A Broad Discussion of Speakers with Major Audio Luminaries

[goat76]

A 24 dB/oct slope is still going to allow quite a bit of music through between 80Hz and 160Hz. Not an effective test setup in my opinion.

I chosed a 24 dB/oct slope as that is likely a common setting and a real-life scenario for people using subwoofers in their systems, so whatever sound comming through between 80 Hz and 160 Hz, that frequency range will also be affected by connecting the subwoofers in mono.

Anyone doing the test can of course choose a steeper slope than that, if they want to isolate the bass range under 80 Hz even further just for the testing purpose, but it may also be a good idea to choose a slope setting that mirrors the one they normally use in their system.

 

[goat76]

And still there‘s no theory behind the claim. So what to test and how? Any effect that may originate in arbitrary phase decorrelation in bass in-room?

For me personally, it really doesn't matter that much what exactly it is in the sound (from recording to recording) that is affected negatively by summing the bass to mono. It can be natural phase differences that occur due to a real capture of acoustic information, or it can be anything else causing the decorrelation, but the fact that I hear it as a negative effect, when taking it away, is enough for me not wanting to alter the signal from its original state.

 

[Heinrich]

For me personally, it really doesn't matter that much what exactly it is in the sound (from recording to recording) that is affected negatively by summing the bass to mono. It can be natural phase differences that occur due to a real capture of acoustic information, or it can be anything else causing the decorrelation, but the fact that I hear it as a negative effect, when taking it away, is enough for me not wanting to alter the signal from its original state.

sorry, that‘s what I was after. No theory, rushing into action. Every difference makes you gravitate towards the new thing. That is not going to be conclusive.

May I reiterate a previous thought? Could the phasing of deep bass help with room resonances? What I‘ve seen so far were spectra of the input signal, not of the actual playback in-room. That may correlate listening to decorrelated bass to an explanation. Patent pending?

Btw: had 4 different subs sealed/reflex recently in asymmetrical positions to some effect.

 

[Newman]

…Our experiments with AE…

Have you opened a thread for discussion of your studies on this? Seems like a good idea …

 

[Newman]

sorry, that‘s what I was after. No theory, rushing into action. Every difference makes you gravitate towards the new thing. That is not going to be conclusive.

The AE discussion in this thread is already showing signs of following the path that Dirac ART threads take: people 'testing' it by doing with/without switching at home and declaring what a big improvement it makes and how they will not be going without it going forward. Except the frequency responses have changed, the levels have probably changed … and they are comparing sighted.

That is how audibly non-transparent cables make their name. Can we maybe do better here on ASR?

Cheers

 

[Sokel]

The AE discussion in this thread is already showing signs of following the path that Dirac ART threads take: people 'testing' it by doing with/without switching at home and declaring what a big improvement it makes and how they will not be going without it going forward. Except the frequency responses have changed, the levels have probably changed … and they are comparing sighted.

That is how audibly non-transparent cables make their name. Can we maybe do better here on ASR?

Cheers

???
Are you talking about @NTK 's test signal along with the rest at the Bass and Subwoofers thread?
The specific requires no change if you already run stereo.

 

[olieb]

Also, for some strange reason second part sounds a little louder.

Actually that is not so strange as the second signal is on average about 2dB louder when comparing the 5s-signals in Audacity "Measure RMS". And the two stereo channels don't have equal loudness either.

So we have the ingredients:
sighted comparison
not level matched
change of FR
And for some funny reason the result is: THIS is BETTER!
I agree with @Newman, we should be able to do better.

I matched the levels and for the problem of higher frequency content in the signal that still might be responsible for part of the difference in spatial perception, I added uncorrelated pink noise with lower level to mask this part of the signal.
I listened over earphones first and I would agree that the difference is still there, even when comparing the mono (correlated) signal to 66% mono (correlated)+33%"stereo"(with randomised phase). But it gets subtle.

Over speakers it is a much more difficult situation in my room. The difference between the signals mono versus full randomised "stereo" in this case was very subtle (maybe I get it right two to one, when I concentrate on this, maybe not). Whether this is due to change of FR or due to phase randomisation, I have no idea.
And l do not hear one version as better over the other, not at all. Not with earphones and certainly not with speakers.

And this is with two speakers in the room without the optimisation that multi subs can bring. So the tradeoff in respect to FR in bass that one has to sacrifice for the "stereo" bass does not even enter the equation.

 

[Sokel]

Actually that is not so strange as the second signal is on average about 2dB louder when comparing the 5s-signals in Audacity "Measure RMS". And the two stereo channels don't have equal loudness either.

So we have the ingredients:
sighted comparison
not level matched
change of FR
And for some funny reason the result is: THIS is BETTER!
I agree with @Newman, we should be able to do better.

I matched the levels and for the problem of higher frequency content in the signal that still might be responsible for part of the difference in spatial perception, I added uncorrelated pink noise with lower level to mask this part of the signal.
I listened over earphones first and I would agree that the difference is still there, even when comparing the mono (correlated) signal to 66% mono (correlated)+33%"stereo"(with randomised phase). But it gets subtle.

Over speakers it is a much more difficult situation in my room. The difference between the signals mono versus full randomised "stereo" in this case was very subtle (maybe I get it right two to one, when I concentrate on this, maybe not). Whether this is due to change of FR or due to phase randomisation, I have no idea.
And l do not hear one version as better over the other, not at all. Not with earphones and certainly not with speakers.

And this is with two speakers in the room without the optimisation that multi subs can bring. So the tradeoff in respect to FR in bass that one has to sacrifice for the "stereo" bass does not even enter the equation.

Nice finds, but a question:
Where did I wrote that this is better?

And how can this thing even remotely can be described as "good" and "better", it's horrible to listen to, I couldn't wait for it to finish

Different? Definitely yes.
Better (and I'm talking about my music, not the torturous signal )? that's up to taste and I would find it funny to argue about taste or preference.

About optimizing low, what stops us to do both? I have a treated room, EQ, the works.
The one does not exclude the other.

 

[Sokel]

..and another, some only talk about phase difference, at the linked thread there are examples with amplitude differences too down low and not from the 50's as the ones I listen to and the usual classical stuff.
That's easy to test too.

 

[olieb]

Where did I wrote that this is better?

I did not say you did.
But others did insinuate that the result is obviously advantageous.

To me, it's easy to hear the effects @Thomas Lund describes as “big”, “open”, “free”, “pleasant”, “light” in favor of stereo bass, in opposite to mono bass, which is described with words like “unpleasant”, “claustrophobic”, “small”, “restricted space”.

Even if this is not with the test signal in question it is about extremely filtered low content only that I would not describe with "pleasant" or "free".

About optimizing low, what stops us to do both? I have a treated room, EQ, the works.

Well If you optimise with four subs you will get a smoother FR (more even excitation of room modes) in all probability than with two. And for each channel only two are left when you use two channels with different signals. So you have to trade "something" for stereo bass. And the difference gets really small once you have not only 40-60Hz in the signal. As mentioned, it's quite subtle.

 

[Sokel]

I did not say you did.
But others did insinuate that the result is obviously advantageous.

Even if this is not with the test signal in question it is about extremely filtered low content only that I would not describe with "pleasant" or "free".


Well If you optimise with four subs you will get a smoother FR (more even excitation of room modes) in all probability than with two. And for each channel only two are left when you use two channels with different signals. So you have to trade "something" for stereo bass. And the difference gets really small once you have not only 40-60Hz in the signal. As mentioned, it's quite subtle.

I use speakers only for music.
But if I was about to engage subs what works in my rig is cutting them at maybe 40Hz and give subs the rest.

Once I have used to listen like that (stereo all the way to 30Hz) I can't go back, maybe it's a vice.
And I have tried and measured anything imaginable as my room is dedicated to fun.

But that's me, only, just a preference.
The same I have for big-ish rooms and speakers.

 

[bmc0]

If I had to describe it, first part is more coherent but confined between the speakers.
Second part sounds like it's fluctuating a little but gives the impression of different things going around at R and L.

In my case, the spatial difference is not at all subtle. Two full range speakers positioned in the typical way (i.e. roughly ±30°) isn't generally optimal for hearing LF phase fluctuations.

My setup is a bit unusual in that I have two subwoofers (15 inch sealed) crossed at 85Hz which have full channel separation and are not located right beside the mains. One sub is in the front left corner and the other is at the midpoint of the right side wall. Frequency responses of L and R are pretty well matched over the frequency range relevant to NTK's test signal (±1dB 40-60Hz, spatially averaged). The room is quite long and my listening chair is a bit forward of the midpoint. It's a basement room with concrete block walls—normally this would be problematic for bass reproduction, but I have about a foot (30cm) of fiberglass in the ceiling which helps immensely. Spatially averaged 1/3rd octave Topt measured by REW is about 300ms in the 50-100Hz range (~270ms above 100Hz).

It should be obvious, that a remastered = manipulated 50s recording cannot stand as an example.

The low correlation at low frequencies is not something added during remastering. It is a product of the concert hall and captured effectively by the microphone technique (in this case, three widely-spaced main microphones plus some additional spot/fill mics). Most 2-channel orchestral recordings I've analyzed (from late '50s up to the present decade) are nowhere close to mono in the subwoofer range.

 

[Heinrich]

The low correlation at low frequencies is not something added during remastering. It is a product of the concert hall and captured effectively by the microphone technique (in this case, three widely-spaced main microphones plus some additional spot/fill mics). Most 2-channel orchestral recordings I've analyzed (from late '50s up to the present decade) are nowhere close to mono in the subwoofer range.

The recording was made when mono was the rule, and for stereo the bass was (mostly?) mono due to the vinyl‘s limitations. Maybe they got the master tape?

Anyway, I‘m curious if the effect could be measured in-room, because I argue it could be just frequency response after room resonances, mitigated by uncorrelated left/right content. We‘ve got a synthetic test file already, thanks @NTK !!

 

[amirm]

FYI Dr. Toole is on vacation and likely won't be responding to the thread.

 

[bmc0]

The recording was made when mono was the rule, and for stereo the bass was (mostly?) mono due to the vinyl‘s limitations. Maybe they got the master tape?

It was near the beginning of commercial stereo, yes (recorded Feb. 8, 1960). The first commercial 2-channel vinyl record was released in 1957, I believe. Engineers had been experimenting with two (or more) channel recording for much longer though. Alan Blumlein, for example, was doing stereo recordings back in the early 1930s.

I'm quite sure it was sourced from magnetic tape (original master or a copy). It would be very unusual for a major label to use a vinyl source unless there were no usable tapes available. Bass was frequently mono'd for vinyl (though not always), but this was generally done by the engineer cutting the lacquer master, not earlier in the production process.

 

[HiMu]

Anyway, I‘m curious if the effect could be measured in-room, because I argue it could be just frequency response after room resonances, mitigated by uncorrelated left/right content. We‘ve got a synthetic test file already, thanks @NTK !!

There are better test files provided by David Griesinger in this post: https://www.audiosciencereview.com/...ass-and-subwoofers.51589/page-10#post-2212227
Here you can download David Griesingers presentation, which might answer your speculation about room resonances: https://www.davidgriesinger.com/vancouver_asa.ppt

Over speakers it is a much more difficult situation in my room.

This is not directed to you as an individual participating in this conversation, but to point out the complexity of discussing a topic/phenomena like this by demanding evidence.
Can you provide any measured data that your system (speakers + room) is able to reproduce that effect? I think it is equally pointless to demand evidence, do some subjective testing without providing anything to back up (biased) observations.

One thing I'd like to ask you to try with speakers, using the Griesinger test tones found in here: https://www.dropbox.com/scl/fo/s09jwe1e3j30p34p4f0d6/APs6kS-Jr3hotJAxwLOD1VM/Decorrelated Noise?rlkey=9mczd805df3r8ywlmu6dlp1w1&e=1&subfolder_nav_tracking=1&dl=0
-Open up for example 80Hz mono and stereo tones to different tabs, set them to repeat. Mute/unmute the tabs so you change which one signal you hear.
-Turn your head like you were in a physical space looking around the walls, floor and ceiling. What differences, if any, do you hear when switching between the signals while "looking around"?

Just to give a reference for discussions sake, these are from GRADE report measured in my room, listening distance about 2.6m. I can hear subtle but clear enough difference down to 50-60Hz between stereo and mono sub configurations, in my room, but I'm biased due to setting up the system to try to achieve AE. I prefer the stereo configuration because the sound stage is, well, more enveloping.
I can't do any scientific double-blind testing but I'm going to play some test tones to visitors and ask them to describe what they hear and whether they prefer one or the other, without telling anything what is the purpose and differences of those sounds.

 

[Sokel]

Problem with test signals intended to test low addressed to many people and rooms is their length.

Continuous, long signals may show some things but their tendency to built up and slow decay (depending the degree of treatment and EQ of the room) may blur things.
Short ones are far more revealing for various effects.

Edit:an intermittent, arc-panned short one at 40-50Hz like the usual one we use for testing 3-D soundstage would be nice.
But it would have to be heavily filtered above that and also kept "tick" -like short .

 

[HiMu]

Continuous, long signals may show some things but their tendency to built up and slow decay (depending the degree of treatment and EQ of the room) may blur things.
Short ones are far more revealing for various effects.

Valid point, partially. There is a reason we have recommendations for critical listening spaces, like the ITU-R BS1116. If a listening space is acoustically problematic, it is not a problem of the source/signal. As you can see from the screenshot of my GRADE report summary, it is not a strict line of usable /not usable, but a combination of gradients spread out on different specified domains.

https://www.itu.int/dms_pubrec/itu-r/rec/bs/R-REC-BS.1116-3-201502-I!!PDF-E.pdf

Scope
This Recommendation is intended for use in the assessment of systems which introduce impairments so
small as to be undetectable without rigorous control of the experimental conditions and appropriate statistical
analysis. If used for systems that introduce relatively large and easily detectable impairments, it leads to
excessive expenditure of time and effort and may also lead to less reliable results than a simpler test. This
Recommendation forms the base reference for the other Recommendations, which may contain additional
special conditions or relaxations of the requirements included in this Recommendation

8 Listening conditions
8.1 General
The term “listening conditions” describes the complex acoustic requirements for a reference sound
field affecting a listener in a listening room at the reference listening point, for sound reproduced by
loudspeakers. This includes:
– the acoustical characteristics of the listening room;
– the arrangement of the loudspeakers in the listening room;
Rec. ITU-R BS.1116-3 13
– the location of the reference listening point or area;
which are producing the resulting sound field characteristics at that point or area.
Because the state of the art does not yet allow the description of the reference sound field
completely and uniquely by acoustical parameters only, some geometric and room acoustic
requirements for a reference listening room are given to ensure the viability of the listening
conditions described.

I find it a bit ridiculous that these conversations have a demand for scientific proof/source, but when it comes to observing, the demands are out the window and can be shrugged off as "I didn't hear anything because of my rooms acoustic problems". This is not pointed to you @Sokel , but as an example of cherry picking.

 

[Heinrich]

As you can see from the screenshot of my GRADE report …summary, …
I find it a bit ridiculous that these conversations have a demand for scientific proof/source, …

The GRADE is a proprietary viewpoint, and its methodology may not be known to many, let alone is agreed on as helpful.

What I find a bit disconcerting is the lack of a consistent, let alone compact theory behind the claim of „AE“. I‘m not into immersion and synonyms when listening to some playback, and I‘m not into ‚classical music‘, or what is deemed to be that.

Of course I have ‚stereo‘ bass in my living (!) room, but never noticed any particular effect from one recording (including difficult stuff, natural stuff, but not classic) to the other. So, I still see „AE“ as a theoretical construction, but the theory is missing.

 

[HiMu]

The GRADE is a proprietary viewpoint, and its methodology may not be known to many, let alone is agreed on as helpful.

What I find a bit disconcerting is the lack of a consistent, let alone compact theory behind the claim of „AE“. I‘m not into immersion and synonyms when listening to some playback, and I‘m not into ‚classical music‘, or what is deemed to be that.

Of course I have ‚stereo‘ bass in my living (!) room, but never noticed any particular effect from one recording (including difficult stuff, natural stuff, but not classic) to the other. So, I still see „AE“ as a theoretical construction, but the theory is missing.

Grade report is a compiled and concentrated measurement data, graded in relation to ITU recommendation. It is as valid as a REW measurement when showing basic speaker-room system information, although in much more simplified form compared to .mdat file.
I don't listen to classical music either, but I still use whatever material that is, allegedly, able to provide an example of a phenomena, the same effect can be observed from festival recordings, well produced electronic music etc.

Did you check the Griesinger powerpoint, which explains the importance of speaker/sub placement in relation to room modes and their velocity/pressure components?

I'd argue that if people are not willing to experiment with stereo subs if they already have the capability, with placement fine tuned to maximize AE based on the provided information, they might not know what to listen to, to even identify it. After that it is just whether the setup is usable* enough for that listening space and whether the user prefers the effect or not.

*I have 12" subs on stands on both side walls, not a living room friendly setup.