Wave Field Synthesis

Wave field synthesis is a spatial audio rendering technique. Comparable to how many small light “pixels” can compose a visual image, wave field synthesis uses many small speakers to produce a soundscape, placing virtual sources of sound in real space. EMPAC, in 2015, started building and designing its own wave field loudspeaker array, seeking a system with good sound resolution that was also flexible for audio research and presentations. On October 16, 2018, the finished system was on display, so I ventured down to EMPAC to check it out.

The setup was housed in a black, dimly lit room; the visuals, while not as important as the sound, still need to be controlled, and I appreciated the reduced visual stimulus – the focus was on the sound, after all. A lone iPad in a stand served to control the demos, and the contents of its screen were projected on the right wall. Along that same wall, set in the darkness, was the speaker array: two large stereo speakers, and hundreds of smaller speakers in a long row, running across most of the room. If EMPAC’s website is to be believed, there are sixteen units with 31 loudspeakers each – 496 small speakers, spanning the wall. Needless to say, I didn’t count them myself.

Importantly, I was alone in the room; since nobody else was around, I got to control the experience for the entire time and thus explored all of the available demos. By myself, I was the audience, experiencing what was essentially a musical tech demo performed by the entire room of speakers and computers…

The first demonstration – the intro – involved differentiating stereo sound, surround sound, and wave field synthesis. Stereo and surround sound, with their limited number of audio streams, can’t usually give each instrument its own sound field; the sensation of location, with respect to a source of sound, is limited. Wave field synthesis, by using hundreds of speakers, can overcome this limitation.

The second demonstration was the first to really play with the “3D audio” concept. Virtual musicians, represented on the iPad’s screen by numbered circles and on the floor by spotlighted areas, played various string instruments. I was left to walk around the room and explore the soundscape, alone. 

It’s hard to describe the sensation you get when you hear and see what is best described an illuminated space on the floor playing a cello. I walked through the spots, though doing so didn’t feel quite as strange as I had hoped. More interesting was walking around the spots; it actually sounded like I was walking around something that was making noise, and hearing an instrument was much easier when you were closer to its corresponding illuminated circle than when you were on the other side of the room, next to a different instrument. Walking between the spots and the speaker array was discouraged, however; doing so would block the sound and interfering with the precise construction of the soundscape. I tried it once anyway, just to see if anything fascinating would happen or if the distortion was significant, but the results were not all that interesting, so I avoided blocking the audio for the rest of my time there. 

For the third and final demo, the virtual musicians got out their reed instruments and started moving around. Now I was really glad that nobody else was watching, because I ran around the room a lot at this stage. I ran back and forth a couple of times lengthwise with respect to the speaker array, just to hear how my movement would match up with the movement of the virtual musicians, and I ran towards and away from the virtual musicians. It was fun, at least in part because the entire thing felt surreal; the lack of visuals left a lot to the imagination.

While I certainly wouldn’t consider myself an audiophile, I would be lying if I said I didn’t enjoy messing around in the soundscape. I’m sure being alone helped a lot, since I was free to run around, switch through the demos, and generally be ridiculous. I’m left to wonder where this technology will find a home; theaters seem like an obvious choice, but what else could find use in this technology? Given that it’s as computationally expensive and monetarily expensive as it is, I don’t think wave field synthesis see widespread adoption anytime soon, but I’m eager to see what happens to the technology as time goes on.