If you are a music or audio professional, the chances are good that you will have a room dedicated to music and its performance or reproduction. For the vast majority of music lovers there is a nearly constant battle between the comfort and décor of a multi-use room and the demands of making the sound the “best possible.”
The interaction of your speaker and your room usually has a bigger impact on the quality of sound than all your choices in electronics. There are ways you can change that interaction to get better sound. Trying different locations for the speakers and listeners can often make a dramatic change at no cost. If you have placement limitations (and most of us do), considering room treatments is the next step.
The lower frequency problems take much larger room treatments than higher frequency problems. While moving a subwoofer four feet can make a big change in standing waves in the room, it would take a substantial bass trap to stop the buildup of the same standing waves. In the treble, much smaller diffusors can do the job for most seating locations.
In general, acoustic “room treatments” fall into several basic categories: Absorbers, Diffusers, and Reflectors.
An absorber is what it does: it absorbs incoming sound energy. The frequencies that are absorbed vary with the material, the size, the shape and the location in the room. Stuffed furniture such as sofas and big chairs are pretty good absorbers over a wide frequency range. Cloth covered furniture absorbs into higher frequencies than leather (or other hard-surfaced material) covered furniture. Carpeting and area rugs can absorb midrange and treble. The thicker the stack, the better the absorption. Real felt rug pads can have a major effect. (Hint: To improve dialog intelligibility in your home theater room, put a thick felt pad under a heavy area rug at the point of the floor reflection from the center-channel speaker.) Absorbers can be important treatment; but don’t get carried away – particularly in the front of your room – or you may lose some of the information from your recordings.
A reflector is the opposite of an absorber. As sound energy bounces off reflectors, it continues on its way. Which frequencies are reflected varies with the material, the size, the shape and the location in the room. Flat, rigid reflectors act as mirrors for the sound; but only reflect effectively when they are about a wavelength in diameter or larger. The major application of reflectors is in concert halls to direct the sound of the performers to the audience and in big recording studios. The outdoor band-shell is a big, full frequency range reflector. Home use of flat reflectors is limited (because of size) except when you are designing a custom-built theater and/or sound room.
Diffusors (aka Dispersers) are a non-flat variation on reflectors. While flat reflectors generally reorient the direction of the sound path over most frequencies in a coherent wave-front, the reflection of a sound hitting a diffusor coming from one direction is spread in many directions. Again, which frequencies are diffused varies with the material, the size, the shape and the location in the room. Again, you need big devices to diffuse low frequencies. Many modern diffusors use fractal designs. With these designs if you look at a 6” x 6” section, it will have a similar shape to 96” x 96” section. This would allow the effective low frequency limit to go from about 2 kHz down to about 125 Hz while keeping the high frequency limit the same (over 20 kHz with the smallest details around 0.5”). Diffusion has the advantage of keeping the sound energy the same while eliminating standing waves and echoes in their useful frequency range. Some of the most natural sounding systems I have ever heard invested a lot of money and time in large diffusors.
You can get great improvements in sound quality with refined room placement and adding some room treatment.
Until next time,