Moulton Laboratories
the art and science of sound
Nick Batzdorf Interviews David Moulton
Interview by Nick Batzdorf, Editor of Recording Magazine
February 1999
1. Balderhash and Hodgepucky

Regarding Acoustics of Control Rooms and Loudspeakers.

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Nick Batzdorf Interviews David Moulton

NB: The conventional wisdom is that you want to absorb sounds coming from the sides of the mix position because they arrive at the same time as the direct sounds, which muddles things up.

You say Balderdash and Hodgepuckey to that.


DRM: I'd like to redefine what we mean by a sound. The conventional definition is that sound is something that emits from a musical instrument. Psychologically speaking, that's not quite true. It's the energy emitting from a musical instrument plus its volley of early reflections that actually goes into our perception of what a sound really is.

So I don't see any difference between a loudspeaker and any other musical instrument, except for one specific and important quirk. We have a long history of knowing that we prefer to hear musical instruments in reverberant spaces with reflections; there's no reason we shouldn't hear loudspeakers the same way.

NB: But with the loudspeaker you're trying to evaluate sounds that have their early reflections recorded.

DRM: That's right, and that's the reason you have to question what I just said!

But if you take a look at what's really going on in recordings, playback rooms are generally small and the early reflections happen very quickly-whereas in a recording space (or simulation of a recording space that we do with artificial reverb), those reflections are much, much later in time.

What happens is that the early reflections of the playback room carry information about the recording room quite well. At this point, I'm satisfied from my own research that this is true.

NB: How did you come to that conclusion?

DRM: At one point I began working with some omnidirectional loudspeakers.

NB: Your own.

DRM: Yup. We invented some prototypes, and I sat down to listen to them. What I heard was phantom images that came from places in the room that were incompatible with what I thought I knew about how phantom images behaved.

It turns out that happens because of the way we gather early reflections from walls in a room. In actual fact, loudspeakers themselves are perceived in stereo as early reflections of a sound whose direct version we missed. So we're listening to the first of a set of early reflections that includes all of the walls and so on.

What we've found in our ongoing research-and there's a substantial body of agreement among other loudspeaker designers-is that imaging and timbre sounds improve when we have good wide dispersion of high frequencies.

For instance, I was one of a group of speakers at the American Loudspeaker Manufacturers Association symposium in January. Both Floyd Toole of Harman International and Joe D'Appolito, who's a fairly well known speaker and systems designer, made the case: we now know that wide dispersion of high frequencies, resulting in a reasonably flat power response laterally, is ideal behavior.

NB: Why laterally and not vertically?

DRM: Right now there seems to be a fairly clear sense that vertical reflections (from the floor to the ceiling) tend to upset our perception. I'm not sure if that's true, but there is some evidence based on the Archimedes Project that was done in the early '90s in Denmark.

NB: Psychoacoustics?

DRM: Yup. And for me the final proof is in the pudding. I have very wide dispersion speakers in a very wet, large room. Intuitively, you'd say that has to be the worst possible setup.

Yet a mastering engineer, Bob Ludwig, said it was fabulous when he came to listen. I've had similar experiences as well. One major loudspeaker designer had to check that the center speaker was off, because in 2-channel stereo the imaging was so good that he couldn't believe he was hearing a phantom.

NB: Is there any reason that wouldn't hold as true in smaller rooms?

DRM: No, it should get better in small rooms.

NB: But the side reflections are going to come to you earlier in a small room.

DRM: Let's think about what happens with, say, a recording of a singer in a concert hall. You get a number of early reflection versions of the singer. But you also get a whole array of versions of the reverberance of the singer, a whole batch of iterations that are phantom images again from left and from right, and those are strongly supported to give you an additional sense of the reverberance in the original recording. I think that's why it works.

I've done enough of this now and designed enough rooms to say that yes, it does work.
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