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MINIMIZING ACOUSTIC DISTORTION IN HOME THEATERS
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Short Description: approach to home theater design will be presented in which the room dimensions, and locations for loudspeakers, listener, and acoustical absorptive and ...
Content Inside: MINIMIZING ACOUSTIC DISTORTION IN HOME THEATERS By Peter D'Antonio RPG Diffusor Systems, Inc., Upper Marlboro, MD Despite the marvelous electronic advances in Speaker-Boundary Interference- digital hardware, sound must eventually travel The coherent interaction between the direct the acoustic analog path from loudspeaker to our sound and the omnidirectional early reflections ears. Since we also have a brain attached to our from the room’s adjacent boundaries ears, a very complex psychoacoustic process is involved in sound perception. 2 0 1 5 The sound that we hear in a critical listening 1 0 room is determined by complex interactions 5 among the quality of the electronics, the quality and placement of the loudspeakers, the hearing 0 0 2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 ability and placement of the listener, the room - 5 Pressure, dB dimensions (or geometry if non-rectangular) and - 1 0 the acoustical condition of the room’s boundary - 1 5 1 B o u n d a r y X = 4 ' surfaces and contents. All too often these factors 2 B o u n d a r i e s X = 4 ', Y = 4 ' - 2 0 are ignored and emphasis is placed solely on the 3 B o u n d a r i e s X = 4 ', Y = 4 ', Z = 4 ' 3 B o u n d a r i e s X = 1 ', Y = 1 ', Z = 1 ' - 2 5 quality of the loudspeakers. However, the tonal F r e q u e n c y , H z balance and timbre of a given loudspeaker can vary significantly, depending on the placement Figure 2. Graph illustrates how the interference of the listener and loudspeaker and the room notch at roughly 80 Hz increases by 6 dB as acoustic conditions. In some cases the additional boundaries are added 4' from source. differences between different loudspeakers The notch also increases in frequency as the located in the same location in a room can be boundary distance is reduced to 1'. less than the differences introduced by moving the same loudspeaker to different locations in a Comb Filtering- room. The coherent constructive and destructive interference between the direct sound and early The causes of acoustic distortion are: reflections Modal Coupling- The acoustical coupling 10 between the loudspeakers and listener with the 5 room’s modal pressure variations or room modes 0 (100) (200) (300) -5 Level, dB -10 0 dB 3 db -15 6 dB 12 dB -20 0 500 1000 1500 2000 2500 3000 Frequency, Hz Figure 3. The infinitely deep comb filter response resulting from a reflection at the same level as the Figure 1. (100), (200) and (300) axial direct sound (0 dB) is reduced when the reflection is modes in a rectangular room with a 15' reduced in level by 3, 6 and 12 dB. dimension are shown at 37, 74 and 111 Hz, respectively.
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