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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2015/09/20 23:22:55」(JST)

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Audio vacuum tube with externally fitted microphonics damper

Microphonics or microphony describes the phenomenon wherein certain components in electronic devices transform mechanical vibrations into an undesired electrical signal (noise). The term comes from analogy with a microphone, which is intentionally designed to convert vibrations to electrical signals.

Description

When electronic equipment was built using vacuum tubes, microphonics were often a serious design problem. The charged elements in the vacuum tubes can mechanically vibrate, changing the distance between the elements, producing charge flows in and out of the tube in a manner identical to a capacitor microphone. A system sufficiently susceptible to microphonics could experience audio feedback, and make noises if jarred or bumped. Certain vacuum tubes were made with thicker internal insulating plates and more supports to minimize these effects.^[1]

With the advent of solid-state electronics (transistors), this major source of microphonics was eliminated but smaller sources still remain.

The ceramic EIA Class 2 dielectrics used in high-K capacitors ("Z5U" and "X7R") are piezoelectric and directly transform mechanical vibration into a voltage in exactly the same way as a ceramic or piezoelectric microphone.^[2] Film capacitors using soft (mechanically compliant) dielectric materials can also be microphonic due to vibrational energy physically moving the plates of the capacitor. Likewise, variable capacitors using air as a dielectric are vulnerable to vibrations moving the plates. Capacitors using glass as the dielectric, while quite expensive, can be made to be essentially nonmicrophonic.

Wiring and cables can also exhibit microphonics as charged conductors move around, and various materials can develop triboelectric ("static") charges that couple to the electronic circuits.

Guitar amplifiers that incorporate the electronic chassis into the same cabinet as the speaker are susceptible to microphonics. Though a guitar amplifier's microphonics distortion is sometimes appreciated as part of the "special sound" of a guitar amplifier, a faulty vacuum tube or other component can cause out-of-control positive feedback. Unwanted microphonics-related audible distortions can often be alleviated by using commercially available vacuum tube mechanical dampers.

The term may also be used to describe a video artifact common in older video cameras. Before the introduction of solid-state CCD sensors to produce the image, vacuum tubes performed this task. Loud noises in the studio, such as rock bands or gunshot effects would cause the tubes to vibrate, producing a characteristic undesirable horizontal banding in the image.^[3]

Other uses

The term is sometimes misused to describe sounds transmitted to the ear physically by mechanical vibrations or knocks on the wires of a headphone or in-ear monitor, when no disturbance of any electrical signal occurs.^[4]

References

^ Robert B. Tomer, Getting the most out of vacuum tubes, Howard W. Sams, Indianapolis, USA 1960, Library of Congress card no. 60-13843, available on the Intenet Archive. Chapters 3
^ [1], Capacitors for reduced sound emissions.
^ http://www.michaeldvd.com.au/Articles/VideoArtefacts/VideoArtefactsMicrophony.html
^ "In-ear-canal headphone primer" by Dan Frakes, Capsule Review, Macworld, 31 January 2007

External links

Valve Microphonics

English Journal

Audibility, speech perception and processing of temporal cues in ribbon synaptic disorders due to OTOF mutations.

Santarelli R1, Del Castillo I2, Cama E3, Scimemi P3, Starr A4.
Hearing research.Hear Res.2015 Jul 15. pii: S0378-5955(15)00147-1. doi: 10.1016/j.heares.2015.07.007. [Epub ahead of print]
Mutations in the OTOF gene encoding otoferlin result in a disrupted function of the ribbon synapses with impairment of the multivesicular glutamate release. Most affected subjects present with congenital hearing loss and abnormal auditory brainstem potentials associated with preserved cochlear hair
PMID 26188103

Audiological changes over time in adolescents and young adults with auditory neuropathy spectrum disorder.

Chandan HS1, Prabhu P.
European archives of oto-rhino-laryngology : official journal of the European Federation of Oto-Rhino-Laryngological Societies (EUFOS) : affiliated with the German Society for Oto-Rhino-Laryngology - Head and Neck Surgery.Eur Arch Otorhinolaryngol.2015 Jul;272(7):1801-7. doi: 10.1007/s00405-015-3505-0. Epub 2015 Jan 13.
Auditory neuropathy spectrum disorder (ANSD) describes a condition in which a patient's otoacoustic emissions (OAE) are (or were at one time) present and auditory brainstem responses (ABR) are abnormal or absent. ANSD is also diagnosed based on the presence of cochlear microphonics and abnormal or a
PMID 25577995

Pannexin1 channels dominate ATP release in the cochlea ensuring endocochlear potential and auditory receptor potential generation and hearing.

Chen J1, Zhu Y2, Liang C2, Chen J2, Zhao HB2.
Scientific reports.Sci Rep.2015 Jun 2;5:10762. doi: 10.1038/srep10762.
Pannexin1 (Panx1) is a gap junction gene in vertebrates whose proteins mainly function as non-junctional channels on the cell surface. Panx1 channels can release ATP under physiological conditions and play critical roles in many physiological and pathological processes. Here, we report that Panx1 de
PMID 26035172

Japanese Journal

Cochlear microphonics and compound action potentials responding to amplitude modulated tones and repetitive clicks in Mongolian gerbil : Comparison between different recording sites, the round window and the brainstem

Onodera Hiroshi,Matsuo Ikuo,Kobayasi Kohta I. [他]
聴覚研究会資料 = Proceedings of the auditory research meeting 44(4), 167-170, 2014-05-30
NAID 40020128251

Noise-induced amplitude shifts found in the cochlear microphonics of Mongolian gerbils

KAWAI Shin,MATSUO Ikuo,KOBAYASI Kohta I. [他]
聴覚研究会資料 = Proceedings of the auditory research meeting 44(4), 161-165, 2014-05-30
NAID 40020128231

Encoding of temporal pitch in the cochlea of Mongolian gerbil

MORIMOTO Takeshi,BOKU Shokei,KOBAYASI Kohta I [他]
聴覚研究会資料 = Proceedings of the auditory research meeting 43(8), 625-629, 2013-11-28
NAID 40019903517

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