Pyramid and egg crate foam - good for acoustics or not?
Making pyramid or egg crate (known as convoluted) foam is not as easy as making flat sheet foam, and so it costs more. You would hope that it gave more absorption since it costs more but it doesn’t. The same depth of flat sheet foam gives you more acoustic absorption because there is more foam!! Not only this, it costs less.
The giant wedges in anechoic chambers work as impedance transformers for sound waves because they are large enough to work at the sort of wavelengths that sound waves exist at. However, down at the size of 50 or 100mm, they are way too small to work like this.
Odd really isn’t it, that the more costly sculpted foam look like it should absorb more but really it doesn’t. So remember, for normal audio applications like studios and theatres, flat foam costs less and provides more acoustic absorption.
If you want to read more from an independent source - https://www.acoustics.asn.au/conference_proceedings/ICA2010/cdrom-ICA2010/papers/p149.pdf