Early Decay Time (EDT) is an important parameter related to reverberation time in indoor and architectural acoustics. It involves the calculation, evaluation and psychological perception of reverberation time.
Simply put: EDT is a parameter used to describe the acoustic properties of a room. It generally refers to the time it takes for the sound to decay by 10 dB from stopping, and is recorded as T10. Multiply this time by 6 to get an approximation of the reverberation time T60. EDT is often used to describe the initial reverberation characteristics of a room.
In practice, EDT is obtained by measuring the slope of the integrated impulse response curve, which is determined by the slope of the best-fitting linear regression line in the initial 10dB (0dB ~ -10dB) section of the decay curve, from which the decay of 60dB attenuation is extrapolated. time.
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To truly understand its concept and importance, we must understand the propagation process of sound waves in closed spaces from the beginning. Understanding the propagation process of sound waves is also the only way to delve into indoor acoustics.
Many of our daily listening environments are in closed spaces of various sizes, such as classrooms, conference rooms, theaters, cars, etc. Only in such closed spaces can a diffusion field/reverberation field be formed.
Sound generally goes through three stages of propagation from the sound source to being heard by human ears：
First is the direct sound
This is very easy to understand. The straight line between two points is the shortest. No matter where we are in space, the direct sound is the first and most primitive sound we hear.
Followed by early reflections
Sounds that are reflected from walls, floors, etc., and reach the human ear immediately after the direct sound are called early reflections.
Finally, there is the familiar reverberation sound
After enough reflections in the space, the sound is mixed and transmitted to the human ear from all directions and paths. These sounds are collectively called reverberation sound. The time difference between all these reverberant sounds (reflected sounds) is minimal.
During this process, reverberation fills the entire space. After repeated reflections, the energy is continuously absorbed by various materials including air, and finally disappears completely. The time it takes for the reverberation to disappear is the reverberation time RT
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The theoretical sound pressure level attenuation process is completely linear, and the entire attenuation draws a straight line. This situation is difficult to simulate even in the laboratory.
For this reason, studying the early decay time EDT is of great significance to psychoacoustics, as it can serve as a powerful complement to the objective parameter T60.
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