Low Frequency Acoustic Absorber Using Velocity Feedback Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing acoustic absorber systems are ineffective in managing low-frequency resonances in enclosed spaces, as they require large dimensions, are non-adaptive, and alter the primary sound source, making them unsuitable for dynamic environments like recording studios.
Innovation Solution
An electroacoustic device with a power amplification electronic system, membrane velocity feedback control, and feedforward control with adjustable gain and band-pass filters, utilizing multiple microphones and acoustic fabrics to achieve adaptive low-frequency absorption across a wide bandwidth, minimizing acoustic pressure and providing a large active absorption area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If passive dampening systems made of fiber material are used to absorb low frequencies, then absorption effectiveness is improved, but the thickness of material must increase significantly (e.g., 1m for 100 Hz)
Solution Approach 1:
The patent replaces the mechanical passive absorption system with an active electroacoustic system. Instead of using thick passive fiber materials to absorb low frequencies, the invention uses electroacoustic transducers (loudspeakers) with electronic control circuits to generate anti-phase sound waves that actively cancel low-frequency resonances. This substitution allows achieving the same absorption effectiveness with much thinner device dimensions.
Solution Approach 2:
The patent changes the operating parameters by using variable gain amplifiers and adjustable filter circuits that can dynamically adapt to different room resonance characteristics. The system measures room transfer functions and adjusts the electroacoustic transducer parameters (gain, frequency response) to optimize absorption for specific low-frequency modes, thereby achieving effective absorption without requiring large physical dimensions.
2Reliability
If electronic equalization systems are used to reduce resonance, then resonance control is improved, but the primary sound emitted by the loudspeaker is altered thus reducing sound fidelity
Solution Approach 1:
The patent introduces an intermediary approach by using a separate measurement microphone to capture room resonance characteristics, which are then processed through digital signal processing to generate correction signals. These correction signals are applied to the electroacoustic transducers independently from the primary audio signal path, allowing resonance control without directly altering the primary sound emission. The system acts as an intermediary between the sound source and the room acoustics.
3Reliability
If passive bass-trap systems are designed to absorb specific low frequencies, then absorption effectiveness is improved, but the system needs large dimensions and is dedicated to a single frequency
Solution Approach 1:
The patent implements a universal system that can handle multiple low-frequency resonances simultaneously. The electroacoustic transducers, controlled by programmable digital signal processing circuits, can adapt to absorb different frequency modes depending on the room characteristics. The system measures the room transfer function and dynamically adjusts to target multiple resonance frequencies, making it versatile rather than dedicated to a single frequency like passive bass-traps.
Solution Approach 2:
The patent employs dynamic adaptation by continuously measuring room acoustic characteristics and adjusting the electroacoustic transducer parameters in real-time. The system can adapt to changing room conditions, such as different seating arrangements or equipment configurations, by re-measuring the transfer function and recalculating the optimal absorption parameters. This dynamic capability allows the system to maintain effectiveness across varying frequency requirements.
4Area of stationary object
If E-bass trap systems are used to absorb specific low frequencies, then footprint is reduced, but the system needs to be adjusted to a specific frequency and is dependent on room specificities
Solution Approach 1:
The patent implements a self-service system that automatically measures room acoustic characteristics using an integrated measurement microphone and processor. The system independently determines the room transfer function, identifies resonance frequencies, and configures the electroacoustic transducers without requiring external setup or adjustment. This self-configuring capability eliminates the need for manual frequency-specific adjustments while maintaining a compact footprint.
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 allows for adaptive control of low-frequency resonances without altering the sound source, offering a compact, mobile solution that maintains sound fidelity and adjusts automatically to changes in room conditions, providing a significantly larger absorption area than traditional systems.
Implementation Method 1
at least one electroacoustic transducer (1), mounted on an acoustic baffle (2)
Implementation Method 2
the front volume (4) being closed by an acoustic fabric (5) of determined acoustic air-flow resistance
Implementation Method 3
a microphone located in front of the acoustic fabric (5) on a side opposite from the front volume (4), connected to a microphone preamplifier (9)
Data Source
Figure 1~3
Figure 2
Figure 4
AI summary
Low frequency active acoustic absorber by acoustic velocity control through porous resistive layers. The invention provides an electroacoustic device for wide band low frequency absorption. The device comprises at least one electroacoustic transducer, mounted on an acoustic baffle, separating a closed rear volume and a front volume, the front volume being closed by an acoustic fabric of determined acoustic air-flow resistance; a power amplification electronic with feedback control, configured to obtain a transducer membrane velocity proportional to an input voltage, coming from a microphone located in front of the acoustic fabric on a side opposite from the front volume, connected to a microphone preamplifier; and a feedforward control, with adjustable gain and band-pass filter, taking a first pressure signal coming from the microphone preamplifier and driving the power amplifier input, the feedforward control gain being equal to Formula (I) where Af is the fabric area, Als the projected transducer membrane area, R the fabric air-flow resistance and G1, the preamplifier gain, minimizing the acoustic pressure in the front volume, thus having a specific impedance, defined as pressure/velocity ratio, in front of the acoustic fabric equal to the determined air-flow resistance of the acoustic fabric.