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Perceptual Effects of Room Reflections

Fitzcaraldo215

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"If you prefer to stick with compressed pop on CD". What a snobbish(Classical?) rash generalisation. Not all CDs are compressed any more than other formats.
My impression is that Sal1950 interests I are much wider than' pop', as are mine. I have no issue with pop as it is presented to its audience. It is also offered on higher Q media. I get the impression that you can't distinguish between the many music genres outside of your chosen ones or relate to other musical preferences.. :eek:
Sorry if my comment was misconstrued, and I fully understand why it might have been. But, let me briefly parse it for you for greater clarity:

"IF [my emphasis] you prefer ["you" in general, not referring specifically to you or Sal, but a better choice would have been "one prefers"] to stick with compressed pop on CD..."

Note that I did not say or intend to imply that all pop was compressed, although a lot of it today clearly is in the "Loudness Wars".

You might be surprised to learn that my SACD library includes over 1,000 non-classical selections, including much pop, jazz, film music, etc. in both stereo and Mch. Adding those to other media types in my collection, the total is more than double that. It would be fair to say I have more diverse musical taste and listening experience than it might appear, but understandably so.

I begrudge no one their choice of musical genres, playback media, channel count or equipment. I also realize full well that my own major preferences are not at all in the main stream of listeners, both here and in general. Nontheless, I can learn much from others, and possibly they can learn something from me, as well.

Again, my apologies for not being more diplomatic. But, I do not have a death wish for anyone else's choices in the audio marketplace, not even vinyl, which I strongly dislike based on much experience.
 

Fitzcaraldo215

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My my, aren't we touchy about the little obsolete piece of optical disc media. Yes, time has moved on, but feel free to also join the vinyl revival gang, get yourself some SQ, QS, and CD4 LP's and really go retro with your mch sources. Maybe you could launch a whole renaissance in quad vinyl gear, it would be great for the industry.
How kool to get some Rice Krispies mixed with your 4 channel sound.

And what did any of that have to do with throwing mud at anyone's musical genre preferences?
You are a testy ole codger aren't ya. ;)

snap-crackle-pop-shirt.png

Actually, Sal, my primary media are all ripped to my NAS, so physical discs are not important to me once ripped. And, my NAS library, in addition to thousands of SACDs, also includes downloads and BDs. Is this still retro in your view?

I also do not believe that there is any evidence to show that SACD is dead or retro, since they are still produced and released in considerable numbers on disc or as downloads. There is an installed base of millions of players out there that can play them, together with other formats, and new ones continue to appear. I do not think you are really in touch with what has been happening, though it is clearly a niche outside the popular main stream.

I do not see how your tangent aligning me with other now clearly dead formats or with vinyl makes any logical sense. And, I do not see why the existence of SACD or its preference by others is so troubling to you.
 

Wombat

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Sorry if my comment was misconstrued, and I fully understand why it might have been. But, let me briefly parse it for you for greater clarity:

"IF [my emphasis] you prefer ["you" in general, not referring specifically to you or Sal, but a better choice would have been "one prefers"] to stick with compressed pop on CD..."

Note that I did not say or intend to imply that all pop was compressed, although a lot of it today clearly is in the "Loudness Wars".

You might be surprised to learn that my SACD library includes over 1,000 non-classical selections, including much pop, jazz, film music, etc. in both stereo and Mch. Adding those to other media types in my collection, the total is more than double that. It would be fair to say I have more diverse musical taste and listening experience than it might appear, but understandably so.

I begrudge no one their choice of musical genres, playback media, channel count or equipment. I also realize full well that my own major preferences are not at all in the main stream of listeners, both here and in general. Nontheless, I can learn much from others, and possibly they can learn something from me, as well.

Again, my apologies for not being more diplomatic. But, I do not have a death wish for anyone else's choices in the audio marketplace, not even vinyl, which I strongly dislike based on much experience.


Maybe I have watched too many episodes of Frasier. ;)
 

eliash

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Thanks for inviting me to your new forum Amir. For my first post, allow me to refute the notion that early reflections are ever beneficial in a home-sized room:

Early Reflections

:D

--Ethan
Going back to the beginning of the discussion, I made similar experience with early reflections.
From my listening interpretation it is far more difficult for the brain to sort out the original sound of instruments with heavy early reflections being present. E. g. identify or "understand" the sound of a snare drum, resulting in my case to perceive some kind of distortion (rather like nonlinear distortion effects, than frequency response effects as mentioned above).
The interesting thing is, when being younger, this did not bother me too much. But sometime from my mid 40´s it started annoying me.
Fortunately I could invest enough time to understand what was going on and hence install some wall and ceiling absorbers (also combined with some diffusors) in the acoustical "mirror areas", actually identified by a real mirror.
Since then, listening to music has become a pleasure again, still lasting in my late 50´s...
 

Trdat

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Audioholics just did a video on Optimizing Small Room Acoustics with a very narrow minded take on the whole issue. Covering issues similar to this thread. I found it misconstrued many of the facts and explained them without context either deliberately to suite an agenda or just by plain lack of effort in providing a history and explanation of the change in the school of thought on acoustics and obviously arguments of both sides of the coin.

I wrote pretty uncalled for comment which was rebutted by Mathew Pose quite elegantly but my counter rebuttal was what I thought my argument was about. Which was their unclear statements and pushiness against Panel Trap guys/companies which has been evident for a while now and then subsequently advertising Auralex. Many contradictions which I still can't put a finger on it. The politics is underlying you need to watch their videos from day one and I am not even sure If I have unravelled why they have taken this approach, I could be wrong but something wasn't right. Although I have not meticulously researched the whole"reflection" thing but it seems there is more to it than meets the eye. And the lack of explanation in their first video seemed very suspicious.

Surprisingly, the week after they posted a new video titled The Acoustics of Studio vs Domestic Listening Spaces which untangled many of the issues related to the RFZ zone and other very interesting points etc etc.... Yes, they still maintain reflections are beneficial and no they didn't bring up counter arguments to this line of thinking but they managed to explain the whole topic within a much better context.

Anyway, I thought for anyone interested in the topic would want to know what is going on in the industry. I have restrained from writing in this response about some of the interesting counter arguments not so academic but a compilation of what I have come across, as not to make this reply to long but I am hoping that I could pop them up soon and see what others take on it is.
 

Ethan Winer

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^^^ I see your comment, and you did a good job. The problem for Gene is he has no real talent for audio and music, and he can't arrive at a conclusion on his own. So all he can do is pick an expert to follow - in this case Floyd Toole - and oppose any other viewpoint. Thanks for mentioning my name, and you should post my Early Reflections article in those YouTube comments. If I do that they'll probably delete my post. If you post it they'll probably leave it. Here it is again:

http://ethanwiner.com/early_reflections.htm
 

Trdat

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Well, I added the link. Curious if they would delete my comment. But anyway it was many suspect things that threw me off. I am also trying to understand and keep an open mind on the whole subject.

1. Gene has made several comments on how, to much treatment is not the best idea, fair enough but why would you then say you have spend thousands of dollars on Auralex treating your home theatre room. Especially when Auralex is seen as the bad guy of acoustics. (Although he has spoken highly of GIK and Ethan on a one or two occasions)

2. In the first video there was no mention of how a well treated room could possibly sound extremely good.

3. In my first comment under the video when I said that back wall needs a lot of absorption Mathew was quick to rebut and say that rear wall absorption is for a mixing environment and for the amateur DIY acoustic guys, okay fair enough. But then why would you suddenly address the issue of reverberance being problematic when in the first video you clearly were pushing for minimal treatment. How else would you slow down decay if you don't add a lot of treatment to the room in general or back wall.

4. Then if you were so adamant to relay the fact that to much treatment is not a good thing then why in your second video you were so quick to say that home theatre can benefit from treatment counter arguing what you had just prescribed in the previous video. Yes, you maintained reflections as beneficial but cleared up that you could possibly leave side wall reflections but cut down reverberation times. But this was not mentioned at all in the first video.

5. Also Floyd although does advocate reflections, excerpt from his work mention that reflections are the preferred taste chosen by his test subjects but no mention in the video that a small percentage still opted for RFZ as a preference over reflections.

6. And Mathew directed me to David Greisenger who has done exemplary study on envelopment and early reflections. But when I emailed him, David sees early reflections in small rooms problematic, I am not saying he advocated absorption but clearly mentioned that they are considered to decrease intelligibility.

In Mathews defence, he is a credible with his work but why so many inconsistencies.

PS. Hopefully my next post will be my opinion on the topic at hand.
 

Hephaestus

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Geoff Martin of Bang & Olufsen:

"The BeoLab 90 has two features that can overcome some detrimental effects of the listening room’s acoustical behaviour (Beam Width Control and Active Room Compensation). However, the sound of any loudspeaker can be optimised by improving the room’s acoustics."

Page 45 Beolab 90 Technical Sound Guide.
 
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amirm

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1. Gene has made several comments on how, to much treatment is not the best idea, fair enough but why would you then say you have spend thousands of dollars on Auralex treating your home theatre room. Especially when Auralex is seen as the bad guy of acoustics. (Although he has spoken highly of GIK and Ethan on a one or two occasions)
I have not read his comments in this regard. But there is an important distinction in these discussions. That is, whether we are talking about everyday spaces where people listen to music, or dedicated theaters. The latter starts with an empty box and no one, including Dr. Toole advocate that you use such a empty room. Indeed, that is a place where you put plenty of acoustic products (which can be purpose built or furnishing).

The arguments are around your everyday listening spaces that already have furnishings and such. Here, sticking acoustic products make little sense and superb performance can be had with multiple subs, EQ, good speakers, placement, etc. The "anti-reflection" folks go crazy plastering absorbers in such rooms which makes little sense from aesthetic or sound point of view.
 

Trdat

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Lets say for arguments say that your side of the coin is correct and because of that Audioholics just went with what was correct scientifically and that they were so confident they didn't need to mention all these other points. It just didn't make sense why their first video put nothing into context that's all I am saying.

Regarding your take on it, its great to hear the other side of the coin. My question is then does a controlled room that is fully treated compare better in terms of subjective day to day listening? Or to put it another way, can a non treated room with what you say, EQ and multiple subs sound as good as a totally treated room which consist of a(nearly) flat frequency response and diffusion?
 
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amirm

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Again, the topic is not "treated vs non-treated." Each reflection has its own psychoacoustic response depending on its angle and postion. And so does the overall room. Only the side reflections have positive effect on listeners, not the rest of them. How you deal with the rest is a topic in its own.

What you don't want to do is assume "all reflections are bad" and keep going after them one by one. By the time you are done, you are guaranteed to have a dead room. Given the sighted test, you may think it sounds better but in reality it may not even to your ears if the test was controlled. I have known people who have wrapped the entire room in fabric, only to then dislike the effect. All because of the "war on reflections."

If I were to write an article on room design, I too would NOT mention RFZ, NE rooms, etc. As far as I am concerned, they are all non-scientific methods invented years ago for studio use. There is no reason to mention them any more than your doctor telling you that there are older options beside antibiotic when you have a bacteria infection.
 

Trdat

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Great! Thanks for your response.

If you have any papers that one can read please link in.

"Only the side reflections have positive effect on listeners, not the rest of them. How you deal with the rest is a topic in its own."

I am keen to know more about how to deal with the rest of the reflections. Any links to articles will be greatly appreciated.

Anyway I can say that this thread has enough information now for everyone to make a descent conclusion on there own.
 

Ethan Winer

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Folks, the requirements for a high quality listening room are the same as for a high quality mixing and mastering room. Either you want to hear things clearly with minimal artifacts or you don't. If your spouse objects to the appearance of the necessary treatment, either get a dedicated room or get a new spouse. I'm serious! Or accept that your system will never sound as good as it could, and go buy some overpriced RCA wires. :D
 

ernestcarl

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Folks, the requirements for a high quality listening room are the same as for a high quality mixing and mastering room. Either you want to hear things clearly with minimal artifacts or you don't. If your spouse objects to the appearance of the necessary treatment, either get a dedicated room or get a new spouse. I'm serious! Or accept that your system will never sound as good as it could, and go buy some overpriced RCA wires. :D

I think most people are already happy to be living in the middle, Ethan. Although, a better listening room never is a bad aspiration to have... When that'll ever happen though (perfect enough) is anyone's guess. :p
 

NTK

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...
If you have any papers that one can read please link in.
...
Dr Floyd Toole wrote a 3 part series on how to design a home theatre. They are free downloads from the companion site of his book.
https://routledgetextbooks.com/textbooks/9781138921368/home-theatre.php

Dr Toole has much to say about room acoustics in Part 1. In particular, sections 6 & 7 are on 'early reflections'. You can tell from figure 2 that he is far from opposed to room acoustic treatments. He is just against overdoing it. On the subject of the first side wall (lateral) reflections, he has the following to say (section 7, page 14, right after figure 2):
Note that the wall surfaces involved with the controversial first side wall reflections are shown as “optional areas: absorb, diffuse, reflect.”

Leaving these areas as flat wall surfaces provides an open and spacious soundstage for those customers who listen in stereo using loudspeakers with well-behaved off-axis performance. If listeners prefer a compact soundstage or have loudspeakers that misbehave off axis, then absorbing the side wall reflections would be appropriate—but do it completely, not partially. With loudspeakers having off-axis problems it will be advantageous not only from a sound quality perspective, but also because reflected sounds that do not resemble the timbre of the direct sound are more likely to be heard as separate spatial events.
 

JoachimStrobel

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Again, what a superb professional thread. Should I as an average amateur comment? May be this:
I love jazz and listen to performances in every room size, from concert halls to small places that are hardly larger than my living room. The main difference? Amplification and loudspeakers kill the good sound, Adding direct sound by speakers aimed towards the audience creates a very unpleasant sound for me. Concerts without amplification sound so much nicer.
And stuffing a 20 piece big band into a 100 sqm does not sound as nice as listening to the same big band in a good concert hall with wooden floor panels marvelously reflecting those trumpet sections.
Bottom line: Aim at good reproduction of music that would “fit” into your listening room and do not try the impossible.
 

Juhazi

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Folks, the requirements for a high quality listening room are the same as for a high quality mixing and mastering room. Either you want to hear things clearly with minimal artifacts or you don't. If your spouse objects to the appearance of the necessary treatment, either get a dedicated room or get a new spouse. I'm serious! Or accept that your system will never sound as good as it could, and go buy some overpriced RCA wires. :D
I am more on Dr. Toole's camp on this, considering stereo sound. Some of my hifi friends have heavily treated specific listening rooms, and yes they sound different, beetter in a way with precise imaging and minimal modes - but listening impression is too immersive, fatiquing, even unnatural to me. A matter of preference.

Typical largish living rooms of houses, with wooden frame/gypsum/plywood walls, bookshelves, sofa, tilted ceiling , large openings to kitchen, corridor etc. can be just fine. Avoid longitudinal listening direction with distance over 3m! Small apartment rooms with concrete/tile walls are almost impossible to get right, they need heavy acoustic treatment.

About first reflections, positioning should be such that different reflection nulls don't all happen at same frequency! Backwall behind the listener is too near in most cases and I find it often the most annoying. It sends early reflections which destroy imaging with phantom images. Low freq boosting happens easily too.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4040828/
https://tech.ebu.ch/docs/tech/tech3276.pdf
http://theaudiolounge.de/rooms.htm
 
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oivavoi

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Only the side reflections have positive effect on listeners, not the rest of them. How you deal with the rest is a topic in its own.

I think this is worded too strongly as a blanket statement. I have looked a bit into the research on this, and several studies indicate that reflections from behind and above the listener can be perceived positively as well. Here is one such study for example, which seems methodologically sound: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.571.7185&rep=rep1&type=pdf

As to ground reflections, there is very little research on it. When it comes to reflections from the front, it is often assumed that they are negative. But it’s difficult to find strong support for this is in the literature. This claim seems to be based on a couple of early psychoacoustic studies, but to my knowledge it has not been replicated or confirmed in later studies. In some of the studies I’ve seen the front reflections don’t seem to be noticed much, because they are perceived as fused with the direct sound. It also seems somewhat counterintuitive that front reflections should only be bad (given proper speaker placement and some delay so the reflections don’t come very early), given that some of the speakers that have fared best in blind tests - the bipolar Mirage speaker which dr Toole got for himself for example - send much sound back to the front wall.
 

Juhazi

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All reflections depend on geometry and wavelength - pathlength difference of direct and reflected wavefronts. This makes phase diffrence and strogest effect comes from nulling at 180deg difference, then at 540deg, 900deg etc. and at low frequency 100-400Hz. A listener with two ears in a room always hears several reflected wavefronts and the mix of those smoothes out in our perception/brains. Add room's standing waves to this! These phase differences make us able to locate sound source, but in a room this is difficult, more difficult with more reflections also from two or more bounces! We must remember, that we have very poor localization of sounds with low frequency.

webpage https://www.bringtheruff.com/early-reflections-impact-home-theater-and-audio-systems/
Seminar lecture http://legacy.spa.aalto.fi/bnam04/webprosari/papers/o23.pdf
Thesis 2015 http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1042&context=archengdiss

https://www.acs.psu.edu/drussell/demos.html
interference.gif

mr1e3hd_RJx6SpuDYlblVhmw3ku4p9KNmAHB0HM-9hnygfOOdEG5iY9tFUS5qQfzOKxZgEWvX_ah9P5vAuYNn8sArEHGxlxvtDCwnG72dUv6U73xEWYtFDUQHlNEpSrNWw


Floor bounce null is often the most prominent in measurements, and is almost unavoidable in practise. But still, it cannot be handled with eq or FIR, because it is so specific to geometry, and a nulling by nature. We often see a too much simplified 2D graphic presentation of only first reflections.

ray-tracing-early-reflections-order-1-3-w620.jpg


But we live in 3D!

Room-Reflections.gif
 
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Hipper

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Floyd Toole mentions two aspects to side wall reflections for stereo listening in his Third Edition - we are talking reflections above the Transition/Schroeder Frequency. All discussions depend on the reflections being a reasonably accurate rendition of the direct sound, that is, it is not damaged by the side wall.

The first is what has been discussed here, namely how these reflections can add to the volume of the sound without damaging the location information of the direct sound, and yet can also add spatial cues. I don't understand how it can do both unless it is second and third reflections that do the spatial effects?

The second is their effect on the stereo phantom image. The left ear will hear the direct sound from the left speaker, but also the sound from the right speaker which has to travel around the left side of your head to get to the left ear. As a result it travels a bit further. The sum of these two signals generates some comb filtering in the 2kHz region which can weaken the phantom image. However, side wall reflections can partly come to the rescue so the dB loss is not so great.

This would seem a good argument for allowing side wall reflections. However, in my limited home listening experience, I find side wall reflections (in a 14' x 13' room) muddy the sound a bit, whereas preventing them (I do this with a panel immediately to the outside of the speaker, not on the side wall) seems to give a clearer phantom image, albeit one stuck to the width of the distance between the speakers (I mostly play studio bound pop recordings).
 
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