Speak to me of Watts and Ohms, amps and Speakers

[Jet-Jaguar]

So, watts in speakers ... how does that math work.  I've heard it's good to have a higher-watt speaker than what your amp is rated for so you don't blow up your speaker.  Is there an issue when you go too far on that? Say, for example, an 80-watt speaker for a 5 watt amplifier ... which theoretically might be showing up in my mailbox Tuesday. :blob7:

All other things being equal, it's my understanding that higher-watt speakers distort less (at least at lower volumes.)  What happens when you have multiple speakers in a cab?

Also, Ohms.  I get the whole "Match your speaker ohms to your amp or bad things happen." But again, what happens when you have multiple speakers in a cab?  I was watching a youtube video where the guy said two 16 ohms would need the 8 ohms output on his amp;  did he have that backwards?

 

[AndyG]

Also, Ohms.  I get the whole "Match your speaker ohms to your amp or bad things happen." But again, what happens when you have multiple speakers in a cab?  I was watching a youtube video where the guy said two 16 ohms would need the 8 ohms output on his amp;  did he have that backwards?

There are 2 ways to wire speakers ... in series (NOT recommended) or in parallel.  When wiring in series, the impedences are indeed additive ... ie: 2 x 16 ohm speakers = 32 ohms impedence.
When wiring in parallel, which is the way ALL speaker cabinets are wired, the formula is the impedence divided by the number of speakers ... ie 2 x 16 ohm speakers = 8 ohm impedence.  That's why 4x12's are rated at 4 ohms ... 4 x 16 ohm speakers = 4 ohms.

 

[Patrick from Davis]

There are a bunch of effects that tend to happen, generalizations.  A speaker rated at 25 Watts will generally break up and sound a bit wilder than the same model that is designed for 75 watts.  Both can still distort (warmth in a lot of cases) but the way it does is makes a difference.  Series and parallel wiring makes some peoples head spin.  All cabinets are not wired in parallel.  Marshall's 1960 cab can be 4, 8, or 16 ohms.  Four 16 ohm speakers in parallel is 4 ohms.  Two speakers in parallel is 8 ohms, so the cab is "stereo" with a right and left side, both using only two speakers.  The two sets of parallel speakers (8 ohms) wired in series makes 16 ohms.  So it is just a trick of switching and getting the speakers impedance to make the overall that are desired.  This is generally pre-done in the cab so you don't have to think about fractions at a gig.  I find 4 ohms tends to be looser in sound than 16 ohms.  So for bluesy I use 4 and for metal I use 16.  Depending on the amp, you can have different speaker loads on them.  But, I always match the proper load to the amp so I don't mess things up.
Patrick

 

[Jet-Jaguar]

How do watts add up? If you have two 50-watt speakers in a cab, does that make it a 100-watt cab?  I doubt I'd ever need a cab like that, but I'm curious.

 

[Cagey]

Yes, but it's not a rule in the expected sense. Generally speaking, if all the speakers are of the same impedance, the watts spread. For instance, the original Marshall 412 bottoms had 4 25 watt Celestions in them, and so were rated at 100 watts.

But, 100 watt heads used to blow up bottoms all the time. Back in the days of Jimi Hendrix, The Who, Deep Purple, et al, you not only carried spare heads, you carried spare bottoms (or at least spare speakers) because you'd toast the things quite regularly. Speaker re-coning used to be a viable business in some areas.