| 摘要 |
PURPOSE:To improve the radiation efficiency in the low frequency range and to flatten the sound pressure characteristic by constituting an acoustic tube in the rear of a speaker and a chamber in front of the speaker, providing a phase inverting device in the chamber, and setting the ratio between the area of the throat of the acoustic tube and that of the opening part of the tube as well as the ratio between the throat's area and the effective area of a diaphragm as a specific value. CONSTITUTION:The continuous acoustic tube 5 whose sectional area increase gradually from the chamber 8a in the rear of the speaker 9, is provided. The ratio St/SD between the effective area SD of the diaphragm and the area St of the throat 6 is set from 0.6 to 1.0 while the ratio SM/St between the area St and the area SM of the opening 7 is set from 2 to 6. In front of the speaker, the chamber 8b is provided, where the port 10 is set and thus the phase inverting device is formed with the port 10 and the chamber 8b. By setting this constitution to resonate at such a frequency as the wavelength which is approximately equal to the length of the acoustic tube 5, a sound in the front radiated through the phase inverting device and a sound in the rear radiated through the acoustic tube 5 become in-phased with each other, hence a flat and highly efficient sound pressure frequency characteristic in the low frequency of sound pressure can be obtained. Also,by determining the area ratios above-mentioned, the sound pressure frequency characteristic can be made flat.
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