Mitchibo

Mitchibo

Audioholic
Well then, I'll try to keep things 'sweet' for you.... :D But believe me, if I could shorten these responses I would! (but it's all condensed info coming from a 500p book)

As for frequency vs amplitude with phase as opposed to waterfall, that is information I am sharing from Floyd Toole's 'Sound Reproduction'. Floyd goes in to it a bit in his CIRMMT video on youtube. But the compromise between frequency vs time is the issue, and can give misleading information that would be wrongly used to input DSP corrections with.

Back to your RT comment: "Voices and musical instruments have limited sound power output, so (concert) halls are kept as reflective as possible to keep loudness high, without interfering with 'intelligibility' of the music. It is a difficult compromise. Typical values for RT in performance venues are in the range of 1-2 seconds, optimized for the music most commonly performed... In sound reproduction, the essential hall reverberation is captured in the recording, so nothing additional is required. Typical RT for domestic listening rooms and recording control rooms are 0.2-0.4 seconds. The reverberation in classical recordings completely overpowers that of the listening room." Pg 281 'Sound Reproduction 3rd Edition'

Point being that RT is not often an issue in small rooms. Understanding the transition frequency is much more important to identifying and treating the naturally occurring room modes or standing waves resulting from the parallel surfaces of your home. As you pointed out, the energy from the first reflection doesn't just dissipate, it keeps bouncing, creating higher order modes that are higher in frequency than the originating modal frequency. That is why I don't recommend adding DSP filters without predicting and verifying room modes, first, due to the near guarantee of unknowingly creating new problems(which may simply, be inaudible). Knowing that the energy keeps going, means you can calculate and KNOW which mode is the issue, and based on it's relation to your LP and your speakers will give you the information needed to constructively or destructively drive those modes.

My 'approach' is outlined in Ch.13 of the second edition, and Ch.8 of the third edition of 'Sound Reproduction - The Acoustics and Psychoacoustics of Loudspeakers and Rooms.' And I'll clarify yet again, my approach has been nothing but information gathering to get started. Applying DSP to create your own idealized graph is a misnomer. It is a complex subject without many simple answers, but gaining a better understanding of the subject of Sound Reproduction enables you to make informed decisions. But you can't do that, without knowing your room's influence.

From Ch. 12 p345 "When one sees a very smooth high-resolution steady-state room curve after equalization, there is a high possibility that something inappropriate has been done, and the sound quality may have been degraded."

When you consider the amount of time being spent measuring and tweaking DSP filters, it is amazing for me to see the resistance to the fact that the physical dimensions WILL correspond to the acoustic measurements. But clearly, my saying that is insufficient for those who haven't read the book. So I will do my best to upload my step by step correlation of predicted modes(and my room has a bunch!) to the acoustic measurements. I have to start a new photo host because all my other threads are picture-less after Photobucket changed their terms.
I think we'd all be interested in seeing a practical lesson in applying predictions. Applying prediction to a square or rectangular room seems ascertainable but what and how to approach a room with openings and dissimilar reflections seems like voodoo.

Seems like the first several chapters in Tooles' book are dedicated to dispelling myths and countering marketing statements made by manufacturers. I also find his take individual listening, vs. some propeller head telling me what I should hear or how I am doing it all wrong, refreshing. My brain and two ears still have the final say. So far, the first chapters relate to his is a philosophical approach to sound reproduction.
 
Mitchibo

Mitchibo

Audioholic
Depending on the room identifying room modes is a fairly easy task. While looking at time delay graphs are really good, most of the time you can find them with the review of a few sweeps. I usually do these across the front sofa.

That said, I don't know anyone so far (Mitch, Jogre etc) who's complained of coming away with loose and muddy bass after identifying a baseline in REW, and smoothing response. You can do this in REW, in the EQ Window, by clicking 'set target level' which automatically adjusts the level of the target response to provide a good match to the measurement over the range selected for EQ. I usually start here, and tweak it +-1 or 2dB or so, but it's really good at what it does.

In order for high RT60 time to become a serious issue one would have to ignore a very noticeable and serious room mode peak, which are usually the first eliminated. I also have had success in eliminating nulls across my listening area (front sofa area) with boost and distance change, and even with boost alone, so I wouldn't definitively dismiss it. However, you'd be correct to say that you should use it judiciously.
Even with the "non-predicted" file created it made my subs play like a completely different setup. I'm still amazed at the change.
 
TheWarrior

TheWarrior

Audioholic Ninja
I think we'd all be interested in seeing a practical lesson in applying predictions. Applying prediction to a square or rectangular room seems ascertainable but what and how to approach a room with openings and dissimilar reflections seems like voodoo.

Seems like the first several chapters in Tooles' book are dedicated to dispelling myths and countering marketing statements made by manufacturers. I also find his take individual listening, vs. some propeller head telling me what I should hear or how I am doing it all wrong, refreshing. My brain and two ears still have the final say. So far, the first chapters relate to his is a philosophical approach to sound reproduction.
Other than 'Science in the service of art is our business, good sound is our product' what do you find to be philosophical within the first few chapters? It's different for me because this 3rd edition is so heavily revised from the previous, I'm still finding my way around it. Still, I'm very pleased with all the new data, there is no shortage of things to learn in this hobby. Just wait though, that propeller has wings, and there's a lot more widely accepted notions about to be torn to shreds in later chapters!

I like your use of the word 'voodoo', seems very appropriate. I will do my best to get something online this week. Really bummed that I have to transfer all my images from photobucket, but oh well!
 
Mitchibo

Mitchibo

Audioholic
Other than 'Science in the service of art is our business, good sound is our product' what do you find to be philosophical within the first few chapters? It's different for me because this 3rd edition is so heavily revised from the previous, I'm still finding my way around it. Still, I'm very pleased with all the new data, there is no shortage of things to learn in this hobby. Just wait though, that propeller has wings, and there's a lot more widely accepted notions about to be torn to shreds in later chapters!

I like your use of the word 'voodoo', seems very appropriate. I will do my best to get something online this week. Really bummed that I have to transfer all my images from photobucket, but oh well!
Perhaps I should transpose the word “philosophy” with “ideology of sound”. After 50 years of being at the top of acoustic science, there are a lot of “notions”, evidently, that he begins poking holes in. Even with his experience, one of the underlying assertions is that the science of sound isn’t exactly fixed as per what reviewers and manufacturers say. The idea of making perfect predictions in lieu of the reality of harnessing the liquidity of sound is affirmed as an undying implication in the early chapters.

There is nothing simple about it. Obviously he is presenting science here, but I thought it very “human” to see what his listening rooms looked like.

The difficult part for us peons is to divine the voodoo of sound; specifically for me to make positive improvements with predictions for an overall better listening environment.
 
TheWarrior

TheWarrior

Audioholic Ninja
Perhaps I should transpose the word “philosophy” with “ideology of sound”. After 50 years of being at the top of acoustic science, there are a lot of “notions”, evidently, that he begins poking holes in. Even with his experience, one of the underlying assertions is that the science of sound isn’t exactly fixed as per what reviewers and manufacturers say. The idea of making perfect predictions in lieu of the reality of harnessing the liquidity of sound is affirmed as an undying implication in the early chapters.

There is nothing simple about it. Obviously he is presenting science here, but I thought it very “human” to see what his listening rooms looked like.

The difficult part for us peons is to divine the voodoo of sound; specifically for me to make positive improvements with predictions for an overall better listening environment.
Now you're cooking! Reviewers and manufacturers allow their marketing departments or endorsers to decide what science is. "Better sound through research" - Sound familiar?

You'll read how Floyd came in to Harman and they hadn't ever done a single blind, let alone double blind test before. "They are all professionals." He was told. In the book you'll find results demonstrating the huge differences in performance ratings of sighted vs. blind testing. It is not a stretch to say, people will hear what they want to hear.

But I see you're hung up on the 'predictions' aspect. Let me reassure you, this ain't Miss Cleo!

Room modes are the interactions of the physical boundaries of your room who's dimensions are similar to the diameter of the sound waves being created.

Speed of sound at sea level: 1131fps/20hz = 56.5 foot diameter sound wave!

That means the lowest audible frequency can't possibly be fully propagated within most homes. Therefore those reflections and interactions with room boundaries will decide when and where you can hear what frequencies.

The only reason they're called predictions is due to the construction of those boundaries having windows and doors that allow the boundary to flex, lowering their resonant frequency. There is no formula to predict the exact frequency, because you can't possibly anticipate the exact construction of every wall. So you have to confirm your predictions, first.

Without knowing your room's modal frequencies, arbitrarily applying DSP filters will boost some frequencies, while canceling others out, meaning you can't hear all of the bass, which is my goal, and I assume is yours too! Our hearing is not linear, and what we hear is not accurately depicted in a steady-state frequency response graph. So while I am sure you are hearing 'more bass' in your current set up, this book gives me the confidence to say you are not likely to be hearing all of the bass due to the method being used.
 
agarwalro

agarwalro

Audioholic Ninja
Well then, I'll try to keep things 'sweet' for you.... :D But believe me, if I could shorten these responses I would! (but it's all condensed info coming from a 500p book)

As for frequency vs amplitude with phase as opposed to waterfall, that is information I am sharing from Floyd Toole's 'Sound Reproduction'. Floyd goes in to it a bit in his CIRMMT video on youtube. But the compromise between frequency vs time is the issue, and can give misleading information that would be wrongly used to input DSP corrections with.

Back to your RT comment: "Voices and musical instruments have limited sound power output, so (concert) halls are kept as reflective as possible to keep loudness high, without interfering with 'intelligibility' of the music. It is a difficult compromise. Typical values for RT in performance venues are in the range of 1-2 seconds, optimized for the music most commonly performed... In sound reproduction, the essential hall reverberation is captured in the recording, so nothing additional is required. Typical RT for domestic listening rooms and recording control rooms are 0.2-0.4 seconds. The reverberation in classical recordings completely overpowers that of the listening room." Pg 281 'Sound Reproduction 3rd Edition'

Point being that RT is not often an issue in small rooms. Understanding the transition frequency is much more important to identifying and treating the naturally occurring room modes or standing waves resulting from the parallel surfaces of your home. As you pointed out, the energy from the first reflection doesn't just dissipate, it keeps bouncing, creating higher order modes that are higher in frequency than the originating modal frequency. That is why I don't recommend adding DSP filters without predicting and verifying room modes, first, due to the near guarantee of unknowingly creating new problems(which may simply, be inaudible). Knowing that the energy keeps going, means you can calculate and KNOW which mode is the issue, and based on it's relation to your LP and your speakers will give you the information needed to constructively or destructively drive those modes.

My 'approach' is outlined in Ch.13 of the second edition, and Ch.8 of the third edition of 'Sound Reproduction - The Acoustics and Psychoacoustics of Loudspeakers and Rooms.' And I'll clarify yet again, my approach has been nothing but information gathering to get started. Applying DSP to create your own idealized graph is a misnomer. It is a complex subject without many simple answers, but gaining a better understanding of the subject of Sound Reproduction enables you to make informed decisions. But you can't do that, without knowing your room's influence.

From Ch. 12 p345 "When one sees a very smooth high-resolution steady-state room curve after equalization, there is a high possibility that something inappropriate has been done, and the sound quality may have been degraded."

When you consider the amount of time being spent measuring and tweaking DSP filters, it is amazing for me to see the resistance to the fact that the physical dimensions WILL correspond to the acoustic measurements. But clearly, my saying that is insufficient for those who haven't read the book. So I will do my best to upload my step by step correlation of predicted modes(and my room has a bunch!) to the acoustic measurements. I have to start a new photo host because all my other threads are picture-less after Photobucket changed their terms.
RT not being an issue in small rooms is an incorrect inference. High RT in treble frequencies, results in overly bright rooms, while at lower frequencies, bass transients and separation are obfuscated. Getting acoustical energy, especially below transition frequency, to dissipate in small rooms needs astute design and significant commitment. If anything, high RT is a big issue in small room acoustics. A significant percentage of maladies misattributed to speakers and electronics is a direct consequence of high RT listening environment.

I didn't have time to watch the CIRMMT video. I did re-read Ch. 13 edition 2.

There two big things I noticed, all analysis is based on ideal (perfectly rectangular) rooms and use of Waterfall Plots to visualize modal ringing.

The inverse correlation of frequency resolution and time resolution in Waterfall Plots is mentioned. I read that as a caveat emptor for the nature of visualizing a plot based on frequency, amplitude and time. I suspect, it is a consequence of the Fourier Transform math. There is no mention of the inverse correlation of resolution generating incorrect filters or resulting in incorrect application of DSP filters. Consequently, I chalk that one to inexperience or overzealous EQ by the user.

I use the Waterfall Plots below transition frequency, toggling frequency resolution with time resolution. Well below transition, I prefer time resolution. Closer to transition, things get murky. Of course, well above transition, only frequency resolution matters, and life is easy completely ignoring time.

Starting with mathematical modeling of an ideal room and then correlating it to observations made in an ideal physical room make perfect sense in the pursuit of science and understanding. This approach is not feasible in the real world. At minimum, the ideal room models completely fail (exempt height, since most of us have a roof exactly parallel to floor across the whole room).

I believe our approaches overlap in that we see EQ as a tool of last resort. I will send days playing with room setup and speaker/subwoofer locations, only adjusting distance and level settings, to get the best possible coupling of source to room. If I notice a persistent peak or dip, I'll break out the room mode analysis spreadsheet to help correlate observations to idealized mathematical expectations. This helps understand which battles are not winnable on placement alone and which to focus on. Only then will I try EQ to control the worst peaks or dips.

I hear you on the topic of people considering EQ their path to audio nirvana or obsessing on speakers and electronics (or cables :rolleyes:) while turning a blind eye to the room or good speaker placement. To them I say, get Bose-d :D.
 
TheWarrior

TheWarrior

Audioholic Ninja
RT not being an issue in small rooms is an incorrect inference. High RT in treble frequencies, results in overly bright rooms, while at lower frequencies, bass transients and separation are obfuscated. Getting acoustical energy, especially below transition frequency, to dissipate in small rooms needs astute design and significant commitment. If anything, high RT is a big issue in small room acoustics. A significant percentage of maladies misattributed to speakers and electronics is a direct consequence of high RT listening environment.

I didn't have time to watch the CIRMMT video. I did re-read Ch. 13 edition 2.

There two big things I noticed, all analysis is based on ideal (perfectly rectangular) rooms and use of Waterfall Plots to visualize modal ringing.

The inverse correlation of frequency resolution and time resolution in Waterfall Plots is mentioned. I read that as a caveat emptor for the nature of visualizing a plot based on frequency, amplitude and time. I suspect, it is a consequence of the Fourier Transform math. There is no mention of the inverse correlation of resolution generating incorrect filters or resulting in incorrect application of DSP filters. Consequently, I chalk that one to inexperience or overzealous EQ by the user.

I use the Waterfall Plots below transition frequency, toggling frequency resolution with time resolution. Well below transition, I prefer time resolution. Closer to transition, things get murky. Of course, well above transition, only frequency resolution matters, and life is easy completely ignoring time.

Starting with mathematical modeling of an ideal room and then correlating it to observations made in an ideal physical room make perfect sense in the pursuit of science and understanding. This approach is not feasible in the real world. At minimum, the ideal room models completely fail (exempt height, since most of us have a roof exactly parallel to floor across the whole room).

I believe our approaches overlap in that we see EQ as a tool of last resort. I will send days playing with room setup and speaker/subwoofer locations, only adjusting distance and level settings, to get the best possible coupling of source to room. If I notice a persistent peak or dip, I'll break out the room mode analysis spreadsheet to help correlate observations to idealized mathematical expectations. This helps understand which battles are not winnable on placement alone and which to focus on. Only then will I try EQ to control the worst peaks or dips.

I hear you on the topic of people considering EQ their path to audio nirvana or obsessing on speakers and electronics (or cables :rolleyes:) while turning a blind eye to the room or good speaker placement. To them I say, get Bose-d :D.
Grab your book!

Why RT is not needed in small rooms:
p.62 Sound Reproduction 2nd Edition Section 4.3.4 "In the acoustical transition from a large performance space to a 'small' kind of room, it seems the the significant factors are reduced ceiling height (relative to length and width), significant areas of absorption on one or more boundary surfaces, and proportionally large absorbing and scattering objects distributed throughout the floor area."

p.63 "These [small rooms] are not Sabine spaces, and it is not appropriate to employ calculations and measurements that rely on assumptions of diffusivity. Schultz [1983] states, 'The amount of sound-absorbing material in the room cannot be accurately determined by measurement, either with the decay-rate (reverberation-time) method or the steady-state (reference sound source) method... One cannot trust the predictions of the Diffuse Field Theory for a non-Sabine room."

p.63 Section 4.3.5 "A measurement of reverberation time in a domestic-sized room yields a number. When the number is large, the room sounds live, and when the number is small, the room sounds dead... The numbers measured are small compared to those in performance spaces, and so the question arises if the late-reflected sound field in a listening room is capable of altering what is heard in the reproduction of music."
p.64 [after explaining that late reflected sounds are diminished in small rooms] "Nevertheless, excessive reflected sound is undesirable, and an RT measurement can tell us that we are in the ballpark, but for that matter, so can our ears or an 'acoustically aware' visual inspection."

Why RT measurements in small rooms are difficult:
p.63 "Reverberation time is a property of the room alone, and a correct measurement of it should employ an omnidirectional sound source capable of 'illuminating' all of the room boundaries. The reason for this is that it is assumed that the boundaries consist of areas or reflection and absorption and the central volume of the room is empty. The several formulae by which we estimate RT confirm this, and the values of absorption coefficient for the materials are 'random incidence' values, meaning there is an assumption of some considerable diffusivity in the sound field. Some practitioners incorrectly use conventional sound-reproduction loudspeakers as sources. The directivity of these is such that the resulting reflection patterns and decays are not properties of the room, but of the room and loudspeaker combination - a very different thing."

Why Waterfalls are NOT being recommended (theres only 4 waterfalls in the 50 page chapter):
p.240 Section 13.4.1 "Natural Acoustical Equalization Versus Electronic Equalization"
"Before moving on, some things should be said about waterfall diagrams:
-They are highly decorative
-They contain a lot of information
-That information is compromised in both time domain and frequency domain axes, and the compromise can be manipulated to favor one or the other, but not both. In other words, one can have high resolution in the frequency domain and sacrifice resolution in the time domain, or the reverse. All of this is most relevant at low frequencies."
p.241 Figure 13.20 Shows 3 waterfalls for a room with a predicted second order length mode. (e) has no visual indication of the mode, with the other two having varying results, whereas (b) the steady-state high resolution measurement shows that predicted mode loud and clear.
p.243 Figure 13.21 "A comparison of steady-state frequency responses.." ... that is extending from p.242 talking about 'positional' equalization vs. electronic equalization. The waterfalls look near identical despite the differing equalization, whereas the steady-state vary hugely.
p.244 Figure 13.22 Is quite similar in it's comparison of steady-state vs. waterfall as above, but it also uses a non-rectangular room.
p.246 Figure 13.23 Is again compared in the same way, after p.245 "However, because we know that low-frequency room resonances generally behave in a minimum-phase manner, we know that if there are no prominent peaks protruding above the average spectrum level, there will not be prominent ringing in the time domain. It it this indirect, inferential knowledge that permits us to confidently use frequency responses as a primary source of information about room behavior at low frequencies."

'Mathematical modeling of an ideal room':
p203 Those are the 'Back of the Envelope' calculations I have been recommending. Perhaps, you will note that the way I have discussed this page on the forum, is to simply encourage people to take the physical measurement of two parallel boundaries and calculate the modal frequency so that can be understood in acoustic measurements. That has nothing to do with an ideal room, and he also verified that the 'ideal' room is very much a myth. How this is 'not feasible in the real world' really comes down to your willingness to understand how much control you do have, and where to apply it. But to have presumption that you can look at a frequency response measurement (without phase, as people here have been doing) and 'know' what to do is absurd. Why would you want to guess, when you can know?
 
ATLAudio

ATLAudio

Senior Audioholic
For a good breakdown on using waterfalls @gene wrote a good article which was peer reviewed by Dr. Toole. It shows a how to scale and interpret a waterfall and what you're looking for. As @gene puts it, Figure 13.21 (Sound Rep, Toole 2008) "demonstrates reduction of ringing due to energy being removed from a pesky mode." One simply needs to know what to look for, but it's not difficult. Moreover, "Unless a waterfall is accompanied by setup data specifying frequency and/or time resolution they are of questionable value."
 
TheWarrior

TheWarrior

Audioholic Ninja
For a good breakdown on using waterfalls @gene wrote a good article which was peer reviewed by Dr. Toole. It shows a how to scale and interpret a waterfall and what you're looking for. As @gene puts it, Figure 13.21 (Sound Rep, Toole 2008) "demonstrates reduction of ringing due to energy being removed from a pesky mode." One simply needs to know what to look for, but it's not difficult. Moreover, "Unless a waterfall is accompanied by setup data specifying frequency and/or time resolution they are of questionable value."
Ah, thank you for finding a copy of those images! To complete the above quote: "Unless a waterfall is accompanied by setup data specifying frequency and/or time resolution they are of questionable value. I think most people simply don't understand that this tradeoff exists."

Not sure why you think that article is a "good breakdown on using waterfalls" tho...
 
ATLAudio

ATLAudio

Senior Audioholic
Breakdown in the context of the the conversation, and a reference for what a waterfall can illustrate when properly scaled and interpreted. In this case illustrating the reduction and presence of ringing.

IMO most people don't know what a waterfall is in the slightest.
 
TheWarrior

TheWarrior

Audioholic Ninja
Breakdown in the context of the the conversation, and a reference for what a waterfall can illustrate when properly scaled and interpreted. In this case illustrating the reduction and presence of ringing.

IMO most people don't know what a waterfall is in the slightest.
Figure 13.23 shows how the choice between time and frequency compromises the measurement, vs. a single high resolution steady state measurement. Figure 13.21 shows when a waterfall does not even resemble the steady-state, despite the differing equalization.

p.246 Figure 13.23 Is again compared in the same way, after p.245 "However, because we know that low-frequency room resonances generally behave in a minimum-phase manner, we know that if there are no prominent peaks protruding above the average spectrum level, there will not be prominent ringing in the time domain. It it this indirect, inferential knowledge that permits us to confidently use frequency responses as a primary source of information about room behavior at low frequencies."

@agarwalro I find it odd that we're discussing a book we both have, and you link to a website, but ok! Much of the information found there reflects data in the book. But I have to question the merits of the article when it depicts measurements being taken with a boom stand between the mic and the direct sound. (Floyd also talks about the corruption of measurements when mics are too close to absorptive furniture, such as when you aim an omni mic down at the furniture)

My aim is not to argue here, but to reinforce the simplicity of steady-state measurements. I'm literally trying to make your jobs easier! 'My method' seems to get a lot of push back for being too complicated, or for being too 'know it all' or 'propeller headed'. Yet you guys want these 'highly decorative' waterfalls without acknowledging the compromise. None of these articles state an optimum compromise between frequency and time, because there isn't one. Yet Floyd fully explains why steady-state is all you need!
 
Mitchibo

Mitchibo

Audioholic
607FF59E-97BA-4F30-9128-12C7DF4B9DE5.jpeg
Figure 13.23 shows how the choice between time and frequency compromises the measurement, vs. a single high resolution steady state measurement. Figure 13.21 shows when a waterfall does not even resemble the steady-state, despite the differing equalization.

p.246 Figure 13.23 Is again compared in the same way, after p.245 "However, because we know that low-frequency room resonances generally behave in a minimum-phase manner, we know that if there are no prominent peaks protruding above the average spectrum level, there will not be prominent ringing in the time domain. It it this indirect, inferential knowledge that permits us to confidently use frequency responses as a primary source of information about room behavior at low frequencies."

@agarwalro I find it odd that we're discussing a book we both have, and you link to a website, but ok! Much of the information found there reflects data in the book. But I have to question the merits of the article when it depicts measurements being taken with a boom stand between the mic and the direct sound. (Floyd also talks about the corruption of measurements when mics are too close to absorptive furniture, such as when you aim an omni mic down at the furniture)

My aim is not to argue here, but to reinforce the simplicity of steady-state measurements. I'm literally trying to make your jobs easier! 'My method' seems to get a lot of push back for being too complicated, or for being too 'know it all' or 'propeller headed'. Yet you guys want these 'highly decorative' waterfalls without acknowledging the compromise. None of these articles state an optimum compromise between frequency and time, because there isn't one. Yet Floyd fully explains why steady-state is all you need!
 
ATLAudio

ATLAudio

Senior Audioholic
Figure 13.23 shows how the choice between time and frequency compromises the measurement, vs. a single high resolution steady state measurement. Figure 13.21 shows when a waterfall does not even resemble the steady-state, despite the differing equalization.

p.246 Figure 13.23 Is again compared in the same way, after p.245 "However, because we know that low-frequency room resonances generally behave in a minimum-phase manner, we know that if there are no prominent peaks protruding above the average spectrum level, there will not be prominent ringing in the time domain. It it this indirect, inferential knowledge that permits us to confidently use frequency responses as a primary source of information about room behavior at low frequencies."
“I find it odd that we're discussing a book we both have, and you link to a website, but ok! Much of the information found there reflects data in the book. But I have to question the merits of the article when it depicts measurements being taken with a boom stand between the mic and the direct sound.”

This is a very dishonest criticism, but that’s nothing new from you. It is blatant interference and of little consequence to the point. Keep taking the lazy way out.

“(Floyd also talks about the corruption of measurements when mics are too close to absorptive furniture, such as when you aim an omni mic down at the furniture)”

Can you wipe your own tuchus? I mean, since Toole doesn’t write about it… Your dogmatic approach to interpreting and promoting that book would suggests this.

“My aim is not to argue here, but to reinforce the simplicity of steady-state measurements. I'm literally trying to make your jobs easier!”

Oh BS! You’re trying to get folks to measure every nook and cranny of their room, when you can more easily get information through other means, like using the waterfall, or other REW tools. When others ask for more concise direction you tell them to go read a whole book which you clearly don’t fully understand yourself. When they don't become the obeying cultists you want, you assume everything, and tell them what they did was horrible, when in fact your assumptions were wrong, and they are beyond delight.

“My method' seems to get a lot of push back for being too complicated, or for being too 'know it all' or 'propeller headed'.”

I find these criticisms appropriate. You don’t have a method, just a bunch of rambling incoherent nonsense backed up with a dogmatic cult of personality you're promoting. This makes conversation itself complicated.

“Yet you guys want these 'highly decorative' waterfalls without acknowledging the compromise. None of these articles state an optimum compromise between frequency and time, because there isn't one. Yet Floyd fully explains why steady-state is all you need!”

Wrong. Again, this is another example of your inability to appropriately relate the context of the text. While Toole does mention limitations of waterfall charts, and you can feel free to cite all references if it makes you feel better, you haven't made a point referencing this use; just broad brush bumper sticker jargon.
 
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agarwalro

agarwalro

Audioholic Ninja
Grab your book!

Why RT is not needed in small rooms:
p.62 Sound Reproduction 2nd Edition Section 4.3.4 "In the acoustical transition from a large performance space to a 'small' kind of room, it seems the the significant factors are reduced ceiling height (relative to length and width), significant areas of absorption on one or more boundary surfaces, and proportionally large absorbing and scattering objects distributed throughout the floor area."

p.63 "These [small rooms] are not Sabine spaces, and it is not appropriate to employ calculations and measurements that rely on assumptions of diffusivity. Schultz [1983] states, 'The amount of sound-absorbing material in the room cannot be accurately determined by measurement, either with the decay-rate (reverberation-time) method or the steady-state (reference sound source) method... One cannot trust the predictions of the Diffuse Field Theory for a non-Sabine room."

p.63 Section 4.3.5 "A measurement of reverberation time in a domestic-sized room yields a number. When the number is large, the room sounds live, and when the number is small, the room sounds dead... The numbers measured are small compared to those in performance spaces, and so the question arises if the late-reflected sound field in a listening room is capable of altering what is heard in the reproduction of music."
p.64 [after explaining that late reflected sounds are diminished in small rooms] "Nevertheless, excessive reflected sound is undesirable, and an RT measurement can tell us that we are in the ballpark, but for that matter, so can our ears or an 'acoustically aware' visual inspection."
It doesn't say RT is not needed. Rather, it is important to understand that RT in large space is a consequence primarily of the room characteristics alone while in a small space it is partially source characteristics and room. Further, using RT as a single number, example, RT60 falling within a time range is ill advised. For example, saying RT60 of 0.2-0.4 seconds is optimal, is advised against. Rather showing RT vs frequency plot is more meaningful. Identifying an echo chamber or anechoic room effect will be easy. Surely, doesn't hurt to have a measurement paradigm for those in between.

Why RT measurements in small rooms are difficult:
p.63 "Reverberation time is a property of the room alone, and a correct measurement of it should employ an omnidirectional sound source capable of 'illuminating' all of the room boundaries. The reason for this is that it is assumed that the boundaries consist of areas or reflection and absorption and the central volume of the room is empty. The several formulae by which we estimate RT confirm this, and the values of absorption coefficient for the materials are 'random incidence' values, meaning there is an assumption of some considerable diffusivity in the sound field. Some practitioners incorrectly use conventional sound-reproduction loudspeakers as sources. The directivity of these is such that the resulting reflection patterns and decays are not properties of the room, but of the room and loudspeaker combination - a very different thing."
Since subwoofers are omnidirectional and sound field not directional below the transition frequency, this contention does not apply when optimizing a subwoofer. Optimizing placement (sub and seat) around room modes is the preferred first step. Next step will be to EQ and tackle the worst remaining peaks and dips (not corresponding with room modes). Finally, broad band absorbers to bring the RT across lower octaves down or at least uniform across the bands in question.

Above transition frequency, getting a flat FR via EQ and first and second reflection strength management via absorption or diffusion panels is sufficient to create a balanced sound field. (Balance between sound stage and imaging.)

Why Waterfalls are NOT being recommended (theres only 4 waterfalls in the 50 page chapter):
p.240 Section 13.4.1 "Natural Acoustical Equalization Versus Electronic Equalization"
"Before moving on, some things should be said about waterfall diagrams:
-They are highly decorative
-They contain a lot of information
-That information is compromised in both time domain and frequency domain axes, and the compromise can be manipulated to favor one or the other, but not both. In other words, one can have high resolution in the frequency domain and sacrifice resolution in the time domain, or the reverse. All of this is most relevant at low frequencies."
p.241 Figure 13.20 Shows 3 waterfalls for a room with a predicted second order length mode. (e) has no visual indication of the mode, with the other two having varying results, whereas (b) the steady-state high resolution measurement shows that predicted mode loud and clear.
p.243 Figure 13.21 "A comparison of steady-state frequency responses.." ... that is extending from p.242 talking about 'positional' equalization vs. electronic equalization. The waterfalls look near identical despite the differing equalization, whereas the steady-state vary hugely.
p.244 Figure 13.22 Is quite similar in it's comparison of steady-state vs. waterfall as above, but it also uses a non-rectangular room.
p.246 Figure 13.23 Is again compared in the same way, after p.245 "However, because we know that low-frequency room resonances generally behave in a minimum-phase manner, we know that if there are no prominent peaks protruding above the average spectrum level, there will not be prominent ringing in the time domain. It it this indirect, inferential knowledge that permits us to confidently use frequency responses as a primary source of information about room behavior at low frequencies."
The steady state frequency response (FR) has a 40dB scale whereas the waterfall plots, 60dB. This will naturally smooth out variations. Further, they have been specifically chosen to highlight the difficulty in generating and reading them. That said, being able to manipulate frequency resolution vs time resolution easily makes this a powerful tool.

From here, is a waterfall plot that absurdly easily shows ringing,


The waterfall plots in the book are from the 1990's. I can imagine they were not easy to generate or manipulate. Even with my science degree they were not easy to grasp (especially the effect of frequency resolution vs time resolution). That said, I feel they are a better tool to demonstrate the detrimental effect of room modes on sound.

'Mathematical modeling of an ideal room':
p203 Those are the 'Back of the Envelope' calculations I have been recommending. Perhaps, you will note that the way I have discussed this page on the forum, is to simply encourage people to take the physical measurement of two parallel boundaries and calculate the modal frequency so that can be understood in acoustic measurements. That has nothing to do with an ideal room, and he also verified that the 'ideal' room is very much a myth. How this is 'not feasible in the real world' really comes down to your willingness to understand how much control you do have, and where to apply it. But to have presumption that you can look at a frequency response measurement (without phase, as people here have been doing) and 'know' what to do is absurd. Why would you want to guess, when you can know?
It is not feasible in the real world since the effect of doors, bathrooms, passages, kitchen windows, slanted ceilings, staircases, or anything other than a concrete floor causes deviations from the math. Add physical and logistical limitations of a shared space like living room setups and one can only understand the cause of an observed peak or dip and move on.

I will concede that in a dedicated HT or listening room, if closer to ideal than not, one would be naive to ignore the "back of envelope" calculations and go with visual appeal or other feng shui paradigm first.
 
agarwalro

agarwalro

Audioholic Ninja
p.246 Figure 13.23 Is again compared in the same way, after p.245 "However, because we know that low-frequency room resonances generally behave in a minimum-phase manner, we know that if there are no prominent peaks protruding above the average spectrum level, there will not be prominent ringing in the time domain. It it this indirect, inferential knowledge that permits us to confidently use frequency responses as a primary source of information about room behavior at low frequencies."
Why infer and believe when one can see and be sure!?

@agarwalro I find it odd that we're discussing a book we both have, and you link to a website, but ok! Much of the information found there reflects data in the book. But I have to question the merits of the article when it depicts measurements being taken with a boom stand between the mic and the direct sound. (Floyd also talks about the corruption of measurements when mics are too close to absorptive furniture, such as when you aim an omni mic down at the furniture)
We are discussing the book. It is not the end of an be all of taking measurements and creating meaningful insight from them. Dr. Toole is a pioneer and deserves credit for moving the industry ahead by significant conceptual leaps. Others have used his work to raise the average listener's knowledge base. The link provides a modern tool that makes it easy to apply difficult concepts encapsulated in recondite text. So, why not?

(Talking specifically about 10Hz to 200Hz band.) Having a boom or a boom boy sitting on a sofa between the subwoofer and mic is not going to make an appreciable difference when we're taking about FR that swings +/- 20dB due to room modes. The mic orientation and line of sight interference when taking measurements matters after the transition frequency.
 
agarwalro

agarwalro

Audioholic Ninja
My aim is not to argue here, but to reinforce the simplicity of steady-state measurements. I'm literally trying to make your jobs easier! 'My method' seems to get a lot of push back for being too complicated, or for being too 'know it all' or 'propeller headed'.
Yes, steady state FR is makes life easy. The minimum phase behavior makes for assurances that make the FR a very handy tool for someone who is looking to just correct the most egregious faults in audio and move on.

REW provides a tool that enables the average user to delve deep into the effects of their choices without having to understand the science. I believe the "back of envelope" has been out moded by the ease with which real time measurements, computations and visualizations can be produced by REW.

To use your words, I too am encouraging you to make your job easier. Your method is getting push back not for too complicated. Rather, it requires a deeper understanding of concepts than just plugging in a mic, blasting an impulse note and letting the app do the heavy lifting.

Yet you guys want these 'highly decorative' waterfalls without acknowledging the compromise. None of these articles state an optimum compromise between frequency and time, because there isn't one. Yet Floyd fully explains why steady-state is all you need!
There is a compromise and if one understands it, there isn't.

REW will let one change frequency or time resolution and redraw the waterfall plot accordingly. This is possible since the measurement and math is the same, only the visualization parameters are being changed. Knowing this, one can pick a preferred resolution and move forward accordingly.
 
ATLAudio

ATLAudio

Senior Audioholic
More citations that aren't applicable to the argument in 3...2...1...
 

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