choosing microphone for "baby monitor" replacement

[keith]

I've given up on useless wireless baby alarms, and just want to set up a
mono microphone in little one's room connected to my spare audio amp + 1
speaker.

But I'm puzzled as to what microphone to use - it's 10 years since I last
played with these...and back then I could have tried several but nowadays I
have to buy the right one.
Please can someone make a suggestion?

If I want to plug the mic into the line in input of a standard audio
amplifier does it have to be :
-condenser/electret/coil ?
-600 ohm//2.2kOhm/50Kohm ?
-would I need to use a preamplifier - is there a sensitivity figure to look
for?


Presume i need omnidrectional to pick up noise in the room?
I do need something that'll reject mains hum well as the speaker will be on
all night.
Thanks for any suggestions

 

[JeffM]

what microphone to use

...into the line in input of a standard audio amplifier
...is there a sensitivity figure to look for?
keith

Right on. It'll range from about -40db to -65dB.
The higher the number (closer to zero), the less gain you will need.
http://www.google.com/search?&q=microphone-sensitivity-*-db

A "standard audio amplifier" needs enough gain
to boost this up to (barely?) audible levels.
I would think all but the whimpiest would get you there.
A $4 set of amplified computer speakers might even do it.
There may even be a mic at the 99 Cent Store that works for you.
Unless you're planning to make an album of your kid's nocturnal noises,
quality shouldn't be a huge issue.
Professional Grade Equipment(tm) is hardly necessary.
Look at surplus/discount places.
A bit of trial & error shouldn't be that expensive.

Presume i need [omnidirectional]?

Does your infant travel that much at night?
Is there a lot of ambient noise when the kid is sleeping?
Try what's cheap / easily available first.