Kinetics Noise Control – High Tones:A True Quadratic Residue Diffuser

High Tones from Kinetics Noise Control is a true Quadratic Residue Diffuser (QRD). The QRD was invented by Dr. Manfred Schroedor in the 1970’s1. He found that a seriesof wells based on a quadratic residue numerical sequence diffused sound in a pre-dictable manner. A few books have described the methodology for designing QRDs2,3.

High Tones was based on the quadratic residue sequence of {0,1,4,2,2,4,1} created withthe prime number of 7. To create this quadratic residue sequence, High Tones wasdesigned with well depths of 0”, 3/16”, 3/4”, 3/8”, 3/8”, 3/4”, and 3/16” that are separatedby 3/16” wide fins. The 0” deep well was split between each side of the High Tones tocreate a symmetrical pattern. The 0” deep well was separated from the 3/16” deep wellby 3/16” to maintain a constant fin width between wells. These dimensions can beverified on our production version of our High Tones and from the High Tones submittaldrawing, shown below. The drawing is also available on-line at KineticsNoise.com.

To confirm the design, Kinetics Noise Control used independent third-party labs tomeasure the scattering of our High Tones by the International Standard Organization(ISO) international standard method4, and the diffusion by an Audio Engineering Society(AES) informational document method5. These reports are attached. These two meth-ods measure the non-specular reflections from an acoustical device in very differentways.

The AES informational document method uses an acoustical goniometer to measure thereflection of sound from a small test sample at discrete angles of incidence andreflection. This method will determine the acoustical diffusion coefficients of a sample.Diffusion is defined as how evenly sound is reflected over all angles from a surface. The

Kinetics Noise Control – High Tones: 2 of 2A True Quadratic Residue Diffuser

Kinetics Noise Control, Inc. 6300 Irelan Place Dublin, OH 43017-0655Telephone 614-889-0480 FAX 614-889-0540 Email Sales@KineticsNoise.com www.KineticsNoise.com

more uniform the reflected sound, the higher the diffusion coefficients. The mainadvantage of this method is that it shows how evenly sound is being reflected off asurface. The disadvantages of this method are that it typically only measures a smallsample size, does not account for the acoustical absorption of the sample, and theresults are not used in commonly available acoustic room modeling packages.

The ISO international standard method uses a rotating turntable and a large samplearea to measure the average sound energy absorbed and reflected in a specularmanner. This method will determine the scattering coefficients of the sample.Scattering is defined as how much (or little) sound is reflected in a specular matter. Theless sound reflected in a specular manner the higher the scattering coefficient. Theadvantages of this method are that it uses a large sample to more accurately representinstalled field conditions, takes into account acoustical absorption of the sample, andthe results are used in all commonly available acoustics room modeling packages. Theonly disadvantage is that is does not determine how evenly sound energy is beingreflected off a surface.

As the reader can clearly see from the attached reports, Kinetics Noise Control HighTones produces significant scattering in the 4000Hz 1/3rd octave band, and significantdiffusion above the 2500 Hz 1/3rd octave band. Thus proving it’s effectiveness as a QRDdiffuser.

Finally, it should be noted that Kinetics used third party labs to measure the response ofHigh Tones with both the ISO international standard method and the AES informationaldocument method, the manufacturer who wrote the now outdated comparison1 only teststo the AES method which they perform in-house.

References:1 Schroeder, M., “Number Theory in Science and Communication: With Applications inCryptography, Physics, Digital Information, Computing, and Self-Similarity” 3rd ed.,Springer (1997)

2 Cox, T. & D’Antonio, P, “Acoustic Absorbers and Diffusers: Theory, Design and Appli-

cation” Spon Press, New York (2004)

3 Egan, M. D., “Architectural Acoustics” McGraw-Hill, Inc, New York (1988)

4 ISO 17497-1, “Acoustics -- Sound-scattering properties of surfaces -- Part 1: Mea-

surement of the random-incidence scattering coefficient in a reverberation room”

5 AES-4id-200 “AES information document for room acoustics and sound reinforcementsystems -- Characterization and measurement of surface scattering uniformity”