Noise Control Archives - AVL Designs, Inc.

WXXI TV reached out to AVL Designs Inc. to design the interior acoustics and assist with noise control in their product 225 control room. They had recently purchased an AVID S4 Yukon console for the suite and wanted a control room that provided a better mix environment.

WXXI production suite

LIMITED HEIGHT The space is an unusual shape with some features that cannot be changed. The oddly trapezoid room with one glass door to the side of the mix position, and a large window to the live room that could not be relocated, was limited in height. It also had an electrical panel that could not be covered for code reasons.

WXXI Production Suite

NOISE The first order of business was HVAC noise control. The background in the space was NC 40+. Ductwork design was what you see in office spaces, not studios. Working with their mechanical contractor we determined to enlarge ducts, change diffusors, move VAV’s, and control velocities. The result ticks in at NC20.

WXXI Audio Production Studio

LAYOUT The new space was to have a mix position and a client listening position in the rear of the space, where it narrows considerably in a “V”. To even out response, we determined to use high order quadratic diffusors on the back wall. An electrical panel presented a problem. It could not move and had to be accessible. Some of the broadband quadratic diffusors were designed into a custom designed rolling cart. This allows them to go over the electrical panel but be legal as they could be moved. This allowed matching the rear sides of the space with broadband diffusion. GUD high frequency diffusors on side walls and the ceiling over the mix position to enlarge the mix image area back to the client desk. The sound at the client desk is just as linear and only down in level by 3dB from the main mix position. All products were from Real Acoustix LLC. Due to the door location and the “V” in the rear of the room, typical placements for bass traps were negated. We decided to use bass traps within the celling system, a bit unusual but it worked. Overall response is very linear, and only two subtle filters were used to final tune the Rogers LS3 main speakers.

WXXI Audio Production 225 sign

One note: Most of the install was done by in house WXXI audio engineers. Andrew Croucher and his team did a spectacular job on this mix suite.

Andrew Croucher – WXXI
Paul Houndt – Carpenter (Contractor)
Greg Carter – WXXI
David Lot – WXXI
Russell Roby – WXXI
Bryan Agnello – WXXI
Ruth Watson – WXXI

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Sound in cafeterias can be harsh. A primary reason for that is that cafeterias are difficult places to design acoustically but why is that?

Well, first, since surfaces must be easily cleaned, so some acoustical treatments cannot be used where they need to be placed. You can’t wash them. So, with that reality plus the sometimes-loud inhabitants of a cafeteria, there is the potential for a lot of noise. We get calls all the time with noise complaints about cafeterias. In most cases, design attempts were made to correct the problem, but the attempts were not well thought-out.

NRC RATING

Sound is absorbed by specific materials. Lab tests provide an idea of how well materials absorb sound know as NRC* ratings. (*noise reduction coefficient) NRC, however, does not tell the whole story on how well a product will perform in a given environment. The way sound impacts an absorbing surface affects the way it performs. When sound strikes at a severe angle the absorption is reduced, and frequency response affected.

Additionally, where absorption is located is crucial in controlling apparent volume. Voices bouncing off parallel walls causes an effect known as “flutter echo.” This repetitive echo makes rooms sound harsh. You cannot control this by placing materials up at higher elevations in the room. It doesn’t work.

FREQUENCY BALANCE

The human ear is very sensitive to certain frequency ranges. If a room has an improper frequency balance it can sound offensive no matter what reverberation level is actually present.

LOUDNESS

There are two primary issues that make a cafeteria sound loud

Reverberation (Sound hanging around in the room over time.)
Frequency balance (The tone of the room: boomy, tinny etc.)

WHY CEILINGS DON’T FIX IT

As cafeteria ceilings are out of the reach of food, (that is except for the cafeterias with gravy-soaked drinking straw wrappers stuck to the ceilings.) the ceiling is often looked to as the first line of defense.17

The ceiling can be used to control reverberation as well as to help balance the frequency response of the room. Some ceiling tiles, though, absorb the wrong frequency ranges in relation to the other materials that are present in the room. Better tiles have a more even spectral performance. But the ceiling alone really won’t fix the loudness. It is simply a first line of defense.

INVERSE SQUARE LAW

Looking at reverberation only, if you need to reduce the reverberation by an amount that most people would hear that requires a doubling of the amount of absorption. If you already did the ceiling, then where do you come up with that amount of surface area? It’s usually not possible.

When panels are placed on the walls, they can perceptually make the room much better, even though the overall reverb time may not shift dramatically. Carefully integrated acoustic absorption on the walls, in the ear-height range on one or two walls, can do a lot depending on all other factors.

HAVE IT MODELED

Acoustic models can predict many factors including reverb, sound levels, flutter echoes and frequency balance. Controlling the noise in a cafeteria may seem simple, but it is still worth modeling.

Note: all three of the images are new cafeterias; acoustical designs by AVL Designs Inc.