Stereo Sub Vs Dual Mono

[hollis]

sounded different

I think we are missing a crucial distinction. How low do your mains go and what was the chosen crossover frequency?

I have crossedover the subs for LXmini+ as high as 150hz, they absolutely needed to be run in stereo.

My genres require a lot of subbass so l added a 4th way. Subs for my subs. It was very interesting adding subs to a full range three way. I spent a few years with various models and ended up with a G22 in front and a F25 in back. Both crossedover at 45hr LR8.

My findings so far suggest stereo bass can be an advantage, down to 40-50hz, below that mono is fine.

This was all with pop/EDM, I have not yet done any testing with orchestral or hometheater. From my reading. Those might want multich deep bass for added envelopment and sense of room size. For that testing l am building a new room with multich deep bass capability. But that alone is taking years

 

[janbth]

I think stereo subs (or stereo bass) is an interesting concept, but what is sorely missed is a discussion about how to handle room modes. For instance, in my case I have some nasty room modes, and I can’t even put a sub close to the left speaker. In that location, there is a null at around 30-40Hz (from memory). Instead, my second sub is at the mid back wall. I play my two subs in mono, and that effectively brings down the modes. But how is that supposed to work with stereo?

 

[Keith_W]

I think stereo subs (or stereo bass) is an interesting concept, but what is sorely missed is a discussion about how to handle room modes. For instance, in my case I have some nasty room modes, and I can’t even put a sub close to the left speaker. In that location, there is a null at around 30-40Hz (from memory). Instead, my second sub is at the mid back wall. I play my two subs in mono, and that effectively brings down the modes. But how is that supposed to work with stereo?

You have hit the nail on the head. Stereo requires that the subs are set up symmetrically in your room, ideally on either side of the listener, as per Griesinger. This may sometimes mean that you lose the advantage of multiple subs filling nulls in the bass.

 

[janbth]

Stereo requires that the subs are set up symmetrically in your room, ideally on either side of the listener, as per Griesinger.

Does it, though? This is another point I would like to understand regarding stereo subs: Is it necessary that the subs are positioned in a stereo triangle, or is it enough that the two subs are located at two different places in the room.

This may sometimes mean that you lose the advantage of multiple subs filling nulls in the bass.

Yes, but it’s not just about filling nulls. In my case, my two subs play in mono - in phase - to counteract my nasty peak at 45Hz. If they were to play in stereo it could happen that we get 45Hz in opposite phase. This would then enforce the mode. What could be done about that?

 

[Keith_W]

Does it, though? This is another point I would like to understand regarding stereo subs: Is it necessary that the subs are positioned in a stereo triangle, or is it enough that the two subs are located at two different places in the room.

The subs ideally should be on either side of the listener to maximize the effect. I can't do that in my listening room, so the subs are in the two front corners. One thing you CAN NOT do is place your subs in non-symmetrical positions in the room, or front-to-back. Read this Audioholics article, it will tell you more. It's also an easier read than Dr. Griesinger's paper (which I can't seem to find at the moment). That Audioholics article does a good job of covering the skepticism in the community, but it is a few years old. Right now there is no doubt that stereo bass is audible in a free field and with test signals, thanks to experiments by Lars Risbo and others. But whether it is audible in a listening room with normal music is another matter. I don't think that study has been done yet. Read this thread if you want to learn more.

Yes, but it’s not just about filling nulls. In my case, my two subs play in mono - in phase - to counteract my nasty peak at 45Hz. If they were to play in stereo it could happen that we get 45Hz in opposite phase. This would then enforce the mode. What could be done about that?

DSP. You can either chop off the peak or adjust the phase of a frequency band in the opposite sub to compensate for the first sub. Results vary.

 

[goat76]

How important the speaker symmetry is in the room, highly depends on the specific room. I think Griesenger talked specifically about placing the subwoofers asymmetrically, for the very reason to excite the room modes in a way to maximize the phase differences, which in turn creates maximum envelopment in a small room.

 

[dan_remaincalm]

The subs ideally should be on either side of the listener to maximize the effect. I can't do that in my listening room, so the subs are in the two front corners. One thing you CAN NOT do is place your subs in non-symmetrical positions in the room, or front-to-back. Read this Audioholics article, it will tell you more. It's also an easier read than Dr. Griesinger's paper (which I can't seem to find at the moment). That Audioholics article does a good job of covering the skepticism in the community, but it is a few years old. Right now there is no doubt that stereo bass is audible in a free field and with test signals, thanks to experiments by Lars Risbo and others. But whether it is audible in a listening room with normal music is another matter. I don't think that study has been done yet. Read this thread if you want to learn more.



DSP. You can either chop off the peak or adjust the phase of a frequency band in the opposite sub to compensate for the first sub. Results vary.

i've heard dramatic stereo sub effects on a few songs - it felt seismic and weird. that's kindof what got me started down these experiments.

here's the stereo image of one of them - Malandro De Culto by Antiguo Automata Mexicano. there's an official version on youtube but the encoder has knocked out a lot of sub compared to my local copy, and the stereo bass effect is substantially reduced.

the thing about my room though is that i'm running the subs in nearfield - i am seated in a triangle 1m from my mains, and the stereo subs are about 1.2m below and 0.2m to the far side of each main. also the back wall has a ton of membrane absorbers. most of the bass i get is direct sound from the speakers/subs (i think!), where a normal room would pressurize and bass would flow around much differently.

 

[sigbergaudio]

well, the published science and dominant narrative says "just run your subs mono, you can't hear directional sub bass without headphones". that doesn't match my blind testing here.

also, if it were just activating different modes, you'd expect the left sub to sometimes sound like it was on the right or whatever, i think (maybe?)? these were 1:1 correlated "panned left"-"sounds like it's the left" etc though.

Your test doesn't really prove that you will find stereo subs to be preferable over mono subs when playing actual music.

As mentioned, if you activate the room differently with subwoofers placed in different places, the frequency response will also change, which no one is disputing that is audible (potentially even with music). But is it just different (if your perception is one of frequency change rather than perception of direction), or actually better?

 

[Sokel]

I would argue the old, good, "as intended" .
Sell was made at the control room with mains playing stereo bass, so that's my take of "what the artist heard" .
(I would probably exclude little home, multi-purpose studios, but ok)

As simple as that.

 

[dan_remaincalm]

Your test doesn't really prove that you will find stereo subs to be preferable over mono subs when playing actual music.

As mentioned, if you activate the room differently with subwoofers placed in different places, the frequency response will also change, which no one is disputing that is audible (potentially even with music). But is it just different (if your perception is one of frequency change rather than perception of direction), or actually better?

but... that track i listed *is* actual music. that whole [antiguo automata mexicano] album has tons of stereo sub, loads of it, constructed in a very deliberate way. it sounds wild, really good. like i said, the effect is seismic - the only thing i can compare with it was when i experienced a mini earthquake on a california visit once.

[edit: obviously it's not common, but there are a bunch of other albums with very wide bass that sound good]

i've also tried doing a mono-sub downmix of the start of that track at 60Hz in software... it sounds way less directional and less impressive.

i also ABX'ed, because science, and i was able to tell it apart from the original track 100% of the time. i'd be happy to privately share the test files if you'd like to try it yourself?

again... the setup here is kindof weird. i'm close enough to the subs from my desk that i can reach them from my chair if i stretch a bit, i and i have four primacoustic fulltraps about 1.5m behind me, plus a ton of DIY treatment. i don't think this is a traditional listening environment. but in this particular room, this particular setup sounds way more impressive with the subs in full stereo mode.

 

[ZolaIII]

Does it, though? This is another point I would like to understand regarding stereo subs: Is it necessary that the subs are positioned in a stereo triangle, or is it enough that the two subs are located at two different places in the room.


Yes, but it’s not just about filling nulls. In my case, my two subs play in mono - in phase - to counteract my nasty peak at 45Hz. If they were to play in stereo it could happen that we get 45Hz in opposite phase. This would then enforce the mode. What could be done about that?

Near the belonging main same direction but you don't nead to aim sub's. Still independent impuls matching is advised (for sub's and mains L&R sub impulse matched and L&R main impulse matched (as thing like perfect placement dosent exit). You still try to avoid back refractions for mains and pick it up for sub's (mains out, sub's to the wall).

45 Hz, hmmm not a long room in listening orientation.

Disclaimer: what's called "stereo sub's" hire or simply 2.2 isn't there for bass directivity or half directivity, it's intended for better ELC integration and there for crossed @ 120 Hz as ELC knew for bass part is @ 105 Hz.
Difference at calibration point (85/88 dB SPL white noise mono/stereo to listening spot) for 75~80 Hz mono and 120 Hz 2.2 are in slight SPL increase in transition area (which shouldn't be there to source) and under it (referring to 45-75 and under 45 Hz). Subjective you would think mono is better (louder).
Things change like a storm when you need to add camel hump of a lower bass boost to compensate psy how we hear to lower SPL and it works down to normal come speach in quite environment (60 dB) when done properly in 2.2. Don't get me wrong when it's less substantial (boost) to average listening lv (73~76 dB) and to speakers which have their own main bass woffer it will work just fine in 2.1.
So it's about being able to hear all 9 octaves on lower SPL lv (boosting parts which you couldn't).

 

[sigbergaudio]

but... that track i listed *is* actual music. that whole [antiguo automata mexicano] album has tons of stereo sub, loads of it, constructed in a very deliberate way. it sounds wild, really good. like i said, the effect is seismic - the only thing i can compare with it was when i experienced a mini earthquake on a california visit once.

[edit: obviously it's not common, but there are a bunch of other albums with very wide bass that sound good]

i've also tried doing a mono-sub downmix of the start of that track at 60Hz in software... it sounds way less directional and less impressive.

i also ABX'ed, because science, and i was able to tell it apart from the original track 100% of the time. i'd be happy to privately share the test files if you'd like to try it yourself?

View attachment 504835

again... the setup here is kindof weird. i'm close enough to the subs from my desk that i can reach them from my chair if i stretch a bit, i and i have four primacoustic fulltraps about 1.5m behind me, plus a ton of DIY treatment. i don't think this is a traditional listening environment. but in this particular room, this particular setup sounds way more impressive with the subs in full stereo mode.

1.How did you perform the mono-downmix @ 60hz ?
2.ABX only allows you to to determine if you can tell them apart, and we have already concluded that it is reasonable to expect that you can do that in your setup (or most dual sub setups) due to differences in how they excite room modes.
3.If you feel like you can reliably tell the difference and stereo subs overall sounds better to you, you should of course configure your subs in stereo.

 

[janbth]

The subs ideally should be on either side of the listener to maximize the effect. I can't do that in my listening room, so the subs are in the two front corners. One thing you CAN NOT do is place your subs in non-symmetrical positions in the room, or front-to-back. Read this Audioholics article, it will tell you more. It's also an easier read than Dr. Griesinger's paper (which I can't seem to find at the moment). That Audioholics article does a good job of covering the skepticism in the community, but it is a few years old. Right now there is no doubt that stereo bass is audible in a free field and with test signals, thanks to experiments by Lars Risbo and others. But whether it is audible in a listening room with normal music is another matter. I don't think that study has been done yet. Read this thread if you want to learn more.

I think you mean Thomas Lund who has been doing the experiments, and not his fellow countryman Lars Risbo. I have read the Audioholics article and the mentioned thread, but I don’t recall any mention of symmetry. (It’s a long thread, so it may have slipped by me.) What I do remember now, is what Matthew Poes writes about lateral modes, but you can excite those without the subs necessarily being placed symmetrically.

DSP. You can either chop off the peak or adjust the phase of a frequency band in the opposite sub to compensate for the first sub. Results vary.

No, it’s not that simple. You can’t just apply separate filters to the L and R channels to chop down peaks. In my case, my two subs are located in opposite polarity regions of the 45Hz mode. If L and R is played at 45Hz in phase, this would lead to a dip, if they are played at 45Hz in opposite phase (as might happen in stereo), this would lead to a peak.

I realize that this is not exactly crystal clear, but room modes needs careful thought. I’ve spent the last couple of years measuring and tweaking my room, getting an overview of the room modes, and have currently excellent results - with mono bass. What I’m trying to figure out is if I can achieve similar excellent results with stereo bass.

 

[thcdru2k]

I’ve ended up in a middle ground between true stereo subs and mono summed multisub: a stereo bass matrix with controlled crossfeed using Flex HTx.

Each sub gets its own channel at 0 dB, but I also feed a reduced amount of the opposite channel into each sub (crossfeed). So it’s not dual mono, and it’s not hard L-only/R-only stereo either. The goal is to preserve some stereo information in the upper bass while keeping some correlation between subs so room modes are a little more predictable. I settled at -3db for the crossfeed but this can be adjusted to taste / or by evaluating graphs.

For multichannel I feed the center to both subs and surrounds to respective sub also at a reduced amount. Crossover is also channel specific.

 

[JRowland]

I think you mean Thomas Lund who has been doing the experiments, and not his fellow countryman Lars Risbo. I have read the Audioholics article and the mentioned thread, but I don’t recall any mention of symmetry. (It’s a long thread, so it may have slipped by me.) What I do remember now, is what Matthew Poes writes about lateral modes, but you can excite those without the subs necessarily being placed symmetrically.


No, it’s not that simple. You can’t just apply separate filters to the L and R channels to chop down peaks. In my case, my two subs are located in opposite polarity regions of the 45Hz mode. If L and R is played at 45Hz in phase, this would lead to a dip, if they are played at 45Hz in opposite phase (as might happen in stereo), this would lead to a peak.

I realize that this is not exactly crystal clear, but room modes needs careful thought. I’ve spent the last couple of years measuring and tweaking my room, getting an overview of the room modes, and have currently excellent results - with mono bass. What I’m trying to figure out is if I can achieve similar excellent results with stereo bass.

Dirac ART works well with room modes. It allows you to assign subs as support and you can control the range (under 150Hz) each support or main speaker plays. It’s very easy to assign left side of the room subs to left side speakers and vice versa. If the equipment produces it allows you to effectively create true full range mains and if the content has the stereo bass it’s there. Room modes are handled as well. Might be worth looking into.

 

[Keith_W]

I think you mean Thomas Lund who has been doing the experiments, and not his fellow countryman Lars Risbo.

You are correct. Sorry.

I have read the Audioholics article and the mentioned thread, but I don’t recall any mention of symmetry. (It’s a long thread, so it may have slipped by me.)

You are correct that the article does not say anything about symmetry. I can't remember where I read it, but it would make sense that you want a subwoofer on either side of the listener, and not, say, one in front and the other on the side.

 

[janbth]

Dirac ART works well with room modes. It allows you to assign subs as support and you can control the range (under 150Hz) each support or main speaker plays. It’s very easy to assign left side of the room subs to left side speakers and vice versa. If the equipment produces it allows you to effectively create true full range mains and if the content has the stereo bass it’s there. Room modes are handled as well. Might be worth looking into.

Agreed! As it happens, I am waiting for the delivery of a Marantz Cinema 30 (ordered on Black Friday!). I have already paid the Dirac ART license. When it arrives, and I have the time to set it up, I will experiment with mono vs. stereo bass.

 

[JRowland]

Agreed! As it happens, I am waiting for the delivery of a Marantz Cinema 30 (ordered on Black Friday!). I have already paid the Dirac ART license. When it arrives, and I have the time to set it up, I will experiment with mono vs. stereo bass.

Enjoy! There is a lot to experiment with, it’s very fun and easy to play around with in my opinion.

 

[thcdru2k]

How important the speaker symmetry is in the room, highly depends on the specific room. I think Griesenger talked specifically about placing the subwoofers asymmetrically, for the very reason to excite the room modes in a way to maximize the phase differences, which in turn creates maximum envelopment in a small room.

My subwoofers are placed symmetrically however the room is asymmetric and it is clear they excite the room differently. Not by design per say but due to wife approval constraints. It is nice however when wife approval coincidentally aligns with positive acoustic properties

 

[EJasonC]

i've heard dramatic stereo sub effects on a few songs - it felt seismic and weird. that's kindof what got me started down these experiments.

here's the stereo image of one of them - Malandro De Culto by Antiguo Automata Mexicano. there's an official version on youtube but the encoder has knocked out a lot of sub compared to my local copy, and the stereo bass effect is substantially reduced.

View attachment 504831

the thing about my room though is that i'm running the subs in nearfield - i am seated in a triangle 1m from my mains, and the stereo subs are about 1.2m below and 0.2m to the far side of each main. also the back wall has a ton of membrane absorbers. most of the bass i get is direct sound from the speakers/subs (i think!), where a normal room would pressurize and bass would flow around much differently.

If possible, try positioning the subs with the drivers facing the back wall or toward the corners.
Especially for near or mid field listening, doing so effectively adds 'distance'
Try it, you may be surprised.
For my setup, the improvement was not insignificant!