3D3A: Creating Three Dimensions from Two Speakers

by Allen Edelstein | October 1, 2010


n addition to being a "cautious objectivist," I am primarily an audio purist. I prefer a straightforward, high-quality two-channel audio system and stereo recordings done relatively simply with minimal processing to a system with more channels and recordings that are processed in any way. I prefer the purist way because I like the sound produced by minimal meddling, and I also believe this approach has the maximum potential to yield the closest re-creation of live music.

Note that I said "primarily." I do leave the door ajar for processing that improves on my audio Puritanism. From experience, I've discovered that interference with the signal may make the sound more impressive in some single way, but usually at the cost of other aspects that are important. However, ignoring all processing techniques leaves the potential to miss a real breakthrough.

So when I was offered the opportunity to be the audio expert in an Internet video about three-dimensional enhancement of conventional stereo recordings, I had mixed feelings. However, I believed that this was one situation in which I should go with an open mind. I was also curious, as a Princeton physicist, Edgar Choueiri, was overseeing the project. Choueiri's specialty is plasma physics; he's currently designing plasma rockets for NASA. He has just the type of scientific background we can use more of in high-end audio: advocating an understanding of what is actually happening (is it really an improvement and not just different?), why it's happening, how it can be repeated.

So on a hot August morning, I met Edgar Choueiri and Nyier Abdou, a New Jersey Star Ledger reporter who was making the short movie about the project (you can view the movie above), at Princeton University for what turned out to be a very interesting and fun hour and a half. The process Choueiri developed, 3D3A, which stands for 3-D Audio and Applied Acoustics, the name of the lab at Princeton, is a new digital version of one from the past that aims at reducing crosstalk between the right and left channels. I recall Bud Fried's MARS process and also another marketed by Polk Audio. Neither of these lasted very long. Choueiri says analog techniques for reducing crosstalk did not allow sufficient control and also introduced tonal colorations. Not having much experience with them, I can't really say, but their short stay in the marketplace lends credence to Choueiri's claims. Choueiri asserts that the more powerful digital processing (he has access to some very powerful digital gear) he employs permits greater control of the 3D effects and unwanted side effects. Indeed, because he is already modifying the signal, he also takes the opportunity to smooth it out, delivering flat frequency response to the ears.

The system can be likened to an open-environment version of binaural headphones, employing two speakers that are close to each other and in front of the listener instead of being over the ears. This has two advantages over headphones: it is more comfortable, and you don't get the "sound inside your head" syndrome, as headphones can produce. It also doesn't take up as much floor space as a more widely spread pair of stereo speakers. The system's software takes into account a generic head shape, but the processing is flexible enough to use the dimensions of an actual listener to enhance the effect. There is a sweet spot that, not surprisingly, is usually centered between the two speakers. But the power of the software allows the sweet spot to be moved to either side of center. In fact, Choueiri told me that he can program in up to three ideal listening positions and cycle among them rapidly enough to produce all three at the same time. Spacing between the two speakers is critical and is very slight -- just a couple of feet or less, which I see as beneficial both for placement convenience and greater isolation from the side walls of the environment.

I experienced Choueiri's 3D3A with two systems in two environments. Most of my listening was to a pair of small, inexpensive two-way speakers on stands with a subwoofer in a small anechoic chamber. Anechoic conditions enhance the results somewhat, but they are fortunately not necessary. The second system employed two larger, more costly two-way monitors, also on stands, with the same subwoofer. But here everything was in a conventional room.

Most of the demonstration used source material supplied and recorded by Choueiri, and the majority of it was binaural. I was both fascinated and impressed by the effect. The first clip played was flowing water. I could hear the water in a 360-degree circle around me -- from two speakers a couple of feet in front of me. When I closed my eyes, it seemed as though I was standing in water up to my neck, and I almost felt the water lapping against me. The other binaural examples were as impressive in their own way as this first one.

Toward the end of the anechoic session I got a more pertinent demonstration for audiophiles. Choueiri played portions of the Reference Recordings Rutter Requiem CD [REF 57] I had brought along. The results were different from the binaural effects -- less fantastic, more real. The primary sounds of the orchestra stayed in the front, as they would with a stereo system, but the reverberant soundfield was both wider and much higher, and I was very aware of a reverberant field behind me. This is the just kind of effect you get at a concert.

I did only a small amount of listening with the larger speakers in the more conventional environment, but this system confirmed what I heard under anechoic conditions. One example stood out. Off to the sides of my seat were two absorbent panels used to control reflection. With a conventional music recording, the results were like those I described with the Rutter Requiem. However, I could clearly hear sound coming from the absorbent panels. If I had not known what the panels were, I would have thought they were planar speakers used to enhance the three-dimensional effect. But I was listening only to the two speakers in front of me.

After listening for 90 minutes, I had to admit that the systems seemed to do just what Choueiri claims without any overt tonal coloration. Choueiri says that preliminary discussions have begun with commercial producers. The technology can be put on a chip and easily added to electronics -- from surround-sound processors to CD players. Perhaps more fascinating is the interest shown by recording engineers -- the 3D3A processing could be used during recording as well. Because of the close spacing of the stereo speakers, I can imagine a single box containing the speakers, the electronics and a subwoofer acting as the stand for the flat-screen TV.

My preliminary thoughts on the applicability of the 3D3A system for audiophiles are positive but a bit fuzzier. After all, we have very high expectations, and an hour and a half is far too short a period to come to meaningful conclusions. But this was a very impressive first audition, and if I have the opportunity to do the kind of follow up needed, I'll now listen with a positive, optimistic attitude rather than a doubting one.

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