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post #31 of 55 Old 05-03-2014, 10:58 AM
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Originally Posted by jim19611961 View Post

I suppose it depends on what we define as real science. Dr. Lawrence Krauss, a theoretical physicist, has said that if one time in a hundred you get a contradictory result, then its not science. That criteria would rule out much we assume to be scientific in regards to this topic.

I find it hard to believe Dr. Krauss would say that. It's like saying that no study whose results have a p>.01 can be considered 'real science'. Do you have a link to his quote?
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post #32 of 55 Old 05-03-2014, 11:11 AM
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Originally Posted by krabapple View Post

I find it hard to believe Dr. Krauss would say that. It's like saying that no study whose results have a p>.01 can be considered 'real science'. Do you have a link to his quote?

I saw him say it on a youtube video. A lecture or panel of his. It would take hours or days to find it. I can give a bit of context though.

He was talking about String Theory. And it was within a context of whether it is real science or not. He went on to define what the scientific method is, and that is of course repeatability and observation. It was then that he made the comment.

Now its possible he meant it in the context of this discussion. That is, what constitutes provability in the field of theoretical physics. Other areas of science, if he were asked, may not need such tight constraints.

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post #33 of 55 Old 05-04-2014, 05:34 AM
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Originally Posted by jim19611961 View Post

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Originally Posted by krabapple View Post

I find it hard to believe Dr. Krauss would say that. It's like saying that no study whose results have a p>.01 can be considered 'real science'. Do you have a link to his quote?

I saw him say it on a youtube video. A lecture or panel of his. It would take hours or days to find it. I can give a bit of context though.

He was talking about String Theory. And it was within a context of whether it is real science or not. He went on to define what the scientific method is, and that is of course repeatability and observation. It was then that he made the comment.

That makes sense to me in the specific context. IME fundamental principles are very reliable. For example, how many contradictions of Ohm's law does one expect to find? A highly probable answer is: none in your lifetime. If you find an apparent contradiction of Ohm's law, then there has to be a hidden influence that makes the situation different from a simple application of Ohm's law.

Over my life I've literally staked my life on physical laws like this again and again, and so has just about everybody else. For example, how many times have you pulled your car out into traffic where a failure of your automobile to respond predictably might have put you in danger of causing an accident? How many times have you flown in a plane or ridden on a train? Each of those acts takes faith in a huge number of applications of a raft of physical laws working out exactly right.

I remember flying to El Paso from Key West to fire a missile at White Sands in an old Lockheed Electra turboprop which used to be a SOTA airplane. Our chief missile mechanic looked out on the wing and noticed a repair. He said that a missile wing with a repair like that could cost him his job. Yet, there we were flying over the Gulf of Mexico hundreds of miles from land with this nasty old repaired wing. We had no choice but to rest our lives in the natural laws that made this repair reliable in that circumstance. It held! ;-)

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Now its possible he meant it in the context of this discussion. That is, what constitutes provability in the field of theoretical physics. Other areas of science, if he were asked, may not need such tight constraints.

The obvious counter examples relate to human performance, particularly near the limits of human achievement. However, even there there are hard and fast rules. For example we might like to think that the threshold of hearing has a flexible limit such as we see in sports events involving say, running a mile. When I was a boy Roger Bannister did it in 4 minutes and that was huge. Wikipedia says that "Currently, the mile record is held by Morocco's Hicham El Guerrouj, who ran a time of 3:43.13 in Rome in 1999." Four minute miles have taken place at high school track events. But, no woman has ever done this, yet. What are the chances of anyone ever running a 2 minute mile? Certainly, far less than once in every million tries.

However, the sensitivity human hearing is actually limited by the ear's ability to detect sound against a background of thermal noise and that woldwide ultimate background noise level isn't going to change because it is set by fundamental laws. No amount of training is going to change the thermal noise level of the air. There is no place to go to find anything better and still be able to breathe! People can say that human hearing varies from person to person, but the threshold of hearing very likely isn't going to be 20 dB less than the current threshold of hearing within our lifetimes.

I get criticized for not backing down on certain points. However, once I can relate a certain question to familiar physical laws and well known performance limits, why should I ever back down? I've been doing this for decades and it always works out when the rubber hits the road. Just because other people don't know the physical laws at the same level of detail, and/or lack the confidence that comes from decades of experience with them related to how they work out in real world applications, why should I change my statements?
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post #34 of 55 Old 05-04-2014, 07:12 AM - Thread Starter
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Originally Posted by arnyk View Post

That makes sense to me in the specific context. IME fundamental principles are very reliable. For example, how many contradictions of Ohm's law does one expect to find? A highly probable answer is: none in your lifetime. If you find an apparent contradiction of Ohm's law, then there has to be a hidden influence that makes the situation different from a simple application of Ohm's law.
There is one strong contradiction: superconductors. As a conductor is cooled, one expects to resistance to keep going down. In superconducting material, there is a "critical" temperature where all of a sudden there is an abrupt drop to zero ohms:

tc_graph.gif

Once there current can remain in the superconductor even when the source of power is taken away! Since the original comment came from a theoretical physicist, we see the appropriateness of of this example as this is a quantum effect.

Another example is the famous double slit experiment where photons in a light source travel as waves when we are not measuring them but when we do, they act as particles. As Einstein said, there is a duality here and both answers are correct.

So the comment from Dr. Krauss has merit in quantum physics. Prior to discovery of superconductive material around 1900, one would have said such a thing does not exist. But post that discovery by Heike Onnes, we had a different view of conductor resistivity than past that event. At quantum level all bets are off.

You might say that in everyday life you don't notice quantum effects so it doesn't matter. Yet something as simple as the GPS in your phone or car relies on such science to provide correct results. The reason is that the satellites are travelling so fast that they demonstrate Einstein's relativity theory. The clock onboard the satellite is measuring a "different time" than what we have on earth. Since location is computed based on differential of time from the satellite and "earth time" we must provide the compensation due to clock drift or we would be way off our target. Fortunately that correction is there in every GPS device so all is well. But the point remains that there are experiments and later discoveries that alter or downright invalidate what we think the reality is.
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Over my life I've literally staked my life on physical laws like this again and again, and so has just about everybody else. For example, how many times have you pulled your car out into traffic where a failure of your automobile to respond predictably might have put you in danger of causing an accident?
Is this a trick question? Because I have and have so many others. Just a couple of months ago I was having some warranty work done on my car and they gave me a brand new $40,000 loaner. I was sitting at a light and decided to change lanes. There was traffic coming in the other lane but I thought I had ample time to pull into that lane. I pushed the gas pedal down the car started to go a few feet and then immediately lost power. The engine did not die or anything but simply decided that the accelerator pedal was not pressed. I thought this was a fluke. A couple of days later, I was making a turn in front of oncoming traffic. Once again the car went a few feet -- and put me at 90 degrees to the oncoming traffic -- and refused to move. I released the gas pedal and floored it and it fortunately got back to normal. This happened a third time before I returned the loaner. I spoke to service manager and he had some theory of what would cause that but I don't recall now.
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How many times have you flown in a plane or ridden on a train? Each of those acts takes faith in a huge number of applications of a raft of physical laws working out exactly right.
Very little on trains except while in Japan. But have flown a few million miles on Airplane. All kinds of unexpected things have happened there. Once we arrived at the gate, the doors opened and we all got our luggage and lined up for our turn to exist the plane. All of a sudden, the plane lurched forward and we all nearly fell on top of each other. Captain got on the speaker and said that a brake was released accidently and that this was the first time it had ever happened to him. He stood by the door and apologized to each one of us as we left!

Another sad example. Was travelling on the plane to a conference with a marketing lady from my team. I saw that she was pretty nervous and I started to explain how rare it is for someone to die from plane crash. She said nothing until I was finished. Then in calm and quiet tone said she had lost both of her parents due to a plane crash when she was young!!!
Quote:
However, the sensitivity human hearing is actually limited by the ear's ability to detect sound against a background of thermal noise and that woldwide ultimate background noise level isn't going to change because it is set by fundamental laws.
It is the case. But that sensitivity is adaptive which doubles our dynamic range to 120 db. There is an electromechanical amplification with feedback that is the source of that very high dynamic range. Your pupil dilating is a visual example of the same.
Quote:
I get criticized for not backing down on certain points. However, once I can relate a certain question to familiar physical laws and well known performance limits, why should I ever back down? I've been doing this for decades and it always works out when the rubber hits the road. Just because other people don't know the physical laws at the same level of detail, and/or lack the confidence that comes from decades of experience with them related to how they work out in real world applications, why should I change my statements?
It all depends on whether you learn something new along the way or not. I used to think that since the sound of speakers were so different, one could judge them sighted without worry. Then I took a double blind test and quickly learned that I was biased in my evaluation of speakers due to their looks and technology within them. Indeed one speaker that I always thought was an excellent one, in double blind testing I rated it as very poor. So poor that I thought it was a "control" to see if we were suitable subjects. Imagine my surprise when the curtains opened and I saw what was behind it.

I don't know all of your life experiences Arny. But do know that you had such revelations in audio when you did your blind testing. And that turned your many ideas you had about audio. If we were debating the Arny's of the time before that event in your life, we would have very different discussions. I know I am a different version of me with respect to audio than I used to be 10 years ago let alone longer.

Now if you want to measure yourself post that realization as being a constant, then I would respectfully say you have stopped learning. smile.gif

Edit: spelling errors smile.gif

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post #35 of 55 Old 05-04-2014, 07:33 AM - Thread Starter
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Relating the above to the context of this thread, nothing has shattered my audio views more than room acoustics. Everything I thought I knew, I didn't. Do you know for example that your hearing system adapts constantly and as such "removes" fair amount of the reflections in the room? Impossible? Think of a fan in your projector running. After a few minutes you "forget" about it, right? The sound is still there but the brain says "no new information there -- I know you are humming but I am going to delete follow on reports." A pretty smart "compression" system.

Here is an everyday example: think back to people in your household speaking to you. When they do that in different rooms, do you notice that their voice has drastically changed? You don't right? Yet, the reflections in each room and position of your loved one and yourself are radically different. The cognitive (thinking) of the brain knows that your aim is to hear and understand the other person, not analyze waveforms on a graph. So it stops recording those variations.

Speaking of a graph, the very foundation of what we suggest and do in a day to day basis in this forum is wrong. You are using a single microphone to measure the combination of two ears and a brain. Neither the mic nor the program showing you the data incorporate a single thing about differential hearing in the two ears and certainly no aspect of cognitive brain. Imagine if you took a single microphone and tried to record a concert. Would that sound identical to what you hear and capture everything that is there in that hall? Of course not. Yet when we try to optimize our rooms we simply close our eyes to such things.

Here is a much more detailed article on our misconceptions about room reflections: http://www.madronadigital.com/Library/RoomReflections.html

I have provided that link and references many times here. What is considered within totally changed my perspective on room acoustics. Nothing I knew is the same. Others however continue to ignore it no matter what. They painstakingly chase changes in the graph and so called targets only to find out at the end that the room no longer sounds good. All the while also ignoring placebo effect of putting something in the room and "hearing" an improvement.

The gut feeling understandings of room reflections is just wrong. We don't buy that a thick interconnect cable is better than a thinner one even though that sounds "intuitive." Yet in acoustics we always trust our gut feeling. We think a reflection is a bad thing since it is delayed and combines with the original. Listening tests however show that we prefer some of these reflections. And taking them away sounds "worse." Instead of trusting listening tests, we trust our gut. Again, we don't do that when comparing two CD players at different price points. But in acoustics, we all tend to be subjectivists smile.gif.

To put this in practical terms, above transition frequencies you almost don't need measurements to optimize your room. Listening tests guide us there and tell us where we may want to put acoustic material and where not.
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post #36 of 55 Old 05-04-2014, 08:01 AM
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I've been in acoustically damped practice rooms that were a little unnerving. You could actually hear blood rushing through your ears. Of course the sound of your instrument was put to the test. You could really hear out of tune notes, sibilance of the tone and needing to empty your spit valve. Then there is the matter of an extremely live room like Old Main that burned down at Sam Houston State University. Back in the early 70's when we practiced in that room, the sound was very lively and bombastic. Actually it sounded great whether at an oboe solo or blasting Tchaikovsky. The hall was built of wood, thus the burning down. What a loss. I actually preferred the sound there as compared to other music venues we played in. I guess the sound just enveloped me and that's what I like to hear...
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post #37 of 55 Old 05-04-2014, 08:57 AM
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It seems to me there are different lines of evidence each with a different criteria for establishing them.

1) Physical Laws: These are nearly absolute. I say nearly given that the ones we know break down under extreme conditions such as black holes and the big bang.
2) Theoretical Laws: Mathematical derived theory that lies outside of provability currently. Or laws/facts predicted by established Physical Law theory that remain unproven.
3) Consensus: An agreed fact established by a majority of opinion.
4) Speculative Facts: Those things thought to be true based on logic, plausibility, common sense or intuition.

Because science is evoked often to bolster an argument, I want to point out that only 1) is factual science. The others could in time turn out to be science, but they cant/shouldn't be evoked as science for the sake of argument.

The above said, much of what we discuss in acoustics is more akin to art than science, IMO. That is to say that what one prefers in terms of ambiance, liveliness, spaciousness, tone, coloration, dynamics, ect..... are more equivalent to texture, style, perspective, hues, color, contrast, ect...than they are to the rigors of Physical Law, and thus science.

My point here is that we may make more headway in acoustic discussion,as it pertains to room goals, if we treat the topic more like an art than hard science. Even in art, there is criteria that establishes good from bad. Likewise, there are criteria that establishes a well treated room from a poorly treated or untreated one, but most of it is not hard science.

For context, I am addressing rooms goals/preferences rather than the properties of those tools and room facts that bring about or determine the realization of those goals/preferences such as diffusion, absorption materials, room modes, ect....

I am not saying that there is not some hard science behind acoustic theory. What I am saying is that acoustic theory is only a tool that when implemented properly, allows us to fulfill a listening preference.
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post #38 of 55 Old 05-04-2014, 10:30 AM
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Originally Posted by jim19611961 View Post

I suppose it depends on what we define as real science. Dr. Lawrence Krauss, a theoretical physicist, has said that if one time in a hundred you get a contradictory result, then its not science.

As Arny said, this is true for Ohm's law, but I doubt it applies to medicine. So I'm not disagreeing with you, and it really depends on the context.

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post #39 of 55 Old 05-04-2014, 09:06 PM
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Originally Posted by amirm View Post

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Originally Posted by arnyk View Post

That makes sense to me in the specific context. IME fundamental principles are very reliable. For example, how many contradictions of Ohm's law does one expect to find? A highly probable answer is: none in your lifetime. If you find an apparent contradiction of Ohm's law, then there has to be a hidden influence that makes the situation different from a simple application of Ohm's law.
There is one strong contradiction: superconductors. As a conductor is cooled, one expects to resistance to keep going down. In superconducting material, there is a "critical" temperature where all of a sudden there is an abrupt drop to zero ohms:

tc_graph.gif

Once there current can remain in the superconductor even when the source of power is taken away! Since the original comment came from a theoretical physicist, we see the appropriateness of of this example as this is a quantum effect.

Another example is the famous double slit experiment where photons in a light source travel as waves when we are not measuring them but when we do, they act as particles. As Einstein said, there is a duality here and both answers are correct.

So the comment from Dr. Krauss has merit in quantum physics. Prior to discovery of superconductive material around 1900, one would have said such a thing does not exist. But post that discovery by Heike Onnes, we had a different view of conductor resistivity than past that event. At quantum level all bets are off.

You might say that in everyday life you don't notice quantum effects so it doesn't matter. Yet something as simple as the GPS in your phone or car relies on such science to provide correct results. The reason is that the satellites are travelling so fast that they demonstrate Einstein's relativity theory. The clock onboard the satellite is measuring a "different time" than what we have on earth. Since location is computed based on differential of time from the satellite and "earth time" we must provide the compensation due to clock drift or we would be way off our target. Fortunately that correction is there in every GPS device so all is well. But the point remains that there are experiments and later discoveries that alter or downright invalidate what we think the reality is.
Quote:
Over my life I've literally staked my life on physical laws like this again and again, and so has just about everybody else. For example, how many times have you pulled your car out into traffic where a failure of your automobile to respond predictably might have put you in danger of causing an accident?
Is this a trick question? Because I have and have so many others. Just a couple of months ago I was having some warranty work done on my car and they gave me a brand new $40,000 loaner. I was sitting at a light and decided to change lanes. There was traffic coming in the other lane but I thought I had ample time to pull into that lane. I pushed the gas pedal down the car started to go a few feet and then immediately lost power. The engine did not die or anything but simply decided that the accelerator pedal was not pressed. I thought this was a fluke. A couple of days later, I was making a turn in front of oncoming traffic. Once again the car went a few feet -- and put me at 90 degrees to the oncoming traffic -- and refused to move. I released the gas pedal and floored it and it fortunately got back to normal. This happened a third time before I returned the loaner. I spoke to service manager and he had some theory of what would cause that but I don't recall now.
Quote:
How many times have you flown in a plane or ridden on a train? Each of those acts takes faith in a huge number of applications of a raft of physical laws working out exactly right.
Very little on trains except while in Japan. But have flown a few million miles on Airplane. All kinds of unexpected things have happened there. Once we arrived at the gate, the doors opened and we all got our luggage and lined up for our turn to exist the plane. All of a sudden, the plane lurched forward and we all nearly fell on top of each other. Captain got on the speaker and said that a brake was released accidently and that this was the first time it had ever happened to him. He stood by the door and apologized to each one of us as we left!

Another sad example. Was travelling on the plane to a conference with a marketing lady from my team. I saw that she was pretty nervous and I started to explain how rare it is for someone to die from plane crash. She said nothing until I was finished. Then in calm and quiet tone said she had lost both of her parents due to a plane crash when she was young!!!
Quote:
However, the sensitivity human hearing is actually limited by the ear's ability to detect sound against a background of thermal noise and that woldwide ultimate background noise level isn't going to change because it is set by fundamental laws.
It is the case. But that sensitivity is adaptive which doubles our dynamic range to 120 db. There is an electromechanical amplification with feedback that is the source of that very high dynamic range. Your pupil dilating is a visual example of the same.
Quote:
I get criticized for not backing down on certain points. However, once I can relate a certain question to familiar physical laws and well known performance limits, why should I ever back down? I've been doing this for decades and it always works out when the rubber hits the road. Just because other people don't know the physical laws at the same level of detail, and/or lack the confidence that comes from decades of experience with them related to how they work out in real world applications, why should I change my statements?
It all depends on whether you learn something new along the way or not. I used to think that since the sound of speakers were so different, one could judge them sighted without worry. Then I took a double blind test and quickly learned that I was biased in my evaluation of speakers due to their looks and technology within them. Indeed one speaker that I always thought was an excellent one, in double blind testing I rated it as very poor. So poor that I thought it was a "control" to see if we were suitable subjects. Imagine my surprise when the curtains opened and I saw what was behind it.

I don't know all of your life experiences Arny. But do know that you had such revelations in audio when you did your blind testing. And that turned your many ideas you had about audio. If we were debating the Arny's of the time before that event in your life, we would have very different discussions. I know I am a different version of me with respect to audio than I used to be 10 years ago let alone longer.

Now if you want to measure yourself post that realization as being a constant, then I would respectfully say you have stopped learning. smile.gif

Edit: spelling errors smile.gif

Already covered under "hidden influences"

Just another example of why you need to think like a lawyer to post on AVS because of the endless one-upsmanship. :-(

And if you do that by putting in relevant caveats, it often appears that they don't get read...
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post #40 of 55 Old 05-05-2014, 06:50 AM - Thread Starter
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Already covered under "hidden influences"

Just another example of why you need to think like a lawyer to post on AVS because of the endless one-upsmanship. :-(

And if you do that by putting in relevant caveats, it often appears that they don't get read...
Thank you for the comment Arny. I am unclear as to its purpose though. Prior to that phrase you said: "A highly probable answer is: none in your lifetime." Your comment was made in response to something Dr. Krauss may have said in the context of quantum physics. As such it is strange that you would stay away from that domain completely and assume we are just talking about newtonian style physics and leave quantum physics to "hidden influences." There is nothing hidden in Einstein's special relativity theory as I explained.

The people quoting Dr. Krauss would have had to have specific interest or knowledge about quantum physics. Jumping into that conversation with newtonian ideas is liable to get responses such as what you got from me smile.gif. When someone mentions terms like "string theory" you know you are not dealing with layman physics topics. So I respectfully disagree that you need to be a lawyer to post. You simply need to know the topic as well as others before engaging in the conversation and making such strong assertions such as "none in your lifetime." In this forum chances of finding people who have physics knowledge is high so generalization like that that run afoul of that science will most likely backfire. If I had not said it someone else would have.

Specific to this thread is that our core disagreement is around science of acoustics. Let's not have a side conversation where we put that in the category of "hidden influences." This thread is meant to shine a light on the science, not dismiss it and stick with "classic" version of it which doesn't follow our latest understanding of room acoustics.

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post #41 of 55 Old 05-05-2014, 07:16 AM
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Quote:
Originally Posted by arnyk View Post

Already covered under "hidden influences"

Just another example of why you need to think like a lawyer to post on AVS because of the endless one-upsmanship. :-(

And if you do that by putting in relevant caveats, it often appears that they don't get read...
Thank you for the comment Arny. I am unclear as to its purpose though. Prior to that phrase you said: "A highly probable answer is: none in your lifetime." Your comment was made in response to something Dr. Krauss may have said in the context of quantum physics. As such it is strange that you would stay away from that domain completely and assume we are just talking about newtonian style physics and leave quantum physics to "hidden influences." There is nothing hidden in Einstein's special relativity theory as I explained.

That's why Newton's theories about gravity stood from 1687 until 1905. Nothing was hidden from anybody. ;-)

I appreciate the use of an out-of-context quote to illustrate the false claim that it seems impossible to head off.

And as before, I'm just going to let this latest attempt at bickermania just acquiesce....
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post #42 of 55 Old 05-05-2014, 07:24 AM
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I like this thread.
I have seen very different opinions and engineering from acousticians from top well respected firms.
These differences have resulted in varying degrees of performance.

I will say that Russ Berger has always delivered stellar results.
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post #43 of 55 Old 05-05-2014, 08:02 AM - Thread Starter
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That's why Newton's theories about gravity stood from 1687 until 1905. Nothing was hidden from anybody. ;-)
Newton's laws of physics are apparent in everyday life. So no doubt nothing "was hidden from anybody." Quantum physics is also everywhere including how the atoms in your body interact! But we lack the ability to look at particles that small and the knowledge to understand advanced theories such as string theory.

The same thing applies to audio. We seem to want to generalize what is apparent to everyone and equate that to the only answer. A reflection from a speaker is delayed and added to the direct sound and therefore it must be bad. We can almost visualize that. The concept however that you head masks what one ear hears versus the other with respect to that reflection is much harder to learn. One has to know that when a wave hits an object, what happens is dependent on the ratio of the wavelength to the object. At 1000 Hz, the wavelength of audio is around 13 inches. The size of your head all of a sudden becomes significant in attenuating that wave. Go down to 20 Hz and that wavelength becomes 678 inches and hence your head does not even exist as far as that energy is concerned.

This by the way is how sonar works. Higher frequencies are used to detect smaller objects/features because their wavelength is smaller. They however get absorbed faster in water so lower frequency signal is used to penetrate deeper, compromising feature resolution. There is another technology called CHIRP that gets around this problem by using frequency modulation. The signal is a simple sweep from low to high frequency. Guess what? That is how REW program works. It uses a sweep signal to capture the full room response.

The above is not visible to the layman or most people learning about this topic. It is a much harder concept to wrap your head around. But wrap we must smile.gif. We have to accept that our two ears pick up a different signal than a single microphone. Not only is the amplitude different but even the frequency! The frequency is impacted because the length of the reflection path determines the delay and hence the comb filtering that occurs when it mixes with direct signal. The brain is presented with two signals and it must adjudicate what it means. It is like trying to pick from two people talking at the same time.

The way it works is that the brain after an initial exposure learns what is common between them which is the direct sound and room reflections start to get filtered out. How well this happens to some extent depends on how good your speaker is. If the speaker has the same tonal quality in its direct sound arriving at your ear vs side radiation which hits the other surfaces in the room better enable the brain to apply this filtering. Reasoning is that the reflections are similar in nature to the direct sound and the brain applies the compression I spoke about and diminishes the effect of reflection.

Note that at all times the brain is applying such a correction as otherwise you would go crazy hearing two versions everyday life.

Back to the speaker, here is a great slide from JBL comparing the performance of their speaker to others: 51oxAa8MXrL.jpg

Focus on the JBL measurements on top left. The top line in green is the direct response of the speaker. That is, what comes right at you if you point the speakers at your face. The other lines in blue and red represent what happens if you take certain percentage of indirect reflections and add them back into the direct sound. They are carefully chosen to represent the typical listening environments. The lines at the bottom are the "directivity index" and they show the difference between these latter responses and that of the direct sound. If the direct and indirect sounds were exactly the same, the directivity index would be zero for all frequencies. We see that in the case of JBL LSR305, there is rather smooth transition from low to high frequencies. There are no sudden jumps until we get to 20 Khz or so which is fine.

Now compare that response to the other speakers. One of the "bad" things is having a dip in directivity index. It indicates that the larger driver in the speaker had too large of a gap relative to the next smaller one. This means that the large driver becomes directional in those frequencies and hence the side reflections lose energy. That creates a dip at that crossover frequency which unfortunately almost always is in mid frequencies where our ears are most sensitive and it is where very important audio information sit. In the samples above they all have such a dip at in the region of 2000 to 5000 Hertz. The $150 LSR305 doesn't have that problem.

Here is another good example, this one from one of the best speakers I have heard, the JBL M2:
2781d310c9200e788f6498d2efab11b5.jpg

The graph on the left is exactly the same as the one before. Note the ruler flat direct frequency response in green! I don't think I have ever seen a speaker measure so well. The indirect responses just have nice reduction in high frequencies. Looking on the right, you see the indirect responses and directivity index isolated. Compare that to the previous slide and you see that "money does buy happiness" sometimes smile.gif.

Are any of this "visible" to a layman or even someone who lives on forums? No. I didn't learn any of this here even though I spend a lot of time on AVS. I learned it by interacting with people who have designed the above products and performed the measurements. That knowledge which is readily accepted as science outside of forum, is hugely rejected here and hence the title of this thread. It is uncanny how the conversations go outside of the forum in real life versus what is talked about it here.
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I appreciate the use of an out-of-context quote to illustrate the false claim that it seems impossible to head off.

And as before, I'm just going to let this latest attempt at bickermania just acquiesce....
No problem. But I hope your comments stay focused on the topics at hand rather than bringing in generalizations about Ohm's law and such into this thread. I am pretty hard core about going after the science here, no matter how deep. That is the nature of this specific thread. If you are looking for the typical food fight about all things audio, this is not the thread.
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post #44 of 55 Old 05-05-2014, 08:07 AM - Thread Starter
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Oh one thing I forgot to mention. My company in my signature does a lot of business in Harman products including JBL. So please keep that potential bias in mind as you read my posts on those specific products smile.gif.

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post #45 of 55 Old 05-05-2014, 08:58 AM
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Originally Posted by amirm View Post

Oh one thing I forgot to mention. My company in my signature does a lot of business in Harman products including JBL. So please keep that potential bias in mind as you read my posts on those specific products smile.gif.

Your off axis analysis is interesting, but mostly only relevant to those set ups where off axis reflections have significant energy at the LP or in recombination with the direct energy. For instance, most speakers which are flat on axis remain so +/-15 degrees as well (accounting for modest toe-in). For those absorbing all first reflections points thoroughly and in a broadband fashion, off axis speaker energy is pretty minimal at the LP and available for recombination. I am not disagreeing with your analysis. Just pointing out that its only relevant in certain situations.

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Originally Posted by jim19611961 View Post

Your off axis analysis is interesting, but mostly only relevant to those set ups where off axis reflections have significant energy at the LP or in recombination with the direct energy. For instance, most speakers which are flat on axis remain so +/-15 degrees as well (accounting for modest toe-in). For those absorbing all first reflections points thoroughly and in a broadband fashion, off axis speaker energy is pretty minimal at the LP and available for recombination. I am not disagreeing with your analysis. Just pointing out that its only relevant in certain situations.
No disagreement there smile.gif. Later on we will get into the discussion of why absorb the first reflection at all. I am laying the foundation for that in that post smile.gifsmile.gif.

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post #47 of 55 Old 05-07-2014, 10:18 AM
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I have seen very different opinions and engineering from acousticians from top well respected firms.
These differences have resulted in varying degrees of performance.

Is there any consensus on who does a good room? I've never see any discussion comparing techniques and effectiveness of one acoustic designer over another.

  1. D.E. uses the riser as a bass trap. As far as I know, no one else does. Why?
  2. KYDG has their super advanced modeling software. Is it really necessary for a good room, or only necessary for, say, the last few %.
  3. PMI is big on baffle walls, but EG only includes them in their designs if the client knows enough to ask. I've talked to 2 other designers. 1 always uses them. The other thinks the advantages aren't significant enough to be worth while.
  4. In the Dedicated Theater section, the noise criteria of the room seem to dominate all other aspects of room acoustics. If 30 - 35dB noise floor is almost enough to hear your own heart beat (according to Shawn B), does it make sense to redirect even more money from a limited budget to push the noise floor even lower? How low does the noise floor really need to be before it no longer has a perceptible impact on the acoustics within the room?
  5. Ted, from Soundproofing Company, thought the flex in my walls was a good thing. I have seen others on AVS recommending this as well. Dennis said it rendered the room unsuitable for playback. Is wall flex really detrimental to interior acoustics?
  6. How much does the construction of the room's isolation shell factor into the acoustic design of the room? Is there merit in designing all surfaces of the room for equal "impedance" ?. The AVS defacto shell design use 2 layers of drywall, but Keith said in his TheaterGeeks interview that 2 layers of gyp was misguided.

The need to treat a room if fairly well ingrained, but who & how?

Is there any consensus on how much money is needed for design and/or treatments to create a decent sounding room?

 

 

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You asked really good questions smile.gif. I will take this one for now:
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[*] In the Dedicated Theater section, the noise criteria of the room seem to dominate all other aspects of room acoustics. If 30 - 35dB noise floor is almost enough to hear your own heart beat (according to Shawn B), does it make sense to redirect even more money from a limited budget to push the noise floor even lower? How low does the noise floor really need to be before it no longer has a perceptible impact on the acoustics within the room?
The spectrum is hugely important as to whether is noise is audible or not. I wrote this article on this issue: http://www.madronadigital.com/Library/RoomDynamicRange.html. As you see there, db numbers without spectrum do not provide valuable data.

A super quiet room *is* very nice. That said, you need to perform ROI on the value of each incremental improvement as you indicate. Our theater was designed by KY and while we followed much of his practice, we drew the line at some points. For example, fully dynamically analyzed AV air flow may cost as much as $20,000! We simply opted by many large louvers and find the noise practically inaudible. It certainly wasn't worth spending more in our application. Likewise, the ideal door would have cost $4000+. We opted for a very heavy door at much lower cost. We did spend money on "room inside of a room" which was the biggest ticket expense.

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Is there any consensus on who does a good room? I've never see any discussion comparing techniques and effectiveness of one acoustic designer over another.

It is hard to compare things that haven't been heard. And the vast majority of posters in blogs (self included) haven't heard these rooms you speak of. An even smaller number of people have actually heard several.

The closest thing to this would be comparisons of some popular models, LEDE, RFZ, FTB, NE and so on. Again, there is a problem in finding those that have heard properly implemented renditions of these models in order to compare them via listening. But sometimes, the criteria for these models gets compared but usually to no satisfactory conclusion.

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Note that at all times the brain is applying such a correction as otherwise you would go crazy hearing two versions everyday life.

Such filtering decreases with age and/or poor health though. This is why older people find it more difficult focusing in on one conversation in a crowded room and find being in such a room tiring, for example.

So I think there is a personal preference level how much of a live room or a dead room an individual would prefer.
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Note that at all times the brain is applying such a correction as otherwise you would go crazy hearing two versions everyday life.

Such filtering decreases with age and/or poor health though. This is why older people find it more difficult focusing in on one conversation in a crowded room and find being in such a room tiring, for example.

So I think there is a personal preference level how much of a live room or a dead room an individual would prefer.

Okay... this has me intrigued. I have a progressive neurological condition and have precisely the irritating issue you describe... a multiplicity of sounds causing aural confusion. Do you have links to more information regarding this condition? This usually only bothers me if I'm trying to decipher human speech. Music and movie sounds are "usually" not a problem (except for voice) unless the liveliness of a room is very high with lots of reverberations and echo. When that happens my brain can't process a darned thing.
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Okay... this has me intrigued. I have a progressive neurological condition and have precisely the irritating issue you describe... a multiplicity of sounds causing aural confusion. Do you have links to more information regarding this condition? This usually only bothers me if I'm trying to decipher human speech. Music and movie sounds are "usually" not a problem (except for voice) unless the liveliness of a room is very high with lots of reverberations and echo. When that happens my brain can't process a darned thing.
+1 Listening to someone talking to me and/or others in a conversation, in a crowded and boisterous multiple conversation environment has become very frustrating with age. I feel I miss half of it unless I focus all energy on what's being said.
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You asked really good questions smile.gif. We did spend money on "room inside of a room" which was the biggest ticket expense.
The notion of the extra "expense" of a room within a room build continues to befuddle me. As part of a dedicated HT build, that has to be one of the highest bang for your buck return...sound isolation (both ways), additional damping of LFE etc. Where's the money pit in this, especially if one goes DIY? Cost of lumber per wall is negligible. Isolation clips, hat channel, pink fluffy, GG. etc. is also negligible in the big picture. Maybe 10% of a $20K HVAC/AV option.

People struggle with that cost time and time again in HT builds. I compare it to building a new house and having the option to add a 1/2 car width to your 2 car garage and stressing over the "apparent cost" of the builders charge while it would only add $10 (or whatever) to your monthly mortgage payment. Just silly. rolleyes.gif
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Okay... this has me intrigued. I have a progressive neurological condition and have precisely the irritating issue you describe... a multiplicity of sounds causing aural confusion. Do you have links to more information regarding this condition? This usually only bothers me if I'm trying to decipher human speech. Music and movie sounds are "usually" not a problem (except for voice) unless the liveliness of a room is very high with lots of reverberations and echo. When that happens my brain can't process a darned thing.

www.soundtherapyinternational.com/v3/improve-your-ear/background-noise.html

www.medicaldaily.com/cocktail-party-effect-why-couples-can-easily-hear-and-ignore-each-other-crowded-room-266080

http://keyhearing.com/Central_Auditory_Processing_Disorder.aspx

www.healthyhearing.com/content/articles/Hearing-loss/Treatments/7821-Understanding-the-noise-problem
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Originally Posted by TinnEars View Post

Okay... this has me intrigued. I have a progressive neurological condition and have precisely the irritating issue you describe... a multiplicity of sounds causing aural confusion. Do you have links to more information regarding this condition? This usually only bothers me if I'm trying to decipher human speech. Music and movie sounds are "usually" not a problem (except for voice) unless the liveliness of a room is very high with lots of reverberations and echo. When that happens my brain can't process a darned thing.

www.soundtherapyinternational.com/v3/improve-your-ear/background-noise.html

www.medicaldaily.com/cocktail-party-effect-why-couples-can-easily-hear-and-ignore-each-other-crowded-room-266080

http://keyhearing.com/Central_Auditory_Processing_Disorder.aspx

www.healthyhearing.com/content/articles/Hearing-loss/Treatments/7821-Understanding-the-noise-problem

Thank you. When I was younger I could listen to two people talking simultaneously regarding different subjects and process about half of what each was saying then reply with reasonable logic and lucidity to both. I could process a third of what three people were saying simultaneously while keeping each subject separate in my mind... at least for a short while. These days, if there's much noise at all, I'll miss much of what a single person is saying so much so that I can't process a simple conversation with one person. It's embarrassing.
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