RT60 Calculator: About

About the RT60 Calculator

If the short description on the homepage didn't make much sense to you, read on. Audiophiles may already know what this is all about and can go ahead and try the RT60 Calculator out...

When building a public space (anything from cafés to theatres to classrooms), various acoustic properties of the space must be considered. One of them is the amount of time that a 60dB sound (about the level of normal speech) takes to completely fade away. This is known as the Reverberation Time (60dB) or RT60.

As its' name suggests, this program enables anyone to quickly calculate the RT60 of a specified room. However, there are drawbacks. The formula that is used does not take into account reflective or absorptive objects inside the room. Also, it does not accomodate for air absorption.

Here's the mathsy-physicsy bit - it's not necessary that you understand this, but the geeks out there can read on, should they wish. There are three formulae that are used to calculate the RT60:

Sabine Formula	Norris-Eyring Formula	Fitzroy Formula
$T_{60}=\frac{kV}{\sum{S\bar{a}}}$	$T_{60}=\frac{-kV}{S\times ln[1-\alpha])}$	$T_{60}=k \frac{V}{S^2}(\frac{-x}{ln[1-\alpha_x]} + \frac{-y}{ln[1-\alpha_y]} + \frac{-z}{ln[1-\alpha_z]})$
Where: k = 0.161 (when using metres) or 0.049 (feet) V = volume of the room Sā = SA for a given surface S = absorption coefficient for a given material A = surface area of given material ∴ ΣSā = S₁A₁ + S₂A₂ ... + S_nA_n	Where: S = the total surface area of the room α = the average absorption coefficient of the room, i.e. (ΣSā)/S	Where: x, y, z = the total surface area of two parallel walls α_x, α_y, α_z = the average absorption coefficient of the corresponding surfaces.

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