Mic capsules distorting at low level in binaural dummy head. Why :(

[Pano]

Nice. Good luck with the recordings, i'd like to hear them. Years ago I had a set of expensive "earbud" style mics that worked in a similar way. The recordings were very nice.

[Poxican]

Aye, I've got a nice pair of Roland CS10EM ear mounted mics, they do a lovely job. The head has the advantage of incorporating replica ear canals for vertical localisation, as well as obvious being a free-standing mic.

This recording was done with the Rolands mounted inside a dummy-head:
Binaural Birds by Nathan Gallardo on SoundCloud - Create, record and share your sounds for free

I'll definitely be back with some more in the next few days

[Pano]

Nice. It is natural enough that I had a hard time differentiating it for sounds around me.
I liked the bee. Listened on Sony headphones, will listen on the big VOTT rig tonight.

[scott wurcer]

Originally Posted by Poxican

Hmm I swapped the connections around on one of the capsules and it seems to have sorted it.. going to solder it up properly this morning and see how it goes. Looking at all the wiring diagrams for the mod I can see what you mean, it does look like I did it back to front!

Is there any chance I'll have damaged the capsule by having it wired back to front?

Very unlikely.

[Poxican]

So that has definitely made an enormous difference. It no longer breaks up at speaking levels as it was before. So thanks Scott for helping me fix the capsule issue. However, it seems there was another issue involved which has only now become apparent.

I've been testing it with two devices: a Zoom H4 and into my Focusrite Saffire 6.
I don't think the Zoom is any good for the head. Shouting at the head creates distortion on the Zoom recordings, but I believe that's the Zoom as opposed to the capsules. It only has 3 input settings, low-medium-high, and an in-menu input level which is digital and hence useless. I understand my circuit outputs a line level signal (I'm looking to you for confirmation here....) and the Zoom inputs are mic level, so while it'll be fine for recording ambience and whatnot but it'll be no good in a gig setting. It even distorted recording a noisy corridor at uni today. Any fix for this?

Into my Saffire 6 is much better, but still seems problematic. With gain set to zero and the pad initiated it still seems to distort a little if I shout into the mic. It's not peaking in Logic or on the interface, so I presume it's happening at the capsule. That said, I'm not sure if the mic should be able to handle that kind of level? Is it realistic to expect it not to break up if I shout directly into it? I did a short recording so you can hear the breakup:
ClapsTesting01 by Nathan Gallardo on SoundCloud - Create, record and share your sounds for free

Those are the hardest claps I can muster at the beginning, followed by my shouting into the ears. This isn't very scientific I know...

Any thoughts?

[AuroraB]

Quite frankly, I cannot hear the overload.....????
Build yourself a decent preamp with padded variable output. TL072s, 5534,5532 or even some of the SSM chips should do the trick of optimizing input volume.

This might also give you some ideas
D.I.Y. Recording Equipment | DIY Microphones, Preamps, Compressors, etc.

[Poxican]

Really? There's very noticeable distortion on the 'testing' shouts.

It doesn't seem to be peaking in Logic though, so I can only assume it's the capsules. But I thought the Linkwitz mod would allow them to stand up to that sort of level...

[Poxican]

Sorry to bump this but I'm still having some troubles :/

I tested the mics in front of a PA the other day and they held out well, but they still broke up at high volume, and I'm certain we didn't reach the 130db limit these capsules are meant to be able to handle post-Linkwitz.

I've measured the voltage across the capsule while powered, ie. between terminals 1 and 2, and it reads consistently at around 14v. This definitely seems wrong, though I worry I am taking the measurement incorrectly.

If that is the correct way to measure the voltage, what would that reading indicate? That the capsules are receiving too much power? What could be the cause for that in the circuit?

I'm sorry for all the novice questions, I really appreciate your efforts to help me though!

[Mooly]

The voltage across the capsule must be within the recommended limits for the particular device.

Refering to your original diagram in post #1 the voltage across the capsule is determined by the 33K and the two 5K6 resistors. If you have used a different capsule to the one the circuit was designed for then the voltages will be different as the capsule will probably have a different current draw.

Altering the 33K will alter the voltage across the capsule. Higher t'ohmage and the lower the volts on the capsule.

[Pano]

I thought these capsules wanted about 5V. No?