Friday, August 23rd, 2019

John Calder : Affordable Phase-Coherent Control Rooms and Studios

By editorJune 1, 2012


John Calder

John Calder has worked as a musician, recording engineer / producer, concert sound mixer, sound designer, marketer, product developer, and instructor.  He has Platinum and Gold Records, and Gold Reel, Monitor, Muse, and AZA Awards.  John is currently the Director of Retail Sales for Acoustic Geometry at Acoustical Surfaces Inc. in Chaska, MN.

“The art and science of acoustic design for control rooms and recording studios has evolved steadily, from 1930’s Bell Labs research, to the ‘70’s nearly-anechoic spaces, to the ‘80’s LA-style compression ceilings, to the 90’s quadratic-residue rooms.  But the continuing trend toward recording in homes and small project studios has left many professionals wondering if studio acoustic design is now ‘devolving’. At Acoustic Geometry, we feel strongly that the challenge of consistent, accurate, and phase-coherent acoustics in smaller rooms is definitely moving forward.

Mastering Room, Treelady Studios, Pittsburg PA

“We recently released a line of products that build on the early research of Bell Labs – specifically, the polycylindrical diffusor – by improving and expanding the capabilities of diffusers and absorbers in studios from bedrooms to high-end commercial spaces. Our Curve Diffusers are a constant-radius cylindrical design which retains the phase-coherence of smoothly-curved surfaces while bringing predictability and plug-and-play simplicity to small-room acoustics.

“Over the past half-century, the importance of coherent phase response in transducers and electronics has been proven repeatedly, but coherent phase response in a commercially-available diffuser product was not available – all phase-grating / quadratic-residue products are phase non-coherent by design. However, our Curve Diffusers feature a phase-coherent cylindrical design – because coherent phase response is just as important in acoustics.

“And we’ve gone a few steps further – our Curve Diffusers have a Mass-Loaded Vinyl (MLV) low-frequency absorption membrane built into each standard size unit (Small, Medium, and Large), and this bass trapping helps tame room modes. The interior absorption material is recycled bonded acoustical cotton, and the fabric wrap is fire-rated and available in dozens of color options.

“Curve Absorbers have the same form factor as the Diffusers, with a different depth profile. When combining Diffusers and Absorbers, the availability of different profiles is important in avoiding comb filtering, and the look and feel of the room treatment remains consistently professional.”

Gotham Hall, Manhattan’s premier event center

“One of our toughest acoustical projects was, curiously, an extremely large space, and our remedy was a very large version of the Diffuser designed to improve small studios. Gotham Hall, Manhattan’s premier event center, is a limestone-faced oval, 110 feet long and 7 stories high, and listed in the National Historic Registry. Needless to say, this beautiful and awe-inspiring room had a serious problem with sound – the echo turned amplified sound into mush. We built twenty-two custom 12-foot tall, 41-inch wide, 11-inch deep Curve Diffusers filled with our proprietary acoustic cotton absorber, and wall-mounted them around the room’s perimeter (even at 12 feet tall, they’re dwarfed by the imposing size of the space). The results astonished Gotham Hall’s manager, and he paid our acoustical treatment the ultimate professional compliment – complaints about sound in the Great Room went from constant to zero.

“By changing a room’s ‘sonic geometry’, our products smooth the high peaks and deep valleys normally caused by sound waves destructively recombining when reflected from flat surfaces (walls and ceilings). A balance of absorption and diffusion is the best way to treat rooms for music and voice – the rooms aren’t ‘dead-sounding’, and the benefits of diffusion have been known since the ground-breaking work at Bell Labs over 80 years ago. The combination of coherent phase, MLV membrane bass control, and ease of use has made Acoustic Geometry products a simple choice for an increasing number of sound professionals, regardless of the size of their rooms.”

John Calder
Acoustic Geometry
June 2012

Our thanks to John for sharing his approach to acoustics design.

Contact Acoustic Geometry at or 888-227-6645


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