Harman Kardon AVP-1 Owners Manual - Page 9

I s s s s s s s s s s s s s s s s s s s s s BACKGROUND NOISE SOLUTIONS Many sources of noise in a home environment can be addressed simply. Locating the home theater in the basement often removes it from many household noises as well as isolating it from the other family members. Taking care to completely seal windows and doors can also make a significant difference in reducing outside noise. Heating and cooling systems are more challenging. Sometimes, the answer may be as simple as using a "whistle-free" diffusion grille rather than one which creates undue noise from turbulence. In cases of new construction, using larger- diameter air ducts for lower air velocity is very beneficial. You can go further by using ductwork which is lined with acoustically absorptive material. Where possible, longer ducts which have several turns further reduce the sound of the airflow, by eliminating the straight path from the heating/cooling system to the room. Some of the construction techniques used to minimize the transmission of external sounds into the listening environment include: ■ Double or triple layers of sheet rock (gypsum board) ■ Double wall construction, meaning two complete sets of studs (preferably stuffed with fiberglass insulation) ■ Double wall construction with staggered studs (minimizes transmission of vibrations from one set of studs to the next) ■ Floating floor construction (again, preferably stuffed with fiberglass; this also can enhance the perceived bass, since the subwoofers may cause structural vibrations through the false floor which then get transmitted through the furniture) ■ Seal all windows, doors, vents ■ Seal and caulk all apertures in the wall (electrical outlets, through-wall plumbing, etc.) Finally, transient noises (traffic on the street, dripping faucets, etc.) distract your attention away from the program material, and remind you that you are in your home theater/living room rather than a participant in the action of a movie. STANDING WAVES A "standing wave" is what causes a pipe of a particular length in a large pipe organ to have its characteristic pitch. The pipe literally amplifies certain frequencies, based on its length and the wavelength of the frequency. A typical rectangular room has three characteristic "lengths," and thus three fundamental standing wave frequencies. In addition, multiples of these frequencies are also amplified. These frequencies are often referred to as "room resonances" or "room modes" - that is, the frequencies at which the room tends to vibrate of its own accord. These resonances lead to uneven frequency response, the greatest problems being in the 60-150 Hz range for a typical domestic living room (at lower frequencies in larger rooms). Unfortunately, there is no way to eliminate the effects of standing waves completely. The best that can be done is to minimize their effect through a variety of strategies. STANDING WAVE SOLUTIONS: ROOM RATIOS In new construction, the best way to minimize the audibility of standing waves is to plan for an even distribution of them, so that their effects do not "pile up" on top of each other. In this regard, the ratios of room dimensions are the critical factor. Rooms having equal dimensions are the worst, since the standing waves in all directions reinforce one another. Room dimensions which are even multiples of one another are also to be avoided where possible. STANDING WAVE SOLUTIONS: SPEAKER PLACEMENT Speaker placement also has an effect on standing waves and their audibility. In particular, placement of any speaker (including subwoofers) 8