Wouldn't they be the same thing, just "tuned" to block out different frequency ranges? I'm guessing the tuning is based on the material and shape of the foam, and thickness and material of the walls? It's all waves.
They are different physical phenomena. Sound is a pressure and is produced by compression and expansion of the (local) environment. RF or light is a self-sustaining electromagnetic wave (assuming we are not right next to the source [i.e. far-field]) produced by a time-variant electric field inducing a time-varying magnetic field, which induces a time-varying electric field, which induces ... All these induced fields end up supporting each other and propagating the wave.
While they are both considered waves, it is not frequency regimes that differentiate acoustic pressure waves and RF waves -- RF waves can be anywhere within the "audio" spectrum and beyond, and audio waves can be well into the ultrasonic range and into the UHF regime.
The idea of the anechoic chamber is the same (blocking all reflections), but it is not just as simple as tuning to different frequencies. They do however need to be designed for a specific frequency range.
I am not an expert on anechoic chamber design (or acoustic wave propagation for that matter), but an RF anechoic chamber is not the same as an acoustic anechoic chamber, although it will show some functionality as one. Does that make sense, or am I just confusing the conversation? It did when I started writing all this. :/
You're right; the RF anechoic chambers are designed to absorb differently. However because they still do that at least partly through thick walls and foam cones; RF chambers are also pretty damn quiet - with the 2 I used for CE mark testing, if you stood two people opposite sides of the chamber, and one spoke 'into the wall' you had trouble hearing them unless they deliberately raised their voice.
Neither of the RF chambers I used had the foam cones on the floor; just carbon tiles.
... and audio waves can be well into the ultrasonic range and into the UHF regime.
Theoretically, at sea level on earth, the mean free path of air molecules allows for 3.4 GHz. But attenuation is proportional to f^2 which results in an upper limit of 100MHz. You need a medium denser than air at sea level for higher frequencies.
EM waves vs pressure waves, they're not the same thing (although the math is basically the same, just with different constants). Something that affects an EM wave won't necessarily affect a pressure wave - a Faraday cage for example will block EM waves but won't do anything to block sound waves.
EM waves are transverse (they oscillate perpendicular to their direction of motion) and sound waves are longitudinal (they oscillate in the same direction as they move).
There are some mathematical differences between transverse and longitudinal waves, so it's not just the same math with a different medium.
They're not the same things, no, but they obey the same wave mechanics, and due to the difference in propagation velocity, their wavelengths are actually very close. A wavelength of 3 meters is about 100 MHz in the RF world, and 1 kHz in audio terms.
That's why an RF anechoic chamber looks a lot like an acoustical anechoic chamber, and often sounds like one too.
