Speaker/Impedance Question...

[neilyoung]

I have a 100w SLP head, into a 4x12 cab....but only 2 speakers (hellatone 60L and G12T 75w)
It totals 135w. they are both 16 ohm

I want a different tone so I bought 2 '25w Greenbacks' and eventually I'm going to fool around with different combinations to see what one i like.

Am I going to damage my transformer in my head?
Is my current setup (hellatone/g12t) damaging my amp at all?

 

[Adieu]

Re: Speaker/Impedance Question...

I'm pretty sure most people just wire greenbacks to add up cumulatively, four to make 100watts. And shoot me for sleeping or womanizing all the way through college physics and not picking up much there, but I vaguely recall that 4x 16ohm speakers wired that way seem to *somehow* make it 4ohm total, no? Just don't ask me how or why...

 

[dr. ad]

Re: Speaker/Impedance Question...

depends on the speakers' ohmage, and how the quad is wired (ie series or parallel)

once you've figured this out, you'll still struggle to hear the 25W greenbacks over the other 2 speakers.

sorry to be the bearer of bad news.

depending on how many inputs/outputs you have on your quad, you could look at setting the box up as two 2x12s in one box, but this could end up being a lot of messing around when you may really just want a more bassy or midrangey box to play with

 

[Adieu]

Re: Speaker/Impedance Question...

Oh! Right... that was the other faint memory I had from physics - something about the wattage and output not distributing equally whatsoever when you're using different-rated mismatched speakers... yeah, the 25-watters probably won't do much to colour that tone.

Might he be fine running his 100w into just 2x 25w Greenbacks, so long as he doesn't crank up Master Volume past 70% or so???

 

[neilyoung]

Re: Speaker/Impedance Question...

depends on the speakers' ohmage, and how the quad is wired (ie series or parallel)

once you've figured this out, you'll still struggle to hear the 25W greenbacks over the other 2 speakers.

sorry to be the bearer of bad news.

depending on how many inputs/outputs you have on your quad, you could look at setting the box up as two 2x12s in one box, but this could end up being a lot of messing around when you may really just want a more bassy or midrangey box to play with

I've been considering making it a 2x12
also ... I've heard you should add 1.5x the wattage of speaker compared your head (ie. 100w head with 150w speakers)

 

[Surgeon]

Re: Speaker/Impedance Question...

If you wire speakers in parallell, you basically half their impedance (two 16 ohms in parallell will yield an impedance of 8 ohms)

SEries: the impedances add up: two 8 ohms = 16 ohms.

Wattage? Yeah, you usually want to go higher than what your amp is capable of to avoid blowing the speaker(s).

First thing you want to do is make sure that you wire things properly to have an impedance that your amp will be able to deal with.

Second, either you have more than 100W for your amp or you gamble your way through making sure you never go too high on your volume knob (not the GAMBLE thingy)...

 

[ratherdashing]

Re: Speaker/Impedance Question...

A 100W Marshall head will put out peaks MUCH higher than 100W. That 100W figure is RMS (average). In other words, a 100W cab will NOT be adequate.

 

[Dr. Vegetable]

Re: Speaker/Impedance Question...

When mixing speakers of different wattages, remember that you can't depend on using the full power handling of all speakers. In other words, if you put a 25W speaker and an 80W speaker in a 2x12 cab, you cannot realistically expect to push 105W (25W + 80W) through it. You should only expect to get 50W (25W + 25W) into the pair before you are in danger of blowing the weaker speaker.

 

[IM4Tone]

Re: Speaker/Impedance Question...

Not sure I followed all the posts here, BUT: if all four speakers are 16 ohms and are wired series/parallel, the combined impedance of the cab will also be 16 ohms. Regarding volume of the speakers, it has nothing to do with their wattage ratings. It depends on their sensitivity (efficiency) and impedance. If all are 16 ohms, all will see 1/4 th of the amp's power output and any volume difference between speakers will be attributable only to their sensitivity. If all are the same or nearly the same sensitivity, all should have nearly identical volume.

 

[neilyoung]

Re: Speaker/Impedance Question...

If you wire speakers in parallell, you basically half their impedance (two 16 ohms in parallell will yield an impedance of 8 ohms)

SEries: the impedances add up: two 8 ohms = 16 ohms.

Wattage? Yeah, you usually want to go higher than what your amp is capable of to avoid blowing the speaker(s).

First thing you want to do is make sure that you wire things properly to have an impedance that your amp will be able to deal with.

Second, either you have more than 100W for your amp or you gamble your way through making sure you never go too high on your volume knob (not the GAMBLE thingy)...

I put the speakers in myself ... and being the lazy me ... I'm pretty sure I did a series connection. Both speakers are 16 ohm, therefore I would need to make my amp setting to 8 ohm ?

 

[IM4Tone]

Re: Speaker/Impedance Question...

I put the speakers in myself ... and being the lazy me ... I'm pretty sure I did a series connection. Both speakers are 16 ohm, therefore I would need to make my amp setting to 8 ohm ?

A series connection of two 16 ohm yields 32 ohms....not useful.
A parallel connection of two 16 ohms yields 8 ohms.
If in doubt and you have a simple multi-meter, check the DC resistance of the circuit. DC resistance is the largest component of impedance. A 32 ohm connection will measure on-the-order of 24 ohms; An 8 ohm connection will measure on-the-order of 6 ohms.