headsets Q?

[stillin1]

I'm offered a set of Bose noise cancelling headsets. There are 2 types - high and low impedence. Any one any idea which I need for a Europa homebuilt?
I assumed impedence was what the wife did twixt payday & happy-hour.:sad:

[GT]

Hi,

In simple terms impedance is the opposition to the flow of alternating current. Signal (e.g. your voice) carrying electrical equipment operating together should have matched impedances in most applications. Which headset you need depends on the electrical characteristics of your radio and intercom installation. Give the manufacturer or distributor a call and they should be able to help.

Regards, GT.

[IO540]

I don't think Bose offer two different impedances. They do offer different connectors: the standard two-jack version (for normal planes) and a single-plug (a plastic Lemo connector) for aircraft-powered installations. I have used both. But the headset and mike are identical.

I would ask the maker of your intercom, if possible.

If I am correct above, and you have the option (ie it's your own plane) I would go for the aircraft powered version. For about £30 you can buy a panel mount socket (e.g. Headset Services, Shoreham) and it saves the need for a battery. The downside is that if you buy an ICOM transceiver with a "headset adaptor" you will need a normal two-jack headset... (one can make an adaptor for that too)

Bose are great headsets, arguably the best there are. But they aren't built to be chucked around in a club environment!

But hang on.... are these aviation headsets or hifi headsets you are talking about???????

[S-Works]

You cant beat BOSE :)

They only do one impedance headset, you are confusing the helicoptor version that is available with different dynamic mikes.

In addittion to my own a/c I fly around 20 others and have never find an intercom or another headset that they won't work with.

Hope this helps!

B

[RichyRich]

From what I can gather, military radios use dynamic microphones (low impedance, Bose spec 5 ohms), and civilian use electret (higher impedance 220 ohms to 2200 ohms, Bose again, and of course electrets need a bias voltage supplied from the radio).

So, you'll need high impedance.

Info gleaned from Bose and David Clark websites.

Hope this helps,
RR

[stillin1]

Thanks all. Sorted.:ok:

[StrateandLevel]

The "military" mics are as stated dynamic, balanced (each wire is balanced either side of ground to cancel unwanted RF pickup) and most importantly cannot support the Electret or Carbon style mic because they have no DC feed to the mic, effectively shorting it. Their audio output is low, typically 3 - 5 millivolts

The twin plug US mic system was originally designed for high output carbon mics producing arround 100 milivolts, with a DC feed to activate the mic. These were replaced initially by dynamic mics which needed an amplifier of about 100x to match the radio, the DC feed drives the amplifier whilst an isolating capacitor is needed to prevent the mic being shorted out. The Electret effectively has an amp built in, though extra amplification is usually required, they are simpler and cheaper that the dynamic type; to produce, not necessarily to buy!

Mixing and matching these devisces generally doesn't work because one invariably shorts out the other stopping it from working altogether.

On the headset side, the impedance is not so critical, most will work anywhere, only the volume level suffers when different headsets are used. The military system uses an impedance of arround 75 ohms whilst the US two plug system is closer to 300 ohms.