Soundman2020 - Studio Design Forum

- Variable Acoustics -

Sometimes it is useful to have an acoustic device that can produce variable response, as you change some physical aspect of it, such as opening, closing, sliding, flipping, rotating, etc.

Here is an example of such a device that I designed for a client's iso room, that he uses for tracking a variety of instruments and vocals.

In this case, there is a central "slot wedge" that absorbs certain frequencies while reflecting others and slightly diffusing yet others. There are also two hinged "wing" modules that are normally tucked up tight against their respective "backer" modules, but they can be swung open to cover the wedges, thus exposing an entirely different set of treatment to the room. There are two devices like this in the room, and each has two wings, so there's a fairly wide range of acosutic response variability as each of the wings is opened or closed, or even left in an intermediate position.

So here's the device under construction, with the wedge already completed (sorry! I can't release the details of that, or what's inside it... it's a proprietary design... ) and the frames for the wings half open:

And another view, with the wings completely open to cover the wedge:

Variable-acoustic-02--panels--construction--fully-open--SML-ENH.JPG (67.02 KiB) Viewed 25675 times

Variable-acoustic-02--panels--construction--fully-open--SML-ENH.JPG (67.02 KiB) Viewed 25675 times

A later stage in the build, with the wings partly completed and closed over the wedge (the thing in the far corner is not part of this device: that's something else).

The final completed room, set up for recording an instrument:

And the actual acoustic response tests graphs, to show what it does:

variable-acoustic-05--acoustic-rt60-plots-all-positions-t20.jpg (64.54 KiB) Viewed 25675 times

variable-acoustic-05--acoustic-rt60-plots-all-positions-t20.jpg (64.54 KiB) Viewed 25675 times

That shows how the decay rates change with the wings open at various angles. You can clearly see that as the wings are swung from one position to another, the room can be made "drier" and "more bassy", as the device absorbs mostly highs while not affecting lows, or it can be made "brighter" by heavily absorbing the lows while reflecting and diffusing the highs. There's a range of about 100ms for the highs and lows, and much less, about 50ms, for the mids. With all the panels open about half way, the response is fairly neutral.

One interesting thing about this design is that it does not change the frequency response of the room much: only the time-domain response.

So "variable acoustics" is a real thing, and not too hard to do. If you have a room that needs to serve several purposes, then it might be worthwhile to consider having variable devices in your room.


- Stuart -

I want it!! I interned at a studio years ago that had an iso booth with a similar variable acoustic design. Always thought it was a great idea and very practical.

Thanks for the info Stuart! I’ve finally made it through all of the reference articles. :

Cheers
Trevor

shybird wrote:Source of the post Thanks for the info Stuart! I’ve finally made it through all of the reference articles.

Then I need to write some more, it seems! I have plans for writing quite a bit more, but not enough time to do it, unfortunately...

Now, have you also seen the section on major things to be aware of, to avoid getting into acoustic trouble? "Fake Acoustics": Myths, legends, mysteries, and scams A little more light reading for you... (but you might have seen that already....)


- Stuart -

Hey Stuart, yes for sure! I’ve made it through some of that section but will go back again to see what I’ve missed. Really enjoying the learning process as it’s making me realize so much about my own potential design/build.

On that note, I’m going to go back and write a new message to you with some updated ideas/realizations I’ve had. Maybe it will save you time explaining some things.

Cheers
Trevor

What do you guys think of an idea I have of a rotating panel, with a centre axel, one side covered in wood veneer, other side absorptive, depth 50 or 60cm? The main axel could be on conical ball bearings, something like this

I think you have a good idea. I know of two studios, including Circle Studios in Birmingham, England, pictured above, that have a similar design on their wall panels. They are hinged at one end so they can swing either way, offering absorbing or reflecting sides.

Hi,

I was thinking that panels should be 60cm deep, so they can act as a really effective absorbers, and not hinged, but centre rotatable, so you can even do 45 degree position. One side reflective, three sides absorptive.

something like this

Looks good. Having the axis close to the front on your initial picture confused me a bit, those ones with it at the centre are a better design.

To contribute to the thread in general, a french cleat can be used for very simple and effective variable acoustics. Here's one where it allows a panel to be rotated from landscape to portrait position. Main use is to reduce side reflections of singers of varying heights, but there are others too.
It would be easy to make a panel with one side reflective and the other absorbent.