Stereo Sub Vs Dual Mono

[chych7]

I’m still none the wiser. How do you send left and right signal’s sub frequencies separately to the left and right subwoofers?

One way would be:

1. Run L/R speakers as large and turn on LFE+main so it gets the full bass signal
2. Connect left subwoofer to left speaker using high level input (speaker wire), same for right sub/speaker. If your subwoofer doesn't have high-level inputs, you have to get a high-level extractor (speaker wire to RCA). It may be possible to simultaneously connect the AVR's LFE signal too, and then LFE+main can be turned off (not sure on this one...).

 

[sarumbear]

One way would be:

1. Run L/R speakers as large and turn on LFE+main so it gets the full bass signal
2. Connect left subwoofer to left speaker using high level input (speaker wire), same for right sub/speaker. If your subwoofer doesn't have high-level inputs, you have to get a high-level extractor (speaker wire to RCA). It may be possible to simultaneously connect the AVR's LFE signal too, and then LFE+main can be turned off (not sure on this one...).

That’s a silly idea!

 

[AdamG]

I’m still none the wiser. How are you sending left and right signal’s sub frequencies separately to the left and right subwoofers?

I’m not. I thought I was but I was incorrect in my understanding of how the 2 channel sub setup works. I do have my subs on each side of the main l and r speakers and incorrectly thought that they were getting left and right sub channel information. Because I can set independent trim and delay settings I associated that in my brain as stereo subs. This is further reinforced by the on screen graphics in the Amp Assign and Level adjustment screen that essentially present Left and Right subs. Assumption is what I apparently did.

 

[Chrispy]

I’m not. I thought I was but I was incorrect in my understanding of how the 2 channel sub setup works. I do have my subs on each side of the main l and r speakers and incorrectly thought that they were getting left and right sub channel information. Because I can set independent trim and delay settings I associated that in my brain as stereo subs. This is further reinforced by the on screen graphics in the Amp Assign and Level adjustment screen that essentially present Left and Right subs. Assumption is what I apparently did.

Many have assumed if an avr is ".2" they have individual subs, let alone stereo, too. Yamaha in setup has a L/R thing for subs, which isn't stereo either but rather about where you put them.

 

[sarumbear]

I’m not. I thought I was but I was incorrect in my understanding of how the 2 channel sub setup works. I do have my subs on each side of the main l and r speakers and incorrectly thought that they were getting left and right sub channel information. Because I can set independent trim and delay settings I associated that in my brain as stereo subs. This is further reinforced by the on screen graphics in the Amp Assign and Level adjustment screen that essentially present Left and Right subs. Assumption is what I apparently did.

We are easily fooled. That’s why subjective observations cannot be trusted. You thought bass is set to stereo and your brain added the non-existing stereo effect for you

 

[sarumbear]

I have my 2 subwoofers set up in stereo right beside/outside of each main speaker, and right from the start I thought it sounded way more spacious than my previous setup with just one subwoofer. It sounds so good I have no urge to even try them in mono.

How do you feed your subs in stereo? What’s the amplifier/crossover system that feeds your speakers?

 

[chych7]

That’s a silly idea!

This is how you'd do it with typical equipment, using the high-level inputs. I don't think it's silly...

Another way that works if you are using an external DAC/player (and not the AVR's DAC) is to split the RCA cable. One set goes to the AVR/amp for powering the speakers, the other set goes to the subwoofer LFE inputs, left/right differentiated. Managing the crossover may be tricky; you could also put a DSP in between to do that. So: DAC/player -> DSP (miniDSP 2x4HD would do it, although with some added noise) -> subwoofer and speaker amp/AVR.

 

[theREALdotnet]

True for pop, rock etc, completely untrue for classical, jazz, acoustic, etc.
Regarding non mono subs, our resident audio perception luminary J_J has not only spoken on this, he has demo'd it for decades.

I’m not sure I’m reading it that way. It seems like @j_j is saying that below 90Hz is not locatable but that multiple subs sound better than a single sub. NB: multiple subs, not stereo subs.

This gels with my own experience. I cannot locate my subwoofers (crossed over at 80Hz), no matter whether they play alone or together. However, having only one sub playing gives a weird in-the-head sensation, plus the bass response is very sensitive to head movement. With two subs (playing the same signal, not stereo) the bass kind of fills the room. I can only assume this to improve with more subs.

Regardless, even with one sub placed on the left, a double bass panned right will sound like being on the right, there is no doubt about that. The subwoofer’s location has nothing to do with it, assuming it is crossed over sufficiently low.

 

[anotherhobby]

So if the audio content has a stereo signal for bass, I can see there being a benefit if you can set it up right. However, if this means you have bass peaks/nulls, then it may negate any improvement to soundstage.

Yes, when sub bass hits in only one channel in a stereo dual sub setup, you are trading some frequency response for the stereo effect. I had a nasty null in each channel with only two subs, and that's one of the reasons I went to four subs. Below are the L/R channels for the mono quad sub configuration (top lines) vs the stereo one (bottom lines), and I was quite happy the additional 2 subs I built eliminated any difference in frequency response. I have a Dirac Live calibration for both mono and stereo, and what's nice about the miniDSP Flex setup is that I can swap configs back and forth on the fly with the presets. The Flex just sees L/R subs, while the downstream miniDSP 2x4HD sets delays and routes L/R traffic to the correct fronts and rears. It's actually fairly simple, with no DSP other than DL.

 

[anotherhobby]

I cannot locate my subwoofers (crossed over at 80Hz), no matter whether they play alone or together. However, having only one sub playing gives a weird in-the-head sensation, plus the bass response is very sensitive to head movement. With two subs (playing the same signal, not stereo) the bass kind of fills the room. I can only assume this to improve with more subs.

Regardless, even with one sub placed on the left, a double bass panned right will sound like being on the right, there is no doubt about that. The subwoofer’s location has nothing to do with it, assuming it is crossed over sufficiently low.

Localizing subs, as well as detecting stereo between them, is much easier when you are using them nearfield. My ears are only 4' from the drivers of each front sub and 6' from each rear sub. All 4 subs are also placed slightly wider than the mains, which also increases the effect.

 

[theREALdotnet]

Localizing subs, as well as detecting stereo between them, is much easier when you are using them nearfield. My ears are only 4' from the drivers of each front sub and 6' from each rear sub. All 4 subs are also placed slightly wider than the mains, which also increases the effect.

What frequency range are your subs playing? I found that if it’s low-passed sufficiently I can only localise a sub if it emits air noises, if it has huffing ports, if it buzzes or produces other kinds of distortion. With a clean, low tone I cannot localise it even from relatively nearby.

 

[anotherhobby]

What frequency range are your subs playing? I found that if it’s low-passed sufficiently I can only localise a sub if it emits air noises, if it has huffing ports, if it buzzes or produces other kinds of distortion. With a clean, low tone I cannot localise it even from relatively nearby.

Crossover is 24dB/Oct LR @80Hz. Everybody's perception is different. I have no reason to not believe you.

 

[theREALdotnet]

I’ll do some experimentation tonight with narrow band noise from REW, and see where the limits of localisation lie with my subs in my room.

 

[jsilvela]

Ha, so ironically, the much maligned "REL way" would give true stereo subs. (let me run for shelter)

I was given a reference to a talk to David Griesinger in another thread at ASR linked below.
And NTK has cited Griesinger in this thread regarding sub placement for stereo LF.

The Griesinger video below talks of envelopment for low frequency, and has some audio samples.
I listened to those samples with headphones that had good sub-bass response, and to be honest, didn't see a big difference.
Always curious to hear more and better though.

Science on low frequency quality?

I've been consuming a lot of information on low frequency reproduction, room modes, correction via DSP, brand wars etc. Something keeps bugging me. For all the effort expended on LF, I wonder if the science really backs it up. I have the first edition of Floyd Toole's book. Reading that, and...

audiosciencereview.com

 

[goat76]

How do you feed your subs in stereo? What’s the amplifier/crossover system that feeds your speakers?

My two REL subwoofers are connected with high-level cables. The left subwoofer to the left binding post on the amp gets the exact same signal as the left main speaker and the right subwoofer is connected to the right channel.

The crossovers and levels of the subwoofers are individually matched to each main speaker and placed close right beside/outside them.
The subwoofers work just as “sub-bass extensions” where the main speakers have their natural roll-off, no low pass filters applied.



I just happen to have my system set up as David Griesinger explains it. My intention was never to copy his description but my speaker set up just happens to be at the long wall, and the speakers just happens to be placed asymmetrically in the room out of practicality.

The only thing that differs from his description is the placements of my subwoofers, otherwise, it seems like he looked at my setup when he wrote his papers.

I have tried listening to different single bass frequencies and can confirm that I can locate some of them coming from either the left or the right side of the stereo field, but some of the frequencies are more diffuse to hear where they are coming from. So I think the theories David Griesinger is talking about really make us hear the localization of deep bass if two subwoofers are fed with different bass information to the left and right channel, thanks to phase differences.

But... I think that the sensation I get of a more enveloping sound is more related to my specific listening rooms characteristics and that the two subwoofers are “feeding” the room with different sub-bass information, and not necessarily that l hear the actual room information from the recorded venue as it was heard IRL.
But no matter what it is I really hear, it still gives me a better sensation of an enveloping sound with subwoofers set up in stereo.

 

[sarumbear]

My two REL subwoofers are connected with high-level cables. The left subwoofer to the left binding post on the amp gets the exact same signal as the left main speaker and the right subwoofer is connected to the right channel.

The crossovers and levels of the subwoofers are individually matched to each main speaker and placed close right beside/outside them.
The subwoofers work just as “sub-bass extensions” where the main speakers have their natural roll-off, no low pass filters applied.

You say crossover but there is only a LP filter on the sub isn't it? There is nothing that "crosses"?

May I ask how you decided on the LP frequency and slope/order of the sub?

 

[FrankW]

I’m not sure I’m reading it that way.

Then read it again as many times as needed; NO mono bass https://www.audiosciencereview.com/...than-digital-right.37657/page-20#post-1514978

multiple subs can also create some effects that mono bass simply can not.

 

[FrankW]

Anyone serious about audio should join AES and read what the science actually point to.
Here is one of the better ones I found, since its a compilation of about 45 studies 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 whichfound 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 frequ encies [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.

Beware online "self" tests at home when the tester is oblivious to confounding factors. The old GIGO concept.

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. The system which has been studied least in the literature is the one where all 5 (or 7) main channel loudspeakers have good low frequency response. This system in combination with appropriate signal processing would seem to present the greatest for controlling room modes, using both modal equalisation and the interaction of multiple drive units, and presenting spatial information.

The last one seems to be exactly what J_J is doing. YMMV.

 

[fishergod]

In my opinion, the difference between the stereo and dual mono is that the dual-mono contains two mono channels which usually share a common source, but are independent of each other. A stereo file or audio setup consists of two channels, which always share a common source, and are always dependent on one another.

 

[sigbergaudio]

Stereo subs can be done with preamplifiers with multiple outputs (both RCA and XLR for instance), or more advanced preamps that actually support individual channels and crossovers (DSPeaker Antimode and MiniDSP primarily comes to mind).

My experience is that for most material it actually doesn't matter much one way or the other. The majority of the signal is mono anyway. With regards to localization getting lost, I think this is also a very narrow use case. Most material that are low frequency and panned, will also have harmonics higher up in the frequency range, which will be played back by the speakers. This means you will have the perception of panned material and get localization cues even though the fundamental is potentially played back in mono.

I think those that find "night and day differences" between these two configurations will be surprised if they test it blind on most material.

EDIT: To add anecdotal evidence (since ASR loves that ): I've switched between dual mono and stereo subs multiple times in several rooms due to testing different components that supported (or not) stereo subs. The difference was always small to non-existant in practice.