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

Hearing Aid Isolation Chamber

Design Review Presentation 04/28/10

SLAC

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

Project Start Date: Spring 2010

Hearing Aid Isolation Chamber

Sound Source

Testing Area

Acoustic Material

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)

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

Conceptual Design

• What is already out there?– Hearing aid test systems are common and

widely used

Fonix 7000 Audioscan Verifit

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

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

Decision Making

•Durability

•Too Small

•Too Heavy

•May have difficult time modifying it

Mesh

•Speaker grill fabric will be used for the material that the hearing aid rests on

•Acoustically transparent and lightweight

Sound Source

Testing Area

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)

Typical Anechoic Chamber

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

Acoustic Materials

2” 2”

•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

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

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

V.U. Meter

Amplifier

Speaker

Microphone

Power Supply

Laptop running test

tone and data collection software

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

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

Detailed Design• Speaker

– Frequency response: flat within ± 3 dB from 200Hz to 10kHz

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

Speaker Enclosure

5”

3.75”

3”

•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)

Project Timeline

• Spring 2010 – Complete design, specify all necessary materials, write instructions for construction

• Fall 2010 – Construction, testing, delivery

Questions?