1. Field of the Invention
The present invention relates to a speaker system in which a pseudo-spherical sound wave is generated by a combination of a plurality of speakers.
2. Description of the Related Art
Generally, speakers used in the pure audio field are required to ensure sufficient sound volume and have a mellow and rich tone quality.
Now, among related art speakers, a cone-type speaker using a cone-shaped diaphragm plate, a dome-type speaker in which the convex side of a dome-shaped diaphragm defines a sounding portion, and other speakers, have been disclosed (see Denkidenshikogaku-Daihyakkajiten, Vol. 25 “AUDIO & VIDEO” compiled by Shigenobu Tsuji, issued in November, 1983, from Denkishoin; and Japanese Unexamined Patent Application Publication No. 11-196485, for example).
Furthermore, in the related art speakers, what is called a tonzoile speaker in which a plurality of speakers having the same kind and same size openings are arranged linearly or along a curved line, a composite speaker in which speakers having different-size openings are arranged in a speaker box so as to be close to each other, and others have been disclosed (see Hosogijutsusosho “Onkyo-kiki” compiled by NHK (Japan Broadcasting Corporation), issued on Jul. 1, 1963, from Gihodou; Japanese Unexamined Patent Application Publication No. 2-239798; and Japanese Unexamined Patent Application Publication No. 5-103391, for example).
Since a sound wave is generated by the back-and-forth piston movement of the cone-shaped diaphragm plate in the related cone-type speaker, a large sound volume is easily obtained. However, since the diaphragm plate only performs back-and-forth piston movements, the radiated wave front of the sound wave forms a substantially flat wave. Since the sound wave is not a spherical wave as in the above-mentioned dome-type speaker, disturbance (turbulent flow) of the air is produced between a vibrating area and a non-vibrating area and it is difficult to obtain a mellow and rich tone quality. Moreover, the vibrating area defines a substantially cylindrical area where the air is directly vibrated by the vibration of the diaphragm plate, the surface of which defines a bottom surface of the cylindrical area.
On the other hand, since the latter dome-type speaker produces a sound wave by the expansion and contraction movement of the diaphragm plate, the sound wave is naturally a spherical wave. Such a spherical wave advantageously generates a mellow and rich tone quality. However, although the whole diaphragm plate moves in the cone-type speaker, the whole diaphragm does not move in the dome-type speaker. The outer edge portion of the semi-spherical diaphragm plate is secured, and a sound wave is generated by the expansion and contraction of the diaphragm plate. Therefore, a large amplitude is not expected, and accordingly, it is difficult to obtain a large volume.
Furthermore, the above-mentioned tonzoile speaker is used to reduce howling effects in a hall and theater such that a sharp directivity is provided in a particular direction by changing the sound volume and phase of each speaker, and, since disturbances of the air are not taken into consideration, tone quality cannot be improved. In particular, when a plurality of speakers are arranged along a curved line, the mounting angle and driving method of each speaker is complicated and difficult to set, and the construction of a speaker box is complicated and more expensive.
Moreover, Japanese Unexamined Patent Application Publication No. 2-239798 discloses that the sound pressure of a speaker in the middle is greater than that of speakers at both ends. In generally, the sound pressure means the pressure of a sound at a point which is a fixed distance away from a speaker. However, in the case of a speaker having a large diameter, even a small amplitude produces a large sound pressure, and in the case of a speaker having a small diameter, even a large amplitude produces only a small sound pressure. As it is understood from the above, the sound pressure does not necessarily mean the amplitude of the speaker. Accordingly, even if a difference in sound pressure is provided, disturbances of the air cannot be prevented.
Furthermore, in the composite speaker, a uniform frequency characteristic as a whole is obtained by providing speakers having large and small diameters that share the frequency range. Therefore, in the same manner as described above, the composite speaker is not intended to improve deterioration of the tone quality caused by disturbance of the air.