5 repeetavx said:

So, why does the discussion about multiple subs defeating room modes not apply to this discussion?

Absolutely it is naturally be part of the dual Subwoofers equation, in stereo or mono, the same contribution in room defeating might be less in a stereo config equally spaced on the same wall with the front speakers then a mono config in diagonally opposite corner, but still exists. The basic condition for room mode defeating is the bass wave must be generated from different place in room to interact differently with the room space.

[donh50]

Aug 26, 2019 14:32:50 GMT -5 frenchyfranky said:

Aug 26, 2019 14:02:47 GMT -5 donh50 said:

I am not sure to whom this was directed? If you really want stereo subs, then you'd have to place them symmetrically about the MLP and in the same relative position on each side (e.g. not one in a rear corner and one in front, etc.) That does not eliminate but severely constrains your ability to place them independently and cancel room modes. Mono or dual-mono lets you place them where they work best with the fewest constraints on placement.

IME/IMO - Don

You're right about this, my concern is about stereo recording, here's the article explaining the situation:

kenrockwell.com/audio/stereo-subwoofers.htm

While low frequencies are less directional, and the direction of a low-frequency sine-wave point-source may be less perceptible, critical to fine music reproduction are low-frequency interchannel phase differences present in true stereo recordings. When reproduced properly with stereo subwoofers (or two full-range speakers), these phase differences are critical to reproducing the sound space of the original concert hall.

Critical even to casual listeners is that if you sum the low frequencies of true stereo recordings into mono by using only one subwoofer, low-frequency interchannel phase differences partially or completely cancel each other, reducing or eliminating low-frequency output levels!

Try jamming a stereo bass signal through one mono subwoofer and you lose a lot of hall ambience as well as bass level.

True stereo recordings are usually classical and other proper acoustic recordings made with pairs of microphones. Most "stereo" pop and jazz recordings are really just multi-miked mono, with each mono mic "panned" someplace between left and right. Pop recordings rarely have low-frequency interchannel phase differences, although they usually have bass information panned one way or another that also should be reproduced through stereo subwoofers if you demand the most accurate reproduction.

Yes, that is exactly the argument made for stereo subs, and why I ran mine that way for decades. However, I'd argue that wavelengths are so long there is little "stereo" bass even in a full-range stereo recording and assuming it is not mixed to mono later. At 100 Hz a wavelength is ~11.27 feet; I have read all sorts of debates on whether a X-Y or M-S mic pair can actually provide stereo bass. I listen to mainly classical and jazz and, in my somewhat modest CD collection (few hundred, down from a few thousand LPs "back in the day"), I only found a couple that might have had stereo bass enough to make a difference. And I am very familiar with the subharmonics and difference tones in music; that is one (if not the main) way we stay in tune when playing on stage, so I was listening for that. After going back and forth, leaving it each way for months at a time, I finally left it in dual-mono and decided to quit fooling with it. I got another pair of subs later and continued the dual-mono path, perhaps just out of laziness.

That said I have not been listening critically lately and may simply not have recordings (or have not listen closely enough) that benefit from stereo subs. The last few times I tried on my system and with friends (couple of whom were hard over on the need for stereo subs) nobody could tell when I switched from stereo to mono subs in my or their systems with a 24 dB/oct crossover. When we did find the rare stereo sub case, we found the directional "stereo" stuff was happening higher in frequency and enough was coming out the subs to be localizable (crossovers are not brick walls). It was not a double-blind test, however, and not instantaneous since I had to change settings, so not a scientific test. And certainly if directional info is coming out of the subs, at whatever frequency, that's is an argument for them.

[frenchyfranky]

Thanks a lot donh50 , it's exactly the type of feedback and experience that I'm looking for with this thread. I'm trying to figure out how I'll set my new pair of subs. Very appreciated your answer.

[donh50]

Aug 26, 2019 16:05:15 GMT -5 frenchyfranky said:

Thanks a lot donh50 , it's exactly the type of feedback and experience that I'm looking for with this thread. I'm trying to figure out how I'll set my new pair of subs. Very appreciated your answer.

NP. I would not treat my experience as definitive; try it and see. I "knew" I needed stereo subs and kept going back to them even in the face of my personal listening and measurements not saying I needed them. I finally just got tired of the hassle, and then when I added another pair, wasn't about to try to deal with aligning them all as stereo pairs. Especially when I could not convince myself I heard a difference. Lazy! Or maybe just ears of clay.

[frenchyfranky]

Aug 26, 2019 16:11:07 GMT -5 donh50 said:

Aug 26, 2019 16:05:15 GMT -5 frenchyfranky said:

Thanks a lot donh50 , it's exactly the type of feedback and experience that I'm looking for with this thread. I'm trying to figure out how I'll set my new pair of subs. Very appreciated your answer.

NP. I would not treat my experience as definitive; try it and see. I "knew" I needed stereo subs and kept going back to them even in the face of my personal listening and measurements not saying I needed them. I finally just got tired of the hassle, and then when I added another pair, wasn't about to try to deal with aligning them all as stereo pairs. Especially when I could not convince myself I heard a difference. Lazy! Or maybe just ears of clay.

I myself stopped many years ago my quest for details and perfection in sounds for simply enjoy listening music, but when I buy a new audio device my old demon of audiophile disease comeback.

[repeetavx]

Aug 26, 2019 15:49:59 GMT -5 donh50 said:

When we did find the rare stereo sub case, we found the directional "stereo" stuff was happening higher in frequency and enough was coming out the subs to be localizable (crossovers are not brick walls). It was not a double-blind test, however, and not instantaneous since I had to change settings, so not a scientific test. And certainly if directional info is coming out of the subs, at whatever frequency, that's is an argument for them.

A good argument for spending money on full range tower speakers. If you're concerned about bass that much, make sure your stereo sources can handle the stereo bass. Yes, once you symmetrically place your bass stereo pair, you're are going to re-enforce certain room modes. That's what room treatments are for, if your spending money for authentic bass imaging. It is easier and cheaper to crossover, sum to mono, and position remote subs for even bass distribution.

[donh50]

I find bass management is an improvement even with "large" speakers. Very rarely is the best place for the subs the same as the mains, and even speakers rated low tend to exhibit very high distortion when driven with large deep bass signals (as many of them are). I found that true with my previous Magnepan MG-IIIa's (-3 dB at 35 Hz) and current Salon2's (-3 dB at 23 Hz). Apparently I'm in good company; Dr. Floyd Toole crosses his Salon2's at 80 Hz for the same reasons.

Since crossovers are not brick walls I prefer good bass response an octave below the crossover, which has pretty much meant I've always had "large" speakers.

YMMV - Don

[Perpendicular]

I voted mono. I’ve tried hard at various times to hear a difference with stereo subs and couldn’t. Besides, defeating room modes and having even bass is way more important.

[thezone]

I vote for mono - but just to throw a spanner in the works I have three subs, two identical and one small. I run a single mono output from the XMC-1 to an external active three way x-over, with the low sub set to 15-60Hz, mid sub set to 60- 90hz and high (small) sub set to 90-120hz. I have the main speakers set to small in the XMC-1 and set the internal x-over to 120hz.

You'd be surprised at how much headroom this creates for the bass signal. And sometimes for experimentation, I add an active 35hz high pass filter in between the XMC-1 and the external X-over to completely eliminate low frequency nasties in rock/pop music or old records where these low frequencies seem to cause more issues to deal with.