Originally Posted by kbarnes701
That is true, but faith is a powerful thing (I am told it can move mountains, but have seen no independent corroboration). Once someone becomes a believer, it is very difficult to change their mind. No matter how much scientific evidence and proof you put before them, their faith generally prevails. Even the results of double blind tests won't convince them ("I know what I hear... the test is flawed.. all I need is my ears... there are audible differences that can't be measured" etc etc
Faith is a powerful thing. So what you say is very true and the source of so many needless arguments on these forums. You seem to be implying that you or a group of you are immune to it and others not. It is trivial to demonstrate this is not the case. Just look at the couple of posters saying they have no use for science and just want know if it is “audible.” Well, how on earth do you know to trust the answer to the question if you don’t “really” know the science as Chris put it? The test could have been wrong and the only way to know that is to understand the audio science. I am glad at least you acknowledge the importance of knowing the science or else, this forum would have to take out the “S” from AVS!
You were kind enough to go and read my company’s web site. I thought it would only be fair for me to go and read your Audyssey FAQ in your signature. I must say, that must be the most comprehensive FAQ I have ever read. True labor of love there. Unfortunately, there are some glaring and important mistakes with regards to how acoustics works in our listening rooms. I thought I hit on one of them and see your reaction to it. It will be a good test to see if stick to your beliefs, or accept the science and listening test results.
You say and I quote:”Room reflections are caused by sound, mostly high frequencies, reflecting off adjacent walls and combining with the direct sounds you hear from the speakers. In most cases, you hear more reflected than direct sounds. The reflected sounds reach your ears milliseconds later than the direct sounds because they travel a longer distance. In general, sound reflections degrade imaging, sound staging and the overall tonal quality, important characteristics of a good sound system.
Poor dialogue intelligibility is often the result of reflections in your room. […] Pay especial attention to the 'first reflections' from your speakers - side walls, floor, ceiling.”
This myth is repeated so much on these forums that it has become “fact” even though it goes counter to countless research on how our hearing system works, and many listening tests. The belief is reinforced because it just makes sense to people. Folks think of how hard it is to hear others in an echo-prone room and imagine the same with respect to room (first) reflections. The belief is cemented, as you stated earlier, by looking at the pictures of mixing/mastering rooms which have walls covered in acoustic material.
Let’s walk through the proof of why your assumption is incorrect using your two metrics: Science and Listening tests.Science:
Let’s deal with the notion of reflections being the same as echo. Research performed by Helmut Haas back in 1940s showed that we simply do not hear reflections as distinct “events.” To actually hear an “echo” requires that the reflection be stronger than the direct sound when delays are short. This doesn't happen with respect to reflections in our rooms because by definition they are weaker than the direct sound. What the brain hears is one event even though it is made up of a direct sound from your speaker and a number of reflections. As such, there is no analogy here at all to the echo you hear in a large space. Just go to your listening room and play something. Do you hear echo? I suspect not.
Even more interesting is that the brain puts the reflections to good use. As you can imagine, we have lived in enclosed spaces for years. Adaptation has allowed us to learn to use reflections to better understand the source signal. Remember, the reflections represent more energy. Sound coming out of your speaker bounces around the room. If you get rid of those reflections, you would be throwing out the speaker’s output in the form of heat generated in those absorbers. Energy lost means there is less for you to hear. Here is the Wiki on Haas effect: http://en.wikipedia.org/wiki/Haas_effect”Haas found that humans localize sound sources in the direction of the first arriving sound despite the presence of a single reflection from a different direction. A single auditory event is perceived. A reflection arriving later than 1 ms after the direct sound increases the perceived level and spaciousness (more precisely the perceived width of the sound source). A single reflection arriving within 5 to 30 ms can be up to 10 dB louder than the direct sound without being perceived as a secondary auditory event (echo).”
Sound travels around 1 foot per millisecond. So you can easily see that your normal room dimensions follow in the area I have bolded. Once more, this is research that is 70 years old. And it still stands without objection. Yet folks still ignore it. Net, net, when dealing with home listening spaces, you need to forget about the term “echo” (there is a thing called slap echo and that is a problem but it is not a factor in first reflections).
Haas also hits on another important aspect: that reflections can actually be a positive thing. In the case of side reflections, the apparent position of the speaker shifts toward the reflection point, resulting in perceiving a larger and more spacious sound field. This is important to have in the case of center speaker as without it, the dialog will seem to come from just the speaker which in a home theater with a projector, it will be smaller than the screen by far. The reflections on each side will stretch that sound to each side and better represent what is being played on screen.Listening Tests:
The foundation of our understanding of reflections is through countless other listening tests conducted since Haas performed his landmark work. In the interest of brevity (yeh, right
), I will only cite a few. There is at least 10X more if you care to see them.
First up is Dr. Bradley of Canadian National Research Council (a non-profit acoustic research organization). Dr. Bradley has Phd from your neck of the woods (Imperial College at the University of London) with the specialty of “electroacoustic enhancement systems in rooms.” He and his counterparts (Sato and Picard) set up a simulation of room reflections using an array of speakers, each of which could be driven to act like a reflection in a real room and therefore their effects examined under controlled situation. Their goal was to determine the effect of room reflections on speech intelligibility – the very point you make in your FAQ. Here is the conclusion in their peer reviewed paper published in the journal of Acoustic Science of America (ASA):”This paper presents the results of new studies based on speech intelligibility tests in simulated sound fields and analyses of impulse response measurements in rooms used for speech communication. The speech intelligibility test results confirm the importance of early reflections for achieving good conditions for speech in rooms. The addition of early reflections increased the effective signal-to-noise ratio and related speech intelligibility scores for both impaired and nonimpaired listeners. The new results also show that for common conditions where the direct sound is reduced, it is only possible to understand speech because of the presence of early reflections. Analyses of measured impulse responses in rooms intended for speech show that early reflections can increase the effective signal-to-noise ratio by up to 9 dB. A room acoustics computer model is used to demonstrate that the relative importance of early reflections can be influenced by the room acoustics design.”
Notice the bolded section. We gain up to 9 db of intelligibility by retaining early reflections than removing them. This of course makes sense in the context of theory I described in how energy is conserved if you let he reflections be, rather than thrown away by absorbing them. Just think of whether someone can hear you better 30 feet away in a big open field vs indoors. Likely you have to raise your voice for them to hear and understand you. Now you know why.
A much more extensive study was performed by Dr. Toole while at NRC and later at Harman, summarizing research in his own group and that of many others including Dr. Bradley above. I will spare you the details of this peer-reviewed paper in Journal of AES, but will give you the punch line summary table:
So there is no annoyance and improvements in critical areas including dialog intelligibility. As Haas had said, localization is not impacted. Again, if you listen to someone indoors, despite huge amount of reflections, you have no trouble telling which direction the sound comes from. And oh, your loved one's voices don't change as they move around the house! You still recognize them as being the voice you know.
Bringing us full circle to the topic of this thread, if someone asks to see blind tests showing no difference in cables and amps, folks usually quote Dave Clark and his tests of that type. What they don’t know is that he also examined this topic and published his work at Audio Engineering Society conference. You can read a much easier to digest version of his experiments in my Widescreen Review Magazine article (http://www.madronadigital.com/Library/RoomReflections.html
). Clark finds that acoustic distortions such as caused by reflections can actually be a positive thing. A mono sound for example played from two speakers, creating clear measurable distortion due to comb filtering, was actually preferred by listeners. The second speaker in this case is what a reflection would be from one speaker yet nothing but goodness came from it. Side reflection was positive as reported by other research (floor is not although even that is not what it seems). In my article, I show the psychoacoustics of why our measurements and gut feelings are incorrect based on psychoacoustics of our hearing system.
So what say you? Do you still believe what you believe?
They have only themselves to blame but I still feel sorry for them because they are spending hard-earned money where it can make no difference, when they could be spending the same money and getting a terrific difference/improvement.
Yet when I try to engage you to talk about acoustics, you ignore that and instead prefer to waste time beating up on someone’s observation of cable differences. Between using the forum bandwidth on one topic vs the other, why do you prefer to do that?
And how about this line from your FAQ:”The first thing to understand is that there are really no 'rights' or 'wrongs' as far as your home cinema goes. It is your equipment, paid for with your money and listened to with your ears.”
If you believe in leaving folks be there, why not here?