Room Treatment or Speakers? - Page 3 - AVS Forum
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post #61 of 73 Old 08-30-2011, 09:16 AM
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here is about how it sounds in opinion of Bob Olhsson (from gearslutz forum):


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Dave Moulton did a simple demo for me in a bare room that turns most of what we thought we knew about acoustic treatment and imaging right on its ear.

He had designed some speakers that deliver a flat response across 180 degrees. The imaging in the bare room was holographic, among the best I've ever heard. His conclusion is that early reflections aren't any problem at all but early reflections that don't have a flat frequency response are a big problem because they change the perceived tonality of the speaker.

If you like reflecting in accurate response curves then you like listening to an inaccurate setup.


btw, that quote was used in this discussion....
http://www.diyaudio.com/forums/multi...eakers-23.html

If the nitty gritty details is what you want then this is a good thread discussion

It is not "open-minded" to reject knowledge - Bob Lee
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post #62 of 73 Old 08-30-2011, 09:25 AM
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Quote:
Originally Posted by localhost127 View Post

GIK's customers probably aren't measuring - so the mirror-trick is a good approximation.


However, you keep insisting on taking measurements. so tell me - if you already love to take measurements and have the equipment, then why on earth would you refuse to actually take measurements for your specular absorbers to make sure they are placed in the proper location to be effective for the entire listening position, and to also make sure the panel is effectively attenuating the reflection to a required gain?

you seem to pride yourself on measurements except for absolute refusal to measure regarding this one very aspect!

then they can ignore the commentary and move on. what's the difficulty in that?

it isn't "cold fusion" to understand how porous absorption works and where it is to be placed in order to be most effective.


Lmao, now mirror trick is a good approximation. You should go through your posting history and correct your previous opinion on this

I also do you think you understand what Im saying about measurements. I do them, I do them when I build speakers, I do them when I treat my room or make changes to my room. I will be doing them in the next couple of weeks again because Im rebuilding my room. I do them for myself and to understand what changes exist. I do not think your tone and your badgering deserves a minute of data from me. I definitely do not need to post to prove my level of understanding to you, Im not looking for your approval, my experience and history speaks to what I have done and know. I will simple decline any request you have so maybe its time to move on??

The OP is gone to the experts and the thread is a dead horse at this point. If it helps I will post that you are right 100% and I hope you utilize your knowledge if you ever have a custom HT room.

It is not "open-minded" to reject knowledge - Bob Lee
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post #63 of 73 Old 08-30-2011, 10:36 AM
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Quote:
Originally Posted by penngray View Post

Lmao, now mirror trick is a good approximation. You should go through your posting history and correct your previous opinion on this

ive stated numerous times: the mirror trick is guesswork. plain and simple. whether this is "good enough" for a user or not is entirely up to that user.

i for one believe in measuring once treatments are in place to verify the treatment has indeed cured the original problem it was procured for.

however, facts are facts - the mirror-trick does not tell you:
  • whether the broadband absorber has attenuated the reflection to a particular gain (eg -15dB down from direct signal)
  • if not, then whether the panel needs to be made thicker or spaced further from the boundary
  • whether the panel is effective (sq area) in attenuating the particular reflection across the entire listening position
  • whether there is other areas of 'early reflections' from not-so-obvious boundaries, surfaces, objects, etc
  • whether one is seeing any energy still impeding the listening position via edge diffraction off of the absorber frame (since many build wooden, exposed frames around their panels)

the mirror-trick is an approximate location of where the place a panel on the main boundaries of the room. it does not give you factual information based on measurements for any of the above scenarios.



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Originally Posted by penngray View Post

I also do you think you understand what Im saying about measurements. I do them, I do them when I build speakers, I do them when I treat my room or make changes to my room. I will be doing them in the next couple of weeks again because Im rebuilding my room. I do them for myself and to understand what changes exist.

can you please answer my question regarding which tool or measurement you use when determining the effectiveness of your sidewall (early reflection point) broadband porous absorber?

i sound like a broken record asking this...but im still looking for what tool you use to measure regarding this context?
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post #64 of 73 Old 08-30-2011, 01:28 PM
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Quote:
Originally Posted by penngray View Post

btw, that quote was used in this discussion....
http://www.diyaudio.com/forums/multi...eakers-23.html

If the nitty gritty details is what you want then this is a good thread discussion

Thanks for this penngray, it will indeed be interesting reading. It looks like some of it goes right along with this article (though it's old so you've probably seen it). Along with this stuff I really need to get to reading Toole. The "ideal loudspeaker directivity pattern" thread there looks interesting too.
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post #65 of 73 Old 08-30-2011, 03:16 PM
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Gentlemen (and the many super attractive woman that I'm sure listen in just to learn what real men is all about), there are many ways to skin a cow...

Stereo reproduction, i.e. trying to reproduce a sonic happening as accurately as possible later in time in another venue using two (or more) speakers is in one way easy and in another way seriously difficult.
The easy part is that the brain and hearing is fairly easily fooled to some extent. With two sound sources smartly placed (as in a normal 2-channel setup) it is possible to form phantom sound sources -sound that appear to come from another place than it really is (since it actually emanate from two sources).

Now, if you compare the sound spectra from a real sound source at say you vocalists favorite angle of incidence, to one projected by a stereo setup mimicing the same angle of incidence as the real sound, as measured at the position of each ear, you'll find that they differ *significantly* to the real source. The stereo reproduction causes significant comb filtering effects (since your ears are spaced apart) and reflections from room boundaries will mess up the sound even more, still it usually sounds pretty damn accurate timbrally even in a not absolutely perfect room, yeah? That's because the brain is filling in the blanks. The hearing/bin is compensating somehow.

Furthermore, the stereo setup creates coloration in itself because how the brain translates the two point sound sources used in the stereo setup to project a phantom sound source, compared to the real sound source (emanating from one point in space). Thanks to the hearing/brain, the seriously distorted signal reaching your ears from the stereo pair is still translated by our hearing and brain into something much closer to the real sound, than what is actually reaching your ears, but it is still slightly distorted, compared to the real source

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post #66 of 73 Old 08-30-2011, 06:48 PM
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Quote:
Originally Posted by aackthpt View Post

It looks like some of it goes right along with this article (though it's old so you've probably seen it).

first time seeing that article - thanks.

but im curious as to why he would make this (to me, overgeneralized) statement:
Quote:
Originally Posted by article View Post

Fabric-wrapped panels and absorber systems are relatively poor off-axis absorbers. That is, when measured off-axis, there is less absorption. When a person is sitting at a listening position with reflections arriving at some angle from the side wall treatments, the panels are actually reflecting a good deal of sound.

...without providing ETCs, material type, thickness, and especially the angle of incidence where he is seeing this high amount of reflection from his absorber.

absorption will generally increase with angle of incidence, as the perceived thickness of the absorber changes (vs at 0*) -- of course this goes out the window once angle of incidence approaches grazing angles (+/- 65*, depending on the material) and absorption goes to zero.

if one is experiencing this, one can always mount a broadband absorber on an angle such that angle of incidence for the specular energy is 0* (versus mounting the panel perpendicular to the wall). that would negate his commentary.

i have great difficulty digesting any commentary regarding whether or not one finds early reflections 'beneficial' without seeing ETC responses of the test room. that is the only significant measurement regarding the context of the discussion, and yet it is also the most highly ignored. it seems many lump all 'first-order-reflections' in as being early-reflections, when the very definition of 'early reflection' is determined by the user and their length of ISD. i think this, may in fact, be a significant root of problem during all of this discussion.
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post #67 of 73 Old 08-30-2011, 08:24 PM
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Quote:
Originally Posted by hevi View Post

Furthermore, the stereo setup creates coloration in itself because how the brain translates the two point sound sources used in the stereo setup to project a phantom sound source, compared to the real sound source (emanating from one point in space).

Exactly! I've always said my stereo sounds BETTER than real. Now I have the answer. REAL PERFORMERS ARE IN MONO!!!!11
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post #68 of 73 Old 08-31-2011, 07:58 AM
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Quote:
Originally Posted by localhost127 View Post

can you please answer my question regarding which tool or measurement you use when determining the effectiveness of your sidewall (early reflection point) broadband porous absorber?

i sound like a broken record asking this...but im still looking for what tool you use to measure regarding this context?

A string and a Can

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post #69 of 73 Old 08-31-2011, 01:34 PM
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Originally Posted by penngray View Post
A string and a Can
Sennheiser or Grado? I just use Sony. Low end, I know.
Also, is that a regular string or a Superstring?
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post #70 of 73 Old 08-31-2011, 01:40 PM
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Quote:
Originally Posted by penngray View Post
A string and a Can
not sure what the can is for but the string is most certainly useful for identifying the surfaces that induces the specular reflection:

Quote:
Originally Posted by SAC
1.) - the most basic mechanical method is the string method.

Quite frankly, I don't expect anyone to do this more than a handful of times until you can more easily visualize the process, but it illustrates the concept very simply and effectively - if a bit awkwardly!

From the total time of travel, you calculate the distance of travel (TOF X 1.13'/ms or .344m/ms). You might want to leave a few inches on each end to hang on to, but mark the precise endpoints corresponding to the distance. Find a few friends who you will not mind being a bit worn out by the process and have then each hold one end of the string, one end with the point marked on the string precisely located where the measurement mic capsule would be (don't move the mic!!!) and the other end placed in the center of the source speaker. Forget the tweeter stuff, as the ETC measures the total energy, and there is much more energy content in the low-mids and mods than in the tweeter. Besides, if you want to determine the actual acoustic origin of the speaker, the ETC can be used to identify this as well! But that's another exercise for some other time!. Now, with the endpoints firmly located, at one point in the body of the string, extend the loop body out and see what boundaries/surfaces you can tangentially touch with the string being stretched taut' The point you can touch, is the point of incidence indicated by that particular spike in the ETC. Note the incident spot on the boundary. Repeat for the other energy returns.
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post #71 of 73 Old 08-31-2011, 08:37 PM
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Originally Posted by penngray View Post

A string and a Can

LMFAO! Really, is there any other answer for that kind of obsessive fixation?

What I can afford, when I can afford it...
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post #72 of 73 Old 09-01-2011, 11:02 AM
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Originally Posted by aackthpt View Post

Exactly! I've always said my stereo sounds BETTER than real. Now I have the answer. REAL PERFORMERS ARE IN MONO!!!!11

Since I'm not sure if you're beeing sarcastic or not, let me elaborate a bit (after all, this is an audio theory forum, right )...

Now, resasonably accurate stereo reproduction is pretty complex stuff once you start disecting it... Thing is, wether you like it or not, the very use of two sound sources to reproduce a soundstage introduces colorations and artifacts.

You can isolate the timbral characteristics of the "stereo reproduction error" by using three identical speakers performing in half space (=outside -That way you take away all differing early reflection between the three speakers and thus can isolate the stereo artifacts). Place two of the speakers as you would a normal stereo setup (say 45 to 60 degrees apart), and the third dead center inbetween the two, equal distance from your head.

Now, play a mono source in the "stereo pair" and compare that to playing the mono source in the center speaker alone. With this setup you can compare phantom reproduction of a true, centered point sound source to a centered phantom source reproduced by a stereo pair. Since you're using three identical speakers and listening in half space, you can use whatever source material you like. All sound sources are voiced identically (since they are identical) and what is left in the comparison is the timbral differences between a mono source and the exact same sound phantom image reproduced by a stereo pair.

You'll notice that the timbral characteristics will differ between phantom reproduction and the real mono source. This is why you can't really talk about "measuring dead flat" as an absolutely accurate reference...

The thing is that in essence, stereo reproduction is an illusion created by the brain. You can affect the percieved timbral accuracy, percieved soundstage depth, spatiousness and soundstage focus by manipulating the stereo geometry (the "opening angle"), the speakers' on and off-axis frequency response, early and late room reflections etc. but the illusion is also severely affected by the way the recording is encoded (what mic tecniques and placement is used etc.).

Basically, when recording you record a three-dimensional soundfield (direct and reflected sound from the recording venue is reaching the mic from all directions) and you reduce it to one dimension (amplitude -per channel), and when reproducing it, you're taking the one dimensional representation of the compled three dimensional sound happening in the venue, and emmit it into three dimensions -the speakers emmit sound into the three-dimensional space, with new reflections, not part of the recording happening in the reproduction venue.

All in all, there are many ways to approach "accurate stereo reproduction" and all the ways have their pro's and cons and depending on what parameters you value, how you want the illusion to be...

A paper that starts to scratch on surface of the subject is this (I have a couple issues with the test setup, but nonetheless it is interesting, but perhaps a bit technical reading):

http://www.hauptmikrofon.de/theile/O...ON_english.pdf

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post #73 of 73 Old 09-01-2011, 12:20 PM
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Quote:
Originally Posted by hevi View Post

Since I'm not sure if you're beeing sarcastic or not, let me elaborate a bit (after all, this is an audio theory forum, right )...

A paper that starts to scratch on surface of the subject is this (I have a couple issues with the test setup, but nonetheless it is interesting, but perhaps a bit technical reading):

I thought it quite obvious that I was being epically sarcastic. This is what I'm going to tell people in the future when they start to get audio-obsessive. Especially if they have cable lifters or exotic power cables in their systems. It also amuses me since it reminds me of this cartoon. Plus I felt it fitting given the increasingly sarcastic tone this thread has taken. And I don't say that as a bad thing - I loves me some sarcasm.

Thank you for the paper, I'll add it to my reading list (along with Toole's book). I've seen a number of things floating around about theoretical attempts to recreate 3-dimensional sound fields using walls made of transducer arrays or whatnot. I haven't paid that much attention because I've plenty to read on regular acoustics anyway. And the more I sit around reading, the more I get antsy to just go out and have some actual musical experiences in real rather than reproduced anyway.

I am interested in ways to improve DIY-budget audio measurements to better correlate to sound perceptions, though, whether that's using IACC, measuring and quantifying amount and density of lateral late arriving soundfields, or whatever.
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