GB2480226A

GB2480226A - Active bass loudspeaker acoustic loading system

Info

Publication number: GB2480226A
Application number: GB201002656A
Authority: GB
Inventors: Randall Decourcy Hewitt
Original assignee: Individual
Current assignee: Individual
Priority date: 2010-02-17
Filing date: 2010-02-17
Publication date: 2011-11-16
Anticipated expiration: 2030-02-17
Also published as: GB2480226B; GB201002656D0

Abstract

The loudspeaker comprises a front loading acoustic chamber 10 which contains an acoustic loading member 4 that is supported by spacers 5 on the front baffle 9. One wall of the chamber is formed by the diaphragm of the bass loudspeaker 1. The diaphragm of the bass loudspeaker 1 is flat-faced because it has a more effective acoustic front loading surface than a conical loudspeaker diaphragm. Front baffle 9 has an exit port 6 located on the centre of the bass loudspeaker 1. The spacers 5 allow sub bass sound to pass into the exit port of the front baffle. The exit port is connected to an acoustic loading channel 7 which has a wide input area and a narrower exit vent 8 for the sub-bass sound output. The back acoustic loading for the bass loudspeaker is provided by an acoustic suspension chamber 11.

Description

[0001] Active Bass Loudspeaker System

[00021 Background

[0003] There are many challenges in designing a compact sub bass loudspeaker endosure to do with controlling the excursions of the loudspeaker diaphragm so that the electncal signal to its voice coil is correctly converted into sound waves. The popular compact bass reflex endosure operating at normal domestic power levels reproduces only a small amount of sub bass heard through the bass reflex port because it is out of phase with sound from the front of the bass loudspeaker and there is a loss of power throughout the enclosure. This means that sub bass is only heard close up to the bass reflex port. The problem is made worst through the loss of acoustic loading resistance at frequencies that are lower than a bass reflex endosur&s peak resonance and the result is distorted sub bass frequencies from the bass reflex port.

[0004] Besides the rapid fall off in audible sound at frequencies below the endosure peak resonance there is also the production of high levels of unwanted colouration from inside the enclosure that radiates through the normal light weight horn shaped loudspeaker diaphragm. The popular compact bass reflex design does not reproduce sub bass frequencies efficiently at domestic listening levels.

[0005] There is an urgent need for a more efficient compact sub bass loudspeaker system as an alternative to the popular but poor performing bass reflex design found in the average size dwelling.

[0006] There is furthermore the need for a compact sub bass loudspeaker system that maintains its efficiency as the input power level is reduced according to the requirements of the listening environment.

[0007] Statement of Invention

[0008] This invention relates to an Active Front and Back Acoustic Loading Sub Bass Loudspeaker System. It is designed to reproduce very low frequency audio (sub bass) sound with greater efficiency, less distortion and colouration whilst using a compact size enclosure.

(0009] The bass loudspeaker is powered by a sub bass amplifier which has a frequency range that extends lower than the enclosure's peak resonant frequency.

[00101 Many of the shortcomings of the popular bass reflex design can be largely overcome by the use of a front loading acoustic chamber design with a front loading acoustic channel and a back loading acoustic chamber. The benefit is that the bass loudspeaker diaphragm has proper acoustic loading resistance to front and back surfaces during forward and backward excursions. There is a further benefit of resonance damping because of compression loading to the moving front and back surfaces. Another benefit is less distortion of the electrical signal because the flat face bass loudspeaker is able to follow long wavelength linear excursions and therefore reproduce sub bass sound more faithfully and with greater efficiency. Sub bass output from this invention is more efficiently reproduced and therefore more audible at low listening levels.

[00111 This is because there is much less phase cancellation or sound output imbalance caused by the sub bass output having to compete with higher frequencies and colouration from the same loudspeaker.

[0012] The use of a sealed back loading acoustic chamber gives the benefit of a greater degree of sub bass extension below enclosure peak resonant frequency.

[00131 The combined effect of the front loading acoustic chamber, acoustic loading member and the acoustic loading channel gives defined front loading acoustic resistance to the bass loudspeaker that is comparable to the back loading acoustic resistance provided by the sealed back loading acoustic chamber. Combined front and back acoustic loading keeps control of the flat face bass loudspeaker as it traces the long wavelength signals and this gives the benefit of lower distortion or colouration at sub bass frequencies.

[0014] A sub bass amplifier is used to reinforce a frequency range below the enclosure peak resonance and therefore enhance the ability of the invention to reproduce sub bass frequencies in that range. The amount of reinforcement can be adjusted to produce a balance across the audio spectrum when used as part of a domestic hi fi system.

[0015] When the Active Front and Back Acoustic Loading Sub Bass Loudspeaker System is compared with a reflex enclosure at frequencies below their respective enclosure peak resonance the efficiency of the front and rear loading technique is much higher and there is less distortion than from the port of a bass reflex design.

[0016] Several prototype flat face bass loudspeakers have been made and they have proved durable and the system has proved successful in trials.

[0017] The enclosure has been made using readily available materials and the present embodiment could be used to reproduce strong sub bass output with much lower distortion and colouration than bass reflex audio hi fl systems.

[0018] The invention could be made to reproduce higher powered sub bass output whilst maintaining the principal features of this Active Front and Back Acoustic Loaded Sub Bass Loudspeaker System.

[0019] The external recess in the front of the enclosure could be used to mount the sub bass amplifier electronic parts.

[0020] Detailed Description

[0021] An example of the invention will now be described by referring to the accompanying drawings at figure 1 and 2.

[0022] The Active Front and Back Acoustic Loading Sub Bass Loudspeaker Enclosure and Flat Face Bass Loudspeaker are shown in figure 1. The flat face bass loudspeaker I has a more effective front acoustic loading surface than the normal horn shaped loudspeaker diaphragm. The flat face bass loudspeaker is secured to a raised mounting frame to form the front loading acoustic chamber 10. The front loading acoustic chamber contains a separate acoustic loading member 4 mounted in dose proximity to the flat face of the bass loudspeaker and it is supported by spacers 5 that secure it to a front baffle 9. The front baffle 9 covers the front loading acoustic chamber and has an exit port 6 located central to the flat face bass loudspeaker.

[0023] The spacers allow sub bass sound to pass into the exit port 6 of the front baffle. The exit port in the front baffle is connected to an acoustic loading channel 7 which is designed with a wide input area and a narrower exit vent 8 for the output of sub bass sound. The tapered design of the front acoustic loading channel 7 gives additional front loading to the flat face bass loudspeaker I and gives the benefit of lowering the system's peak resonance. It also greatly reduces turbulence by restricting the re-entry of reflected sound waves from outside the endosure.

[0024] The back acoustic loading for the flat face bass loudspeaker is provided by a back loading acoustic chamber 11 which is designed to have a peak internal resonance that is selected with regards to the free air resonance of the flat face bass loudspeaker and the frequency range of the sub bass amplifier all of which determine the overall frequency range of the complete Active Front and Back Acoustic Loading Sub Bass Loudspeaker System.

[0025] The front and back acoustic loaded flat face bass loudspeaker I is powered by a sub bass amplifier that produces an input which is limited to the maximum power rating for the Active Front and Back Acoustic Loading Bass Loudspeaker System.

[0026] Greater efficiency reduces the excursions of the flat face bass loudspeaker resulting in less energy being transferred to the rest of the endosure structure and this allows for a lighter endosure construction material.

[0027] The recessed space 12 to the front of the cabinet can be used to house the sub bass amplifier electronic parts.

Claims

Claims 1. The Active Front and Back Acoustic Loading Sub Bass Loudspeaker System consist of a Loudspeaker Enclosure that has a front loading acoustic chamber which contains a separate acoustic loading member mounted on spacers The front loading acoustic chamber is enclosed at its rear by a fiat face bass loudspeaker on a mounting frame and that same chamber is endosed to the front by a front baffle The front baffle has an exit port located on the central line of the fiat face bass loudspeaker and that same port is connected to an acoustic loading channel that has an exit vent for sub bass sound output The Loudspeaker Enclosure has an air tight back loading acoustic chamber The assembled enclosure is effective in damping its internal resonances by balancing the acoustic load resistance to forward and backwards excursions of the flat face bass loudspeaker.
2. The flat face bass loudspeaker according to claim I has an effective front acoustic loading surface for compressing air against the separate front acoustic loading member according to claim I that is mounted in close proximity to the fiat face bass loudspeaker according to claim I The separate front acoustic loading member according to daim I is effective in damping the flat face bass loudspeaker free air resonance and greatly reducing the amount of unwanted colouration that would otherwise pass into the exit port in the baffle according to claim 1 The benefit is of greater efficiency that reduces the excursions of the flat face bass loudspeaker according to claim I resulting in less energy being transferred to the rest of the endosure structure according to claim I and this allows for a lighter enclosure construction material.
3. The separate acoustic loading member according to claim I situated in dose proximity to the fiat face of the bass loudspeaker according to claim I gives the benefit of much higher efficiency because of improved acoustic resistance loading that results in a higher output at the exit vent according to claim I even when the bass loudspeaker is driven at low input power levels as found in domestic hi ti systems.
4. The spacers according to claim I allow sub bass sound to pass into the exit port according to claim I of the front baffle.
5. The exit port in the front baffle according to claim I is connected to an acoustic loading channel according to daim I which is designed with a wide input area and a narrower exit vent according to claim I for the output of sub bass sound
6. The design of the acoustic loading channel according to claim I gives additional front loading to the flat face bass loudspeaker according to claim I and lowers the enclosure peak resonant frequency The acoustic loading channel according to claim I greatly reduces turbulence by restricting the re-entry of reflected sound waves from outside the enclosure according to daim 1 The acoustic loading channel according to claim I also lowers the combined resonant frequency of the sealed rear cavity according to claim I and the flat face bass loudspeaker according to claim I and gives the benefit of a broader and flatter sub bass frequency response range.
7. The back loading acoustic resistance for the bass loudspeaker according to claim I is provided by a sealed back loading acoustic chamber according to claim 1 that is designed to have a known peak internal resonant frequency which together with the selected free air resonant frequency of the flat face bass loudspeaker and the frequency range of a sub bass power amplifier all together determine the frequency range of the complete Active Front and Back Acoustic Loading Sub Bass Loudspeaker System according to claim I When sub bass output at the same low power input level is compared with a reflex enclosure, the efficiency of the Active Front and Back Acoustic Loading Sub Bass Loudspeaker system according to claim us much higher than from the port of a bass reflex design The resulting sub bass output is clearer and well damped.
8. The Active Front and Back Acoustic Loading Sub Bass Loudspeaker System according to claim I is driven by a sub bass power amplifier according to daim 6 which provides an input that is used to reinforce the bass frequencies that are lower than the peak resonant frequency of The Active Front Loaded Sub Bass Loudspeaker System according to daim I The sub bass amplifier can be mounted in the recess to the front of the cabinet
9. The Active Front and Back Acoustic Loading Sub Bass Loudspeaker System according to claim I gives the benefit of much higher efficiency because of improved front and back acoustic resistance loading that results in a higher output at the exit vent according to daim I, even when driven at low input power levels as in domestic hi fi systems The combined front and back acoustic resistance loading keeps control of the fiat face loudspeaker according to claim I as it traces the long wavelength signals giving the benefit of much less distortion of sub bass frequencies below endosure peak resonance.
10. The present embodiment shown in figure 1 and 2 is designed to reproduce strong sub bass output with low distortion or colouration as part of a hi fi audio system
11. This invention could be made to reproduce higher powered sub bass output and would still maintain the principal design of this Active Front and Back Acoustic Loading Sub Bass Loudspeaker System The external recess in the front of the endosure could be used to mount the sub bass amplifier electronic parts.
12. Several fiat face bass loudspeakers according to claim I have been made and the prototypes have proved durable and the Active Front and Back Loading Sub Bass Loudspeaker System to claim I has been successfully on thaI.
13. The Active Front and Back Acoustic Loading Sub Bass Loudspeaker System according to claim I has been made using readily available materials.