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Acoustic Attenuator Front Cover

IP.com Disclosure Number: IPCOM000101985D
Original Publication Date: 1990-Oct-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 2 page(s) / 48K

Publishing Venue

IBM

Related People

Gaunt, DS: AUTHOR

Abstract

Acoustic noise emitted from the ventilating cover of a disk file or similar device is reduced at a selected predominant tone by means of a helmholtz cavity. Reduction in other wide-band noise components is reduced by absorbent polyurethane foam. A hole in a foam component in the air path, plus a recess in an exterior plastic cover, forms a 'helmholtz cavity' which has the ability to absorb certain frequencies so attenuating noise levels. By choosing physical characteristics, the cavity is tuned and the bandwidth increased on either side of resonance.

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Acoustic Attenuator Front Cover

       Acoustic noise emitted from the ventilating cover of a
disk file or similar device is reduced at a selected predominant tone
by means of a helmholtz cavity.  Reduction in other wide-band noise
components is reduced by absorbent polyurethane foam.  A hole in a
foam component in the air path, plus a recess in an exterior plastic
cover, forms a 'helmholtz cavity' which has the ability to absorb
certain frequencies so attenuating noise levels.  By choosing
physical characteristics, the cavity is tuned and the bandwidth
increased on either side of resonance.

      An embodiment consists of a shaped foam pad 3 which is attached
to the inside of the louvered 2 front cover 1 of a device, as shown
in Fig. 1.

      The pad 3 has a dimensioned hole 4 in the center of the top
of its horizontal bar 5 which aligns with the center of the insert 7
in a plastic cover 1 when the pad 3 is in place, as shown in
Fig. 2. When assembled, the top horizontal bar 5 of the pad 3 forms,
in conjunction with the cover 1, a tuned Helmholtz resonator with a
neck length 6 that is the depth of the pad and with an open area
determined by the diameter of hole 4.

      The dimensions of the cavity 4 and the neck length 6 are such
that the resonator can be tuned to a specific audio frequency by
varying the hole open area.  The frequency is tuned to cover one of
the problem frequencies from the noise source.  Since the neck length
6 is long and foam...