Headrest Bass-Reflex Speaker Ducting for Low-Frequency Output
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Solution Overview
Problem
Conventional acoustic devices struggle to effectively reproduce low-frequency sound pressure using small speaker units due to limited resonant frequency range and increased load on damper and edge 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 generating sound pressures of opposite phases, where the resonant frequency of the vibration unit is set lower than the Helmholtz resonator, with a duct configuration that increases air mass load and positions the listening point to receive unoffset low-frequency sound pressure from the duct without interference from the speaker unit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the mass of the vibration unit is increased to lower the resonant frequency, then the resonant frequency can be reduced, but a large load is exerted on the damper member and edge member, causing the diaphragm to incline and increasing failure risk
Solution Approach 1:
The patent changes the physical parameters of the damper member and edge member (increasing their diameter and adjusting their stiffness) to modify the spring coefficient of the support system. This allows the resonant frequency to be lowered without increasing the mass of the vibration unit, thereby avoiding excessive load on the support members and reducing failure risk.
Solution Approach 2:
The patent makes the support system dynamically adjustable by providing multiple damper members and edge members with different dimensions and stiffness characteristics. This allows optimization of the spring coefficient to achieve the desired resonant frequency while maintaining adequate load-bearing capacity and preventing diaphragm inclination.
2Volume of moving object
If a small speaker unit is used to fit narrow space, then the device can be mounted in limited space, but the frequency band that can be emphasized remains relatively high
Solution Approach 1:
The patent changes the parameters of the support system (damper member and edge member dimensions, material properties) to adjust the spring coefficient. This enables a small speaker unit to achieve a lower resonant frequency by optimizing the mechanical properties of the support components rather than increasing speaker size or vibration unit mass.
Solution Approach 2:
The patent applies different local qualities to different parts of the support system by using damper members and edge members with specific diameter ranges and stiffness characteristics. This localized optimization allows the small speaker unit to achieve low resonant frequency performance through enhanced local structural properties rather than overall size increase.
3Speed
If the diameter of damper member and edge member is increased to lower spring coefficient, then the resonant frequency can be lowered, but the speaker unit size increases
Solution Approach 1:
The patent optimizes the parameters of the damper member and edge member within specific diameter ranges (5-15mm for damper, 3-10mm for edge member) to achieve the desired spring coefficient. This parameter optimization allows lowering the resonant frequency while constraining the increase in speaker unit size to a minimal acceptable range.
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
Enables effective reproduction of low-frequency sound pressure even with small speaker units by setting the resonant frequency in a lower band, enhancing sound pressure sensitivity and widening the frequency band emphasis, while minimizing the risk of diaphragm inclination and failure.
Implementation Method 1
a speaker unit (20) attached in the enclosure (11), the speaker unit (20) generating first sound pressure toward the outer space (So) and also generating second sound pressure toward the inner space (Si), the first sound pressure and the second sound pressure having mutually opposite phases
Implementation Method 2
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 (11) and the duct (12)
Data Source
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.