Noise attenuation

Abstract: Noise attenuation apparatus comprising an enclosure having a wall separating an interior and an exterior. The enclosure defines a volume. The volume is characterized by an acoustic compliance and includes a device producing noise. The noise has spectral components predominantly in a noise frequency range. A first port has a first acoustic mass. The port passes through the wall between the interior and the exterior wherein the acoustic compliance and the first acoustic mass are configured to establish a resonant frequency outside the noise frequency range.

Description: The invention relates to noise attenuation and heat dissipation in electronic systems, and more specifically to the use of ported enclosures to attenuate fan noise in an electronic device, such as a multimedia computer system and still more specifically to the use of a ported loudspeaker system for attenuating fan noise, dissipating heat and reproducing sound. For background reference is made to U.S. Patent Nos. 4,549,631 and 5,092,424. It is an important object of the invention to provide improved noise attenuation and heat dissipation. US-A-5508477 discloses an apparatus for acoustic noise reduction of office automation devices utilising helmholtz resonance theory. JP-A-63074297 discloses a system to suppress the temperature rise of an amplifier by arranging plural ports above and beneath a cabinet so as to dissipate heat. WO-88/10054 discloses ultralight loudspeaker enclosures. According to the invention, there is provided a loudspeaker system comprising, a wall defining an enclosure, said enclosure having an interior of predetermined volume and acoustic compliance, a first port through said wall; a second port through said wall; an electroacoustical transducer, a heat producing device disposed in said interior, and characterised in that said electroacoustical transducer is mounted in a divider of the enclosure, said volume, said first port and said second port are configured to have a resonant frequency, wherein said first port and said second port are configured so that an airflow enters said first port, flows across said heat producing device and exits through the second port, and said ports and said acoustic compliance being constructed and arranged to act as a filter that allows direct current airflow to pass freely through said ports while significantly attenuating any noise spectral components above said resonant frequency. Other features, objects and advantages will become apparent from the following detailed description, which refers to the following drawings in which: Fig. 1 is a diagrammatic view of a first embodiment of the invention; Fig. 2 is a diagrammatic view of a second embodiment of the invention. With reference now to the drawings and more particularly Fig. 1, there is shown an apparatus according to the invention. A loudspeaker system 40 includes an enclosure 41 having two chambers, 42, 44. Chamber 44 may have two sections, 45, 46, each having a port, 64, 68, respectively, in an exterior wall. The first chamber 42 and the second chamber 44 are separated by a divider 52; the sections 45, 46, may be separated by a divider 52; the sections 45, 46, may be separated by a baffle 54. An elctroacoustical transducer 56 is positioned in divider 52 with one side of the radiating surface (in this embodiment, the front side 58) facing into the second chamber 44 and another side of the radiating surface (in this embodiment, the back side 60 facing into the first chamber 42. In an opening 57 in baffle 54 is a fan 62 which draws air into the first section 45 through port 64 and blows said air out across heat producing device 66, thereby cooling the heat producing device. The cooling air exhausts through port 68 in the second section 46. The heat producing device may be placed in a ventilated enclosure 70. The opening 57 in the second baffle 54 is large enough to be of extremely low impedance at audio frequencies, so the second baffle 54 is essentially "transparent" to sound waves, and the combined volume of the first and second sections 45, 46 of second chamber 44 presents a single acoustic compliance. The combined volume of the first and second sections 45, 46 and the dimensions of the two ports 64, 68 are configured such that they function acoustically in a manner similar to one of the chambers 16a, 16b of U.S. Pat. 4,549,631, and the loudspeaker system is acoustically equivalent to the loudspeaker system shown in Fig.1 of the above referenced U.S. patent and described in the accompanying disclosure. Additionally, the portion of enclosure 41 including the first and second sections 45, 46, and the ports 64, 68 function as a filter that attenuates the noise produced by the fan 62. Thus ports 64, 68 allow direct current airflow to pass freely, while significantly attenuating the noise produced by the fan 62. The elements of the embodiment of Fig. 1 can be arranged in other configurations while still performing the same function as the embodiment of Fig.1. For example, the electroacoustical transducer 56 can face into the first chamber 42, the fan 62 can draw air through port 68 in the second section 46, and exhaust the air through port 64 in the first section 45, or the heat producing device can be placed in the first section 45. A loudspeaker system according to Fig. 1 is advantageous, because it permits a single enclosure to enhance loudspeaker performance, enclose heat producing electronic components and devices for cooling the electronic components, and reduce undesirable noise heard outside the enclosure produced by the cooling devices. A loudspeaker system according to Fig. 1 is particularly advantageous for use in high performance multimedia computers providing high quality sound and housing components such as power supplies that generate significant heat. In one embodiment, the dimensions of port 64, 68 and volumes of first and second sections 44, 46, are configured to resonate at a frequency of approximately 45 Hz and fan 56 produces noise having frequencies predominantly above 100 Hz. Referring to Fig. 2, there is shown an alternate embodiment of the invention. The elements of Fig. 2 are similar to the elements of Fig. 1, except that the first port 48 (of Fig. 1) is not present, so that the first chamber 42 is sealed. The cooling of electronic component 66 and the attenuation of noise produced by fan 62 are performed in a manner similar to the embodiment of Fig. 1. For acoustic purposes, the combined volumes of first and second sections 45, 46 have an acoustical compliance equivalent to a single chamber with the same volume. The dimension of ports 64, 68 in the first and second sections can be selected such that the embodiment of Fig. 2 is equivalent acoustically to a multi-chamber, single ported sealed chamber loudspeaker, familiar to those in the acoustic art. Additionally, the portion of enclosure 41 including the first and second sections 45, 46, and ports 64, 68 functions similarly to the embodiment of Fig. 1 to attenuate the noise produced by fan 62, and the embodiment of Fig. 2 has the same advantages as the embodiment of Fig. 1. For purposes of clarity, the embodiments have been shown with rectangular enclosures. However, the invention can also be implemented with enclosures of many different shapes. Additionally, the techniques disclosed herein may be applied to any ported loudspeaker system regardless of the number of volumes and the number and placement of ports. A baffle having a low acoustic impedance at audio frequencies and designed and constructed to direct airflow across a desired location can be placed in a loudspeaker chamber, and a port can be replaced by two or more ports having an equivalent combined acoustic mass.

Claims: A loudspeaker system (40) comprising, a wall defining an enclosure (41), said enclosure having an interior of predetermined volume and acoustic compliance, a first port (64) through said wall; a second port (68) through said wall; an electroacoustical transducer (56), a heat producing device (66) disposed in said interior, and characterised in that said electroacoustical transducer (56) is mounted in a divider (52) of the enclosure (41), said volume, said first port (64) and said second port (68) are configured to have a resonant frequency, wherein said first port (64) and said second port (68) are configured so that an airflow enters said first port (64), flows across said heat producing device (66) and exits through the second port (68), and said ports (64, 68) and said acoustic compliance being constructed and arranged to act as a filter that allows direct current airflow to pass freely through said ports (64, 68) while significantly attenuating any noise spectral components above said resonant frequency. A loudspeaker system (40) in accordance with claim 1 further comprising, a fan (62) disposed in said enclosure (41) for causing said airflow, said fan (62) producing noise having spectral components predominantly in a noise frequency band, wherein said resonant frequency has a value below said noise frequency band. A loudspeaker system (40) in accordance with any of the preceding claims wherein said divider (52) divides said interior of said enclosure (41) into first (42) and second (44) chambers. A loudspeaker system (40) in accordance with claim 2 further comprising, a baffle (54) for directing a flow of said air across said heat producing device (66), and wherein said fan (62) is arranged so as to cause the air to flow in at said first port (64), across said heat producing device (66), and out at said second port (68). A loudspeaker system in accordance with any of the preceding claims, wherein said resonant frequency is of the order of 45 Hz.

Inventors: ARNOLD FINN, O'DEA STEPHEN R, ARNOLD, FINN, O'DEA, STEPHEN R.
Applicants: BOSE CORP, BOSE CORPORATION
Application year: 1998
Main classification: H04R1
IPC codes: H04R1, G10K11