Use Floor Pads To Minimize Feedback At Live ShowsJuly 15, 2011 6:00 am Live Sound
This summer Rusty Strings, the band I run sound for, had one of their strangest gigs ever! It was a reunion-style party, held in a park-like setting featuring a good-sized pond with an island in the middle of it. Here’s the strange part: the band was set up on a covered wooden dock/pier projecting into the pond, and the “audience” was partying on the mid-pond island, several hundred yards from the “stage”. I hope they could hear the band way over there, since we could barely hear them. And they were pretty loud!
Anyway, my topic today is not the weird gig where the band played on a dock (and yes, they did play “Dock Of the Bay”!). My topic today deals with the problems we had with setting up the sound system in this unique location. One problem was that the sheer distance to the audience, plus the fact that we were outdoors, required us to turn the two main speakers WAY up, thus flirting with distortion at those moments when everyone was playing. (See my article Playing Outdoor Gigs: What’s the Difference? for some tips about outdoor shows.)
A much worse problem, though, was our inability to turn the vocal monitor speakers up far enough to be useful (i.e. audible to the singers) without producing howls of feedback from the three vocal mics. We repositioned the speakers, we repositioned the mics, we did all the things you do in this situation, but still the feedback came. Then we discovered what the real problem was!
Remember when I said we were playing on a wooden dock? The flooring of the dock was nothing more than a series of planks, which turned out to be very sensitive to vibration. Especially, it seemed, the vibration of the vocal monitor speakers, which were being transmitted directly to the planking under the monitors, and thence to the mic stands sitting on the planking and finally to the microphones themselves. Aha - there’s our feedback loop!
In retrospect, we could hardly have designed a more efficient method of getting the monitors to feed back into the mics. This explains why no amount of repositioning of speakers or mic stands quelled the squeal: no matter where we put the speakers or mic stands, they were always on that flooring!
Once we realized the problem, we began a scavenger hunt of band members’ vehicles for mats or pads or blankets or anything we could set the speakers and mic stands on to isolate them as much as possible from the floor. Luckily, the band is up from four members to six now, so we had a fair amount of stuff to choose from and we got the job done. What an improvement!
Pads R Us
This same problem, though probably not quite this bad, can happen with any kind of floor other than perhaps concrete or marble. Sound is vibration, after all, and the more sound you make the more everything is going to vibrate. So don’t get caught by surprise like we did! Do yourself a favor and take a set of inexpensive pads with you to your gig. Surprisingly, these can improve the sound of the monitors even in cases where feedback is not an issue, by “decoupling” them from the floor and allowing their natural resonance to operate.
Before closing, I should mention that the “Lo Cut” buttons on your mixer channel strips should always be activated for every mic channel as your first line of defense against all low-end and subsonic floor rumble, including the kind that leads to feedback. There is no energy at those very low frequencies in a vocal signal so there will be no change to the actual sound of the channel, just less energy wasted amplifying subsonic “sounds” caused by footsteps, speakers, or other equipment. And less feedback! So keep the button down.Tags: feedback, microphones, stage practice, vocals -->