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As the result of its size and geometry, a room excessively amplifies sound at certain frequencies. This is the result
of standing waves (acoustic resonances/modes) of the room. These are waves whose original oscillation
is continuously reinforced by their own reflections. Rooms have many resonances, but only the
low-frequency ones are discrete, distinct, unaffected by the sound absorbing material in the room,
and accommodate most of the acoustic energy build up in the room.
In a typical room similar in size to a home-theater, a listening room, an office or an owner's suite in a yacht the resonant frequencies of these standing waves fall in the bass frequency region. Provoking these low-frequency resonances result in boomy noise in a room. |
DEICON has developed a novel, small electronic feedback control solution for adding damping to the first two acoustic modes of a room. This patented technology which is licensed to a premiere U.S. based speaker manufacturer, is a stand-alone active bass treatment scheme custom tuned to the room. |
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| Mode Shapes and Resonant Frequencies |
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At certain frequencies the dimensions of a room are integer multiples of
the wavelength of the tones corresponding to those frequencies. This causes the
reflection of the wave from the walls reinforce each other and
establish standing waves in the room. These
frequencies are called resonant frequencies (known also as characteristic frequencies)
of the room and their corresponding
standing wave pattern are called mode shapes of the room. The resonance
frequencies and the corresponding mode shapes
depend primarily on the shape and size of the room.
The slide show depicts 4 of such standing waves in a rectangular room. |
Slide show depicting the first 4 standing waves (modes) of a room
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Figure 1 depicts the
sound transmission,
over the frequency range of 20 to 80 Hz, from a source
located in one corner of a 7 by 5 by 3 meter room to a microphone located
at the opposite corner.
The marked influence of the room on the low-frequency sound transmission, in terms of
favoring some frequencies (resonances) over the others, is quite apparent. Moreover,
the first few (specially the first) room resonances are more discrete, distinguishable,
and contain most of the bass acoustic energy.
Figure 1 Acoustic frequency response of a 7 by 5 by 3 meter rectangular room
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DEICON's electronic feedback control solution can be used for damping the boom noise and rumble in cabins (PDF). Noise and vibration solutions for yachts | Boom noise damping in cabins (PDF)
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