This is all fine and dandy, but what do we build if we want EVERYONE who walks into our room to say, "This sounds good. I can work here."? Drawing upon our collective experiences as recording engineers, a lot of good published acoustical research and some very strong anecdotal evidence from our work with ultra-wide dispersion loudspeakers, my partners and I think we have pieced together a good bit of the "sounds good" puzzle.

Let's start with the obvious. Loudspeakers and rooms form an acoustic transmission path. They both affect what we hear and how we perceive it (two VERY different,but related, things). Loudspeakers need to have low distortion and flat frequency response, and to be free of audible resonances. They also need to have good off-axis response. At the very least, rooms need to minimize standing wave problems and not have excessive reverberation times. On these basic points there is little, if any, disagreement.

However, (and this is not yet widely appreciated in the recording industry) loudspeakers ALSO need to have horizontal coverage angles of 140° or more across the audio bandwidth. Meanwhile, control rooms should have hard side walls to generate lateral specular reflections that make full use of the off-axis acoustic information and power generated by such loudspeakers. Control rooms also need to be very well damped at the front and on the ceiling. Non-specular diffusion (such as quadratic residue diffusers like RPG diffusers) should by and large be avoided for such applications, particularly on the rear wall. (No offense to the diffuser makers here. Diffusers are great devices, with lots of good uses.)

If we take a quick look at the photos of studios in this magazine, we are not likely to find many pictures of control rooms that look like this. That's OK. Studio design is what it is today as a process of evolution, and the room designs are generally based on common-sense approaches to the apparently obvious solutions to some perplexing acoustical problems.

One of the most basic of these approaches has been what I like to think of as the "pseudo-anechoic" approach. The basic principle here is based on the assumption that the signal emitting directly from the loudspeaker is some sort of "acoustic truth," and that it would be best if we could listen to just that signal and nothing else. This seems like a reasonable approach. However, it turns out that we need an anechoic chamber to do this, and such chambers turn out to be unsatisfactory as control rooms for a variety of reasons. So we rationalize a bit and allow as how we do need some reverberance maybe, but not "early reflections." Some of us even characterize those reflections as "acoustical distortion." So we attempt to suppress those reflections, or we use quadratic residue and similar diffusers to convert those reflections into "reverberance."

Now this flies in the face of some 7,000 years of acoustical experience (the first "auditorium" was built around 5,000 BC), experience which suggests quite compellingly that reflections and reverberance are ESSENTIAL when it comes to listening to music. Musicians refuse to play without reflections and reverberance, as a rule, and the general acceptance of listening to music in reverberant spaces (i.e. rooms) is, well, universal.

If this is so, how can early reflections be thought of as "acoustical distortion?" The answer is that reflections are distortion, insofar as measurement microphones are concerned. That's why we need anechoic chambers to make measurements with microphones. However, for human hearing, such reflections aren't distortion at all. Instead, those reflections are an important central part of the acoustical sound that us humans enjoy so much.

So, the specular early reflections that come from hard side walls in the control room provide the listener with full-spectrum, phase-coherent information that our ear/brain uses to localize the loudspeakers and their related phantom images, as well as to help determine the timbre of the sound. (Believe me, this is not snake oil. This is an essential part of how humans perceive and localize sounds in rooms.) The more closely those reflections match the direct sound in terms of frequency and phase response, the better we can perceive all the timbral, timing and ambience cues in the recording that the loudspeakers, especially in stereo or surround arrays, are playing back. This may seem a little counter-intuitive, but with strong, full-spectrum lateral reflections, phantom images become more stable and "palpable" and the depth of the stereo sound-field increases, with strikingly more resolution of the ambience and reverberance of the recording.