Wattage and ohm ratings between amps & speakers

[somanytoys]

Quick (specific) question about the relationship of watts & ohms with amps & speakers.

I'm getting an AC15, that's 15 watts and 16 ohms to the internal speaker. It has a selector for 8 or 16 ohms, but I think that's only for the external speaker, which switches the internal speaker off when plugged in. There's also an out for extension speaker to work along with the internal speaker (just throwing that in there...)

I bought a Celestion G12 Alnico Blue that's 15 watts and 8 ohms, that I want to install in the amp.

Is the speaker's rating too close to the wattage rating of the amp to be safe? If so, is it only safe at less than max volume, not pushing the amp up to the wattage ceiling?

Does the fact that the speaker is only 8 ohms make a difference in the wattage output of the amp (raise the wattage with less speaker resistance) that might to put me over the top for this speaker?

I'd appreciate any advice.

[ludobag1]

normally need the speaker be more watt than a amp cause if you use it longtime ,the speaker heat ,and too muc heat can kill it
if you use the 15 watt but with the amp no at full and too much time it will works
but if you use it with the amp at 11 during long time it could be endomaged by heat
also if you have output 8 and 16 it will be loud the same, choosing the impedance of speakers is necesserary and double output is more to put an extra cab

on fender they said is safe to be 50 pourcents to plus 100 pourcents but Vox ?

[somanytoys]

Yeah, all that's what worries me.

I think I'm just going to install it and mostly go light, and if I turn it up, not go full tilt and not for too long. It would be a shame to fry this speaker.

Thanks, I appreciate the reply.

[øøøøøøø]

In a 15 watt tube/valve amp you would generally want a 30w speaker to be safe.

The 15w rating generally implies "15w RMS at 1% THD."

When a tube amp is at 1% THD you won't notice. There's a fair chance that in a guitar amp you won't notice even when it reaches 10% THD. When it's at 20% THD it will start sounding good.

All the while, it keeps getting louder (and outputting >15w power).

By the time it's outright clipping and creating crunch, it's putting out considerably more power than 15w.

[somanytoys]

That sucks, I was really looking forward to putting it in the amp when it comes in. Although I have to say, the British Greenback that came in it sounds pretty damn good, especially after loading it with a Groove Tubes 12AT7 (V1) and pairs of Tung Sol 12AX7's and EL84s.

Well, I'd hate to ruin such a nice speaker.

So basically, my best bet with this speaker would be to put it in a double speaker cab with another speaker just like it, to bring the total wattage capacity to 30 watts, so that they split the wattage from the amp?

[Embenny]

That sucks, I was really looking forward to putting it in the amp when it comes in. Although I have to say, the British Greenback that came in it sounds pretty damn good, especially after loading it with a Groove Tubes 12AT7 (V1) and pairs of Tung Sol 12AX7's and EL84s.

Well, I'd hate to ruin such a nice speaker.

So basically, my best bet with this speaker would be to put it in a double speaker cab with another speaker just like it, to bring the total wattage capacity to 30 watts, so that they split the wattage from the amp?

Correct. It's called power handling, and the formula for the power handling of a cabinet is (number of speakers) x (rating of lowest-wattage speaker). So, if you use two 15W speakers, you are correct - the cabinet will have a 30W power handling. FYI, even if you combine the 15W speaker with a 100W one in the same cabinet, the power handling of the cab would still be 30W. It's kind of bottlenecked by the weakest link, so to speak.

Edit to add: your options for wiring those two 8-ohm speakers will give you either a 4 ohm (parallel) or 16 ohm (series) cab.

[somanytoys]

Thanks a lot for that info.

Yeah, I always have to refer back to something to correctly remember the formula for series vs parallel, with wattage and ohms. However, I didn't realize that the lowest wattage changes the formula, so that you would basically just multiply the # of speakers by whatever the lowest wattage speaker is. That's a variation I hadn't thought about, but electricity and its components is a very finicky thing that I'm just now learning a lot more about.

I would have to buy a 2nd identical speaker (~$200+) and another dual cabinet for them, to be able to do that. Maybe down the road, but not now.

I think what I'm going to do instead is, since it's 15 watts and I don't want to use it with a higher powered amp by mistake, put it in one of the V112 cabs, and probably use it with the smaller AC4C1 TV BC combo, though its speaker out. That will at least be safe. And that way, I can see whether I want to get a 10" blue to put in that amp, to replace the Vintage 30 that's in it now.

So in my depression, I just bought an old handmade 12", 50w/8 ohm Weber Alnico Silver Bell that I had been watching. That's going to go into the AC15 instead, so that should at least solve that disappointing problem...

I'm going to have to start selling some speakers soon, damn.

[cestlamort]

Ohms aside, people have been running Alnico blues in AC15s and AC30s for years, and are actually stock in some Vox amps (AC15 = 1, AC30 = 2 speakers).

(something that may have led to countless blown speakers over the years).

Other options:
Higher powered Weber equivalent
Celestion Gold

[somanytoys]

Yeah, I just don't want to blow that speaker. I'll just repurpose it with another amp and play it safe. I think that they make those Blues in 30 or 50 watt versions, I just got the 15 watt without really thinking too much about it.

That's kind of what I did - I bought a 12" Weber Silver Bell 50w/8 ohm speaker to go into the AC15 instead. But I want to keep the amp at a lower volume and switch between the internal Silver Bell and the Blue in a cab, to see if there's enough difference between them to warrant buying a higher powered Blue one day instead. I think I'm really going to like the Silver Bell, though, the Blue would really have to be a lot better for me to buy a higher powered Blue to move the Siver Bell, although I'm not averse to using the Bell wherever it works best.

At some point, I'm probably going to buy a 10" Weber Blue Pup to go into the 4 watt combo version, I'll have to figure out what to do with the 50th Anniversary Vintage 30 that's in there now, I'm not sure I would want to sell it yet.

I was actually looking at a Celestion Gold for a while, and read up on them, but then decided to go with a Blue. They seem good, but are they really great with Vox amps? I mean, I would use them with other amps like the Frenzels if they're better with Plexis or Deluxes, or as extensions for the Laney VC30, that isn't exactly a Vox anyway, but is very cool in its own right.

Right now I have an old (probably '60's) reconed Greenback and a newer Creamback in individual cabs to use with the Frenzels. And I have a deLisle amp/speaker switcher, so I can check different speakers out with different amps pretty quickly and easily, and decide what works best with each.

But I always like to get some guidance/opinions from people that know what they're talking about, even if they aren't the same as mine.