Audio
There are two separate audio systems in the helmet: one for talkin' and one for listenin'.
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System 1 is pretty similar to
MoeSizzlac's simple helmet speaker system which can be found
here, with a couple of small changes to improve volume and clarity. I had initially planned on using an electret microphone, but wasn't happy with the volume level I was getting. Electret microphones are quite sensitive, so you can't turn your amplifiers up very far before the system starts feeding back. I hopped on Ebay and for about 10 bucks found a microphone designed for handheld radios. This microphone is dynamic which tend to be less sensitive and more directional than electret mics. I also ordered some cheap preamp boards, since the mic didn't have a built in preamp like the electret mic. From the preamp I wired up two little amplifiers, the same ones Moe used I think, and hooked up a speaker to each one. I mounted the grills of the ODST helmet, and crammed the amplifiers and preamp into the right cheek. The microphone attaches to the helmet right in front of my mouth with some velcro.
The talkback system before I added the second amplifier:
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Microphone mounting:
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Amplifier and speaker mounting:
View attachment 297053
Speaker grill from the front:
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So, this design is pretty loud, but I'm a sound guy and I figured it couldn't hurt to try getting it a little louder. I designed a notch filter centered at the frequency of the feedback I was getting (about 1500HZ), and added it into the signal chain. It does eliminate feedback at that frequency, but is a little too drastic in the way it effects the overall sound. I think I may try designing a little equalizer to put in the left cheek.
The Filter board:
View attachment 297059
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