Topic: Advice on custom mic setup

[co9ol]

Hello there, I'm looking for some advice on a custom mic setup. The plan is to replace the speakers in a pair of headphones I already have with larger electret microphones.

The headphones:
https://www.sony.ca/en/electronics/headband-headphones/mdr-xb550ap
These will sit around my neck and the pads will rotate to face forward. I plan on using some aluminum tape to line the inside to shield emf then foam to isolate the mic from the headphones them selves to minimize handling noise.

The capsules:
https://www.jlielectronics.com/microphone-capsules/jli-3413au01/
These or another pair from the site that's similar. I was going to reuse the headphones wire for the mics into a 9v battery box then recorder.

Main concerns:
1 Will this work electrically? The headphones jack is trrs so I'm aware it may need to be converted to trs but that shouldn't be to hard.
2 Emf, will I need to replace the headphones wire with something more shielded? I'd rather not as I'm trying to keep expenses down.

Secondary concerns:
- they're probably going to go through an x-ray at some point, hopefully they don't look too suspicious.
- A spaced pair sitting on my clavical isn't perfect placement but not terrible for someone who's 6'2"?

Let me know if you have any thoughts or advice to give.

[grawk]

EMF is unlikely to be a problem.

Given the level of work involved, you’re probably better off replacing the cable while you’re replacing the speakers. Then you can have exactly the connectors you need.

As to whether it will work, it sounds clever so experiment and let us know!

[joeldotc]

Unfortunately that type of capsule likely isn’t going to work for this for two main reasons.

First, directional capsules like that need to have both sides open to the air, so having one side facing the inside of the headphones won’t work. Those capsules are designed for condenser mic tube style casings (like the u47, C414, etc). You could maybe get around this somehow by modifying the headphones heavily, but I don’t think it’s worth the effort. This would be a problem for any directional capsule you choose, so you’d probably be limited to omni capsules, which I don’t think would be ideal for mounting inside of headphones.

Second, that’s the electret capsule only, without any of the components which pre-amplify/convert the impedance of the signal (most of the DIY projects you see online have people using capsules that have integrated JFET impedance converters). You can add a circuit to the build to do this though.

If anyone sees anything wrong with that I’ve said let me know 

[fanofjam]

Unfortunately that type of capsule likely isn’t going to work for this for two main reasons.

First, directional capsules like that need to have both sides open to the air, so having one side facing the inside of the headphones won’t work. Those capsules are designed for condenser mic tube style casings (like the u47, C414, etc). You could maybe get around this somehow by modifying the headphones heavily, but I don’t think it’s worth the effort. This would be a problem for any directional capsule you choose, so you’d probably be limited to omni capsules, which I don’t think would be ideal for mounting inside of headphones.

Second, that’s the electret capsule only, without any of the components which pre-amplify/convert the impedance of the signal (most of the DIY projects you see online have people using capsules that have integrated JFET impedance converters). You can add a circuit to the build to do this though.

If anyone sees anything wrong with that I’ve said let me know 

I might not understand your response, but how is what he wants to do any different than hat mounting a pair of cardioids for stealth recording, where the back of the capsule is either an inch from your head on the brim of a cap or directly contacting your head if the capsules are inside your hat?  Not ideal, but it absolutely works...I've done it many times with fantastic results.

[Gutbucket]

Yes, as joeldotc mentions that type of capsule will require an impedance conversion circuit, along with good shielding around both mic capsule and the conversion circuitry, adjacently mounted near each other somehow inside the headphones. See the OPA Alice single channel impedance conversion board listed under related products on that webpage. You'd need two of those, one for each channel.  Doing all that will be quite an undertaking. That capsule is also overly sensitive and its SPL max is a bit low for typical concert recording.

Will be much easier to simply install a small pair of omni lavalier mics in there.  They'll be smaller, and will complete with an inbuilt FET stage and will have the cabling and connector all nicely worked out.. or easily reconfigurable.

Install them facing outward and wear the 'phones normally on your head to produce a pseudo-binaural recording.  Hang them around your neck and the outside faces will angle outward and downward somewhat, which should also work even though the downward angle, close spacing, and lower height will be less ideal than head-worn where the mics are up high and your head serves as baffle.  If the cups rotate so that they lay flat on your chest and face forward, you'd want as much spacing between them as you are able to manage, 12 inches would be good and is possible with other chest mounting schemes, but probably hard to manage with headphones.  Worn that way the sensitivity pattern of the omnis effectively becomes forward-facing cardioid-like for most of the frequency range due to the baffling provided by your torso.

I recorded a bunch of stuff way back in the 80's using a pair of Sony MDR-V6 / 7506 headphones as mics plugged directly into a cassette recorder.  The dynamic drivers in the headphones work as dynamic mics.  Worked much better than you might think, but you are likely to get better results from installing actual mics.

[co9ol]

Thank you for the advise everyone. The idea started with the headphones thinking about how much room there would be inside. Unfortunately, it seems a smaller Primo capsule may be the way to go because of the lack of a JFET in the capsules I already found.