How do I determine wattage and ohmage of a speaker

[echoshock]

Hi yall,

How can you determine the wattage and ohmage of a speaker set? Its one of those cheapo craigslist buys but there is no indication of the speaker info.

 

Thanks

[franknputer]

You can use a volt meter on its ohms setting to test the speaker (It probably looks like this: ? ). It won't be exact, but whatever number that it's less than (4, 8, 16, or whatever) should be about right, i.e. if it tests 3.3 ohms then it's a "4 ohm" speaker.

 

Watts - you're on your own. Can you tell who made it? Is there any kind of part number stamped on it? You might be able to do some detective work & find out.

[MikeRivers]

 

Hi yall, How can you determine the wattage and ohmage of a speaker set? Its one of those cheapo craigslist buys but there is no indication of the speaker info.

A cheapo craigslist speaker should never be used in any application where you care what the impedance or power handling capacity is. Connect it to what you plan to use it for, start playing some music through it and bring the volume up SLOWLY. You'll hear when it starts to crap out before you do any damage to it.

 

If it gets loud enough without breaking up, use it. If not, put it up for sale on eBay as "Power and impedance unknown but sounds great."

[Billster]

If it gets loud enough without breaking up, use it. If not, put it up for sale on eBay as "Power and impedance unknown but sounds great."

 

:lol::lol:

[philbo]

You can use a volt meter on its ohms setting to test the speaker (It probably looks like this: ? ). It won't be exact, but whatever number that it's greater than (4, 8, 16, or whatever) should be about right, i.e. if it tests 5.3 ohms then it's a "4 ohm" speaker. Watts - you're on your own. Can you tell who made it? Is there any kind of part number stamped on it? You might be able to do some detective work & find out.

 

Nope, nope, nope - - won't work. An ohm meter measures only DC resistance. What he's looking for is impedance.

 

The right way: Feed a small 1 KHz signal into the speaker, with a small value (like 100 Ohms) potentiometer in series with the speaker. Adjust the potentiometer till you get the same AC voltage across the speaker as you do across the potentiometer.

Then carefully disconnect the potentiometer so you don't disturb its setting, and use the ohm meter to measure the potentiometer resistance. That number is the impedance in Ohms of the speaker at 1 KHz.

 

There is no way to measure power handling capability with a non-destructive test. Destructive test: Apply increasing amounts of AC power to the voice coil till it smokes or flies out across the room. Divide that number of watts in half.

 

Actually, you're right on the mark on the power thing - - the only way to get that data is to get the speaker make & model & look up the manufacturer data.

[Lee Knight]

It was cheap right? I say just plug a Marshall Major into it and go. Make sure you're mic'ed and you're recording and just solo. Once. Really loud. Rock.

[franknputer]

Oops, my mistake - actually, measuring with the ohm meter should be slightly below, not above.

 

philbo, your testing may be more accurate - but for a quick & dirty check of "is-this-a-4-or-8-ohm-speaker", then using an ohm meter is close enough to make an educated guess. I suspect that, given that the OP bought a cheap, unidentified speaker off of CL and now has to ask this question, my method is sufficient. However, if he wants to get a tone generator out & wire up a pot, by all means.

 

Feed a small 1 KHz signal into the speaker, with a small value (like 100 Ohms) potentiometer in series with the speaker. Adjust the potentiometer till you get the same AC voltage across the speaker as you do across the potentiometer.

Don't you mean DC voltage, though?

[philbo]

Oops, my mistake - actually, measuring with the ohm meter should be slightly below, not above. philbo, your testing may be more accurate - but for a quick & dirty check of "is-this-a-4-or-8-ohm-speaker", then using an ohm meter is close enough to make an educated guess. I suspect that, given that the OP bought a cheap, unidentified speaker off of CL and now has to ask this question, my method is sufficient. However, if he wants to get a tone generator out & wire up a pot, by all means. Don't you mean DC voltage, though?

 

No. If it's a 1KHz tone, it's got to be AC. DC is, like, zero Hz.

 

You're right about quick & dirty, and it is better than nothing, but it can be pretty misleading... for example, a 500 Watt 8-Ohm speaker is going to use much larger wire in the voice coil than a 50 Watt 8-Ohm speaker, so the 500 Watt speaker might read very low on an ohm meter, like maybe 1.8 ohms of DC resistance.

 

Another little-appreciated fact is that the impedance of a speaker will vary dramatically over frequency (it's not unusual for an '8-Ohm' speaker to vary from 2 to 15 ohms as you sweep through 20 Hz to 20 KHz). This is why 1 KHz is frequently used as a standard test frequency.

 

BTW, the 'Your Band is Awesome' link is broken.

[the stranger]

Thanks for the class, guys.