Reflection-type speaker apparatus

Abstract: A speaker apparatus includes a speaker (11) having a diaphragm (17), a frame (15) having a mouth (19) and a reflector (25). The speaker (1) is mounted inside a cylindrical box (13), and the frame (15) is formed cylindrically and covers over the diaphragm. The mouth opens perpendicularly to an axis of the diaphragm for an angle of 180 degree from a center of the frame. The reflector (25) is positioned opposite the diaphragm (17) in the frame (15) and is formed roughly conically but asymmetrically between the mouth side and the opposite side. Sound waves radiated from the diaphragm (17) are reflected by the reflector (25) and an inner surface (23) of the frame, and are released outside through the mouth (19).

Description: FIELD OF THE INVENTION The present invention generally relates to the field of speakers, and more particularly, is directed to a reflection-type speaker apparatus which has a directional characteristic capable of directing sound waves radiated from a diaphragm in a specified direction. BACKGROUND OF THE INVENTION Figure 1 is a perspective view illustrating a known speaker system, and Figure 2 is a diagram showing frequency curves of sound pressure level in the known speaker system of Figure 1. In Figure 2, the vertical axis shows sound pressure level, and the horizontal axis shows frequency. In Figure 1, speaker 1 is secured in box 3, and sound waves are radiated from diaphragm 5 of speaker 1. Suppose that solid line indicates the central axis (0 degree) of speaker 1, and the broken line and the single-dot broken line indicate the directions at angles of 30 and 60 degrees from the central axis, respectively. These three types of line in Figure 2 respectively indicate the sound pressure levels at the corresponding angles. As is apparent from Figure 2, the larger the angle from the central axis, at 30 and 60 degrees, and the higher the frequency component, the less the sound pressure level. Figure 3 is a cross-sectional view showing the known speaker system of Figure 1 and will now be used for explaining the reason for the above phenomenon. The sound waves radiated from each part of diaphragm 5 are at the same distance from diaphragm 5 on the central axis. However, in the diagonal direction of 30 and 60 degrees,. the distances from each part, for instance, from points P1 and P2, are different. Therefore, in the high frequency band of sound waves which have a short wavelength, since half the wavelength becomes equal to the difference D between these distances, the sound waves become weaker due to mutual cancelling out. For this reason, in the known speaker system, the sound pressure level is reduced for directions at an angle from the central axis of the speaker. Moreover, the greater such angle and the higher the frequency band of sound waves, the more noticeably the sound pressure level is reduced. EP 0409360 discloses a sound output system having a right and left speaker and a pair of audio mirrors for respectively controlling directivities of sounds which are output from the speakers. The shapes or arrangements of the audio mirrors are adjusted so that the difference in arrival time of the sounds which are respectively output from the pair of speakers can be compensated by a sound pressure difference. DE 3 710 464 relates to a speaker system in which an acoustic reflector is provided opposite a speaker diaphragm in order to determine the directivity of the sound perpendicular to the diaphragm of the speaker. WO 92/07449 relates to a speaker unit in which an acoustic reflector is provided opposite a speaker diaphragm, the axis of the acoustic reflector and the diaphragm being offset from one another. SUMMARY OF THE INVENTION In accordance with the present invention, there is provided a speaker apparatus as claimed in claim 1. Sound waves radiated from the diaphragm are reflected by the reflector and an inner surface of the shield, and are transmitted from the opening. In a preferred embodiment of the present invention, the reflector has a roughly conical shape but has an asymmetrical shape with respect to the side of the shield having the opening and the opposite side of the shield. The present invention seeks to provide a speaker apparatus with improved sound pressure level for directions at an angle to a central axis of sound distribution. For a better understanding of the present invention reference will now be made, by way of example, to the accompanying drawings, in which:- Figure 1 is a perspective view illustrating a known speaker system, Figure 2 is a diagram showing frequency curves of sound pressure level for the known speaker system of Figure 1, Figure 3 is a cross-sectional view showing the known speaker system of Figure 1, Figure 4 is a perspective view illustrating a speaker apparatus in accordance with an embodiment of the present invention, Figure 5 is a vertical cross-sectional view showing the speaker apparatus of Figure 4, Figure 6 is a perspective view showing the shape of reflector 25 in Figure 4, Figure 7 (a),(b) and (c) are respectively a plan, a front elevation and a side elevation views showing reflector 25 of Figure 6, Figure 8 is an exploded perspective view showing frame 15 and reflector 25 in Figure 4, Figure 9 is a plan view showing the radiation state of the sound waves radiated from the speaker apparatus of Figure 4, and Figure 10 is a diagram showing frequency curves of sound pressure level in the speaker apparatus of Figure 4. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A representative embodiment of the present invention will now be explainedwith reference to the accompanying drawings. Figure 4 is a perspective view illustrating a speaker apparatus in accordance with an embodiment of the present invention, Figure 5 is a vertical cross-sectional view showing the speaker apparatus of Figure 4, and Figure 9 is a plan view showing the radiation state of the sound waves radiated from the speaker apparatus of Figure 4. As shown in Figure 4 and 5, speaker 11 is mounted inside cylindrical box 13 which has one end open for installing speaker 11. Frame 15 having a cylindrical shape is provided over diaphragm 17 of speaker 11, and includes mouth 19 for radiating sound waves in the horizontal direction and shield 21. Mouth 19 opens perpendicularly to the central axis of diaphragm 17 in an angle of 180 degree from the center of frame 15. The inner surface 23 of shield 21 opposite mouth 19 reflects sound waves. In addition, frame 15 encloses reflector 25 which is positioned opposite diaphragm 17 and has a roughly conical shape. Accurately speaking, the shape of reflector 25 is conical in the half portion thereof at the side of mouth 19 with the centerline as a boundary, but the shape of the other half at the side of shield 21 has a slope with a steep inclination. Figure 6 is a perspective view showing the shape of reflector 25. Figures 7 (a),(b) and (c) are respectively a plan, a front elevation and a side elevation view showing reflector 25 of Figure 6. As is apparent from these Figures, reflector 25 has an asymmetrical shape with respect to the centerline. Figure 8 is an exploded perspective view showing frame 15 and reflector 25. Frame 15 and reflector 25 are formed as separate pieces and combined by screw 27 through their central axes. Note that frame 15 and reflector 25 may be composed of a single moulding. In the speaker apparatus of this embodiment, sound waves radiated from diaphragm 17 are reflected and diffused by reflector 25 and inner surface 23 of shield 21 inside of frame 15, and then are radiated outside. Therefore, variation of the sound pressure level due to difference of directions is reduced. Figure 9 is a plan view showing the radiation state of the sound waves radiated from the speaker apparatus of Figure 4. Figure 10 is a diagram showing frequency curves of sound pressure level in the speaker apparatus. In Figure 10, the vertical axis shows sound pressure level, and the horizontal axis shows frequency. In addition, the solid line indicates the sound pressure level on the central axis (0 degree) of the sound distribution in Figure 9, and the broken line and the single-dot broken line respectively indicate the sound pressure levels in the directions at angles of 30 and 60 degrees from the central axis. As shown in Figure 9, sound waves S are distributed from mouth 19 equally to each direction in an angle of 180 degrees. Thus, as shown in Figure 10, the energy distributions of the sound waves and the sound pressure levels in the directions at an angle of 0,30 and 60 degrees to the central axis of the speaker are approximately equal even in the high frequency band. Therefore, as is apparent by comparing with the characteristic of the conventional system in Figure 2, the sound pressure level is noticebly improved. Moreover, reflector 25 has an asymmetrical shape with the centerline as a boundary at the sides of mouth 19 and shield 21. Thus, interference of sound waves inside of frame 15 is prevented. In addition to this effect, since sound waves are radiated from mouth 19 outside of frame 15 in order to prevent dispersion of the sound waves, the radiation energy can be efficiently released. As described above, the present invention provides a speaker apparatus which can improve a sound pressure level in a direction having an angle from a central axis of sound distribution. Moreover, the present invention provides an efficient reflection-type speaker apparatus. While the present invention has been illustrated and described in detail in the drawing and foregoing description, it will be recognized that changes and modifications can and will occur to those skilled in the art.

Claims: Speaker apparatus comprising: a box (13) with a speaker (11) having a diaphragm (17) for radiating sound waves; and a reflector (25) for reflecting said sound waves radiated from said diaphragm (17); characterised in that the speaker apparatus also comprises a frame (15) having a portion positioned over said diaphragm (17) for supporting the reflector (25) and positioning the reflector (25) opposite of and co-axially with the diaphragm (17), the frame (15) also including a cylindrical shield (21) arranged between the portion of the frame positioned over said diaphragm (17) and the box (13), the shield (21) having an inner surface (23) for reflecting said sound waves and having an opening (19) therein which allows said sound waves to be radiated outside said apparatus in a direction generally perpendicularly to the central axis of said diaphragm (17). Speaker apparatus as claimed in claim 1 wherein said speaker (11) is provided so that said central axis of said diaphragm (17) points in a vertical direction, and said opening (19) radiates said sound waves in a horizontal direction. Speaker apparatus as claimed in claim 1, wherein said reflector (25) has an asymmetrical shape with respect to the side of the shield (21) having said opening (19) and the opposite side of said shield (21). Speaker apparatus as claimed in claim 3, wherein said reflector (25) is formed conically on the side of the reflector (25) nearest to the opening (19) of said shield (21). Speaker apparatus as claimed in claims 1-3, wherein the reflector (25) is conical in the portion thereof facing said opening (19), and has a slope having a steeper inclination in its remaining portion.

Inventors: SANGO HITOSHI, SANGO, HITOSHI, SANGO, HITOSHI, C/O INTELLECTUAL PROPERTY DIV.
Applicants: TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA
Application year: 1993
Main classification: H04R1
IPC codes: H04R1