Inverted Speaker Headphone for Earplug Testing
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Solution Overview
Problem
Conventional headphones fail to produce consistent sound amplitude across the frequency range of interest (250 Hz to 4000 Hz) for earplug testing, often resulting in low speaker output and potential damage from excessive electrical input, while the speaker placement can interfere with earplug installation and wearer comfort.
Innovation Solution
A headphone design with a speaker mounted in reverse orientation, where the diaphragm faces away from the ear and holes on the rear side direct sound through a tapered tube to the ear, ensuring high sound levels (at least 120 dB SPL) across the desired frequency range with a 25 mW electrical input, accommodating earplugs and enhancing comfort.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional speaker orientation is used with diaphragm facing the ear, then sound delivery is straightforward, but the speaker output amplitude is insufficient across the frequency range and requires excessive electrical input causing distortion and potential damage
Solution Approach 1:
The patent inverts the conventional speaker orientation by positioning the diaphragm to face away from the ear and the rear of the speaker (with holes) to face toward the ear. This reversal allows sound to be delivered through the rear holes directly into the ear canal, achieving high output amplitude across the frequency range (250 Hz to 4000 Hz) with only 25 mW electrical input, thereby avoiding speaker distortion and damage while maintaining reliable performance
2Power
If the speaker is placed close to the outer ear for effective sound delivery, then sound amplitude is sufficient, but the earplug can touch the headphone grille preventing proper seating or disturbing earplug installation
Solution Approach 1:
The patent extracts the sound delivery function from the conventional speaker grille configuration and relocates it to the rear of the speaker facing the ear. By using a tube structure with holes in the rear, the sound delivery path is separated from the outer ear contact area, allowing the earplug to be inserted without touching the headphone grille while still delivering sufficient sound amplitude (at least 120 dB SPL) to the ear canal for effective earplug testing
3Power
If higher electrical input is applied to compensate for low speaker output, then sound amplitude increases, but the speaker becomes distorted and may be damaged
Solution Approach 1:
The inverted speaker orientation with rear-facing holes and tube structure enables efficient sound delivery with low electrical input (25 mW). This configuration achieves high sound amplitude (at least 120 dB SPL) directly at the ear canal without requiring excessive electrical input, thereby avoiding speaker distortion and potential damage while maintaining adequate sound output for earplug effectiveness testing across the frequency range of 250 Hz to 4000 Hz
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 headphone achieves a 5 to 10 dB higher sound pressure level across the frequency range compared to conventional audiometric headphones, ensuring effective earplug testing without speaker damage, while accommodating earplugs and improving user comfort.
Implementation Method 1
a speaker (42) is mounted at the rear R end of the passage... The speaker has first and second sides 44, 46. A diaphragm 50 that lies at the second side 46, vibrates inward and outward to generate sound
Implementation Method 2
a tube in the headphone frame has an outer end with a diameter that encompasses the ring of holes to direct sound from the holes to the person's ear
Implementation Method 3
The tube in the headphone frame has a tapered outer end that is enlarged to encompass the ring of holes
Data Source
AI summary
A headphone that is especially useful to test the efficacy of an earplug installed in an ear canal, by using the headphone to produce sound and by sensing sound pressure at the ear drum despite the presence of the earplug. Applicant uses the speaker (42) in the headphone to produce a smooth and reasonably “flat” frequency response by reversing the speaker orientation. In the reversed orientation, the front side of the speaker diaphragm (50) faces into the headphone cup and away from the ear. The rear side of the speaker that has a circle of holes (52), faces toward the ear. The headphone frame has a cylindrical passage (40) for carrying sound to the person's ear, which has an outer end (78) that is tapered to encompass the holes in the speaker back side (44). The axial distance (L) from the speaker rear side to the ear, is at least 0.6 inch to accommodate the protruding end of an earplug.