Music – Instruments – Electrical musical tone generation
Patent
1998-10-06
2000-06-20
Sircus, Brian
Music
Instruments
Electrical musical tone generation
84723, 84DIG24, G10H 304
Patent
active
060780061
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a stringed musical instrument transducer for converting string vibrations into electric signals, and to a procedure for its fabrication. The transducer is especially applicable for use with a guitar.
PRIOR ART
Saddle transducers for acoustic guitars, designed to convert string vibrations into electric signals, are mounted under the saddle of the guitar. They have a transducer part of a length corresponding to that of the saddle and typically containing different layers of electromechanical material, dielectric material and electrically conductive electrode layers, and a connection cable part in which the signals are taken to a preamplifier inside the guitar via a small hole (diameter typically 3 mm) bored in the guitar's resonance box under the saddle. Saddle transducers may typically have a single-layer or a multi-layer structure.
As electromechanical material, piezoelectric crystals or piezoelectric sheet (e.g. polyvinylidene fluoride PVDF) are currently used. In the commonest transducer structures, the connecting cable part is implemented using screened coaxial cable, which is connected to the electrode layers of the transducer part by soldering. Such a transducer is presented e.g. in U.S. Pat. No. 5,319,153. A drawback with this type of structures is the difficulty of fabrication of the transducer and relatively high manufacturing costs, because much of the work has to be done manually. Moreover, the connections to the preamplifier generally have to be made by soldering, because no connectors of sufficiently small size to go through the hole provided under the saddle are available for coaxial cables and because the connection between the transducer itself and the cable makes it impossible to mount the transducer from below. In addition, piezoelectric crystals and sheets are associatd with a certain characteristic sound that is not quite in keeping with the guitar's own acoustic sound.
The so-called electret field, or the permanent electric charge injected into dielectric material (may also contain semiconducting material) by ionizing, is based on interlocking of ions with molecules and crystal structure.
A dielectric film and manufacturing process for same, applicable for use as electromechanical material for a stringed musical instrument transducer, is described in U.S. Pat. No. 4,654,546, said dielectric film comprising a biaxially oriented foamed homogenous film layer containing flat lenslike or "shredded" or cavitated gas bubbles. The term "dielectric electret bubble film" is used here to refer to electromechanical film manufactured as described in that patent and having an permanent electric charge injected into material.
WO-publication 96/06718 presents a procedure for pressure inflation of a prefoamed plastic film, that makes it possible to manufacture strongly foamed film products, involving a high foaming degree and allowing the thickness of the product to be increased without increasing the amount of plastic material. The term "swelled dielectric electret bubble film" is used herein to refer to a foamed film-like plastic product manufactured as described in that WO-publication and having a permanent electric charge injected into material.
SUMMARY OF THE INVENTION
The object of the present invention is to eliminate the drawbacks of prior art and achieve an improved transducer of a completely new type for a stringed musical instrument, in which a swelled dielectric electret bubble film is used to convert the vibration of strings into electric signals. Flat lenslike gas bubbles in the electret film effectively limit the mobility of electret charges in the dielectric material, because the gases have an electric resistance five decades better than the best solid insulating materials have. At the same time, they act as an elastic layer during the conversion of string vibrations into electric signals.
A further object of the invention is to produce a new type of stringed musical instrument transducer which, due to its elastic structure containing gas bubbles, i
REFERENCES:
patent: 4382328 (1983-05-01), Janszen
patent: 4654546 (1987-03-01), Kirjavainen
patent: 5123325 (1992-06-01), Turner
patent: 5204487 (1993-04-01), Turner
patent: 5319153 (1994-06-01), Fishman
patent: 5670733 (1997-09-01), Fishman
Raisanen Heikki
Raisanen Lasse
EMF Acoustics Oy Ltd.
Fletcher Marlon T.
Sircus Brian
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