Sound reflection

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Sound reflection on a flat surface with a mirror sound source

The sound reflection is the reflection in the optical comparable if the dimensions of the reflector at least five times the wavelength corresponds. In the other cases there are diffraction effects . The simplest case is a reflection on a flat surface. The following rule applies here: the angle of incidence is equal to the angle of reflection. This also applies locally to homogeneously curved surfaces. The tangent through the reflection point is used as a reflection surface. The sound source can be virtually reflected on the reflective surface and reproduced on the other side of the surface. This new sound source is called a mirror sound source .

In binaural hearing, a delay of 0 to 1 ms between the original and the mirror sound source results in cumulative localization . The precedence effect works between 1 and 50 ms (speech) or 80 ms (music) . Above this, the second sound event is perceived as an echo . 1 ms corresponds to a travel difference of 34.3 cm (at 20 ° C). When recording with a microphone (sometimes even with one-eared ( monaural ) listening), a discoloration of the sound is perceptible, which is caused by a comb filter-like superposition of the two sound signals.

In addition to the direct sound wave, reflected waves hit the immission location . Even if there are no reflective objects - such as walls or buildings - there is usually always a sound reflection as sound pressure on the floor. The direct and the reflected waves are superimposed at the immission location , and this leads to constructive or destructive interference , which leads to level increases or decreases.

The following terms are related to disturbed sound propagation: sound reflection, sound absorption , sound transmission and sound dissipation .

Correlations: The sound reflection factor ρ is a measure for the reflected sound intensity. The sound absorption coefficient α is a measure of the absorbed sound intensity . The sound transmittance τ is a measure of the transmitted sound intensity, the sound dissipation factor δ is a measure of the “lost” sound intensity.

ρ + α = 1
ρ + τ + δ = 1
α = τ + δ

From the last equation it can be seen that the proportion of the absorbed sound intensity, i.e. the sound absorption, is made up of the sum of the proportions of transmitted (transmitted) and "lost" (dissipated) sound intensity from sound transmission and sound dissipation. The first equation shows that the sum of the reflected and absorbed sound intensity, i.e. sound reflection and sound absorption, corresponds to the total sound intensity.

See also