Soundproofing Material Calculator

Because the underlying mass law is TL = 20 x log10(frequency x mass) - 47.3, Surface Mass and Frequency enter the formula symmetrically -- they're multiplied together inside a single logarithm, so proportionally equal nudges to either one pull Transmission Loss by essentially matching amounts. Don't assume Surface Mass is "the" dominant input just because it's the material property you're choosing; Frequency has a mathematically equivalent pull on the result at the default single-layer configuration. Number of Layers is easy to misread as having no effect: it's a small coded 1-4 input, and testing a fractional value near any of its integers lands back on that same integer once the engine rounds -- yet it is very much not inert.

With no air gap (the default), the calculator treats multiple layers as simply adding mass together into a single combined surface mass, so going from 1 layer to the 4-layer maximum at this calculator's default surface mass and frequency raises Transmission Loss by roughly 12 dB, purely through the mass-law term -- a large, real effect that a narrow probe around the default won't reveal. Air Gap only changes behavior once Number of Layers is 2 or more; with a single layer, Air Gap changes nothing in the output, since there is no second leaf for it to separate. Once a gap is introduced between two or more layers, the calculator checks the frequency against a mass-air-mass resonance point: well above resonance, the layers act more independently and Transmission Loss can exceed the simple mass-law estimate; right around resonance the calculator blends smoothly between the below- and above-resonance estimates rather than jumping between them, so there's no sudden step in the predicted result as Frequency crosses that point; below resonance, coupling through the air gap can make performance up to 3 dB WORSE than the single-mass-law estimate, not better -- so a poorly sized air gap for a given frequency can backfire.