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Stereo Bass using subwoofers

Pdxwayne

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Last set up I tried today. Spent half the day scraping wax from concrete countertops and moving speakers into another room in my house.
After the 2nd hour of moving speakers I was disheartened, then I though of Amir moving large speakers up and down steps and I felt better.

Based on the 2 positions tried today, to the side and to the rear extending 24 inches past apex I can say that for me, these to set ups are very immersive like you are on the stage and just feet away from live show.

Time alignment and EQ and FR are done for each step.
View attachment 154696
Try this one and see if you can sense a difference between stereo vs mono. Pay attention to the double bass.

 

DonH56

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I'm going to just give up on having an accurate system and stick with my el-cheapo party system with mono subs since the in-room response is much better and my ears of clay cannot tell the difference on 99.99% of the recordings I own.
 

Kvalsvoll

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Setting aside the question whether hearing can detect direction at low frequencies, it is useful to look into what is going on with the sound field - is it at all possible to have direction at low frequencies in a room, and does this direction actually correlate to the location of the sound source.

Here is a measurement of the 90 degrees - that means left-right - particle velocity measured at the listening position, comparing front left subwoofer only to both front left and right:

4x 2x 1x V110 v 90.png


Green is FL, red and blue is FL+FR.

Indeed, we see a very significant increase in left-right velocity, with only the left unit playing. But this increase only happens inside a limited frequency range - at very low frequencies, the direction is similar. And this can be explained - the direction of the sound field inside a room is not only determined by the location of the source, but also the boundaries of the room, at very low f the velocity also decreases because energy transfer now decreases inside the constricted space.

In a different room, with different placements, this situation will be different, and not necessarily correlate well to where the source of the sound is located.

To be able to hear direction, there has to be a sound field with direction. If the velocity in the sound field is very low, or this direction does not correlate well to the placement of the source, it will not be possible to hear any direction regardless of what capability hearing has is that regard.

Higher up in frequency, there will be a direction that correlates better to the source location, depending on properties of the sound source directivity, placement of this source, and room acoustic properties. It is the directional cues in this higher frequency range that determines how we perceive location of low frequency instruments.
 

NTK

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Matthew Poe wrote the article in Audioholics because of @David Griesinger's work and his conversations with Griesinger. Let's go to the source. Here are some excerpts of Griesinger's writings.

Below is a screen clip from Griesinger's website (http://www.davidgriesinger.com/). The other quotes are from his paper "Loudspeaker and listener positions for optimal low-frequency spatial reproduction in listening rooms".

griesinger-a.png


Griesinger's explanations -- on low frequency localization and its spatial impression ...

griesinger-b.png


His conclusions (for this paper) ...

griesinger-c.png
 

EJ3

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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.
I run my pair of 12" bass boxes in 2ohm stereo (+6db over 8 ohms), crossed over at 80 Hz, with 800 watts each on tap. (again this is @ 2ohms and their own stereo amp). They are placed under the main speakers (which have their own amp each). The woofers fire toward the floor. They are on each side of a brick fireplace that has a one foot high X 1 foot deep floor ledge jutting into the room about 1 & 1/2 feet & 5 feet wide. The Subs are about 6 feet apart & a foot from the wall. The ceiling is cathedral. I don't find that I have a lack of bass or any suck outs with this setup. Summed to mono overpowers everything else. So it stays in stereo, which is smother but still thumping on impact notes. This is a large room.
 

Pdxwayne

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One video to check mono vs stereo subs. Can you precisely place the positions of the drum kicks when using mono?

What do you sense when using single mono sub on the right?

 

Soundmixer

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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.
You have two subwoofers, not stereo subwoofers. Research has shown over and over that stereo cannot be perceived at frequencies below 80hz. Also, not much material (especially music) has stereo in the bass frequencies except with movie soundtracks.
 

digitalfrost

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You have two subwoofers, not stereo subwoofers. Research has shown over and over that stereo cannot be perceived at frequencies below 80hz. Also, not much material (especially music) has stereo in the bass frequencies except with movie soundtracks.
I can control whether or not I send a mono or a stereo signal to the subwoofers. I do not care what you say, the difference is so very obvious that I do not need to ABX that. And in fact, you if made me ABX that, I could easily.
 

Pdxwayne

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Drum kicks have information that extends from 60-150hz, and above 120hz, direction can be perceived when listening to stereo.
I tried with stereo subs and a single sub on the right in mono. I have two distinct setups in my living room so I can easily compare.

The mono sub on the right crossed at 60hz. It is part of setup using AV preamp, thus got the full room eq treatment already. The stereo subs crossed at around the same freq. Speakers are bookshelf in both cases and similar in size.

The lower tones of the drum (in the setup with the mono sub on the right) would pull the feel of the punch closer to the middle or even to the right sometimes. The stereo subs imaging is more stable to the left.

What setup do you have?
 
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GimeDsp

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I know people don't want to hear it, but:

1. Sine waves do not represent musical content
2. bone conduction and Structure born vibration also account for localization
3. If you have 2 subs with discrete L/R signals you have stereo subs REGARDLESS of perception.
(this Logic is FAULTY, it's arguing a tweeter doesn't play music out to 50,000hz because you don't hear it)

No amount of acoustic treatment or quality of speaker can reduce bone conduction.
Sound travels faster through the floor and through your bones, roughly 3500 M/S, so you receive this info WAY, like 10 times before the sound info to your ears.
 

GimeDsp

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Try this one and see if you can sense a difference between stereo vs mono. Pay attention to the double bass.

Great song, on desktop speaker, meh, on full system it was really pleasant.
I've been spending all day in research and notes so haven't had much time to check the song out critically.
 

MakeMineVinyl

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I can control whether or not I send a mono or a stereo signal to the subwoofers. I do not care what you say, the difference is so very obvious that I do not need to ABX that. And in fact, you if made me ABX that, I could easily.
Yes, it is painfully easy in my room to tell which subwoofer is on using test tones and all other speakers off in my large room. Room interaction undoubtedly plays into this, but rough direction can definitely be sensed if one or the other sub is turned off.
 

Soundmixer

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I tried with stereo subs and a single sub on the right in mono. I have two distinct setups in my living room so I can easily compare.

The mono sub on the right crossed at 60hz. It is part of setup using AV preamp, thus got the full room eq treatment already. The stereo subs crossed at around the same freq. Speakers are bookshelf in both cases and similar in size.

The lower tones of the drum (in the setup with the mono sub on the right) would pull the feel of the punch closer to the middle or even to the right sometimes. The stereo subs imaging is more stable to the left.

What setup do you have?
My friend, you don't get imaging at low frequencies. You MAY be able to locate where the pressure wave is coming from, but our ability to perceive "stereo bass" has been tested over and over, and the conclusions have always been it is not possible for imaging to occur at low frequencies.
 

Soundmixer

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If you have 2 subs with discrete L/R signals you have stereo subs REGARDLESS of perception.

If you cannot perceive it, then what is the point? Not all discrete L/R signals have stereo bass. A great majority of the time, the bass is downmixed to mono below 150hz - even in discrete L/R stereo signals.
 

Pdxwayne

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My friend, you don't get imaging at low frequencies. You MAY be able to locate where the pressure wave is coming from, but our ability to perceive "stereo bass" has been tested over and over, and the conclusions have always been it is not possible for imaging to occur at low frequencies.

So what is the correct term for "locate where the pressure wave is coming from"?
 

GimeDsp

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"you cant locate bass under 80hz" ~
If you cannot perceive it, then what is the point? Not all discrete L/R signals have stereo bass. A great majority of the time, the bass is downmixed to mono below 150hz - even in discrete L/R stereo signals.
I use to think that was true from hearing it, then I tested it and found it to be false so far. 7nation Army, "Sunflower" and "Won't get Fooled Again" are the last 3 I tested and they all have a LOT of panned/stereo LF content.

Today marks 7 WEEKS of tested stereo vs mono bass. that's right, I have been doing this for that long, taking notes, and repeated.
And today I got a box made that is a L/R flip box so I can switch while listening to the test music/content.

Even I have been able to localize subwoofers all my life at every event, concert, gathering, and studio I started this journey still believing that there must be some other reason why I could and that "you can't localize" was still true, now I know it's not true.

So far the ONLY tru-ish version would be

In a room with
1. Concrete floors and wall
2. In a system with the sub crossed over at 40hz
3. with LF content that doesn't span the Xover region

Then you can't totally localize bass.

For the majority of people who have room issues , sub-optimal placement, and less than 48db per octave slops, localization is for real.
 

GimeDsp

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So what is the correct term for "locate where the pressure wave is coming from"?
Sound stage, sound field, image are all the same thing.

As proved by the subs-at-sides location, for two channel playback LF content can create an immersive effect.

"No imaging for LF" is incorrect. On a system that is accurate in the 3 catagories

1. Spatial location
2. Time Domain
3. frequency response

You would expect to get as much imaging content as is possible for the sound source. Since a bass guitar amp, kick drum, floor tom will never naturally be located in the same manner or as precise as a hi hat or triangle, an accurate image of those would be same as what is natural not more or less.
 

GimeDsp

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If you cannot perceive it, then what is the point? Not all discrete L/R signals have stereo bass. A great majority of the time, the bass is downmixed to mono below 150hz - even in discrete L/R stereo signals.

Depending on crossover slopes even mono'd bass music may have some overlap with the persons sub. But I agree on some content it's a non issue, but having resolution and having content that uses it are 2 different things.

A stereo system can resolve stereo content and also mono content, a mono system can't

I want to apologize if the tone has gotten less than friendly. The fact of the matter is this:

1. Those who deny localization of LF have a much bigger hurdle to jump over then just quoting someone else's study or statement, and until they have a good enough DSP or enough data to form an opinion based on actual testing then their opinion while important isn't in the same category.

2. Those who hear a difference must not be "shouted down" to say they're wrong. I started this 7 week journey believing all the statements against localization and my mind was changed when every single set up had unique qualities and feel of localization effecting the whole sound stage.

I am leaving this thread now because my team has enough data on subwoofer configs and we are moving on. For those how care, this is what we found.

1. If running a mono sub, run it centered and crossed as low as possible (this means you still have to deal with the Allison effect.

2. 2 subs are preferred and if they are just inside of the main speakers or outside they give great results.
a. The higher up you run the subs the closer to the speakers they should be.
b. If running stereo subs the closer they are to mains will give a tighter sound stage
c. Stereo subwoofers to the sides creates an immersive experience like being on the stage of a concert instead of looking to the stage.

On a side note we tried 4 sub positions with the subs to the rear, here are 3:

1. Subs 2 feet past LP/apex inline/extending with listening triangle, subwoofers on ground
2.((same )) one subwoofer elevated 20" one on ground
3. Subs 6 feet past, still in line, both on ground

The only set up that was not distracting was #2,

If you listen to material with low LF content or high-LF mono content then you will not experience these phenomena as much.

SIDE NOTE-if you run mains full range and only have a 24db Xover on subwoofer then you may get best results running the Xover down low, ex. 40/50hz then bringing the volume up of the sub slowly until it just begins to add and balance out the mains.

Mono subs for more energy
Stereo subs for realism

Stereo subs if you can achieve balanced response in room
Mono subs if you can't (this will smooth out any stereo/panned content)
 
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MakeMineVinyl

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Depending on crossover slopes even mono'd bass music may have some overlap with the persons sub. But I agree on some content it's a non issue, but having resolution and having content that uses it are 2 different things.

A stereo system can resolve stereo content and also mono content, a mono system can't

I want to apologize if the tone has gotten less than friendly. The fact of the matter is this:

1. Those who deny localization of LF have a much bigger hurdle to jump over then just quoting someone else's study or statement, and until they have a good enough DSP or enough data to form an opinion based on actual testing then their opinion while important isn't in the same category.

2. Those who hear a difference must not be "shouted down" to say they're wrong. I started this 7 week journey believing all the statements against localization and my mind was changed when every single set up had unique qualities and feel of localization effecting the whole sound stage.

I am leaving this thread now because my team has enough data on subwoofer configs and we are moving on. For those how care, this is what we found.

1. If running a mono sub, run it centered and crossed as low as possible (this means you still have to deal with the Allison effect.

2. 2 subs are preferred and if they are just inside of the main speakers or outside they give great results.
a. The higher up you run the subs the closer to the speakers they should be.
b. If running stereo subs the closer they are to mains will give a tighter sound stage
c. Stereo subwoofers to the sides creates an immersive experience like being on the stage of a concert instead of looking to the stage.

On a side note we tried 4 sub positions with the subs to the rear, here are 3:

1. Subs 2 feet past LP/apex inline/extending with listening triangle, subwoofers on ground
2.((same )) one subwoofer elevated 20" one on ground
3. Subs 6 feet past, still in line, both on ground

The only set up that was not distracting was #2,

If you listen to material with low LF content or high-LF mono content then you will not experience these phenomena as much.

SIDE NOTE-if you run mains full range and only have a 24db Xover on subwoofer then you may get best results running the Xover down low, ex. 40/50hz then bringing the volume up of the sub slowly until it just begins to add and balance out the mains.

Mono subs for more energy
Stereo subs for realism

Stereo subs if you can achieve balanced response in room
Mono subs if you can't (this will smooth out any stereo/panned content)
I might add that with the specific type of music I listen to and record a lot, large pipe organs in large churches, there can be plenty of random phase information down to below 20Hz, and this can include low frequency 'room tone'. This is particularly true with the microphone setups I use with antiphonal organ ranks. This is usually 3 spaced omni microphones in front and 2 or 3 spaced omnis near the rear of the chruch with the spacing from the front mics to the rear mics usually 50 feet or so. This can introduce lots of random low frequency time/phase information which is preserved in the listening room (especially mine which is quite large) when using stereo subwoofers, but would be totally lost with mono subwoofers.

The result of preserving this random low frequency ambience is increased realism.

What happens with popular music etc with low bass is another issue, and frankly I don't care about that.
 
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