Stereo Bass using subwoofers

[Soundmixer]

The Welti study fails on all accounts.
Is you have a legit study, please post it.

You sure it fails, or you just don't accept the results? I have asked you to support your notion with ANY study that there is stereo bass below 80hz. You have posted nothing but still insist there is. How can you dismiss one result while not providing support for your own?

So let's just find something that breaks down your entire opinion.


"Inter-aural delay shifts the sound received by one ear as opposed to the other and introduces a phase difference between the ears. Phase denotes the particular point in the cycle of a sound or a waveform. Our ears are very sensitive to phase differences, more than the inter-aural delay itself: inter-aural delay is only perceptible when the sound reaches your ears, while phase differences still exist afterwards.

Unfortunately, phase differentiation fails when the frequencies are too low. For example, at the bottom of the human hearing range, the wavelength is almost 20 meters long. What does 20 cm - the average distance between our ears - represent compared to 20 meters? Not much, as a pure tone waveform won't significantly change over 1/100th of its cycle. As both of our ears will perceive a very similar signal, the sound will simply be interpreted as coming frontally, even though it comes from your side.

So, as the frequency drops below a critical frequency - usually around 80 Hz - it becomes very difficult to determine a sound's location. "

Low Frequency (Subwoofer) Sound Localization Test

Why you really don't want to hear where your low frequencies are coming from!

www.audiocheck.net

What this page is saying is once the wavelengths become so long there is no longer a perceived separation of channels (Interaural time difference), then it becomes difficult to hear stereo. The threshold of localization STARTS at 80hz and gets easier to ascertain as the frequency increases.

 

[Kvalsvoll]

So, as the frequency drops below a critical frequency - usually around 80 Hz - it becomes very difficult to determine a sound's location. "

Exactly. And since sensitivity for hearing direction increases as frequency goes up, everything that happens at very low f will be totally masked.

 

[Kvalsvoll]

Im not trying so sound like a know it all.
I've spent tbe last 8 weeks almost full time setting up studio systems with stereo/mono subs and gathering data for symmetrical and asymmetrical rooms. We have used numerous music and test signals and have noted stereo subs have a large impact on sound location.

When you say "studies" you have to cute the study, otherwise its worthless.

The Welti study fails on all accounts.
Is you have a legit study, please post it.

I acknowledge your observations, but since those observations contradict already accepted and acknowledged knowledge, it really is up to you to show that your experiment and results are valid.

You need to set up a controlled test - with sufficient description of equipment and procedure, so it is possible to verify that the experiment is valid for its intended purpose.

First you need a stereo system, where both L and R channels has a sufficiently similar response from each channel at lower frequencies, including frequency response and sound field properties. The L+R sum at low freq must also match the individual responses from each channel. This is verified with measurements.

 

[GimeDsp]

I acknowledge your observations, but since those observations contradict already accepted and acknowledged knowledge, it really is up to you to show that your experiment and results are valid.

You need to set up a controlled test - with sufficient description of equipment and procedure, so it is possible to verify that the experiment is valid for its intended purpose.

First you need a stereo system, where both L and R channels has a sufficiently similar response from each channel at lower frequencies, including frequency response and sound field properties. The L+R sum at low freq must also match the individual responses from each channel. This is verified with measurements.

I have that now in the test room, along with full ASC traps.
What is interesting also is crossover slopes system design and how that affects a whole lot of stuff!

In the current set up we(The Team) left the mains running full range (they go to about 40hz) and we have the subs pushing into those. This gives an average of the signal through a speaker at 48" high and the sub ground level.

I am considering writing a paper on it so wish me luck. A realize peoples opinions are strong a a proper, peer reviewed paper is the next step in this debate.

 

[Kvalsvoll]

I have that now in the test room, along with full ASC traps.
What is interesting also is crossover slopes system design and how that affects a whole lot of stuff!

In the current set up we(The Team) left the mains running full range (they go to about 40hz) and we have the subs pushing into those. This gives an average of the signal through a speaker at 48" high and the sub ground level.

I am considering writing a paper on it so wish me luck. A realize peoples opinions are strong a a proper, peer reviewed paper is the next step in this debate.

It is often best to do any experiment as simple as possible, isolate one property that is to be investigated. To first establish whether stereo bass makes any audible difference on location of bass instruments can be a good starting point.

To do this, you do not need to deal with different system configurations for stereo and mono bass, just create file samples - one with stereo bass, one with mono bass. Analysis of the samples can verify that they behave as intended - only difference should be that bass is mono below a certain frequency, in the mono file.

This eliminates any issues with the speaker system itself, and testing is much easier because you can now use foobar abx and switch instantly, and you can verify and document that there is actually a difference using abx. Though I suspect there will be audible difference, even if the mono does not change location in a dramatic way.

When you have similar L, R and sum L+R responses, it should not be important that it is "perfect" with flat response down to single digits. Or have prefect timing.

 

[GimeDsp]

It is often best to do any experiment as simple as possible, isolate one property that is to be investigated. To first establish whether stereo bass makes any audible difference on location of bass instruments can be a good starting point.

To do this, you do not need to deal with different system configurations for stereo and mono bass, just create file samples - one with stereo bass, one with mono bass. Analysis of the samples can verify that they behave as intended - only difference should be that bass is mono below a certain frequency, in the mono file.

This eliminates any issues with the speaker system itself, and testing is much easier because you can now use foobar abx and switch instantly, and you can verify and document that there is actually a difference using abx. Though I suspect there will be audible difference, even if the mono does not change location in a dramatic way.

When you have similar L, R and sum L+R responses, it should not be important that it is "perfect" with flat response down to single digits. Or have prefect timing.

Thank you.
I was thinking about this today. and first I will use the simple approach and see what's possible.
I just found out my company may be pulling the test set up so I may need to do it on my own.

I have a $1000 budget for subs to use for this paper/test.
I am looking at SVS sb-1000 sealed now, those should be as good as any since the testing will be done in the 85DB range.

I am disappointed that my company team members are too busy to join in but hay, sa la vie.

 

[GimeDsp]

I just asked an AES member to check the database and he said they have 50 papers on stereo bass localization.
I will now be spending my time on something new like finding ET life.

 

[Pdxwayne]

I just asked an AES member to check the database and he said they have 50 papers on stereo bass localization.
I will now be spending my time on something new like finding ET life.

You meant there are 50 papers that confirmed stereo bass can be localized?

 

[Sancus]

To do this, you do not need to deal with different system configurations for stereo and mono bass, just create file samples - one with stereo bass, one with mono bass. Analysis of the samples can verify that they behave as intended - only difference should be that bass is mono below a certain frequency, in the mono file.

In fact, I would argue you CANNOT have different system configurations to test this question. For example there is at least one existing AES paper(probably many more) that show that two subwoofers are more difficult to detect than one, and this no doubt improves further with more subwoofers.

So if your stereo bass test involves testing mono bass with one sub, and stereo bass with two subs, then it is already an invalid test before you've even started!

I just asked an AES member to check the database and he said they have 50 papers on stereo bass localization.
I will now be spending my time on something new like finding ET life.

OK this is funny to me, AES membership only costs $125. You can use the search for free. 5 minutes easily found at least 7 relevant papers other than the Welti one:

AES E-Library » Perceptibility of Direction and Time Delay Errors in Subwoofer Reproduction

Large loudspeakers are needed for good bass response at high ground levels. To find aesthetically and acoustically acceptable placements for large loudspeakers is, however, difficult not only in a living room but also in larger spaces such as theaters and multipurpose halls. Separate subwoofers...

www.aes.org

AES E-Library » Detection of Subwoofer Depending on Crossover Frequency and Spatial Angle between Subwoofer and Main Speaker

Since the direction of sound is not perceived at very low frequencies, it is feasible to use only one subwoofer for low frequency reproduction in commercial multi-channel audio setups. A listening test was conducted to find the crossover frequency where the listeners begin to detect the...

www.aes.org

AES E-Library » Detection of Two Subwoofers: Effect of Broad-Band-Channel Level and Crossover Frequency

The use of multiple subwoofers can be advantageous compared to a setup consisting of a single subwoofer due to the cancellation of room modes. We investigate the effect of subwoofer crossover frequency and program material on the perceived localization of bass frequencies using single or dual...

www.aes.org

AES E-Library » Loudspeaker Reproduction: Study on the Subwoofer Concept

A stereo pair of full range loudspeakers and a stereo pair of loudspeakers reproducing the mid to high frequencies (satellites) plus one common low frequency sound loudspeaker (subwoofer) are compared. AB-AB listening tests were used to determine the absolute threshold of audible differences...

www.aes.org

AES E-Library » Modeling Auditory Localization of Subwoofer Signals in Multi-Channel Loudspeaker Arrays

For economical reasons home entertainment surround sound systems are usually equipped with a single subwoofer channel. The main argument for this procedure is the believed inability of the auditory system to localize low frequencies in small reverberant rooms. However a psychoacoustic...

www.aes.org

AES E-Library » On the Perceptual Advantage of Stereo Subwoofer Systems in Live Sound Reinforcement

Recent research into low-frequency sound-source localization confirms the lowest localizable frequency is a function of room dimensions, source/listener location, and reverberant characteristics of the space. Larger spaces therefore facilitate accurate low-frequency localization and should gain...

www.aes.org

Here's one that even supports some limited ability to localize the lowest frequencies:
https://www.aes.org/e-lib/browse.cfm?elib=13041

Surely if one were planning to spend money/time on researching any audio topic where one disagrees with the "common knowledge", the very first step would be to do a serious literature review of the existing research!

I'd argue this whole topic is sort of missing the forest for the trees though, as the biggest limitation of stereo bass is that it's still stereo, and stereo is deeply and fundamentally flawed. What's the point of incrementally improving a minor facet of a broken format? That last study at least addresses the topic from the perspective of multi-channel.

 

[GimeDsp]

You meant there are 50 papers that confirmed stereo bass can be localized?

Still reading through the many papers.
Looks like Welti has a lot of never-mentioned-here studies on bass but a lot of them are with non-music stuff, Pink noise and such.
He also admits the the psychophysical part of it is beyond current testing so they can only look at some parts.

It's really a toss up!
Music and material with badly balanced low end will likely sound better on a mono sub system, If you run your mains down low enough they will give a lot of the spatial info anyways.

Stereo subs have a "breath" and more relaxed live feel to them.
I know one thing. The closer you are to speakers I prefer mono subs, further back the stereo affect is less pronounced.

 

[Tangband]

Theres is much confusion here.
What is music? Its not sine-sweeps or a tone at a single frequence. Music is ordered sounds in the time/frequency domain.

One simple explanation:

An electric bass plays frequencies from about 41 Hz to 8 KHz . Each tone the bass player plays has information from about 41 Hz and up to 8 KHz . If you change the spectra at 5 kHz just a couple of Hz, the sound from the electrical bass will start to sound slightly out of tune. The perceived pitch of the tunes the bass player plays, has become worse.

Now you can start to count and make questions for yourself .

1. How long is the wavelenght at for example 5 KHz ?

2. After counting , is the placement of the two subwoofers important ? Should the subwoofers be placed near the main speakers, or far away ? Maybe you´re now saying it dont make any sense because you´re crossing at 80 Hz - a much lower frequency than 5 kHz ? But hear this….

3. There is no such thing as a perfectly steep crossover, because the subwoofer itself is making noise above the crossover region. Always. Its mecanical distortion from the drivers and the loudspeakerbox AND the room . The last thing is very important to understand.
A subwoofer placed against a wall thats not very rigid is gonna distort the wall- and its very audible. The floor also distort the sound.

When one understands this , its clear that two subwoofers in stereo placed near the main speaker is the best option, if we are talking two channel sound. This is also very easy to verify with listening tests with real music.

5.1 is a somewhat different story, because you have an active channel ( 0.1 ) for the subwoofer with real effects recorded in the studio.

The confusion continues.
The reason stereo-subs is perceived as sounding better than mono is that real instruments dont play tones in a single area below 80 Hz . Music is ordered sounds in the time / frequency domain.
Read it again.

 

[sigbergaudio]

The reason stereo-subs is perceived as sounding better than mono is that real instruments dont play tones in a single area below 80 Hz . Music is ordered sounds in the time / frequency domain.

I don't understand what this means. Care to rephrase?

 

[sigbergaudio]

Thats true, but if the crossover slope is just 6 or 12 dB/oct at 200 Hz , theres gonna be much energi even at 100 Hz.
And much worse, letting the 5,5 inch woofer roll of naturaly without HP filtering its gonna have severe distortion at 100 Hz. Even if the 5 1/2 driver manages to play music with 1,5 mm excursion, at 200 Hz, it gonna do it with more distortion than an equally good 6 1/2 inch woofer.

If you look at Amirms loudspeaker measurements regarding distortion, you can se that all speakers with 5 1/2 inch woofer has high distortion numbers lower than 150- 200 Hz if playing at 96 dB.

Using subwoofers at floor level is only usable up to about 100 Hz anyway - my experience. Crossing higher , you have to build the subwoofer into the same cabinet as the mid-woofer.

( Edit : a three way active loudspeaker containing subwoofers is a bigger compromise than a 4-way, but if you cross it at 80 Hz and 2 kHz the problems are manageable, using for example a 12 inch subwoofer, 6 1/2 inch woofer and a tweeter with a waveguide.
An active loudspeaker with a 5 inch mid- woofer would have to have the subwoofer built in to the same cabinet for high spl and short distance between subwoofer and midwoofer, crossing at 125 -250 Hz instead of 80 Hz - my opinion.)

In the example of LS50, it will be limited in output. But as mentioned elsewhere, a 5.5" driver is a good choice for a coax. The problem of distortion could be reduced by adding an additional driver (5.5" or of another size) between the coax and the subwoofer.

 

[Soundmixer]

The confusion continues.
The reason stereo-subs is perceived as sounding better than mono is that real instruments dont play tones in a single area below 80 Hz . Music is ordered sounds in the time / frequency domain.

This is not quite right. Two subs sound better than one because it provides less seat to seat variation over a single row of seats. One sub can only be optimized for just one seat., and every other seat is left to chance. Two subs are stimulating a different set of room modes than one does depending on placement.


If you played pink noise through two subs, and filtered out all frequencies above 80hz, you still would have a difficult time ascertaining stereo. The perception of stereo requires ITD, and there are no ITD below 80hz, the wavelengths are too long.

Your explanation here does not make much sense honestly.

 

[Soundmixer]

For example there is at least one existing AES paper(probably many more) that show that two subwoofers are more difficult to detect than one, and this no doubt improves further with more subwoofers.

I absolutely agree with this. You could even raise the crossover above 100hz, and it will still be difficult to detect 4 subs, especially if they are located in the corners of the room.

However, detection does not equal ITD, and you need interaural time differences to ascertain stereo.

 

[GimeDsp]

I don't understand what this means. Care to rephrase?

Take a floor tom for example
Leading edge edge transient at 50hz, and and 3rd transients at 125 and 200hz, these are amplitude and time domain.

first resonances at 75-250hz that happen before sustained resonances that drop in frequency until the drum/drum heads resolve no sound output.

Which parts are most important and how they related to each other audibly and psychoacoustically is a much more complex idea then what I have read so far in the AES papers.

 

[sigbergaudio]

Take a floor tom for example
Leading edge edge transient at 50hz, and and 3rd transients at 125 and 200hz, these are amplitude and time domain.

first resonances at 75-250hz that happen before sustained resonances that drop in frequency until the drum/drum heads resolve no sound output.

Which parts are most important and how they related to each other audibly and psychoacoustically is a much more complex idea then what I have read so far in the AES papers.

But this would confirm the idea that you can place a tom in the stereo soundstage despite having mono subs, because it has higher order elements that are reproduced (in stereo) by the speakers.

 

[Tangband]

In the example of LS50, it will be limited in output. But as mentioned elsewhere, a 5.5" driver is a good choice for a coax. The problem of distortion could be reduced by adding an additional driver (5.5" or of another size) between the coax and the subwoofer.

Yes ! The Kef R3 is a good example.

 

[Tangband]

This is not quite right. Two subs sound better than one because it provides less seat to seat variation over a single row of seats. One sub can only be optimized for just one seat., and every other seat is left to chance. Two subs are stimulating a different set of room modes than one does depending on placement.


If you played pink noise through two subs, and filtered out all frequencies above 80hz, you still would have a difficult time ascertaining stereo. The perception of stereo requires ITD, and there are no ITD below 80hz, the wavelengths are too long.

Your explanation here does not make much sense honestly.

Pink noise has nothing to do with how music with real instruments works. You also have a time domain parameter when musicians play real music thats very important. Using only one subwoofer, even if its the worlds best, in a stereosystem will always mess up the perceived pitch of each bass tone, because of the ( to long ) distances and phase distortion between the subwoofer and L/R loudspeaker. Thats the reason why two main loudspeakers always sound better in some parameters of music reproduction, if you turn off the single subwoofer completely.

 

[Pdxwayne]

But this would confirm the idea that you can place a tom in the stereo soundstage despite having mono subs, because it has higher order elements that are reproduced (in stereo) by the speakers.

When I look at pictures in Google search, I see plenty of examples where a floor tom is recorded with single mic. I wonder if it is a good example to use for testing stereo bass....

Let's say we have electronic music where bass notes are panned hard side to side, would you not "feel" (body feels) a difference using single mono sub on one side vs stereo subs?