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Is There Really Anything You Can Do About Acoustics?

November, 08 2012 |
By Shure Notes Editors

Contributors: Frank Gilbert, FOH Engineer at Chicago's Mayne Stage, The Vic and Park West; Kent Morris, Peavey Electronics, Cornerstone Media; Stuart Rosenberg, Partner - SPACE and League of Creative Musicians

Live performance venues deal with it all the time. In this post, we'll break down the subject of acoustics for you into its most basic components, talk with a trio of our experts about how they handle venue challenges and offer some helpful hints that won't require you to hire an acoustician.

A little history

The study of acoustics goes all the way back to the 6th century, but the study of modern architectural acoustics is as recent as the 1900 when Wallace Clement Sabine designed Boston's Symphony Hall according to scientific acoustic principles (based largely on reverberation time). Before then, the creation of great sounding concert halls was more a matter of luck than good design. Now concert hall acoustics is a recognized area of acoustics that straddles architecture, engineering and physics.  And Sabine must have done a pretty good job, since Symphony Hall is cited as the #2 concert hall in the world for acoustical quality. (Vienna's Grosser Musikverinsaal is #1 and Carnegie Hall is #8.  London's Albert Hall, which most of us know from "A Day in the Life" is ranked a distant #58.)

Acoustics By Definition

Acoustics is total effect of sound, especially as produced in an enclosed space. It's the scientific study of the generation, transmission and reception of sound.  But here's a simpler definition: It's the total effect of sound in a room.

Audio expert Pat Brown explains how it relates to live sound reinforcement: "The sound heard in an auditorium by a listener is a complex combination of the sound produced by the gear and the way that it interacts with the room. It's a fact that most of the sound heard by any listener gets there only after many, many interactions with the room's surfaces. Each reflection modifies the sound a bit, and after several interactions, it looks nothing like what left the loudspeaker in the first place. The room places its own signature on all sounds radiated into it, which can either enhance or corrupt the sound. Good gear doesn't sound good when used in a bad room".

The fact is, there are no "good" or "bad" acoustics, only "appropriate" or "inappropriate" acoustics for the intended application.  Appropriate acoustics are those transmission and reception qualities in a room that enhance the musical performance and/or improve the ability of the listener to understand speech.  Music benefits from longer reverb time and constructive delay, so a room with those characteristics is considered "wet".   On the other hand, speech reinforcement benefits from a "dry" room without the reflections that cause reverb.

So many advances have been made in the area of sound, that the bar for acoustical standards has been raised, along with the expectations of the audience.  No matter how great the performance is, it's going to be a bad experience for the audience that can't understand it."

Structural Concepts and Solutions: Isolation, Absorption and Diffusion

Isolation prevents sound from escaping its intended destination. By using dense door materials, tight seals, and double pane windows, transmission can be kept in check. Additionally, minimizing wall and ceiling penetrations will improve isolation.

Absorption uses a combination of dead air and mass to prevent the reflection of acoustic energy back into the occupied space. From mineral fiber to acoustic foam, different types of absorbers stop detrimental reflections that mask intelligibility.

Diffusion creates multiple small reflections from one or two large ones. The result is more pleasing to the ear, with an increased sense of "space" and "depth" as compared to a harsh two-dimensional slapback reflection. In a large space - where the slap and flutter from large parallel surfaces creates unpleasant sound -  diffusion, in the form of acoustical clouds and canopies, can rearrange the reflected energy into a usable soundscape.

[caption id="attachment_8226" align="aligncenter" width="553"]Acoustical Clouds from Armstrong SOUNDSCAPES Example of acoustical clouds – Armstrong SOUNDSCAPES[/caption]

With a careful study of the desired room signature, changes can be made to improve the overall sound in any room, whether the need is for isolation, absorption or diffusion.

We asked Kent Morris, President at Cornerstone Media and Worship Market Manager at Peavey Electronics, for some tips and tricks that you can use to improve room acoustics:

1. Divide and conquer. There is no rule that says the drums have to be placed at center stage. Move the drums to one side and place the singers and musicians on the other side. The physical separation will improve the clarity of each section and might increase gain before feedback in the vocal mics.

2. Baffle the sound. Build inexpensive sound baffles out of 2x4 wood frames and fill them with mineral fiber. Cover the sides with acoustic cloth and place the baffles (also called gobos) between the instrument amps and vocal mics to prevent sonic bleedthrough.

3. Aim high. Point the instrument amps at the people using them to decrease stage volume and prevent high levels from reaching the front rows.

4. Isolate the drummer. Use a panel behind the drummer to reduce rear reflections while improving the direct energy reaching the drum mics

5. Ditch the dish. In fan-shaped rooms, avoid aiming speakers directly at the rear wall. With a curved back wall, energy is reflected onto the stage, causing detrimental delays.

It can also happen that the solution is surprisingly simple and maybe even accidental.   A favorite venue of this Shure Notes editor is Space – a completely rehabbed and intimate music venue that has boasted the likes of Leon Russell, Taj Mahal, Dr. John and many others.  When we asked Stuart Rosenberg, the impresario behind the club, for an example of an acoustical problem and solution, here's what he told us:

"When we built out our control room, we discovered that our design yielded significant resonance in the area of 30-100 Hz - a classic problem encountered in rectangular spaces, and potentially a vexing one that can prevent accurate low-end monitoring.  Much to our amazement and delight, we discovered that whenever we opened the door to the studio storage closet, the bass loading immediately disappeared - the volume of that space acted as an extremely efficient bass trap - and the frequency response of the room became linear. Problem solved!"

What a Sound Engineer Can Do

Let's assume there's nothing more you can do with the physical space.  Now what?  For another perspective, we turned to Frank Gilbert who is FOH and Monitor engineer at three popular music venues (once movie theaters and vaudeville houses) Park West, Mayne Stage and The Vic. We asked him to choose one and he talked about some of the challenges at The Mayne Stage.

[caption id="attachment_8236" align="aligncenter" width="498"]Mayne Stage Mayne Stage, formerly The Morse Theater circa 1912[/caption]

"It's a very deep room and I've noticed that unlike other places, when the room fills up with people, it doesn't deaden up some of the bouncy low-mids.  We do drape the stage on all three sides with heavy-duty curtains and that helps a bit. At Mayne Stage, the FOH PA is a mono cluster with a pair of flown subs.  We do a lot of jazz trios., and with the upright bass, the flown subs start to rattle because they're not coupling with any other speakers.

It's a great sounding room with a great sounding system but with some of that deep stuff below 80 Hz, it shakes the HVAC in the room, so I just end up putting a high-pass filter on the upright bass and sometimes I even mute the subs and let the amplifier in the backline fill the room.   It's such a live room that sometimes that's enough, especially with those quieter shows.

With a rock show, you've already got a couple of guitar amps and a drum kit banging away, then your acoustic focus becomes getting the vocals to be heard. My favorite move in one of those situations is to use a Beta 58 instead of an SM58 – that always helps.   Sometimes in that room, a Beta is the right vocal mic.

We haven't done anything in terms of acoustical treatments.  It would be really nice if we put curtains on the walls behind all the audience areas to deaden it up a little, but it's actually a great-sounding room.  It's well suited to piano jazz and cabaret but lately we're doing more and more rock shows.   That room is about controlling bass and trying to control low-mids – bass management is really the name of the game there and when we have a full-on rock band, getting the vocals to sit well above the band is al little bit of a trick because there are no front fills at the lip of the stage – just the big cluster of speakers flown at the top of the room.  If it's going to be a really loud band, sometimes I'll take a couple of little speakers and put them at the lip of the stage, close to the audience."

Frank Gilbert played in a band at age 15 and almost 25 years later, handles FOH sound at Chicago's The Vic, Park West and The Mayne Stage.  He has a home studio and also does location recording for Metro Mobile Recording.

Kent Morris is the President of Cornerstone Media, worship market manager for Peavey Electronics, a speaker and a writer on pro audio topics.  He is a frequent contributor to Shure Notes.

Stuart Rosenberg is a musician, composer and producer. He is also the force behind SPACE, the Society for the Preservation of Art & Culture that brings live music and legendary musicians almost every night of the week to an intimate performance venue in Shure's former hometown of Evanston, Illinois.
Davida Rochman
A Shure associate since 1979, Davida Rochman graduated with a degree in Speech Communications and never imagined that her first post-college job would result in a lifelong career that had her marketing microphones rather than speaking into them. Today, Davida is a Corporate Public Relations Manager, responsible for public relations activities, sponsorships, and donation programs that intersect with Shure at the corporate and industry level.

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