Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
  • H04R1/00—Details of transducers, loudspeakers or microphones
  • H04R1/20—Arrangements for obtaining desired frequency or directional characteristics
  • H04R1/22—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired frequency characteristic only 
  • H04R1/28—Transducer mountings or enclosures modified by provision of mechanical or acoustic impedances, e.g. resonator, damping means
  • H04R1/2807—Enclosures comprising vibrating or resonating arrangements
  • H04R1/2815—Enclosures comprising vibrating or resonating arrangements of the bass reflex type
  • H04R1/2823—Vents, i.e. ports, e.g. shape thereof or tuning thereof with damping material
  • H04R1/2826—Vents, i.e. ports, e.g. shape thereof or tuning thereof with damping material for loudspeaker transducers

Definitions

• a loudspeaker system which comprises an enclosure with a loudspeaker and a bass reflex port made up of a plurality of parts.
• This bass reflex port comprises a visco-elastic part formed by two rubber outer cylinders disposed in line with one another and an air-permeable part formed by a felt inner cylinder, the inner cylinder extending between and for a substantial part in the outer cylinders, to which it is connected.
• the bass-reflex port used therein serves to counteract undesired sounds, particularly duct resonant sounds.
• the multi-part port also forms a drawback of the known loudspeaker system because the manufacture of such a bass-reflex port is rather laborious owing to the necessity of positioning various parts relative to one another and subsequently securing them to one another.
• the loudspeaker in accordance with the invention is characterized in that the means for the suppression of noises comprise a central area of the port, which area is situated centrally with respect to the open ends and has been provided with perforations, as well as a foam material provided in and/or on the perforations.
• the bass-reflex port has a circumferential wall, the perforations being consequently situated in this wall.
• Undesired sounds arise in that air vortices are produced at the two open ends of the port. This effect occurs particularly in the case of small and slender ports which are usually employed in small enclosures.
• the vortices arising at the open ends of the port produce sound dominated by certain frequencies. These frequencies correspond to the so-called l/2 ⁇ resonant frequency of the port and harmonics of this frequency.
• Undesired sounds produced at the l/2 ⁇ resonant frequency are reduced effectively by the measure taken in the bass-reflex port of the loudspeaker system in accordance with the invention.
• the l/2 ⁇ resonance exhibits a maximum pressure level in the center of the port but as a result of the perforations present in the central area the sound pressure remains limited owing to leakage of air through the perforations, the presence of the foam material providing the necessary damping.
• the measures taken have a favorable effect on the so-called Q factor of the port.
• this quality factor is a measure of the damping of sound. In the case of a favorable, i.e. comparatively low Q factor the decay time is comparatively short, as a result of which both desired sounds and undesired sounds are sustained for a shorter time.
• the bass-reflex port which essentially has the shape of a tubular body, can in principle be manufactured from any regular solid material such as a hard plastic, for example polystyrene.
• the basically hollow port can be of round or non-round cross-section.
• the foam material can be any regular porous air-permeable foam plastic, such as polyurethane foam, polyether foam and PVC foam, or air-permeable rubber.
• JP-A 4 114598 a loudspeaker system of the bass- reflex type is known, which employs a pipe having a communication opening halfway its length.
• this known system relatively many undesired sounds are produced, while the damping is comparatively low (high Q factor).
• the known system only the 1/2 ⁇ resonance is suppressed.
• perforations are situated along the circumference of the central area of the port. In this embodiment the l/2 ⁇ resonance is suppressed most effectively.
• An embodiment of the loudspeaker system in accordance with the invention has the characteristic features as defined in Claim 3.
• the use of this embodiment also leads to a reduction of undesired sound caused by further resonant frequencies, particularly harmonics of the l/2 ⁇ resonant frequency.
• perforations are present along the circumference in one or more non-central areas situated outside the central area.
• An embodiment of the loudspeaker system in accordance with the invention has the characteristic features as defined in Claim 5. The use of this embodiment makes it possible to achieve an optimum reduction of undesired sound caused by the l/2 ⁇ resonant frequency and harmonics of this frequency.
• the foam material takes the form of a layer surrounding the port and deposited on an outer wall of the port.
• a layer is obtained, for example by the provision of a collar or cuff of a foam material.
• the invention further relates to a bass-reflex port intended for use in the loudspeaker system in accordance with the invention and constructed as defined in any one of the Claims 1 through 6.
• the port With a passage which flares towards the two open ends, flared portions being provided, which portions extend over a substantial part of the length of the port and, in a longitudinal section of the port, have bounding lines which extend at an angle having a value of between 3° and 12° with respect to the longitudinal axis of the port.
• a port consequently has inner walls which are slightly inclined with respect to its longitudinal axis.
• the rounded end portions at both open ends, which portions adjoin the slightly inclined inner walls, may change into flanges situated outside the port, for example flanges which are oriented transversely to the longitudinal axis of the port. This measure may yield a further improvement of the loudspeaker system at certain sound levels.
• One of the flanges can be integrated in a wall portion of the enclosure.
• FIG. 1 diagrammatically shows an embodiment of the loudspeaker system in accordance with the invention
• FIGS 2 through 4 diagrammatically show variants of bass-reflex ports suitable for use in the loudspeaker system in accordance with the invention.
• FIG. 5 is a graph representing the sound pressure as a function of the frequency.
• the loudspeaker system in accordance with the invention shown in Figure 1 comprises an enclosure 1 which accommodates a loudspeaker device 3, taking the form of a cone loudspeaker known per se, and a bass-reflex port 5.
• the enclosure 1 forms a chamber 2 of a given volume, for example 2.5 dm3.
• the port 5, which provides open communication between the chamber and an environment of the enclosure, has a wall 5g and a longitudinal axis 51.
• the port 5 has two open ends 5b and 5c, of which one end 5b is situated inside the enclosure and the other end 5c is situated on or near an outer side, particularly a wall portion la of the enclosure 1.
• the parabolic bounding lines 7 extend at an angle ⁇ of maximum 12° with respect to the longitudinal axis 51.
• a central area c situated near the center M the port has perforations 9 formed in the wall 5a, which perforations are shown diagrammatically in broken lines in Figure 1.
• perforations 9 may be provided in one or more non-central areas d between the center M and the open ends 5b and 5c. The perforated areas in combination with the foam material form an effective means for the suppression of noises.
• the embodiments 105 of the bass-reflex port in accordance with the invention shown in Figure 2 which is intended for use in a loudspeaker system in accordance with the invention, comprises a tubular body 120 of a hard material such as a hard plastic, in the present case in the form of a hollow cylinder, having a longitudinal axis 1051 and a wall 120a, in the present example a cylindrical wall.
• a hard material such as a hard plastic
• the port 105 further has two open ends 105b and 105c.
• the wall 120a In an area c which is situated centrally with respect to the open ends, the wall 120a has perforations 109 in the form of small through-holes in the wall, the perforations being uniformly spaced along the circumference of the port.
• the embodiment 205 of the bass-reflex port in accordance with the invention shown in Figure 3 has a wall 220 which surrounds a longitudinal axis 2051 and which has inner surfaces 205dl and 205el, respectively, which are slightly inclined with respect to the longitudinal axis 2051. In the present example, these surfaces extend at an angle ⁇ of maximum 6° with respect to the longitudinal axis 2051.
• the port 205 has end portions 205f and 205g, respectively, which are radially rounded towards the exterior and which in the present example have a radius r of approximately 5 mm. A slightly smaller or greater radius of, preferably between 3 and 10 mm, is also suitable.
• the rounded end portions 205f and 205g smoothly adjoin the gently inclined surfaces 205dl and 205el, respectively.
• the port has a perforated wall portion 220a around which a cuff
• the embodiment 305 of the bass-reflex port in accordance with the invention shown in Figure 4 has two open ends 305b and 305c.A central part c and two non-central parts d have perforations 309 and have a foam material 311, such as a polyester foam, in and/or on the perforations 309. In the present example, annular layers of a foam material have been provided around the port.
• the graph in Figure 5 successively shows results of measurements carried out on a loudspeaker system including a conventional bass-reflex port, a bass-reflex port as shown in Figure 2 and a bass-reflex port as shown in Figure 4.

Landscapes

• Health & Medical Sciences (AREA)
• Otolaryngology (AREA)
• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Acoustics & Sound (AREA)
• Signal Processing (AREA)
• Details Of Audible-Bandwidth Transducers (AREA)

Priority Applications (3)

Applications Claiming Priority (2)

Publications (1)

Family

ID=8233770

Family Applications (1)

Country Status (5)

Cited By (3)

Families Citing this family (20)

Citations (4)

Family Cites Families (2)

• 1999
  • 1999-05-24 US US09/316,982 patent/US6275597B1/en not_active Expired - Fee Related
  • 1999-05-25 DE DE69911545T patent/DE69911545T2/de not_active Expired - Fee Related
  • 1999-05-25 WO PCT/IB1999/000940 patent/WO1999062292A1/en not_active Ceased
  • 1999-05-25 EP EP99919482A patent/EP1000525B1/en not_active Expired - Lifetime
  • 1999-05-25 JP JP2000551574A patent/JP2002517148A/ja not_active Abandoned

Patent Citations (4)

Non-Patent Citations (1)

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