WO2012080879A1 - Haut-parleur - Google Patents

Haut-parleur Download PDF

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Publication number
WO2012080879A1
WO2012080879A1 PCT/IB2011/055297 IB2011055297W WO2012080879A1 WO 2012080879 A1 WO2012080879 A1 WO 2012080879A1 IB 2011055297 W IB2011055297 W IB 2011055297W WO 2012080879 A1 WO2012080879 A1 WO 2012080879A1
Authority
WO
WIPO (PCT)
Prior art keywords
damping material
loudspeaker
acoustic
port
bass reflex
Prior art date
Application number
PCT/IB2011/055297
Other languages
English (en)
Inventor
Sheng Bo Li
Fuyu Wang
Original Assignee
Koninklijke Philips Electronics N.V.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Koninklijke Philips Electronics N.V. filed Critical Koninklijke Philips Electronics N.V.
Publication of WO2012080879A1 publication Critical patent/WO2012080879A1/fr

Links

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

  • the invention relates to a loudspeaker arrangement and in particular, but not exclusively, to loudspeakers for providing high audio quality at low frequencies.
  • loudness is related to the amount of air that a loudspeaker displaces and in order to displace large amounts of air at low frequencies, large sound transducers (with large effective areas) are typically required.
  • a number of different speaker designs have been developed.
  • the simplest speaker design tends to be a closed speaker but unfortunately this design also tends to result in a restricted bass output.
  • a more efficient way to reproduce low frequencies is to use a bass reflex design wherein a bass reflex port acts as a lumped mass and the volume of the cabinet acts as an additional spring.
  • Such a bass reflex design may provide an additional low frequency resonance, which can be used to augment the bass response of the driver and which may extend the frequency response of the driver/enclosure combination to below the range the driver could reproduce in a sealed box.
  • the Helmholtz frequency ft h of the bass reflex system is determined by the port length L p , the cabinet volume Vb, and the port area A p , according to: In practice, the values for Vb, and fth are chosen to give the desired frequency response.
  • a long port tends to exhibit standing waves in the midrange frequency band which causes coloration in the sound of the loudspeaker system.
  • a small port area is responsible for an increase of the air velocity in the port which eventually leads to unwanted turbulent noise.
  • Such effects tend to reduce the audio quality and may introduce discoloration of the sound or the generation of additional noise sources and effects.
  • the turbulence may often be audible as a "hissing" or "chuffing" noise.
  • an improved loudspeaker would be advantageous and in particular an arrangement allowing increased flexibility, improved audio quality, reduced size, increased sound levels, improved mechanical operation, and/or improved performance would be advantageous.
  • the Invention seeks to preferably mitigate, alleviate or eliminate one or more of the above mentioned disadvantages singly or in any combination.
  • a loudspeaker comprising: an acoustic enclosure; an active sound driver mounted in the acoustic enclosure; and an elongated bass reflex port having an inner surface forming a free air flow channel; and wherein at least part of an area of the inner surface is formed by an acoustic damping material.
  • an improved low frequency sound quality may be achieved from a smaller loudspeaker enclosure.
  • the presence of the acoustic damping material may modify the air velocity profile to provide increased viscous forces relative to the inertial forces thereby mitigating, reducing or preventing turbulence.
  • the presence of the acoustic damping material may reduce the risk or magnitude of standing waves in the base reflex port.
  • the performance may improve for an increasing area of the inner surface that is formed by the acoustic damping material. Indeed, in many scenarios, at least 50%, 90% or even substantially all of the inner surface may advantageously be formed by the acoustic damping material.
  • the acoustic damping material may e.g. be any material that allows air flow but reduces the air speed velocity.
  • the acoustic damping material may be a material which attenuates or obstructs vibrations or oscillations in the air (i.e. sound).
  • the acoustic damping material may provide increased resistance to air flow relative to the free air flow channel yet allows air flow through it.
  • the inner surface is formed by an element comprising the acoustic damping material and an outer wall formed by an air impermeable material, the damping material being adjacent to an inner wall surface of the outer wall.
  • This may provide improved performance and/or may facilitate operation. In particular, it may allow facilitated manufacturing, reduced cost and/or may provide improved reliability e.g. due to improved mechanical stability.
  • the air blocking material may be any material that does not allow any air flow through it, i.e. which completely blocks airflow.
  • the damping material is attached to the inner wall surface.
  • This may provide improved performance and/or may facilitate operation. In particular, it may allow facilitated manufacturing, reduced cost and/or may provide improved reliability e.g. due to improved mechanical stability.
  • a minimum depth of the acoustic damping material is no less than 2 mm.
  • a minimum depth of the acoustic damping material is no less than 2 mm.
  • the maximum depth of the acoustic damping material is advantageously no more than 10 mm.
  • a depth of the acoustic damping material is no less than 2 mm and no more than 8 mm.
  • a minimum depth of the acoustic damping material is no less than a tenth of a square root of a cross sectional area of the free air flow channel.
  • the cross section may specifically be in a plane perpendicular to the longitudinal direction of the elongated bass reflex port.
  • a minimum depth of the acoustic damping material is no more than one half of a square root of a cross sectional area of the free air flow channel.
  • a cross sectional area of the free air flow channel varies by less than 25%.
  • This may in many embodiments facilitate implementation, design and manufacturing. In many scenarios it may result in a more homogenous air flow in the free air flow channel thereby allowing improved audio quality to be achieved.
  • the elongated bass reflex port forms a substantially straight free air flow channel.
  • Fig. 1 illustrates an example of a loudspeaker design
  • Fig. 2 illustrates examples of bass reflex port designs
  • Figs. 3 and 4 illustrate examples of air flows in bass reflex ports
  • Fig. 5 illustrates examples of bass reflex port designs
  • Fig. 6 illustrates examples of standing waves in bass reflex ports
  • Figs. 7-9 illustrate examples of measurements of loudspeakers having different bass reflex ports.
  • Fig. 1 illustrates an example of a loudspeaker design.
  • the loudspeaker of Fig. 1 comprises a cabinet or acoustic enclosure 101 which forms the external enclosure of the loudspeaker.
  • the acoustic enclosure 101 comprises a single chamber 103 formed by the enclosure but it will be appreciated that in other embodiments the acoustic enclosure or cabinet 101 may comprise a plurality of chambers formed by internal walls or dividers.
  • the loudspeaker comprises an audio radiator or driver 105 which is mounted in the acoustic enclosure 101 and which has a rear part extending into the chamber 103.
  • the audio driver 103 is mounted on an external wall of the enclosure 101. Specifically, it is mounted such that the main radiation direction of the audio driver 103 is directly out into the acoustic environment in which the loudspeaker is located. Thus, the main radiation direction of the audio radiator 103 is outwardly from the enclosure 101.
  • the loudspeaker of Fig. 1 furthermore comprises a bass reflex port 107 which provides a pneumatic connection between the internal chamber 103 and the outside.
  • substantially the only air flow and between the internal chamber 103 and the exterior of the loudspeaker 101 is via the port 107.
  • a bass reflex port is typically used to enhance lower frequencies of the generated sound.
  • the bass reflex port 107 can be tuned to a low resonance or Helmholtz frequency thereby extending the effective frequency range of the audio driver 105.
  • the loudspeaker is designed such that the resonance of the bass reflex port 107 is lower than a cut-off frequency of the audio driver 105.
  • the free air acoustic resonance frequency of the audio driverl05 is modified by the enclosure 101 and the bass reflex port 107 to provide an acoustic resonance frequency of the combined system which is typically lower than the free air acoustic resonance frequency of the audio driver. Consequently, the frequency response of the loudspeaker extends to lower frequencies than the frequency response of the audio driver itself.
  • the bass reflex port will thus extend the low frequency response of the speaker and typically the bass reflex port may be tuned to a frequency from around 40-50 Hz to 150Hz.
  • bass reflex ports may be used to extend the effective frequency range for a given size of a loudspeaker
  • conventional bass reflex port designs have a number of disadvantages.
  • traditional designs tend to introduce degradations to the audio quality and in particular may introduce noise and/or distortion.
  • the Inventors have realized that one or more disadvantages of traditional bass reflex port designs may be mitigated or removed by a modified design of the bass reflex port, and in particular by modifying the materials that form the bass reflex port.
  • substantially improved performance can be achieved by controlling and varying the effective speed profile for air through the bass reflex port. Indeed, rather than use a conventional homogenous design with the walls of the bass reflex port being made by air impermeable material forming a pipe which is empty or fully filled with damping material, highly advantageous performance is achieved in the loudspeaker of Fig. 1 by forming the bass reflex port 107 by an element that is fully or partially made from acoustic damping material.
  • FIG. 2 shows a pipe used to form the bass reflex port 107.
  • Cross section A illustrates the conventional approach of forming the wall of the bass reflex port from an air impermeable material such as typically plastic or cardboard.
  • the bass reflex port 107 creates an internal air channel defined by the inner surface of the wall made of air impermeable material.
  • cross section B illustrates the bass reflex port 107 of the loudspeaker of Fig. 1.
  • an air channel 201 is formed by an inner surface 203 of an element which is formed by an acoustic damping material 205.
  • the acoustic damping material 205 forms a pipe which has an internal cavity that allows a substantially free air flow.
  • the acoustic damping material 205 is attached to the inside of a wall of air impermeable material 207, such as plastic or cardboard.
  • air impermeable material 207 such as plastic or cardboard.
  • the bass reflex port 107 may in some embodiments be formed only by the air damping material. However, in some cases such embodiments may require a thicker air damping material.
  • the inner surface of the bass reflect port of the loudspeaker of Fig.1 is made from a damping material which covers the inside of the solid wall of the bass port outer element.
  • the damping material may be many different types of acoustic damping material and will reduce air flow speed when air travels through it. Thus, the damping material provides a resistance to air flow. Suitable damping materials may for example include virtually all fibrous materials used for acoustic isolation (such as felt, DacronTM, NylonTM, RockwoolTM etc.). The damping material may specifically be a foam with open- cells.
  • a conventional bass reflex port is relatively susceptible to turbulence and standing waves thereby introducing noise and distortions.
  • Turbulence in the air can typically arise at louder volume levels. Indeed, complications occur in vented designs as the output is increased beyond the point where the air in the port is able to respond in a linear fashion. This can result in undesirable extraneous noises being generated within the port as well as acoustic compression and distortion. These noises are generally broad-band "chuffing" noises due to fast moving air.
  • Turbulence can be defined as an eddy-like state of fluid motion where the inertial vortex forces of eddies are larger than other forces, such as viscous or buoyant forces that arise to damp out the eddies. This leads to random fluctuations in the flow velocity with amplitude variations of up to 20% of nominal and with a wide frequency band-width of the resulting noise components up (typically to around 10kHz). Physically, turbulence occurs when viscous forces are unable to damp out the nonlinear inertial vortex forces vxco that arise in the pipe .
  • Fig.3 illustrates and example of viscous flow in a conventional bass reflex port corresponding to a simple pipe.
  • the flow is to the right, and the vortex rings appear clockwise, facing downstream.
  • the direction of vortex forces is inward and these are balanced by the viscous forces that are directed outward.
  • This equilibrium is delicate and can be upset as the velocity increases. Beyond a critical value Rea any small perturbation will cause the formation of eddies that are too large to be damped. These tiny eddies will cause other eddies to form in the opposite direction and these may then pair up.
  • the swirling eddy pair will similarly lead to other eddy pairs , two of which will pair , and so on, from small scale to large and growing larger until the entire pipe is full of eddies of all sizes and the flow is fully turbulent.
  • Rea is known as the Reynolds number and can for a flow in a circular pipe be determined as
  • Fig. 4 illustrates the air velocity or speed profile close to the solid wall of a conventional bass reflex port. As illustrated, the air has reduced velocity in the boundary layer 401 compared to the free air flow channel 403.
  • the typical width of a boundary layer in conventional bass reflex ports is on the order of 1mm.
  • the modified design of the bass reflex port 107 in Fig. 1 tends to mitigate these effects.
  • Fig. 5 provides a detail illustration of an example of the difference between the conventional and the modified approach.
  • the use of a solid pipe is compared to the use of the same pipe lined with a damping material.
  • the damping material may specifically be attached to the pipe, e.g. by a using a suitable adhesive.
  • the conventional design results in the creation of a boundary layer 401.
  • the modified design uses a damping material 205 to modify the velocity profile proximal to the solid wall of the pipe 207.
  • the damping material 205 provides an area in which the air velocity is gradually reduced when approaching the solid pipe.
  • the velocity transition from full air flow speed to virtually no air flow speed at the solid pipe wall is extended over a larger distance.
  • the introduction of the damping material can be considered to effectively create a significantly larger boundary layer.
  • the modified approach of the loudspeaker of Fig. 1 provides improved audio quality of the rendered sound.
  • the extraneous noises and distortions tend to deteriorate sound quality, and as these effects are reduced an improved sound quality is achieved.
  • the stabilized tuning frequency improves the timbre and bass reproduction.
  • Figs. 7-10 illustrate measurement results demonstrating the improved performance.
  • the measurements are performed for a loudspeaker cabinet with a volume of 7 liters and provided with a 5 1/4" woofer (low frequency audio driver).
  • the performance of the loudspeaker was measured for a traditional port made of paper with an inner diameter of 39 mm and a length of 130 mm).
  • measurements were performed using the same port but lined with a damping material in the form of a chemical fiber. As the two designs have the same acoustic inertia, the resonator of the loudspeaker has the same resonance frequency.
  • Fig. 7 illustrates a measurement of Sound Pressure Level (SPL) as a function of frequency measured 1 cm away from the port edge for the traditional port as the solid line and the modified port as the dashed line. As can be seen the noise levels are higher for the traditional port than for the modified port at higher frequencies.
  • SPL Sound Pressure Level
  • Fig. 8 and 9 illustrate the SPL as a function of frequency for four different output levels for respectively the traditional port (Fig. 8) and the modified port (Fig. 9). As can be seen the variation in the tuning frequency is reduced for the modified design.
  • the depth of the damping material may be measured orthogonally to the inner surface of the damping material.
  • the minimum depth may specifically be the minimum dimension of the damping material in any direction.
  • Particularly advantageous performance is in many scenarios found for a depth of the acoustic damping material of no less than 2 mm.
  • Such dimensions will typically provide substantially improved audio quality by allowing sufficient amounts of damping material to mitigate the detrimental effects while still allowing practical bass reflex ports and allowing sufficiently small designs.
  • the depth of the acoustic damping material may advantageously also have suitable values relative to the size of the bass reflex port.
  • depth may advantageously also have suitable values relative to the size of the bass reflex port.
  • depth may advantageously also have suitable values relative to the size of the bass reflex port.
  • the cross-sectional area may be measured for a cross section perpendicular to the direction or axis of the bass reflex port.
  • the cross sectional area may typically be the smallest area for the free air flow channel that can be measured in any plane.
  • the free air flow channel defined by the damping material may have a diameter of 10 mm, corresponding to an area of 78.5 mm 2 .
  • the square root thereof is 8.86mm.
  • the damping material may often advantageously be between 0.9 mm and 4.4 mm.
  • the damping material is advantageously arranged to provide a bass reflex port that does not vary substantially along the longitudinal axis of the port.
  • the cross sectional area of the free air flow channel varies relatively little, and often advantageously less than 25%, or even 10%. This may often result in a more regular and homogeneous air flow thereby further reducing the risk of eddies and turbulence.
  • the cross sectional area it is not essential for the cross sectional area to remain relatively constant. Also, it is in many scenarios advantageous for the elongated bass reflex port to form a substantially straight free air flow channel.
  • the centroid of a cross sectional area of the free air flow channel may in many scenarios advantageously vary by less than 25% of the largest dimension of the cross section of the channel relative to a straight line. This may often result in a more regular and homogeneous air flow thereby further reducing the risk of eddies and turbulence.
  • the damping material forms substantially all of the inner surface. This may in many scenarios be advantageous and may result in a more regular and homogeneous air flow thereby further reducing the risk of eddies and turbulence.
  • the advantageous effect may in many scenarios be achieved by with only part of the inner surface being formed by the damping material.
  • a bass reflex port may be implemented by a solid air impermeable material.
  • a plastic pipe may be attached to the cabinet.
  • a pipe made from damping material may then be attached to the plastic pipe thereby creating a single port having a length corresponding to the combined lengths of the plastic pipe and the damping material pipe. This may e.g. allow a short pipe made from damping material to be used to provide a bass port which is longer than can be mechanically supported by the typical relatively soft damping material.
  • the part of the surface formed by the damping material is in many scenarios advantageously no less than 50%, 70%, 90%, or 95%
  • the bass reflex port may have any suitable dimensions and may for example in some embodiments be short and narrow or may be long and wide. Also, the shape and/or dimensions may be varied along the port. For example, a long port may be folded or the port may for example have a conical shape with an increasing (or decreasing) cross sectional area. The port may have any cross section and may for example have rounded edges in order to reduce turbulences.
  • the invention can be implemented in any suitable form.
  • the elements and components of an embodiment of the invention may be physically, functionally and logically implemented in any suitable way.
  • the present invention has been described in connection with some embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only by the accompanying claims. Additionally, although a feature may appear to be described in connection with particular embodiments, one skilled in the art would recognize that various features of the described embodiments may be combined in accordance with the invention. In the claims, the term comprising does not exclude the presence of other elements or steps.

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  • 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)

Abstract

L'invention porte sur un haut-parleur comprenant une enceinte acoustique (101) et un équipage mobile sonore actif (105) montée dans l'enceinte acoustique (101). Le haut-parleur comprend un port basse réflexe allongé (107) ayant une surface interne formant un canal d'écoulement d'air libre où au moins une partie d'une zone de la surface interne est formée par un matériau d'amortissement acoustique. La surface interne peut, de manière spécifique, être formée par un élément comprenant le matériau d'amortissement acoustique (205) et une paroi externe (207) formée par un matériau imperméable à l'air. Le matériau d'amortissement peut réduire les turbulences et les ondes stationnaires, permettant ainsi d'améliorer la qualité audio.
PCT/IB2011/055297 2010-12-15 2011-11-25 Haut-parleur WO2012080879A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
EP10195062.4 2010-12-15
EP10195062 2010-12-15

Publications (1)

Publication Number Publication Date
WO2012080879A1 true WO2012080879A1 (fr) 2012-06-21

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PCT/IB2011/055297 WO2012080879A1 (fr) 2010-12-15 2011-11-25 Haut-parleur

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WO (1) WO2012080879A1 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2523143A (en) * 2014-02-14 2015-08-19 Gb Acoustics Uk Ltd Loudspeaker bass reflex system
CN109314809A (zh) * 2016-07-07 2019-02-05 雅马哈株式会社 低音反射端口以及音响设备

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2852087A (en) * 1955-02-15 1958-09-16 Dolph W Ruschhaupt Sound reproducing devices
EP0361445A2 (fr) * 1988-09-28 1990-04-04 Yamaha Corporation Appareil acoustique
US5012890A (en) * 1988-03-23 1991-05-07 Yamaha Corporation Acoustic apparatus
US5333204A (en) * 1991-08-09 1994-07-26 Pioneer Electronic Corporation Speaker system

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2852087A (en) * 1955-02-15 1958-09-16 Dolph W Ruschhaupt Sound reproducing devices
US5012890A (en) * 1988-03-23 1991-05-07 Yamaha Corporation Acoustic apparatus
EP0361445A2 (fr) * 1988-09-28 1990-04-04 Yamaha Corporation Appareil acoustique
US5333204A (en) * 1991-08-09 1994-07-26 Pioneer Electronic Corporation Speaker system

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2523143A (en) * 2014-02-14 2015-08-19 Gb Acoustics Uk Ltd Loudspeaker bass reflex system
GB2523143B (en) * 2014-02-14 2021-04-28 Gp Acoustics Uk Ltd Loudspeaker bass reflex system
CN109314809A (zh) * 2016-07-07 2019-02-05 雅马哈株式会社 低音反射端口以及音响设备
US11240592B2 (en) 2016-07-07 2022-02-01 Yamaha Corporation Bass reflex port and acoustic device

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