How NOT to set up speakers and room treatment ( Goldensound)

[maverickronin]

True, film and stage are essentially different art forms.
So are live and recorded music these days. Not being constrained by reality puts more tools at a musician's disposal as well.

Totally agree on that.

But let's admit it: recordings don't sound as good as being in the room with the musicians, at least for unamplified music.

Not so much for this. That's probably because I'm an introvert so crowds and live events are automatically negatives but I understand why extroverts would hold the opposite opinion.

 

[fpitas]

Not so much for this. That's probably because I'm an introvert so crowds and live events are automatically negatives but I understand why extroverts would hold the opposite opinion.

Agreed on that. I'm much more of a fan of studio production than live. Each to his own.

 

[Kvalsvoll]

It was asked how can measure the effect of diffusers. Here's a neat presentation. In this case the room was measured empty vs one wall covered with diffusers. The graph is a three dimensional model which shows the field direction.

View attachment 293970

Here are decay graphs of both.

Without:
View attachment 293971

With:
View attachment 293972

While we see a difference in the decay as well, the three dimensional model of the field direction is showing a different view and with a much bigger change.

Measurements in a real room, treated, shows similar behavior, where magnitude of velocity drops for reverberated sound, and the delayed room sound has little directivity. This can be seen by comparing decay of sound in different directions, where on-axis velocity drops faster and more than pressure, and other (90 degrees, vertical) directions show a much slower decay.

At the low end of the frequency spectrum, where room treatment becomes less efficient, there is a significant change in behavior, where now you have highly directive sound. In a non-treated space this transition occurs much higher in frequency, and thus has much more detrimental effect.

In a fully developed diffuse sound field net velocity is zero, sound intensity is zero, there is only pressure.

 

[amirm]

It was asked how can measure the effect of diffusers. Here's a neat presentation. In this case the room was measured empty vs one wall covered with diffusers. The graph is a three dimensional model which shows the field direction.

What? The graphs say "E" and "H" fields which means electronical and magnetic fields (they are orthogonal to each other). Not acoustics. Maybe that is why you didn't give us the title of the paper?

 

[Philbo King]

Yeah, the frequencies on the graph are low microwave frequencies; this is RF.
While there are some surpising analogies between audio and RF in terms of physical wavelengths, the materials and techniques are far different for steering, absorption and diffusion. For example, ferrite has little effect on sound but a drastic effect on microwaves. And generally microwave spectra don't span 4 decades of frequency like sound does.

 

[Guermantes]

What? The graphs say "E" and "H" fields which means electronical and magnetic fields (they are orthogonal to each other). Not acoustics. Maybe that is why you didn't give us the title of the paper?

The paper is on the AES site. The authors tested using an electromagnetic model in MATLAB which is why they show frequencies in the MHz range.

AES Convention Papers Forum » Diffuse Versus Non-Diffuse Energy and the Effect of Acoustic Diffusors

The AES Forum is where our members get to interact with each other in between conferences and section meetings.

secure.aes.org

Diffuse Versus Non-Diffuse Energy and the Effect of Acoustic Diffusors​

This paper discusses the effect of diffusers on the diffuse and nondiffuse sound energy in a room. The paper first defines diffuse versus nondiffuse energy, then presents a simple means of measuring it. It also discusses the effect of diffusers on the diffuse energy using a simple theoretical model. The paper presents simulations on an electromagnetic scale model of a reverberant room which show the beneficial effect of diffusers on diffuse versus nondiffuse energy ratio.

Authors: Angus, James A.; Clegg, J.; Marvin, A. C.; Dawson, J. F.
Affiliation: University of York, York, United Kingdom
AES Convention: 100 (May 1996) Paper Number: 4250
Publication Date: May 1, 1996
Subject: Architectural Acoustics and Sound Reinforcement

 

[youngho]

The paper is on the AES site. The authors tested using an electromagnetic model in MATLAB which is why they show frequencies in the MHz range.

AES Convention Papers Forum » Diffuse Versus Non-Diffuse Energy and the Effect of Acoustic Diffusors

The AES Forum is where our members get to interact with each other in between conferences and section meetings.

secure.aes.org

Diffuse Versus Non-Diffuse Energy and the Effect of Acoustic Diffusors​

This paper discusses the effect of diffusers on the diffuse and nondiffuse sound energy in a room. The paper first defines diffuse versus nondiffuse energy, then presents a simple means of measuring it. It also discusses the effect of diffusers on the diffuse energy using a simple theoretical model. The paper presents simulations on an electromagnetic scale model of a reverberant room which show the beneficial effect of diffusers on diffuse versus nondiffuse energy ratio.

Authors: Angus, James A.; Clegg, J.; Marvin, A. C.; Dawson, J. F.
Affiliation: University of York, York, United Kingdom
AES Convention: 100 (May 1996) Paper Number: 4250
Publication Date: May 1, 1996
Subject: Architectural Acoustics and Sound Reinforcement

Perfect, a simulation based on a scale model at frequencies outside of human perception, but expected to extrapolate to perceptual relevance?

 

[Guermantes]

Perfect, a simulation based on a scale model at frequencies outside of human perception, but expected to extrapolate to perceptual relevance?

There is no discussion of perceptual aspects in the paper, just measurement on the effects of diffusion within the "room". As to the scaling down to acoustic parameters, the authors use this method for a few other papers, too, so they seem to have faith in it. For example:

AES E-Library » The Effect of Diffusers on Frequency Dependent Room Mode Decay

This paper discusses what modal decay is, the effect of diffusers on room mode decay using a simple theoretical model, and the implications of this model on their bandwidth and decay. The theory indicates that the decay rate increases and gives a relationship between this and the diffuser order...

www.aes.org

Edit: corrected wrong link

 

[Curvature]

I'm sorry, but this isn't terribly accurate. First, 'space monkeys' are only produced by some codecs, other codecs produce different artifacts, or at proper rates, none.

Second, listening to the 's' channel is not very reliable, since you have no idea from just the 's' channel what will come out of the actual channels, especially in multichannel. Furthermore, different codecs (say AAC vs. MP3) will have totally different 'S' channels working from a proper encoder (but of course all results for any perceptual coder depend on the encoder so that can change sometimes.

When you get to the MP4 codec system, or other multichannel systems, this is very much more complicated. Note, I do not mean the "backward compatible" stuff, please forget that existed.

Those characteristic MP3 warbles aren't the only kind of audible compression artefact? Do you have examples?

AES E-Library » Introducing the Free Web Edition of the "Perceptual Audio Coders — What To Listen For" Educational Material

In 2001, the AES Technical Committee on Coding of Audio Signals (TC-CAS) produced the legendary educational CD ROM 'Perceptual Audio Coders - What To Listen For'. It contains a taxonomy of common types of codec artifacts, as well as tutorial information on the background of each one. Example...

www.aes.org

@j_j Would you consider this a good start?

 

[j_j]

AES E-Library » Introducing the Free Web Edition of the "Perceptual Audio Coders — What To Listen For" Educational Material

In 2001, the AES Technical Committee on Coding of Audio Signals (TC-CAS) produced the legendary educational CD ROM 'Perceptual Audio Coders - What To Listen For'. It contains a taxonomy of common types of codec artifacts, as well as tutorial information on the background of each one. Example...

www.aes.org

@j_j Would you consider this a good start?

I'd go as far as saying "it's a start', at least.

For various reasons, it's shy some of the imaging issues. Pardon my weird fonts, I'm not sure how I did that.

 

[amirm]

Diffuse Versus Non-Diffuse Energy and the Effect of Acoustic Diffusors

Thank you. This is the simulated room:

So it really was a "box." Using RF frequencies (going up to microwave) allows them to simulate situations that has no parallel in a practical home listening space. Their goal was to show that a diffuser can go down to modal region. Sure, if I could have 10 foot deep diffusers, I could do that for sound energy as well but we are not going to have that.

The notion then that this was actual room measurement with a diffuser in the context of sound is quite misleading then:

It was asked how can measure the effect of diffusers. Here's a neat presentation. In this case the room was measured empty vs one wall covered with diffusers. The graph is a three dimensional model which shows the field direction.

 

[j_j]

Thank you. This is the simulated room:
View attachment 294119

So it really was a "box." Using RF frequencies (going up to microwave) allows them to simulate situations that has no parallel in a practical home listening space. Their goal was to show that a diffuser can go down to modal region. Sure, if I could have 10 foot deep diffusers, I could do that for sound energy as well but we are not going to have that.

The notion then that this was actual room measurement with a diffuser in the context of sound is quite misleading then:

Microwave frequencies are simply not germane here. A few centimeters can scatter them.
Scattering 50Hz means depths of diffusors of 1115/(50*4), or about 5'9" deep. 25Hz, double that, etc.

 

[youngho]

There is no discussion of perceptual aspects in the paper, just measurement on the effects of diffusion within the "room". As to the scaling down to acoustic parameters, the authors use this method for a few other papers, too, so they seem to have faith in it. For example:

AES E-Library » The Effect of Diffusers on Frequency Dependent Room Mode Decay

This paper discusses what modal decay is, the effect of diffusers on room mode decay using a simple theoretical model, and the implications of this model on their bandwidth and decay. The theory indicates that the decay rate increases and gives a relationship between this and the diffuser order...

www.aes.org

Edit: corrected wrong link

I was writing in jest, but there seem to have been significant issues in simulations and scaling: https://audioxpress.com/article/r-d-stories-acoustic-diffusion-research

 

[Flaesh]

If that happened, it would be readily apparent in the magnitude response graph.

This (and something else) can be seen in the filtered IR graphs. For example, here is -6 dB peak at cursor:

in 4000 and 8000 bands

 

[Guermantes]

Thank you. This is the simulated room:
View attachment 294119

So it really was a "box." Using RF frequencies (going up to microwave) allows them to simulate situations that has no parallel in a practical home listening space. Their goal was to show that a diffuser can go down to modal region. Sure, if I could have 10 foot deep diffusers, I could do that for sound energy as well but we are not going to have that.

The notion then that this was actual room measurement with a diffuser in the context of sound is quite misleading then:

I note that a later paper (2001) by one of the authors no longer uses the electromagnetic modeling though still simulated in MATLAB. I wonder why they used the MHz modeling previously. Ease of simulation with what was available to the researchers at the time (1995-1999)? Was it piggy-backing on other research that actually was dealing with RF, thus saving time and money?

AES E-Library » The Effects of Specular Versus Diffuse Reflections on the Frequency Response at the Listener

It is shown how the frequency response of the sound from a monitoring loudspeaker in a control room is affected by the presence of specular or diffuse early reflections. The effect of specular and diffuse early reflections on the frequency response described by means of a simple theoretical...

www.aes.org

The room has grown to 6m x 4m:

The frequency scaling is now in the humanly perceptual range:

 

[amirm]

The frequency scaling is now in the humanly perceptual range:

It is but measurements show now that they made the low frequency response worse, not better with diffusion:

Quite backward of what they were aiming for. It leads to this conclusion:

5 CONCLUSION A comparison of the frequency response variations due to specular and diffuse reflections has been presented. Although diffusion results in a lower level of early reflection amplitude, paradoxically it does not necessarily result in a lower level of frequency response variations. This is due to the correlation of frequency response ripples because of the close time spacing of the low-level diffuse reflections However, a diffuse wall may result in a frequency response performance that is less critical of the listener's position in the room.

Diffusion is so poorly understood by folks. I am convinced many buy them because they look fancy and "professional," not because they get useful results from them.

 

[Axo1989]

I was writing in jest, but there seem to have been significant issues in simulations and scaling: https://audioxpress.com/article/r-d-stories-acoustic-diffusion-research

Interesting article at the link, thanks. Of course it also functions as advertorial, but as I mentioned upthread I've been interested in cylindrical and poly cylindrical reflectors and their characteristics/application in small-medium listening rooms in any case. Those clear ones can go in front of windows too, which is cool.

 

[poxymoron]

Diffusion is so poorly understood by folks. I am convinced many buy them because they look fancy and "professional," not because they get useful results from them.

My thoughts too.

 

[Guermantes]

It is but measurements show now that they made the low frequency response worse, not better with diffusion:

Quite backward of what they were aiming for. It leads to this conclusion:

5 CONCLUSION A comparison of the frequency response variations due to specular and diffuse reflections has been presented. Although diffusion results in a lower level of early reflection amplitude, paradoxically it does not necessarily result in a lower level of frequency response variations. This is due to the correlation of frequency response ripples because of the close time spacing of the low-level diffuse reflections However, a diffuse wall may result in a frequency response performance that is less critical of the listener's position in the room.

Diffusion is so poorly understood by folks. I am convinced many buy them because they look fancy and "professional," not because they get useful results from them.

Well, that's science for you -- hypothesise, test, analyse results and gain new knowledge whether they support the hypothesis or not. Then publish the findings, warts and all.

 

[goat76]

I have a small exercise for all of you, and maybe especially for you who seem to believe that reflections from your listening room's side walls are necessary for your two loudspeakers in a simple stereo configuration to be able to reproduce a fully convincing enveloping sound (or a wider sound than the position of your loudspeakers).

Listen to the following song, first without any acoustic treatment on the left wall. Do you hear the reverberation of the singer's voice coming from a position somewhere to the left of the left speaker?

Now you find something to treat that left wall, you can use whatever you find at home that you think will be sufficient to treat the first side reflection, a couple of thick mattresses, or something similar. Do you still hear the reverberation of the singer's voice coming from a position somewhere to the left of the left speaker?

I think that this test will most probably show you that just two loudspeakers in a traditional stereo configuration are perfectly capable of reproducing a three-dimensional sound, with or without side reflections. What we hear is a stereo illusion that is carried by the direct sound from our loudspeakers to our ears, we really don't need to add much of our listening room's reflections to perceive a more enveloping sound, that's part of a good recording.

So, do you hear it the way I hear it?

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