[Ethan Winer]

John,

> I'm surprised though that this isn't already known <

It is known! Look here:

www.acousticsfirst.com/eggc.htm

As you can see, they do nothing useful below 500 Hz, and the absorption is quite frequency-selective above that.

The report doesn't say if the egg crates tested are cardboard or styrofoam, but the test was done in 1988 so I'm guessing cardboard.

--Ethan

[JohninCR]

Thanks Ethan,

That has to be the cardboard, .40 and up, not bad for so cheap.  You were correct about vocal range and up.  The celing area that I covered is adjacent to a room with the same height flat wooden ceiling.  Even with only the egg carton layer and only ambient room noise, the acoustic difference was quite noticeable, so much so that going from the treated ceiling room to untreated one caused a feeling of discomfort, like you were very closed in with a low ceiling pressing down on you.  After adding more absorbent layers, the sense of spaciousness compared to the untreated room is remarkable despite having several inches less height.

[PhilNYC]

I've found that putting real chicken eggs into the compartments helps with diffusive properties but not as much as stapling the fully grown chickens to the wall.  The clucking can be a nuisance but you simply increase the program level to compensate.  A chicken wire cylinder stuffed with roosters makes an excellent bass trap as well.

If you cook them first, their density increases and improves low frequency absorption...

[BrunoB]

If you cook them first, their density increases and improves low frequency absorption...

Cooking an egg does not affect its density because the mass and volume does not change ... anyway, I prefer omelettes.

[PhilNYC]

Cooking an egg does not affect its density because the mass and volume does not change ... anyway, I prefer omelettes.

I thought volume does change...?