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Stereo Bass using subwoofers

pjug

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In summary of the last couple of pages:

You can detect the direction of the subs when:
  • One is 20 dB louder than the other
  • You sit close to it
Would this represent a real-world scenario where someone is trying to achieve "stereo bass"?
Probably not for me. But maybe:

- For a desktop setup
- In a car (I have no idea by maybe)

And certainly with headphones, even though this is not the question in the OP.
 

youngho

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My tests were more about stereo. For me, stereo means there are differences between channels. As long as I can sense differences between channels, then I consider I have sensed stereo bass. So it is a lot more lenient than your precise placement requirement.
The word stereophonic derives from the word stereoscopic, which relates to the creation of illusion of depth that results from the brain being able to integrate visual input from two slightly different angles into a single image, also known as stereopsis. Stereopsis can be disrupted by a difference in visual acuity or a misalignment of the eyes, among other things. Patients with issues in either can cover one eye and see that there is a difference between each eye, but they may be unable to "fuse" the two inputs into a single image, resulting in the failure of stereopsis and therefore absence of stereoscopy, so images remain two-dimensional.

"Stereo" for "stereophonic" is generally interpreted to mean something other than "use two speakers that are at least somewhat different" What exactly that means is somewhat variable but generally has to do with the creation of a sense that the sound is not coming from the loudspeaker itself. It's not just depth, since a single speaker playing a mono signal can reproduce some perception of depth or ambiance in a recording. However, if you use two speakers, so now dual mono, and if you're sitting centered and equidistant, then the sound will appear to come from a space between the two speakers. THAT would fall under what most people consider to be stereo.

In terms of Greisinger's use of the term stereo bass, he's discussing asymmetric loading of certain room modes to create a sense of envelopment at low frequencies. It's not just different between right and left. By the way, I tend to consider Earl Geddes's multisub and @Duke 's SWARM approaches in the same vein, with their presentation of decorrelated bass energy to the listener, in addition to smoothing out the frequency response.
 

Pdxwayne

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The word stereophonic derives from the word stereoscopic, which relates to the creation of illusion of depth that results from the brain being able to integrate visual input from two slightly different angles into a single image, also known as stereopsis. Stereopsis can be disrupted by a difference in visual acuity or a misalignment of the eyes, among other things. Patients with issues in either can cover one eye and see that there is a difference between each eye, but they may be unable to "fuse" the two inputs into a single image, resulting in the failure of stereopsis and therefore absence of stereoscopy, so images remain two-dimensional.

"Stereo" for "stereophonic" is generally interpreted to mean something other than "use two speakers that are at least somewhat different" What exactly that means is somewhat variable but generally has to do with the creation of a sense that the sound is not coming from the loudspeaker itself. It's not just depth, since a single speaker playing a mono signal can reproduce some perception of depth or ambiance in a recording. However, if you use two speakers, so now dual mono, and if you're sitting centered and equidistant, then the sound will appear to come from a space between the two speakers. THAT would fall under what most people consider to be stereo.

In terms of Greisinger's use of the term stereo bass, he's discussing asymmetric loading of certain room modes to create a sense of envelopment at low frequencies. It's not just different between right and left. By the way, I tend to consider Earl Geddes's multisub and @Duke 's SWARM approaches in the same vein, with their presentation of decorrelated bass energy to the listener, in addition to smoothing out the frequency response.
What would you call able to hear bass coming mostly from right, mostly from middle, and mostly from left?
 
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youngho

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Somewhat localizable. Not the same as stereo for me.
Play mono signal from right speaker only, play mono signal from both speakers, play mono signal from left speaker only. Localizable, not the same as stereo for me.
 

Pdxwayne

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Play mono signal from right speaker only, play mono signal from both speakers, play mono signal from left speaker only. Localizable, not the same as stereo for me.

Ok. Let's say you are using one music clip to simulate the effects you talked about.
You can achieve this kind of effects using what kind of audio file? Stereo music file or mono music file?
 

youngho

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Play mono signal from right speaker only, play mono signal from both speakers, play mono signal from left speaker only. Localizable, not the same as stereo for me.

I liken Thievery Corporation, but I find most of their recordings relentless in this respect. Bajofondo, on the other hand, “places” their instruments in a variety of lateral positions.
 

youngho

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Ok. Let's say you are using one music clip to simulate the effects you talked about.
You can achieve this kind of effects using what kind of audio file? Stereo music file or mono music file?

The Stereophile test CDs have pink noise tracks, dual mono for stereo, individual tracks for the surround version (disc 3?). I also have the Beatles recordings in mono and stereo, which were absolutely terrible up until a certain point (drums over on one side, singers on the other, so different between right and left but not really stereo for me).
 

Pdxwayne

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The Stereophile test CDs have pink noise tracks, dual mono for stereo, individual tracks for the surround version (disc 3?). I also have the Beatles recordings in mono and stereo, which were absolutely terrible up until a certain point (drums over on one side, singers on the other, so different between right and left but not really stereo for me).
Fine, for you, I will use your term of "different between left and right, but not really stereo".

The issue in this thread is that many claimed that "different between left and right, but not really stereo" can't even be heard for bass below 80hz.

Are you trying to support the statement that "different between left and right, but not really stereo" can be heard for tones below 80hz?
 
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youngho

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Fine, for you, I will use your term as "different between left and right, but not really stereo".

The issue in this thread is that many claimed that "different between left and right, but not really stereo" can't even be heard for bass below 80hz.

Are you trying to support the statement that "different between left and right, but not really stereo" can be heard for tones below 80hz?

I was just trying to point out some of the potential issues with the use of the term stereo. It had occurred to me that some of the localization effects occurred with bleed through higher frequencies despite use of the crossover, since I had some interference at certain times of the day resulting in audible radio station voices coming from my Hsu TN1220HO subwoofer, but that was already brought up by other posters. It seemed like discussion about what stereo means to different people hadn’t gotten very far. I haven’t done any experiments on the subject of asymmetric bass yet myself, so I don’t have a horse in this particular game. I am sensitive to the stereoscopic issue since I have asymmetric astigmatism resulting in occasional failures in stereopsis requiring periods of the equivalent of self-patching to re-entrain the brain. Oliver Sacks has written about the opposite, people unusually sensitive to stereoscopy.

I used to use a JBL BassQ processor but could not reliably hear any differences between the stereo and dual mono settings for the listening material that I normally enjoy. This whole discussion reminds me a little of phase shift, where phase distortion may be audible under specific conditions and test signals but not reliably so in real-world circumstances with music, but I don't have any good experience with either, myself (pressing the stereo button on the BassQ didn't really count).

I can’t remember if it’s been discussed or not that the Lexicon bass enhancement circuit derived from Greisinger’s work drove one lateral subwoofer 90 degrees out of phase with the other to create the pressure differential at the listening position.
 
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Soundmixer

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In summary of the last couple of pages:

You can detect the direction of the subs when:
  • One is 20 dB louder than the other
  • You sit close to it
Would this represent a real-world scenario where someone is trying to achieve "stereo bass"?
I don't know any mixing or mastering engineer that would purposefully create a track that had bass 20dB louder in one channel than the other. Even if you could find a track that had its bass heavily decorrelated, it would not have a channel disparity of 20dB in the low frequencies. Music isn't mixed that way.

If envelopment (which decorrelated bass provides) is what one is looking for, you could put 4 subs in each corner of a room, cross them over to the mains at 40hz, and you will get the same effect. The bass could be mono, and it would still be enveloping. My 4 subs are in an SFM setup, and the bass is very enveloping even though it is monophonic.
 

abdo123

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I don't know any mixing or mastering engineer that would purposefully create a track that had bass 20dB louder in one channel than the other. Even if you could find a track that had its bass heavily decorrelated, it would not have a channel disparity of 20dB in the low frequencies. Music isn't mixed that way.

If envelopment (which decorrelated bass provides) is what one is looking for, you could put 4 subs in each corner of a room, cross them over to the mains at 40hz, and you will get the same effect. The bass could be mono, and it would still be enveloping. My 4 subs are in an SFM setup, and the bass is very enveloping even though it is monophonic.
I agree that's why i don't go for stereo sub-bass, but at the same time that doesn't stop me from recognizing that some people might hear it or feel it differently.

the optimal home cinema setup is to have each speaker running full-range 20Hz-20KHz and have subwoofers only for the Low Frequency Effects channel. As this is how the track was mixed. so the High-Fidelity decision would be to maintain that, regardless of how expensive that would be.

I feel that a discussion that is rooted in fidelity and a discussion that is rooted in enjoyment are two different things.
 

Soundmixer

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the optimal home cinema setup is to have each speaker running full-range 20Hz-20KHz and have subwoofers only for the Low Frequency Effects channel. As this is how the track was mixed. so the High-Fidelity decision would be to maintain that, regardless of how expensive that would be.
Actually, this is not correct. Every studio I know of that does HT mixes does them on a bass-managed system. All Atmos tracks are mixed and mastered on a bass-managed system for both the cinema and home environment. Considering there is not much bass information below 40hz in the front main speakers, and not much (if anything) below 60hz in the surrounds, there are zero reasons to have five full-range speakers and a sub as a system. The great thing about bass management is even if you use 5-7-9 bookshelf speakers along with a sub, you are essentially getting 5-7-9 full-range channels. That eliminates the need for 5 full-range floor standers.
 
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abdo123

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Actually, this is not correct. Every studio I know of that does HT mixes does them on a bass-managed system. All Atmos tracks are mixed and mastered on a bass-managed system for both the cinema and home environment. Considering there is not much bass information below 40hz in the front main speakers, and not much (if anything) below 60hz in the surrounds, there are zero reasons to have five full-range speakers and a sub as a system. The great thing about bass management is even if you use 5-7-9 bookshelf speakers along with a sub, you are essentially getting 5-7-9 full-range channels. That eliminates the need for 5 full-range floor standers.

I have never ever seen a movie mix that is bass managed, it's almost always that it's there is upward slope towards 40Hz with F10 of 20Hz or so.
Few nights ago i watched Deadpool, here is a spectrum analysis of the center channel, doesn't look bass managed to me!

So yeah, please substantiate your claims because it looks like you're either a big phony or very confused.


Edit: I'm the one who was very confused.

1634107783255.png
 

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youngho

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High-Fidelity reproduction of...Deadpool...I never considered the possibility...

I don't know much about these matters, but it almost looks to me like the center channel was crossed over at around 40 Hz, which appears to be about -3 dB. Presumably content below that was summed into the LFE or other channels. I thought that was basically the definition of bass management. Could you possibly provide spectrum analyses of the other channels, including the surrounds, please? Sorry, I don't own this movie.
 

abdo123

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High-Fidelity reproduction of...Deadpool...I never considered the possibility...

I don't know much about these matters, but it almost looks to me like the center channel was crossed over at around 40 Hz, which appears to be about -3 dB. Presumably content below that was summed into the LFE or other channels. I thought that was basically the definition of bass management. Could you possibly provide spectrum analyses of the other channels, including the surrounds, please? Sorry, I don't own this movie.

you can do a similar analysis yourself on any mix, in fact i would welcome it. below is one of the surround. I think your interpretation is valid, but at the same time so little things create sub-bass content below 40Hz to be 'recorded' by a microphone and mixed. The LFE channel is mostly generated rather than 'recorded' by an effects studio.

I just find it so strange that the industry would 'bass-manage' thinks like voices, instruments .etc instead of relying on the end device to actually do the bass management.

Also what's wrong with Deadpool? it's a really finely produced movie with a gigantic budget.

1634130551342.png
 

andyc56

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the optimal home cinema setup is to have each speaker running full-range 20Hz-20KHz and have subwoofers only for the Low Frequency Effects channel. As this is how the track was mixed. so the High-Fidelity decision would be to maintain that, regardless of how expensive that would be.

In this document by Floyd Toole, he explores this very idea in the second picture on page 10 and its accompanying text. He measures the response of five identical full-range speakers in different locations, and shows the response of each one. This is depicted below.

toole_mch_bass.png


At some frequencies, there is a 40 dB variation between the measured bass responses as shown. This difference in bass response is entirely due to room effects. So it is one thing to listen to the mix using a similar configuration as that used by the mixer (if indeed that is true), and quite another to hear what was heard in the control room in the bass region.
 

Pdxwayne

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In this document by Floyd Toole, he explores this very idea in the second picture on page 10 and its accompanying text. He measures the response of five identical full-range speakers in different locations, and shows the response of each one. This is depicted below.

View attachment 158771

At some frequencies, there is a 40 dB variation between the measured bass responses as shown. This difference in bass response is entirely due to room effects. So it is one thing to listen to the mix using a similar configuration as that used by the mixer (if indeed that is true), and quite another to hear what was heard in the control room in the bass region.
Would room eq capability of modern AVR help?
 
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