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Reverberation

All rooms contain reverberation. Reverberation is sound energy bouncing off of hard surfaces that make up the room. If a room has many large, hard surfaces, such as bare walls, ceiling and floor, the sound is reflected from surface to surface until it loses enough energy to become inaudible. Soft and/or porous materials absorb sound energy and convert them into heat energy.

Reverberation is measured by the amount of time it takes for the sound energy to die down 60 decibels below the original signal. If there is too much reverberation, spatial cues and speech become smeared and confusing. If there is too much absorption, the sound becomes unnatural and uncomfortable. Unless limits are placed on the project, A/V RoomService can make sure that the ideal reverberation is met.

Lower frequencies will have longer decay times than higher frequencies because there is little but the structure of the room itself to absorb such large wavelengths. For example: 20Hz is about 56 feet long compared to 20 kHz., which is only about of an inch.  Typically, absorption material the thickness equal to a quarter wavelength of the lowest frequency to be absorbed is required. 

A/V RoomService suggests that an ideal home cinema should have reverberation times around 0.25-0.35 of a second across the audible bandwidth in order to portray accurate localization cues and excellent speech intelligibility. Often rooms are over treated with absorption panels, resulting with too much attenuation around 500 Hz. and above, and not enough below. The proper balance of reflective, diffusive and absorptive materials must be used in order to achieve natural reverberation times across the audible bandwidth.

Lower reverberation times also improve room modes by broadening their bandwidths, thus smoothing their peaks and valleys. Calculated to 3 dB from peak point, an ideal mode bandwidth is 5 Hz or more.

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