noizformoney Posted December 23, 2000 Share Posted December 23, 2000 A freind has an old Supro amp w/ 2 12" speakers that are 12 ohms each. He would like to know how many ohms the amp really puts out because he would like to change the speakers. How can he measure that? Thanks, Roscoe Link to comment Share on other sites More sharing options...
Caevan O’Shite Posted July 28, 2005 Share Posted July 28, 2005 Probably actually 16-ohms each... If you try to measure a given speaker's impedance with a meter, it will always read off like that. Note the fairly well-known example of how an incorrect impedance was listed for many "tweed" Fender Champs, where the speaker's resistance was measured, instead of its true impedance. True impedance measurement requires specialized equipment. Ask yourself- What Would Ren and Stimpy Do? ~ Caevan James-Michael Miller-O'Shite ~ _ ___ _ Leprechaun, Esquire _ ___ _ Link to comment Share on other sites More sharing options...
Blue Strat Posted July 28, 2005 Share Posted July 28, 2005 Caevan is right. A multi-meter sends a small electrical current through whatever it's measuring and then calculates the DC resistance. A speaker also has capacitance and inductance which effect the impedance of the speaker, and the meter can't measure those. There are two types of circuits: series and parallel. If the two speakers are wired in series, measuring from the positive terminal of one speaker to the negative terminal of the other speaker will give you double the resistance of one speaker. If you measure 12 ohms on speaker one, you'd get 24 ohms when you measure them both like I explained above. In parallel, you'd get 1/2 the resistance, or 6 ohms. BlueStrat a.k.a. "El Guapo" ...Better fuzz through science... http://geocities.com/teleman28056/index.html Link to comment Share on other sites More sharing options...
Caevan O’Shite Posted July 28, 2005 Share Posted July 28, 2005 Isn't speaker-impedance also measured and rated over a range of varying/multiple signal fequencies, as well, Blue'? Ask yourself- What Would Ren and Stimpy Do? ~ Caevan James-Michael Miller-O'Shite ~ _ ___ _ Leprechaun, Esquire _ ___ _ Link to comment Share on other sites More sharing options...
BluesWithoutBlame Posted July 28, 2005 Share Posted July 28, 2005 Excuse me for being presumtive, but I think the original post was most interested in what impedance the amp wants to see, or is designed for. I could be wrong, but I think that was the main point. I don't have the answer but am sure that a google search for the amp would give you the answer. Quick answer, he can't measure what impedance the amp is designed to handle. You have to find out what the amps specs want. Still, everyone her is on the right track because you can assume the original speakers are correct in their impedance. ==================================================== Check out my original music at http://www.soundclick.com/bands/jacker "In theory there is no difference between theory and practice, but not in practice." Link to comment Share on other sites More sharing options...
BluesWithoutBlame Posted July 28, 2005 Share Posted July 28, 2005 To add to what I said, it is really important to find out which way the two speakers are configured. As bluestrat said, if they are parallel (meaning the + lead goes seperately to each plus side of the speakers, and there is a path to ground seperate on each - side of each speaker) the amp wants to see half of their vallue (12 ohms is not standard...you need to find out what the real rating of each speaker is in impedance) but if they are wired in series (just follow the wiring, if it is series the plus side of the wire will go to one speaker, that speakers negative side will go to the plus side of the other speaker and THEN to ground (or back to the negative side on the jack). In that case the rating is addative...so two 8 ohm speakers would be 16 ohms, two 16 ohm speakers would be 32 ohms. ==================================================== Check out my original music at http://www.soundclick.com/bands/jacker "In theory there is no difference between theory and practice, but not in practice." Link to comment Share on other sites More sharing options...
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