MichaelCRobertson Posted March 16, 2011 Report Share Posted March 16, 2011 basically, if anyone could explain in a very simple way if i can or cant run an amp head into a cab with a different ohm rating?if i can, what will it effect? sound? volume?if not, why not? will it ruin or damage the amp or cab in anyway? Quote Link to comment Share on other sites More sharing options...
Soda Jerk Posted March 16, 2011 Report Share Posted March 16, 2011 Ideally, ohms should match. However, I've been told that if they don't match, it is much better for the amp if the amp ohms are lower than the cab ohms, so 4ohms amp into 8ohms cab is fine, but not ideal to do over a long period of time. Putting 8ohms amp into a 4ohms cab is regarded as a bit more damaging as far as I'm aware.Ohms not matching will affect the volume a little, but won't really be noticeable. If the ohms on the amp are lower than the cab, then it can often sound a bit different. Different sometimes meaning bad. Depending on the amp and cab Quote Link to comment Share on other sites More sharing options...
MichaelCRobertson Posted March 16, 2011 Author Report Share Posted March 16, 2011 Damn. i'm going into a studio to do some recording, and i'm hoping to borrow a Park JTM45, which is 16 ohms, and the only cab i has is 4/8 ohms.....is there any sort of.... magic box you could plug the head into, and then the cab into, that drops the ohm down? Quote Link to comment Share on other sites More sharing options...
fatboy Posted March 16, 2011 Report Share Posted March 16, 2011 Damn. i'm going into a studio to do some recording, and i'm hoping to borrow a Park JTM45, which is 16 ohms, and the only cab i has is 4/8 ohms.....is there any sort of.... magic box you could plug the head into, and then the cab into, that drops the ohm down?What kinda cab is it you have and how many speakers? Quote Link to comment Share on other sites More sharing options...
MichaelCRobertson Posted March 16, 2011 Author Report Share Posted March 16, 2011 i have a hartke 4x8, but thats only 4 ohmsand i have a marshall 4x12, thats the 4/8 ohms Quote Link to comment Share on other sites More sharing options...
fatboy Posted March 16, 2011 Report Share Posted March 16, 2011 Assuming from working out that your Hartke is wired parallel, each speaker is 4 ohms?if you connect all 4 speakers in series then that will render the cab as 16 ohms Quote Link to comment Share on other sites More sharing options...
MichaelCRobertson Posted March 16, 2011 Author Report Share Posted March 16, 2011 boom, just the kind of quick fix i was hoping for!thanks a bunch Quote Link to comment Share on other sites More sharing options...
fatboy Posted March 16, 2011 Report Share Posted March 16, 2011 boom, just the kind of quick fix i was hoping for!thanks a bunch I trust you know how to do this. Quote Link to comment Share on other sites More sharing options...
MichaelCRobertson Posted March 16, 2011 Author Report Share Posted March 16, 2011 nope, but i know a man who will, even if i knew how, i wouldn't trust myself with something like this Quote Link to comment Share on other sites More sharing options...
Cabbage Posted March 16, 2011 Report Share Posted March 16, 2011 You could do some major damage to the output transformer running a mis-matched cab, worst case I think you can melt it with heavy (ab)use!! I'd not take that gamble with someone else's Park!Rewiring your cab, or borrowing a 16ohm cab are by far the easiest options! Quote Link to comment Share on other sites More sharing options...
Yh_Buddy_ Posted March 16, 2011 Report Share Posted March 16, 2011 I have a similar question. I've got a Vox CH-30 which has an 8 Ohm/30 watt output for an external speaker/cab. Does that mean i have to get a cab which is only 30 watts or a cab (e.g 4 X 12) which has the same Ohms impotence as my amp? Quote Link to comment Share on other sites More sharing options...
fatboy Posted March 16, 2011 Report Share Posted March 16, 2011 you would get a cab that has an 8 ohm impedancewhether that would be a 2x12, 4x10 or 1x12just make sure that if it does end up to be a single speaker cab that the speaker is capable of taking 30watts, impedance and wattage should be on the back of the speakermy amp is 120 watts but my speakers are only 75watts but there is 4 of themto work out series just adding up the individual impedance of the speakers4 speakers all 4 ohms = 16ohmswiring speakers in parallel is differentfirst multiply the amount of speakers by impedance say a 4 x 10 at 4ohms each speaker4 x 4 = 16then add the the same numbers together 4+4 = 8then divide the first result with the second16/8which is 2 ohms Quote Link to comment Share on other sites More sharing options...
James Broonbreed Posted March 16, 2011 Report Share Posted March 16, 2011 I have a similar question. I've got a Vox CH-30 which has an 8 Ohm/30 watt output for an external speaker/cab. Does that mean i have to get a cab which is only 30 watts or a cab (e.g 4 X 12) which has the same Ohms impotence as my amp?Your Vox will output 30 watts. An 8ohm speaker rated below 30 watts wouldn't be a good idea but 30watts or over will be fine, although the closer to 30 the better.I believe you'd be fine running a cab with a higher impedance than your amp, although the power output of your amp would be reduced. I think it would be about half if you had a 16 ohm cab.If you use a cab with a lower impedance than the amp, you will probably damage your amp. So don't.Please feel free to correct me if I'm wrong folks. It's been a while since I researched speaker impotence. Quote Link to comment Share on other sites More sharing options...
James Broonbreed Posted March 17, 2011 Report Share Posted March 17, 2011 I've always been under the impression that if in doubt use 16ohms. Ohms is resistance, so if you don't want to blow the speaker than you want to use 16 to prevent putting to much through.A decent rule of thumb. Obviously if you know the signal impedance, then it's better to match it to the speaker to get maximum power. I think some people reckon it can affect tone too. But I'd contest that. Quote Link to comment Share on other sites More sharing options...
Yh_Buddy_ Posted March 17, 2011 Report Share Posted March 17, 2011 That's great help, thanks, that answered my question. Quote Link to comment Share on other sites More sharing options...
Monk Rocker Posted March 17, 2011 Report Share Posted March 17, 2011 As far as I understand, the impedance rating on most amps relates to the minimum impedance cab you can safely use.Eg, if an amp is rated at 8 ohms, then it will deliver it's maximum output at this impedance. If you attach a cab rated at 16 ohms then all that's likely to happen is the amp won't be able to deliver it's maximum output. If you attached a cab rated at 4 ohms then the amp would get damaged, I believe most commonly it would be the output stage that would suffer.If in doubt, match your amp to your cab or use a cab with a higher impedance. Quote Link to comment Share on other sites More sharing options...
Huw Posted March 17, 2011 Report Share Posted March 17, 2011 How to Hook Up Heads and CabinetsThat's pretty much my reference point for all impedence issues. Quote Link to comment Share on other sites More sharing options...
Hugh_Jazz Posted March 17, 2011 Report Share Posted March 17, 2011 you would get a cab that has an 8 ohm impedancewhether that would be a 2x12, 4x10 or 1x12just make sure that if it does end up to be a single speaker cab that the speaker is capable of taking 30watts, impedance and wattage should be on the back of the speakermy amp is 120 watts but my speakers are only 75watts but there is 4 of themto work out series just adding up the individual impedance of the speakers4 speakers all 4 ohms = 16ohmswiring speakers in parallel is differentfirst multiply the amount of speakers by impedance say a 4 x 10 at 4ohms each speaker4 x 4 = 16then add the the same numbers together 4+4 = 8then divide the first result with the second16/8which is 2 ohmsMy recollection of school physics is that for parallel circuits:1/Rtotal = 1/R1+ 1/R2 + 1/R3 + 1/R4 etc.........so if you've got 4 x 4 ohm cabinets, you get the following:1/4 + 1/4 + 1/4 + 1/4 = 1/Rtotal....so Rtotal = 1 ohmWouldn't 2 x 4 ohm cabinets go to 2 ohm, rather than 4 cabs?ie. 1/4 + 1/4 = 1/Rtotal....so Rtotal = 2Dunno if I'm right, just interested is all. Quote Link to comment Share on other sites More sharing options...
James Broonbreed Posted March 17, 2011 Report Share Posted March 17, 2011 My recollection of school physics is that for parallel circuits:1/Rtotal = 1/R1+ 1/R2 + 1/R3 + 1/R4 etc.........so if you've got 4 x 4 ohm cabinets, you get the following:1/4 + 1/4 + 1/4 + 1/4 = 1/Rtotal....so Rtotal = 1 ohmWouldn't 2 x 4 ohm cabinets go to 2 ohm, rather than 4 cabs?ie. 1/4 + 1/4 = 1/Rtotal....so Rtotal = 2Dunno if I'm right, just interested is all.That's the proper way to work out impedance in a parallel circuit. I think the afore mentioned one works too though. I've seen it before anyway. Quote Link to comment Share on other sites More sharing options...
Hugh_Jazz Posted March 17, 2011 Report Share Posted March 17, 2011 That's the proper way to work out impedance in a parallel circuit. I think the afore mentioned one works too though. I've seen it before anyway.Well they can't both work cos they give different answers! Quote Link to comment Share on other sites More sharing options...
James Broonbreed Posted March 17, 2011 Report Share Posted March 17, 2011 Well they can't both work cos they give different answers!Ha, just as well you actually bothered to check.Yup, do it the proper way4x4ohm speakers in parallel would equate to 1 ohm, not 2. Quote Link to comment Share on other sites More sharing options...
fatboy Posted March 18, 2011 Report Share Posted March 18, 2011 My recollection of school physics is that for parallel circuits:1/Rtotal = 1/R1+ 1/R2 + 1/R3 + 1/R4 etc.........so if you've got 4 x 4 ohm cabinets, you get the following:1/4 + 1/4 + 1/4 + 1/4 = 1/Rtotal....so Rtotal = 1 ohmWouldn't 2 x 4 ohm cabinets go to 2 ohm, rather than 4 cabs?ie. 1/4 + 1/4 = 1/Rtotal....so Rtotal = 2Dunno if I'm right, just interested is all.you are correct with your formula, but the formula you chose is for working out the RESISTANCE of a circuit based on voltage and current not impedance Quote Link to comment Share on other sites More sharing options...
James Broonbreed Posted March 18, 2011 Report Share Posted March 18, 2011 Well they can't both work cos they give different answers!I totally misread your original post pointing out the two methods were different.As for resistance and impedance. Good point; my bad. Although, the ohm rating in this case will still be the same, as nominal impedance should pretty much be the same as if it were purely resistive, would it not? I'm a bit rusty with reactance and inductance and sll that shite at the moment. Quote Link to comment Share on other sites More sharing options...
fatboy Posted March 19, 2011 Report Share Posted March 19, 2011 I totally misread your original post pointing out the two methods were different.As for resistance and impedance. Good point; my bad. Although, the ohm rating in this case will still be the same, as nominal impedance should pretty much be the same as if it were purely resistive, would it not? I'm a bit rusty with reactance and inductance and sll that shite at the moment.using the formula to work out resistance for impedance wont give you the same results as impedance formula because they are differentexampleTo calculate the load impedance for the series-wired channel in the picture , add up the impedances of each speaker in the chain. The math involves a simple equation in which Zt stands for the cab as a whole, Za and Zb represent the impedances of Speakers A and B, respectively:Speakers in SeriesZt = Za + Zb Calculating the load impedance for the parallel-wired channel, multiply the impedances of each speaker and then divide the result by the sum of the speakers' impedances, whol;e cab is Zt. Za and Zb represent the impedances of speakers A and BEquation 4: Speakers in ParallelZt = (Za x Zb) / (Za + Zb)substituting the resistance with ohms will not end up in the same resultits like working out accelaration using the time, distance and speed triangle you wont get the right answer if you use the wrong formula Quote Link to comment Share on other sites More sharing options...
soundian Posted March 19, 2011 Report Share Posted March 19, 2011 using the formula to work out resistance for impedance wont give you the same results as impedance formula because they are differentexampleZt = (Za x Zb) / (Za + Zb)substituting the resistance with ohms will not end up in the same resultits like working out accelaration using the time, distance and speed triangle you wont get the right answer if you use the wrong formula1/Zt=1/Za+1/ZbMultiply 1/Za by Zb/Zb(=1) and 1/Zb by Za/Za(=1)1/Zt= Zb/ZaZb + Za/ZaZb1/Zt= (Za+Zb)/ZaZbZt=ZaZa/(Za+Zb)Same thing innit. A common way of wiring is parellelled series With a 4 speaker cab this results in the same cab impedance as speaker impedance.2 *2 8 ohm speakers in series=2 16 ohm pairs. wire them in parallel and you get 8 ohms total. Quote Link to comment Share on other sites More sharing options...
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