Voice Amplifier
This project uses a hyper-directional microphone, connected to a small amplifier and loudspeaker, to help the client, who has very quiet speech, be understood whilst in bed. If this helps the client dictate into her mobile phone that will be a great bonus.
The Challenge
The client has quiet speech secondary to a neurodegenerative disorder. When laying down in bed it can be difficult to make herself heard by carers. She is successfully using a voice amplifier in the day when sat upright in her wheelchair. But whilst in bed and being moved for care or to reposition it’s not possible to wear a microphone or be attached to the amplifier, as this gets in the way.
If the clarity of the resulting voice was correct, this could help the client dictate into her mobile phone and this will be a great bonus.
The system should also be simple for the support staff to set-up.
The solution
The key to the solution was the selection of the microphone. As the system was to be used while the client was in bed and not able to move the microphone herself once set up by the carers, it was important that the microphone could detect the voice without having to be too close to the client’s mouth. It should also not have to be directly in front of the client’s mouth.
A low cost, omni-direction microphone would have to be very close to the client’s mouth in order to detect the voice over any general background noise. This type of microphone would also increase the likelihood of feedback between the microphone and the speaker.
The solution was to use a hyper-directional microphone. This would allow the microphone to be held further away from the client’s mouth, while reducing the pickup of background noise. In addition this would reduce the chance of feedback.
The selection was a trade-off between the size (length) of the microphone (and hence the level of directionality) and cost. The Audio-Technica ATR6550X Cardioid Condenser Shotgun Microphone was a good compromise.
The microphone is battery powered, but it is expected that the AA battery should last at least 4 or 5 months based on the expected usage.
The pre-amplifier and amplifier were ready built units, housed in a spare external speaker for a PC. The unit was modified to add a power connector (for standard 12V power adapter), a 3.5mm jack-plug (for the microphone connection), an on/off switch and a volume control.
To support the microphone an LED desk lamp with a long metal swing arm was purchased. This looks like as Anglepoise lamp arm (but considerably cheaper!), but sufficient to support a lightweight microphone.
The LED lamp and cabling was removed and replaced with an adaptor enabling the fixture of the microphone clip. The microphone cable was run along the same route as the power cable for the lamp.
A 3D printed clamp was produced to which the support arm could drop into. This clamped on to the rear headboard of the bed.
The final installation can be see below.
The benefit
The benefit is best summed up by the client herself:
“I’ve had fun using the mic and amp of the past few days and I can report that things are working well. It has proved straight forward for staff and made a difference to my use of speech to text software on my phone and tablet when in bed. Many thanks for using your creativity and knowledge to devise this.”
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