Acoustics – Plural diaphragm sound sources – Plural chambers
Reexamination Certificate
1995-12-19
2001-05-01
Gray, David M. (Department: 2851)
Acoustics
Plural diaphragm sound sources
Plural chambers
C181S148000, C181S155000, C181S160000, C181S199000
Reexamination Certificate
active
06223853
ABSTRACT:
The present invention relates to a loudspeaker system incorporating one or more acoustic filters, in particular waveguide filters, and to a method of construction thereof.
The term waveguide originates from general Electromagnetic wave theory wherein it describes the general form of a bounded region for guided propagation of waves. This general electromagnetic case and the acoustic case considered herein are analogous.
The present invention is restricted to the dominant mode of propagation of sound waves and therefore the filter sections could alternately be referred to as transmission line sections, as the mode of propagation obeys frequency independent phase velocity (analogous to Transverse Electro Magnetic (TEM) modes in waveguides).
However, the term transmission line in audio parlance has become associated with particular enclosure designs wherein heavy loss is introduced for one side of the transducer. The common use of the term transmission line is thus no longer understood to relate to supporting a mode of propagation over the frequency range as is the case with the electromagnetic domain. Hence the term acoustic waveguide is used herein in preference.
There are many applications for acoustic filters and the techniques described herein are relevant to many of them. Accordingly, although the present invention is described herein in relation to and in the context of loudspeaker systems, it is to be appreciated that it is not thereby limited to such applications.
Loudspeaker systems include a combination of one or more electro-acoustic transducers or drivers together with a partial or complete enclosure (referred to herein as an enclosure) and may be categorized by the nature of their frequency response when driven from a constant amplitude sinusoidal voltage source. Closed or sealed enclosures, also known as infinite baffle or acoustic suspension enclosures, provide high pass systems with second order roll off at relatively low frequencies. Vented enclosures, also known as bass reflex or Helmholtz resonator enclosures, provide high pass systems with fourth order roll off. Conventional closed/vented or double vented enclosures provide bandpass systems having an additional second order roll off at relatively high frequencies. Variants of these basic enclosures have been proposed which use additional chambers and/or additional vents between chambers and/or folded ducts exiting internally or externally.
Many attempts have been made over the last seventy years to construct low frequency loudspeaker systems with optimum performance subject to various physical constraints. The most sophisticated prior art loudspeaker designs are based on techniques which utilize lumped component equivalent circuits. All of the categories of enclosures described above can reasonably be modelled with lumped equivalent circuits. However, these models are restricted in usefulness to special cases. One known design disclosed by Schreiber in U.S. Pat. No. 5,092,424 incorporates a multi-chamber enclosure. However, the latter system still only employs one resonance per chamber and has attendant space utilization problems.
A disadvantage of prior art lumped equivalent circuit modelling techniques is that they fail to assist designers to recognize or exploit the benefits of undamped waveguides or waveguide sections in the design of acoustic filters.
An object of the present invention is to provide an improved method of constructing a loudspeaker system. The method of the present invention includes a relatively sophisticated modelling technique which may assist designers to recognize and exploit a more diverse range of acoustic elements including elements having predominantly distributed natures.
A further object of the present invention is to provide an improved loudspeaker system and in one embodiment a loudspeaker system having improved acoustical response for reproducing frequencies at the low end of the audible/infrasonic spectrum.
It has long been understood that selected multiple resonances are a means of improving performance in loudspeakers. The problem has been that the obvious means of providing multiple resonances namely by adding resonators has consequent cost, space and complexity problems and in any case provides only one beneficial resonance per resonator in the pass band, this resonance being the fundamental resonance for that resonator.
The present invention addresses these limitations by utilizing as a filter at least one acoustic waveguide or waveguide section. A waveguide or waveguide section may be arranged to provide a plurality of resonances. Significantly the resonances may be non-fundamental resonances. The resonances also may be substantially undamped i.e. the may not require damping. The present invention also provides a technique for beneficially selecting and methodically placing such resonances to shape the response of the filter. The filter may be adapted to improve flexibility in alignment of response characteristics of a loudspeaker system and/or to enhance performance of the system. The filter may be integrally built into the loudspeaker system or otherwise attached thereto.
Whilst it is not possible to say with absolute certainty that prior art loudspeaker enclosure designs (especially those which were experimentally derived) have not accidentally incorporated a non-fundamental resonance in one of its air paths for a beneficial result, applicant is not aware of any prior art enclosure designs that have consistently incorporated substantially undamped non-fundamental resonances in a methodic way or that have optimally placed a single non-fundamental resonance to maximum benefit. To applicants best knowledge, in no prior art enclosure designs has placement of non-fundamental resonances been a cause of improved performance over conventional methods and no designer has to date deliberately designed non-fundamental resonances into enclosures.
As indicated above a variant of prior art designs has been the addition of folded ducts, sometimes called “transmission lines” or “quarter wave labyrinths”. Although the latter terms are borrowed from transmission line theory they are not the result of any generalised modelling technique as is the case in the present invention and do not incorporate the advantages offered by the present invention. On the contrary prior art transmission lines are designed to be deliberately highly absorptive, lossy and of low efficiency. Any non-fundamental resonances which may exist are so heavily damped that labyrinthine ducts are regarded as one of the least resonant enclosures known. In contrast an important feature of the present invention is the use of waveguide filter sections which are substantially reactive, undamped, low loss and therefore high efficiency.
Conventional acoustic horns have also been used as filters as they provide certain advantages over other designs in controlling the behaviour of drivers. Finite acoustic horns represent a monotonically increasing cross section filter, which limits their usefulness for low frequency applications where impractical dimensions are required for effective horn loaded operation. Some instances have achieved limited compaction by the use of folded horn configurations but size is still a limitation. The present invention provides an alternative to conventional horn design with potentially improved and more compact design characteristics by the use of waveguide filter sections.
The present invention provides a new and fundamentally more accurate method for modelling and constructing acoustic filters. The method of the present invention differs from previous modelling methods in that it allows recognition of filter elements that are predominantly distributed in nature and their beneficial incorporation into the design. This may be achieved by treating appropriate components as waveguide filter sections defined by characteristic impedance and length and analysing the components accordingly.
The above approach may provide a suffficiently accurate analysis to allow controlled utilization of non-fundament
Cambrell Gregory Keith
Dower Walter Melville
Huon Graeme John
Gray David M.
McDermott & Will & Emery
LandOfFree
Loudspeaker system incorporating acoustic waveguide filters... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Loudspeaker system incorporating acoustic waveguide filters..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Loudspeaker system incorporating acoustic waveguide filters... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2503206