The main acoustical test we use at Auralex is ASTM C423, a certified test measuring the absorptive properties of a material between 100 and 5000 Hz. These numbers are then boiled down to an overall NRC and SAA numbers, an average for how well the product absorbs across those frequency bands.
All materials are tested at accredited testing facilities across the country.
Most of our acoustic materials range between 0.70 and 1.10, which has traditionally been thought of as absorbing between 70% and 100% of the sound that hits the panel in those frequencies. If you were to look at individual frequencies, that wouldn’t be the case, but it is a helpful way to compare different panels easily and quickly to get a sense for what you might need.
When it comes to bass trapping, you are mainly dealing with frequencies below that testing threshold mentioned above. When you look at bass trapping numbers, those are usually a projected number based on measurements taken in that same testing lab, but are a bit less definite than numbers in the typical testing spectrum. You still get a good sense of how the product will perform, it just isn’t as exact due to the wavelengths being long enough in the room that it is difficult to get an accurate test.
Finally, we come to diffusion. Diffusion is a bit more nebulous as there isn’t a recognized standard for these tests, but it is generally thought that polar plots showing the reflections at different frequencies are a good way to show how a given diffusor will react. This way you can see the usable diffusion frequency range and how the shape of the diffusor will effect those frequencies to learn how best to use them in your space.
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