Recording

Practical Acoustics

Many small- to medium-sized concert venues in urban settings started out as something else. For business purposes, almost any room can be converted into 6/01/2001 8:00 AM Eastern

Many small- to medium-sized concert venues in urban settings started out as something else. For business purposes, almost any room can be converted into a live music/performance club. Some will sound good, some will sound bad, but just about any of these converted places can be treated successfully to sound better.

Some owners and sound engineers seem to think that they can just drop an amazing sound system into any old room and it will sound good. Well, sometimes this is true, but it's not the entire answer. It can be relatively inexpensive to treat a small venue with adjustable acoustics, and it would be downright silly not to explore this option. In this article, I will explain an effective acoustic treatment plan based on one I developed for a small venue in Toronto that has proven to be very successful over the past couple of years since it was installed. The treatment plan didn't cost a lot to implement, and it looks great, but it did require the investment of some time and energy. The tools I used include ray-tracing diagrams, SPL meter (both “C” and “A” weightings), laser pointer, tape measure, my ears and the ears of many others.

The Royal Canadian Legion Branch #360 is a very nice-looking hall that serves as a clubhouse for vital legion meetings and extravagant dinner parties; at night, it becomes the 360 Club. The hall is located in the fashion district of Toronto (Queen Street West), a tourist trap of gigantic proportions riddled with production offices, wholesalers, retail clothing outlets, record stores and night clubs. Oh, and Steve's Music Store is right across the street, a landmark for professional musicians and sound engineers. So, why is there a Legion hall among the savvy rabble? There's a whole history there, but it has nothing to do with sound.

TREATING THE ROOM

The untreated room had a few acoustic shortcomings, including an inferior dimensional ratio, lots of flutter echoes/delays and plenty of hard surfaces. The distance from the stage to the bar is about 100 feet, and the room is 25 feet across and 12.5 feet in height, a dimensional ratio that pretty much guarantees mode pileups.

The floor of the room is wood, the east wall is heavy drywall and the west wall is solid glass from the ceiling down to shoulder height (7.5-foot-long by 4-foot-wide mirror panels cover almost the entire length of the wall). The ceiling consists of perforated ceiling panels, which might have provided some helpful mid- to high-frequency absorption had somebody not covered the holes with a coat of latex paint. Among the room's positive features are four evenly spaced columns on each side, essentially concrete studs that stick out about seven inches from the wall. These serve as natural diffusers.

The front portion of the stage floor is made from plywood risers, while the side walls to the rear of the stage are wood and the stage ceiling is thick plywood. A solid wooden riser — originally the entire stage area — is used as a drum riser (see Fig. 3). The front section of the stage is open.

Because the room still hosts traditional Royal Canadian Legion functions, any acoustic treatment must be easily removable by a single person in a matter of minutes. Also, capacity crowds assembled for a well-known guest speaker would absorb quite a bit of sound, making it difficult for quiet speakers, so there are acoustic reasons for having removed panels.

For the room treatment, I began by building hanging absorber panels made of 1×2-inch spruce frames filled with Roxul fiberboard and covered with raw muslin, which is softer and thinner than canvas (see Figs. 1 and 2). The absorbers are hung six inches out from the walls by means of “G” mountings in order to keep an air space between wall and absorber for in-creased absorption. (Published absorption coefficients show that the fiberboard absorbs 100% at 1 kHz, 2 kHz and 4 kHz, the frequency range I mostly wanted to control.)

Using a laser pointer/mirror setup, I made measurements to trace sound waves in the “ray” category in order to estimate approximately how much sound energy would be absorbed on the underside of the absorber from off-axis reflections. Measurements also ensured that any reflections from the uncovered wall spaces between panels would be absorbed by panels on the opposite wall. The treatment proved very effective at absorbing most early lateral reflections and excess sound energy coming from the stage, resulting in a cleaner FOH mix. Aside from the standing wave anomalies, the room can sound great when treated. Extra panels were later built for the walls near the open front section of the stage.

TREATING THE STAGE

I treated the 360 Club stage as I would a rehearsal room for really loud bands. I have found that the trick to mixing really loud bands in smaller venues is to absorb as much stage sound energy as possible. This not only minimizes microphone feedback problems, early reflections and cymbal bleed, but it also tends to make the musicians more comfortable while performing. I have developed a simple, cost-effective acoustic treatment plan for the 360 Club stage, and have used it successfully for many shows. The components are surprisingly cheap, easy to install, and include foam bricks, a soft fabric (muslin), theater drapes, moving blankets and homemade “ceiling pillows.”

Foam bricks are made of open-celled foam, which is excellent for absorbing high and upper-middle frequencies, such as cymbals. Spacing the bricks a few inches apart achieves almost as much total absorption as treating the entire surface, because the exposed sides of the 4-inch-thick bricks absorb a considerable amount of sound energy. The bricks are also hollowed out to half-depth in the middle, which helps absorb even more sound energy. Any remaining unabsorbed sound energy is diffused and returned to the stage in random reflections. After treatment, the vocal mics pick up much less cymbal and snare drum bleed, and the FOH mix is much easier to control.

I loosely covered the foam bricks with black muslin arranged in a convex drooping pattern. In theory, any high frequencies that make it through the muslin on the way up and bounce off the foam bricks, or spaces between them, will be further attenuated on the way back down, once again by the muslin. But the muslin is mainly there for looks. Also, the back wall of the stage is covered with a loose-fitting, heavy, theater-style drape, which I re-hung to create some space between the drapes and the wall.

If you've ever been in an elevator on moving day, then you know just how much quieter it is with heavy moving blankets on the walls; they are an excellent choice for absorbing unnecessarily excessive sound energy on the sides of the stage. Another useful feature of moving blankets is that the material is fire retardant.

Placing a medium-pile carpet under a drum kit will help absorb cymbal and snare drum energy, plus it will help stabilize the drum kit and the bass drum spikes will hold better. Without this damping, excess sound energy from cymbals will be reflected into the off-axis side of the drum microphones, which tend to give the FOH mix a strident quality.

Because of the many different types of performances at the Legion hall — dancers, fire breathers, hard-core bands, etc. — the low-pile carpeting on the front section of the stage is not permanently fixed to the floor and can easily be removed. I like to keep it there when the extra absorption is needed, such as when bands insist on pointing really loud guitar amps toward the audience.

My last sound-absorption device is a pair of “ceiling pillows,” which are fixed to the ceiling on either side of the foam brick area. The ceiling pillows are homemade from thick insulation and muslin with a cardboard backing and are placed under the drooping muslin near the corners of the stage ceiling. A small air space above the pillows aids in further absorbing ceiling reflections.

BETTER SOUND LOCALIZATION

The result of treating the stage as I've described it is a rather dead-sounding, echo-less stage area. Musicians report that they can better localize sound sources onstage, and, when the stage treatment is used in conjunction with the aforementioned room treatment, a competent mixer can achieve a great overall sound quality in this otherwise difficult venue. Not bad for a total materials cost of about $400, considering that the present sound system costs at least 30 times more.

And the overall sound quality is further improved when the band sets up with an ideal stage plot — all onstage speakers pointing in toward the musicians. Add in a great sound system, and the venue has proved itself an excellent choice for CD release parties, the NXNE festival and Canadian Music Week (CMW), events where the majority of the performing musicians felt comfortable, because they could hear themselves and all other instruments onstage. Equally important, the overall audience response has been very positive, and, all technical data and measurements aside, the fact that people enjoy performing at the venue and the audience enjoys what they hear has justified the modest treatment plan.

I would like to thank my silent mentors — sound engineers Ian Carkner, Wayne Green and David Walsh — who have helped me out during the entire process by offering suggestions and/or sharing their wealth of knowledge in live sound applications. Special thanks to Bill Ovenstone for assisting me in building the panels. Thanks guys!


Buck Moore is a freelance sound engineer living in Toronto. Moore has been the house sound person at the 360 Club for the past few years, where he takes copious notes and conducts extensive experiments in constant pursuit of the ultimate live mix. He can be reached at www.moodswing.com.