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Old 3rd September 2019
Lives for gear

what frequencies can I expect to be reflected back into the room?
There is a simple principle in acoustics: sound waves are only reflected by solid objects that are similar in size to the wavelength of the sound, or larger. In other words, if the object is 5 cm wide/high, it will only affect waves that are 5cm long, or shorter (shorter wave=higher frequency). That would mean waves with a frequency of about 7,000 Hertz, or higher. If the object is 10cm wide/high, then it would reflect frequencies above 3400 Hz. For an object 1 meter wide/high, that would reflect down to much lower frequencies: around 340 Hertz and higher.

There's also the issue that very thin, flexible objects might act like membranes or foils, in which case they could absorb some sound at the frequencies related to that, and there's the issue that the mass of the object itself will attenuate sound above certain frequencies (prevent i from passing through).

And finally, if you place wood slats over some type of cavity, such as the interior of a wall, then you have created a Helmholtz resonator, which will resonate at some frequency governed by the Helmholtz equations, and will therefore absorb that frequency very well, while reflecting higher frequencies, and perhaps somewhat absorbing lower frequencies, depending on mass, etc.

So there's lots of stuff to take into account. Its not really a simply as just nailing up some slats to get the high end back into the room. That's the general concept, yes, but there's a lot to take into account when you decide how to implement that in practice.

- Stuart -