From the editors at CEPro magazine: Setting the Record Straight on Room Acoustics
CEPro Advantage Series • June 2011• Road to Better Audio
“One of the most overlooked aspects of establishing a quality listening environment is the room you will be sitting in. For decades audiophiles have searched
for the Holy Grail of sound. Most of their efforts focus on equipment changes that range from swapping out amps and cables, to turntables and CD players, to loudspeakers. With endless equipment combinations and tweaking ability, most of those audiophiles are in a neverending quest. Tony Grimani, president and lead consultant at PMI, Ltd.,
as well as a principal at MSR Acoustics, has spent over two decades educating electronics dealers about pitfalls of home acoustics. We talked to him about the importance the room itself plays in the listening environment. It’s an aspect to the Holy
Grail search that gets lost amid the turntables and speakers.
Understanding Acoustical Products
Grimani says that when someone examines the solutions available in the residential acoustic product market, they should learn what they are buying before the make their
purchasing decisions. He says that it’s been his experience that many of the bass traps in the market don’t actually improve the performance of in-home, small-room acoustics. “We have found that a lot of bass ‘traps’ are in fact nothing more than absorbers for mid-bass frequencies and they are often ineffective below 100Hz,” he points out. “Most home theaters and listening rooms have standing wave resonance problems in the 40Hz to 80Hz region, therefore most of those bass absorbers aren’t going to cure low-frequency issues.” He says what someone should look for when considering the addition of acoustical products in their homes are products the control room reflections down to 500Hz. This means that absorbers should be at least two inches thick, and preferably four to six inches thick. He adds that manufacturers should back up their claims with test results from reputable independent labs, and that only a quarter of a room’s walls should be covered with absorbers or else the room will be overly dampened.
A Closer Look at Solutions
One thing that would help consumers and pros better understand the category, Grimani theorizes, is a redefining of the products used in the field. “For bass traps, I’m going to go out on a limb and say the term means nothing at all, while it means everything too,” he explains. “Most absorbers work through a process of friction of air molecules against fibrous materials. Frictional absorbers are basically a chunk of material that absorbs sound and in some cases the sound being absorbed is bass, but it is not being ‘trapped,’ it is being absorbed into the fibrous material.” A product that does “trap” low frequencies, he notes, is commonly known as a Helmholtz resonator. “
A device that really does ‘trap’ bass sound is actually a resonator device that uses a tympanic membrane or a ported resonator enclosure [often known as a Helmholtz],” says Grimani. “This trap uses resonating technologies to convert bass into heat.” When it comes to diffusers, Grimani says he usually breaks them down into two types of designs: 2D and 3D. “A 2D diffuser is one that turns an oncoming sound vector into a two-dimensional hemidisc plan, and is best used toward the front half of a room’s side walls,” explains Grimani. “A 3D diffuser turns an oncoming sound vector into a three-dimensional hemisphere, which is good to use on the back half of the side walls and the back half of the ceiling.” One final point about absorption panels, Grimani mentions, is the misuse of the term dampening. He says that dampening is defined as the act of putting water on something, whereas damping is the act of reducing a resonance. Grimani’s point in noting the verbiage is that putting acoustical panels on a wall damps a room’s reflections, echoes and reverberation, they don’t dampen the room.
Tackling the Equalization Myth
Another development that’s happened within the consumer audio market has been the advancement of room equalization (EQ) technologies. These products are designed to overcome the typical sound quality problems associated with reproducing audio within media rooms, and over the past few years they have become increasingly popular with A/V receiver manufacturers. Grimani says that while these EQ technologies have become quite sophisticated, they are not a fix-all solution for homeowners. “To get great sound you need a room with the right proportions and the right amount of absorption, diffusion, bass absorption; you need to sit at the right location in the room, the speakers have to be placed correctly in the room, and you need equalization as the final touch to tie it all together,” he emphasizes. “Simply put, you must have an equalizer [because] all rooms are going to affect the voicing of a
loudspeaker, and its response needs to be equalized for the room … as for auto EQ, I guess that technology is fine for low- to middle-end systems. Anything above that should be measured and adjusted manually, and it should be listened to carefully for proper results.” Explaining why EQ isn’t a complete problem solver, Grimani adds that homeowners cannot strictly rely on the measurements of an analyzer because electronics don’t hear like human ears, and software doesn’t fix other elements that need to be addressed in the home. “Equalization cannot get ride of sound echoes, so on the front all bets are off,” he warns. “However, equalization can mitigate some of the audibility of bass standing waves and is therefore worth doing even if the homeowner cannot afford acoustical engineering or treatments. It’s one of the tools, and you may as well use it if you have no other choice.”
Overall, Grimani stresses the importance of treating a listening room’s acoustics, because bad sound deprives someone of experiencing the full impact of their system purchase. “I would say you’re only getting half of your sound quality if you don’t design and tune the room correctly … you could be wasting 50 percent of your investment.”