November 1, 2018
I saw your interesting videos on youtube and thought you might be of a good help in my situation, I'm currently doing my master thesis in sound barriers and had tested the absorption coefficient for some sound barriers made by a company, the structure is basically constructed of two concrete panels with lots of holes in it of about 2 cm diamter, and filled with different materials in between which makes a Sandwich profile of about 20 cm in thickness, I've tested the structure both with and without the concrete panel and found that the max. absorption coefficient are shifted towards the low frequency region when mounting the concrete panel while increases and goes to higher frequency regions when removing it.
I wonder if you have any explanations for such behavior.
My explanation was, since at the low frequency region the wavelength are quite long so the sound wave tends more to jump over the barrier and got absorbed by the air itself rather than propagating through it, which makes it seems as if the barrier has absorbed the sound wave in the low frequency region, while at higher frequencies the waves will tend to go through the holes in the concrete panel, then through the fillings and give lower efficiency compared to the case without the concrete panel, due to the low absorption coefficient of the concrete panel itself and hence lower absorption coefficient for the whole structure at higher frequency compared to the case for the structure without the concrete panel. But I'm not sure I got it right.
Please advise :).
August 12, 2013
S, When you mount the panel on the concrete structure, it compliments the mass of the existing structure thus increasing lower frequency performance. Low-frequency barrier technology is mass related. When you remove it from the concrete, the unit must now stand on its own without the assistance of the original concrete structure. It will then have a new resonant frequency based upon its thickness and other variables.