#1
I recently purchased a JCM2000 DSL100. My understanding is this is a 100 watt amp head. I bought a 1960a 4x12 which has as I understand four g75s that are each 75 watts. So with those four speakers combined that makes 300 watts.

So how does this work with the amp head and the speakers? Does that mean it can put potentially 100 watts of power towards each speaker? It's the first time I've owned something other than a combo amp. What I was wanting to do is possibly load v30s in with the g75s, or greenbacks. I know v30s are 60 watts while greenbacks are... 25?

How does this all work when the amp head is 100 watts and their wattage is 300 combined or 75 seperate?
My gear
Ibanez RGA42E (6-string), Ibanez RG7421 (7-string w/Dimarzio Evo 7 and Ionizer), ESP LTD MH-50 w/floyd rose
Flashback Delay, Digitech RP1000
Marshall JCM2000 Dsl 100
Marshall 1960a W/ Eminence Governors and Patriot Red White Blues
#2
No. The amp can push 100 watts* total, so the speakers each get one quarter (in a four speaker setup) of the wattage, or 25 watts each. If it pushed 100 watts to each speaker it would be a 400 watt amp, no? The amp cannot magically summon more output every time a new speaker is connected. It pushes 100 watts* into whatever cab is plugged into it, whether it's one speaker or 16.

This of course makes sense when you figure that the cab's wattage rating is calculated simply by multiplying the number of speakers by the wattage rating of each speaker. It's not as complicated as you are making it. There's no more math involved in wattage pairing beyond making sure that the cab number is higher than the head number. 300>100 and done. Of course, you can always get more involved with headroom, impedance, etc, but as far as power handling goes, it really is that simple.


*Amps, specifically tube amps, will often put out more wattage than they are labeled for. Sometimes it's quite a lot more, 150% is not uncommon and even higher is not unheard of. Speaker companies account for this when rating speakers. Amps can also be made to be less efficient by mismatching impedances, so technically you can force an amp to have "less wattage" than its rating, but you cannot get more wattage for free thanks to Mr. Newton and his pesky laws.
#3
You Explained that perfectly. Glad I asked because every other search confused me more and more. Thanks!
My gear
Ibanez RGA42E (6-string), Ibanez RG7421 (7-string w/Dimarzio Evo 7 and Ionizer), ESP LTD MH-50 w/floyd rose
Flashback Delay, Digitech RP1000
Marshall JCM2000 Dsl 100
Marshall 1960a W/ Eminence Governors and Patriot Red White Blues
#5
Since you ask "how it works with speakers" it might be useful to add that speakers also have a sensitivity rating that you an idea how much sound they put out relative to the power being fed to the speaker. So a more efficient speaker will be louder at the same watts as a less efficient speaker. Here is an article that explains it. And explains why I'm wrong using the term "efficient" instead of the correct term "sensitive".

http://www.audioholics.com/loudspeaker-design/loudspeaker-sensitivity
#6
Speaker wattage is just power handling. You have a 100 watt amp so you don't want to use speakers that can't handle the wattage (well, it's doable with lower wattage speakers if you don't crank the amp up). But the speaker wattage has nothing to do with power or how loud the speakers are. It's just power handling. If you want a louder/quieter speaker, look at the speaker sensitivity.
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#7
I don't think Roc mentioned it, but also remember that your total cab wattage handling = # of speakers X wattage of lowest rated speaker.

So for instance if you had 2 60W V30s and 2 25W Greenbacks, you would have a 100W cab. Because you have 4 speakers, and the lowest rated of them is 25W.

Your amp's power is divided equally among the speakers, so say if you were running a 150W Triple Rectifier dimed, each speaker would be getting 37.5W, which would be more than the Greenbacks can handle and they would blow.
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#8
Good point, I assumed that all the speakers were identical which is not always the case.