How Acoustic foam works – Absorption
Open cell foam has been proven to exhibit good sound absorption characteristics especially at the medium to high end of the frequency spectrum. The CNC Computer cut profiled structure of acoustic foam tiles is optimally designed to allow the foams air pockets exhibit dual action on any incident waves applied upon them. Firstly the waves hitting the peaks and troughs of the foam panels will get deflected in several directions thus weakening them, and secondly a portion of the waves that penetrate the foam will get absorbed.
This dual action means that you almost totally eliminate echoes from the top end of the frequency spectrum.
To tackle the lower frequency with foam absorption you will need a thicker foam tile always look for the NRC ( noise reduction coefficient ) results as this information will tell you the sound absorption the tile achieves the average NRC gives you the overall sound absorption i.e and average NRC of 0.7 gives you 70% sound absorption. But if the results are published in full you will see the tiles performance across the whole frequency spectrum.
Really low frequencies are hard to eliminate and would require gigantic blocks of foam to completely absorb the sound incident on them, however with the right combination of foam pads and acoustic panels you can reduce lower frequency distortion.
Frequency & Sound
Every sound created that you can hear or not hear is created from the resonance of the material creating the sound. Every material resonates in a particular manner and at a particular frequency (number of times a second or Hertz(Hz). The human ear is capable of hearing sound from about 50Hz right up to and over 20KHz although with age this level drops to about 10KHz.
Whilst most music will consist of a broad spectrum of audible and inaudible sound, Speech and vocals are known to generally consist of two levels of frequency the lower range of about 1KHz for vowels and the higher 3KHz for consonants. Acoustic foam from 40mm in thickness of varying designs can significantly reduce echoes created from speech and processed vocals.
The rule of thumb is that a piece of foam will be effective in absorbing frequencies whose wave length is four times its thickness and below.
It is therefore important to ensure any vocal booths are covered with patterned foam or at very least the back sides and top around the microphone is padded. This will improve the vocal clarity and quality captured by your microphone by simply reducing unwanted sound interference.