Acoustical Interferences

Acoustical interferences occur when the direct sound from a loudspeaker interacts with the reflected sound inside a room. This interference can either be constructive or destructive.

Destructive interference occurs when two sounds are out of phase that is, one half wavelength apart in time. Whereas constructive interference arises when two waves are in phase with each other. Destructive interference in high frequency ranges occurs with dips spaced relatively close to each other what makes it become less audible.

How does acoustical interferences occur?

This can be explained through the perception of sound in the inner ear. The basilar membrane within the cochlea, where the frequency content of sound gets separated spatially, can be divided in 24 bands that can be seen as an array of band-pass filters, also called auditory filters.

Frequencies that fall within a critical bandwidth (rises with increasing frequency), are assessed mutually what makes the ear perceptually incapable to separate the spectral features. Whereby fluctuations in low frequency ranges can become unpleasantly audible if the dips are isolated and far from each other.

Moreover, the perceived spectrum is a result of a summation of the spectra at each ear, which makes coloration from lateral reflections less problematic. Krumbholtz et al. could show that this summation can even be emulated by presenting the summation of two the different sound events arriving at both ears identically to both ears.

As mentioned earlier in Figure 1. in Spatial Effects, listeners tend to adapt to the acoustics in rooms and have the ability of listening “through” the room to perceive the natural image of the sound source. It can be considered as an ability to separate between a changing (the program) and a stationary (the transmission path) spectrum. Yet, this perceptional adaptation is only possible as long as the sound source is stable.

Listening Test!

According to a listening test (1984) with acoustic professionals made in their own listening rooms, the sound reproduction from a loudspeaker, set up in a stereo left location, perceived in the “sweet spot” was enjoyable even with the flaws in the frequency response shown in figure 1:

Figure 1: Measurements made in the sweet spot of six different listening rooms.

What has been said so far and what we will discuss in the future, will pave the way for creating a home theater of the highest quality. The audio products offered in Saba Smart systems, which include Dali speakers, Yamaha amplifiers and inakustik cables with their great variety and high quality, make it possible to implement any type of equipment according to the relevant needs.

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