Any advantage to stereo subs?

[Greg Dunn]

To be perfectly clear, I'm NOT talking about multiple subs vs. one sub - I understand that's a separate issue and merits its own discussion.

What I'm curious about is whether having two subs in stereo is preferable to having two subs with a mono derived signal. That is: is there enough stereo content in recordings to matter, and even if so, will it make a difference in room?

What I currently have is none of the above. I am using a DSP to sum the stereo signal from my system and send a mono signal to a bridged Crown XLS and thence to a Dayton Ultimax 18" sub unit. It is currently crossed over at 60 Hz with L-R 24dB filters on both the mains and the sub. I cannot hear any localization cues from the sub, so I believe 60 Hz is below my threshold for hearing directional information. The system really sounds good to me as it is currently configured; I've taken the time to position, EQ and time align the sub and I'm not noticing any specific issues such as irregular bass response, etc. The response in my 2000 cubic foot room from about 100 Hz down to ~15 Hz measures pretty flat with both sweeps and pink noise at the listening position.

However, I am curious as to whether I'm losing anything musically by mixing the low frequency signal to mono and sending it to a single sub. Most of my music is rock, jazz and classical (I originally added the sub for listening to organ recordings), and all from digital sources - but very little of it is newly recorded. There does not seem to be a consensus as to whether the extreme lows are mixed to mono already on most commercial recordings except for those already mastered for LPs.

I have no easy way to add another sub just for the purpose of testing this - especially a matching unit! My HT system does have an old M&K 15" sub I could borrow but I question whether hooking it in would do much but confuse the issue. So I'd like to hear from the forum denizens - am I likely to hear any useful differences just from having stereo below 60 Hz? Depending on what I hear, I can either start thinking about a second sub or discard the notion as being of little benefit. Again, this is a separate notion from the benefits of adding multiple subs to improve room response; I don't think adding a sub for that purpose is likely to help much in my small room since the LF response is satisfactorily smooth already.

 

[Tony V.]

Good morning Greg, Low frequencies below 80Hz are non directional so any so call stereo imaging of those frequencies would end up being lost in the room and not heard as left or right just a blended sound anyhow.

 

[DanDan]

Vinyl could not handle non coherent LF so imposing Mono was mandatory. Later media have no such issue so you will find Recordings mixed with radical LF differences. e.g. Beatles Mixes. Bands with two drummers. Such material sounds quite different with two subs.

 

[Greg Dunn]

Vinyl could not handle non coherent LF so imposing Mono was mandatory. Later media have no such issue so you will find Recordings mixed with radical LF differences. e.g. Beatles Mixes. Bands with two drummers. Such material sounds quite different with two subs.

So just what effect is it that you're hearing with the addition of stereo below 60 Hz? All the directional cues ought to be in the mains, so I'm not clear on what is being added. On my system, even bass drum and other LF content (synth, electric/acoustic bass) with overtones seems to be distinct in its channel even with the sub content summed, assuming it was mixed in stereo.

 

[DanDan]

The theoretical doesn't really pan out in practice.....;-) I am in the Office not the Studio so I can't grab a Kick Drum Waveform for you. Perhaps you know or will take it that the first cycle or half cycle can be very very asymmetrical. With good speakers this hits like an explosion. If panned it is entirely obvious which side it comes from, even with the mains turned off.

 

[Greg Dunn]

This sounds quite plausible - it's just that I haven't experienced it (not having two subs). Maybe I will haul that M&K downstairs and see what happens... Worst case, I'll learn something!

 

[Sonnie]

For music drum setups are typically center stage, at least for most of the concerts I've ever been to or watched on TV. There have been some that are off center, but they are mic'd to stereo speakers in mono. I think it would sound odd to my ears not having those low frequencies centered.

Movies on the other hand might be different... as you do have explosion and other sounds coming from different directions, and there are times where I can sense the direction they are coming from... possibly because of the higher frequencies blended in with the lower frequencies.

 

[Greg Dunn]

I'm definitely not using this as my HT setup - there's no room for a TV for one thing. I've run a few of my favorite bass-heavy tracks through MusicScope and there doesn't seem to be much stereo information below 60 Hz - probably just characteristics of the analog recordings anyway.

Now, oddly, when I set a reasonable time delay for my sub (after consulting the REW forum), I did sense a slight improvement in transient reproduction which corresponded to the "right" delay. And that was repeatable. I'm not sure whether it had any effect on the image or not, because it was extremely difficult to A/B the settings.

 

[Tony V.]

Ya, I still dont believe that any bass below 80Hz is discernable as to where it comes from the sinewave is just too large to come from a specific location in stereo. Maybe in a nearfield setting but certainly not in a setting where your sitting 10 feet away

 

[JStewart]

Thought you might be interested in this Stereo Bass article be @Matthew J Poes

Spaciousness of Bass: Is Stereo Bass a Myth or Reality?

Stereo Bass- Myth or fact? A must have feature for some, but neglected by most. In this article explores the concept of stereo bass and provides guidance on maximizing it’s effect vs the tradeoffs.

www.audioholics.com

 

[DanDan]

Tx for that JStewart it is nice when science, theory, and perception, all come together.
I think Classical music and the ambition to represent 'being there' is a scenario where multiple bass sources is pretty obviously nicer. @Sonnie, drums centre, tell me about it. Our guitarist has a coniption when I set up at the side. Given small pub stages I simply will not have my cymbals almost touching the back of the singers head, while the continually steps onto my wooden bass drum hoop. Drums to the side very significantly reduces the horrible sound caused by all the vocal mics picking up just the harshness. Then there are all those great bands with two drummers. From James Brown to The Allman Bros, to Gary Glitter..... Ooops. I had the rare opportunity to Mix in Surround some time ago. I had to gear up and read up a bit. I gathered a clear consensus from Speaker Manufacturers to the NARAS Pro Group that Full Range Speakers are preferable. http://www2.grammy.com/pdfs/recording_academy/producers_and_engineers/5_1_rec.pdf

 

[Greg Dunn]

I'm trying to approach this without bias (until I get a chance to test for myself - which means putting together an extension cable for the second sub, hopefully this weekend) but I've been doing a lot of communicating and reading on the subject so as to go in well informed. It's interesting to note that Dr. Floyd Toole recommends multiple mono subs, as per studies like the one from Harman (Welti and Devantier) and his own JAES paper. Tom Nousaine was also a strong proponent of mono subs; if you can find his articles in Speaker Builder and Stereo Review / S&V they're worth reading.

In the linked NARAS article, it seems that they are aiming strongly at HT surround systems with an LFE channel; in fact, they specifically discourage putting musical content in the LFE channel and therefore leaving it in the regular L and R channels. Of course, most bass-managed music systems derive the sub signal from the L and R channels - I never play surround content in my music system - only in my upstairs AVR-based video system - so that's true here for certain.

And the reason they are recommending stereo sources for the actual LF signal (as opposed to LFE) is because, as they state, many systems are not correctly configured to handle or propagate the LFE bass information, which would result in loss of the bass info. This is a sensible decision, I think. Again, though, it's focused on HT systems - stereo audio doesn't have a LFE channel and the bass (no matter how presented) is still sourced from the L and R channels.

I agree that it could well come down to what music sources you have available; only a small amount of my library has non-centered bass instruments as well as being mixed for stereo later than the 1980s. For example, I don't even have the early Beatles stereo mixes, because I chose the EMI masters when I bought them on CD - and most of those were originally mixed for mono. If anyone has a particularly good example of distinct stereo bass, I wouldn't be averse to buying an album or two for my testing.

 

[DanDan]

Unless you listen to Classical or other extremely realistic music this is hardly a big deal. Although I guess many of us relished the freedom to pan LF when the CD came along. Bird on a Wire by Jenny Warners, Remaster Bob Ludwig has a lot of stereo tom action. Peter Gabriel - No Way Out from the Up album has some extraordinary things going on. Here's one with quite a bit of LF doubled instrumentation https://www.dropbox.com/s/e704rkd0wuq0ifm/Cain and Abel.aiff?dl=0

 

[BenToronto]

There are no feasible fixes for room acoustics in the LF except multiple subs. But one good sub is just fine.... esp if Klipschorn bass.

Labs tests show conclusively you can detect location north of 80 Hz. But the all but universal opinion of those who have tried it, a XO as high as 130 was no issue on music and has zero consequences for locating drums. But that requires a sharp slope and low give-away distortion. Greatly simplifies mid-range speaker design and sound quality if you don't try to get a mid-range to handle music below maybe 110.

So with no localization you can put subs in good spots in your room and if there's no localization that makes having stereo meaningless. BTW, what the mic picked up in the recording is pretty meaningless apropos stereo too and all the "stereo" tracks are just "photo-shopped" in the control room.

Not long ago, i once more tried to decide if mixed bass is better than stereo bass. All things considered, I kind of favour mixed bass (and certainly if you have vinyl or old stuff, in order to cancel rumble if using today's LF subs). Hint: a Behringer DSP lets you peruse dozens of the most interesting comparisons at the click of a button, and all the questions raised in this tread.

B.

 

[Eric SVL]

Stereo bass creates several problems that are discussed here:

Floorstanding speakers vs bookshelf speakers

I think the ratio between direct and reflected sound is important. While reflections are not totally bad, too much is not good either (if you want to reproduce the recorded acoustics). At the larger listening distance required for floorstanders, reflected sound is typically dominant. So I think...

www.audiosciencereview.com

 

[Juan Acevedo]

To be perfectly clear, I'm NOT talking about multiple subs vs. one sub - I understand that's a separate issue and merits its own discussion.

What I'm curious about is whether having two subs in stereo is preferable to having two subs with a mono derived signal. That is: is there enough stereo content in recordings to matter, and even if so, will it make a difference in room?

What I currently have is none of the above. I am using a DSP to sum the stereo signal from my system and send a mono signal to a bridged Crown XLS and thence to a Dayton Ultimax 18" sub unit. It is currently crossed over at 60 Hz with L-R 24dB filters on both the mains and the sub. I cannot hear any localization cues from the sub, so I believe 60 Hz is below my threshold for hearing directional information. The system really sounds good to me as it is currently configured; I've taken the time to position, EQ and time align the sub and I'm not noticing any specific issues such as irregular bass response, etc. The response in my 2000 cubic foot room from about 100 Hz down to ~15 Hz measures pretty flat with both sweeps and pink noise at the listening position.

However, I am curious as to whether I'm losing anything musically by mixing the low frequency signal to mono and sending it to a single sub. Most of my music is rock, jazz and classical (I originally added the sub for listening to organ recordings), and all from digital sources - but very little of it is newly recorded. There does not seem to be a consensus as to whether the extreme lows are mixed to mono already on most commercial recordings except for those already mastered for LPs.

I have no easy way to add another sub just for the purpose of testing this - especially a matching unit! My HT system does have an old M&K 15" sub I could borrow but I question whether hooking it in would do much but confuse the issue. So I'd like to hear from the forum denizens - am I likely to hear any useful differences just from having stereo below 60 Hz? Depending on what I hear, I can either start thinking about a second sub or discard the notion as being of little benefit. Again, this is a separate notion from the benefits of adding multiple subs to improve room response; I don't think adding a sub for that purpose is likely to help much in my small room since the LF response is satisfactorily smooth already.

 

[AJ Soundfield]

This question arises over the years on audio forums and the pattern is always the same, much like Groundhog Day.
If you are interested in what the science doesn't say, see above.
If you interested in what the science does say, see below.

However, I am curious as to whether I'm losing anything musically by mixing the low frequency signal to mono and sending it to a single sub. Most of my music is rock, jazz and classical (I originally added the sub for listening to organ recordings

For rock, no, jazz yes, classical, absolutely!
This a compilation of 45 different bass studies and is critical for any understanding of the issue.
https://secure.aes.org/forum/pubs/conferences/?elib=17270

3.3 Is the perception of spatial information in a recording affected by the decay time of room modes in the listening room?
This question is largely answered by the papers summarised in section 2. Papers describing tests which found little or no spatial effect at low frequencies [31][32][33] were all done in listening rooms with long decay times at low frequencies. Papers which describe tests showing detection of spatial information at low frequencies [37][38][39] were done in rooms with lower decay times. [39] used two rooms with different decay times and found that discrimination was noticeably easier in the room with lower decay time. [25] and [41] point out that it is easier to hear in to the recording when the modal artifacts in the listening room do not dominate.
4 CONCLUSION
The standard 5.1 configuration has two fundamental weaknesses at low frequencies: a) no opportunity to transmit low frequency spatial information present in a recording, and b) limited opportunity to control room modes. Some control of room modes can be achieved
by experimenting with location in the room or by modal equalisation. Use of a mono signal, replayed via multiple subwoofers with suitable signal processing, allows one to present more uniform bass over a listening area. However there is still no opportunity to present spatial information. Use of two subwoofers placed to the left and right of the listener and playing left and right LF signals allows presentation of spatial information.

And http://www.acoustics.asn.au/conference_proceedings/AAS2008/papers/p47.pdf
I could go on, but it usually makes no sense.
Good luck.

cheers,

AJ

 

[BenToronto]

Yes, you could go on with your nicely posted and welcome summary but it adds up to what I earlier suggested: 80 Hz in lab tests and maybe 130 Hz on music at home (with sharp slopes XO and low distortion). Those living in a lab and listening to trick test tones should take extra care.

Moreover, strong reasons not to feel handcuffed to stereo locations for subs which are likely to be non-optimal locations.

 

[Juan Acevedo]

Hope the attached pdf can be read. Don't know much about attachment rules in this program.

 

[BenToronto]

The attachment talks about how anyone with 7th grade geometry will understand the necessity of time alignment as applied to sub location.

Unfortunately for that compelling Euclidean analysis, from posts I've read and from my own experience (DSP is wonderful for experimenters), you can hardly detect a difference fooling with time-alignment of subs to main speakers, again thinking of music not trick test signals. It has something to with our insensitivity to phase because at low frequencies, alignment is generally a matter of phase rather than clock time, in so far as one can speak of them distinctly.

Which again is very good for the point of view of being free to put subs in the best locations in your room using mixed bass and not getting stressed about localization or time-alignment.

 

[ddude003]

I remember, back in the day, seeing a Hammond Organ with a Leslie Speaker cabinet at the Village Recorder... The engineers had four mics positioned two high and two low on each side of the Leslie... I don't remember who the setup was for in 1994... Maybe had something to do with Robbie Robertson?... And... I wonder if they really mixed two stereo pair, two Left and two Right, into a single mono track...

Maybe @Sonnie can tell us if the guys at Martin Logan are wrong about placing woofer/subwoofers into his Renaissance ESL 15As... Two 12 inch subs in each L&R, I think those things go down to around 22Hz... Is there life below 20Hz and above 20KHz? It is not just about what you can hear... It is also about what you feel...

Anyway, I would expect more content to become available that would take advantage of stereo subfrequencies as recording, mixing production chains and digital delivery move forward...

 

[DanDan]

The full Fender Rhodes experience has two 'suitcase' speakers, each with 4x 10" speakers afaik. The classic vibrato which really adds life and dimension to that instrument, is cyclical hard panning from from speaker to the other. I guess we could include moving sounds with the impulsive in terms of those benefitting from multiple LF sources. Steady state, sine waves, below 60Hz should sound like they are coming from everywhere, if they have low distortion and port chuffing. With all full range speakers the sines really ARE coming from everywhere. Different types of everywhere? Mono should still appear centred, and indeed more than usual if only in the Centre full range speaker. The elements that work with sourced LF will show off.

 

[frangle]

In my experience (with 2 subs) when you can find material with distinct LF stereo content (tends to not be acoustic), there is a detectable difference with a stereo sub config versus mono below 80Hz, but I reckon it is entirely due to different engagement of room modes. You can also get a different room mode engagement just by moving the subs, and this works with all recordings and is deterministic. So outside of performing an experiment, I don't know why you would ever pursue stereo LF below 80Hz. Much better to use multiple subs positioned to optimize room mode engagement.

For acoustic music recordings, I expect you'll only find stereo content sub 80Hz if it has been artificially mixed that way, but it is pointless, as it won't replay meaningfully.

Furthermore. mono LF content has the benefit of distributing excursion load between your speakers, lowering distortion at higher playback levels.

So I'd say no - no benefit.

 

[DanDan]

"For acoustic music recordings, I expect you'll only find stereo content sub 80Hz if it has been artificially mixed that way, but it is pointless, as it won't replay meaningfully"

Realistic recordings of Acoustic Music, from Jazz to Quartet to Orchestra, should portray the LF where it actually was, and they do.
It will replay meaningfully in a decent room with decent full range speakers.
I am a bit puzzled by the term 'artificially mixed' I mix, it's all artificial and it's all deliberate.
I try to conjure up a credible scenario which the audient can lose themselves in. Like a Movie.

 

[ddude003]

How many ways can you mic a grand piano? And if you toss in the vocalist player? And just how low does that piano go? @DanDan mentioned Jennifer Warnes as a good example and I am thinking of Freya Riding Live At St Pancras Old Church... There are many of these solo acoustic examples... Would any recording/mixing engineer in their right mind mix out the Stereo LF?