The Behavior of a Mirror

A mirror is a reflective surface where all of the energy is reflected back into the space. A feature of mirrors is that we don’t perceive them as surfaces, but rather as windows. We don’t perceive the mirror itself, we perceive the space whose image has been reflected, including three-dimensional depth in the perceived reflected space. The better the mirror is, the better the reflected image. If we degrade the mirror, by the addition of a tint, for instance, or by smudges on the surface, or cracks in the surface, the resulting image is similarly degraded and the “mirror as surface” becomes increasingly apparent.

So it is for reflected sounds, particularly from loudspeakers.

What About Comb Filtering?

One part of the mythology regarding early reflections is that they generate interference patterns with the direct sound, resulting in comb filtering and timbral degradation. Interestingly, this problem is a severe one for microphones, but not so for ears. For reasons related to our integration of that volley of sound artifacts, we don’t perceive comb filtering of phase-locked sounds that arrive from significantly different directions. Further, what little comb-filtering we perceive is diminished as the volley of early reflections in the playback room becomes richer. So, in a highly reflective room, comb filtering will be essentially inaudible, while it is generally quite audible even between the speakers themselves in an anechoic chamber, where only two artifacts exist.

So, comb filtering problems exist primarily in the domain of microphones and recording, and not significantly in the domain of loudspeakers and playback, except possibly under highly damped or anechoic conditions. Consider again the volley of sound artifacts that constitute the perceptual construct we call “a sound.” We identify members of the volley via their related spectra and phase-locked qualities. These are spread out over time. When we emit recordings of these volleys from loudspeakers into a playback room, if the early reflections from the playback room walls are similar in spectra, particularly at high frequencies, the ear accepts that these are additional information regarding the recording, NOT the playback room. And it is the high frequencies that especially help us form really solid and palpable phantom images.

Happily, such an illusion supports the reverberant information from the recording as well. This means that the early reflections in the playback room carry not only the direct sound and early reflections from the recorded space but also the reverberance to the listener, in an expanded and enriched way. Spaciousness is enhanced, depth is enhanced, images are enhanced, envelopment is enhanced. It’s a win/win/win/win kind of situation!