Active Absorption – Reverse Sound Reproduction and Virtual Bass Correction

Reverse Sound Reproduction

Reverse sound reproduction can be used so that two interfering sounds will cancel out each other. This can be achieved by usually placing one or two sound sources at the opposite end of two walls, working together as primary and a secondary sources.

The secondary source is equipped with a microphone to record the sound from the opposite source location. Based on the recorded sound there will be a reproduced sound from that source that has reverse polarity in order to attenuate the incident sound leading to a suppression of the adjacent wall reflection.

Virtual Bass Room Mode Correction

The idea for creation of a virtual bass is motivated by a psychoacoustic phenomena as a result of the pitch-extraction in the inner ear and the brain. The presence of higher order harmonic components creates the impression of the missing fundamental frequency, e.g. 100 Hz in presence of 200 and 300 Hz.

Room resonances can be filtered and further replaced by virtual bass components leading to the illusion of the filtered frequency. One has to note that by increasing the introduced higher order harmonics will result in a change of the overall sound quality.

Figure 1: Concept of a room within a room.

Figure 1. depicts the virtual room correction procedure of creating the missing fundamental.

The unprocessed signal is routed to a parametric equalization routine (PEQ) with notch filters to even out the peaks of the room resonances. Simultaneously, the signal is routed to a set of bandpass filters (BPFN ) placed at each of the problematic room modes and eventually processed by the virtual bass unit.

The output of each virtual bass unit is summed, amplified (G) and recombined with the equalized signal and further fed to the designated loudspeaker channel.

In this post, we explained Reverse Sound Reproduction and Virtual Bass Correction for active absorption; Other types of these methods that need to be mentioned to improve the sound will be published in future posts. These will pave the way for creating a home theater of the highest quality.

Although, we explored two types of sound absorbers that are effective in controlling sound reflections; Other types of these absorbers and the things that need to be mentioned to improve the sound will be published in future posts. These will pave the way for creating a home theater of the highest quality.

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