A Philosophy of Monitoring

The above set of needs pretty well defines the range of monitoring solutions used in the recording and music production processes. Obviously, it is really cool to have BIG, back-listening reference monitors, and we can make a strong argument that they are really necessary. Trouble is, like really accurate microphones, they are expensive and usually a royal pain to install! Meanwhile, it also seems essential to have forward-listening monitors, which are cheap and easy to install! You just set ‘em on the meter bridge!

Given the above and the fact that we’re human, we tend to talk ourselves into only solving, fairly cheaply, the listening-ahead part of the problem, while ignoring the more expensive reality-checking quality-control part of the problem. This is why the current practice is to use In-Yer-Face® monitors. These are listening-ahead speakers, and we take the theory even further by listening to ‘em really close up so we think we don’t hear what the control room is doing to the sound quality. This leads to the delightfully absurd expression: “All you hear is what’s on the tape!” A quick physical observation (holding the tape close up to your ear) will reveal that there is no sound on the tape. Ah, the Zen of Audio . . .

Whatever. To really cover the monitoring problem, you need to be able to listen back to what you’ve done, listen forward at how what you’ve done will sound to others, and to listen to the badnesses of what you’ve done so you can fix them.

The Nature of Control Room Acoustics

The next layer of complexity to confuse issues even more has to do with the control room. All enclosed spaces have reverberance, except anechoic chambers. Along with the concern with standing waves (which are comparatively easily managed, thank God), the placement of loudspeakers in a room, relative to walls and listeners, seriously affects the low frequency performance of the speaker in the room. There are two primary engineering approaches to dealing with this: (a) mount the speakers in the wall, so that it becomes part of the boundary of the room, or (b) place them far enough into the room that the low frequency interference problems become low enough in frequency to not be an issue. Five feet from the nearest wall would be probably minimum – I know, I know, you’ve still got the floor to worry about, but it turns out that the first null from the floor reflection is usually high enough (ca. 500 Hz.) that it can be dealt with other ways, if you want to bother.

Anyway, the former solution requires a false wall and a lot of carpentry, some of it moderately tricky, while the later demands a big control room, which is intuitively sensible if you want BIG monitors, but not easy to pull off and sometimes just plain impossible.

High Frequency Dispersion

Another issue has to do with loudspeaker dispersion. Loudspeakers tend to be omnidirectional at low frequencies and highly directional at high frequencies. This means that a typical loudspeaker can only have flat frequency response in one direction, typically on-axis. In all other directions, the high frequencies will be rolled off, usually quite severely (10 dB or more) by the time you get to 60° off-axis. There are some important psychoacoustic implications to this that I will talk about in the sidebar.

What About Subwoofers?

One way to cut costs and still get gobs of low-frequency energy is to use subwoofers. The theory is that low frequencies are “non-directional” and impossible to localize, so it doesn’t matter if they emit from the same point in space as the audio from, say, 100 Hz. on up. This is all well and good, but speaker design still calls for time and frequency response accuracy, which in turn calls for very careful integration of crossover design and relative positioning of speaker elements. Use of a subwoofer usually sacrifices such integration, and so while the spectral content of a subwoofer-supplemented system might be OK, its problem-solving capabilities may be seriously compromised.