Can small rooms have real reverb?
Ethan Winer
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15th March 2013
Old 15th March 2013
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Lightbulb Can small rooms have real reverb?

After the unfortunate demise of my previous thread about small rooms and reverb, the Gearslutz mods said I should try again. They also told me they will not stand for any insults or bickering, so let's please keep this on topic.

For my earlier thread I posted an audio clip of clapping and whistling in my garage, along with a photo and dimensions. This time I was much more thorough: I removed my car so the garage was empty, measured the RT60 in third-octave bands and made a new recording, then wrote the following as an article to describe the test. Some people believe that small rooms can't have real reverb due to Critical Distance (Dc) limitations, so I also show the math used to calculate Dc and list the distance for my garage. Enjoy.

--Ethan

==========================================

It's common knowledge that a small room used for playing or recording music doesn't have true reverb. Rather, a typical furnished room has a series of individual reflections that die fairly quickly. In order to obtain true reverb, sound waves must reflect off multiple surfaces, rather than only one or two bounces before being absorbed by a carpet or soft couch. However, an empty room can have real reverberation, even if it's fairly small.

I first began to question the conventional wisdom that small rooms can't have real reverb when I noticed how smooth and even the reverb is in my two-car garage. Hand claps sustain without flutter echo, and whistling different notes gives the same uniform extended decay. To my ears this space gives real reverb even though it's nowhere near the size of an auditorium. The live reverb chambers in many famous recording studios are similar in size to my garage, and nobody would argue that those rooms don't produce real reverb!

After this came up in an audio forum I decided to measure the reverb times in my garage. I also recorded myself yelling and clapping so people can hear it to judge for themselves if it sounds like real reverb, MP3 file attached.

My garage is 24.5 feet long by 22 feet wide by 8 feet high as shown in the drawing below. The photos show the setup with a Dell laptop computer and Mackie HR 624 loudspeaker in one corner, and a DPA 4090 omni microphone in the opposite corner:







Here's the reverb decay time (RT60) measured with that setup:



CRITICAL DISTANCE?

Some people claim that you can't have true reverb unless you're beyond the critical distance in the room, abbreviated Dc. This is defined as the distance from the sound source at which the direct and reverberant sounds are the same volume. Pop music recordings usually place the microphones close to the source to get mostly direct sound. But in a reverb chamber you need to be much farther away so the reverb dominates. This formula shows one method for calculating Dc based on the volume of the room (in meters) and the measured RT60:



This simplified formula assumes that the sound source is omnidirectional, which is not the case for either a person singing or speaking, or for a loudspeaker. The formula below includes a "Q" parameter to take directivity into account, and uses feet instead of meters. See the sidebar at left for a more detailed explanation of RT60 and sound source directivity.

Dc = 0.03121 * SQRT(Volume * Q / RT60)

The volume in my garage is its length times width times height:

24.5 * 22 * 8 = 4300 cubic feet (rounded for simplicity)

We'll use a Q value of 3.5 because that's about what you get from a typical box loudspeaker at midrange frequencies, and we'll use an average RT60 of 1.5 based on my measurements shown in the graph above:

Dc = 0.03121 * SQRT(4300 * 3.5 / 1.5)
Dc = 0.03121 * SQRT(15050 / 1.5)
Dc = 0.03121 * SQRT(10033)
Dc = 0.03121 * 100
Dc = 3.1 feet

So even 3.1 feet away from the sound source in my garage is enough to be beyond the critical distance. So much for claims that critical distance prevents true reverb from existing in a small room!

Understand that our concern here is mainly with midrange frequencies between about 300 and 3,000 Hz. When reverb is used as an effect, low frequencies are routinely removed to avoid a muddy sound. Further, in rooms the size of my garage and the live chambers in pro studios, low frequency decay times are selective and related to the room's modes.

It's also important to recognize that reverb calculations are only an approximation. Especially in a small room, and doubly so if the room contains any absorbing materials. In that case the placement of the absorbers - or couches or carpet - affects the RT60 measured, and also causes the measurements to vary around the room. Therefore, the calculations in this article are by necessity approximations because few rooms are totally reverberant. But even allowing for these minor variations, it's clear that a small empty room with reflective surfaces can have true reverb.

Special thanks to Amir Majidimehr for his technical expertise and valuable advice writing this article.

==========================================

SIDEBAR: DEFINING THE TERMS

RT60: Reverberation Time, abbreviated RT60, is defined as how long it takes for sound in a room to decay by 60 dB after the source stops. But unless the room is very quiet, the noise floor will likely prevent measuring the full duration. In other words, once sound has decayed by 60 dB it's too soft to measure accurately because the room's own background noise dominates. Sound decays linearly, so acousticians often measure how long it takes to decay by only 30 dB, then double that to get RT60.

While RT60 is a useful metric, for rooms where music is played it's even more useful to know the decay times in each octave or third-octave band. Modern room measuring software can display RT60 in third octaves, including the freeware Room EQ Wizard program I used to create the RT60 graph that accompanies this article.

Q = DIRECTIVITY: The Q parameter is usually associated with filters to define their bandwidth, or range of frequencies affected. But Q is also used to state the directivity of a sound source. A Q of 1 means the source radiation is perfectly omnidirectional, emitting in all directions equally. A human voice has a Q of about 2 because most of the sound goes forward, and less emits toward the rear behind your head. When speaking through a megaphone the Q can be as high as 15 or 20.

Taking into account typical horizontal and vertical dispersion, most loudspeakers fall somewhere between these extremes. So a Q of 3.5 was used for the critical distance calculations in this article. This Directivity article gives a more detailed explanation.
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File Type: mp3 reverb.mp3 (107.7 KB, 176 views)
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#2
15th March 2013
Old 15th March 2013
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Nice! I love stuff like this. I've always wanted to build a reverb chamber and have often used spare rooms as imitations. Nothing beats real environment ambience whether it's true technical reverb or not.
#3
15th March 2013
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What if the source was flush mounted?
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15th March 2013
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Ethan, I think it would help if you better defined what direction or objective(s) you are trying to accomplish. While the data and your insights are interesting, I think I would have a better handle on your take if I knew what applications or real world value they apply to.

Are you:

1) Trying to validate RT60 in some way
2) Trying to define reverb in a different way
3) Trying to expose flaws in the running assumption that RT-60 is meaningless in small rooms
4) Trying to make a case that reflections in a typical room are a form of reverb
5) Leading up to an application whereby reverb can not only be measured by some means but applied to room models
#5
15th March 2013
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http://www.rpginc.com/docs/Technolog...ons/Drv8i1.pdf

Have a look at page2. "How does one
calculate reverberation time correctly when the sound field
is not diffuse or mixing?" etc

What I read here would imply a broader use of the term "reverberation".

Also this (talking about big rooms): "Signs of the non-diffuse
field in such rooms are double-sloped or otherwise non-linear
(when expressed in dB) decay curves."
Which supports what I already wrote in the poly thread: some big rooms do not fulfill the definition as well.

Third: a reverberation chamber. Isn't this by definition a smal room ? How can it be called a reverberation chamber ?
#6
15th March 2013
Old 15th March 2013
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Slope

For musical purposes using reverb from rooms, I like the decay spectrum to be as even as possible. The BBC used to specify that Third Octave RT60 bands should be within 10% of each other.

But regarding the issue in general perhaps pictures speak better than words.
This is the Abbey Road Echo Chamber.
The first shows how the Reverb Time was adjusted by the inserting of
rounded and bearded individuals, the second shot seems to suggest something a bit more romantic.

Can small rooms have real reverb?-abbey-road-echo-chamber.jpg

Can small rooms have real reverb?-images.jpeg

DD
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#7
16th March 2013
Old 16th March 2013
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Quote:
Originally Posted by Ethan Winer View Post
So even 3.1 feet away from the sound source in my garage is enough to be beyond the critical distance. So much for claims that critical distance prevents true reverb from existing in a small room!
Who actually claimed this? Critical distance has nothing to do with the existence of reverb. It is simply the point in the room where the reverb level meets the direct level.
#8
16th March 2013
Old 16th March 2013
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Fuzzmeasure: a few quesions about frequency, reverberation and waterfall

Excerpted (bolded by me):

Originally Posted by SAC
Read Schroeder and Ted Schultz regarding the existence of reverberant fields in a Small Acoustical Space.

To quote Schultz, of Bolt, Beranek and Newman, regarding the non-existence of reverberant sound fields and small room reverberation times in small acoustical spaces, RT times "do not provide a valid measurement of the reverberation in the room".

And Davis: "In small control rooms there is no Dc (critical distance), no well-mixed sound field, and, hence, no reverberation. There is merely a series of early reflected energy. Consequently, the measurement of RT60 becomes meaningless in such environments."

And "it is fundamental to remember that modal decay rates are not reverberation."

And it was Schroeder who determined the equation determining the definition of a Large Acoustic Space and a Small Acoustical Space. And while "many large rooms have small room properties at certain frequencies (especially with regards to specular reflections), below F sub L, the Schroeder Large room effective frequency, "that we have small rooms in the acoustic sense that we will be dealing with room modes rather than a statistical reverberant field."

Its fascinating to read here how there seems to be no distinction between the behavior of Large Acoustical Spaces and Small Acoustical Spaces, and tha measurements, simpoly because you have a function assigned to a button can supposed measure that which does not exist.

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Originally Posted by DanDan View Post
the second shot seems to suggest something a bit more romantic.
So much for staying on topic...
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#9
16th March 2013
Old 16th March 2013
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Anybody...

who can explain what is it that we hear when a small room is empty compared if it is damped. I can clearly hear a diffrence between a empty or a room that is filled with furniture. There is a difference in "the reverb" in that room. Maybe a different name is in order here than reverb.

Is this not measureable? or what is it that we see in the measurement then. According to ISO 3382 one measures the T30 or T20 and a estimation/calculation to get T60. For me I can see a difference in measurement between a empty room verses a damped/treated. The slope and values in T30 is changing.

In small room we indeed are within the Dc all the time but is it not the slope that is changing when a treatment is in progrees in a room.

When we compare with outside environment there is no Dc, only the the natural slope(6dB) per doubling of distance from the source. The distance from the source then determance if one can hear the source or not.

http://www.sengpielaudio.com/DirectF...erantField.pdf

Last edited by Bobecca; 16th March 2013 at 07:48 AM.. Reason: Added link
#10
16th March 2013
Old 16th March 2013
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Quote:
Originally Posted by jim1961 View Post
Ethan, I think it would help if you better defined what direction or objective(s) you are trying to accomplish. While the data and your insights are interesting, I think I would have a better handle on your take if I knew what applications or real world value they apply to.

Are you:

1) Trying to validate RT60 in some way
2) Trying to define reverb in a different way
3) Trying to expose flaws in the running assumption that RT-60 is meaningless in small rooms
4) Trying to make a case that reflections in a typical room are a form of reverb
5) Leading up to an application whereby reverb can not only be measured by some means but applied to room models
+1 Jim

Ethan. I think you must expect a bumpy ride here. You are going to get some very erudite, theoretically talented forum members testing your assumptions.

Others above have started the "reference" trail regarding theoretical definitions. Part of the problem with this particular acoustic property you are analysing is that the average musician, or indeed any layman, refers to "reverb" as a generic term to describe any sort of decay beyond the direct sound. Actually I have not met a musician yet who noted ".. Heh that's not a statistically diffuse soundfield I'm hearing there!"

So, Ethan, the important point here is what are your terms of reference for this discussion? What is your point? Jim asked some important questions that would go a long way to clarifying where we all go with this one. Thanks
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16th March 2013
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Quote:
Originally Posted by jim1961 View Post
Ethan, I think it would help if you better defined what direction or objective(s) you are trying to accomplish. While the data and your insights are interesting, I think I would have a better handle on your take if I knew what applications or real world value they apply to.

Are you:

1) Trying to validate RT60 in some way
2) Trying to define reverb in a different way
3) Trying to expose flaws in the running assumption that RT-60 is meaningless in small rooms
4) Trying to make a case that reflections in a typical room are a form of reverb
5) Leading up to an application whereby reverb can not only be measured by some means but applied to room models
Indeed good questions.

But at the same time intresting topic.
#12
16th March 2013
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I maintain my main question: how big is a reverberation room ?
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Ethan,

The term "reverberation" is based on observations related to what occurs within a space that has enough room volume to allow the development of a reverberant field.

It not only has to do with reflections - but also takes into account the decay of those reflections....... the intensity of those reflections with the space, etc.

We know that we can get reflections in small spaces - in fact we can make small spaces extremely lively - however you will not develop (in that space) a "reverberant sound field".

If you choose to call any series of reflections "reverb" I have no issue with that...... in fact here are plenty of dictionaries where the definition of reverb is loose enough that it would pretty much fit in anywhere......

However - the very basis for the term stems from the examination of reverberant sound fields - and when it comes to that there are definitely limits/descriptions as to what constitutes such a field.

So perhaps (depending on how you choose to define "reverberation") you can have reverb in a small room - however you cannot develop a reverberant sound field in that same room.

Quote:
Reverberant Sound Field:

A sound field made of reflected sounds in which the time average of the mean square sound pressure is everywhere the same and the flow of energy in all directions is equally probable.
I will have to agree with others here that you should probably more clearly define what you are trying to achieve with this...
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#14
16th March 2013
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Quote:
Originally Posted by Rod Gervais View Post

So perhaps (depending on how you choose to define "reverberation") you can have reverb in a small room - however you cannot develop a reverberant sound field in that same room.
+1

Right on cue, very eruditely put Rod. That is about the sum of it...
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16th March 2013
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Quote:
Originally Posted by Icecube1 View Post
+1

Right on cue, very eruditely put Rod. That is about the sum of it...
Is this true? Perhaps the link provided in my previous post has to be read again, if not allready!

Reverberant sound field is due to all the reflection caused from the room and due to the source itself when the direct sound slope meet the reverberant field, D/R.

There is no reverb sound field if there is no source. Correct me if wrong here!

Terminology is a factor here. It has to be sorted out first before we can continue.
#16
16th March 2013
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Quote:
Originally Posted by Bobecca View Post
There is no reverb sound field if there is no source. Correct me if wrong here!
Well yes, I would have thought that is a given? I am sure Rod did not mean that a reverberant sound field magically appeared without any source of sound to produce it?
#17
16th March 2013
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"If a tree falls in a forest and no one is around to hear it, does it make a reverberant sound field?"

The philosophical stuff always makes me dizzy... And hungry... :-D
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#18
16th March 2013
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Quote:
Originally Posted by SörenHjalmarsson View Post
"If a tree falls in a forest and no one is around to hear it, does it make a reverberant sound field?"

The philosophical stuff always makes me dizzy... And hungry... :-D
I would say yes it is

An event has happened and it follow the physics involved.
#19
16th March 2013
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Quote:
Originally Posted by Bobecca View Post
Is this true? Perhaps the link provided in my previous post has to be read again, if not allready!
It was read (by myself, and (I would imagine) many others ) a long LONG time before you ever linked to it..... perhaps you need to re-read it if you disagree with my statement.......

At which point (in an acoustically small room) do you reach critical distance?

Quote:
There is no reverb sound field if there is no source. Correct me if wrong here!
Who suggested that there wasn't a source? Perhaps you could quote whatever statement was made that suggested there was no sound involved.

Rod
#20
16th March 2013
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Quote:
Originally Posted by Bobecca View Post
I would say yes it is

An event has happened and it follow the physics involved.
You ignore the philosophical quandary - and that is the crux of the question - the question is (philosophically not scientifically) is sound in and of itself an "thing" - or does it become a thing at the moment of perception......

For a completely deaf person there is no existence of "sound" - this even though they can often feel the existence of the pressures that provide the essence of sound to those who can hear....... do you somehow suggest that their existence in this regard somehow needs to be defined by the experiences of others?

So we accept the physical when we examine the scientific - when a physical event occurs there may well be the creation of certain measurable pressures that are resultant of the occurrence - but the philosophical question as to whether or not this is (in and of itself) sound (sans the physical evidence being witnessed) is still a valid question.

There are plenty of questions science might have an answer for that philosophy might yet have to ponder.

Even science accepts the fact that things sometimes appear to experience a change in physical properties simply due to observation by man (study Quantum Physics if you don't understand the phenomena.)

Rod
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#21
16th March 2013
Old 16th March 2013
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Quote:
Originally Posted by Rod Gervais View Post
You ignore the philosophical quandary - and that is the crux of the question - the question is (philosophically not scientifically) is sound in and of itself an "thing" - or does it become a thing at the moment of perception......

For a completely deaf person there is no existence of "sound" - this even though they can often feel the existence of the pressures that provide the essence of sound to those who can hear....... do you somehow suggest that their existence in this regard somehow needs to be defined by the experiences of others?

So we accept the physical when we examine the scientific - when a physical event occurs there may well be the creation of certain measurable pressures that are resultant of the occurrence - but the philosophical question as to whether or not this is (in and of itself) sound (sans the physical evidence being witnessed) is still a valid question.

There are plenty of questions science might have an answer for that philosophy might yet have to ponder.

Even science accepts the fact that things sometimes appear to change physical properties simply due to observation be man.

Rod
Rod Gervais ... the hairy Buddha.

You go deep, man, and I dig that.
#22
16th March 2013
Old 16th March 2013
  #22
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Quote:
Originally Posted by Rod Gervais View Post
Ethan,

The term "reverberation" is based on observations related to what occurs within a space that has enough room volume to allow the development of a reverberant field.

It not only has to do with reflections - but also takes into account the decay of those reflections....... the intensity of those reflections with the space, etc.

We know that we can get reflections in small spaces - in fact we can make small spaces extremely lively - however you will not develop (in that space) a "reverberant sound field".

If you choose to call any series of reflections "reverb" I have no issue with that...... in fact here are plenty of dictionaries where the definition of reverb is loose enough that it would pretty much fit in anywhere......

However - the very basis for the term stems from the examination of reverberant sound fields - and when it comes to that there are definitely limits/descriptions as to what constitutes such a field.

So perhaps (depending on how you choose to define "reverberation") you can have reverb in a small room - however you cannot develop a reverberant sound field in that same room.



I will have to agree with others here that you should probably more clearly define what you are trying to achieve with this...
Wow Rod that was very well said. Can't tell you how many times I wrote and deleted because I did not want to come off argumentative. That is a very balanced post.
#23
16th March 2013
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Quote:
Originally Posted by Rod Gervais View Post
You ignore the philosophical quandary - and that is the crux of the question - the question is (philosophically not scientifically) is sound in and of itself an "thing" - or does it become a thing at the moment of perception......

For a completely deaf person there is no existence of "sound" - this even though they can often feel the existence of the pressures that provide the essence of sound to those who can hear....... do you somehow suggest that their existence in this regard somehow needs to be defined by the experiences of others?

So we accept the physical when we examine the scientific - when a physical event occurs there may well be the creation of certain measurable pressures that are resultant of the occurrence - but the philosophical question as to whether or not this is (in and of itself) sound (sans the physical evidence being witnessed) is still a valid question.

There are plenty of questions science might have an answer for that philosophy might yet have to ponder.

Even science accepts the fact that things sometimes appear to experience a change in physical properties simply due to observation by man (study Quantum Physics if you don't understand the phenomena.)

Rod
To take this even further, we live in a reality of fields, not particles. Only upon observation do the fields collapse into particles.

Sean Carroll - The Particle at the End of the Universe - YouTube
#24
16th March 2013
Old 16th March 2013
  #24
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Big

Quote:
I maintain my main question: how big is a reverberation room ?
It depends on what you mean Yannick, but I will try to cover it.

The Rev Rooms, Echo Chambers, of Cello Studios, Abbey Road etc. are quite small. However they have very reflective boundaries. Abbey Road is ceramic tile on concrete with the scattering pipes, which may also have some LF effect.
The thing about these, when you actually use them, is that they are remarkably even, and they are NOT dominated by modes. As I said cello can handle toms and kick really cleanly, if a bit Spector.

Rev Rooms for measurement are big. I can't remember the numbers the size is directly related to their lower operational limit.
This is of course because the classical definition of diffusion falls down. Typically these rooms will hold true to 100Hz, 70 for Riverbank afaik.
BUT, these rooms are used below that frequency. By randomising locations of driving speakers and the mic, and by hanging large sheets of ply to break up the waves, we can do useful testing down to much lower frequencies.
BUT, it will not be to the classical spec, you can't derive a quality figure for the randomness introduced by the methods described.

Overall, it would be purely silly to try to insist that the world stick to the classical defined meaning of RT60 or Reverberation.

<snip by mod - off topic randomness...>
DD
#25
16th March 2013
Old 16th March 2013
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Quote:
Originally Posted by DanDan View Post
The Rev Rooms, Echo Chambers, of Cello Studios, Abbey Road etc. are quite small. However they have very reflective boundaries. Abbey Road is ceramic tile on concrete with the scattering pipes, which may also have some LF effect.
The thing about these, when you actually use them, is that they are remarkably even, and they are NOT dominated by modes. As I said cello can handle toms and kick really cleanly, if a bit Spector.
I just see (hear) them as effects, regardless of what they are called. I don't worry about if they sound like small room reflections, slap back, big room reverb or whatever. Give them a signal and see what the device does to it and if it fits with the music. My early days in audio consisted mostly of micing pianos and trying to find THAT place in the auditotium where the piano was faithfully represented in its space. We didn't add reverb in mixdown so it had to be captured live while being damn certain the balance was correct.
#26
16th March 2013
Old 16th March 2013
  #26
Hello everyone. New to this forum but have learned a lot from past searches that got me here. Since I was incriminated in Ethan’s article above , I thought I chime in with some answers. Hope I don’t get too many tomatoes thrown at me.

Quote:
Originally Posted by Syncamorea View Post
Fuzzmeasure: a few quesions about frequency, reverberation and waterfall

Excerpted (bolded by me):

Originally Posted by SAC
Read Schroeder and Ted Schultz regarding the existence of reverberant fields in a Small Acoustical Space.

To quote Schultz, of Bolt, Beranek and Newman, regarding the non-existence of reverberant sound fields and small room reverberation times in small acoustical spaces, RT times "do not provide a valid measurement of the reverberation in the room".

And Davis: "In small control rooms there is no Dc (critical distance), no well-mixed sound field, and, hence, no reverberation. There is merely a series of early reflected energy. Consequently, the measurement of RT60 becomes meaningless in such environments."

And "it is fundamental to remember that modal decay rates are not reverberation."

And it was Schroeder who determined the equation determining the definition of a Large Acoustic Space and a Small Acoustical Space. And while "many large rooms have small room properties at certain frequencies (especially with regards to specular reflections), below F sub L, the Schroeder Large room effective frequency, "that we have small rooms in the acoustic sense that we will be dealing with room modes rather than a statistical reverberant field."

Its fascinating to read here how there seems to be no distinction between the behavior of Large Acoustical Spaces and Small Acoustical Spaces, and tha measurements, simpoly because you have a function assigned to a button can supposed measure that which does not exist.
Thanks for posting that. What you quote while correct, to some extent has become a bit of fish story. The true nature of those statements differs from conclusions drawn from them. If you actually drill into quotes provided, you see that the present day conclusions drawn from them are not supported by the very references.

For example, if you read the Dr. Schultz’s 1963 AES Journal paper referenced there, ”Problems in the Measurement of Reverberation Time," you see that he is critical of two things:

1. Relying on RT60 measurements in low/modal frequencies. We don't care to analyze our small rooms using reverberation time there (have better tools such as frequency response). The value of RT60 use in small rooms is to determine if our rooms are too live/dead in mid-frequencies (e.g. to determine impact on speech intelligibility). To do that, we look at frequencies in the range of 500 of 1000 Hz. Those frequencies are above transition region for small rooms and hence, a lot of modal behavior has been dialed out. And randomness has set in sufficiently due to modes now being packed tightly. And whatever inaccuracy remains is not material since we are not looking for a precise determination.

By the same token, other classic requirements of statistically diffused spaces do not apply to our application. For example, unlike a large performance space, we sit in specific areas in our room or at the ceiling/floor. So the requirement that we need to achieve fully diffused space independent of space (location) need not occur here.


2. Difficulties of measuring impulse response of the room. Modern day tools like REW deploy much better methods such as log swept sine and filtered RT60 response which enable us to get a much better grasp of the data we are looking for per #1 above. The “button” as you call it, is a very smart one in this regard . It becomes even smarter if a human knows how to further post process the measurement and use the narrow information we need to get (again the aforementioned 500 to 1000 Hz). We can for example exclude the early portion of the impulse response that is dominated by sparse reflections. As with modal region, that is not an area of interest to analyze using RT60.

Likewise Don Davis' concern is around using RT60 calculations (distinct from measurement) of small rooms with lots of absorption. Real-time measurements side step many of the problems and indeed Don uses them himself in his book! Absorption does disturb diffusivity but it does so in both small and large rooms as someone correctly mentioned/referenced to the RPG article.

I provided answers to these in far more detail and organization here: Do bass traps produce noticeable audible difference?

And here: Do bass traps produce noticeable audible difference?

And the punch line here: Do bass traps produce noticeable audible difference?

Yes, there are differences in small vs. large rooms. Large spaces have very low transition frequencies and hence, RT60 has broader applicability there. But the measure doesn’t become useless automatically in small spaces as claimed because of that. Diffusivity has set in sufficiently at our listening position above transition frequencies as to allow us to extract useful information from it. I show all of this in very high level of detail in above post. I know you were in that thread and so apologize for pointing them out to you again . Pleas chime in if you feel there was a point that was missed that I did not address there.
#27
16th March 2013
Old 16th March 2013
  #27
Lives for gear
Quote:
Originally Posted by amirm View Post
Pleas chime in if you feel there was a point that was missed that I did not address there.
First and foremost, the point brought by localhost is obvious - if Ethan really believes that his calculated Dc is accurate, he should go to 3.1' and measure it. Does anyone really believe that at 3.2 feet from the monitor, the reverberant sound field is higher gain than the direct? Really?

Models can be great - sometimes they are all we have. But one of the keys to doing science is to do reality checks. If your model predicts something, don't just accept it. Measure it and use the results to think about your model. This is a critical issue in this thread. If 3.1' is not the actual Dc in Ethan's garage, then tell me what is wrong. Could it be that SAC's comments do apply and ignoring them had produced a result that is not valid? What else could have gone wrong in this simple calculation? Determination of room volume? I doubt that Ethan's estimate if off by more than a few percent. What else has been measured to plug into the equation? RT60? Look at Dan's comment about about 10% variation across 1/3 octave as the BBC guideline. Does this room fit that spec?
#28
16th March 2013
Old 16th March 2013
  #28
Gear addict
 
Bobecca's Avatar
 

Quote:
Originally Posted by Rod Gervais View Post
It was read (by myself, and (I would imagine) many others ) a long LONG time before you ever linked to it..... perhaps you need to re-read it if you disagree with my statement.......
Reading is one thing, understanding is another My only disagreement would be that you wrote "reverberation field" and "reverberation sound field". The meaning must differ or?

Quote:
Originally Posted by Rod Gervais View Post
At which point (in an acoustically small room) do you reach critical distance?
When direct sound is at equal size of reverberant sound and at what distance it is to the source. But you allready know this.

Quote:
Originally Posted by Rod Gervais View Post
Who suggested that there wasn't a source? Perhaps you could quote whatever statement was made that suggested there was no sound involved.

Rod
You didnt wrote a sound source
#29
16th March 2013
Old 16th March 2013
  #29
Lives for gear
Quote:
Originally Posted by Bobecca View Post
Rod, please move on. This is emberassing
Actually, Rod wrote great, wise words. Learn them.
Ethan Winer
Thread Starter
#30
16th March 2013
Old 16th March 2013
  #30
Gear Guru
 
Ethan Winer's Avatar
 

Thread Starter
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Quote:
Originally Posted by jim1961 View Post
Ethan, I think it would help if you better defined what direction or objective(s) you are trying to accomplish.
My sole objective is to debunk the common myth that small rooms can't have real reverb. Nothing more, nothing less.

Quote:
Are you:
3) Trying to expose flaws in the running assumption that RT-60 is meaningless in small rooms
Yes, exactly.

Quote:
4) Trying to make a case that reflections in a typical room are a form of reverb
No, on this we all agree. As explained in the first paragraph of my article: "a typical furnished room has a series of individual reflections that die fairly quickly. In order to obtain true reverb, sound waves must reflect off multiple surfaces, rather than only one or two bounces before being absorbed by a carpet or soft couch."

--Ethan
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