Stereo Bass using subwoofers

[dkinric]

I found this article timely for me as I have 2 subs and have recently experimented with running stereo bass.

https://www.audioholics.com/room-acoustics/stereo-bass

Anyone have experience running 2 subs in a stereo vs mono configuration?

Disclaimer: Subjective discussion, take with as any gains of salt as needed.

After I got the Topping DX7PRO, I tried using it as a pre-amp, with the RCAs to my subs, and XLRs to my Hypex DIY amp. Bass was noticeably different - much less bass impact than previous setup. Even adjusting the sub levels did not help enough. Thinking the issue must be the 2v vs 4v output level mismatch between the XLR and RCA outputs, I got a small in-line adjustable line level gain amp (up to +12db), and this helped a little, but bass still seemed lacking. (Rest of freq spectrum was fantastically detailed, btw)

Hooking back in my previous integrated amp to be used as a pre-amp, and splitting the sub out RCAs of the integrated (back to mono bass), the bass was much more prevelant - smoother, more impactful.
I realize there are a lot of variables such as room acoustics, but my experience here is that there was a benefit to the mono bass - the subs working in tandem provided a much more uniform and powerful bass response vs each fed a separate L/R channel signal in the same locations.

Curious as to others who have compared mono and stereo sub signals in their setups? What were your experiences?

 

[sergeauckland]

I used a pair of Meridian DSP1500 subs to supplement the bottom end of my DSP5000s. I used them located right next to the mains, effectively ending up with larger mains.

For logistic reasons, I couldn't use a single sub centred between the mains, and a single sub anywhere except half way just didn't work. It wasn't so much that I could hear the bass being off centre, more that I knew it was off centre, and that just bothered me, offended my sense of symmetry.

I don't use subs now, but can't see myself ever using just one.

S

 

[digitalfrost]

Have stereo subwoofers here, can easily sum the signal to mono and send it to both. Did that before. Can confirm your findings. Mono bass has more impact/slam.

 

[Berwhale]

Is it possible that you had the stereo subwoofers out of phase?

 

[March Audio]

I found this article timely for me as I have 2 subs and have recently experimented with running stereo bass.

https://www.audioholics.com/room-acoustics/stereo-bass

Anyone have experience running 2 subs in a stereo vs mono configuration?

Disclaimer: Subjective discussion, take with as any gains of salt as needed.

After I got the Topping DX7PRO, I tried using it as a pre-amp, with the RCAs to my subs, and XLRs to my Hypex DIY amp. Bass was noticeably different - much less bass impact than previous setup. Even adjusting the sub levels did not help enough. Thinking the issue must be the 2v vs 4v output level mismatch between the XLR and RCA outputs, I got a small in-line adjustable line level gain amp (up to +12db), and this helped a little, but bass still seemed lacking. (Rest of freq spectrum was fantastically detailed, btw)

Hooking back in my previous integrated amp to be used as a pre-amp, and splitting the sub out RCAs of the integrated (back to mono bass), the bass was much more prevelant - smoother, more impactful.
I realize there are a lot of variables such as room acoustics, but my experience here is that there was a benefit to the mono bass - the subs working in tandem provided a much more uniform and powerful bass response vs each fed a separate L/R channel signal in the same locations.

Curious as to others who have compared mono and stereo sub signals in their setups? What were your experiences?

Below around 80Hz you cannot localise the direction the sound is coming from, so stereo subs (one sent left and one sent right channel) are a tad pointless. So sum to mono. Im assuming your subs have left and right inputs? In which case send both channels to both subs.

2 subs are however very beneficial as you can use them to cancel room modes and provide a smother bass around the room. I would recommend properly crossing the subs over and filtering out what goes to the mains.

 

[Biblob]

After 80 Hz localisation of notes becomes very poor. So that's why you could use a mono signal. If you listen to a lot of pop, you might come across some songs where bass is panned, but that's not very often. In other genres this isn't done, so no worries

 

[dkinric]

Thanks Alan, I'm familiar with sub basics
Maybe I should have posted in the Topping DX7PRO forum, for others that use it in this way. Maybe a better question is in the recordings - is there separate info recorded below 80 hz in the L and R channels of most music? If so, this would help explain the discrepancy - each channel is adding to the sum whole.

 

[Severian]

For quite a while I had 2x12" subs flanking my mains. Four drivers total, but I had them wired as a single channel getting a summed mono signal from my DSP. I recently doubled up to 4x12" subs on each side, wired as two channels to enable stereo bass. My first attempt at it did not sound good at all - far less bass with 8 drivers than I had with 4. No punch at all. I copied the mono bass signal over to the new channel and it sounded awesome again. Honestly I haven't investigated it too much since I don't think many recordings use stereo bass in a meaningful way.

 

[Krunok]

Thanks Alan, I'm familiar with sub basics
Maybe I should have posted in the Topping DX7PRO forum, for others that use it in this way. Maybe a better question is in the recordings - is there separate info recorded below 80 hz in the L and R channels of most music? If so, this would help explain the discrepancy - each channel is adding to the sum whole.

If there is a difference in bass level in left and right channel you will always get more bass in scenario where bass is summed up to mono and then sent to both channels vs when it is played as stereo.

Let's assume that recording of one channel has 80dB bass and the other 75dB bass. If played in stereo this equals to 81.2dB but if played as 2 times summed mono it is 81.2+81.2=84.2dB. Those 3dB of difference would certainly be audible.

 

[Mnyb]

The room completely dominate in these frequencies so even if there where different info in L and R it does not matter , sum it up and use 2 subs to combat some room modes would still be the way to go , as the ear can not tell direction at these frequencies so 1 or n subs does not alter the strereo image.

Curiously Vinyl was/is mostly mono bass .

Yes you can probably locate subwoofers if the xover is not steep enough and/or they produce a lot of distortion, you can localise the overtones port noises and rattle

Get good subs , I suppose most are quite underpowered compared to the other speakers in thier effective range

 

[dkinric]

For quite a while I had 2x12" subs flanking my mains. Four drivers total, but I had them wired as a single channel getting a summed mono signal from my DSP. I recently doubled up to 4x12" subs on each side, wired as two channels to enable stereo bass. My first attempt at it did not sound good at all - far less bass with 8 drivers than I had with 4. No punch at all. I copied the mono bass signal over to the new channel and it sounded awesome again. Honestly I haven't investigated it too much since I don't think many recordings use stereo bass in a meaningful way.

Thanks, Severian, seems you had a similar experience. Interesting. My impression is that the woofers all firing in tandem makes a big difference in output (duh) vs even increased levels of stereo (independent) signals. My initial thought was that this could be overcome with increasing the signal levels, but not so much in my experience.

My interest in this is that it determines my equipment list - I had planned on completely eliminating the integrated amp - running the Topping as a pre-amp/DAC, with the advantages of one less component, using XLR and the resulting extremely clean signal path of DX7PRO to a Hypex 122MP based amp along with the RCAs to the powered subs.

This bass "issue" however make that not the favored approach. Although the rest of the spectrum is astonishing, the lack of bass and how the subs and mains gain up differently with volume adjustment makes the Topping not a good performer as a pre-amp.
Disappointing, but hey, first world problems...

 

[Ron Texas]

I used a pair of Meridian DSP1500 subs to supplement the bottom end of my DSP5000s. I used them located right next to the mains, effectively ending up with larger mains.

For logistic reasons, I couldn't use a single sub centred between the mains, and a single sub anywhere except half way just didn't work. It wasn't so much that I could hear the bass being off centre, more that I knew it was off centre, and that just bothered me, offended my sense of symmetry.

I don't use subs now, but can't see myself ever using just one.

S

I used to have the same perceptual problem. It took me a while to get over it.

 

[March Audio]

Thanks Alan, I'm familiar with sub basics
Maybe I should have posted in the Topping DX7PRO forum, for others that use it in this way. Maybe a better question is in the recordings - is there separate info recorded below 80 hz in the L and R channels of most music? If so, this would help explain the discrepancy - each channel is adding to the sum whole.

Its of course possible but unlikely. You will increase the volume by adding the 2 channels together.

 

[Mnyb]

If you got a room mode in the form of a “suck out” ie suddenly -10dB or even more energy could disappear at some frequency.
You can’t really compensate by pouring more power into to this “black hole” so if the multsub arrangement smooths out these room modes you get a very good result indeed i’m Quite envious of you that can effectively use multiple subs ,

 

[sergeauckland]

If there is a difference in bass level in left and right channel you will always get more bass in scenario where bass is summed up to mono and then sent to both channels vs when it is played as stereo.

Let's assume that recording of one channel has 80dB bass and the other 75dB bass. If played in stereo this equals to 81.2dB but if played as 2 times summed mono it is 81.2+81.2=84.2dB. Those 3dB of difference would certainly be audible.

That raises the question, What is mono? We had endless arguments over this in the past. Is it A+B, (A+B)/2, (A+B)/Sqrt2? Or something else.....A+B -4dB for instance. All have their adherents.

S

 

[Thomas_A]

If there is a difference in bass level in left and right channel you will always get more bass in scenario where bass is summed up to mono and then sent to both channels vs when it is played as stereo.

Let's assume that recording of one channel has 80dB bass and the other 75dB bass. If played in stereo this equals to 81.2dB but if played as 2 times summed mono it is 81.2+81.2=84.2dB. Those 3dB of difference would certainly be audible.

You should not mono that way. The benefit if you do it correctly is that you win headroom if the bass is different in the channels.

 

[Krunok]

That raises the question, What is mono? We had endless arguments over this in the past. Is it A+B, (A+B)/2, (A+B)/Sqrt2

Very true. Frankly, I'm not aware if there is a "standard" way how subs do summation of stereo bass to mono.

 

[dkinric]

If you got a room mode in the form of a “suck out” ie suddenly -10dB or even more energy could disappear at some frequency.
You can’t really compensate by pouring more power into to this “black hole” so if the multsub arrangement smooths out these room modes you get a very good result indeed i’m Quite envious of you that can effectively use multiple subs ,

My point was comparing these two audio component chains with the same subs in the same places gave significantly different results.

Regarding multiple subs, DSP is key to an easy and successful integration. My subs (Martin Logan Dynamo 800x) both have built in DSP using an app based interface. Highly recommended.

 

[digitalfrost]

That raises the question, What is mono? We had endless arguments over this in the past. Is it A+B, (A+B)/2, (A+B)/Sqrt2

So here's how I do the downmix:

# Stereo Bass
Copy: RL=1*L RR=1*R C=0 SUB=0 SL=0 SR=0
# Mono Bass
#Copy: RL=0.707*L+0.707*R RR=0.707*R+0.707*L C=0 SUB=0 SL=0 SR=0

Channels RL and RR go to the subwoofer DAC. I don't perceive the mono bass as much louder and -3dB should be correct for summing two channels, right? I can switch between mono and stereo just by switching the comment statement between the Copy commands. The mono bass is more central than the stereo bass (not that the stereo bass wouldn't be in the middle), and seems more defined, but the stereo bass has more detail. Checked polarity just now, it's correct.

 

[Krunok]

That raises the question, What is mono? We had endless arguments over this in the past. Is it A+B, (A+B)/2, (A+B)/Sqrt2

When I think of it, if done with analog circuit it will probably look like this and you will end up with voltage summation.