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 myth or true?

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Michael Green
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PostSubject: myth or true?   Sun Jun 03, 2012 9:29 pm

What is excepted as true for some may be the opposite for others. In high end audio I have always been faced with this 2 edged sword it seems. I have one side of my experienced life based in the reality of what is real. When I say real I am referring to the recording room, concert hall, small acoustical assembly and real space real size playback. The other side is the surreal world that the listener has developed. Lets make it clear right up front that the thought that these miniature sound stages that are being listened to as if they were representatives of the true sound are any thing but real. It's fun that the high end audio industry has developed it's own little cult based on it's own rules, but lets be honest and admit it is a little far fetched to call a tenth the scale reproduction live. I have spent my life creating the worlds largest most in depth sound stages and at no time have I fooled myself into thinking that I have reached the absolute at any time. This at best is a vain pursuit that keeps the audio enthusiast market place coming back for the next best thing based on monthly magazine updates. Most high end audio products sold are nothing more than the flavor of the month based on a space that seldom reaches beyond 12wide 6deep 8tall. Is this real? Of course not! We live in 3d and recorded music can match this when we decide to break away from the things that hold us back.

Let me explain something to you. Audio is the involvement of energy vibrating in 3 basic areas, acoustical, mechanical and electrical. These three energy sources combined make up what you are listening to. Over the years of the hobby of listening we have used the room (our space) as the criteria for the size we listen to our sound in. There have been rules made along the way that dictate what we except as real and accurate. Unfortunately along with rules comes the penalties of breaking them. In our hobby we call the breaking of rules distortion. This is and always has been a cop out to keep the game of the absolute sound alive. We all can walk into a performance hall and studio and hear that these spaces provide a much more involved 3d event but in our development over the years we have excepted something far less than this reality. Can 3d be achieved by a stereo setup? Absolutely, and in my opinion is the correct approach for obtaining reality. I remember the first time I turned someone on to 3d sound in my room. They told me that I was doing something wrong and the sound should be coming from a much smaller space. I asked the question why? Are the microphones in the studio not picking up all the energy? Are the speakers limited to only presenting music so big? Do the components have size settings? Is there something in the system itself that makes the sound only a certain size, and what determines this size as being right?

In "82" was the first time I remember making a dead room for high end audio listening to see if I could make a system that operated off of the theory of removing the room from the equation. The theory says that if you remove the room you will end up with the true size of the recording. I had a few friends over to explore this with me. Some were from the music world, Atlanta Symphony and others and we used their recordings to do the tests with because of how familar they were with the recordings. We also used recordings I worked on along with other recordings that we spent much time listening to. We had instruments on hand as well to test the effects on instruments vs speakers. Others who wrote articles for the EAS were helping with the testing. The 2 main things I wanted to see, was the reflection theory true (does sound travel in straight lines), and secondly are we able to remove the room from acoustical reaction. The materials we used were the same materials used in anechoic chambers and others excepted for acoustical deadening. After testing the room going from full live to full dead we determined that the dampening only cause the sound stage to become much smaller than it should and the room absorbed most of the soundwaves. The room did not become louder and the music did not represent a true size image. Instruments tuned in the outer room also went out of tune when brought inside of the dead room and the sound gathered around the high frequencies with any harmonics disappearing. We also noticed that amplifiers started to heat up and speakers excursions had to pumped beyond a safe point to reach listenable volume levels. The reality was the room no matter what we did was not able to be removed from the equation and dampening products absorb crucial parts of the music. Not only did the music sound terrible but we had to shout at each other to hear what the other was saying.

This, even back then, had me wondering if the people who do reporting on such things actually are doing them to test if their theories were only in word and not deed? We also came to the conclusion that in a room the straight line theory of sound had no truth to it.

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PostSubject: Re: myth or true?   Mon Jun 04, 2012 12:51 am

Is there such a thing as the first wall reflection?

An article came out years ago that went against findings we had made many years before this and we wanted to find out if this was true. It was a theory based on reflections in a room correlating with straight lines being produced by lights and mirrors. A whole series of listening tools have been made and this has become an excepted myth in high end audio.

Do sound waves travel in straight lines?

This needs to be answered in two ways, outside or inside? The answer outside is far different from the answer inside. Out side you can make the argument that it is a relative curved wave that can appear to be straight from the point of view of detecting the origin of the sound. Higher frequencies react as if they travel more in a straight line than do lower ones. But the answer is still no. Sound travels in a curve (sphere).

In your listening room? The answer is also no. Sound does not travel in a straight line from the speaker to your ears. We have tried many tests and experiments to show that it does and can not find any that show that the drawings that manufacturers use to show sound traveling straight as being true. We are not even sure why these types of drawings would ever be used to represent sound waves. The speed in which sound pressures build up in rooms is so fast that rooms under between 50 and 85 feet depending on conditions do not even consider there to be a delay. In your listening room the sound is traveling 1100 feet per second. You are not hearing your speakers as much as you are sound pressure that builds in the mathematical loads in the room. In reality your listening to pressure zones with your speakers being little more than the source of origin. These pressure zones pre-exist in every room and are constantly exercising their properties with the slightest movement of energy.

We did find in our multi-mic setup the presence of laminar flow as a real science and pressure zones along with nodes and standing waves, but the existence of first wall reflections and sound waves traveling in straight lines through a room did not happen. Even when we turned the speakers directly facing the supposed direct reflection point we could not measure an effect distinguishing itself independent of the pressure zones. We placed microphones in the exact pathways of the reflection at the points where these reflections were supposed to take place and one foot on either side of these pathways and tried to make a reasonable science and couldn't with one exception. Depending on the density of a given wall we could get higher frequencies to beam if the speaker was close enough to a wall and the tweeters were pointing directly at it. Still this did not play a role in how our rooms make sound or the need for tuning the room on the basis of reflections bouncing around the room in straight lines.

If we are to take this portion of the industry further we need to practice sound theories. These straight line diagrams are very deceiving and give the impression that there are far less waves than what is really in the room. Our microphone testing showed the room to look more like the diagram below as it becomes activated.






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PostSubject: Re: myth or true?   Thu Jun 13, 2013 3:06 pm

Years ago UMI was kind enough to send me a horn for testing. Some of the engineers wanted to see why they were getting different test measurements when playing horns outside as opposed to in a studio or hall. Everytime they took their horns into a different space the recorded information was different. Their on and off axis testing was also extremely different depending on where the tests were being done. Asking me what I thought was going on I invited them to a visit at TuneVilla. I told the guys I would set up mics and we will take a look at note responces. When we tested on and off axis in a normal room the readings told us that the horn was extremely directional and depending on where it was pointing would go in and out of tune. Next we tested the horn in a tuned room and found that the horn played more even and even though you could tell direction the notes sounded the same throughout the room. We added funiture and people to the room and the horn started sounding more directional but not as bad as the untreated room did. Latter we focused our attention to speakers. We tested two speakers, one was an B&W 801 and the other a Rev80. The B&W at first sounded very directional and when the room was foamed and trapped the problem still was there. The futher you went off axis the more rolled things would get. Then the room was stripped down and we set up our typical studio setup, which is a tunepak plus 2 echotunes. This did not do the trick on it's own but with a little tuning we started to see the off axis extend dramatically. Next was the free resonate speakers. In the foam room the 80's closed in like the B&W but not quite as much. After the basic tuning the off axis jump way past the B&W and after some serious tuning was able to get very close to the same frequency balance throughout the room with only 6 minor dip areas. This once again told us the a room response is far different from a driver test response.

Since I don't believe in straight line wave response a tweeters measurements from the factory means very little to me.

Another thing to look at when checking specs and comparing to the physical testing lab is, in most testing labs the cabnet being used to do the testing has a rubber seal gasket that is placed between the tweeter and the wood of the cabinet. Every test we have made with these gaskets being used we have see the off axis response shrink to nothing. Tweeters (like anything else) become a part of what they are attached to. Limit the vibratory response and watch the performance shrink. I've done these tests on tons of different tweeters and cabinets with the same results. Conclusion, dampening is what makes the response shrink, free resonance along with mechanical tuning is what makes the response grow.

Most tunees who have free resonant speakers are more concerned about energizing the pressure zones in balance than they are caring about facing a dampen speaker at them because of the speakers limitations. The days of pointing speakers in a room for me has long past. It's more about properly energizing the real speaker (the listening room).
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