ASC, The World's Best Studio Acoustics

Acoustic Sciences Corporation
TubeTraps

--By Michael Cooper--

You probably remember the ubiquitous ad that appeared in the late '80s in trade magazines, in which Pete Townshend extolled the virtues of Acoustic Sciences Corporation's Tube Traps. And perhaps, like me, you also wondered just exactly what the heck those tubular gadgets did. And, more importantly, if entities with the financial means of Pete Townshend and Hollywood's The Record Plant studio were using them, what practical relevance did these devices have to the smaller studios that did not command mondo equipment budgets? As it turns out, an interview with ASC's founder and President, Art Noxon, and subsequent testing of the company's Tube Traps in my recording studio dispelled any notions of voodoo acoustics and big budget requirements.

The two products that I tested were the company's Studio Traps and Trim Traps. Studio Traps are full-round devices, in which the fiberglass cylinder is inserted under very strong pressure inside a galvanized, woven, metal-mesh screen (hardware cloth). A lightweight plastic reflector and a non-absorptive Dacron float material separate the fiberglass from the metal screen. The Dacron prevents the fiberglass and reflector from contacting the other layers of material and decomposing under conditions of vibration. Polyester cloth covers the entire cylinder on the outside. The entire assembly is 4 feet long and mounted on a stand that can lower it to within 6" of the floor or raise it up to 6' feet off the ground. The Studio Trap's mobility makes them a good choice for encircling a performer in front of a microphone.

ASC's Trim Traps are third-round devices. They differ compositionally from Studio Traps (and all the full-round models) in that they forego the Dacron float and substitute a plastic woven-mesh screen for the metal one. These are lightweight, glue-up, wall- or ceiling-mounted products with back sides made out of cardboard. They are easier, less costly ($21.12 per foot), and arguably more aesthetically appealing than half- or full-rounds to mount on walls. They also take up less space.

Let's examine how Studio Traps change the acoustic properties of the field in which they are placed. The front half reflects frequencies above 400 Hz and absorbs frequencies below 400 Hz. The back half is absorptive to essentially all frequencies, with the effective lower cut-off frequency determined by the diameter of the cylindrical Traps (the length of the Traps makes no difference)—the larger the diameter, the lower the cut-off frequency. Tube Traps are offered in three different diameters: the 9" standard size absorbs down to 110 Hz, the 11" diameter absorbs to 90 Hz, and the 16" diameter is good to 55 Hz. Studio Traps are 9" diameter.

The front reflective side of the Studio Traps is faced towards the performer/microphone and causes a diffusion of wave source midrange frequencies that is so random, it mitigates reinforcement and/or cancellation of frequencies (comb filtering) due to room reflections. According to Art Noxon, the Studio Traps provide "so much of a random scattering of midrange energy that the room reflections arrive in the middle of this melee of reflections and are unnoticed." He further asserts that the Studio Traps provide a "phase coherent" type of diffusion. The early reflections have random offset time delays, but no resonances. What this means is that instead of masking, they add to the presence of upper partials of the direct sound source. You get a better-defined high end than you would if the Studio Traps were not there.

The physical placement of the Studio Traps helps facilitate their absorptive properties. Their centers are usually placed about a foot to a foot-and-a-half apart in a roughly circular orientation around the microphone. The openings between each of the traps provide slots for the wave source to leak through. Due to the laws of physics, that portion of the mid-bass energy that leaks through these slots will spread most easily laterally as it exits the slots, producing a diffractive type of diffusion of the wave source before it hits any room boundaries.

Art Noxon explains the benefit of this diffusion thus: "You can't have a flutter echo or phase 'add and cancel' if you don't get a decent wave coming back to you." Furthermore, when this diffused wavefront is reflected back off the room boundaries, it is absorbed by the rear half of the traps. What makes Studio Traps so attractive is that they preclude the (costly) need to acoustically treat the room itself, because the traps create a near-field environment that diffuses the wave source before it reaches the room's boundaries.

Interestingly, Trim Traps have similar acoustical properties and frequency response curves as the full-round Studio Traps; they just have less surface area, so the roll-off is at a slightly higher frequency (150 Hz). When it comes to room acoustic treatments, however, as sound absorption is in part a function of surface area, the full-round Studio Traps are more effective for use in problem areas of a room. A good example of this would be in the corners, where the boundary effect causes pressure peaks for all room resonances. On the other hand, wall-mounted Trim Traps are used to bust up flutter echoes and other problems which abberate the directional perception of sound, and therefore compromise imaging.

In the Laboratory
My first tests were to record lead vocals, both with and without Studio Traps, onto my Fostex G16 recorder and directly to DAT. No compression, EQ or other processing was used in any of the vocal (or later instrumental) tests, and the standard 9" diameter Studio Traps were used. Vocals were recorded with a Neumann U87A microphone in omni mode as an acid test of how Studio Traps affected the "room sound" picked up by the mic. Vocals were recorded both in the main room of my studio (which has a twenty-foot high wood ceiling) and in a small vocal iso booth with dubious acoustical properties. In the main room, the singer was positioned about four feet from the 7' x 8' plate glass control room window in order to accentuate reflections. In both rooms, the singer was encircled by five Studio Traps, with the reflective side of the traps facing the performer/microphone.

The vocals recorded in the iso booth were another matter. This booth, though irregularly shaped, has only about 20 square feet of floor space as well as large glass windows on three of its four sides. With the singer about 8 inches from the mic without Studio Traps, the vocal sounded somewhat thin, honky, hollow (comb-filtered) and choked (almost as if it were poorly compressed) to my ears. Singing the same passage, this time surrounded by five Studio Traps, the vocal sounded round, robust, intimate, detailed and dynamic. The only drawback was that the iso booth was much more cramped with five Studio Traps in mere with the vocalist and mic stand.

Simple chords were played over the entire range of the piano from top to bottom, and then a short musical performance was recorded. Listening back to the DAT recordings of the piano with and without the Studio Traps, the pitch was slightly more defined and the timbre more pleasing to my ears in the recordings made with the Traps. The room sound was subjectively eliminated and the stereo image was likewise more coherent in the midrange and upper range of the piano.

For my next tests, a strummed and finger-picked Vega V244 acoustic guitar was recorded in stereo with two ATM 33Rs, directly to DAT and in the big room. Five Studio Traps were assembled in an approximately 300-degree arc around the front of the guitarist/microphone. Recordings made with the Studio Traps sounded, again, slightly more defined and tighter-sounding, drier (but not choked), and simultaneously crisper and warmer.

My final tests were to see how Trim Traps would affect the near-field listening environment in my control room. These third-round Traps are flat on one side, and therefore easy to place on a mix table or up against a wall. I placed five Trim Traps in various positions around the mix table: one on either side of the mixer (on the mix table) and in front of my Yamaha NS-10M and Tannoy PBM-8 near-field monitors to tame monitor-console splash, one against the side of my effects rack (opposite the left monitors) and two on the left wall of the control room. This last placement was made to compensate for my left monitors being situated closer to a wall than my right monitors, causing more apparent bass energy (due to the boundary effect) on the left side.

For my listening tests, I listened to CDs of Don Henley's 'The Boys of Summer' and Peter Gabriel's 'Sledgehammer' both with and without Trim Traps in place (since the Traps were not glued in place they were quickly and easily removed, providing a fairly immediate A/B test). Listening to 'The Boys of Summer' with Trim Traps, the stereo image seemed wider and more distinct; spatial localization of different elements of the mix was more discernible. Listening with Trim Traps to 'Sledgehammer,' the "ghost-in-the-middle" effect was particularly strong on the opening flute line; localization of the instrument was almost palpable! Additionally, the apparent ambience (including, of special note, the front-to-back depth placement) belonging to different elements in the mix was a lot more coherent. Indeed, without Trim Traps in place in the near-field environment, the mix was a bit more splashy. It seemed to be somewhat chaotically splattered both in the left-to-right and the front-to-back planes. Note that this improvement in the listening environment was achieved with approximately $300 worth of Trim Traps—in my book, that's a lot of bang for the buck.

All in all, the differences I noted using Studio Traps in my studio's main room— a room encompassing an area of about 10,000 cubic feet and possessing a short RT60—were subtle. If you're recording with inexpensive mics and close-miking onto a narrow-gauge cassette multitrack format and then mastering to cassette, I would hazard a guess that you might not even be able to hear a difference with the Studio Traps. On the other hand, the small professional studio or more upscale home recording studio (as well as larger, high-end installations) will definitely gain more control over their recordings by using Studio Traps and improve their monitoring by using Trim Traps, in particular, while mixing.