Electrical audio signal processing systems and devices – Electro-acoustic audio transducer – Having acoustic wave modifying structure
Reexamination Certificate
1999-10-12
2001-11-27
Kuntz, Curtis (Department: 2643)
Electrical audio signal processing systems and devices
Electro-acoustic audio transducer
Having acoustic wave modifying structure
C381S345000, C381S348000, C381S351000, C381S353000, C181S151000, C181S160000
Reexamination Certificate
active
06324292
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a speaker apparatus capable of suppressing a standing wave in the cabinet of the speaker apparatus.
2. Description of the Related Art
As is well known, speaker units are acoustic transducers for emitting sound waves by vibrating diaphragms in response to electric signals (hereinafter called aural signals) carrying acoustic information. Such a speaker unit is rarely employed alone and it is usually fitted to a baffle plate in order to improve sound reproduction and used as a speaker apparatus.
Supposing the size of the baffle plate to which the speaker unit is fitted is unlimited, the interference of the sound wave emitted from across the diaphragm could be prevented completely. However, the speaker unit is actually fitted to a baffle plate of finite size.
The cabinet used in such a speaker is the one embodied therein. A baffle plate of finite size is generally used for one wall surface of a sealed-up or partially opened acoustic box.
FIG. 12
shows an example of a conventional speaker aparatus S showing one speaker unit fitted to a rectangular sealed-up cabinet.
As shown in
FIG. 12
, a speaker unit
102
is fitted to a baffle plate
101
a
of finite size formed on one side of a sealed-up cabinet
101
. The diaphragm of the speaker unit
102
is driven longitudinally by an aural signal supplied from an input terminal (not shown), whereby sound waves corresponding to the aural signal are emitted from the surface side (the external space side) of the diaphragm so as to effect acoustic reproduction.
As the internal space of the cabinet
101
is a finite space of a cube in this case, the sound wave emitted from the back (on the internal space side) of the diaphragm into the internal space of the cabinet is reflected from a back plate
101
b
opposite to the baffle plate
101
a
or a base plate
101
d
opposite to a top plate
101
c
and caused to produce standing waves with the opposing wall surface positions as nodes.
The standing wave produced between the wall surfaces at this time includes a higher mode corresponding to a resonance frequency n times (n=positive integer) as great as the lowest resonance mode in addition to a standing wave (the lowest resonance mode) having a wavelength equivalent to what is substantially twice as great as the distance between the wall surfaces.
FIG. 12A
shows the lowest resonance modes
103
and
104
out of the standing waves respectively produced between the top plate
101
c
and the base plate
101
d
and between the baffle plate
101
a
and the back plate
101
b
in the cabinet
101
, and
FIG. 12B
shows higher modes
103
a
and
104
a
respectively having resonance frequencies twice as great as the lowest resonance modes out of the standing waves thus produced, that is, having a wavelength half as short as the lowest resonance mode.
These standing waves produced within the cabinet
101
function as those which impair the movement of the diaphragm of the speaker unit
102
, which constitutes a primary factor of deteriorating the quality of the sound reproduced by the speaker apparatus S.
Consequently, various contrivances have heretofore been made to ease the standing waves produced in a cabinet as much as possible as shown by examples of speaker apparatus in
FIGS. 13A
to
13
C.
More specifically, the sound pressures of the standing waves have been attenuated by mounting an acoustical material
105
such as glass wool on the inner wall surface of the cabinet
101
as shown in FIG.
13
A. The standing waves within the cabinet
101
have also been suppressed as much as possible by mounting a Helmholtz resonator
106
exhibiting resonance at a particular frequency on the inside of the cabinet
101
as shown in
FIG. 13B
or otherwise using a cabinet
107
having an irregular shape in place of the cubic cabinet
101
so as to eliminate the parallel wall surfaces as shown in FIG.
13
C.
In order to satisfactorily attenuate the sound pressures of the standing waves produced in the cabinet
101
by mounting the acoustical material
105
on the inner wall surface of the cabinet
101
, however, a considerable amount of acoustical material
105
needs using and as this results in increasing the acoustic resistance, the lower register would be absorbed too.
Though the helmholtz resonator
106
acts on a standing wave at the specific wavelength generated in the cabinet, for example, because it has the effect of absorbing sound at a single resonance frequency, it will not effectively act on a standing wave having any other wavelength.
Moreover, the use of the cabinet
107
having an irregular shape tends to make the speaker apparatus complicated in structure and costly and furthermore to restrict its designing.
SUMMARY OF THE INVENTION
An object of the present invention made in consideration of the foregoing problems is to provide a speaker apparatus which is quite simple in structure and capable of satisfactorily suppressing standing waves in a cabinet.
A speaker apparatus according to a first aspect of the invention comprises a speaker unit, a cabinet for forming an internal space on the rear side of the speaker unit with a plurality of wall surfaces including a baffle plate for use in mounting the speaker unit, a acoustic tube which is formed along at least one wall surface out of the plurality of wall surfaces and has not only a substantially uniform hollow section but also an opening at one end, and an acoustical material for separating the internal space from the internal space of the acoustic tube by closing the opening of the acoustic tube, wherein the acoustic tube has a tube length about 1/(2n) (n=positive integer) time as large as a wavelength corresponding to the lowest resonance mode of the standing wave produced along the one wall surface out of the standing waves produced in the internal space and that the opening is disposed close to the node of the standing wave.
According to a second aspect of the invention, in the speaker apparatus of the first aspect, the wall surface of the acoustic tube constitutes at least part of the wall surface belonging to an acoustic path formed in the internal space.
According to a third aspect of the invention, in the speaker apparatus of the first aspect, at least part of the acoustic tube constitutes a reinforcing material for reinforcing the structure of the cabinet.
According to the invention, even though a standing wave is produced in the internal space of the cabinet when the speaker unit is driven to operate, the standing wave is satisfactorily suppressed because the acoustic tube attenuates and absorbs the standing wave by performing tube resonance together with using the acoustical material fitted to the acoustic tube so as to negate the standing wave.
REFERENCES:
patent: 1901388 (1933-03-01), Wolff
patent: 3680658 (1972-08-01), Goeskel
patent: 4837837 (1989-06-01), Taddeo
patent: 4889208 (1989-12-01), Sugihara
patent: 5333204 (1994-07-01), Hamada et al.
Hamada Hiroyuki
Mitsuhashi Takashi
Kuntz Curtis
Ni Suhan
Pioneer Corporation
Sughrue Mion Zinn Macpeak & Seas, PLLC
LandOfFree
Speaker apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Speaker apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Speaker apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2581541