Instructables

How do you use speakers?

I am new to using speakers(the only audio project being the Hallmark Gift Card Speakers) and was wondering how to properly use a speaker that was taken out of, say, an alarm clock. Would it be similiar to the gift card speakers, where you just have to solder the wires to a set of headphones and it works, or what?

framistan4 years ago
A speaker is just a stationary magnet and a movable coil of thin wire (near each other). As electrical pulses enter the coil wires.... it causes the magnetism of the coil to push against the stationary magnet. A cone of paper or thin plastic attached to the wire-coil moves up and down SLIGHTLY with each electrical "sound" pulse. You asked about the difference between gift card speakers and alarm clock speakers. The only difference might be slightly larger SIZE of the paper-cone.. and possibly slightly larger "voice-coil"
some gift card speakers are piezo elements - different mechanism, same result, voltage = vibration.
lemonie4 years ago
What do you want to power the speaker(s) with and what is printed on the back like "16 ohm 1W" "8 ohm 3W"?

L
I'd say the most important characteristic of a speaker, electrically, is its impedance, in ohms.  I don't know if you know anything about electricity, but if you do impedance is just the voltage across a circuit element divided by the current flowing through that element.  Impedance is defined the same way as resistance via Ohm's law, but for AC signals. 

If you don't know anything about electricity, than that first paragraph didn't make any sense to you.

Nonetheless, I claim that the main difference, electrically, I mean in terms of driving it with a circuit, the main difference between a magnet-coil-paper-cone speaker, and one of those shiny piezo-disc-shaped speakers, like found in alarm clocks, is impedance.  The magnet-coil-paper-cone speaker will typically have an impedance of 8, 16, or 32 ohms, at say 1 KHz, and the piezo-disc-shaped speaker will have an impedance of several thousand ohms at the same frequencies.

A consequence of this is that if you just solder a piezo disc speaker onto some headphone wires, and plug it into your mp3 player, this new speaker will not overload the player, and it also won't be very loud, because the player will have difficulty driving any current through this large impedance.  Another way to say this is the electrical power dissipated by this speaker will be small, assuming P=V2/Z, and P is small when Z is large.

Trying to put a low impedance speaker into a circuit designed for a high impedance speaker will not work as well.  For example suppose you try to solder a  8 ohm magnet-coil-paper-cone speaker, into your alarm clock, in place of the original piezo-disc speaker.  The result would be that this speaker would overload the driver.  That is to say if you calculate P=V2/Z, with the new small Z, it comes out to an answer that's more audio power than the alarm clock circuit can comfortably supply.
The physical result is that you again get weak sound, no sound, or the circuit just doesn't work.  Maybe even some part of the circuit, e.g. a transistor,  burns out, maybe.  Stuff like that can happen when a driver is overloaded. 

This is in contrast to the mp3 player driving a piezo, which could be called underloaded.  The piezo speaker, electrically, looks like, like there's no speaker even there, almost like an open circuit. 

More here:
http://en.wikipedia.org/wiki/Loudspeaker
http://en.wikipedia.org/wiki/Electrical_impedance
http://en.wikipedia.org/wiki/Audio_frequency
http://en.wikipedia.org/wiki/Low_fidelity