Stereo Bass using subwoofers

[youngho]

This might be of interest: https://www.audiosciencereview.com/forum/index.php?threads/bass-and-subwoofers.51589/#post-1857133

 

[807Recordings]

In most recordings, the utility is intentionally destroyed.

Now, if you have a good, well-designed acoustic recording that hasn't been treated with the "mono bass" routine, etc, you may get quite a bit from it, especially if you have 2 front, 2 back, properly (that word!) recorded.

Below 40Hz it's not as much of an issue, but between 40 and 90Hz, yes, there is "stereo content" possible in a good venue with a good recording.

Interesting this topic as a producer (yes electronic) I have found with synthesizers and bass if I mono the signal at say 80Hz something did get lost. Often I would do this because the end format was vinyl. What I have done though is started to go lower X-Over to say 50Hz with a different slope that tend to narrow to mono at 40Hz. That said many records I have had cut with the bass not altered and the Mastering Engineer handled the rest and surprisingly the black art of cutting vinyl is not just as black and white as make bass mono, as they can run curves to which degree.
Digital of course is much simpler.

 

[j_j]

Interesting this topic as a producer (yes electronic) I have found with synthesizers and bass if I mono the signal at say 80Hz something did get lost. Often I would do this because the end format was vinyl. What I have done though is started to go lower X-Over to say 50Hz with a different slope that tend to narrow to mono at 40Hz. That said many records I have had cut with the bass not altered and the Mastering Engineer handled the rest and surprisingly the black art of cutting vinyl is not just as black and white as make bass mono, as they can run curves to which degree.
Digital of course is much simpler.

I'm going to send you a message, stay tuned.

 

[goat76]

Below 40Hz it's not as much of an issue, but between 40 and 90Hz, yes, there is "stereo content" possible in a good venue with a good recording.

As we probably can't hear any directional cues at those low frequencies between 40 and 90 Hz in small rooms, what is it that we will experience with a good recording made in a good venue?

When I added my second subwoofer and set them up in a stereo configuration, my experience was (and still is) an increased sense of envelopment compared to one subwoofer in mono. I have had a few discussions about my experience on another forum, but they always end with someone saying it's impossible to hear directions that low in frequency, so the experience I have must therefore be something I made up.

I have made some analyses of many music tracks and many of them show pretty large differences under 80 Hz, some deviations between the channels even reached up to 20 dB and there are constant changes throughout the whole span of the tracks. Today I did some listening tests where I compared some of these tracks with and without a "mono maker" set at 80 Hz, and I could hear how the sound "shrank" (almost a bit claustrophobic) and stayed more in the area between the speakers with the bass in mono. When turning the "mono maker" off it sounded more open and airy with a larger sense of envelopment.

So what is your take on this?

 

[HiMu]

When I added my second subwoofer and set them up in a stereo configuration, my experience was (and still is) an increased sense of envelopment compared to one subwoofer in mono.

I set up my small closed subs in stereo based on the David Griesinger presentations, it was meant to be an experiment but the enveloping effect was much more noticeable than I expected, and after a few weeks the subs are still on the side walls on top of stands at ear level.
The trade off is less punchy bass but a lot larger soundstage that kind of "spills" around, but still very strong and stable phantom center. At least with coaxial L&R in a reasonably well treated small room.
Highly recommend to test some festival/live show recordings with enough ambience mixed into it and pay attention to the noise of the crowd. In mono the "crowd noise is in front of you" but with stereo subs it sounds more like "being in the noise". This effect was also noticed by a friend who visited and was highly skeptical of running subs in stereo.

I have 2 subs in stereo on side walls close to middle of room height, 1 in the front of the room in mono on the floor. L&R positioned roughly 1/3 from the front wall, subs 1/3 from the rear wall. XOver @ 90Hz.

 

[Duke]

As we probably can't hear any directional cues at those low frequencies between 40 and 90 Hz in small rooms, what is it that we will experience with a good recording made in a good venue?

When I added my second subwoofer and set them up in a stereo configuration, my experience was (and still is) an increased sense of envelopment compared to one subwoofer in mono...

My understanding is that the ear can detect inter-aural pressure differences at low frequencies (which give rise to the perception of "envelopment") far better than it can detect arrival direction at low frequencies in a fairly small reverberant space (home audio listening room).

I set up my small closed subs in stereo based on the David Griesinger presentations, it was meant to be an experiment but the enveloping effect was much more noticeable than I expected, and after a few weeks the subs are still on the side walls on top of stands at ear level.

The trade off is less punchy bass but a lot larger soundstage that kind of "spills" around, but still very strong and stable phantom center...

I have 2 subs in stereo on side walls close to middle of room height, 1 in the front of the room in mono on the floor. L&R positioned roughly 1/3 from the front wall, subs 1/3 from the rear wall. XOver @ 90Hz.

Nice!!

If you have phase controls on the side-wall subs, have you ever experimented with introducing a significant phase differential between them? Like setting their phases at 90 degrees apart, or even 180 degrees apart?

 

[goat76]

I set up my small closed subs in stereo based on the David Griesinger presentations, it was meant to be an experiment but the enveloping effect was much more noticeable than I expected, and after a few weeks the subs are still on the side walls on top of stands at ear level.
The trade off is less punchy bass but a lot larger soundstage that kind of "spills" around, but still very strong and stable phantom center. At least with coaxial L&R in a reasonably well treated small room.
Highly recommend to test some festival/live show recordings with enough ambience mixed into it and pay attention to the noise of the crowd. In mono the "crowd noise is in front of you" but with stereo subs it sounds more like "being in the noise". This effect was also noticed by a friend who visited and was highly skeptical of running subs in stereo.

I have 2 subs in stereo on side walls close to middle of room height, 1 in the front of the room in mono on the floor. L&R positioned roughly 1/3 from the front wall, subs 1/3 from the rear wall. XOver @ 90Hz.

I have never tried to position my subwoofers on the sides as David Griesinger does in his presentation as that would not work with my current room layout. But I still have my subwoofers fairly wide as they are positioned outside each main speaker, and I use a small equilateral listening triangle of just about 2 meters for my main speakers so the subwoofers end up at about 40 degrees to the sides. I think it makes a big difference to the sensation of envelopment, and sometimes even to the point that it sounds like surround sound depending on the recordings.

 

[bmc0]

As we probably can't hear any directional cues at those low frequencies between 40 and 90 Hz in small rooms [...]

I grant that this idea seems to be fairly widely accepted, but I believe that David Griesinger, Thomas Lund, and j_j would all say that it is false (hopefully I'm not putting words in their mouths).

My experiences with stereo bass reproduction are similar to yours and @HiMu's. Approximately a year ago, I decided to experiment with running my two subs in stereo (having previously summed L and R). I found the difference in envelopment and spatial impression quite convincing in my (admittedly informal) tests, so I've not gone back to summed mono.

 

[HiMu]

If you have phase controls on the side-wall subs, have you ever experimented with introducing a significant phase differential between them? Like setting their phases at 90 degrees apart, or even 180 degrees apart?

Only fine tune for phase in my dsp are all-pass filters, I'll experiment and try to remember to reply if there is any significant change.

I think it makes a big difference to the sensation of envelopment, and sometimes even to the point that it sounds like surround sound depending on the recordings.

Yes there's surprisingly strong resemblance of surround sound but of course still a difference. With higher xover the sub levels need to be balanced to the mains even more so than in mono or the effect changes from subtle envelopment to overpowering, shouty/bloated, masking higher frequencies, overall sloppiness of rhythm and easy to localize.

 

[j_j]

When I added my second subwoofer and set them up in a stereo configuration, my experience was (and still is) an increased sense of envelopment compared to one subwoofer in mono.

Yep. That's what you hear. More so if you have a very complex relationship between the two subs (better at least 3, one behind, since your head moves, by the way) that mimics what you get in a real room.

You don't hear "direction". This is a classical case of someone taking a correct result (not much directional sensation below 90Hz, if any) and forgetting that there are other perceptual cues beyond "direction", in particular, as you found, envelopment.

This was a particular lesson in the pipe organ recordings I made back at AT&T Research long ago. We could play them in 2 or 5 channel (5 full range speakers, no subs). In 2 channel, the usual "recording is too far, it's all boomy and such". In the 5 channel recording, the sensation, rather than being "in front" was around, and it sounded (lo and behold) like the room.

Yes, we did filter out everything over 100Hz to check on that. Yes, it still mattered.

I did more than a few demos where I would play one, two, and then 5 channels, and the effects became very, very obvious to nearly all listeners.

 

[goat76]

Yes there's surprisingly strong resemblance of surround sound but of course still a difference. With higher xover the sub levels need to be balanced to the mains even more so than in mono or the effect changes from subtle envelopment to overpowering, shouty/bloated, masking higher frequencies, overall sloppiness of rhythm and easy to localize.

Yes, not like a surround mix where instruments are all around me, but not that far behind those surround mixes where the musicians are still on the stage in front of the listener, and the surround speakers just take care of ambience in the mix.

 

[EJ3]

Yep. That's what you hear. More so if you have a very complex relationship between the two subs (better at least 3, one behind, since your head moves, by the way) that mimics what you get in a real room.

Yes, we did filter out everything over 100Hz to check on that. Yes, it still mattered.

I did more than a few demos where I would play one, two, and then 5 channels, and the effects became very, very obvious to nearly all listeners.

My pair of subs have both the ports & the speakers firing at the floor. I run them in stereo and the mains sit on top of them. The mains can do 26Hz-20KHz +-2db with no EQ.
The subs FR is listed as being 20Hz-80Hz (don't know the +-db). I high pass at 60Hz & low pass at 70Hz. And run the whole setup in stereo.
If I disconnect the mains I cannot tell that a bass sound is left or right (which is certainly going to be audible at 90Hz & lower with over 1700 watts at 4 ohms on each sub).
Can I tell from which sub a BASS note is originating from? Not unless I am turning the balance to full left or full right.
But, when 1 of the subs is not on, I feel less "envelopment".
And if the subs have been arranged to be in dual mono, there is still more envelopment than if there is only 1 sub but less envelopment than if they are in stereo.
Of course, that is just my opinion and YMMV.

 

[j_j]

My pair of subs have bot the ports & the speakers firing at the floor. I run them in stereo and the mains sit on top of them. The mains can do 26Hz-20KHz +-2db with no EQ.
The subs FR is listed as being 20Hz-80Hz (don't know the +-db). I high pass at 60Hz & low pass at 70Hz. And reun the whole setup in stereo.
If I disconnect the mains I cannot tell that a bass sound (which is certainly going to be audible at 90Hz & lower with over 1700 watts at 4 ohms on each sub).
Can I tell from which sub a BASS note is originating from? Not unless I am turning the balance to full left or full right.
But, when 1 of the subs is not on, I feel less "envelopment".
And if the subs have been arranged to be in dual mono, there is still more envelopment than if there is only 1 sub but less envelopment than if they are in stereo.
Of course, that is just my opinion and YMMV.

You've proven my point, exactly.

 

[Keith_W]

The trade off is less punchy bass but a lot larger soundstage that kind of "spills" around, but still very strong and stable phantom center. At least with coaxial L&R in a reasonably well treated small room.

Not that I don't believe you, but I am wondering why "less punchy bass" should be the result of setting up subs in stereo?

If you have phase controls on the side-wall subs, have you ever experimented with introducing a significant phase differential between them? Like setting their phases at 90 degrees apart, or even 180 degrees apart?

Wouldn't subs being out-of-phase by 180deg result in cancellation?

 

[j_j]

Not that I don't believe you, but I am wondering why "less punchy bass" should be the result of setting up subs in stereo?

Set up properly, that shouldn't be the case.

Wouldn't subs being out-of-phase by 180deg result in cancellation?

Would they now? You'd have pressure cancellation directly between them, but that would be a point of maximum volume velocity, rather obviously, because the air is, so to speak, going back and forth. In a free field, there is pressure cancellation due to the peak volume velocity.

Now your body interacts with the volume velocity to create pressure, so now what? If you're 6' tall, that gives you some notable interference in the volume velocity along your 6' axis to at least 40 Hz, and some possible down into the 20Hz range. (1/4 to 1/8 wavelength).

Remember, there are FOUR variables to a soundfield at any given point, 3 volume velocities (or one velocity and 2 angles, same thing, i.e. v(x),v(y),v(z), or v(r), theta, phi) and a pressure measure. In general, in a soundfield where there is interaction between a room or two sources, pressure nulls are generally velocity peaks, and vice versa.

This is the same reason that in general, adding more energy to a room will not cure room modes (although source position or virtual position can somewhat mitigate them) because a big bass zero in a room is the result not of "zero bass" but rather of "way too much energy stored at that frequency, creating pressure zeros, etc". Adding more energy to a storage problem is not generally a big help.

 

[Keith_W]

Would they now? You'd have pressure cancellation directly between them, but that would be a point of maximum volume velocity, rather obviously, because the air is, so to speak, going back and forth. In a free field, there is pressure cancellation due to the peak volume velocity.

Now your body interacts with the volume velocity to create pressure, so now what? If you're 6' tall, that gives you some notable interference in the volume velocity along your 6' axis to at least 40 Hz, and some possible down into the 20Hz range. (1/4 to 1/8 wavelength).

That is an interesting proposition. Are you saying that a null from cancellation is an area of minimal pressure but maximum air particle velocity, but your body's interaction with the area of maximum velocity results in interference that allows you to perceive sound pressure? A microphone is very small compared to a body, so there is minimal interaction with maximal velocity, which is why it measures a null?

Remember, there are FOUR variables to a soundfield at any given point, 3 volume velocities (or one velocity and 2 angles, same thing, i.e. v(x),v(y),v(z), or v(r), theta, phi) and a pressure measure. In general, in a soundfield where there is interaction between a room or two sources, pressure nulls are generally velocity peaks, and vice versa.

I can't remember something which I did not know in the first place. Thank you, JJ.

 

[j_j]

That is an interesting proposition. Are you saying that a null from cancellation is an area of minimal pressure but maximum air particle velocity, but your body's interaction with the area of maximum velocity results in interference that allows you to perceive sound pressure? A microphone is very small compared to a body, so there is minimal interaction with maximal velocity, which is why it measures a null?

Well, yes. HRTF's (head related transfer functions) come from the same interaction between volume velocity, pressure, and your head, for instance, although "head" by itself isn't very important to very low frequencies, to say the least.

I can't remember something which I did not know in the first place. Thank you, JJ.

Hmm. I think I have a tutorial on that tucked away somewhere. I'll have to go look.

 

[dualazmak]

My pair of subs have bot the ports & the speakers firing at the floor. I run them in stereo and the mains sit on top of them. The mains can do 26Hz-20KHz +-2db with no EQ.
The subs FR is listed as being 20Hz-80Hz (don't know the +-db). I high pass at 60Hz & low pass at 70Hz. And reun the whole setup in stereo.
If I disconnect the mains I cannot tell that a bass sound (which is certainly going to be audible at 90Hz & lower with over 1700 watts at 4 ohms on each sub).
Can I tell from which sub a BASS note is originating from? Not unless I am turning the balance to full left or full right.
But, when 1 of the subs is not on, I feel less "envelopment".
And if the subs have been arranged to be in dual mono, there is still more envelopment than if there is only 1 sub but less envelopment than if they are in stereo.
Of course, that is just my opinion and YMMV.

I have/had very similar implementation and results in my PC-DSP-based multichannel multi-SP-driver multi-amplifier fully active audio rig with L&R large-heavy subwoofers YAMAHA YST-SW1000; please refer to my post #931 on my project thread for details of the latest system setup.

Within DSP "EKIO" in PC, I set low-pass -12 dB/Oct at 50 Hz, and in YST-SW1000 itself I have additional -24 dB/Oct low-pass at 55 Hz.
For the main SP's woofers, YAMAHA JA-3058 directly and dedicatedly driven by YAMAHA A-S3000 amp, I set high-pass -12 dB/Oct at 55 Hz in DSP "EKIO".

I decided the XO configurations (XO-Fq, polarity, group delay, filter-type, slopes, etc.) between L&R subwoofers YST-SW1000 and woofers JA-3058 based on my rather intensive "time alignment measurements/tunings" and "transient behavior measurements" for the subwoofers and woofers.

Spoiler

- Precision measurement and adjustment of time alignment for speaker (SP) units: Part-1_ Precision pulse wave matching method: #493
- Precision measurement and adjustment of time alignment for speaker (SP) units: Part-2_ Energy peak matching method: #494
- Precision measurement and adjustment of time alignment for speaker (SP) units: Part-3_ Precision single sine wave matching method in 0.1 msec accuracy: #504, #507
- Measurement of transient characteristics of Yamaha 30 cm woofer JA-3058 in sealed cabinet and Yamaha active sub-woofer YST-SW1000: #495, #497, #503, #507

As for listening tests including L&R subwoofers, using DSP "EKIO", I can do it very easily and flexibly even on-the-fly (while listening to music/test-tone tracks) like L-only, R-only, L+R mono, and L + R stereo.

I have very flexible relative gain controls not only in digital domain but also in analog domain as shown in this diagram;

Just for your additional reference, my present Fq-SPL at my listening position is like this;

Please note that, in addition to above DSP-EKIO's low-pass -12 dB/Oct at 50 Hz for subwoofers, I have -24 dB/Oct low-pass at 55 Hz within active subwoofers YST-SW1000.

The actual SP physical alignment and the listening triangle is shown in this photo;

I also intensively measured Fq-SPL at various "stages" in digital domain and analog domain, as well as of course in actual air-sound at listening position, as summarized in my post here #404 on my project thread.

Spoiler

- Frequency (Fq) responses in the completed system measured by using “cumulative white noise averaging method” under the present standard crossover configurations and relative gains_Part-1_Fq Responses in EKIO’s digital output level: #394

- Frequency (Fq) responses in the completed system measured by using “cumulative white noise averaging method” under the present standard crossover configurations and relative gains_Part-2_Fq Responses in DAC8PRO’s analog output level: #396

- Frequency (Fq) responses in the completed system measured by using “cumulative white noise averaging method” under the present standard crossover configurations and relative gains_Part-3_Fq Responses in amplifiers’ SP output level before protection capacitors: #401

- Frequency (Fq) responses in the completed system measured by using “cumulative white noise averaging method” under the present standard crossover configurations and relative gains_Part-4_Fq Responses in amplifiers’ SP output level after protection capacitors: #402

- Frequency (Fq) responses in the completed system measured by using “cumulative white noise averaging method” under the present standard crossover configurations and relative gains_Part-5_Fq Responses in actual SP room sound at listening position using one measurement microphone: #403

- Frequency (Fq) responses in the completed system measured by using “cumulative white noise averaging method” under the present standard crossover configurations and relative gains_Part-6_Summary, discussions, and a little step forward: #404, #405-#409

These posts under the below spoiler cover would be also of your interest and reference;

Spoiler

- Perfect (0.1 msec precision) time alignment of all the SP drivers greatly contributes to amazing disappearance of SPs, tightness and cleanliness of the sound, and superior 3D sound stage: #520

- Not only the precision (0.1 msec level) time alignment over all the SP drivers but also SP facing directions and sound-deadening space behind the SPs plus behind our listening position would be critically important for effective (perfect?) disappearance of speakers: #687

- Reproduction and listening/hearing/feeling sensations to 16 Hz (organ) sound with my DSP-based multichannel multi-SP-driver multi-amplifier fully active stereo audio system having big-heavy active L&R sub-woofers: #782

- A nice smooth-jazz album for bass (low Fq) and higher Fq tonality check and tuning: #910, #63(remote thread)

For the total tuning of our audio setup, including the L&R subwoofers, I believe we need to have our/your own consistent "reference/sampler music playlist"; in my case, as I share in this my hosting thread.

 

[Keith_W]

Well, yes. HRTF's (head related transfer functions) come from the same interaction between volume velocity, pressure, and your head, for instance, although "head" by itself isn't very important to very low frequencies, to say the least.

Well your insight has turned my understanding of measurements upside down. Until now, I believed that if you measure a null, you hear a null. But you don't hear a null, because your body converts that null back (i.e. maximum velocity) back into pressure. Instead, you hear god-knows-what depending on the size of your body.

Geez that complicates things. Now I see why some people measure from their listening position with dummies to simulate bodies. And I am starting to see why BACCH's ORC (which uses in-ear microphones) makes sense.

 

[Lion♡]

Excluding the common ITD and comparing 0°, 30°, 60°, and 90°...

And the ILD difference between 30° and 60°...
What j_j mentioned about the head itself having little influence on lower frequencies is likely referring to this aspect.


I received AE samples from Thomas Lund and listened to them, then sent him my small test results.
I compared them using basic binaural IEMs/headphones as well as speakers (virtualized HRIR/BRIR). Additionally, I applied a 450Hz LR 6th-order crossover, extending the ITD to 750µs below approximately 700Hz, similar to a side bass setup. I also configured it to have a total phase difference of 90° between the left and right low frequencies for further testing.
And after completing the test, I found myself agreeing exactly with the comment below.

In case LF inter-aural time and magnitude differences have been recorded across channels, and made it safely through a reproduction chain, it is such a pity to kill Auditory Envelopment (AE) at the last stage, by using mono sub(s) with bookshelf/nearfield monitors. That’s game over before even started.