Pat Brown answers the question, “Can a reflection be equalized?”. He shows through a video demonstration that it is indeed possible under some conditions. Edge diffraction in a loudspeaker is used as an example.
This is an old topic that I will revisit using some of the newer tools. I offer it as a complement to two excellent articles from the SynAudCon Library, noting that nothing has fundamentally changed since they were written.
The concept of equalizing reflections remains a hot topic in audio. I show in the video below that it is indeed possible under some conditions. I use edge diffraction in a loudspeaker as an example. Modern technology has expanded this to include room reflections that arrive considerably latter in time. Acoustic Echo Cancelers (AEC) have made modern teleconferencing systems possible.
The prevailing “water cooler chat” theory is that IIR filters work only in the frequency domain, where as FIR filters can work in the time domain. This is not necessarily true, as these domains are completely inter-dependent and a filter of any type cannot change one without changing the other. A better statement is that “IIR filters can correct minimum phase anomalies, where as FIR filters can correct (some) non-minimum phase anomalies, such as the phase shift introduced by a crossover network.”
Who Gets the Benefit?
A severe limitation is poised by consideration of the area over which the benefit of equalization can be realized. In many, if not most cases, the benefits are confined to a single point in space, such as a microphone position in a conference system. My edge diffraction example extends to a larger area, but the only solution that benefits all listener positions is the removal of the reflection using acoustic treatment. Another benefit of treatment vs. equalization is that we spare the loudspeaker the 10 dB of boost required to fill the dip. As is true with most problems, the best solutions are always made at the source. pb
Video – Demonstration of simulated edge diffraction equalization. Note: This video is HD, so you can play it on a large monitor for a better view.
Below are some related excerpts from the SynAudCon OptEQ manual.