# How do you tell the difference between speakers and microphones?

How do you tell the difference between speakers and microphones?

I pulled the following two components out of an old cell phone and cannot tell them apart.

Each have two metal contacts on the back.

• Are you sure they're not both speakers? One for external and one for the ear? May 2, 2011 at 19:25
• I thought about that but the component with the three holes in the center was located underneath the hole at the mouth piece end of the phone. I'm starting a Circuits and Devices class here soon so I'm going to hook the 'microphone' up to a function generator and then an oscillator to see what happens. The speaker I've already hooked up to a function generator. May 7, 2011 at 14:47
• If you pulled a component out of the mouthpiece, doesn't that mean it's a microphone? May 7, 2011 at 23:16
• True but it was awhile ago and I couldn't remember which came from which end. May 9, 2011 at 4:49

The speaker is the yellow device on the right-hand side, the microphone is the device on the left, with blue plastic/metal visible.

The speaker will almost inevitably be larger then the microphone. Also, you can actually see the voice-coil in the speaker - it is the copper colored oval.

@markrages - is somewhat correct about measuring impedance, but not correct about the internals. The speaker should read as a fairly low impedance - less than 100 ohms.

However, in all likelyhood, the microphone is a Electret Microphone, which uses a capacitor which varies in capacitance in response to air pressure waves, e.g. sound.

Getting a meaningful signal out of an electret microphone is pretty simple, but they do not produce an output without being biased with a power supply. Basically, they need a little bit of power to run, and you have to supply them with that.
Fortunately, there are lots of schematics freely available, and they're generally pretty simple.

• An electret doesn't need bias. See your citation. May 18, 2018 at 14:51

You can measure the impedance. Speakers generally have lower impedance than microphones. Otherwise they are really the same thing, a transformer between sound and electrical energy.

• Otherwise they are really the same thing - This hasn't been true in anything but some (musical) instrument microphones for decades. Everything on the market at this point pretty much uses little electret mics, which are a whole different ball-o-wax. Apr 30, 2011 at 8:11
• The little speaker in my older PC is a piezo disk with a high impedance, 250ohms at 2khz, no continuity with dc. Nov 15, 2012 at 14:40