Please enjoy the following condensed excerpt from a paper written by Art Noxon for a HiFi show in Hong Kong. Some of these myths persist today. The truth has not changed.

Read the whole paper, then, fix your audio room the right way.

Old Wives’ Tales

The first idea the HiFi person usually has about bass these days is about room modes or room resonances. The basic expectation is: if the room has the correct ratio, it will sound great. Another popular idea is to build a room that has no parallel walls, even the ceiling could be at an angle. This is supposed to eliminate standing waves. Another often heard notion is that of “killing” resonance by adding bass traps or an equalizer. Amazingly, all of these too common ideas about bass and rooms are simply incorrect.

The search for the perfect room dimension is a very old one and it is based on the good idea of evenly distributing the resonances. Originally this concept belonged to the art of building reverberation chambers that are used to test acoustic properties of materials. Reverb chambers have their speaker located in one of the tri-corners (floor/wall/wall) and the microphone in the opposite tri-corner (ceiling/wall/wall). Every room mode can be stimulated by the speaker in the tri-corner, and the mic will hear every mode loudly. This very unique property only belongs to the corners of the rooms.

There are certain room ratios that give evenly distributed resonant frequencies. However, the HiFi listening room is not an acoustic test chamber. Hifi speakers are almost never in a corner (except for Klipsch) and the listeners are surely never sitting in a tri-corner of the room. In a HiFi room the speaker is located away from the corner, and from there it cannot stimulate all the room resonances; which are stimulated depends where the speaker is located in the room. There is zero guarantee that a room with reverb-chamber-quality, well-spaced modes will also have well-spaced modes when the speaker is moved out of the comer.

The non-parallel wall is another magic carpet concept in audio. It is true that non-parallel walls reduce flutter echo, but that is a treble effect. Sound is energy. Put this energy into a room and it stays there until one of two things happen. Sound can be absorbed by bass traps and wall friction or it can be leaked out of the room. Sound energy is stored in the room in either of two forms, organized or disorganized. Disorganized sound dies out faster in rooms than does organized sound. Organized storage of acoustic energy is a room resonance. Because the room resonance is so efficiently stored, it is the sound in the room we mostly hear. It causes “room boom” and we wish it would go away. No matter what shape the room has, the room still has room resonances. If a room has walls it has resonances. The only effect the shape of a room has on resonance is which frequency it is and how the resonance is laid out in the room. Resonance is not eliminated by changing the angle of walls.

Bass traps actually improve bass in rooms. Designer-built, pro sound recording studios have bass traps usually built into walls and they are not visible. In HiFi and the smaller project studios, bass traps are set up in front of the existing walls and corners of the room. And regardless of their location, bass traps can never totally “kill” room resonances.

Properly designed bass traps do not weaken bass in the room because bass traps do not affect the direct wave from the speaker. They actually increase the bass power delivered to the listener by reducing the strength of the room resonances that interfere with the direct wave. Bass traps reduce the sound of the room and let you hear more of the sound from the speaker.

Rooms have resonances because rooms have walls, floor and a ceiling. This is a fact of physics. Bass traps do change the sharpness, or “Q”, of the room resonance – no different than adding resistance to a resonant electrical circuit. No matter what the resonance, there will always be an intense sound pressure in the corners of the room. That is why pressure zone bass traps loaded into the corners of the room are so effective. By converting 1% of your listening room volume into highly efficient corner loaded bass traps, an amazing conversion, a stability in the room acoustic sets in. Bass trap all four vertical corners and the ceiling perimeter comer with a soffit bass trap. This is the best way to control the behavior of bass in the room and causes as little visual impact as possible.