Twin driver earphone
Provided is a technique for improving frequency characteristics by an acoustics-related method so that a sound is heard with natural frequency characteristics when a sound-isolating earphone is fitted in a human ear. A sound-isolating earphone is provided with two or more electroacoustic transducers, wherein independently generated sound waves are passed through isolated sound leading pipes and are mixed just before an entrance of an external auditory canal, and a sound wave of which is twice the difference between path lengths of the two sound leading pipes is attenuated. This serves to provide an easy-to-hear improved sound quality by suppressing the sound wave at around 6 kHz that is transmitted with characteristically high intensity in a sound-isolating earphone.
1. A sound-isolating earphone used with a sound-emitting portion thereof inserted in an entrance of an external auditory canal, the sound-isolating earphone comprising:
at least two electroacoustic transducers; and
at least two sound leading pipes having different path lengths, each sound leading pipe being associated with a respective electroacoustic transducer;
wherein sound waves generated by the at least two electroacoustic transducers at the same phase and passed through the respective sound leading pipes are combined at the entrance of the external auditory canal, and wherein the sound pressure of a frequency component of which half the wavelength equals a difference between path lengths of the at least two sound leading pipes is suppressed.
2. The sound-isolating earphone according to claim 1 , wherein the difference between the path lengths of the at least two sound leading pipes is substantially equal to the distance between a sound outlet of the sound-isolating earphone located near the entrance of the external auditory canal and an eardrum located in a deep part of the external auditory canal, and wherein a primary resonant frequency of a both-end closed pipe resonance space formed between the sound outlet and the eardrum is suppressed.
3. The sound-isolating earphone according to claim 1 , wherein the at least two electroacoustic transducers are mounted in such a manner that an arrangement axis which connects central points of diaphragms thereof to each other is parallel or generally parallel to the direction of a sound emitted from a sound outlet of the earphone, and wherein sound-emitting directions of the two electroacoustic transducers are oriented in opposite directions.
4. The sound-isolating earphone according to claim 1 , wherein an entirety or part of the length of each of the at least two sound leading pipes is made replaceable so as to vary the path length, thereby altering the difference between the path lengths.
5. The sound-isolating earphone according to claim 1 , further comprising a regulating valve disposed in one or more of the at least two sound leading pipes at a halfway point thereof, wherein a cross-sectional area of a sound-conducting path is varied by adjusting an inserting position of the regulating valve.