wattage question for you pro's

recto-robbie

Member
Messages
2,322
Hello, question for you guys

if I wire two 25 watt speakers in series in a cab, that makes the cab 50 watts, Right?

I assume I would be safe running a 50 watt amp safely into the cab, right???

Doing this wouldn't hurt the 25 watt speakers will it?

My brain is not working anymore figuring out this wiring stuff.

anyway thanks
 

PushedGlass

Member
Messages
716
Whether in series or parallel, yes, two 25W-rated speakers will give you a 50W-rated cab, but please be mindful of the impedance expected by your amp vs. the impedance presented by your cab. If you are going to run this from a 50W-rated amp, you're pushing things...what if it's really putting out 55-60W, or if one or both of the speakers gives up at 48? If your amp expects 8 ohms, then you might only get away with maxing out the amp using a 16-ohm cab (i.e., two 8-ohm speakers in series). Me, I'd be a lot more comfortable using a cab with the same impedance as the amp calls for and over-rating the speakers at least a little bit.

Remember that open-circuiting is one possible cab failure mode and that will likely fry things upstream (especially the output transformer).
 

pdf64

Member
Messages
7,912
The Scumback FAQ explains it well http://www.scumbackspeakers.com/pick.html

'AMP Wattage!

Please understand one thing. Most amps are rated for their advertised RMS wattage at clean signals. On most amps that's going to be at 3-5 on the volume knob. So your 100 watt Marshall puts out 100 watts at 4. You like to play it at 7, and if your amp is healthy, that's when it puts out 150-180 watts (or more). The guys at Marshall knew what they were doing when they put the "100" logo in the corner of the cabs, but that still meant that you needed two of them to handle a 100 watt amp that put out 180 watts at the levels you set the amp! Get your amp tested for it's real output wattage, no one likes the smell of a melted speaker, OK? Always figure you need twice your RMS wattage in speaker power handling to safely run your amp on 10.

If you get two 30 watt speakers to run with your 50 watt amp, and dime it, they'll be good to go for awhile. I don't know what timeframe "awhile" is. I've safely done it for 2 hours straight, without issues. I have not done that for extended periods, so you want to take that into consideration with all the OD pedals, clean boosts, and so forth that push speakers to raise your level for solos. Use your good old common sense here. Sure, your old small block sounded great and was running awesome at 8000 rpm for "awhile", then the crank, piston, or connecting rod broke, and you weren't mobile anymore. Use the same common sense judgment with choosing your speaker wattage.'
 

Rockinrob86

Silver Supporting Member
Messages
3,862
To be safe, I almost always run only cabs that are double the rating of the head, meaning you need a 100w cab for your 50w amp if you would like to reliably not blow the speakers.
 

bigtone23

Member
Messages
6,577
^^^^
This. I also Like to wire my 2-speaker cabs in parallel. This way, if a speaker blows, the other is there to keep a load on the head.
 






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