Cathedral vs flat ceiling

[Ethan Winer]

Originally Posted by dykstraster@gmai

Is there nothing to the effects on air regarding humidity and temperature given of the retention properties of wood vs concrete?

Probably not enough to worry about. When absorbers are tested in a lab the room is controlled to tight temperature and humidity tolerances. But that's because repeatability and absolute values are important. The data we're using for absorption was (presumably) measured in a real lab, so that should already be taken into account. Now, one might argue that wood at 50 degrees F reflects differently than at 100 degrees F. And it probably does! But I can't imagine the difference is significant, or more than the typical sub-dB differences we see between various materials.

--Ethan

[DanDan]

Ethan, there is a great advice (from one of your Presidents I think?) :- " It is better to keep ones mouth shut and appear a fool, than to open it and remove all doubt."
So, completely ignoring that, I would be happy to join a discussion on how various materials 'sound'. I do however think it best to start a new thread with an appropriate title, and I still think this one should be culled.

I, like you, have gradually removed quite a few of the myths and contradictions in my own mind, and would happily share this.
e.g.
Wood, presumably reasonably hard wood, with a surface finish, mounted somewhat resiliently, sounds bright in a listening room. However, a recording of an acoustic instrument in a room with a significant amount of such wood, sounds warm. Go figure. I have no need to prove this. I can extrapolate from my listening and recording experiences. I could take a few bits of Physics and Maths to further shore up my observations, but is there hardly a need.


Absorption Coefficients are typically measured in a historic manner. The method reflects the intended use in the field of Building Acoustics.
This field is more concerned with Noise than 'Sound'. I reckon any attempt at putting numbers on a 'Sound' or perhaps 'Tonality' in the context of recording or listening to music, has to be full range. Omitting below the 125Hz and above the 4kHz Octaves is ignoring three musically vital octaves. Furthermore those Coefficients apply to a diffuse sound field, which doesn't exist in our listening rooms. There are a couple of other factors, but clearly that set of numbers is not musically complete and it is not mathematically applicable to our rooms.

Regarding Concrete vs Wood. I believe the only test which would answer our enquiring minds would be to take a finished treated listening room with a finished Concrete floor. Measure it in terms of averaged Frequency Response, EDT, and whatever you fancy. I also recommend playing reference music over the speakers and recording it with a high quality stereo pair, suitable for later headphone listening. Install a wooden floor. Repeat the process using the same measurement locations. Wouldn't that be interesting?

Alton Everest had many great wisdoms.
My favourite paragraph of his is:-
The pioneering scientist was right when he said 'to measure is to know'
Only in this way can subjective factors be controlled. However the very act of hearing is subjective and the trained ear might very well detect flaws in a studio, elegant graphs and measurements to the contrary. This does not mean that measurements are worthless. It only means that if one is processing programs for ultimate consumption by the human ear, a trained ear and measurements must supplement each other. The science of acoustics has grown to maturity during the past 100 years but there is still something of an art about it's practice.

Warm Regards, Dan FitzGerald

[Ethan Winer]

Originally Posted by DanDan

So, completely ignoring that, I would be happy to join a discussion on how various materials 'sound'.

Great, back on track again.

I do however think it best to start a new thread with an appropriate title, and I still think this one should be culled.

As far as I'm concerned this thread could be snipped right after my Post #5 where I said, "There's no difference in sound between concrete and wood, or at least not enough to worry about. Both reflect sound."

Omitting below the 125Hz and above the 4kHz Octaves is ignoring three musically vital octaves.

Agreed completely. I'm not so concerned about below 125 Hz in this case because we're talking about solid slabs. But I do wish the data included 8 KHz because if there's a meaningful difference between drywall and glass, it will be up there. I'm still hoping Max will come back with the data from Table 10 in Beranek's book he mentioned. Maybe that includes the 8 KHz band?

those Coefficients apply to a diffuse sound field, which doesn't exist in our listening rooms.

Yes, but that doesn't mean they're not useful. Absorption coefficients apply nicely to bass traps and RFZ panels in a bedroom size studio.

Alton Everest ... said 'to measure is to know'

Hey, that's been my point all along!

hearing is subjective and the trained ear might very well detect flaws in a studio, elegant graphs and measurements to the contrary.

This is where we part views because I firmly believe that measuring trumps hearing every time. Assuming you know what and how to measure of course! Hearing is very fragile, and a mix that sounds great one day can sound terrible the next even when nothing has changed. If you've ever tweaked the EQ on a snare track to perfection only to discover later you were adjusting the vocal, you know what I mean. That, and all the people who believe they hear the sound change when they replace a power cord. Measuring is the only way to separate fact from belief.

--Ethan

[spencerc]

Originally Posted by Ethan Winer

This is where we part views because I firmly believe that measuring trumps hearing every time.

--Ethan

Our ears are much more fine tuned than any measuring device that is run into a computer Ethan. There can be so many flaws along the way...imperfect microphone response, imperfect cable, imperfect preamp, imperfect converters (both AD and DA). Not to mention the whole subject of physcoacoustics as Andre was bringing up...

Getting back to what Frank was originally saying...

If 10/10 or even 8/10 TRAINED ears can hear a difference between wood and concrete, then there must be one. To not agree with this statement is insulting to those people who have spent their lives in this field and have so much experience. You are calling them liars...

And for the love of pete, PLEASE stop bringing up your power cord analogy. I feel like I'm listening to a broken record. I would bet you money that these people are not the same people that we are referring to as "TRAINED" Listeners who have experience in the professional audio field such as recording engineers. Audiophiles are not the same thing.

Ethan, remember that I am mostly AGREEING with you on this topic - For a small home studio (as in this case), money is most likely better spent on other things. A cement and a wood floor will both reflect...true! and so is it worth the few thousand dollars to switch a cement floor to a wood one? Well that is totally dependent on budget. If this guy has tons of cash to spend, then why not? If he is on a tight budget, I would have to say it is probably not worth it to switch the floor as I'm sure you would have reached/pasted the point of diminishing returns.

That being said, please don't be so ignorant to ignore the fact that a wood floor and a cement floor will not reflect exactly the same.

Our brains are so much more complex than any computer system and I truly believe that human experience is not worthless.

Computers haven't replaced us yet Ethan

-Spencer

[Glenn Kuras]

Ok so it seems as we all agree (well one guy is out but hey that's how it goes) that wood does produce a different sound in a room vs concrete. Now the big question is WHY!!!!
I think Bryan gave the best answer but I would like to hear others also.

Glenn

[DanDan]

Clearly neither logic or rationale will modify the absolute intransigent statement ' Measurement trumps hearing every time'.
I have voided the source of your calculations, those numbers, as incomplete, and inapplicable. You have not validated them using accepted Science, but simply brushed aside the voiding argument.
Once again, the wood is normally resiliently mounted, not a rigid slab. The three octaves being omitted contain more musically vital energy than all the rest combined. The numbers do not apply in a non diffuse space. How can you simply say they are still useful? Show me the science behind that assertion? Can you Prove or even show that your numbers, which came from where? can be usefully applied to how something 'sounds'. Even when applied correctly in the right space, Sabine calculations rarely come near reality.
By all means prove your point, by using full scientific method, not some cherry picked aspects which simply ignore and omit bigger realities. Please, no more of that Hi Fi myths stuff. You are the only one here who said wood sounds 'warm', which it isn't, when placed in context. The repeated suggestions that our opinions are in some way related to buyers of 2000 dollar power cables is silly. All of the contributors here have expressed the considered conclusion that science cannot stand alone in the evaluation of heard sound, coincidentally agreeing with Everest. So, are we all simply wrong?

Dan

[Ethan Winer]

Originally Posted by spencerc

If 10/10 or even 8/10 TRAINED ears can hear a difference between wood and concrete, then there must be one.

I agree with this 100 percent. As soon as someone auditions and/or measures two identical rooms that vary only by the floor surface - or some other single variable - I'll switch sides.

Seriously, this is exactly the problem. Nobody I know of has ever done a proper comparison. Often, what seems true intuitively turns out not to be true at all when properly analyzed.

And for the love of pete, PLEASE stop bringing up your power cord analogy.

But that is totally relevant! Power cord proponents are absolutely certain their replacement cord changed the sound. These are not all stupid people, and many of them are experienced listeners and very serious about their hobby. So let me put it back at you - what would you say to a friend who you like, and who you know is not stupid, who tells you he is certain beyond doubt that the new power cord he bought makes a big difference? This is a serious question and I hope you'll answer.

Our brains are so much more complex than any computer system and I truly believe that human experience is not worthless.

Of course not worthless. But not more accurate than measuring, which wins by at least two orders of magnitude. Do you happens to live anywhere near me in Connecticut? If so, I invite you here for an hour or two of playing around with subjective experience, blind testing, and so forth. I promise you will leave with a different opinion of this stuff.

--Ethan

[johndykstra]

If graphs are the be all end all, how come I keep hearing experiences where someone shoots their room and the graph looks different everytime?

For the record, my guitarist got one of those inch thick Monster power cables for his guitar amp. It defineatly made it louder, which makes it sound better. I suspect that if you used a standard cable and turned the amp up, it'd be the same thing. None the less, he swears by that thing. It's not a psycho-symatic difference, that thing IS louder with the beefy power cable. So there is a difference.

Feel free to completely discredit me at this point.

[Ethan Winer]

Originally Posted by DanDan

The three octaves being omitted contain more musically vital energy than all the rest combined.

If that were true, why do the acoustic standards focus on the six octaves that were included and ignore the rest?

Dan, I already agreed with you that 8 KHz is important, and I wish I had that data. If I do a surface reflectivity test here of concrete versus wood, will you and others accept the result as valid? I have no idea what the result will be! But there's no point in my bothering if you guys will then find something else to object to.

Even when applied correctly in the right space, Sabine calculations rarely come near reality.

Again, I was and still am willing to test materials here. Then I can test pure reflectivity, rather than rely on absorption data from someone else. My fear is I'll go to the trouble to do this, and y'all will some up with some other reasons to dismiss the results.

So, are we all simply wrong?

I honestly don't know, but it's certainly possible. So far I have seen nothing but opinion. Indeed, for all the talk of "we demand scientific proof" I'm the only person who has actually done that.

Tell you what. All of you, not just Dan. Let's devise a practical test that you all agree in advance will be valid, no matter the outcome. It must be practical and possible! Not "Build two rooms" but something that can reasonably be achieved in a day or whatever. Then I'll do it here, and hopefully one or two others will do the same so we can compare results.

Deal?

--Ethan

[johndykstra]

Originally Posted by Ethan Winer

If that were true, why do the acoustic standards focus on the six octaves that were included and ignore the rest?

Dan, I already agreed with you that 8 KHz is important, and I wish I had that data. If I do a surface reflectivity test here of concrete versus wood, will you and others accept the result as valid? I have no idea what the result will be! But there's no point in my bothering if you guys will then find something else to object to.



Again, I was and still am willing to test materials here. Then I can test pure reflectivity, rather than rely on absorption data from someone else. My fear is I'll go to the trouble to do this, and y'all will some up with some other reasons to dismiss the results.



I honestly don't know, but it's certainly possible. So far I have seen nothing but opinion. Indeed, for all the talk of "we demand scientific proof" I'm the only person who has actually done that.

Tell you what. All of you, not just Dan. Let's devise a practical test that you all agree in advance will be valid, no matter the outcome. It must be practical and possible! Not "Build two rooms" but something that can reasonably be achieved in a day or whatever. Then I'll do it here, and hopefully one or two others will do the same so we can compare results.

Deal?

--Ethan

I'd like to see a way to make the test more cumulative. Meaning, not just one bounce off a small surface and into a microphone. It seems to me, that multiple bounces of 2nd, 3rd, etc... reflections in a full room are going to add up to a measureable difference.

[Ethan Winer]

Originally Posted by dykstraster@gmai

If graphs are the be all end all, how come I keep hearing experiences where someone shoots their room and the graph looks different everytime?

I can't speak for others, but that never happens to me. However, moving the measuring microphone even 1/4 inch can make a real difference in the results. And if a loud truck rumbles by outside for one test but not another, that will change the readings too of course.

For the record, my guitarist got one of those inch thick Monster power cables for his guitar amp. It defineatly made it louder, which makes it sound better.

LOL, this is exactly what I'm talking about! Thanks for making my point for me. I'm sure you agree that if nothing was changed but the power cord, and the amp was suddenly louder, that difference could be measured with a simple VU meter and microphone, yes? But when you challenge the power cord companies about their claims, they say the improvements cannot be measured. You just have to listen and the difference in quality is apparent. These people are very smart because they understand how fragile human hearing really is. Hence, all the full page ads in hi-fi magazines for wire. Wire selling is a huge business based entirely on wishful thinking and placebo effect.

When you get a chance, take an SPL meter or microphone etc and measure the amp with both power cords. Don't play the guitar though, because you can't play the same way every time. So use a test tone or some other repeatable source. Then change to the Monster power cord and come back to tell us what happened.

--Ethan

[Ethan Winer]

Originally Posted by dykstraster@gmai

It seems to me, that multiple bounces of 2nd, 3rd, etc... reflections in a full room are going to add up to a measureable difference.

Yes, any differences will be magnified by repeated passes. Just like passing light through one pink filter versus three pink filters. But measuring software is more than sensitive enough to get good data from one bounce.

--Ethan

[johndykstra]

Originally Posted by Ethan Winer

Yes, any differences will be magnified by repeated passes. Just like passing light through one pink filter versus three pink filters. But measuring software is more than sensitive enough to get good data from one bounce.

--Ethan

But that's a real world difference that your initial numbers don't take into account. I forget how much, but there was a "slight" difference in reflectivity between concrete and wood at certain frequencies. Now put it in a room and lets watch slight morph into noticable

[johndykstra]

Originally Posted by Ethan Winer

When you get a chance, take an SPL meter or microphone etc and measure the amp with both power cords. Don't play the guitar though, because you can't play the same way every time. So use a test tone or some other repeatable source. Then change to the Monster power cord and come back to tell us what happened.

--Ethan

I'll use my synth, but I need to track down an SPL meter first.

[Ethan Winer]

Originally Posted by dykstraster@gmai

there was a "slight" difference in reflectivity between concrete and wood at certain frequencies. Now put it in a room and lets watch slight morph into noticable

Yes, I agree that the total sound in a room will experience multiple bounces, and that will be audible. But each bounce is softer than the one before, so then we have to decide how bounces are practical to allow. If we have a room that's totally empty with 10 audible bounces, that has no relation to a studio anyone would actually use!

This is why I continue to emphasize that my intent has always been a single surface only, especially a floor on solid ground. But not an entire room made of cement versus entire room made of wood, which is what this thread has morphed into.

--Ethan

[Ethan Winer]

Originally Posted by dykstraster@gmai

I'll use my synth, but I need to track down an SPL meter first.

A microphone plugged into anything with a VU meter is fine. Just don't move the microphone!

[DanDan]

Sorry I don't know how to do the Quote and retort thing properly. I will put DD- in front of my answers.

If that were true, why do the acoustic standards focus on the six octaves that were included and ignore the rest?

DD- I don't understand the 'if'. Do you not accept that the two bass octaves contain enormous amounts of energy, compared to the upper octaves? Challenge my point if you will, but please no inuendo.
I will repeat again. Building Acoustics is focussed on Noise issues, not Tonality. Noise above 4kHz does not often make it through a wall. Below 125 Hz is not measured because the Measurement rooms would be too enormous and thus expensive. Thus we used to expediently ignore those lower and top octaves. This has been changing, modern test standards do measure higher and lower, but the LF Measurement difficulty is unresolved. Audiologists also used and often still use, a similarly restricted spectrum. These are matters of History and there is a need to catch up.

Dan, I already agreed with you that 8 KHz is important, and I wish I had that data. If I do a surface reflectivity test here of concrete versus wood, will you and others accept the result as valid? I have no idea what the result will be! But there's no point in my bothering if you guys will then find something else to object to.

DD- If the 8kHz Octave is important, how can your 'proof' be valid.
Your proposed test has already been rejected. I have proposed a different one. It doesn't require two rooms, but it is unlikely to happen. I reckon anyone who finishes a concrete floor properly will not move on to wood. Concrete sounding warmer, of course.

Quote:
Even when applied correctly in the right space, Sabine calculations rarely come near reality.
Again, I was and still am willing to test materials here. Then I can test pure reflectivity, rather than rely on absorption data from someone else. My fear is I'll go to the trouble to do this, and y'all will some up with some other reasons to dismiss the results.

DD- Reflectivity is not enough to describe how something sounds. This has been repeatedly stated, and thus such a test will not be useful.
The source of all of this is the statement that a concrete floor will sound the same or near enough to wood. Changing horses to just Reflectivity is an extrapolation none of us will accept.

Quote:
So, are we all simply wrong?
I honestly don't know, but it's certainly possible. So far I have seen nothing but opinion. Indeed, for all the talk of "we demand scientific proof" I'm the only person who has actually done that.

DD- Of course it is possible but what are the chances.
You have not provided a 'scientific proof'. I have voided your 'proof' using simple science which you have not challenged. Didn't someone way back run the same numbers and come up with a 3dB difference? Not that I would accept that as a proof either, more of an illustration which happens to agree with trained professional perception and experience. Once again those numbers are not applicable to the subjective experience of hearing a sound. Your foundations are sand.

Tell you what. All of you, not just Dan. Let's devise a practical test that you all agree in advance will be valid, no matter the outcome. It must be practical and possible! Not "Build two rooms" but something that can reasonably be achieved in a day or whatever. Then I'll do it here, and hopefully one or two others will do the same so we can compare results.

Deal?

DD- I proposed a test several posts back. It is a single room. This test was designed by me to be very like a typical EW test which we know and love you for. This is the fist time I have seen you stongly promote a concept without your normal test. It ain't working.
I would love to hear the result of a test, if anyone does it please include the reference music bit. Unfortunately this will probably will never happen.
FWIW I suspect it would go as follows.
The resilient mounting of the wood will diminish VLF a little. The room will be lossy at the lowest frequencies. The same mounting, functioning slightly as a panel trap, will help a little with vertical modes, evening out the response a tad. The acoustically bright finish on the wood will prove nasty and the concrete will be preferred due to being warmer. A rug will appear on the wood floor. ;-)

Best, DD

[Weasel9992]

John, Dan, Spencer, et al...I just realized that part of the problem is that Ethan is reasoning deductively while the rest of us are reasoning inductively. There's no solution to that problem. No two people reasoning from opposite directions will ever convince each other of the truth of their respective statements because they can't even agree on what constitutes "proof". In other words, everyone might as well quite trying so Ethan can stop repeating himself. If we continue this way there is an inevitable outcome in terms of the argument. It'll go something like this:

Ethan: "It doesn't."
Everyone else: "Yes it does."
Ethan: "No it doesn't"
Everyone else: "Yes it does."

There is one thing I'm confused about though. Ethan, you threw out Bryan's assertion than the surface reflection properties extrapolated to a larger scale to mean something concrete; how then do you plan to conduct a small scale test with large scale implications? Wouldn't that require you to extraploate your results in the same way bryan suggested? And what would you hope to prove after saying what you said after Bryan's post?

Furthermore, please explain how Bryan was wrong to begin with. You stated that things are scaled so that whatever is true of one unit is true of 100,000 units. True, the scale remains the same relatively speaking, but the net result is much, much larger. The difference is that .14dB is not audible where 3dB most certainly is. It's exactly the same thing as saying that there is a one degree difference between two headings; that doesn't make any real difference over one foot, but it at 100,000 feet the difference is 100,000 times as large even though the azimuth difference has not changed. It's still one degree though there is a huge space between the two end points at 100,000 feet vs a single foot.

Frank

[Ethan Winer]

Too busy to deal with all of Dan's good points, so I'll do that later or tomorrow. But I have just enough time now for this:

Originally Posted by Weasel9992

they can't even agree on what constitutes "proof".

Yes, and this is why I asked above for clarification on what sort of practical tests we can do that will be accepted. Once we agree on a test, the rest is downhill!

you threw out Bryan's assertion than the surface reflection properties extrapolated to a larger scale ... please explain how Bryan was wrong to begin with.

Sure, glad to. I'm sure most here understand the concept of absorption coefficient, and how it differs from sabins of absorption. An absorption coefficient is a dimensionless spec. For whatever size sample you have, you get some percent amount of absorption. Reflectivity is exactly the same. Indeed, it's the reciprocal of absorption. If a sample is one square foot, some amount of the sound is reflected. This too is a dimensionless spec.

Now, we all know that a large empty space has more reverb, and longer reverb, than a bedroom. But in the context of discussing reflectivity, that's an unrelated issue that just confuses things. It's much more sensible to stick with the "coefficient" concept which is dimensionless to stay focused on the one attribute that matters - loudness of the reflections at different frequencies. So whether a wall is 10 square feet or 100 square feet, sound in the room will strike the wall and be reflected by some percentage versus frequency.

True, the scale remains the same relatively speaking, but the net result is much, much larger.

Yes, but again this happens regardless of the surface types just because large rooms have more reflecting surface area, and thus more reverb, than small rooms. This is unrelated to the percentage of reflectivity, and so is best omitted from the discussion.

The difference is that .14dB is not audible where 3dB most certainly is.

Right, but this is exactly why applying scaling is wrong in this context. If the entire room is cement first, then lined with wood, the difference in reflected sound will be 0.14 dB (or whatever) regardless of the room size. Yes, the total amount of reverb will change, but not the ratio difference between cement and wood

Since the data my "reflecting" formula is based on is dimensionless, how could one know how much to multiply the dB values by for 10 square feet? Or 1000 square feet?

--Ethan

[Weasel9992]

Totally understand and agree, but the excel spreadsheet you provided expressed the difference in terms of decibels. Again I ask how you get around the fact that there is a .14 dB difference between wood and concrete, and that when that is extrapolated to 1440sqft it amounts to a 3dB net difference? You haven't answered that question. I'm not asking about the coefficient. You're right, that is "dimensionless" so to speak...so are degrees of separation; three degrees of difference is the same at one foot as it is at 100,000 feet, but the distance the two points are from one another will drastically change. Please explain how my metaphor expresses a different truth than your statement.

Secondly, you also didn't explain how you would extrapolate the test results to a larger scale and what the data would mean in view of your dismissal of Bryan's extrapolation of the data in your spreadsheet.

Frank

[DanDan]

Frank, agreed almost entirely. However I don't think the conclusion is inevitable. I believe the direction is currently positive.
We are indeed working with undefined terms. Proof, Science, Warm, and so on. Perhaps some of us are not qualifed enough to be dipping our toes in the Science. My understanding of these matters is that generally there is a hell of a lot more to it than I know, but a combination of methods gets me done successfully. One cannot dismiss things like; Coefficients are only valid in Diffuse spaces, the multiple bounces, changing coefficients with angles of incidence. If these tests were scalable why would the ISO etc. tests require such large rooms and large samples? Are they wrong? Perhaps Brian would jump back in to explain how he got that 3dB. It would save me a lot of head scratching and trawling through text books here. I am very interested in that point in particular.
Regarding a Reflectivity test, if the concrete is finished with the same say Epoxy finish as the wood, they will surely be close at MF and HF. Reflectivity is not enough ( A New Bond Movie ;-) )
I suspect there may be a Test Method which would yield something useful. Sound Intensity methods can be wonderfully blind to the test circumstances. Even with such a Reflectivity Test, I think we would still end up with vastly intricate statistical predictions to extrapolate to a real world situation- multiple bounces, angles of incidence and so on. It is my opinion that many theories of Acoustics have come from tests, often involving massive resources, thus the dearth of them, restricted bandwidths etc. The theory is later developed to put some numbers on it.

I have another catch- phrase- joke, I promise the last one. :-)

That's all right in Practice, but what about the Theory?

Best. DD

[Ethan Winer]

Originally Posted by Weasel9992

the excel spreadsheet you provided expressed the difference in terms of decibels.

Yes, assuming a rigid massive backing so whatever is not absorbed is reflected. Which is how the underlying data was measured.

Again I ask how you get around the fact that there is a .14 dB difference between wood and concrete, and that when that is extrapolated to 1440sqft it amounts to a 3dB net difference?

You can't extrapolate because the data itself is dimensionless. That's my whole point. Absorption coefficients are dimensionless, and so are reflection coefficients. And, by extension, the reflection dB equivalents.

you also didn't explain how you would extrapolate the test results to a larger scale

I honesty don't know how else to say this. There is nothing to extrapolate. The idea that you can scale the dB numbers, or would need or want to scale them, is fundamentally flawed. In the same way it is flawed to try to convert absorption coefficients from being dimensionless to having a dimension. Once you understand why you can't extrapolate absorption coefficients, you'll understand why you can't extrapolate reflection coefficients either. This is exactly why coefficients are used in the first place!

--Ethan

[Weasel9992]

Originally Posted by Ethan Winer

The idea that you can scale the dB numbers, or would need or want to scale them, is fundamentally flawed.

Why?


Frank

[Weasel9992]

Originally Posted by Ethan Winer

You can't extrapolate because the data itself is dimensionless. That's my whole point. Absorption coefficients are dimensionless, and so are reflection coefficients. And, by extension, the reflection dB equivalents.

If the data is "dimensionless" and have relevance only within the experimental context, then what use is it? You are answering the question by repeating the statement I am questioning. Please explain fully your reasoning.

Frank

[Ethan Winer]

Originally Posted by DanDan

Do you not accept that the two bass octaves contain enormous amounts of energy, compared to the upper octaves?

Absolute energy levels don't matter because Fletcher-Munson evens that out.

Building Acoustics is focussed on Noise issues, not Tonality.

That's simply not true. The design of recording studios focuses on both equally.

Noise above 4kHz does not often make it through a wall. Below 125 Hz is not measured because the Measurement rooms would be too enormous and thus expensive.

Yes, and that might be why whoever gathered the data failed to include lower and higher ranges. Because of the presumed audience. But I'm sure those ranges were measured in the lab! When I've tested my products the report covers from 25 Hz up to 10 KHz. The data below 100 Hz is not certified as accurate, but it's not useless either.

but the LF Measurement difficulty is unresolved.

I totally agree. But in the context of surface reflectivity for materials placed on a rigid concrete floor, we all know that LF absorption is not relevant. Believe it or not, I'm still trying to stick to what happens with wood flooring over solid concrete.

If the 8kHz Octave is important, how can your 'proof' be valid.

You are correct, which I already acknowledged. But at least the "proof" is relevant for the vast majority of the range.

Reflectivity is not enough to describe how something sounds.

In the context of a surface applied over rigid concrete, what else is there? Please be very specific.

The source of all of this is the statement that a concrete floor will sound the same or near enough to wood.

The source of this is a guy who has an existing rigid concrete floor, who was considering adding wood on top.

Of course it is possible [everyone else is wrong] but what are the chances.

Pretty high IMO! And Yes, I'm serious.

Didn't someone way back run the same numbers and come up with a 3dB difference?

See my post above about that. The whole notion of expanding numbers like that is flawed.

--Ethan

[Ethan Winer]

Originally Posted by Weasel9992

If the data is "dimensionless" and have relevance only within the experimental context, then what use is it? You are answering the question by repeating the statement I am questioning. Please explain fully your reasoning.

Frank, I've explained as well as I can so I'm going to have to turn this back on you. Please explain fully your reasoning for why a surface reflectivity coefficient should not be dimensionless. Please show each math step as you go from sealed cement that differs from parquet over cement by 0.18 dB at 1 KHz. Use only hard numbers, not letter variables. No assumptions or guesses. No gut feeling or intuition. Simply outline all the steps needed to get from 0.18 dB to 3 dB in a room of any size you choose.

--Ethan

[Glenn Kuras]

Originally Posted by Ethan Winer

Frank, I've explained as well as I can so I'm going to have to turn this back on you. Please explain fully your reasoning for why a surface reflectivity coefficient should not be dimensionless. Please show each math step as you go from sealed cement that differs from parquet over cement by 0.18 dB at 1 KHz. Use only hard numbers, not letter variables. No assumptions or guesses. No gut feeling or intuition. Simply outline all the steps needed to get from 0.18 dB to 3 dB in a room of any size you choose.

--Ethan

Slow down there big boy. I still think you need to answer Frank, which you called Bryan wrong.
I for one know that if you put one piece of 4x8 piece of board down test then put down a full room of wood them MORE will be absorbed. So if you test with one piece of board in your "basement test room" it ain't going to tell us anothing. If you want to prove use all wrong you are going to have to go all the way on this one.
Get building those rooms Ethan.

[DanDan]

The Fallacy of ignoring the two Bass Octaves has been pointed out over and over again. The wood is not rigidly mounted. Even in those dubious figures, (Lino, Cork, jeez) the Absorption coefficients show the largest difference at LF, so the actual difference between actual installed wood and actual concrete will probably be big at LF. Fletcher Munson will not iron out
You chose to ignore the relevance of below 125 Hz in music, with this rigid slab justification.
Wood is never securely glued to concrete with say epoxy or whatever. There is a damp issue. This rigid slab sandwich is not of this world. Wood is normally resiliently mounted and will vibrate at LF unlike Concrete.
Can you describe to me the sound of a Jazz Trio omitting below 125Hz?

The term Building Acoustics as commonly understood over here is focussed on Noise issues. The term Architectural Acoustics is used when it comes to Theatres, Studios, Concert Halls etc. I have explained that those coefficient type measurements come from the world of Building Acoustics. Thus the restricted spectrum. In BA practice even those figures are simply averaged to derive an RT figure. This is used to calculate Noise issues. It is well recognised that these historical restricted spectra are inadequate, and progress is being made. I believe you would find much better private sets of coefficients gathered from actual Halls and Studios, measured with and without the installation of materials, seats, etc. in the world of Architectural Acoustics. As before, Sabine calculations are notoriously divergent with measured reality and do not apply in non diffuse environments. They may be used to get to the Ball Park, but they won't get you in.


I think many of us have explained already why we will not accept Reflectivity or any other singular measurement to describe tonality. That is a bit like saying that Frequency Response alone can describe the sound of speakers in a room, omitting all else. If you want to advance the discussion we need to leave that behind unless you can prove your case or refute ours.
Similarly changing the goal posts won't pass muster. The original statement was that Concrete and Wood, for practical purposes sound the same. Later restricting that to tightly defined issues of Reflectivity only, in a limited spectrum, on a rigid slab, not in a structure, is simply not fair play.

I am pleased to note that your 'proof' has shifted from absolute to qualified, i.e relevant over the 'majority' of the range. :-) However I don't think that you can call those six octaves a majority, certainly in terms of music. For instance, when mixing, using Eq in those missing octaves is very powerful. Smiley curve. Or back to the Jazz Trio with no bottom two strings and no cymbals :-)

If polished and varnished Hard Wood has a much higher Reflectiivity than acid stained Concrete in the 8kHz Octave, and I suspect it has, I think even you would concur that it sounds different?

Till Tomorrow, DD

[DanDan]

I believe there is some issue around Scalability which we are missing. This reflects my earlier comments about our Scientific inadequacies, Faux Science etc.
Frank, Glenn, I took a look, Brian's 3dB seems to be a full room, which is stretching a point, adjusting goalposts etc. Ethan's calculations look fine to me. I believe he is correct within the unworldly parameters he has latterly applied. It is those parameters I have an issue with.
A point to ponder perhaps- If Ethan were to test a patch of material, say 4 x 4 anechoically, I suspect it would have very little reflectivity below say 250 Hz? I presume that is why ISO use 10 sq metres in rev rooms big enough to be diffuse down to 125Hz.

DD

[spencerc]

Hey Everyone...I haven't had time to catch up on the many new posts today (but I will later tonight).

I only have a minute and so I wanted to say, I think I have a way of solving this for good (hopefully). I'm going to be constructing my studio this spring/summer, and I will do tests before/after I lay down the hardwood.

Thanks,

-Spencer