Bone Conduction Stereo Headphones

Hello, I’m trying to make a DIY wired bone conduction headphones for music listening/production to replace my Aftershokz bone conduction headphones.

I have a couple of small transducers (15mm) attached to a makeshift headphone case. I currently use this together with an audio interface.

I want to improve the sound quality and loudness - but I’m new to this and I’m not sure what I’m looking for. The sound currently has a lot of bass and high frequencies, and needs more midrange.

I was thinking it needs some sort of amplifier to increase the gain and an EQ (maybe a high pass filter/low cut filter).

I would appreciate any advice/tips on where to start - I also have a limited amount of experience with electronics. I’ve attached a photo of my current prototype. Thank you.

Hi Daniel,

Awesome project idea! Most complex digital audio sources (computers and smartphones) will have a digital EQ built-in you could play around with that to see how you go.

If you want to take a more scientific approach you’d need a proper sound level metering setup so you can plot the frequency response of the drivers - or at least be methodical about playing with the audio response qualitatively.

Here’s a great research paper with some details on audio perception through bone conduction:

Once you’ve got something a bit more locked in, you coud set up a hardware EQ to improve the sound from the headphones :slight_smile:

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i was thinking of a active e.q of some description …browse the web for a 12 volt preamp…there are many out there that don’t cost the earth and there quite small devices in most cases.

.but i was wondering of your output audio level voltage if you know this …it would help in your equation
weather its simple low level or speaker voltage … …if it is speaker level and your just driving them to hard without realizing .i`d suggest put a 10 k resistor in the audio lines to cut the level down you may have to increase your input voltage somewhat,… but also try different values like 8.2 k or go higher etc…etc… just have a play around with the levels… you may find this an easier alternative…

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Thank you Oliver! That research paper is excellent.

I’ve tried using digital EQ. Whilst it helped, it was changing the eq of the music rather than the headphones. A hardware eq could be more like what I’m after.

Do you mean to have sound level metering to measure the frequency response coming out of headphones? Just for further background, I currently use BAHA (bone anchored hearing aid) for daily use and don’t hear sound through air.

Thank you

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Thank you for the reply Brian, I’m going to look for active EQs and preamps.

I don’t quite understand the output audio level voltage though. Wouldn’t turning down the volume prevent it from driving too hard? Is there a benefit to adding a resistor in the audio lines?

Thank you

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Hey Daniel,

Your project looks very cool!

From my understanding, the resistor will limit the current to the transducer and hence the power (speakers and transducers have a max-rated power that you have to take into consideration when designing the circuit).
Turning down the volume would prevent it although having extra safety factors is always good.

Cheers,
Liam.

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Thanks Liam, that makes a lot of sense.

I am curious about headphone impedance, and was wondering if it is important to know when making the headphones.