Dipole Microphone Array for Acoustic Guitar Feedback Control
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Solution Overview
Problem
Acoustic feedback from amplified guitar signals is a persistent issue with existing transducers, particularly affecting hollow-body electric guitars, as they are more sensitive to uncontrolled vibrations that lead to unstable feedback oscillations, and current solutions either fail to suppress feedback effectively or alter the fidelity of the electric signal.
Innovation Solution
A dipole microphone array is positioned in close proximity to the vibrating strings of an acoustic guitar, with each microphone assembly comprising a pair of microphones out of phase to suppress uncontrolled acoustic feedback while enhancing sensitivity to the acoustic waves from the strings and sound hole, using a baffle and precise orientation to improve performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a magnetic induction pickup is used to suppress acoustic feedback, then feedback control is improved, but high frequency structure and acoustic sound fidelity are lost
Solution Approach 1:
The patent replaces magnetic induction pickups with microphones that convert acoustic waves directly to electrical signals. This substitution allows the system to capture authentic acoustic sound waves from the guitar body and sound hole while using electronic signal processing to suppress feedback, thereby maintaining acoustic fidelity while achieving feedback control.
Solution Approach 2:
The patent introduces an intermediary acoustic waveguide structure between the guitar body and the microphones. This waveguide enhances the capture of authentic acoustic waves from the sound hole while isolating the microphones from direct exposure to amplified feedback sounds, thus improving both fidelity and feedback suppression.
2Measurement precision
If vibration sensors are used to achieve closer sound image, then sound image fidelity is improved, but acoustic feedback sensitivity remains high
Solution Approach 1:
The patent replaces vibration sensors with acoustic microphones that detect pressure waves in the air rather than mechanical vibrations. This allows the system to capture the authentic acoustic sound field around the guitar while being less susceptible to direct coupling with body vibrations that cause feedback.
Solution Approach 2:
The patent uses an acoustic waveguide as an intermediary structure that directs authentic acoustic waves from the sound hole to the microphones while preventing direct exposure to feedback sounds from the amplifier, thus maintaining sound image fidelity while reducing feedback sensitivity.
3Measurement precision
If microphones are placed close to strings to enhance sensitivity, then acoustic signal sensitivity is improved, but acoustic feedback from loudspeaker is increased
Solution Approach 1:
The patent positions microphones at specific locations on the guitar body, particularly near the sound hole, where authentic acoustic waves are concentrated. This localized positioning enhances sensitivity to genuine guitar sounds while the acoustic waveguide structure directs the microphone sensitivity away from the amplifier direction, reducing feedback exposure.
Solution Approach 2:
The acoustic waveguide acts as an intermediary structure that channels authentic acoustic waves from the sound hole to the microphones while providing acoustic isolation from the amplifier direction. This allows close proximity positioning for high sensitivity while maintaining feedback suppression through the waveguide's directional acoustic properties.
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 dipole microphone array effectively suppresses acoustic feedback from amplified sources while maintaining high fidelity to the acoustic signal, allowing for increased amplifier gain without feedback, as demonstrated by the enhanced gain margin and flattened frequency response.
Implementation Method 1
an array of dipole microphones each in very close proximity to a vibrating acoustic guitar string to both faithfully reproduce the sound one hears while also suppressing uncontrolled acoustic feedback
Implementation Method 2
The second microphone is out of phase with the first microphone so as to provide a dipole microphone assembly
Implementation Method 3
Some embodiments include a small baffle in the array, and diffraction over this baffle further improves performance
Data Source
AI summary
A dipole microphone array is provided for an acoustical stringed instrument of the type having a body and a plurality of strings spaced from the body. The array includes a plurality of microphone assemblies each having a first and a second microphone. The second microphone is out of phase with the first microphone so as to provide a dipole microphone assembly. Each of the microphone assemblies is mounted on the body of the instrument in close proximity to one of the strings.