There is much talk about egg cartons and whether they have any acoustic value that I thought it was time to address it. The egg carton structure has been referred to as a sound absorber and a sound diffuser. Neither could be further from the truth. An egg carton does not have the correct material in its construction to absorb much of anything when it comes to sound absorption power. In fact, most absorption, if any, is narrowband and is centered around middle frequencies with a start point of 600 – 700 Hz. and that could be kind. This blog updated on 12/7/19 to reflect current changes in technology and knowledge with regards to the egg carton acoustic myth.
A True Acoustic Myth For Our Times
It is also not a sound diffuser. It may redirect sound energy out into various patterns depending on the internal egg holding container, but it can not be a true sound diffuser because it can not produce energy that contributes to a diffuse room sound field. A sound diffuser takes reflected energy in and then redistributes that energy back into the room in much smaller increments. Quadratic diffusion is the most popular sound diffusion technology and an egg carton never could correspond to the science inherent in any quadratic diffuser.
Limited Sound Absorption
So in this week’s video, I examine the egg carton acoustic myth. I look at the ability or lack of ability of an egg carton to absorb energy. People search for egg tray as a sound absorber and ask the question do egg cartons absorb sound. Absorption that is present is focused mainly around frequencies between 600 and 700 cycles. This narrow band of absorption is useless when it comes to small room acoustic absorption coefficients. The narrow band of absorption and the surface area required with most sound absorption materials, negates any possibility of an egg carton becoming a viable room acoustic tool.
Absorption Open Celled Foams
Let’s use open-celled foam for our comparison. Our 2″ foam for music and voice is 2″ thick. It starts absorbing energy at 125 Hz. and then goes higher. If open-celled foam that is 2″ thick starts at 125 Hz. and goes up, what chance to absorb does a 1/8″ thick egg carton have in answering the question do egg cartons absorb sound or does an egg tray as a sound absorber.
Studio Pro – Foam: https://acousticfields.com/product/acoustic-foam/
One Frequency Diffusion
I know why people think an egg carton could be a diffuser. It does look similar to a diffuser, especially a quadratic diffuser because it has wells or troughs. These wells or troughs are what the egg sits in for transportation purposes. In quadratic diffusion, each well depth corresponds to the quarter wavelength rule. With an egg carton having all “well” depths the same, I calculate that the average depth of a traditional egg carton which is around 2″ could only diffuse energy in the 3,000 – 4,000 Hz. range. This is too narrow of a band of frequency diffusion to be useful as an acoustic tool. Diffusion technologies must diffuse energy across a much broader frequency range to be useful in any acoustical design setting.
A quadratic diffuser is a series of weels or troughs of different depths. Each well depth is calculated using one quarter wavelength rules. Each well width is calculated at half-wavelength rule. You design the frequency response around the usage and distances from person to wall surfaces. Every quadratic diffuser is based upon a prime number. The higher the prime number, the wider the frequency range, the deeper and wider the cabinet. Think of a diffuser as a speaker you don’t power up. It relies on reflected energy from the room as its power source and it has a frequency response just like a speaker does.
Quadratic Diffusers: https://acousticfields.com/product-category/sound-diffusion/qd-series/
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