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Hearing Aid Isolation Chamber

Hearing Aid Isolation Chamber. Design Review Presentation. SLAC. 04/28/10. Project Members. Project Partners Dr. Robert Novak Speech, Language, & Hearing Sciences Department Head Dr. Joshua Alexander Assistant Professor of Audiology/Hearing Sciences Team Michael Reutman Qixing Weng

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Hearing Aid Isolation Chamber

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  1. Hearing Aid Isolation Chamber Design Review Presentation SLAC 04/28/10

  2. Project Members • Project Partners • Dr. Robert Novak • Speech, Language, & Hearing Sciences Department Head • Dr. Joshua Alexander • Assistant Professor of Audiology/Hearing Sciences • Team • Michael Reutman • Qixing Weng • Philip Zumbrun

  3. Hearing Aid Isolation Chamber Testing Area Acoustic Material Sound Source Project Start Date: Spring 2010

  4. Project Background • Dr. Alexander researches hearing aid performance • We are working to make a hearing aid test unit that will address specific needs in his research • Successful delivery of this project will benefit Dr. Alexander’s research, which in turn contributes to the innovation and improvement of hearing aid technology • About 10 million Americans use hearing aids *Statistics retrieved from NIDCD (National Institute on Deafness and Other Communication Disorders)

  5. Specifications • Acoustic performance • Testing chamber must have a flat frequency response from 200Hz-10KHz • Speaker • Must be able to test up to 110db without distortion • Reasonably flat frequency response from 200Hz-10KHz • Interface • The speaker and microphone must be able to interface with a computer • Microphone will be provided by Dr. Alexander • Speaker will be accessible to external audio via a BNC connection • Size • Unit should be 9” x 9” x 9” within ± 3” • Weight • Unit must weight under 25lbs total

  6. Conceptual Design Fonix 7000 Audioscan Verifit • What is already out there? • Hearing aid test systems are common and widely used

  7. Conceptual Design • Key difference in our design: computer interfacing capabilities • Existing systems are meant to be “all-in-one,” performing the tests and displaying the results all within their system • Our project will allow for results to be recorded and analyzed on an external computer and for audio to be routed to the speaker for specific tests

  8. Detailed Design • Box materials • Researched various materials and boxes • Eventually decided it would be best to use something pre-made, as it would save significant time in construction • Security box • 13.5x13x10 in • 7 lbs

  9. Decision Making • Too Heavy • May have difficult time modifying it • Durability • Too Small

  10. Mesh Testing Area • Speaker grill fabric will be used for the material that the hearing aid rests on • Acoustically transparent and lightweight Sound Source

  11. Detailed Design • Acoustic considerations • Anechoic design • For a space to have a flat frequency response over a certain range, the space must be anechoic over that range – free from internal reflections and external sound • Anechoic spaces are limited in their ability to isolate low frequencies by the size of the space (more specifically, the size of their absorbers) • Challenge: Our space if very small! (~1 ft3)

  12. Typical Anechoic Chamber

  13. Detailed Design • Acoustic considerations • Cutoff Frequency • Due to size limitations, our cutoff frequency estimate is around ~3kHz with typical absorbers • Completely anechoic design is not possible • Isolating the space from outside noise • Decoupling from surroundings • Testing in quiet environment

  14. Acoustic Materials • We only have about 4” of possible material to work with • The inner material will be wedge shaped absorbers • The outer material will be a denser fiberglass • Inner material will absorb higher frequencies while the outer material will absorb the lower frequencies 2” 2”

  15. Detailed Design • Acoustic considerations • Estimated attenuation • Compare to FONIX specification: 18 dB of reduction at 1 kHz • Concept of a “pressure box” at 200 Hz

  16. Detailed Design • Speaker • Due to specific requirements, we will be building most of the speaker system from scratch • Key components include power supply, amplifier, V.U. meter, speaker cone, and speaker enclosure

  17. Components - Amplifier: Qkits FK607 15 Watt Power Amp - V.U. Meter: Qkits FK101 LED Meter - Power Supply: ARM 12vDC 1.5 Amp - Speaker: Vifa NE85W 2.5” Full Range Microphone Speaker V.U. Meter Power Supply Laptop running test tone and data collection software Amplifier

  18. Integrating Components • The electrical components will be exterior to the box • This is so that they are easily accessible for maintenance and so that the amount of perforations in the box may be minimized for acoustic considerations

  19. Detailed Design • Speaker • Frequency response: flat within ± 3 dB from 200Hz to 10kHz

  20. Detailed Design • Speaker • No speaker has a completely flat frequency response • A reference measurement will be used to account for the frequency response of the speaker

  21. 3.75” 5” 3” Speaker Enclosure • The ideal volume of an enclosure for the speaker based on its specifications is 0.0328 ft3 • Dimensions of length = 5”, width = 3”, and depth = 3.75” satisfy this requirement and avoid standing waves due to square dimensions • 0.5” plywood will be used the build the enclosure (standard material used for small speakers)

  22. Project Timeline Spring 2010 – Complete design, specify all necessary materials, write instructions for construction Fall 2010 – Construction, testing, delivery

  23. Questions?

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