Modal decay times below 80 Hz are achievable with parametric equalization

Evidence

Here we introduce electronic manipulation of a physical acoustical phenomenon. It is possible because low-frequency room resonances behave as minimum-phase systems, and therefore respond to corrective equalization of the frequency response peak by attenuating the time-domain ringing. To be clear, this does not eliminate the resonance when there is no equalized audio signal present. Pause the playback, have an interlude of live acoustical music and the room resonances will have their effects. However, press the “play” button and music reproduced through loudspeakers supplied with the appropriately equalized signal will be heard with the problematic room resonance(s) attenuated. This works best for one listener, where the mike is located, or possibly for a few in a row or column of listeners oriented with respect to simple axial modes. — , Toole, Floyd E - Sound reproduction-…, 942 (#corroborates, via linked claim)

A related and important area of signal processing to filtering is equalization. Unlike filtering, equalization is not interested in removing frequency components but in selectively boosting, cutting or reducing them to achieve a desired effect. The process of equalization can be modeled as a process of adding or subtracting a filtered version of the signal from the signal, as shown in Figure 7.40. Adding the filtered version gives a boost to the frequencies selected by the filter, whereas subtracting the filtered output reduces the frequency component amplitudes in the filter’s frequency range. The filter can be a simple highor low-pass filter, which results in a treble or bass tone control, or it can be a band-pass filter to give a bellshaped response curve. The cutoff frequencies of the filters may be either fixed or variable depending on the implementation. In addition, the bandwidths of the band-pass filters and, less commonly, the slopes of the highand low-pass filters can be varied. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 2419 (#expands, via linked claim)

Categorization

• XREF: connects to: Signal processing compensates reproduction deviations through equalization; Minimum-phase loudspeaker resonances are correctable with parametric equalization. — Toole, Floyd E, Sound reproduction- the acoustics and…, 510; Isolated low-order axial modes cause the worst and most treatable problems (+3 more)

Broader Connections

• Room resonances are minimum-phase and yield to frequency equalization #corroborates (0.85) — , Toole, Floyd E - Sound reproduction-…, 942
• Equalization selectively boosts or cuts frequencies rather than removing them #expands (0.72) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 2419