Headrest Bass-Reflex Speaker Duct Layout for Low-Frequency Output
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Solution Overview
Problem
Conventional acoustic devices in vehicles face challenges in effectively reproducing low-frequency sound pressure using small speaker units due to limited resonant frequency range and increased load on damper members, leading to potential failures and restricted low-frequency band emphasis.
Innovation Solution
An acoustic device design featuring an enclosure with a duct open to the outer space and a speaker unit that generates sound pressures of opposite phases, where the resonant frequency of the vibration unit is set lower than the Helmholtz resonator, with a duct sound generation direction opposite to the unit sound generation direction, and a listening position optimized to receive low-frequency sound pressure without phase offset.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a small speaker unit is used in narrow space, then the device can be mounted in limited space, but the resonant frequency remains relatively high and low-frequency reproduction is limited
Solution Approach 1:
A duct is introduced as an intermediary component between the speaker unit and the outer space. The duct communicates with the inner space of the enclosure and opens toward outer space, serving as a mediator to transmit and amplify low-frequency sound pressure generated by the small speaker unit, thereby enabling effective low-frequency reproduction despite the small speaker size
Solution Approach 2:
The invention utilizes the spatial dimension by extending the duct from the enclosure to the outer space, creating a three-dimensional sound transmission path. This dimensional extension allows the system to overcome the limitations of the small speaker unit by leveraging the spatial relationship between the enclosure, duct, and listening position
2Reliability
If the mass of the vibration unit is increased to lower resonant frequency, then low-frequency reproduction improves, but the load on damper member and edge member increases causing potential failure
Solution Approach 1:
The duct acts as an intermediary that amplifies the acoustic output of the vibration unit. By properly designing the duct dimensions and resonance characteristics, the system can achieve enhanced low-frequency sound pressure without needing to increase the mass of the vibration unit, thereby avoiding excessive loads on the damper member and edge member
Solution Approach 2:
The invention changes the acoustic parameters of the system by introducing the duct with specific dimensions and resonance characteristics. This allows the resonant frequency to be optimized for low-frequency reproduction while maintaining the original mass and structural integrity of the vibration unit, avoiding the need to increase mass that would overload the support members
3Reliability
If bass-reflex speaker system is structured, then low tones can be reproduced, but in narrow space only small speaker can be mounted limiting the frequency band
Solution Approach 1:
The invention optimizes the acoustic parameters by designing the duct with specific length, cross-sectional area, and resonance characteristics. This parameter optimization allows the small speaker unit to effectively reproduce a broader frequency band including low tones, achieving adaptability comparable to or exceeding traditional bass-reflex systems with larger speakers
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 design allows effective reproduction of low-frequency sound pressure even with small speaker units, widening the resonant frequency range and enhancing sound pressure sensitivity in low-frequency bands, while minimizing the risk of diaphragm inclination and failure.
Implementation Method 1
the resonant frequency of a vibration unit in the speaker unit is set in a frequency band lower than the resonant frequency of a Helmholtz resonator composed of the enclosure and the duct
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
With a vehicle-mounted acoustic device, a bass-reflex speaker system, composed of an enclosure, ducts, and a speaker unit, is accommodated in a head restraint. Each duct has a large ratio of the duct length to the area of the duct cross section to increase the load mass of air in the duct, so that the resonant frequency of the vibration unit in the speaker unit can be set in a frequency band lower than the resonant frequency of a Helmholtz resonator. Thus, sound pressure in a low-frequency band equal to or lower than the resonant frequency of the Helmholtz resonator can be emphasized and the emphasized sound pressure can be given to the ear.