Vehicle Stereo Sound Phase Equalization and Time Alignment
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Solution Overview
Problem
In vehicles, the stereo signal delivery often results in phase opposition effects between left and right sound channels, leading to an unpleasant listening experience for passengers, as the sound image is not centered in front of each passenger.
Innovation Solution
The method involves equalizing the phase of stereophonic sound signals and applying all-pass filters to minimize phase opposition effects, along with introducing delays to time-align speakers, ensuring that the sound image appears centered in front of each passenger, either in the 'driver' or 'all passengers' mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the stereo signal is delivered through front and rear transducers without phase equalization, then the sound can be distributed to multiple positions, but phase opposition effects occur between left and right channels causing unpleasant listening experience
Solution Approach 1:
The patent applies phase equalization by introducing frequency-dependent phase shifts to the left and right audio channels. Specifically, a phase equalizer is used to adjust the phase relationship between channels, compensating for the phase opposition effects that occur when sound is delivered through distributed transducers. This parameter change in the phase characteristic allows the system to maintain versatile sound distribution while eliminating harmful phase opposition effects.
2Manufacturing precision
If delays are introduced to equalize phase and center the sound image, then listening quality improves, but the system complexity increases due to additional processing requirements
Solution Approach 1:
The patent introduces a phase equalizer as an intermediary component between the audio signal source and the transducers. This intermediary device performs the complex phase adjustment and time-alignment operations automatically, handling the complexity of sound image positioning without requiring manual intervention or overly complex system architecture. The phase equalizer mediates between the simple stereo signal and the complex requirements for precise sound placement.
Solution Approach 2:
The system changes the phase parameters of the audio signals through frequency-dependent phase shifting. By adjusting these phase parameters dynamically, the system achieves precise sound image positioning and centers the sound in front of the listener. This parameter-based approach allows for accurate control of sound placement while keeping the overall system relatively simple, as it relies on mathematical phase adjustments rather than complex physical modifications.
3Object-affected harmful factors
If all-pass filters are applied to minimize phase opposition, then the phase difference curve bypasses phase opposition points, but the filter design and implementation become more complex
Solution Approach 1:
The patent employs all-pass filters that modify the phase characteristics of audio signals without changing their magnitude response. These filters introduce frequency-dependent phase shifts that specifically target and bypass phase opposition points in the phase difference curve. By changing the phase parameters through carefully designed filter characteristics, the system eliminates phase opposition effects while maintaining a relatively simple filter implementation, as all-pass filters have straightforward magnitude responses that are easy to realize.
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
This approach effectively minimizes phase opposition effects, providing a more pleasant and immersive audio experience by aligning sound waves to seem to originate from the same distance and position for all passengers, enhancing listening quality.
Implementation Method 1
the phase of these electric sound signals is equalized so as to minimize the phase opposition effects in frequency bands of these left and right signals received at approximately the location of one passenger's head
Implementation Method 2
all-pass filters are applied to the left or right signal, these all-pass filters each having a cutoff frequency substantially equal to a middle frequency of the frequency band for which the left and right electric sound signals received are in phase opposition
Implementation Method 3
delays are introduced in the frequency bands of each speaker so that all of the speakers seem to be at the same distance as the one furthest from the driver
Implementation Method 4
delays are introduced in the front channel signals so as to time-align the 'tweeter/woofer' pairs
Implementation Method 5
a transducer means a system that transforms an electric sound signal into an acoustic sound signal
Data Source
AI summary
The invention relates to a method for the sound processing of a stereophonic signal inside a motor vehicle. In a first implementation (“driver” mode) the stereophonic sound source is centered in the middle of the dashboard for the ‘driver’ listen position. For this purpose, delays (t1-t4) are introduced into the frequency bands of the channels transmitted by the speakers, such that the driver appears to be at the center of a circle on which the car speakers are positioned. In a second implementation (“all passengers” mode), the phases of the signals of the two front channels are equalized, such that the sound source appears to be centered on the driver and the front passenger of the vehicle.