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Does it feel like you are on an Island?

Published On: July 24, 2020Tags:

Just Because You are in a Small Room…

Doesn’t mean your recordings need to sound lifeless and dry. By utilizing the psychoacoustics of early reflections, your voice can sound full, clear, articulate, and present.

What does a combination of coherent specular diffusion, acoustic shadow casting, RC-constant bass absorption, and temporal sound fusion give you? One of the best vocal and instrumental recording environments in the world.

This week we learn about the earliest days of the QuickSoundField from another of Art Noxon’s breakthrough AES papers, first presented in New York City, 1987.

The Tool

The Acoustic Island uses TubeTraps. Here is a quick reminder of their construction and function: An interior air volume (C) is surrounded by a dense fiberglass wall (R). This is a lumped parameter design whose acoustic RC time constant helps to access the low frequencies. Half the surface is covered by a “limp mass” acoustic choke (L) that reflects mid and high frequency sound but passes lows to be absorbed.

The Setup

The setup for the Acoustic Island gobo is in the form of a horseshoe pattern. Typically, 7-8 StudioTraps are placed on a 2 foot radius centered about the mic. The reflectors of the traps are directed inward.

This gobo system performs two acoustic functions at the same time. The absorptive side of each trap faces the room, intercepting the sound of the room. This acoustic shadow zone feature develops 5dB isolation from room ambience. The second feature is supplied by the reflectors. The direct signal is immediately followed by a dense fill of diffuse signals, strong in the first 10ms, which provides a boost of 4.7dB in the nearfield ambience.

Energy Time Curve: no Island

A simulated voice was played back in a sound testing room with no Acoustic Island used. The ETC shows very few signals in the first 10ms compared to the second 10ms period. The direct-to-reverb energy ratio is 8.1 dB with an early decay rate of 0.2sec. Note the first 20ms has sparsely distributed returns. TEF waterfall chart shows the room holding energy up through 5k, but notice the rapid shift from the full spectrum direct signal to the mid/low heavy set of room reflections. This lacks tonal balance throughout the decay.

Energy Time Curve: Island with Reflectors OUT

The same voice was played in the same room, this time using the island setup with the reflectors positioned to the outside. The room reverberant field is weakened, direct-to-reverb ratio is 13.1dB, as the direct sound is absorbed by the traps. The TEF waterfall and ETC show some increased density of early reflections, due to the impedance continuity of the absorbers. This is a little more “dead” than we like.

Energy Time Curve: Properly Built Island

Here was have the correct setup, with reflectors toward the mic. Note the ETC, with its tremendous early reflection backfill. Direct-to-reverb ratio is 8.85dB, with an early decay rate of 0.05 sec. Reflections from the gobo immediately follow the direct signal for 10ms. The ETC has the classic QuickSoundField signature: an immediate and strong backfill of diffuse energy lies just behind the direct signal. This feature establishes the “quick” quality of sound, giving it a lifelike, snappy presence.

The Quick Sound Field Room: Built-in

Success with the Acoustic Island gobo in larger studio spaces led to an extension of the principles into the smaller, dedicated sound rooms such as vocal booths, drum rooms, broadcast voice-over rooms, and home “bedroom” studios.

The acoustic devices used are Half and QuarterRound TubeTraps, each of which have reflectors covering the central 1/3 to 1/2 of the surface of the trap. They are easily mounted in any position: horizontal, vertical, or upside down.

The 1/2 and 1/4 round TubeTraps are typically spaced on 18″ centers on the walls and ceiling of a small gypsum board sound room. They’ll usually run vertically from the ceiling to the floor, leaving a distribution of 6-7 inch wide strips of reflecting surfaces throughout the room. These strips scatter the low frequency sounds through diffraction while the integral reflectors scatter the mids and highs. The effect on recordings is quite similar to the free-standing QSF including a dense backfill of early reflections with a neutral tone and lifelike presence.

Just Because You are at Home…

…doesn’t mean your recordings need to be compromised. You have the mics, preamps, outboard gear, software, and the talent… now add the last piece of the signal chain: professional-grade acoustic treatment. You and your followers will be happy you did.

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