JPH04351098A - Ultrasonic parametric loudspeaker - Google Patents

Abstract

PURPOSE:To make the loudspeaker thin in profile and to make the size small by arranging a reflection material reflecting a primary sound wave more than a secondary sound wave to the speaker and allowing a sound absorbing member to reflect and absorb the primary sound wave. CONSTITUTION:An ultrasonic wave generating means 1 is formed by arranging lots of ultrasonic wave vibrators 1a to a base 1b. Moreover, a film-made reflection material 5 is provided to a side of the generating means 1a from a sound wave incident face 3a of an acoustic filter 3. The material 5 reflects a primary sound wave made incident in the filter 3 in the inside of a speaker and the energy is absorbed to the absorbing material 4. Then the interruption quantity of the primary sound wave required for the filter 3 is made smaller than the case without the material 5. Furthermore, since the reflection material 5 decreases the reflection capability of the secondary sound wave, the filter 3 is made thin without deteriorating the performance of the ultrasonic parametric loudspeaker A. Thus, the loudspeaker is made small and thin.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvements in ultrasonic parametric loudspeakers.

0002

[Prior art]

[0003] When the ultrasonic generator is driven at two different frequencies, the primary sound waves output from the ultrasonic generator interfere with the air, and the difference component and sum component of the frequencies of the primary sound waves are generated as a secondary sound wave. This is conventionally known as nonlinear parametric action. The secondary sound waves generated by this type of action can be brought to a practical level if an extremely strong sound field is created by using ultrasonic waves with sharp directional characteristics for the primary sound waves, and at this time, the frequency difference between the primary sound waves becomes audible. If the frequency is set at the same frequency, a secondary sound wave at an audible frequency will be generated as a difference component. The secondary audible sound waves generated at this time have blunter directional characteristics than the primary sound waves, but they show a pattern relatively similar to the primary sound waves, so if an ultrasonic wave with sharp directional characteristics is used as the primary sound waves, Directional characteristics can be sharpened. Sound wave generating means using such a principle has been put to practical use as a parametric speaker, and its basic structure is as shown in FIGS. 3 and 4. That is, an ultrasonic generator 1 for generating primary sound waves is disposed at one end of the enclosure 2, and an acoustic filter 3 is disposed at the sound emitting port 6 at the other end of the enclosure 2. A sound absorbing material 4 is provided on the inner peripheral surface of the enclosure 2. Further, the ultrasonic wave generating means 1 is constructed by arranging a large number of ultrasonic transducers 1a on a substrate 1b so as to form a strong sound field of ultrasonic waves, which are primary sound waves. In such a parametric speaker, an acoustic filter 3 made of a material such as urethane foam or film is used to prevent primary sound waves at levels harmful to the human body from being emitted outside the enclosure 2. There is usually one.

[Problems to be Solved by the Invention] As mentioned above, in parametric speakers, it is necessary to use strong primary sound waves in order to obtain secondary sound waves at a sound pressure level that can be put to practical use. Acoustic filters are indispensable in order to prevent primary sound waves with harmful sound pressure levels from being radiated to the outside. However, when using reflective materials such as films as acoustic filters, the emitted primary sound waves and the primary sound waves reflected by the acoustic filter may interfere with each other, causing problems such as the generation of standing waves. Although porous materials such as urethane foam are used for ease of handling, this increases the thickness of the acoustic filter, which hinders miniaturization and thinning of speakers. The present invention was made in view of the above-mentioned circumstances, and aims to reduce the thickness of the acoustic filter by reflecting the primary sound waves on the ultrasonic generation means side rather than the incident surface of the acoustic filter. This is an attempt to make the speaker smaller and thinner.

0004

[Means for Solving the Problems] In the present invention, in order to achieve the above object, the primary sound waves output from the ultrasonic wave generating means are arranged closer to the ultrasonic wave generating means than the sound wave incidence surface of the acoustic filter. A method is adopted in which the energy of the primary sound wave (ultrasonic wave) is reflected by a reflective material and absorbed by a sound absorbing material provided inside the speaker without disturbing the sound field of the primary sound wave. For this reason, it is possible to lower the primary sound wave blocking ability on the sound wave incidence surface of the acoustic filter and inside thereof, and as a result, it is possible to make the acoustic filter thinner.

[0005]

[Function] According to the ultrasonic parametric speaker of the present invention, the strong primary sound waves emitted from the ultrasonic generator are reflected by the reflective material disposed closer to the ultrasonic generator than the sound wave incident surface of the acoustic filter. The sound absorbing material installed inside the speaker absorbs the sound wave energy.
The amount of sound wave intercepted by the acoustic filter can be reduced, and therefore the acoustic filter can be made thinner without generating standing waves or significantly affecting the sound field of primary sound waves inside the enclosure.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the ultrasonic parametric speaker A of the present invention will be shown below. In FIG. 1, reference numeral 1a denotes an ultrasonic transducer, and a large number of ultrasonic transducers are arranged on a substrate 1b to constitute an ultrasonic generating means 1. 2 is an enclosure, 3 is an acoustic filter provided at the sound emitting port 6, and 4 is a sound absorbing material provided inside the speaker. A reflective material 5 made of a film such as polyethylene terephthalate is provided on the side closer to the ultrasonic wave generator 1a than the sound wave incidence surface 3a of the acoustic filter 3, and this reflective material 5 prevents the sound from entering the acoustic filter 3. The primary sound waves generated are reflected inside the speaker, and the energy is absorbed by the sound absorbing material 4. Therefore, with such a structure, the amount of primary sound wave blocking required by the acoustic filter 3 is smaller than that in the case without the reflective material 5, and the acoustic filter 3 is cut by that amount.
It becomes possible to make it thinner.

[0007] In addition, such a reflective material 5 has a large ability to reflect primary sound waves, and has an ability to reflect secondary sound waves as small as possible compared to the above-mentioned ability (blocking of secondary sound waves). capacity is required to be as small as possible). In the case of an ultrasonic speaker, since the frequency of the primary sound wave and the frequency of the secondary sound wave are more than 10 times different, it is thought that materials such as films can be used sufficiently. However, when a reflective material such as a film is used inside the enclosure 2, it is necessary to consider the influence of the reflection and direct the sound waves reflected by the reflective material 5 toward the sound absorbing material 4. Therefore, in a general ultrasonic speaker shown in FIGS. 3 and 4 in which the inner peripheral surface of the enclosure 2 is covered with a sound absorbing material 4, the primary sound waves reflected by the reflective material 5 reach the sound absorbing material 4. The reflecting surface 5a is directed toward the ultrasonic wave generating means 1a.
What is necessary is just to make it convex toward the ultrasonic generation part side where is provided. The convex shape in this case may be an arc shape as shown in FIG. 1, or a triangular shape as shown in FIG. 2. Furthermore, the shape of the reflective material 5 should be determined based on the relationship with the position of the sound absorbing material 4, but the method for determining the shape also depends on the relationship between the frequency of the primary sound wave and the dimensions of the enclosure. However, it seems that the geometric sound line method can adequately handle this problem.

[0008]

[Effects of the Invention] As described above, according to the present invention, the acoustic filter can be made thinner without degrading the performance of the ultrasonic parametric speaker, so the speaker can be made smaller and thinner. becomes.

[Brief explanation of drawings]

FIG. 1 is a longitudinal cross-sectional structural diagram showing an embodiment of an ultrasonic parametric speaker according to the present invention.

FIG. 2 is a longitudinal cross-sectional structural view showing another embodiment of the ultrasonic parametric speaker according to the present invention.

FIG. 3 is an explanatory diagram of a conventional ultrasonic parametric speaker.

FIG. 4 shows a vertical cross-sectional structural diagram of the speaker shown in FIG. 3.

[Explanation of symbols]

A...Ultrasonic parametric speaker 1 of the present invention...
・Ultrasonic generating means 2...Enclosure 3...Acoustic filter 3a...Sound wave reflecting surface 4...Sound absorbing material 5...Reflecting material 5a...Sound wave reflecting surface

Claims (1)

[Claims] Claim 1. A parametric speaker which is provided with an acoustic filter at the sound emitting port and emits an audible secondary sound wave from the sound emitting port by a nonlinear parametric action of the primary sound wave output from the ultrasonic wave generating means, the acoustic filter as described above. −
A reflective material that reflects primary sound waves better than secondary sound waves is provided on the side closer to the ultrasonic generation means than the sound wave incidence surface of the speaker, and the primary sound waves are reflected and absorbed by the sound absorbing material provided inside the speaker. Ultrasonic parametric speaker.