Members Guitin Better Posted October 9, 2008 Members Share Posted October 9, 2008 My church was looking to get rid of some cabinets that were no longer used from our old sanctuary. I brought them home and wired them up to my 50 watt guitar amp. They sound find but I'm worried about mismatched impedance. They are custom cabs and the impedance is not shown anywhere on the cab. The amp is rated for no less than 8 ohms. The cabs each have a 15" woofer, a 6" mid and a horn tweeter. I have now idea what the impedance of the cab would be and I'm concerned about roasting my amp. Any thoughts?? Link to comment Share on other sites More sharing options...
Members mrmax Posted October 9, 2008 Members Share Posted October 9, 2008 Use a Volt/Ohm meter (set for Voltage) on the 2 wires from the cabinet (+ with + / - with -) should give you an idea where you should adjust your amp's impedance. Hope this helps, Mac Link to comment Share on other sites More sharing options...
Members Guitin Better Posted October 9, 2008 Author Members Share Posted October 9, 2008 My amps impedance is not adjustable. Link to comment Share on other sites More sharing options...
Members mrmax Posted October 9, 2008 Members Share Posted October 9, 2008 Ok but you would still need to know what the cabinet's impedance is. For example if the cabinet is 4 ohms and your amp want to see 8 ohms ( you did say that your church had more cabinets), you could run 2-4 ohm cabinets in series and create a 8 ohm load. But you need the meter to know what impedance is. Link to comment Share on other sites More sharing options...
Members Guitin Better Posted October 9, 2008 Author Members Share Posted October 9, 2008 Well, I did some reading earlier on how to measure impedance and evidently you need some gear I don't have like a pure tone generator. I originally thought I could simply measure the resistance across the speaker terminals thinking impedance and resistance were essentially the same . . . boy was I wrong. Link to comment Share on other sites More sharing options...
Members Guitin Better Posted October 9, 2008 Author Members Share Posted October 9, 2008 bump Link to comment Share on other sites More sharing options...
Members mrmax Posted October 9, 2008 Members Share Posted October 9, 2008 Volt/Ohm meter works fine for me:snax: Link to comment Share on other sites More sharing options...
Members Efekkt Posted October 9, 2008 Members Share Posted October 9, 2008 Don't know if Link to comment Share on other sites More sharing options...
Members knucklefux Posted October 9, 2008 Members Share Posted October 9, 2008 a VOM works fine for measuring resistance, but it cannot directly measure impedance. thanks for playing, though. if this is a tube amp we're talking about, MOST output transformers can handle a 2X mismatch without any undue strain on it or the power tubes. this means that if your amp has an 8 ohm tap, it should be safe with either a 4 or 16 ohm load. don't go beyond that, though. lastly, i have a hard time believing that full range speakers will sound better with a guitar amp than "normal" guitar amp speakers. the highs tend to be piercing in a very unpleasant way, IMO. as for the answer to your question, try pulling the speakers out of the enclosures. the impedance should be indicated on the magnets. you also need to take note of how they're wired. the total impedance will depend on the wiring (series or parallel). good luck. Link to comment Share on other sites More sharing options...
Members mrmax Posted October 9, 2008 Members Share Posted October 9, 2008 What kind of amp do you have? Link to comment Share on other sites More sharing options...
Members DeadManWalking Posted October 9, 2008 Members Share Posted October 9, 2008 MEasuring resistance should tell you what rating the cab is though.. It wont be exact, but it will let you know what you have. Just plug in the speaker cable to the cabinet and if its a 1/4 TS cable, just measure one lead on the tip and the other on the sleeve.. I.E> If you get a reading of 5-6 ohms then it will be safe to assume its an 8 ohm cab. 12-14 ohm will tell you its a 16 ohm cab etc.etc.. Link to comment Share on other sites More sharing options...
Members mrmax Posted October 9, 2008 Members Share Posted October 9, 2008 MEasuring resistance should tell you what rating the cab is though.. It wont be exact, but it will let you know what you have. Just plug in the speaker cable to the cabinet and if its a 1/4 TS cable, just measure one lead on the tip and the other on the sleeve.. I.E> If you get a reading of 5-6 ohms then it will be safe to assume its an 8 ohm cab. 12-14 ohm will tell you its a 16 ohm cab etc.etc..That's what I do ...never had a problem... Link to comment Share on other sites More sharing options...
Members SloanStewart Posted October 9, 2008 Members Share Posted October 9, 2008 ^same hereeverything's fine, y'alls. Link to comment Share on other sites More sharing options...
Members guitarbilly74 Posted October 9, 2008 Members Share Posted October 9, 2008 MEasuring resistance should tell you what rating the cab is though.. It wont be exact, but it will let you know what you have. Just plug in the speaker cable to the cabinet and if its a 1/4 TS cable, just measure one lead on the tip and the other on the sleeve.. I.E> If you get a reading of 5-6 ohms then it will be safe to assume its an 8 ohm cab. 12-14 ohm will tell you its a 16 ohm cab etc.etc.. that's correct. Link to comment Share on other sites More sharing options...
Members HKSblade1 Posted October 9, 2008 Members Share Posted October 9, 2008 If it's a PA cabinet, it has a crossover and that is the impedance you are reading. Disconnect the tweeter and that should kill any hiss. Most PA speakers are 8 ohm commonly. Link to comment Share on other sites More sharing options...
Members Guitin Better Posted October 9, 2008 Author Members Share Posted October 9, 2008 lastly, i have a hard time believing that full range speakers will sound better with a guitar amp than "normal" guitar amp speakers. the highs tend to be piercing in a very unpleasant way, IMO.good luck. I was wondering about this too before I got everything hooked up but it actually sounds MUCH better with the full range speakers than with the guitar speakers loaded in my amp BUT my amp is 2x8 Rocktron that is pretty much just a practice amp. The 50 watts of power drive these "new" cabs nicely. I have to tweak the "high" and "presence" adjustments down but it sounds really good to me. I love the growl of the 15" woofers. Link to comment Share on other sites More sharing options...
Members cap'n'crunch Posted October 9, 2008 Members Share Posted October 9, 2008 Use a Volt/Ohm meter (set for Voltage) on the 2 wires from the cabinet (+ with + / - with -) should give you an idea where you should adjust your amp's impedance. Hope this helps, Mac I usually set my meter to "ohms" to read ohms and "volts" to read volts. Have I been doing this wrong?? Link to comment Share on other sites More sharing options...
Members mrmax Posted October 10, 2008 Members Share Posted October 10, 2008 I usually set my meter to "ohms" to read ohms and "volts" to read volts. Have I been doing this wrong?? You're doing it right. I use the setting with the Omega symbol on my meter, which measures impedance. Link to comment Share on other sites More sharing options...
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