Harman Kardon AVP-1 Owners Manual - Page 7

II II II III II III • Ill II III III III Ell II II II II WOW! laser disc. If you can move the cloth in front of the speaker without hearing a difference, you are all set. Large expanses of glass can be challenging. They reflect mids and highs but often pass bass through almost as though they didn't exist. The result is a characteristically bright, rough sound which can be difficult to correct electronically. The best treatment is generally the heaviest insulated drapes which can be found (incidentally, these serve double duty, controlling light which might otherwise fall on the screen). The materials just discussed here are ineffective at lower frequencies. See the discussion on Standing Waves for more information about treating environments with low frequency response problems. EXCESSIVE USE OF ABSORPTIVE MATERIALS People are sometimes tempted to go overboard with absorptive material once they discover how powerful its use can be. While the ideal home theater should be considerably "deader" acoustically than a typical living room, it still needs some reflectivity and diffusion. In particular, the surround speakers depend on non-absorptive surfaces for the operation, since they radiate virtually no sound directly at the listeners. The best arrangement of the absorptive and non-absorptive surfaces in the room can be seen in the diagram below. Most of the room surfaces are relatively absorptive, with the notable exception of the rear wall and the highest portions of the other walls which should be diffusive. "SLAP" ECHOES "Slap" echoes are common in rooms which have parallel walls with little or no absorption or diffusion. Sounds tend to bounce back and forth between the parallel wall many times before they die out, causing a Room Absorption for Home Theater Systems Surround speaker Screen speakers • "Dead" zone absorbs front speaker reflection • "Live" zone provides surround propagation Reflective "live" zone Absorptive "dead" zone figure 4 characteristic bright, "zingy" sound and interfering with the intended tonal balance and acoustic nature of the soundtrack. Walk slowly through the room, clapping your hands. No clear reflections should be heard at any point in the room - especially not near the primary seating area. Listen for a "flutter echo" of the hand clap ( a rapidly-repeating percussive sound, indicative of the sound bouncing between two parallel walls). Again, the best home theaters are fairly "dead" acoustically. This allows the program material and the playback system to create the environment, rather than having the room's native acoustic signature color everything. You can also use the hand claps in chapters 17 and 18 of WOW! The solution for slap echoes is usually a combination of absorption and diffusion. Specifically, placing absorptive material behind the front speakers (heavy drapes, fiberglass, dense foam) and diffusion in the rear of the room (bookcases irregularly-shaped furniture, etc.) will deliver the greatest benefits. This will effectively suppress the slap echoes while at the same time providing a diffusive surface in the rear 6