Topic: Impedance Matching?

[HazyShadeofWinter]

I would like to record audio from a source that is putting out an audio feed with an impedance ranging from 260 to 300 Ohms.

The input on the recording device is 2.2 Ohms.

In order to match the two impedances, what is the best approach to achieve the highest audio quality? Is a transformer preferred over a series of resistors?

By the way, is there a ready-made device that can perform that impedance matching, either automatically or manually?

Thanks.

[jefflester]

The input on the recording device is 2.2 Ohms.

Hard to imagine a recording device with an input impedance of 2.2 ohms. Sure it's not 2.2 kohms?

You don't want to match the impedances, you want the receiving device (recorder in this case) to be 10x or more the impedance of the source.

There are probably better explanations, but here is one (6th post by Steve Hogan):
http://repforums.prosoundweb.com/index.php?topic=1151.0

[HazyShadeofWinter]

According to the manufacturer's literature, the GoPro Hero 3+ has a 2.2 Ohm mic input.

The output device is the intercom audio output of a Cessna 172.

[jefflester]

According to the manufacturer's literature, the GoPro Hero 3+ has a 2.2 Ohm mic input.

Amazingly:
http://gopro.com/support/articles/hero3plus-external-microphone-information
does say
"GoPro mic input impedance is 2.2 Ohms, any mic that has impedance that's close to 2.2 Ohms should be OK"
But yes, they must clearly be wrong.

This Shure site:
http://shure.custhelp.com/app/answers/detail/a_id/5395/~/shure-mic-with-gopro-camera
says
"Actual impedance of HERO3 mic input: 2,200 ohms
Note: A microphone with an impedance of 2,200 ohms or less is acceptable."


The other factor is what is "audio output of a Cessna 172" - is that like a headphone jack? If it is, that signal level might be too high and drive the GoPro input into distortion.

[HazyShadeofWinter]

The intercom "output" is a 1/4" jack.

According to literature available for General Aviation headsets (see David Clark) the impedance is 300 Ohms.

[aaronji]

It has been a long time since my aviation school days, but I don't think you'll have any problems.  Before I shelled out the (pile of) cash for a nice Peltor headset, I tried a bunch of different regular headphones and they all worked fairly well.  Some needed the volume to be jacked up a bit, though.

[HazyShadeofWinter]

Thanks for all the suggestions. Much appreciated.

[Gutbucket]

    I guess the ground is an impedance mismatch to the sky 

Can’t say it ever occurred to me that I would come across a situation where horn-loading and landing-gear were somehow analogous.  Wondering if I will start thinking of various forms of human interactions in terms of impedance.

[Gutbucket]

The inverse roundover prevented him from defracting all over the place.