On a recent weekend I attended an event that was held in a very challenging space for sound reinforcement, and thought I’d detail it because it’s a good way to discuss some basic audio principles.
This particular event was held in a very, very nice pole barn. Really beautiful. It’s a large steel building, the walls covered by solid wood paneling, the floor a stained and sealed concrete, the ceiling made up of flat steel decking with no acoustical treatment. Dimensions were about 60 feet by 100 feet, forming a rectangle with parallel walls.
We were there for a formal ball, with dancing directed by a “caller” and CD tracks for music, both sources fed into the sound system. When I arrived, the person setting up sound was trying to get an omnidirectional lavalier microphone working. Not a good start. Even before hearing anything in the room, it was obvious there were going to be problems, and using an omni mic—particularly one that would be placed on the chest rather than at the mouth—is not a good way to capture strong, consistent vocal signal.
The system also included a simple 8-channel mixer, CD player, amplifier and a single 15-inch, 2 way loudspeaker (circa 1970s). In a lot of ways things were getting even tougher…
First, as predicted, the omnidirectional lav placed at mid-chest made gain before feedback tough. This became immediately obvious during the brief sound check. Second, the loudspeaker, with its “smile-shaped” horn, had very little effective pattern control.
Third, the mixer had minimal EQ, just some high/mid and low knobs usually associated with very inexpensive units. Fourth, the loudspeaker stood over three feet tall and probably weighed north of 100 pounds, so even if the sound person had a tripod stand, the loudspeaker would be too heavy for it. So instead, it was left sitting on the floor, and with associated equipment sitting on top of it.
Thankfully, he also had a wireless handheld on site, and switched to that instead. Once he got that working, he began testing the CD player. Right away I thought, “You’re playing everything way too loud. In this situation, less is definitely more.”
After some (very loud) feedback, caused when the caller for the dance went to turn off the CD player (one of those pieces of gear on top of the loudspeaker) while holding handheld mic by his side (and pointed right into the high-frequency horn), the event began.
Right away, it was obvious that the space was being excited with way too much energy, and unless you happened to be in the direct coverage pattern of the high-frequency horn, all you could hear was the mash being created by the reflected sound that was bouncing around in the room.
Besides the fact that this venue, while nice, wasn’t conducive to this type of event, the primary problem was direct versus reflected energy. Simply, this means to direct as much energy into the coverage area as feasible while minimizing energy that can reflect off of surfaces.
What would I have done?
1) Outfit the caller with a headset mic. It would sit consistently at the same distance from his mouth, thus providing a much more consistent vocal signal. Further, the caller would have been spared to problem of trying to explain/demonstrate a dance while holding a mic.
2) Add more loudspeakers, and these would be distributed around the edge of the dance floor. More sources of sound, more evenly distributed, helps achieve better direct energy while limiting reflected energy.
3) At a minimum, place the loudspeakers at ear height, or if possible, place them higher and then angle them downward. Again, this focuses the energy on to the coverage space and off the walls.
4) Turn it down! Always remember that in a situation like this, “less is more.”
Thankfully there was just the one mic and the CD player. If there had been a live band—wow it would have been really, really ugly!
As a side note, after the event was over, about a dozen or so attendees got together on one end of the building and sang a song a capella in four-part harmony. It sounded absolutely beautiful. The direct-to-reflect energy was just about right, and the natural reverberation of the room added an incredible effect to the voices of the singers.
Gary Zandstra is a professional AV systems integrator with Parkway Electric and has been involved with sound at his church for more than 30 years.