Frequency and Depth

Meet the man building his own sound diffuser panels for better listening

In Thu Duc District in Ho Chi Minh City, accountant Pham Khac Tuong is turning discarded wood into one-of-a-kind, handmade sound diffuser panels worth thousands of dollars. Used by professional musicians or the most discerning music lover, a sound diffuser is an acoustic panel used to treat echoes and reflections. If that sounds similar to sound absorption panels, then it is—because on the base level the sound diffuser and sound absorber function on the same acoustic principle of using certain materials to affect sound waves. Instead of absorbing sound energy, however, a diffuser disperses sound waves on particular frequencies, thus giving extra depth to and increasing the musical quality of sounds.

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“It filters, magnifies and enriches sounds all at once,” explains Tuong. “That may not sound very impressive on paper, but in real practice that is the difference between listening to an old cassette tape in a cramped shoebox apartment and listening to a full-blown orchestra in an auditorium.”

There are a number of different diffusers, with each specialized for specific sound ranges, from bass to soprano. The more popular ones include maximum length sequence diffusers, quadratic residue diffusers, primitive- root diffusers, and hemispherical diffusers.

Sound diffusion is an exact science. High-quality sound diffusers, like expensive bespoke ones, are custom- designed to a specific space and sound range. Tuong says the idea of making his own came out of necessity. “You cannot buy diffusers in Vietnam,” he claims, “because nobody sells them. The closest manufacturer is in Europe. And even if you are willing to shell out USD600 plus 40kg worth of global shipping charges per panel, those generic store-bought panels are not going to fit the acoustics of your room to a tee.”

The first sound diffuser Tuong made was in 2011 and took him two years of research before the actual project took off. “A hemispherical diffuser is not something just about anybody can build. It takes a lot of skill, knowledge and interpersonal resources,” he points out. With the help of audiophiles in his circle and studying from books such as Robert Harley’s The Complete Guide to High- End Audio and John M. Woram’s Sound Recording Handbook, Tuong educated himself on topics such as soundstages, harmonics, and the Helmholtz resonatorprinciple. He measured the resonance of his room with equipment borrowed from a friend who worked at the city conservatory and mapped out an exact configuration using an acoustic auralization software.

After designing was done, the panel itself took a month to complete. For materials, Tuong collected old pinewood crates, broken fences or tables from recycling centers and even waste byproducts from carpenters’ workshops. “Pinewood is considered junk by furniture factories, but it is actually the best building material for diffusers. Anybody who knows a thing or two about musical instruments knows that wood conducts sound beautifully. Commercial diffusers in stores are usually made of styrofoam to save cost, but styrofoam is only number three on the scale of sound conductivity.”

The pinewood Truong collected was laser cut into 841 rectangular blocks of various lengths by commissioned woodworkers, and then painstakingly assembled piece- by-piece by Tuong and his family over the course of a month into the final product: a hemispherical sound diffuser panel made out of solid pinewood. The panel weighs over 40kgs. Affixed to the wall like a piece of art, the effect the diffuser has on the acoustic resonance of Tuong’s listening room is something he says has to be experienced in person.

“The reason I wanted a diffuser in the first place is because I noticed no matter how good the sound system, music from home audio still isn’t on the same level as live performances. I won’t say having a sound diffuser in your room erases that difference, but it’s certainly getting there.”

Since building his first diffuser in 2011, Tuong has made several more, one of which is a monstrosity as big as four other panels combined. He hangs the big one from the ceiling to further improve the acoustics of his listening room. He likes the sound of guitar clear and deep.

As far as Tuong knows, he’s the only one in Vietnam who has ever successfully built a hemispherical diffuser. Friends, acquaintances and those who know about his work have asked if he plans to make a business out of building diffusers. As of now, Tuong’s answer is a solid no. “I’m happy with my accounting job,” he explains. “Perhaps in the future when I’m near retirement. In the meantime, I’ll gladly share my experience with fellow connoisseurs who want to build their own diffusers.”

Images by Ngoc Tran

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