Solid-State String Position Transducer for Acoustic Bass
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Solution Overview
Problem
Existing string motion transducers for musical instruments primarily measure velocity rather than position, resulting in inadequate frequency response and sound representation, particularly for acoustic bass instruments, which affects the naturalness of the transduced sound.
Innovation Solution
A solid-state position transducer using a novel 'disk of magnetic field' created by spot-magnetizing a ferromagnetic string or rod, allowing for 2-D position measurement with sensors configured in a 2×2 matrix, enabling accurate measurement of string position and motion, and producing a signal proportional to 1/R from the center of the magnetic field.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If velocity measurement is used in string transducers, then the transducer can detect string motion, but the frequency response becomes proportional to frequency with zero output at zero frequency, resulting in inadequate sound representation
Solution Approach 1:
The patent replaces velocity-based electromagnetic induction with position-based magneto-resistive sensing. Instead of measuring string velocity through induced voltage, the system uses magneto-resistive elements to directly sense string position by detecting changes in magnetic field strength, enabling accurate low-frequency and DC response
Solution Approach 2:
The patent changes the measurement parameter from velocity to position. By using magneto-resistive elements that respond to magnetic field strength variations caused by string position changes, the system achieves flat frequency response from DC to beyond audibility, eliminating the frequency-proportional response limitation of velocity pickups
2Measurement precision
If conventional electromagnetic pickups are used, then string vibration can be detected, but the sound representation fails to capture the true acoustic properties of the instrument
Solution Approach 1:
The patent measures string position directly rather than velocity, fundamentally changing the measurement parameter to achieve flat frequency response from DC to beyond audibility. This position-based measurement captures the true acoustic properties of the instrument by faithfully reproducing the string's actual motion characteristics
Solution Approach 2:
The patent uses a 2×2 matrix configuration of magneto-resistive elements, adding spatial dimensionality to the sensing system. This arrangement enables precise 2-D position measurement in the measurement plane, providing comprehensive string motion detection that captures true acoustic properties
3Adaptability or versatility
If a magnetic field source is placed near the string, then position measurement can be achieved, but the solution becomes inapplicable to non-ferromagnetic strings such as gut strings on violin-family instruments
Solution Approach 1:
The patent introduces a ferromagnetic rod as an intermediary between the magnetic field source and non-ferromagnetic strings. The rod, positioned near the string, becomes magnetized by the magnetic field source and interacts with the string through magnetic coupling, enabling position measurement of non-ferromagnetic strings without direct magnetic contact
Solution Approach 2:
The patent replaces direct magnetic interaction with indirect magnetic coupling through a ferromagnetic rod. This substitution allows the system to measure position of non-ferromagnetic strings by detecting the position of the magnetized rod, which follows the string's motion through magnetic attraction
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides a more natural sound representation by measuring string position directly, offering a flat frequency response from DC to beyond audibility, with an amplitude response two times greater per octave, enhancing the fidelity of acoustic bass instruments and extending applicability to all stringed instruments, including those with non-ferromagnetic strings.
Implementation Method 1
A first 3-pole permanent magnet may be positioned near but not touching the ferromagnetic string or rod so as to create a magnetic field
Implementation Method 2
The ferromagnetic string or rod is spot-magnetized by bringing a permanent magnet into contact with the string or rod at a spot
Implementation Method 3
The electrical pickup of the patent thus senses the position of the vibrating string by measuring changes in the magnetic field applied to opposite sides of a giant magneto resistance (GMR) sensor
Data Source
AI summary
A single axis position transducer uses an elongate permanent three pole magnet having a radial magnetic field at a spot along the magnet in which the magnetic field has radial field lines that decay as 1/R. R is the distance from the center of the magnet along a radial field line perpendicular to the axis of the magnet. The spot has a first pole of one polarity, and the magnet has poles of the opposite polarity spaced along the magnet on opposite sides of the first pole of the radial magnetic field located at the spot. At least one magnetic field sensor is positioned proximal to the spot along the elongate member that detects the motion of the spot and electrically amplifies the sensor output.