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Acoustic treatment for my living room

49K views 593 replies 32 participants last post by  Ethan Winer 
#1 ·
This link shows the layout of my living room.



It is an L shape. The living room is opened on the right side to the dining area, with more openings to kitchen and stairs. Ceiling height is about 9 feet. The "hot movie zone
" is within the 16' x 13' area only.


The TV is on the 16' wall.


The round circles denote my Klipsch Synergy speakers in 5.1 + Front Wide DSX setup.


Any good recommendations/tips on acoustic treatment for my living room?
 
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#452 ·

Quote:
Originally Posted by kromkamp /forum/post/21933835


As if anyone would prefer a non-pleasing listening space! Accurate is a canard here anyways - the best anyone could do would be "more accurate for a majority of source material", no one can have an accurate room for all source material.

why does modifying the source make a difference? are the speaker-room interactions changing based on what CD you are listening to?


Quote:
Originally Posted by kromkamp /forum/post/21933835


I also find it amusing that you continually accuse Amir of having ZERO real-world experience - it is you who has ZERO real world experience, or else you would have posted some evidence of it by now.

now that i see how easy it is to make money of audio chumps who are more interested in marketing brocuhes than basic physics - sure! ill start my own company and post plenty of photos and fancy graphs for you in my quest for free marketing on this forum like some of our other users



don't worry, krompkamp - i'm certainly not here to impress you! after all, im already satisfied with myself for helping to assist YOU in learning how to take basic measurements of your theater.



and it is funny for you to respond in this thread - as you first used absorption at sidewall reflection points and now use a absorber/diffuser combo! certainly NOT what amir thinks you should do. maybe you should take down the sidewall treatments and see how it sounds. it seems to go against what toole states, yet you seem to prefer the treatments on the sidewalls. the silence is deafening here -
 
#453 ·

Quote:
Originally Posted by mtbdudex /forum/post/21934620


2 of my neighbors want advice on what to do in their living room, not a dedicated HT space like I have.

I hesitate to point them to this thread.
Quote:
Originally Posted by mtbdudex /forum/post/21934755


Thank you, there is a lot of good discussion here, but the "noise" clouds it up.


A summary post can then be linked.

One who tries to cast doubts about acoustic treatments and diminish their values in an attempt to bolster the sales of overpriced electronic audio gears he sells is the last one you want to pay attention to regarding this subject.
 
#454 ·

Quote:
Originally Posted by amirm /forum/post/21934141


The problem is yours my friend. You put forward an expert witness, Dr. Toole to back your position. When it is then pointed out that he says otherwise in the rest of his teachings, you attack the poster and claim Dr. Toole is not qualified to have an opinion in that regard.

toole said absorbing sidewall reflections allows for more precise (accurate) imaging. i say it's the user's choice what they want. toole says it is a matter of taste.

Quote:
Originally Posted by toole /forum/post/0


If reflected sounds are absorbed, the listener is placed in a predominantly direct sound field, making the experience more intimate, and the imaging tighter and more precise. If the reflections are allowed to add their complexity, the overall illusion is altogether more spacious and open, to many listeners, more realistic. In part, this is a matter of taste.

toole also agrees with me that if a user decides to absorb such reflections, then the treatment needs to be broadband and NOT alter the spectral content of the reflection.


toole and myself are mostly on the same page, but his publishing deal more with what is pleasurable and what the bulk of his lab rats "preferred" --- which is subjective testing. and here i go again saying it's the USER'S CHOICE whether they want an accurate, critical listening space (eg, with precise imaging and localization), or a subjective pleasing listening space based on THEIR preferences or the research of others.




Quote:
Originally Posted by amirm /forum/post/21934141


And that you know more than him because you have seen pictures of a studio with 4 foot diffusers. I have repeatedly asked why we should care about such a project and you have put forward nothing. No other examples related to home listening environment is put forward by you, showing that listeners like the results of the technique you recommend. But yet, we go on because as I said, the discussion does, in a strange way, lead us to more insight into where we need to go with respect to our room acoustics, whether you acknowledge that or not.

again, you blame the messenger. it is not MY fault that sound has size! it is not MY fault for the basic behavior of sound. it is not MY fault for basic physics...


if you're using diffusers for specular reflections in such a scenario, then as toole states, they SHOULD BE BROADBAND and NOT alter the spectral content of the reflection! but it is not MY issue that such a requirement with respect to diffusers requires 4ft sticks of wood! sound has SIZE. my or your recommendations DO NOT ALTER PHYSICS.


Quote:
Originally Posted by amirm /forum/post/21934141


You challenge the credibility of Dr. Toole. So I answer how he is more qualified than all of us combined in this thread. Then you come back and say "sigh" that you were talking about providing choices? What does have to do with the challenge you put forward regarding Dr. Toole's credibility?

why is it you're able to utilize the quote feature for my other commentary, but here when you say im quote - "challenging the credibility of toole" - you provide no statements from my commentary.


toole and i are in agree-ance on many many factors, as listed above.

Quote:
Originally Posted by amirm /forum/post/21934141


As to choices, please put forward listening tests showing which models are more preferred or that none is more than others.

accurate imaging and localization has nothing to do with preference. it's either accurate or it's not. what i "prefer" does not change this.


Quote:
Originally Posted by amirm /forum/post/21934141


Besides, you don't let them have a choice. You keep complaining about someone showing them the other points of view. You insist that the only answer is no answer per above. Well, that is not a position you have managed to back up with data.

where in this thread have i told anyone specifically what to do and that that solution is the ONLY solution. why would i quote toole with respect to absorbing reflections as "a matter of taste", as he says, if i "don't let them have a choice".


Quote:
Originally Posted by amirm /forum/post/21934141


As I have said repeatedly and so does Dr. Toole, the choices people make for a business of mixing and mastering music is different than the choices consumers need to make. Dr. Toole has even tested the two audiences and found their preferences for good music to be different. So it matters not if the expert you want to quote has done one or a million control rooms.

so you're saying that because a user is not mixing/mastering at home that they DO NOT HAVE THE CHOICE to emulate such models to maintain accurate imaging and localization within their home reproduction space? and to think, just above you attempted to say it was ME who doesn't give the user a choice



Quote:
Originally Posted by amirm /forum/post/21934141


As to why keep quoting Dr. Toole on control rooms, you are the one who asked me about it! And continue to do so in this quote. I provided data as to his expertise, yet you don't acknowledge it and keep going. So here it is again, hoping you will read this one. From AES Journal paper, The Modification of Timbre by Resonances: Perception and Measurement" biography at the end:

"Dr. Toole has designed recording studios, control-room monitor loudspeakers and sound-reinforcement systems for large multipurpose concert halls and theaters."


In his presentations he talks about Ron Howard's Todd-AO studio and Disney hall. I am sure there are countless others. In the next post I hope you share with us how many more control rooms you have designed than Dr.Toole.

cool - where is the data on such rooms?


Quote:
Originally Posted by amirm /forum/post/21934141


You seem to be stuck in this grove of cookbook models for rooms. If cookbooks were so good, why did the Blackbird studio not follow the ones before it? Why have others not followed that? You need to learn how to fish rather than how to buy one if you want to be set for life. Dr. Toole is a fan of analyzing how technology can produce the highest fidelity experience. He has proven that time and time again. And then provides insights that let you design your room appropriately.

for the 3rd time, blackbird C is a surround sound acoustic model - LEDE/RFZ are 2channel. so it makes sense to "not follow the ones before it" considering the mixing envirnoment is different.
but you probably wouldn't catch these basic facts in your frantic search of AES papers



Quote:
Originally Posted by amirm /forum/post/21934141


For your part, you have not even shared with us which one of these cookbooks you have followed. You say there are choices. Please show us your choice and explain why. Of course you won't do that because you either have no system to talk about, or have one that you know won't stand up to test of accuracy. I am confident you won't post one frequency response chart showing you have flat response. The #1 metric we use for accuracy in audio is that. Who would buy an amp with 20 db fluctuations in frequency response? Yet that is likely what we have in our homes while you talk about screwing around with a reflection point. Forrest is lost from the trees...

yes, exactly what im looking for --- to give you more ammunition to dance and deflect more by attempting to turning the focus of the conversation AWAY from acoustics and physics and more into MY personal choices. does MY personal choice affect what toole states regarding accurate imaging? i dont think so -

Quote:
Originally Posted by amirm /forum/post/21934141


All buzzwords. Yet if I asked you to post a sentence from the presentations on those models in journals, you wouldn't be able to do it because you have never read them. Why? Because the sum total of your experience is what someone has post on a forum. On top of that, it is not like you have designed such rooms or compared them to others. You have just read about them and they sounded good to you, in words, not real experiences of being there. I get that. But that is not what it is about. It is about whether we as home listeners would like such environment. I hear you. You don't know what that answer is. But others do.

ignorance preserved -


Quote:
Originally Posted by amirm /forum/post/21934141


Closed source? This is closed source? http://www.aes.org/e-lib/browse.cfm?elib=3965

"The LEDE- Concept for the Control of Acoustic and Psychoacoustic Parameters in Recording Control Rooms."

http://www.aes.org/e-lib/browse.cfm?elib=11805

"History and Development of the Lede Control Room Concept"

http://www.aes.org/e-lib/browse.cfm?elib=3744

"Translating LEDE- Control Room Design into Practical Experience"

http://www.aes.org/e-lib/browse.cfm?elib=3688

"Engineering an LEDE- Control Room for a Broadcasting Facility"

http://www.aes.org/e-lib/browse.cfm?elib=2852

"The -Lede- Concept for the Control of Acoustic and Psdychoacoustic Parameters in Recording Control Rooms"

so you think that just because there is information on AES that that is all of the information out there? lol.


and im glad you've put forth the proof that you are in fact able to work the search engine on AES website. if only you would have actually read some of them, you probably wouldn't have made the constant misunderstandings of LEDE earlier of which i had to correct you.

Quote:
Originally Posted by amirm /forum/post/21934141


The list goes on. Of course, if you can't fill in the login information to download the papers then you do have the problem you state. Not an issue for me because I am an AES member and pay out of my personal pocket to be informed and learn.

good - i hope you write the membership fees off on your company's taxes.


Quote:
Originally Posted by amirm /forum/post/21934141


Same back at you partner
. I am super comfortable saying that I could care less about LEDE or RFZ even though I have read some of the papers. Nothing about research or application to our homes says we should care or attempt to duplicate what they have done. And we know for certain some of the models were misguided and therefore have no applicability even in pro space even though people still follow them in some instances.
Quote:
Originally Posted by amirm /forum/post/21934141


I already answered. That the key researcher that designed that room gives him credit for informing him those reflections in rooms may be something that should be preserved.

no - tell me specifically how toole was involved in blackbird C? his name listed on a powerpoint slide with respect to history does not mean he was critically involved in the design.
weasel out of this any way you wish. what testing has toole done in blackbird C (an effectively anechoic environment!)

Quote:
Originally Posted by amirm /forum/post/21934141


And that perceptual tests and measurements are important and will follow. What other engagements he has had, I don't know and is not important. I did ask you however to tell us how many other rooms have been designed that way since. You seem to have difficulty answering that question.

so now we're basing this conversation based on what is "popular" and how many rooms are built. how big is the market for new multi-million dollar control room builds today?



still waiting for your answer on how to utilize rt60 to know how much and where to place treatment (and what types of treatment).
 
#455 ·

Quote:
Originally Posted by diomania /forum/post/21935291


One who tries to cast doubts about acoustic treatments and diminish their values in an attempt to bolster the sales of overpriced electronic audio gears he sells is the last one you want to pay attention to regarding this subject.

i can't wait to start my own audio company so i can go parading around photos of rooms and graphs and fancy charts to impress and court potential clients!
 
#456 ·

Quote:
Originally Posted by Ethan Winer /forum/post/21934302


Yes, of course, I meant an untreated small room. Even absorption makes music sound larger because, as I explained, the larger sound embedded in the music is no longer drowned out by the small-room ambience of the room.


--Ethan

the time-delay of the first significant indirect energy dictates the perceived acoustical size of the space. absorbing such first-order reflections delays in time until indirect energy impedes the listening position, increasing the perceived size of the acoustical space while the physical size does not alter.


a simple test anyone can do is to blindfold yourself and talk to yourself in your bathroom, and then do so in a much larger room.


if these guys think there is so much worthwhile "ambiance" in our home listening rooms, then why are recordings made in concert halls or expensive tracking rooms? someone should clue those studio guys in and let them know they could be saving a lot of money and still get excellent recordings and brilliant "ambiance" by recording in a living room!
 
#457 ·

Quote:
Originally Posted by amirm /forum/post/21931803


Importantly, his name and this project, are associated with a more acceptance of reflections relative to older approaches of removing them (LEDE, RFZ, etc).

you realize RFZ (which uses geometry to achieve a LEDE specular response) does not have any broadband absorption within the room, yes?


so how is RFZ "removing reflections"??
 
#458 ·
Amir, I scanned the thread again after your last post to me, I think you did answer my 'questions' better than I had recalled during it. It happens



I am glad we sorted the 'timing' thing..that we do agree on the basics..that timing per se is not handled by Eq (my only point of contention). Else we would not have those thread talking about slow bass!


Ok, definitely NOT blind so subject to all the vagaries we talk about ad nauseum here....very rough initial first impressions of putting up firszt reflection points...


Firstly, it IS subtle as I thought it might be, yet also (I think, not blind remember) one that can be determined.


I do need to back this up with measurements (eg, does a spike appear that was not there previously? ie a FR has been put in place) so I could end up with egg on my face
and of course needs to be done blind.


Contrary opinion first, the centre image seemed to be more firm with the reflection. That surprised me, yet bear in mind it is subtle and I could be fooling myself. But, that it is not what I expected might indicate a reality.


It is not what I prefer however, it came at the expense of expanse, and the term I'd use (rather than distort for example) is 'thickened'. It seemed to concentrate things toward the middle with lessened width (part of what I enjoy)...but that also could be due to bias, the thing I have been arguing against in this thread.


My preliminary thoughts? Prefer without it, but then again I'd only estimate maybe seventy percent confidence that what I am hearing is real. As I said, subtle. (tho on one track I am very confident I detected a distinct image shift, but then that too could be down to poor placement of the reflectors)


What I have to determine is whether or not it is worth the effort to go more rigorous with it...and as it seems I am only answering my own questions on it (ie no-one else seems interested enough to try) why bother.


And, that whatever the findings it would only apply to my room and my system, bigger fish to fry in audio is my gut reaction.
 
#459 ·

Quote:
Originally Posted by localhost127 /forum/post/21935275


why does modifying the source make a difference? are the speaker-room interactions changing based on what CD you are listening to?

I have no idea how this sentence relates to the statement I made. Perhaps you misread my post (the same way you misread my name)

Quote:
and it is funny for you to respond in this thread - as you first used absorption at sidewall reflection points and now use a absorber/diffuser combo! certainly NOT what amir thinks you should do. maybe you should take down the sidewall treatments and see how it sounds. it seems to go against what toole states, yet you seem to prefer the treatments on the sidewalls. the silence is deafening here -

To be more correct, I am currently using absorption and will be switching it for abfusion when it arrives. This will allow me to listen for myself the difference between absorption and diffusion - something I am now certain you have never done for yourself.


And I think you are completely misreading what Amir/Toole are saying. At this point I'm starting to believe that is willful.
 
#460 ·

Quote:
Originally Posted by Ethan Winer /forum/post/21934302


Yes, of course, I meant an untreated small room. Even absorption makes music sound larger because, as I explained, the larger sound embedded in the music is no longer drowned out by the small-room ambience of the room.


--Ethan

Oh sure, I agree with you - any room (even a furnished living space) can benefit from acoustic treatments. For me it's an absorption/reflection vs diffusion question, and at what locations and in what proportions. My opinion is that there is no "larger sound embedded in the music" for the majority of modern recordings - but that is only based on my own experiences.


As I said above, I'll be able to do somewhat of a comparison myself shortly, but your opinions are appreciated.


Cheers!
 
#461 ·

Quote:
Originally Posted by terry j /forum/post/21932508


I am often astounded what these guys can do with studio tricks! Sometimes I wonder if those things are accidental, but I can't imagine that to be true. Guys like Royksopp spring to mind...Have a listen to caribou swim if you want amazing envelopment etc, anything from trentemoller, the list goes on.


It might not be 'natural' ambience if you will, but strangely I think the LEV and ASW of quality studio electronic music to be tha greatest of all, by a wide margin.


Maybe it is the type oif music I listen to which gives me 'luck' and sways my opinion of how common it is, dunno.

I have no doubt you are hearing something pleasing, but I admit I am skeptical that it is what the artist specifically intended



I'm wondering - are there software tools that can synthesize a virtual space during the mastering phase?
 
#462 ·

Quote:
Originally Posted by kromkamp /forum/post/21936662


To be more correct, I am currently using absorption and will be switching it for abfusion when it arrives. This will allow me to listen for myself the difference between absorption and diffusion - something I am now certain you have never done for yourself.

i built my ~150lbs RPG diffusers on casters (as gobos) and also incorporated 4" oc703 on the rear side such that they could easily be moved around the room and spun around for absorption vs diffusion change. but i can assure you, im most certainly not here to impress you.


as for the abfusion? maybe you will like it, but im not interested in diffusers that do not offer temporal dispersion.
 
#463 ·
As promised, here is my summary post for this thread. A much more detailed article with more measurements, facts and references will follow. But for now, here is a quick primer.


At high level, the key thing that unlocked this mystery for me, and hopefully will do for you, is to understand some fundamental points about sound reproduction in our homes. Once you have that knowledge, it will then enable you to easily understand people's argument and a lens through which to evaluate them. Without it, you will be flailing in the wind. Here they are:


1. Sound behaves differently in your room depending on its frequency. Here is the opening graph and point in my article on low frequency optimization of your room :




As you see there is a critical band called the transition frequency. I won't get into how that is calculated but for now, assume it is in the 200 to 400 Hz range depending on the size and attributes of your room. Below that we have distinct patterns of reflections interacting with each other, creating very significant frequency response anomalies. Above that, the reflections become chaotic and how they interact with each other highly complex, resulting in very different impact on the frequency response of the speaker. In the middle, during the transition frequencies, a bit of both is going on.


2. Now look at the notations on the graph. To the left of transition frequency it says the room has the largest impact. Indeed it does. Massive frequency response variations exist due to so called room modes. You can change your speaker all you want and you will still get massive peaks and valleys as shown. Therefore, if there is one area that needs immediate attention, it is in that region! This is why the first installment of my articles on room acoustics started there. Get this region right and you are well on your way to good sound.


3. Below transition frequency, measurements tell the whole story. Psychoacoustics does not enter the equation. You see a 20 db peak at 50 Hz (for example)? You have a problem. There is no way that is not audible. And frequency response measurements tell you the exact problem you have. This is a great thing as we all understand frequency response graphs. It is the bible of high fidelity in audio. You want a flat response there.


4. As frequencies get lower, the effectiveness of acoustic products such as absorbers and diffusers goes down. So with some rare exceptions (such as tuned absorbers), you simply cannot think of solving those problems with putting acoustic material on the wall. Part of the solution is to have flexible walls that absorb energy. But much more powerful techniques exists with making the problem less severe by better placement of speakers/listeners, and deploying multiple subwoofers and electronic correction (both EQ and Sound Field Management). A detailed and high level view of that is covered in my article: http://www.madronadigital.com/Librar...imization.html


Note that if you have not done anything about your room's low frequency response, then you are guaranteed to have problems here. Get a mic and run a frequency sweep and be ready to be horrified!



So summarizing where we are so far, you need to optimize the low frequencies in your room and that optimization does not involve arguing about diffusion, vs absorption, vs first reflection, etc. All of that is for the next section, above the transition frequency.


5. So now we get to where the debate is: what happens above transition frequency. As you have seen, you can have 1000 page debates about this. But most of that is for not! Why? Look at the chart again: it says that the speaker is in control there. If you don't believe me, take two different speakers in your room. Do they sound different? Answer is obviously yes. So if you want good sound there, there is no getting around having a good speaker. Don't think you can start with a bad speaker and then by magic, there is some acoustic product that goes on the wall that fixes such things.


6. The sound that reaches you is a combination of reflections in the room and that of the direct sound of the speaker. Measuring the speaker in an acoustic chamber at one point in front gives the direct sound performance. If you augment that with many more measurements on horizontal and vertical axis, another view appears: what the reflections would sound like. After all, reflections are mostly made up of sounds going at a different angle than straight on sound of the speaker.


7. Turns out you can predict with high confidence what a speaker would sound like above transition frequency with the above measurements! Let me repeat: you can mostly predict what a speaker will sound like in real rooms from measurements you perform in an acoustic chamber. Indeed that is what Harman has demonstrated by measuring a large sampling of speakers and showing how their in-room response can be computed from a 70-point measurement in the acoustic chamber. The correlation is something like 90%.


So if you are a capable designer, you can design a speaker that behaves and works very well in a real room. And you can design what the sound should be like to be accurate. Accuracy there means a smooth frequency response as the angle of sound changes from dead on. Poorly performing speakers have wild response as the angle changes. Those poor reflections combine with direct sound and color the overall sound you hear. It has been said that this was the origins of the so called LEDE or Live-end, Dead-End room model and the strong emphasis to do away with strong reflections. They did have a problem to fix, but instead of fixing the problem (speaker), they thought it was the room that needed fixing. Thankfully we have come a long way in the last three decades when these models were developed and know how to build much better speakers that are no broken this way.


So take a listen to your speaker. Do you like how it sounds in the mid to high frequencies? If not, it is time for a new speaker. Don't go putting things on the wall hoping that is the path to better sound. Likely it is not and will cost you money fixing something that is better fixed in the source: the speaker.


8. This is another key point: above transition frequencies psychoacoustics enters the equation and there is no getting around it. Psychoacoustics says that what you measure is not what you are potentially hearing. If I take a 128 Kbps compressed music and run a measurement on it, I might find horrendous distortion figures at times. Yet, to listeners it is often similar sound to the CD. How often do you see various encoders compared using harmonic distortion (THD) figures? Never. What people do instead is perform listening tests.


The same is true here. We have two ears and a brain that is interpreting what is almost always two different signals. When the speaker sound goes sideways hits the refection on the right wall and comes to you, you hear two versions of it. The right ear is closer to it so it hears it earlier. The left ear hears is 0.4 msec later and with its frequency response changed due to your head masking some of the sound. The brain then attempts to interpret what it is hearing. You would go mad if that were two different sounds. Fortunately adaptation kicks in because we hear reflections all the time and we *interpret* what we are hearing. We do not at all see a single measurement as people post in these discussions.


So run, and run fast if all someone wants to talk about is showing you measurements above transition frequencies. Listening test results must accompany any such discussion. And then back correlation to why we perceive what we perceive.


How many singers do you know that like to sing outside where there are almost no reflections? Have you tried to sing yourself there? Fact is that some of these effects are totally non-intuitive. We think a reflection is a bad thing. But clearly no singer thinks that. I know it is hard to let go of these notions but let go we must.


9. As we have heavily discussed, there are arguments over reflections and tendency to want to follow the pros as far as mixing and recording rooms. Having worked for companies that sold products to this industry, I am telling you, they have different reasons and priorities than you do enjoying movie and music at home. A post would not be complete without a quote from Dr. Toole
. So here it is from his CEDIA Course:

Musicians who perform live tend to be hypersensitive to reflected sounds -

judging them to be as much as 7 times as large as ordinary listeners. Why?

Perhaps because in concert venues what they hear of themselves playing and of

their colleagues playing is substantially learned from reflected sounds coming

back to them from the audience area and from the stage house. Recording

engineers are unusually critical of early reflections in recording control rooms.

Why? Perhaps because adding and manipulating reflected sounds are

fundamental operations in the creation of a mix. They can turn reflections on or

off, up or down, and thereby learn to distinguish components of sound that they

are creating from those existing in the room. Not surprisingly, they want the room

sounds to go away. Interestingly enough, there is some evidence that these

same people like lateral reflections when listening for entertainment at home.


But neither of these is home theater, and these people are not our average

customers. When put to the test, most listeners prefer additional reflected

sounds in small rooms. Alarmist talk about reducing the precision of image

localizations have not been proved. The much touted comb filtering turns out

not to be an audible problem, unless it is in the program itself, which is certainly

not our problem. On the positive side, it turns out that reflections increase our

ability to hear timbral subtleties in the program.


About the only negative that can be raised against early lateral reflections is that

they will mercilessly reveal loudspeakers that have poor off-axis frequency

response. Over the years there have been lots of these, including some prime

examples in the studio monitor category. The best solution in these instances is

to absorb the off-axis misbehavior. This, in fact, became a bit of a fashion in the

dead end control rooms of a couple of decades ago. But, why start with bad

loudspeakers to begin with?



10. The next step is to determine how reflective our room is. While some reflections are good, there comes a limit after which intelligibility suffers. Fortunately, most well furnished rooms are where they need to be. I described the formal test for this which is an RT60 measurement around 500 Hz and getting a value of 0.4 to 0.6 sec range. But an approximation is to have someone stand by your speakers and talk to you in normal voice. Are you able to understand them? If so, you are probably good to go. If you have trouble, it is likely too live. The reason is that the human voice has slightly wider dispersion than a typical speaker. So if it sounds good, then a speaker is going to sound good.


An empty dedicated room is likely to need help in this regard. A well-furnished living room however is probably fine based on large scale research into this area (some 600 homes were surveyed). The reason is that the typical furnishings and items in a room such as carpets, bookshelves, furniture, drapes, etc. all contribute to bringing the reverberation time down to a comfortable and desirable level. Note that we are not trying to achieve precision here but to get us in the ballpark.


11. In a dedicated space the carpet can be an important element of bringing our reverberation time down. Ideally you would want to make that broadband by using the appropriate lay-up such as felt underlayment and the right carpet material. If we do the math based on the RT60 reverberation time mentioned before, you would need to cover 25%-30% of the rest of the surfaces with absorption material.


Such material should be broadband going all the way down to transition frequencies. Otherwise, you would be shaping the response of a good speaker by taking out its high frequency reflections and not low frequencies. So this usually calls for 4 inches of standard absorbers.


12. Location-wise, we want to put absorbers where they will be eliminating reflections we don't care about. A good choice here is front and back walls. The sound coming out the back of your speakers is going to have pretty poor response so doing away with it is a good thing. But importantly, we tend to prefer lateral, side-to-side reflections because that gives us more realism. Front to back reflections don't accomplish this because the much stronger direct sound from the speaker masks these reflections. So they become a good spot for absorbers.


Additional ones can go on the side walls as needed, avoiding the lateral reflection points which you may want to enhance with diffusers to increase that realism.


So how about we stop here and look at test case. In a parallel thread someone went on an adventure to measure his room and to apply treatment to it: http://www.avsforum.com/avs-vb/showthread.php?t=1401657


Here is a sample full frequency measurement:



What do we see? At 60 Hz the response peaks to 76 dB. At 20 Khz, the response is down to 37 dB. Put another way, his 20 to 20Khz frequency response varies by a whopping 40 dB!!! What happened to +- 3db that we often hear? Now maybe some of that is due to measurement errors. But even if I stop at 5 Khz, he has 20 dB fluctuations. That is hugely audible.


Second, we see the wild fluctuations in low frequencies as with the measurement I post at the beginning of this thread. Just the same, his high frequencies are much smoother. If you read the thread, you see that most of the discussion is around acoustic treatments. Well, he tried that. Here are his results with or without so called corner bass traps he built out of triangle fiberglass pieces:




Translation: it didn't make a darn bit of difference! Now you see why my low frequency optimization article does not even talk about using acoustic products. While they can be useful (especially in the hands of a pro), far more powerful tools are at our disposal. In this case OP has 4 subs already. So while better placement could be had than lining them up on the front wall as he has done, I am not going to suggest that he put more in there as he might throw a rock at me
. We can however use one of our other tools: EQ. If we had a parametric EQ, we could set it to the center frequencies of those peaks, adjust the bandwidth to match it, and then pull down that level. He has one of these for example a hair below 60 Hz.


If we did that we not only would reduce the boominess he is getting from that, but increased clarity and definition. This is because when we fix such resonances in frequency domain, transients in time domain take less time to settle down. Popular music has a rhythm of about 0.4 seconds. Room resonances cause reverberations that are longer than that, causing distinct bass notes to run into each other. Pull that peak down and you not only get smoother frequency response but also better definition.


I should note that you will lose some of your bass power. So there is a cost to it and you have to compensate with more powerful subs.


Now read the thread and tell me how much of this simple insight was shared. You will see very little of it. Instead, he is told to keep messing with acoustic products and pick up woodworking as another hobby to build them! As a fellow woodworker, I don't mind that advice but it really is not the right solution. He can pick up a cheap DSP box and put it in line with his subs and go to town there. If you are buying new subs yourself, look for ones with DSP built in. Even a single band EQ is of great help but may provide three of them which is quite sufficient to tame the low frequencies.


Throughout this thread and elsewhere, vocal opposition keeps talking about specular reflections and how you need ETC type analysis to find and fix them. Well, OP in that thread ran such an analysis. Here it is:




I ask you: what on earth does this tell you? Compare it to the frequency analysis I discussed above. Which is telling you the story better and what you need to do immediately to fix your room issues? Clearly it is the frequency response chart. So take Dr. Toole's advice and ignore these charts and techniques that are devoid of the frequency spectrums. Your ears can easily tell if you screw up the frequency response. Time domain however is subject of psychoacoustics and not so easily analyzed.


Well, here it is
. Now you have some of the high level points, I suggest buying Dr. Toole's book and digging deep. It will all make much more sense now than if you had read it cold. And oh, read it multiple times. The more you learn, the more you pick up on the finer points.
 
#464 ·

Quote:
Originally Posted by localhost127 /forum/post/21936960


i built my ~150lbs RPG diffusers on casters (as gobos) and also incorporated 4" oc703 on the rear side such that they could easily be moved around the room and spun around for absorption vs diffusion change. but i can assure you, im most certainly not here to impress you.


as for the abfusion? maybe you will like it, but im not interested in diffusers that do not offer temporal dispersion.

So, even if you space those away from the wall, the massive diffusers will look like a new wall behind the fiberglass - effectively giving you only 4" of treatment, rather than the 8" you continually advise. You aren't even following your own recommendations!


You're right - that isn't impressive



What does temporal diffusion sound like?
 
#466 ·

Quote:
Originally Posted by hd_newbie /forum/post/21938308


That summary seems to need a "summary"

He already made it on page 2 of this thread:
Quote:
Originally Posted by amirm /forum/post/21857938


Honestly guys, you are not going to get to the truth here by glancing at stuff post on forums. You either need to bite the bullet and spend good bit of time reading expert's writings such as Dr. Toole above, hire an expert, or do nothing. Doing something *can* make things worse. Do not let folks guilt you into putting stuff on your wall and don't use your intuition of something sounding like it would work (like all the talk of absorbing reflections). They are both liable to get you in the ditch more than helping you
. And cost you money to boot. The real data is much more complex and not understanding it at least to a proper level can be problematic.
 
#467 ·

Quote:
Originally Posted by kromkamp /forum/post/21936698


I have no doubt you are hearing something pleasing, but I admit I am skeptical that it is what the artist specifically intended



I'm wondering - are there software tools that can synthesize a virtual space during the mastering phase?

You are 'right', I have so many times wondered that exact same thing (was THAT effect intended or did it somehow 'just happen?')


Obviously I don't have a definitive answer on that, but I tend towards intended more often than not for a couple of reasons-none of which have any basis of knowledge on my part I must add
.


The types of things I have in mind that 'show' intent is that 'this instrument in this track which is coming towards me and then swooping off to the left' is only that instrument if you follow me. If it were somehow a psychoacoustic phenomenon brought about because of some FR anomaly (as an example of system induced effect) then it would always happen when those frequencies were excited. But no, that is not what you hear. The rest of the track stays stable with clearly defined depths and positions across the soundstage, yet floating upon it is this effect on this one instrument/melody line.


It could be in the mids, treble or bass depending on what is being listened to.


Fascinating stuff. I am also sure a lot of it is phase based (??) so to realise what is on the recording requires the speakers to be able to decode it, and there are many instances where it is not decoded.


Amir, just a quick comment on you qucik comment (
), yes there may have been a lot of discussion about thinsg above the transition frequency, but I think you have been very unfair to 'dsimiss' *our* thoughts on the bass region by implying *we* ignore it, I don't think you will find anyone of us disagrees with your comments about the need for smooth bass or that it IS the most problematic area and one that is vital to get right. It is not called the 'foundation' of music for no reason.
 
#469 ·

Quote:
Originally Posted by amirm /forum/post/21937322


1. Sound behaves differently in your room depending on its frequency. Here is the opening graph and point in my article on low frequency optimization of your room :




As you see there is a critical band called the transition frequency. I won’t get into how that is calculated but for now, assume it is in the 200 to 400 Hz range depending on the size and attributes of your room.
constructive criticism - i'd highly recommend at least detailing how the sound behavior is different "depending on its frequency", versus merely saying it is different and not refining any further.


i would also detail how schroeder cut-off frequency is calculated and determined, as i think there is a sub-set of users out there who may be interested in such information.


it may also be beneficial to label the two regions (modal and specular), vs confusing labels like "room" and "speaker".

Quote:
Originally Posted by amirm /forum/post/21937322


Below that we have distinct patterns of reflections interacting with each other, creating very significant frequency response anomalies. Above that, the reflections become chaotic and how they interact with each other highly complex, resulting in very different impact on the frequency response of the speaker. In the middle, during the transition frequencies, a bit of both is going on.
constructive criticism - i would refine the commentary to note that the frequency response impact does not change based on whether the energy is in the modal or specular region. all wavelengths sum at the listening position in 3space to give you the local variable pressure with respect to the ambient noise floor. superposition in the modal region is no different than superposition in the specular region. constructive and destructive acoustical interference are common.


Quote:
Originally Posted by amirm /forum/post/21937322


2. Now look at the notations on the graph. To the left of transition frequency it says the room has the largest impact. Indeed it does.
constructive criticism - i wouldn't imply a statement or fact based on how a graph is labeled. just because a graph is labeled "room has largest impact" does not make it so. this is a wording issue and easily corrected.

Quote:
Originally Posted by amirm /forum/post/21937322

Massive frequency response variations exist due to so called “room modes.” You can change your speaker all you want and you will still get massive peaks and valleys as shown. Therefore, if there is one area that needs immediate attention, it is in that region! This is why the first installment of my articles on room acoustics started there. Get this region right and you are well on your way to good sound.
constructive criticism - massive frequency response variations exist due to constructive and destructive acoustical interference (polar lobing), SBIR phasors, and room modes (resonances). but the summation (superposition) of two or more signals to create a frequency response anomaly (interference pattern) does NOT automatically imply a room mode. a room mode is a resonance. as it exists, this arrangement of vocabulary may be confusing to the reader and give a false impression that any acoustical interference is solely due to a room mode.

Quote:
Originally Posted by amirm /forum/post/21937322


3. Below transition frequency, measurements tell the whole story. Psychoacoustics does not enter the equation. You see a 20 db peak at 50 Hz (for example)? You have a problem. There is no way that is not audible. And frequency response measurements tell you the exact problem you have. This is a great thing as we all understand frequency response graphs. It is the bible of high fidelity in audio. You want a flat response there.
constructive criticism - since the modal region will have drastic varying decay times (due to inherent energy of the longer wavelengths and contributions via modal ringing (room modes/resonances), a reference to the waterfall plot is really required here to see not just the frequency response, but the LF decay times as well.


i would add and refine that you want not just "a flat response there" --- but low and even decay times in the modal region as well (hence, waterfall plots are the relevant measurement here to provide such information).

Quote:
Originally Posted by amirm /forum/post/21937322


4. As frequencies get lower, the effectiveness of acoustic products such as absorbers and diffusers goes down. So with some rare exceptions (such as tuned absorbers), you simply cannot think of solving those problems with putting acoustic material on the wall.
constructive criticism - this is a poor assumption at best. what could be better said is, as frequencies get lower, the treatment (eg, absorbers or diffusers) must be designed with respect to the longer wavelengths in order to maintain effectiveness. a diffuser does not become less effective at lower frequencies unless it was not designed for the lower frequencies. you can't blame physics for this, as this is a design problem with respect to the absorber or diffuser. such treatments can be refined based on a particular set of design requirements.


i would modify your statements to say that tuned/resonate pressure-based absorbers are most certainly not a rare exception in the real world, but merely here at the AVS forums where the bulk of the users rely solely on porous, velocity-based absorption.


Quote:
Originally Posted by amirm /forum/post/21937322


Part of the solution is to have flexible walls that absorb energy.
constructive criticism - this needs to be refined such that the primary problem with this is that you need to understand the complex acoustical impedance of the boundary such that it is not modifying the spectral content of the specular region bandwidth (regardless of the modal region). i would go into more detail regarding wall construction and provide some further documentation (BBC and NRC have some solid foundational documents that are highly common within the acoustic community that would be very beneficial to the audience and thus, would be wise to be linked to here).


Quote:
Originally Posted by amirm /forum/post/21937322


But much more powerful techniques exists with making the problem less severe by better placement of speakers/listeners, and deploying multiple subwoofers and electronic correction (both EQ and Sound Field Management).
constructive criticism - i would refine on the EQ solution and note that EQ is only relevant for minimum phase issues; and you may wish to go into further detail with respect to what this means vs that of non-minimum phase issues and how they cannot be EQ'd.


and note to the audience that speaker/listener placement is already and has been commonly recommended by insisting that the user obtain measurement equipment such that they can move the LF driver(s) and speaker position into an area of less acoustical interference. eg, find the best "starting point" locations in 3space, as that is essentially a "free lunch" increase in acoustical response.

Quote:
Originally Posted by amirm /forum/post/21937322


So summarizing where we are so far, you need to optimize the low frequencies in your room and that optimization does not involve arguing about diffusion, vs absorption, vs first reflection, etc. All of that is for the next section, above the transition frequency.
constructive criticism - you do not have an audience that is under the assumption that LF/modal region should not be optimized. no one here is debating otherwise so there is little reason to waste commentary on a topic that has no contention.



Quote:
Originally Posted by amirm /forum/post/21937322


5. So now we get to where the debate is: what happens above transition frequency. As you have seen, you can have 1000 page debates about this. But most of that is for not! Why? Look at the chart again: it says that the speaker is in control there. If you don’t believe me, take two different speakers in your room. Do they sound different? Answer is obviously yes. So if you want good sound there, there is no getting around having a good speaker. Don’t think you can start with a bad speaker and then by magic, there is some acoustic product that goes on the wall that fixes such things.
constructive criticism - logical fallacy. you cannot determine (as in the two-speaker test) whether it is a speaker-room interaction issue or speaker alone issue. you say that if you want good sound to get a good speaker, but a room can impart a poor response at the listening position based on any speaker design. a proper speaker cannot save or eliminate the issues of a bad room.


Quote:
Originally Posted by amirm /forum/post/21937322


6. The sound that reaches you is a combination of reflections in the room and that of the direct sound of the speaker. Measuring the speaker in an acoustic chamber at one point in front gives the direct sound performance. If you augment that with many more measurements on horizontal and vertical axis, another view appears: what the reflections would sound like. After all, reflections are mostly made up of sounds going at a different angle than straight on sound of the speaker.
constructive criticism - i'd go into more detail with respect to the types of reflections. their gain, arrival time, sparse, dense/dense-diffused, etc. and what happens as N-order reflection increases.


Quote:
Originally Posted by amirm /forum/post/21937322


7. Turns out you can predict with high confidence what a speaker would sound like above transition frequency with the above measurements! Let me repeat: you can mostly predict what a speaker will sound like in real rooms from measurements you perform in an acoustic chamber. Indeed that is what Harman has demonstrated by measuring a large sampling of speakers and showing how their in-room response can be computed from a 70-point measurement in the acoustic chamber. The correlation is something like 90%.
constructive criticism - i would reiterate that no speaker can solely eliminate the issues of a bad room.


Quote:
Originally Posted by amirm /forum/post/21937322


Poorly performing speakers have wild response as the angle changes. Those poor reflections combine with direct sound and color the overall sound you hear.
constructive criticism - following on your logic about poor reflections coloring the overall sound you hear, you would want to note that a solution to address such "poor reflections" is to attenuate them (eg, with absorption or redirection at those reflection points).



Quote:
Originally Posted by amirm /forum/post/21937322


It has been said that this was the origins of the so called LEDE or Live-end, Dead-End room model and the strong emphasis to do away with strong reflections. They did have a problem to fix, but instead of fixing the problem (speaker), they thought it was the room that needed fixing. Thankfully we have come a long way in the last three decades when these models were developed and know how to build much better speakers that are no broken this way.
constructive criticism - logical fallacy. while there were inherent issues with speaker technology at the time-period of the development of such control room acoustic models, the room's specular and psycho-acoustic response foundations do not change with the advent of better performing speakers. as such, control rooms are still relevant today for maintaining a neutral environment of which critical mixing and mastering decisions can be made such that they will translate into a variety of acoustical setups, rooms, and environments. i would elaborate that better performing speakers did not eliminate the need for a neutral control room based on said acoustic model. clarity needs to be communicated that a good speaker and a good control room model are not mutually exclusive.


Quote:
Originally Posted by amirm /forum/post/21937322


So take a listen to your speaker. Do you like how it sounds in the mid to high frequencies? If not, it is time for a new speaker. Don’t go putting things on the wall hoping that is the path to better sound. Likely it is not and will cost you money fixing something that is better fixed in the source: the speaker.
constructive criticism - unfortunately, one simply not "preferring" the mid-HF specular band does not imply with absolute confidence that the speaker is the problem. the room could be imposing non-preferred acoustical destructive interference of which gives the perceived notion that there is a problem. i would clarify your statements and add that one should not "blindly" "put things on the wall hoping that is the path to better sound", but that one would need to measure and identify the ACTUAL boundaries incident of such problematic destructive acoustical interference before making a decision as to the best solution to address such issues. it would also be beneficial to note that the user can quickly experiment with such room modifications by utilizing thick blankets to function as ad-hoc absorbers at such specular reflection points to see if they notice any increase in perceived acoustical quality of the reproduction space. this is a free experiment, and while not the ideal treatment - if there is a perceived benefit then proper bandwidth absorbers will only perform even better.


this is a free and easy experiment as there are many who are not able to simply run out and replace their speakers with better performing models...

Quote:
Originally Posted by amirm /forum/post/21937322


8. This is another key point: above transition frequencies psychoacoustics enters the equation and there is no getting around it. Psychoacoustics says that what you measure is not what you are potentially hearing. If I take a 128 Kbps compressed music and run a measurement on it, I might find horrendous distortion figures at times. Yet, to listeners it is often similar sound to the CD. How often do you see various encoders compared using harmonic distortion (THD) figures? Never. What people do instead is perform listening tests.
constructive criticism - i would remove this paragraph entirely as it is not clear as to what a listening test with respect to compressed sources has to do with psycho-acoustics.


Quote:
Originally Posted by amirm /forum/post/21937322


The same is true here. We have two ears and a brain that is interpreting what is almost always two different signals. When the speaker sound goes sideways hits the refection on the right wall and comes to you, you hear two versions of it. The right ear is closer to it so it hears it earlier. The left ear hears is 0.4 msec later and with its frequency response changed due to your head masking some of the sound. The brain then attempts to interpret what it is hearing. You would go mad if that were two different sounds. Fortunately adaptation kicks in because we hear reflections all the time and we *interpret* what we are hearing. We do not at all see a single measurement as people post in these discussions.
constructive critisim - you should go into detail of what the haas interval is and the psycho-acoustics of such gain and time-arrival of indirect specular energies and how we "interpret what we are hearing".


Quote:
Originally Posted by amirm /forum/post/21937322


How many singers do you know that like to sing outside where there are almost no reflections? Have you tried to sing yourself there? Fact is that some of these effects are totally non-intuitive. We think a reflection is a bad thing. But clearly no singer thinks that. I know it is hard to let go of these notions but let go we must.
constructive critisim - not how things are done in the real world. a quick and effortless way to track vocals is to construct a highly damped vocal booth. if the signer is singing against a reflective boundary, then you will have a mirror-copy of the signal being recorded by the mic at a slightly later time-arrival. the signer's reflection will also be high in gain which will cause the mic to record the comb-filter interference pattern based on the summation (superposition) of the direct and indirect signals.


Quote:
Originally Posted by amirm /forum/post/21937322


9. As we have heavily discussed, there are arguments over reflections and tendency to want to follow the “pros” as far as mixing and recording rooms. Having worked for companies that sold products to this industry, I am telling you, they have different reasons and priorities than you do enjoying movie and music at home. A post would not be complete without a quote from Dr. Toole
. So here it is from his CEDIA Course:

” Musicians who perform live tend to be hypersensitive to reflected sounds –

judging them to be as much as 7 times as large as ordinary listeners. Why?

Perhaps because in concert venues what they hear of themselves playing and of

their colleagues playing is substantially learned from reflected sounds coming

back to them from the audience area and from the stage house. Recording

engineers are unusually critical of early reflections in recording control rooms.

Why? Perhaps because adding and manipulating reflected sounds are

fundamental operations in the creation of a mix. They can turn reflections on or

off, up or down, and thereby learn to distinguish components of sound that they

are creating from those existing in the room. Not surprisingly, they want the room

sounds to go away. Interestingly enough, there is some evidence that these

same people like lateral reflections when listening for entertainment at home.


But neither of these is home theater, and these people are not our average

customers. When put to the test, most listeners prefer additional reflected

sounds in small rooms. Alarmist talk about reducing the precision of image

localizations have not been proved. The much touted “comb filtering” turns out

not to be an audible problem, unless it is in the program itself, which is certainly

not our problem.
constructive criticism - logic inconsistency. above, you indicate that the singer should not be in a free-field space but instead one where reflections are present. unfortunately, such high-gain reflections cause severe constructive and destructive interference known as a comb-filter interference pattern within the frequency response in the recording. toole here states that comb-filtering is not an audible problem unless it is in the source material - and with your above recommendation, there would be comb-filtering within the source material. i would modify the statements above to note that signers tracking vocals in damped rooms are common and a very inexpensive way to efficiently and accurately record vocals.


i would also note that here, toole refers to them as "average customers" --- is your audience an average customer or a more refined, (educated with respect to sound) customer? who is the target audience?


Quote:
Originally Posted by amirm /forum/post/21937322

About the only negative that can be raised against early lateral reflections is that

they will mercilessly reveal loudspeakers that have poor off-axis frequency

response
. Over the years there have been lots of these, including some prime

examples in the studio monitor category. The best solution in these instances is

to absorb the off-axis misbehavior.
This, in fact, became a bit of a fashion in the

“dead end” control rooms of a couple of decades ago. But, why start with bad

loudspeakers to begin with?”[/i]
constructive criticism - i would add commentary to note that the majority of consumer speakers out there have poor off-axis response and thus, the majority would require room modification to account for such speaker issues - explicitly as toole states (and also referring to the OP). it may also be beneficial to note that the majority of consumer speakers also do not even provide objective measurements with respect to the polar radiation/off-axis plots such that the user has the information to make an informed decision on whether or not the speaker is a good performer or not (and thus, whether or not they need to absorb the "poor reflections" as indicated by toole).


i would also remove toole's commentary with respect to LEDE, as it is a simplified and highly non-descriptive account of what that particular studio model attempts to accomplish. anyone reading your article who does have a understanding of LEDE might take a negative impression from the integrity of the article based on such misinformed commentary.



Quote:
Originally Posted by amirm /forum/post/21937322


10. The next step is to determine how reflective our room is. While some reflections are good, there comes a limit after which intelligibility suffers. Fortunately, most well furnished rooms are where they need to be. I described the formal test for this which is an RT60 measurement around 500 Hz and getting a value of 0.4 to 0.6 sec range. But an approximation is to have someone stand by your speakers and talk to you in normal voice. Are you able to understand them? If so, you are probably good to go. If you have trouble, it is likely too live. The reason is that the human voice has slightly wider dispersion than a typical speaker. So if it sounds good, then a speaker is going to sound good.
constructive criticism - i would note that the human mouth, while having wide dispersion, does not have such well behaved off-axis response throughout the frequency range as would a good performing speaker. this test should not be put forth as a credible alternative to testing intelligibility of the source from a speaker.


i think it would also be beneficial here to go more in depth with respect to what types of reflections are beneficial to intelligibility and which types may be detrimental to intelligibility.


Quote:
Originally Posted by amirm /forum/post/21937322


11. In a dedicated space the carpet can be an important element of bringing our reverberation time down. Ideally you would want to make that broadband by using the appropriate lay-up such as felt underlayment and the right carpet material. If we do the math based on the RT60 reverberation time mentioned before, you would need to cover 25%-30% of the rest of the surfaces with absorption material.


Such material should be broadband going all the way down to transition frequencies. Otherwise, you would be shaping the response of a good speaker by taking out its high frequency reflections and not low frequencies. So this usually calls for 4 inches of standard absorbers.
constructive criticism - logical inconsistency. above, you recommend carpet being used and to make it broadband by using under-layment and the right carpet material, but in the following paragraph you state that such a requirement usually calls for 4" of standard absorbers. i would refine whether such a requirement applies to the floor and whether the carpet does indeed require 4" thickness as with the absorbers.

Quote:
Originally Posted by amirm /forum/post/21937322


12. Location-wise, we want to put absorbers where they will be eliminating reflections we don’t care about. A good choice here is front and back walls. The sound coming out the back of your speakers is going to have pretty poor response so doing away with it is a good thing. But importantly, we tend to prefer lateral, side-to-side reflections because that gives us more realism. Front to back reflections don’t accomplish this because the much stronger direct sound from the speaker masks these reflections. So they become a good spot for absorbers.
constructive critisim - i would again note here what toole stated about absorbing "poor reflections" with respect to speakers with bad off-axis response. i would refine your commentary to include the particular type of speaker required for your recommendation to only absorb front and rear wall reflections. i think it would also be beneficial to go into detail for the audience the particular measurement tool used to identify exactly where the front and rear reflection points are.

Quote:
Originally Posted by amirm /forum/post/21937322


Additional ones can go on the side walls as needed, avoiding the lateral reflection points which you may want to enhance with diffusers to increase that realism.
constructive critisism - i would reiterate again here what toole has stated with regards to the treatment being broadband and not altering the spectral content of the reflection. i would advise that the audience understand that this is based on physics and that the diffusers must be large with respect to wavelength of the lower schroeder cut-off frequency. as such, applying "diffusers to increase that realism" will require that they be large and deep. this may not be an option for a majority of average customers in your target audience.

Quote:
Originally Posted by amirm /forum/post/21937322


So how about we stop here and look at test case.


If you read the thread, you see that most of the discussion is around acoustic treatments. Well, he tried that. Here are his results with or without so called corner bass traps he built out of triangle fiberglass pieces:




Translation: it didn’t make a darn bit of difference! Now you see why my low frequency optimization article does not even talk about using acoustic products. While they can be useful (especially in the hands of a pro), far more powerful tools are at our disposal.
constructive critisim - logical fallacy and deception. you are taking a poor and insufficient example of the application of porous insulation for LF absorption and attempting to imply that this example alone dictates that such absorption is ineffective. such deception is obvious and may degrade the integrity of the rest of your commentary within this article.


i would also link to some examples of pressure-based resonate absorbers, as those are highly effective at attenuating even down to the lowest octaves of the modal region.



Quote:
Originally Posted by amirm /forum/post/21937322


If we did that we not only would reduce the boominess he is getting from that, but increased clarity and definition. This is because when we fix such resonances in frequency domain, transients in time domain take less time to settle down. Popular music has a rhythm of about 0.4 seconds. Room resonances cause reverberations that are longer than that, causing distinct bass notes to run into each other. Pull that peak down and you not only get smoother frequency response but also better definition.
constructive critisim - i would note that "reverberation" at 80hz would require ~35,000f^3 acoustical space and as such, reverberation is not the right vocabulary for what you are attempting to describe. and that the rate-of-decay of the room mode is not altered in such a scenario. the direct signal modification will not alter the acoustical behavior of the room that dictates such room modes.

Quote:
Originally Posted by amirm /forum/post/21937322


Now read the thread and tell me how much of this simple insight was shared. You will see very little of it. Instead, he is told to keep messing with acoustic products and pick up woodworking as another hobby to build them! As a fellow woodworker, I don’t mind that advice but it really is not the right solution. He can pick up a cheap DSP box and put it in line with his subs and go to town there. If you are buying new subs yourself, look for ones with DSP built in. Even a single band EQ is of great help but may provide three of them which is quite sufficient to tame the low frequencies.
constructive critisim - refine this as it is a bit unprofessional commentary within this article to be utilized for marketing purposes.

Quote:
Originally Posted by amirm /forum/post/21937322


Throughout this thread and elsewhere, vocal opposition keeps talking about “specular reflections” and how you need ETC type analysis to find and fix them. Well, OP in that thread ran such an analysis. Here it is:




I ask you: what on earth does this tell you?
constructive criticism - i would note here that the ETC displays the ACTUAL destructive interference of the acoustical space. most importantly, is the appearance of an issue with edge diffraction either from the speaker cabinet itself (indicating poor speaker/cabinet design), or a speaker-room interaction (reflection of specular energy) that has a path length of less than 6inches of the direct signal. there are also some obvious high-gain reflections that have less than 2-3ft path length differences with respect to the direct signal. so either the speaker is placed very close to a boundary, or there are physical objects within the speaker path that are inducing very high-gain indirect energies. and if the energy is from edge diffraction or reflection from small objects within the room, then there is obviously spectral changes in those reflections of which toole dictates would not be good reflections. i would go into detail for the audience how one could utilize the information provided within the ETC response to identify the boundary or source of indirect energy and take action to mitigate such high-gain indirect specially-altered energies from impeding the listening position.


edge diffraction from speaker/cabinet indicates a poor speaker choice and the ETC will clearly show this indirect early arriving energy.

Quote:
Originally Posted by amirm /forum/post/21937322


Well, here it is
. Now you have some of the high level points, I suggest buying Dr. Toole’s book and digging deep. It will all make much more sense now than if you had read it cold. And oh, read it multiple times. The more you learn, the more you pick up on the finer points.

i hope you found my editorial comments informative. free of charge
 
#470 ·

Quote:
Originally Posted by kromkamp /forum/post/21937706


So, even if you space those away from the wall, the massive diffusers will look like a new wall behind the fiberglass - effectively giving you only 4" of treatment, rather than the 8" you continually advise. You aren't even following your own recommendations!

the psychological problem you are displaying is that you are attempting to assume exactly what and how i am performing such tests within my room. i will give you another day or so to re-evaluate your previous statement to see if you have the acoustical knowledge to acknowledge why your assumption above is invalid.
 
#471 ·

Quote:
Originally Posted by localhost127 /forum/post/21939319


it may also be beneficial to label the two regions (modal and specular), vs confusing labels like "room" and "speaker".

The graph came from Allan Devantier. You probably don't know him but he is one of the top researchers at Harman, working with Dr. Toole among other. You can see his name on the graph (see top right). Dr. Toole also has his version of it:




The labels accurately reflect the fact that if you take a speaker and put it in two different rooms, by far the most impact on its response is on the left-hand side. Dr. Toole shows these measurements in this book. As noted, the right hand can actually be controlled when the speaker is designed. So in that sense, we can factor out the room for the most part.

Quote:
i hope you found my editorial comments informative. free of charge

I have to apologize for ignoring the rest of your post after the first paragraph based on the point above. As I said, that picture is the heart of the matter. Unless you internalize that and accept it, the rest is for not. You will be lost without a compass in the wilderness.
 
#472 ·

Quote:
Originally Posted by terry j /forum/post/21938788


Amir, just a quick comment on you qucik comment (
), yes there may have been a lot of discussion about thinsg above the transition frequency, but I think you have been very unfair to 'dsimiss' *our* thoughts on the bass region by implying *we* ignore it, I don't think you will find anyone of us disagrees with your comments about the need for smooth bass or that it IS the most problematic area and one that is vital to get right. It is not called the 'foundation' of music for no reason.

The point is stronger than not ignoring it Terry. If you have a good speaker and you smooth out the low frequency response, you are essentially done. It is that important. It may be the whole game.


To wit, for my new theater my starting point is absolutely there. I just bought a JBL Synthesis SDEC-4500 processor/EQ and paired with two subs. I don't have a single bit of room acoustic material. It simply is not the priority to mess with that region until the low frequencies are taken care of. It is that important to the success of a room.


Think of your own experience of how subtle the room treatment effects are. That is also the point Dr. Toole made that in stereo and especially multi-channel, reflections get dwarfed by the overall experience. Not so with low frequencies. If you have 20 dB swings, it is not going to sound good.


Everyone should make it a priority especially since it is so easy to investigate.
 
#473 ·
one more time,

Quote:
Originally Posted by amirm /forum/post/21931803


Importantly, his name and this project, are associated with a more acceptance of reflections relative to older approaches of removing them (LEDE, RFZ, etc).

you realize RFZ (which uses geometry to achieve a LEDE specular response) does not have any broadband absorption within the room, yes?


so how is RFZ "removing reflections"??
 
#474 ·

Quote:
Originally Posted by amirm /forum/post/21939438


The graph came from Allan Devantier. You probably don't know him but he is one of the top researchers at Harman, working with Dr. Toole among other. You can see his name on the graph (see top right). Dr. Toole also has his version of it:




The labels accurately reflect the fact that if you take a speaker and put it in two different rooms, by far the most impact on its response is on the left-hand side. Dr. Toole shows these measurements in this book. As noted, the right hand can actually be controlled when the speaker is designed. So in that sense, we can factor out the room for the most part.

so do you understand the fundamental behaviors of acoustical energy with respect to the modal and specular region?

your original statement: "1. Sound behaves differently in your room depending on its frequency." --- then you refrain from actually detailing how the behavior differs??


it's funny that you quote harman and still no schroeder documentation - you know, the guy who is somewhat responsible for a lot of this ...


Quote:
Originally Posted by amirm /forum/post/21939438


I have to apologize for ignoring the rest of your post after the first paragraph based on the point above. As I said, that picture is the heart of the matter. Unless you internalize that and accept it, the rest is for not. You will be lost without a compass in the wilderness.

to dance, to deflect, ... to be corrected!
 
#475 ·

Quote:
Originally Posted by amirm /forum/post/21939468


The point is stronger than not ignoring it Terry. If you have a good speaker and you smooth out the low frequency response, you are essentially done. It is that important. It may be the whole game.

Aw man, no-one can win with you eh.


NONE of *us* would for one second ignore the bass region. It is imperative. It must be done if you want any chance of quality sound.


Completely a given. No argument. It would be the single most important thing a person could do.


You, I feel, have been the only one arguing that point. We just accept it and move on to the discussion at hand. And YES, it may be the whole ball game, the improvements are that significant and important.


We accept fully that Toole is correct when he says that a normally furnished living room can give more than accpetable results. There are millions around the world who are completely happy with the sound they have from their living room. Who is disputing that point?


However, rarely would any of them start a thread wondering how they might be able to IMPROVE that experience. We are not talkinf to the dumb masses, few of which would want or feel they need a Mark Levinson monster amp to take them that 1/10 of a percentage point towards better sound.

Quote:
To wit, for my new theater my starting point is absolutely there. I just bought a JBL Synthesis SDEC-4500 processor/EQ and paired with two subs. I don't have a single bit of room acoustic material. It simply is not the priority to mess with that region until the low frequencies are taken care of. It is that important to the success of a room.

Preaching to the converted amir, I have four 18's covering my bass needs, distributed thru the room, fully eq'd as well as phase and time aligned. I can match your in room graph and raise you a few


Quote:
Think of your own experience of how subtle the room treatment effects are. That is also the point Dr. Toole made that in stereo and especially multi-channel, reflections get dwarfed by the overall experience. Not so with low frequencies. If you have 20 dB swings, it is not going to sound good.

Of course, you are talking to me who has his bass sorted. If you are now defining the question to 'what do you do first, smooth accurate bass or treating the 'speaker region' I say go the bass. First, last and always (great album btw)


In any case, you have misremembered or misread me. I have NEVER said my room treatment is subtle!! I have made it abundantly clear I would never be without it.


I have wondered if the first reflection point is subtle however, so please don't muddy the waters.


IF all we need is to sort the bass, why then do you have your Keith Yates designed room? I am no longer sure exactly what you are arguing, if it is 'leave open the possibility that sidewall reflections are more benign than often thought' then great. I for one, well the only one it seems, was intrigued enough to find out for myself.


Yet you seem to now be going further, 'just fix the bass'. Yes, fantastic massively worthwhile improvements, no-one here thinks otherwise. But, on top of nthat, you CAN go further (even if only applicable to 0.001% of the listening public) and that WILL involve treatments.

Quote:
Everyone should make it a priority especially since it is so easy to investigate.

Indeed, glad you are retracting your 'expensive experiment' argument on this stuff. I just happened to use raw f/glass batts, others can use a spare mattress, very heavy drapes or multiple blankets for the job.


As it is ultimately a personal reaction and preference, they can (if they wish...gasp...) even go as far as trying etc for themselves and make their own mind up.


Quote:
Why? Look at the chart again: it says that the speaker is in control there. If you don't believe me, take two different speakers in your room. Do they sound different? Answer is obviously yes.

What about the flip side of your 'proof'? Take the same speakers and put them in different rooms, do they sound the same? The answer is obviously no.


What is different? It can't be the speakers can it, hence it must be the room.
 
#476 ·

Quote:
Originally Posted by localhost127 /forum/post/21939538


you realize RFZ (which uses geometry to achieve a LEDE specular response) does not have any broadband absorption within the room, yes?

RFZ stands for "Reflection Free Zone." How that is achieved, is varied. From AES Paper, THE RFZ/RPG APPROACH TO CONTROL ROOM MONITORING

by PETER D'ANTONIO and JOHN H. KONNERT

"A design for implementing a LEDE control room is proposed. The dead end is achieved by creating an RFZ by flush mounting the monitors as close to a trihedral corner as is physically possible and splaying the absorbent side walls and ceiling to minimize interfering reflections at the mix position. "


From AES paper, Controlling Early Reflections Using Diffusion by

JAMES A S ANGUS


"1.1 Reflection free zones

[...]What is required is a means of making the sound from the loudspeakers appear as if it is coming from a larger space by suppressing the early reflections from the nearby walls, as shown in figure 3....The idea is simple, by absorbing, or reflecting away, the first reflections from all walls except the furthest one away from the speakers the initial time delay gap is maximised."


From AES paper, AUDIO CONTROL ROOM DESIGN by Lindy Oekker, Sontron Instruments, Oakleigh, Victoria, Australia:.

"Early reflections in the control room are controlled with absorption and room geometry, the aim being to create a reflection free zone at the primary listening position."

Quote:
so how is RFZ "removing reflections"??

See above. The aims is 100% what I said which is the fear of reflections being harmful and attempting to do away with it using various means.
 
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