how to choose 4, 8, 16 ohms

[Geardog]

I'm a bit green in this area, and as there are no silly questions here are mine. I'm thinking of mating an egnater amp to an avatar 4X12 cab. I can choose speaker wire configuration of either 4, 8 or 16 ohms. I'm not sure how to select what's best for me, and how the selection may affect wattage output or any other factors that may be important.

Also, how does one go about choosing the appropriate speaker wattage in relationship to the amps (especially if I may want to run other higher wattage heads). Lastly, as I only will use one head at a time, any pluses to having a stereo speaker setup vs mono. Thanks for your time mates.

 

[soundchaser59]

Is there some reason why you dont want to match the speaker cab ohm rating to your amps output ohms? Is the amp selectable? Then it wont matter. Otherwise, match the cab to the amp, 8 ohm amp jack = 8 ohm cab, etc... The exception is if you know you will always be running, for example, two cabs. If you will always be playing thru 2 4x12 cabs each one rated 8 ohms, then use a 4 ohm output from the amp, etc.... probably safer to use 2 16 ohm cabs in parallel into the 8 ohm jack on the amp.

Wattage is easy, a good rule of thumb is double the amps output. 50 watt amp = 100 watt speaker cab. Just dont ever go less than the amps output. They add up, regardless if they are wired parallel or series. Generally speaking, two 50 watt speakers will give you a 100 watt cab, four 30 watts will give a 120 watt cab, etc. Depends on the speakers also. The good ones are usually rated conservatively, and can usually take almost twice the rating. Like 40 watt Tone Tubbys can usually take instantaneous (not sustained) peaks of 80 watts. Same with Webers. If you aren't sure, just use EV's and never worry about it.......but you'll need body builders to move your 4x12.

Stereo is only worthwhile if you are playing alone, or if you are sure your audience can hear it and benefit from it. The vast majority of house systems are run mono, as far as I know.....which probably isn't very far.

 

[Geardog]

Thanks soundchaser. The amp (egnater) is selectable between all three. But I wanted to build a cab that was flexible enough for future amps as well, and I was wondering how my selection now may effect the future use of diff amps as far as the cab ohms config. I can't afford to have several dedicated setups. Your right about the weight, maybe avatar 2X12 will be better... er.. easier on the back. So selecting ohms ratings for speakers doesn't affect wattage put thru them (yes, a further silly question)?

Also, what if you have speakers more than double the wattage? What does this underpowering the speakers do besides not reaching a breakup/distortion tone (of which I like to get sometimes)?

Thanks again for the reply SC, it was instructive.

 

[rockon1]

Thanks soundchaser. The amp (egnater) is selectable between all three. But I wanted to build a cab that was flexible enough for future amps as well, and I was wondering how my selection now may effect the future use of diff amps as far as the cab ohms config. I can't afford to have several dedicated setups. Your right about the weight, maybe avatar 2X12 will be better... er.. easier on the back. So selecting ohms ratings for speakers doesn't affect wattage put thru them (yes, a further silly question)?

Also, what if you have speakers more than double the wattage? What does this underpowering the speakers do besides not reaching a breakup/distortion tone (of which I like to get sometimes)?

Thanks again for the reply SC, it was instructive.

Tube amps put out rated power when matched with the proper impedance-it doesnt matter whether its 4,8 or 16.
Having speakers rated ,for example ,at 3 or 4 times the amps output will work fine. Yes there will be less speaker "break up" (if any) with a high powered speaker vs one closer to the amps output. Thats a matter of personal preference. A speaker rated at 50 watts and 100 db sensitivity will be the same volume as one rated at 150 watts and 100db sensitivity will say a 30 watt amp. The only difference this that the 50 watt model will probably add more cone break up to the sound as the amp is cranked up.

I should add that if you get a 4x12 cab with 16 ohm speakers you can add a switch to go from 16 ohms or 4 ohms easily. Or you could get a 2x12 with 8 ohm speakers and add a switch to select between 4 and 16 ohms too. Bob

 

[Geardog]

Rockon, Thanks a lot. It's interesting that a tube amp will work with all three, I still am personally unclear on mating an amp to the 3 options. On further consideration (weight), I probably will go the 2x12 cab route. For fun I may want to throw a solid state amp (I love tubes) on the cab, I understand the watt rating on those affect the speaker rating differently ie: a 100 watt solid state is not same as 100 watt tube. So do you know how I make sure there is enough speaker to handle the solid state's wattage?

 

[rockon1]

100 watts is 100 watts -tube or solid state. That said the
tube amp however may produce more power fully cranked than the SS amp so if you have enough speaker to handle the tube amp you should be fine.
Of more importance with the SS amp is impedance. Most are rated to deliver full power at a certain load -usually 4 ohms but not always. If the impedance is higher ie: 8 ohm speaker load into a 4 ohm SS amp its power output will be cut in half-more if its 16 ohm. Like I stated though you could get a 2x12 with 8 ohm speakers and add a switch to select between 4 and 16 ohms. Bob

 

[Geardog]

Thanks Bob. I'm not that experienced & Someone mentioned watt output on a SS is not as strong, perhaps the impedance issue you mentioned was what they were referring too. I actually didn't know about the ohm switch, so I appreciated the info.

 

[rockon1]

Thanks Bob. I'm not that experienced & Someone mentioned watt output on a SS is not as strong, perhaps the impedance issue you mentioned was what they were referring too. I actually didn't know about the ohm switch, so I appreciated the info.

Yes heres a diagram for a 2x12 with a switch. Bob

 

[Geardog]

Thanks Rockon1 for the switch diagram. Is there anything that happens with tone if you run say a 8 ohm amp with a 16 ohm cab?

 

[rockon1]

Thanks Rockon1 for the switch diagram. Is there anything that happens with tone if you run say a 8 ohm amp with a 16 ohm cab?

Yes this affects tone-whether or not its to your liking is subjective and also amp dependant. most amps will tolerate the mismatch but not all. Bob

 

[epluribus]

Geardog, if I get your OP correctly, what you're really asking is whether the taps on your OT can change the performance of your amp, presuming matched speaker loads in each case. (IOW, 8 ohm tap, 8 ohm cab, and so on. No mismatch.)

This very question just popped up on another thread, and was inconclusive, but it suggested some interesting solutions. The theory is based on the fact one tap will use all the windings on your OT, and the others don't--true enough. What that, according to this line of thinking, means is that the OT may indeed have different saturation characteristics depending on the tap.

Frankly, insofar as winding architecture is well known to have an impact on performance in transformers with the same nominal specs, I suspect the tap-theory may be on to something.

But how do you find out? Trouble is, your test cabs need to have different speakers in them to match the selected transformer load, or...They'll have to be wired differently to do match OT load (Series v. parallel v. series/parallel array.), and unfortunately wiring design can also color cab tone.

About the closest way I can think of to test one multi-tap OT with a single un-altered cab (same speakers, same wiring, no switching) would be to use a Weber Z-Matcher. But that also presumes the WZM won't color your OT/speaker interaction. Ted could (and would) probably tell you (if you e-mail him) just how transparent a Z-Matcher would be in that case. An A/B comparison with clips would be great if anybody's got the gear handy... Hm...

O'scope anyone?

--Ray

 

[Mark Robinson]

If the amp you are using or buying has a 16 ohm tap, consider going for that, and get the cabinet equipped with speakers that can be wired for 16 ohms as well. Here is why.

I play outdoors a bunch and I have a pair of 4 x 12" cabs and a pair of 2 x 12" cabs. All my cabs are 16 ohms individually. My amps have switchable impedance too. I can mix and match, and have choices. I can use just a single 16 ohm cabinet. I can use 2 of anything or go with one of each. With very little reflected sound available playing outdoors, one of my favorite things is to use a 4 x 12 on my side and then put a 2 x 12" over on the other side, then it doesn't matter if my rig is in the monitors. I can get my amp up into the tractable power, instead of being miked and having a miniscule on stage volume, but placement is critical. I don't aim my amp cabs at the singer's mike or ego if at all possible.

I like the fact that many multi-tap amps utilize the whole transformer winding at 16 ohms and can be run just a bit harder to attain the same volume, driving that higher resistance. But that is barely audible for most folks. A mentor of mine in my earliest playing days avowed that tube amps liked making volts into higher impedances and that was safe for them, less likely to fail an output tube. He also opined that solid state power was more able to dish big current into lower impedances. So I took that seriously. It may just be opinion YMMV etc.

The flexibility of having a bunch of cabinets all the same impedance is real handy though.

 

[epluribus]

I like the fact that many multi-tap amps utilize the whole transformer winding at 16 ohms and can be run just a bit harder to attain the same volume, driving that higher resistance. But that is barely audible for most folks...

Interesting, 'preciate the info. Haven't fiddled with this whole concept on the workbench much, so whether any difference is worth spending time and money on seems to be the question here. Useful opinion, thanks.

--Ray

 

[Geardog]

Thanks all. Maybe the best is to have amps with selectable ohms, and have 1 or 2 cabs that works with them all at the same impedence.

 

[mikey1]

If I hook up a 100 watt head with only 1 output.(why a 100 watt amp would have only 1 speaker output, I don't now), to (2) (4x12) cabs , and both cabs are 16 ohms is this ok with a mesa boogie parallel box. The 2 outputs coming out of parallel box should be the same as if my amp had 2 built into the amp and not harm the amp correct. NEEEDING ADVICE
Thanks

 

[grumphh]

If I hook up a 100 watt head with only 1 output.(why a 100 watt amp would have only 1 speaker output, I don't now), to (2) (4x12) cabs , and both cabs are 16 ohms is this ok with a mesa boogie parallel box. The 2 outputs coming out of parallel box should be the same as if my amp had 2 built into the amp and not harm the amp correct. NEEEDING ADVICE
Thanks

You need to know what impedance the output on your amp is. Until then no correct advice can be given.

But let's imagine that your amp output is 8 ohm. this would mean that you could connect/wire two 16 ohm cabs in parallel or two 4 ohm cabs in series.

 

[Rossi163]

I also have been under the impression that if an amp has 4, 8 & 16 ohm switchable loads you will get all of the windings of the OT with the 16 ohm tap. More windings = better tone?

Would like to have this theory confirmed or debunked by someone knowledgeable as I am also looking to match a new cab to an existing head.

 

[FbIsNotE]

If I hook up a 100 watt head with only 1 output.(why a 100 watt amp would have only 1 speaker output, I don't now), to (2) (4x12) cabs , and both cabs are 16 ohms is this ok with a mesa boogie parallel box. The 2 outputs coming out of parallel box should be the same as if my amp had 2 built into the amp and not harm the amp correct. NEEEDING ADVICE
Thanks

Go on the Boogie site, look up your amp manual and look at the "Acceptable Mismatch" section near the end. Generally Boogies have no problem with a mismatch of 1/2 or double the impedance, but check to be sure.

The Mesa Parallel box will put the two 16 Ohm cab at 8 Ohm. That's provided the cabs haven't been modified and are in fact 16 Ohm.

 

[Oatie]

If the head has the 16 ohm tap, wire the 4x12 with four 16 ohm speakers putting out 16 ohms. This way it will use all the windings on the OT USING THE 16 ohm select. My vote is 16 ohms if you use a single cab, full stack use the select to 8 ohms.

 

[TJT79]

All my homemade cabs are 16ohms. I put two jacks on the back, which gives me the option to run two in parallel (daisychained), and plug into 8ohms.