Multiple Small Subs - Geddes Approach

[gedlee]

Originally posted by markus76
Earl, how far is your dummy head project? Would love to hear your home theater with different speakers.
Best, Markus

Markus

Interesting that you should ask. I ran into a guy that I knew many years ago at my sons holiday play and he was using a Neuman dummy head to do some recording. We talked and he is very interested in what I want to do and believes that the system would work ideally in that application and offered his help.

Now I need to arrange to get "other" loudspeakers in my room to record and compare. This later aspect is now the problem as there aren't many people with "good" loudspeakers that can bring them here. In fact it may not even be a reasonable thing to do at all and I may have to go to the few installations that I know of that are even remotely comparable to mine. I am definately going to record the Summas, Abbeys and Nathans all in the same exact situation as I am personally very interested in this.

[markus76]

Originally posted by gedlee
(see the latest JAES).

Will you respond to "CABS" by CELESTINOS and NIELSEN as proposed in the November issue? It's basically a double bass array (DBA) as described by Goertz/Wolff/Neumann 5 years ago (sorry, only available in German): http://www.monkeyforest.de/Page10383...2003-Paper.PDF

Best, Markus

[gedlee]

I can hardly respond to something that I can't read.

[markus76]

? The Celestinos/Nielsen paper is in the latest JAES.

[john k...]

Originally posted by gedlee
John

I think that its even more difficult than that. A wall (or window, door) that flexes doesn't actually have a single wall impedance - its a fluid coupled structure - that would be very difficult to measure and specify. And then there is the problem that the real situation may not even have a closed form solution like both of us use in our "simpler" models. One would have to use a full finite difference model like are just now being developed (see the latest JAES).

Remember I am looking at this from the position of 30+ years experience in CFD (computational fluid dynamics) and related areas. This is really just a different type of aeroelasticity problem, i.e. coupling of a fluids problem to a structural problem. The problem is riddled with details, but still isn't all that complicated.

[gedlee]

Originally posted by john k...
... all that complicated.

"all that complicated" is relative. CFD is usually more static without a high importance placed on HFs, which get tough fast. But yes a room at LFs would be very similar to a low wavenumber CFD problem.

[john k...]

Originally posted by markus76

John, software isn't only about algorithms but mostly about usability. Do you know CARA

Best, Markus

I looked briefly at their web page some time ago but you can't tell much from that.

Form a mathematical point of view room acoustic is a simple interior problem for which the solution is governed by boundary conditions at the bounding surfaces. As with any mathematical problem it is the boundary conditions which make the solution unique. In this case the boundary conditions are what happens on the surfaces that define the room. The solution offered by any room simulation tool, mine, Sound Easy's FEA analysis, CARA or otherwise, is only going to be as good as 1) how well the interior physics is modeled and 2) the representation of those bounding surfaces; How much acoustic energy is lost to the surface? How much is stored and then returned to the interior. When a wall flexes is it because it is acting as an accelerating mass in response to an applied force, or a spring?

The interior is easy. The wave equation is suitable. And there are any number of way we might attempt to solve the wave equation. But what of the boundary conditions? We might parameterize them. For example we might assume that all sheetrock walls have similar properties, windows have a different set of properties, HVAC vents some other properties, doors.... and then segment areas of each surface in to the appropriate generic family. But if your wall or door or window doesn't fit the generic model the results still won't match with measurement.

We all know how sound waves propagate. The problem is what happens when the wave interact with a surface.

[markus76]

I don't care how exact the model is as longs as it's exact enough. Auralization ist the key point to me. The conventional approach of measurement, construction and measurement is time consuming, error-prone, expensive and allows no A/B comparison - or even A/B/C/D/E/...n comparison.

[soongsc]

Originally posted by markus76
I don't care how exact the model is as longs as it's exact enough. Auralization ist the key point to me. The conventional approach of measurement, construction and measurement is time consuming, error-prone, expensive and allows no A/B comparison - or even A/B/C/D/E/...n comparison.

Sound like you are doing this for a living?

[soongsc]

Originally posted by gedlee


"all that complicated" is relative. CFD is usually more static without a high importance placed on HFs, which get tough fast. But yes a room at LFs would be very similar to a low wavenumber CFD problem.

I tend to agree. Normally CDF is used to solve very specific problems. Very seldom if any is it used to model blanket range scenarios. Even with todays PC computing power, it takes too much computing time could take a few days; and then if the results are not good enough, human intelligence still is needed.