Small Room Acoustics and Diffusers

[mikebse2a3]

Hey artto

Not to detour this thread but I thought since your room is treated so well I would imagine you hear tonal issues with recordings very easily.

Sometime you might be interested in trying this with the Behringer. I've found it to be very intuitive to use in a short period of time and many recordings are much more realistic and enjoyable in my experience.

http://community.klipsch.com/forums/p/112125/1127557.aspx

miketn

[garyrc]

What do you guys think of Space Arrays designed by Berger (or some such name)? A few years ago forum member mas thought they were promising, but not all the data was published yet.

[mikebse2a3]

What do you guys think of Space Arrays designed by Berger (or some such name)? A few years ago forum member mas thought they were promising, but not all the data was published yet.

I haven't used them myself but I would like to hear them in actual situations to see what positives and negatives they bring to the table.

[artto]

Hey artto

Not to detour this thread but I thought since your room is treated so well I would imagine you hear tonal issues with recordings very easily.

Sometime you might be interested in trying this with the Behringer. I've found it to be very intuitive to use in a short period of time and many recordings are much more realistic and enjoyable in my experience.

http://community.klipsch.com/forums/p/112125/1127557.aspx

miketn

Thanks Mike! I've saved a copy of your post for reference. Interesting.

Yes, it's true how sensitive the recording process is and how that translates to reproduction as well. I'm just finishing up a recording for CD production of the Glen Ellyn Wheaton Chorale's Christmas concert. (I know, it's almost May ~ but had pneumonia for 2 months after Xmas and my ears were so plugged up I didn't listen to any music during that time).

What's interesting here is that I've recorded the GEW Chorale in this room (College Church, Wheaton, IL) many times now over many years. I have a very good idea of how my setup should be. Last spring I recorded what I consider to be my best recording yet. It included Gabriel Faure's Requiem which Telarc also recorded with Robert Shaw and the Atlanta Symphony and I must say, what I recorded is sonically very much on par with Telarc, maybe even better since digital technology has improved since then (my Card Deluxe is higher resolution & most likely of higher sound quality than what Telarc was using back then). What amazes me is that although the orchestra part of this last Xmas' concert was primarily horns and percussion verses strings on Faure, and my mikes were in (almost) exactly the same place, I had such a difficult time getting the Xmas concert to "sound right" during mastering while last spring's concert was the best ever without having to touch anything! Same mikes, same equipment, same hall, same setup and yet such a difference in sound!

I'm glad to hear you were able to basically duplicate what the Cello EQ was capable doing with the Behringer. An audiophile acquaintance of mine who has since moved back to Japan had a Cello in his system. He had some pretty expensive stuff in his system, like the Goldmund turntable and linear tracking arm, Tannoy supertweeters, etc. His room, while having "some" acoustic treatments was nothing to write home about. He was interested in my "American" audiophile opinion of his system. I thought it sucked, but didn't tell him that. Instead I invited him to my place. All he kept saying is "Ahhhh......AHHHHH" "It's so.....how you say....so realistic". He told me he went back home and listened to his system afterwards, and said "I hate my system now". "It sounds so small, so distorted, like looking through a telescope." I'm quite sure the room had a lot to do with this. Not to down the Cello at all, its a fine piece of equipment to say the least. But the above situation also underscores how spending really big, big bucks on audio components doesn't necessarily result in great sound reproduction.

[WMcD]

So there are questions about why I'm skeptical. After thinking about it, I'm really just skeptical about what I'll call the Bauhaus chandelier set up. That is where there is a single or a few assemblies attached to a ceiling in a room with a relatively low ceiling.

The data shown ("balloon"?) shows the efffect for sound arriving normal to the array. Let me say that we see scattering or diffusion. Well enough. But that would be sound originating from the floor, if I understand correctly. That is hardly the typical situation.

In our typical situation, the sound is hitting the side of the array or at some angle which is not from the floor. I don't see data for that situation.

This takes some visualization. We can consider it a checkerboard with tall elements on each square and the height is of some calculated value so that looking down on the checker board, we see, arguably, reflections at what I'll call pseudo random delays. This adds up to the balloon pattern of a phased array antenna with many elements. And let me add that I believe the well-type design is such that sound approaching from an oblique angle is also subject to delays.

But what is not shown in the skyline is what happens when the sound arrives from the side. We can think about it. Specfically, the checkerboard is at eye level, and you're at a right angle to "your" side of the checkerboard, and you send in an impulse.

In this situation, the sides of the elements rising out of the checker board are spaced at some regular intervals according to the width of the checkerboard squares. The ones at the side near you are a x distance, the next row is at x + 1 squares, the next is at x + 2 squares, etc. Now, maybe this has all been considered because even though they regular in delay, they are spaced out, left to right, in some pattern. I don't know.

My thought is that if there is a regular, incremental delay, you're going to get an artifact which is not random.

Some years ago I visited http://en.wikipedia.org/wiki/Chichen_Itza Highly recommeded by the way. So impressive. A ziggurat. The outlying buildings are worth seeing too.

In one case a fellow was standing out on the plain at a right angle to the steps of the pyramid. He clapped loud. The reflected sound sounded like a flying insect going by. A buzz. I attribute that to the regular delay from the faces (risers) of the steps.

I wonder is that too not going on with the skyline.

WMcD

[artto]

I think Gil has hit it on the head (again). []

Many, if not most (or all?) of these sort of data displays are somewhat contrived, of course, to show their products in the best light. They are trying to sell something (I'm not saying that is a bad thing). But it underscores a point I made earlier. For instance the criteria used is often not what is encountered in real world conditions, certainly not from time to time as the in-use circumstances change. Its done that way to "prove a point" and provide a demonstration of its potential value in an clear and understandable way. For the same reason things like STC or absorption ratings have to be taken with a grain of salt as the actual in-use performance of the products rarely equals the results under test conditions.

The second point Gil made, I think is a very important one ~ visualization. This is were a lot people (including their computer models) don't get it right. Visualization can be a very powerful thing. And from what I've seen/heard from those who keep tryng to convince me that polycylindricals are not really diffusers, and that these new fangled devices are superior, regardless of the application or how they are implemented, these are the same folks that I see lacking in the visualization department. I'm an architect so obviously I've had some training in that even though much it comes very naturally to me. At the same time I admit I'm not as good in the number crunching department as the average engineer. But I do have very strong visualization skills and indeed was deeply involved with using and developing CAD and imaging systems for the architecture and engineering community more than 25 years ago. Believe me when I say I know how all the "tricks" are played. Been there, done that.

Another visualization problem Gil has brought up is "what happens when the sound arrives from the side" (of the Skyline diffuser). Many times people will ask me why I don't have the sides of my vertical polys on the front wall "enclosed". Again, this is a visualization problem. Khorns being a corner type speaker with the corner of the room literally being part of the bass speaker are projecting the sound wave out into the room along the walls. I don't need nor want the diffusers doing anything to the sound wave as it eminates from the Khorns. Obviously this is not completely possible with the large vertical diffusers being located in the vicinity of the Khorns, but to a great exent, much of the wavefront is allowed to "pass-through" the diffuser at that point. Only after the wave front makes its way into the rest of the room and reflects back at some angle does it encounter the polycylindrical surfaces for some greater amount of diffusion. It is this kind of phenomena that all these computer model comparisons are not showing or taking into account.

[mikebse2a3]

The data shown ("balloon"?) shows the efffect for sound arriving normal to the array. Let me say that we see scattering or diffusion. Well enough. But that would be sound originating from the floor, if I understand correctly. That is hardly the typical situation.

You I believe are assuming ceiling mounting. The example ballon plot represents any energy (direct or reflected) that strikes the diffuser array at a normal incidence angle regardless of where the diffuser array is mounted (ie: ceiling, walls or floor) and will have this scattering response at that frequency in this specific example. To be clear I just posted this ballon plot as one example of RPG's ability to measure a diffuser and of course this was just one data point they would have gathered to give a complete picture of the diffusers measured performance. Normal as well as random incidence angles representitive data would be obtained by rpg for a complete analysis of any of their acoustical products.

In our typical situation, the sound is hitting the side of the array or at some angle which is not from the floor. I don't see data for that situation.

I agree that in most typical situations a diffuser array will experience many random angle incidence strikes and how it performs under these conditions is very important. Please see rpg's technical and white papers for a more complete understanding of how they measure acoustical products.

This takes some visualization. We can consider it a checkerboard with tall elements on each square and the height is of some calculated value so that looking down on the checker board, we see, arguably, reflections at what I'll call pseudo random delays. This adds up to the balloon pattern of a phased array antenna with many elements. And let me add that I believe the well-type design is such that sound approaching from an oblique angle is also subject to delays.

But what is not shown in the skyline is what happens when the sound arrives from the side. We can think about it. Specfically, the checkerboard is at eye level, and you're at a right angle to "your" side of the checkerboard, and you send in an impulse.

In this situation, the sides of the elements rising out of the checker board are spaced at some regular intervals according to the width of the checkerboard squares. The ones at the side near you are a x distance, the next row is at x + 1 squares, the next is at x + 2 squares, etc. Now, maybe this has all been considered because even though they regular in delay, they are spaced out, left to right, in some pattern. I don't know.

My thought is that if there is a regular, incremental delay, you're going to get an artifact which is not random.

Now for random incidence visualization pleasure..[]

[mikebse2a3]

For anyone interested this paper show's some of rpg's measurement methods and standardization efforts.

State of the Art in Measuring Acoustical Coefficients.pdf

State of the Art in Measuring Acoustical Coefficients.pdf

State of the Art in Measuring Acoustical Coefficients.pdf

State of the Art in Measuring Acoustical Coefficients.pdf

[mikebse2a3]

Better graphics and photos if you go here and under the presentation tab select and download Acoustical Coefficients (5.55MB)

http://www.rpginc.com/Technology.cfm

[mikebse2a3]

My info on the skyline is on another computer that is not operational at this time but I did find this info for anyone interested.

RPG® Skyline 7" 2D Primitive Root Diffuser

Interfering reflections can be controlled by absorption or diffusion. In small rooms, it is often desirable to control interfering reflections and provide an ambient sound field using diffusion instead of absorption. When the room’s surfaces are relatively close to the listener, a very efficient diffusing surface is needed. To solve this problem, RPG® patented the Skyline®. It is the industry’s first — and most efficient — omnidirectional primitive root number theory two dimensional diffusor. The Skyline® scatters incident sound uniformly so that the acoustic glare in all directions is minimized.

Small rooms like Project Studios need a very efficient surface to diffuse interfering rear wall reflections and provide a diffuse sound field.

Solution
To solve this problem, RPG® utilized advanced primitive root number theory to design the most powerful and aesthetic two dimensional omnidirectional diffusing surface in the acoustical industry.

Diffusion
The uniformity of diffusion is characterized by the standard deviation of the 1/3 octave polar response, for a given angle of incidence. For each of the 37 angles of incidence, 37 backscattering impulse response measurements are made at 5° increments between 0° and 180°. The Diffusion Coefficient is the mean standard deviation for all angles of incidence, normalized to the standard deviation of a delta function (1 equals ideal diffusion). The data illustrate the exceptional uniformity of diffusion above the diffraction limit (565 Hz = 1130 ft/sec/2'), which is related to the 2' dimension of the panel. The Diffusion Coefficient of a flat reflective panel is shown for comparison.

Installation
The Skyline® is very easy to install on walls or ceilings using the supplied hook and loop fasteners. Apply both sides of the hook and loop fastener to the rear of the Skyline® in each corner on a flat area. Remove the protective paper from the exposed side and apply to the wall. For permanent mounting, construction adhesive must also be applied, where space allows on the back of the unit, along with the hook and loop fasteners.The Skyline® can also be inserted into a T-bar ceiling grid

WARNING:

The Skyline® is fabricated from flame- retardant, high- density expanded polystyrene foam. It is the nature of this material to have rough surface imperfections and contain steam vent

[mikebse2a3]

Diffusion
The uniformity of diffusion is characterized by the standard deviation of the 1/3 octave polar response, for a given angle of incidence. For each of the 37 angles of incidence, 37 backscattering impulse response measurements are made at 5° increments between 0° and 180°. The Diffusion Coefficient is the mean standard deviation for all angles of incidence, normalized to the standard deviation of a delta function (1 equals ideal diffusion). The data illustrate the exceptional uniformity of diffusion above the diffraction limit (565 Hz = 1130 ft/sec/2'), which is related to the 2' dimension of the panel. The Diffusion Coefficient of a flat reflective panel is shown for comparison.

[mikebse2a3]

absortion characteristics of skyline

[mikebse2a3]

Well look what I was able to find it with the wayback machine.

The orginal PDF for the skyline if anyone is interested.

skyline.pdf

skyline.pdf

skyline.pdf

skyline.pdf

[artto]

Hey Mike, why are we even bothering with all of this? I mean, take a look at Robert Greene's listening room of Absolute Sound, and Kal Rubinson's of Stereophile. These guys know what they're doing, right?

Greene's Main Listening Room

[artto]

And Kal Rubinson's

[artto]

[+o(] [+o(] [+o(] [N]

These guys evaluate and critique and write about the best audio equipment on the planet?

If they're not deaf, you have to admit they certainly have bad taste in room decor.

Hey Kal, where's the peanuts? Oh wait, I think I see some on the floor.

[Marvel]

RPG® Skyline 7" 2D Primitive Root Diffuser

It was interesting reading the BBC paper on building these. RPG was the only company that could build them in a cost effective manner.

Bruce

[mikebse2a3]

Wow..! artto

You know this just goes to show that all reviews should be accompied with pictures of the setup conditions before any trust is put into the validity of any review of equipment but especially loudspeakers....!

[Chris A]

Quote

...take a look at Robert Greene's listening room of Absolute Sound...These guys know what they're doing, right?

Greene's Main Listening Room

Well, that's interesting: here is a 1961 paper by PWK (PDF enclosed) that would probably be of interest ref. the speakers on stands. He's violating cardinal point #5, isn't he?

Chris

Eight Cardinal Points by PWK4.pdf

[Chris A]

Quote

And Kal Rubinson's...

One thing that I've found is that anything between you and your speakers--like that coffee table with all that stuff on it--disrupts stereo imaging quite a bit.

I keep the area between my listening position and my speakers and out to about 90 degrees left and right clear of reflectors within 30-40 inches of my listening position or the exit plane of the speakers, or at least covered with absorbing material if you are listening to your setup within ~12-15 feet of each speaker.

These early reflectors do raise havoc with human perception of stereo images unless the close reflections are really diffuse, i.e., their magnitude is at least 10 dB down from the incident SPL from about 400 Hz up to about 2-3 Khz. The listening effect is like adding noise to the stereo imaging...and sometimes much worse.

I believe this is why a lot of people place their speakers out into their listen room - like these two guys above have done. The downside of placing speakers out into the room of course is the loss of smooth lf response and much higher lf modulation distortion.

Chris

P.S. I also noticed that this he hasn't toed-in his speakers, nor has he spread his speakers to the angles recommended. Those two points are also addressed in PWK's "Eight Cardinal Points" paper, above.