Sound Coloration due to Surface Stimulation.
High-energy sound waves cause surfaces to move; some more than others. As a generally accepted rule, those dabbling in precision audio do not want their room surfaces to contribute to the sound by resonating. Several negative outcomes result when the walls, ceiling or floor “sing”:
- increased reverberation time
- uneven frequency response
- degraded musical articulation (transient response)
- blurred imaging
These issues cannot truly be solved by DSP or equalization. Altering the mechanical characteristics of the problematic surface to minimize the effects is the appropriate solution. As with most solutions, the degree of commitment you are willing to make has a strong effect on the final outcome. Like a well-designed loudspeaker, a good room surface does not possess large unsupported sections that are free to vibrate. Windows and plain drywall on studs are common examples.
Go around your room and find the most resonant surfaces by thumping with the bottom of a closed fist. You will probably hear a tone that aligns with one you always thought seemed a little louder than it should be in your music. After you find the offenders, you can do several things calm down the surface:
- install rigid bracing across the unsupported section, anchoring to strong points and fastening to the section*
- install an extra layer of sheet material (drywall, plywood, hardboard) with damping sandwiched
- remove the bad surface and rebuild with better bracing or stronger material
One common exception to this general rule applies to solid natural wood room skins. Like a classic violin or guitar, the type, thickness, age, and finish of the wood have a strong influence on the final sound generated. And in a cheap violin or guitar, an average wooden body still sounds better than one made of cardboard or plastic. Perhaps it is purely psychoacoustic, but the sound of lightly resonating real wood boards seems to appeal to most humans’ sense of sound quality. So if you find yourself surrounded by gorgeously stained maple or mahogany tongue-and-groove, consider yourself lucky, put on your favorite record, and enjoy!
*tip: for freely vibrating glass surfaces, use wood strips and a strong adhesive!