Abstract: Acoustic waveguides can be used to improve audio performance of playback devices, such as a soundbar. Such a playback device can include an elongated body defining an outer perimeter with a forward surface, an upper surface, and a rounded edge between the forward surface and the upper surface. An up-firing transducer is configured to direct sound along an axis that has a vertical oblique angle with respect to a forward axis. A waveguide in fluid communication with the up-firing transducer includes a sidewall extending circumferentially around the transducer, the sidewall having a first end adjacent the up-firing transducer and a second end adjacent the outer perimeter, such that an opening defined by the sidewall has a larger area at the second end than at the first end. A rear portion of the sidewall is more steeply angled with respect to the axis than a forward portion of the sidewall.

Abstract: An earphone has a housing with a signal process unit to output sound. The housing has a chamber and a speaker mounted inside the chamber. The chamber is defined as a front volume and a rear volume by the speaker, and the rear volume having a port. Wherein the speaker in the volume outputting a chamber frequency response curve is at least a portion higher than the earphone's ideal frequency response curve at the bandwidth ranging from 20 Hz to 1000 Hz, where creates a gain difference between the chamber frequency response curve and the ideal frequency response curve to be decreased the (superfluous) positive value by a signal process unit at the bandwidth ranging from 20 Hz to 1000 Hz. Therefore, the total acoustic energy is maintained, the earphone acoustic quality is preserved, and the earphone volume may output even higher power to be deduced by the signal process unit for lowering down the circuit power consumption.

Abstract: Embodiments of the present invention are directed to security systems for securing an item of merchandise from theft or unauthorized removal. For example, the security system may include a sensor configured to be coupled to the item of merchandise and a base configured to removably support the sensor and the item of merchandise thereon. The base includes a sidewall and a bottom surface, and the sidewall defines an opening. The security system also includes an alarm configured to generate sound in response to a security event. The alarm includes a sound chamber configured to direct sound exiting the sound chamber towards the opening in the sidewall.

Abstract: An arrayable loudspeaker (11) has at least one high frequency driver (39) mounted to a horn (37) and at least one pair of low frequency drivers (41) configured behind and in a closely spaced relationship to the horn to form low frequency side chambers (71) between the drivers and the horn from which acoustic energy produced by the low frequency drivers can propagate. Low frequency exit channels (77) above and below the horn are coupled to the low frequency side chambers (71). The configuration of the horn and low frequency drivers and the low frequency side chambers and low frequency exit channels is such that acoustical outputs of all drivers radiate coaxially from the loudspeaker with substantially constant wide beamwidth in the non-arraying plane. Signal processing can be added to enhance beamwidth control critical frequency ranges above crossover.

Abstract: A non-reciprocal acoustic device that accomplishes non-reciprocity via linear or angular-momentum bias. The non-reciprocal acoustic device includes an azimuthally symmetric or planar acoustical cavity (e.g., ring cavity), where the cavity is biased by imposing a circular or linear motion of a gas, a fluid or a solid medium filling the cavity. Acoustic waveguides are connected to the cavity or the cavity is excited from the surrounding medium. A port of this device is excited with an acoustic wave. When the cavity is biased appropriately, the acoustic wave is transmitted to one of the other acoustic waveguides while no transmission of the acoustic wave occurs at the other acoustic waveguides. As a result, linear non-reciprocity is now realized in acoustics without distorting the input signal or requiring high input power or bulky devices.

Abstract: Provided are a sound amplification box and a sound amplification device. The sound amplification box includes a body including a predetermined resonance space therein and having a surface contacting an electronic device, a resonance hole formed in at least one surface of the body, and a vibration transmission part in a predetermined region of the surface contacting the electronic device.

Abstract: An amplifying cover for an audio device that enhances the audio output of the device, such as voice or music, louder and clearer, without adding to the bulk of the device. The cover redirects the audio output of the device to a different location that enhances the ergonomics of the device. The amplifying cover can redirect the sound (while also amplifying it) to the top of the device, closer to the user's ear, or to the side of the device. The amplifying cover can redirect the sound to a plurality of different directions, making it easier to make conference calls. The cover is a protective case for an electronic device that also amplifies the sound produced by the electronic device. The cover provides a portable and compact acoustic amplifier for an electronic device that can be permanently or semi-permanently attached to the electronic device.

Abstract: A phasing plug for a compression driver includes a base portion and a hub portion. The base portion includes a first side, a second side, and a plurality of apertures extending between the first and second sides. The hub portion extends from the base portion along an axis. The hub portion includes an outer surface and a plurality of ribs disposed on the outer surface. A plurality of recesses are defined by the outer surface and respective pairs of adjacent ribs. At least one aperture fluidly communicates with at least one of the recesses.

Abstract: A high frequency horn for use in a multiple frequency loudspeaker system having a midrange transducer and a high frequency transducer is disclosed. The high frequency horn includes a horn chamber, horn mouth, a horn throat, a tuned resonant cavity, and a port connected to both the tuned resonant cavity and the horn chamber. The horn throat and horn chamber are located on opposite sides of the horn chamber, the port is located proximate to the horn throat, and the horn throat is configured to be connected to the high frequency transducer. The tuned resonant cavity is tuned to reduce high frequency standing waves produced by the midrange transducer within the horn chamber.

Abstract: A mobile communication device is provided. The mobile communication device includes a terminal body, and a speaker module located in the terminal body. The speaker module includes an enclosure located in the terminal body, the enclosure defining a chamber therein, and a speaker having a front surface and a rear surface, the speaker being located in the enclosure such that the front surface of the speaker is exposed from the enclosure and the rear surface thereof is positioned within the chamber, to allow a sound generated from the rear surface to resonate within the chamber. A mutual interference between the sound generated from the front side of the sound emission part and the sound emitted from the rear side thereof can be reduced to thereby improve the performance of the middle and low sound.

Abstract: An electrical horn includes a horn housing, an oscillation member located at the horn housing to generate a sonic wave, and a resonance tube in which the sonic wave generated by the oscillation member flows. In the electrical horn, the resonance tube has a plurality of sonic outlet portions that are open in different directions. Accordingly, when the electrical horn is mounted to a vehicle, it is possible to reduce an amount of foreign material entering into the resonance tube while increasing a sonic pressure toward a vehicle front side.

Abstract: A computer system may include a keyboard housing that is capable of being moved at least partially into or out of a chassis. The chassis is associated with a transducer and an air chamber. Movement of the keyboard housing may cause size of the air chamber to be adjusted. When the size of the air chamber is increased, the transducer becomes more sensitive to sound in lower frequency ranges.

Abstract: An electroacoustic system includes a transducer having a front volume and a back volume. The transducer has a sound inlet port that is in communication with the front volume. An acoustic coupling is joined to the transducer. The acoustic coupling has a passageway comprising a first end and a second end. The second end is acoustically coupled to the sound inlet port for altering the peak frequency response of the transducer.

Abstract: A method and system for reducing noise associated with an internal combustion engine comprises operating an engine at an initial speed. An exhaust system has a resonant cavity to attenuate exhaust noise. A microphone detects a sound level at or near an exhaust system of the engine operated the initial speed. A controller controls or adjusts the initial speed to a revised speed if the detected sound level does not meet or fall below a desired sound level.

Abstract: The invention relates generally to the field of audio loudspeaker enclosures, and more particularly to a method of mounting the internal components in the loudspeaker so as to control the loudspeaker output. Specifically a mounting structure and method for mounting the loudspeaker horn to its associated compression driver are disclosed. The mounting structure allows the directivity of the loudspeaker output, and the frequency/phase control of the loudspeaker, output to be controlled by the spatial arrangement of these components in the loudspeaker enclosure.

Abstract: A method for displaying horizontally aligned characters on a radial display is disclosed. Each range bin for each scan line is associated with a rectangular grid location to determine the character located in the grid location and the background color and foreground color for the grid location. A font matrix corresponding to the appropriate character is then used to determine if the range bin corresponds to one of the pixels that make up the character or if the range bin corresponds to a background pixel. This determines if the range bin is assigned the foreground color or background color. The method is done for each range bin value and for each scan line. The range bin and scan line information is sent to a display.

Abstract: A module adapted for use in a noise reduction headset earcup has an enclosure having walls separating an interior of the enclosure from an exterior of the enclosure outside the earcup. There is a driver with a diaphragm. A port connects the interior and exterior. An acoustically resistive opening connects the interior and exterior in parallel with the port.

Abstract: A speaker has a very small size and is arranged to emit sound waves in a non-directional manner. The speaker includes a case and a speaker unit attached to a plate provided at an opening of the case. The speaker is arranged so that the speaker unit is mounted or attached to a floor or support surface such that a space formed by the case, the plate and the speaker unit is airtight and so that the back-and-forth motion of a vibrator of the speaker unit generates expansion and contraction of the case.

Abstract: A speaker device includes an acoustic capacity unit; an acoustic pipe connected to the acoustic capacity unit; and a driving speaker attached to the acoustic capacity unit. The acoustic capacity unit and the acoustic pipe constitute the Helmholtz resonator, and resonate at a predetermined Helmholtz resonant frequency. On the other hand, the acoustic pipe itself has a resonant frequency. By setting the resonant frequency of the acoustic pipe to be 0.5 to 2.5 octaves higher than the Helmholtz resonant frequency, the speaker device can be obtained which outputs signals of continuous frequency band from the Helmholtz resonant frequency to the resonant frequency of the acoustic pipe.

Abstract: The invention features an acoustic waveguide and system for transmitting pressure wave energy produced by an electroacoustical transducer in a medium that propagates pressure wave energy. The acoustic waveguide and system includes a tube defining a spiral-shaped channel with a length of L. The tube has a first end and a second end with the first end closed and the second end open to the medium. The tube has a transducer opening for accommodating an electroacoustical transducer located between the first and second end of the tube. The system includes an electroacoustical transducer mounted to the acoustic waveguide.

Abstract: The invention relates generally to the field of audio loudspeaker enclosures, and more particularly to a method of mounting the internal components in the loudspeaker so as to control the loudspeaker output. Specifically a mounting structure and method for mounting the loudspeaker horn to its associated compression driver are disclosed. The mounting structure allows the directivity of the loudspeaker output, and the frequency/phase control of the loudspeaker, output to be controlled by the spatial arrangement of these components in the loudspeaker enclosure.

Abstract: A loudspeaker system containing wave-shaping sound chambers with approximately rectangular inlets and outlets of substantially the same size that are used to flatten or control the curvature of the acoustic wavefronts contained within system waveguides. Control of the degree of curvature of the wavefront enables the development of a wide variety of multi-waveguide arrays. The sound chambers are placed between a waveguides and a flattened conical horns of secondary waveguides. The sound chambers transform the curvature of the typical fan shaped wavefront that results from a conical horn throat into a wavefront that approximates a planar or curved rectangular ribbon of sound.

Abstract: A reduced-size speaker for generating sound waves in wide low frequency audio region includes a cylindrical main body which is open at the top and bottom surfaces, a top lid being provided on the top surface of the main body and a circular ring-shaped base, which has a hole in its center, being provided on the bottom surface of the main body. A circular sound pipe is provided approximately in the center of the top lid and extends from the upper surface of the main body through the inside of the main body. A disc-like film is provided over the opening of the hole of the base, which is located at the outer side with respect to the main body, the disc-like film being held between the base and a circular ring-shaped bottom lid. A disc-like sound generator is provided in the opening of the hole of the base, which is located at the inner side with respect to the main body, with a circular ring-shaped damper provided in between.

Abstract: A speaker has a very small size and is arranged to emit sound waves in a non-directional manner. The speaker includes a case and a speaker unit attached to a plate provided at an opening of the case. The speaker is arranged so that the speaker unit is mounted or attached to a floor or support surface such that a space formed by the case, the plate and the speaker unit is airtight and so that the back-and-forth motion of a vibrator of the speaker unit generates expansion and contraction of the case.

Abstract: A loudspeaker enclosure having an improved full range driver and an improved enclosure assembly.

Abstract: The sonic soot blower includes a sonic wave oscillator that oscillates sonic waves by compressed air or steam, a frequency-regulating portion that varies the frequencies of the sonic waves oscillated by the above-described sonic wave oscillator, a resonance tube that resonates the oscillated sonic waves, and a horn that amplifies the same, wherein powdery dust adhered to members installed inside a boiler furnace, etc., are removed, and are prevented from adhering to the above-described members. The above-described frequency-regulating portion is a gas mixer which is connected to the upstream side of the sonic wave oscillator and is provided with two or more gas conducting flow channels for conducting a compressive gas whose temperatures and/or densities are different from each other, or a slide mechanism that varies the length of the above-described resonance tube.

Abstract: The invention relates to a horn loudspeaker system. The horn loudspeaker system includes a pair of vertically displaced horns with cross-fired aiming angles. A common throat section couples the horns to a driver. A substantially asymmetrical baffling is incorporated into the loudspeaker system to further improve the acoustic performance. One advantage of the unique horn loudspeaker system is that it provides a wide horizontal directivity response. Another advantage is that it provides a narrow vertical directivity response.

Abstract: A loudspeaker system containing wave-shaping sound chambers with approximately rectangular inlets and outlets of substantially the same size that are used to flatten or control the curvature of the acoustic wavefronts contained within system waveguides. Control of the degree of curvature of the wavefront enables the development of a wide variety of multi-waveguide arrays. The sound chambers are placed between a waveguides and a flattened conical horns of secondary waveguides. The sound chambers transform the curvature of the typical fan shaped wavefront that results from a conical horn throat into a wavefront that approximates a planar or curved rectangular ribbon of sound.

Abstract: An audio apparatus for an equipment relates to an improvement of the sound quality in an acoustic apparatus of the equipment in which for an equipment having a woofer (4) and a tweeter (5), the acoustic apparatus (10) of the equipment includes a panel portion (3) which forms a part of a casing (2) of the equipment and has a plurality of holes (H), a sound conductor (8) which is arranged between the woofer (4) and the panel portion (3), and a buffer member (9) which is provided between the sound conductor (8) and the panel portion (3) and absorbs any woofer vibration.

Abstract: An animal call device includes a sound generator part and a sound amplifier part preferably directly connected to the sound generator part for producing an amplified and reverberating or echo-like animal call signal. The sound generator part includes a mouthpiece and a vibrating reed for producing staccato so-called grunt-like acoustic vibrations, particularly for attracting deer and similar mammals. A sound emitter member of the sound generator part is connected directly to a housing for the sound amplifier part which supports, in one embodiment, two spaced apart flexible diaphragms interconnected by a tension coil spring to produce complex echo-like amplified sounds. An alternate embodiment includes a single flexible diaphragm connected to a tension coil spring and supported in a frusto-conical housing for amplifying and modifying the staccato grunt signals produced by the sound generator part.

Abstract: A loudspeaker horn has straight wall section and a curved wall section. The straight wall section has diverging walls defining a coverage angle and the curved wall portion is connected to the straight wall portion at a point tangent thereto, and has a proximal end disposed perpendicular to the plane of the throat entrance. At least one coverage angle in orthogonal planes has a common apex in the plane of the throat entrance and along the horn axis.

Abstract: Aqueous solutions of N-methylol compounds of carboxamides, urethanes, ureas and aminotriazines or of N-methylol ethers of these compounds that are suitable for finishing cellulose-containing textile materials are prepared by reaction of compounds having one or more N--H groups in aqueous solution with formaldehyde and, in the case of N-methylol ethers, with an alcohol by adding boron trifluoride, a boron trifluoride addition compound or tetrafluoroboric acid or a salt thereof to the aqueous solutions during or immediately after the reaction.

Abstract: A speaker system provides good acoustic characteristics for use in visual equipment, by controlling the turbulence in mid-range of response frequency characteristics to be flat so as to produce an excellent speech articulation. This is accomplished by coupling an acoustic pipe to the front of a speaker unit to guide sound waves through an opening of generally rectangle shape. A resonance absorption section is formed by a tube, one end of which forms a hole for absorbing sound facing to a sound path running within the acoustic pipe from the front of speaker unit to an opening, and a cavity having a small gap along the edge, except the area where is coupled through with the other end of tube. By constructing the speaker system in this way, the width of band to be absorbed and the Q of a dip can be controlled to suppress the peaks and dips, thereby providing a speaker system of good acoustic characteristics where the response frequency characteristics are flat and the speech articulation is excellent.

Abstract: A speaker system provides good acoustic characteristics for use in visual equipment, by controlling the turbulence in mid-range of response frequency characteristics to be flat so as to produce an excellent speech articulation. This is accomplished by coupling an acoustic pipe to the front of a speaker unit to guide sound waves through an opening of generally rectangle shape. A resonance absorption section is formed by a tube, one end of which forms a hole for absorbing sound facing to a sound path running within the acoustic pipe from the front of speaker unit to an opening, and a cavity having a small gap along the edge, except the area where is coupled through with the other end of tube. By constructing the speaker system in this way, the width of band to be absorbed and the Q of a dip can be controlled to suppress the peaks and dips, thereby providing a speaker system of good acoustic characteristics where the response frequency characteristics are flat and the speech articulation is excellent.

Abstract: A speaker system for a computer includes at least one speaker disposed within a computer case, at least two sound emitting ports disposed on an exterior of the computer case, at least two sound transmitting paths each disposed within the computer case and connected to the at least one speaker and a respective one of the at least two sound transmitting paths for receiving sound waves from the at least one speaker and transmitting the sound waves to a respective one of the at least two sound emitting ports.

Abstract: A speaker system provides good acoustic characteristics for use in visual equipment, by controlling the turbulence in mid-range of response frequency characteristics to be flat so as to produce an excellent speech articulation. This is accomplished by coupling an acoustic pipe to the front of a speaker unit to guide sound waves through an opening of generally rectangle shape. A resonance absorption section is formed by a tube, one end of which forms a hole for absorbing sound facing to a sound path running within the acoustic pipe from the front of speaker unit to an opening, and a cavity having a small gap along the edge, except the area where is coupled through with the other end of tube. By constructing the speaker system in this way, the width of band to be absorbed and the Q of a dip can be controlled to suppress the peaks and dips, thereby providing a speaker system of good acoustic characteristics where the response frequency characteristics are flat and the speech articulation is excellent.

Abstract: A megaphone includes a pair of hollow bodies which are assembled at a connecting portion to open and close freely, wherein a tuning part is formed by denting the center of a flat part of each hemiconical main part to provide a level face around the tuning part.

Abstract: A waveguide for projecting a longitudinal acoustic wave of wavelength .lambda. from an ultrasound energy source toward a target area. The waveguide has at least one tubular channel. The channel has inwardly tapered, conical inlet and outlet ports separated by a venturi. The inlet port taper defines a sharply rimmed entry orifice around the inlet port. A separation distance equal to one wavelength .lambda. is maintained between the source and the waveguide's inlet port. The waveguide shears off a cross-section of the wave emitted by the energy source and ejects it at accelerated velocity toward the target area. The channel has a length L and the venturi has a diameter D, such that the waveguide has an emitted beam angle equal to 2 (tan.sup.-1 (D/L)). Preferably, a plurality of tubular channels are aligned concentrically around and longitudinally parallel to the one tubular channel, each channel having a selected length and a selected diameter.

Abstract: A dual-speaker unit providing improved stereo base response and directionality for portable computer applications is disclosed. The small speakers direct low end frequencies into a mixing chamber which directs these frequencies out through a central exit port, thereby providing clearer base response without sacrificing psychoacoustic directionality.The speakers are mounted on the mixing chamber and also rotatable relative to it, for adjustable stereo imaging and compact portability.

Abstract: A system for low frequency sound production in vehicular passenger compartments, comprising an electrodynamic driver, having a first acoustic mass and a first acoustic compliance; and a Helmhotz resonator, affixed to one side of said electrodynamic driver means and having a second acoustic mass and a second acoustic compliance, the second acoustic mass being affixed to a baffle facing the passenger compartment. The first and second acoustic mass have substantially similar magnitudes, and the Helmholtz resonator and the electrodynamic driver being substantially tuned to the highest and lowest frequencies of a desired passband, respectively, so as to provide a substantially flat pressure vas. frequency characteristic when the passenger compartment has dimensions generally smaller than one eighth wavelength of the lowest frequency.

Abstract: A horn loudspeaker has an opening formed in a wall of a horn, and a tubular duct is provided along the horn and communicated with the opening. The length L of the duct is expressed as, L.perspectiveto.c/4fr-0.4d where c is a velocity of sound, fr is a frequency a sound pressure of which is to be reduced, and d is an inner diameter of the duct.

Abstract: A multiport underwater sound transducer including a hollow resilient housing enclosing a volume with at least two ported resonant chambers and a transduction driver disposed within the volume with opposite sides of the driver driving the two chambers. The two ports are set to resonate at slightly different frequencies and the tranducer proudces an additive output at frequencies between the two slightly different frequencies due to phase reversals of oppositely phased sound waves.

Abstract: A baseball bat having the functions of resonators and microphones is designed to be hollow and has a receiver cup disposed at its inner top end in such a manner that a spring may be hooked to its bottom while the other end of the spring is hooked to a tuning bar fixed at an end cap fittedly adhered to the bottom end of the bat. Besides, a plurality of sound-amplifying holes are formed on the surface of the bat at proper positions. Whenever the bat is vibrated by external force, the spring inside it shall vibrate accordingly and the sound-wave so produced resonates within the hollow bat which serves as a resonance box. When the sound-wave passes through the sound-amplifying holes on the surface of the bat, a special striking tone shall be produced. Such special tone can be produced either when the bat stikes a ball or when the bat is purposely vibrated or waved. When speaking into the receiver cup, the wave of voice may be amplified through the resonance effect of the hollow bat.

Abstract: A megaphone apparatus includes an elongate conical conduit directed into an outwardly flaring forward body portion. The conduit includes an entrance opening, with the flaring body including a plurality of exit openings defined by a central outlet conduit coaxially aligned with the inlet conduit, with a plurality of right and left branch conduits extending laterally to each side of the central conduit aligned in a single plane along a common diameter of the various conduits. A modification of the invention includes various residence modulating caps selectively positionable over the conduits to include a flexible web, with at least one slit directed diametrically therethrough, and including a plurality of pockets arranged in a spaced relationship relative to the slit to include a flexible rod selectively positioned within each pocket as desired for varying modulation of the flexible web of each cap in use.

Abstract: A flextensional sonar transducer comprising a first cavity defined by an elliptical shell and end plates covering the two ends of the shell, vibration drive means inside the cavity and coupled between portions of the shell wall at opposite ends of the major axis of the shell, a further cavity connected to the first cavity and an opening between the two cavities for coupling the two cavities for the further cavity to affect the resonant frequency of the first.

Abstract: An acoustic apparatus comprises a resonator, a vibrator, and a vibrator drive circuit for an improved bass sound reproduction. The resonantor has a resonance radiation unit for radiating an acoustic wave by resonance, and the vibrator has a diaphragm constituting a part of the resonator and disposed in the resonator. The vibrator drive circuit for driving the vibrator has a negative impedance component in an output impedance, and a reaction from the resonator to the diagram is canceled upon driving of the resonator. Accordingly, the presence of the vibrator is invalidated as viewed from the resonator, and the vibrator and the resonator can be independently designed. As a result, the resonator can be realized in a compact size, and the resonance acoustic wave can be radiated powerfully.

Abstract: An acoustic apparatus comprising a resonator having a resonance radiation unit for radiating an acoustic wave by resonance, a vibrator arranged in the resonator, and a vibrator drive means for driving the vibrator. The vibrator has a diaphragm having a direct radiator portion for directly radiating an acoustic wave, and a resonator driver portion for driving the resonator. The vibrator drive means has a drive control means for controlling the drive condition so as to equivalently reduce or invalidate the internal impedance inherent to the vibrator.

Abstract: A resonator for internal combustion engines having intake and exhaust pipes connected with a cylinder of said internal combustion engines comprising resonator means for absorbing resonant noises generated in said engines, a plurality of tubular connecting members disposed between said resonator means and one of said pipes for forming a continuous passage from said one pipe to said resonator means, and switch means connected with said tubular connecting means for changing said tubular connecting members in accordance with operational conditions of said engines to absorb said noises from said engines.

Abstract: A resonator for internal combustion engines, having an enclosed chamber of predetermined volumn connected to an intake duct by a tubular connecting member which is composed of an external member and an internal member. The internal member is disposed within the external member and moved by an actuator which is controlled by an electrical signal corresponding to a resonant frequency calculated by a computer in synchronism with engine rotational speeds. The resonator thereby functions to absorb resonant noises from the engines by appropriately changing the length and/or cross-sectional area of the tubular connecting member.

Abstract: A mobile communication device is provided. The mobile communication device includes a terminal body, and a speaker module located in the terminal body. The speaker module includes an enclosure located in the terminal body, the enclosure defining a chamber therein, and a speaker having a front surface and a rear surface, the speaker being located in the enclosure such that the front surface of the speaker is exposed from the enclosure and the rear surface thereof is positioned within the chamber, to allow a sound generated from the rear surface to resonate within the chamber. A mutual interference between the sound generated from the front side of the sound emission part and the sound emitted from the rear side thereof can be reduced to thereby improve the performance of the middle and low sound.