Another of those Ohm vs. speakers question

[Disturber]

I am no expert at these things, so I use the google (a virtual monster that know "all") for information. But as always I know you guys know more. So, my question:

If I hook up three Celestion speakers at 16 ohm each, does that give a 5,3 OHM load?

Got my source from here http://www.regiscoyne.com/tech/spk_cab_wiring/

and if I get it correctly - if I have three speakers, each at 16 ohms, dividing 16 by three I get a total impedance of 5,33ohms.

If so, then there is no problem what so ever to run the Marshall amp on a 4ohm load, with the 5,33ohm cab, right?

Reason I ask is I found this pretty cool 3x12 cab. UK made from the 60's. Looks like a vox cab, but the logo says MAXX. It's pretty cool. No speakers in it, so I hope I can get it for cheap.

[Thundersteel]

If they are all wired in parallel, then yes, the load would be 5.33 ohms. It would be a safe load for the amp's 4-ohm output.

[SSII x 2]

You can always safely use a higher impedance cabinet than the amp's output. May

not sound the greatest, but also might not make much difference at all. But don't

ever use a lower impedance cabinet than the output...

[Disturber]

You can always safely use a higher impedance cabinet than the amp's output. May

not sound the greatest, but also might not make much difference at all. But don't

ever use a lower impedance cabinet than the output...

Yes, that is the rule I've always lived by. But calculation ohms is something I rarely do, so I wanted to make sure I was thinking right. Thanks!

[velorush]

Three sixteen-ohm speakers wired in parallel would equate to a total load of

1/((1/16) + (1/16) + (1/16)) = 5.33Ω

If you'd like to use more windings in your output transformer, you could wire two in parallel with each other and the final in series with those two:

16 + (1/((1/16) + (1/16)) = 24Ω (useful if you have a 16Ω tap in your OT).

[crunchee]

Cool setup! Fender used a similar 3 x 10" speaker arrangement on Tweed and very early Brownface Bandmasters:

http://www.fender.com/guitar-amplifiers/vintage-pro-tube/57-bandmaster/product-8170500.html

[veatch]

Are you sure they are all 16 ohm speakers? A better option would be two 16 ohm speakers in parallel (for 8 ohms) in series with an 8 ohm speaker. This will give a "more standard" 16 ohm output...

[gorch]

Should work well on a 4 Ohm configured amp. The load could drive the amp a bit more. Crunching a bit earlier than usual.

[Disturber]

Are you sure they are all 16 ohm speakers? A better option would be two 16 ohm speakers in parallel (for 8 ohms) in series with an 8 ohm speaker. This will give a "more standard" 16 ohm output...

Its an empty 3x12 cab. And I have 3 16ohms G12 30s that I could put in there.

[gorch]

However, on the speaker side I would never come to the idea to connect two speakers in series. I would expect sound variances on the second one. Just like with pickups on the guitar side. The principal is almost the same. So, I would expect similar behaviour.

Parallel wiring would provide the original signal to all speakers. Pretty much like parallel wired pickups sound cristal clear.

[veatch]

So, no 4x12 cabs fer you...

[Disturber]

Three sixteen-ohm speakers wired in parallel would equate to a total load of

1/((1/16) + (1/16) + (1/16)) = 5.33Ω

If you'd like to use more windings in your output transformer, you could wire two in parallel with each other and the final in series with those two:

16 + (1/((1/16) + (1/16)) = 24Ω (useful if you have a 16Ω tap in your OT).

I have a 16Ohm tap on the amp.

Do you mean it's better to wire the speakers for 24ohm and use the 16ohm tap, than to wire for 5,33ohm and use the 4ohm tap?

That would give a little less output volume wise, won't it?

[velorush]

I have a 16Ohm tap on the amp.

Do you mean it's better to wire the speakers for 24ohm and use the 16ohm tap, than to wire for 5,33ohm and use the 4ohm tap?

That would give a little less output volume wise, won't it?

"Better?" - I have no idea. I thought we were having a theoretical discussion here!

Seriously (and in full disclosure): my response was to provide an alternative, but here is the basis for my suggestion: a multi-tap output transformer provides nothing more than several "exit points" for the signal along the secondary windings. The 16Ω tap is at the end of the secondary windings, whereas the 8Ω tap 'exits' halfway through the secondary windings and the 4Ω tap 'exits' one fourth of the way through the secondary windings.

It seems intuitive to me that using all of the secondary windings would provide all of the amp's output (by all I mean note fundamentals and the full gamut of harmonics). That said, there could be things about your amp that make it sound "better" with some of these things attenuated - and this "better" could vary depending on your choice of speaker(s) and the volume at which you are playing. It'd make for a great experiment!

"Power?" Since P = E²/R, Power halves as we double impedance. Sounds drastic, but since the relationship between watts and output is logarithmic rather than linear, halving wattage reduces output by approximately 3dB (I'll spare everyone the math). That is the output at maximum. If you're not running everything wide open, the volume is what the volume is.

Caveat: my experience in this is limited to the theoretical and what I've read from people who design and build tube amps (and obsession I've yet to indulge). The only real-world experience I have with this is my Mesa Subway Blues' "half power" OT tap. In my opinion, with the stock Mesa speaker and at every volume I've played that amp, the "full power" tap sounds "better" to me.

[Disturber]

Not sure I got all of that, ha ha.

But could I also wire it this way? Using 2 x G12H30 16 ohms in parallel (8 ohms) - and these in series with 1 Celestion greenback 8 ohm, making the cab a 16 ohm cabinet.

Would that work. And how many watts would it be able to handle then?

[velorush]

Not sure I got all of that, ha ha.

But could I also wire it this way? Using 2 x G12H30 16 ohms in parallel (8 ohms) - and these in series with 1 Celestion greenback 8 ohm, making the cab a 16 ohm cabinet.

Would that work. And how many watts would it be able to handle then?

Exactly, that would present (8Ω + (1/(1/16Ω + 1/16Ω))) = 16Ω

Power handling: the G12H30 is rated at 30 watts. It is my understanding three 30-watt speakers, wired in series or in parallel, would have a power handling capacity of 3 X 30 watts, or 90 watts, max.

(I am certainly open for correction if anyone else wants to weigh in ).

[Disturber]

So, this is how I wired the new cab up today.

I know the wattage load is uneven as I mixed Ohm's. But I tried it out for like 15 minutes in the basement, with the kids watching tv upstairs, and It sounded good. Perhaps the 16ohm G12H-30 is a bit louder than the other two. But I need to try it out further to know If I think it works - or if I'll try three 16ohms instead.

[veatch]

That's the way I would do it. By the way, if I recall correctly, twice the power in watts is about 3 DB of difference and loudness, which is just noticeable to the human ear, so the one speaker will be louder but not by much. Hope that makes sense.

[Bobby Marshall]

Pic of new cab???

[Disturber]

Pic of new cab???

I´ll shoot some new picks of the whole new rigg and post them soon. New 1960's 3x12 cab and a 1973 50w JMP. Life is good.