Speaker And Amp Wattage Questions

Torren61

Member
Messages
2,035
So, I'm having an empty 2X12 cab being built. I have a 12 inch 16 Ohm 25 watt UK made Celestion Greenback and a 12 inch 16 Ohm 15 watt UK made Celestion Alnico Blue to put in the cab. Gonna make it an 8 Ohm cab.

I understand the wattage rating will be twice the lowest rated speaker. 30 watts. Correct?

What is the wattage limit I can throw at this cab?

Next question. I had an amp completely rebuilt but using the transformers from a 50 watt rated Traynor BassMaster.

1 EF86, 2 12AX7s and two EL34s. What is the maximum wattage this amp could be?
 

FourT6and2

Member
Messages
2,109
I wouldn't push that cab with more than about 15 watts if you plan on actually cranking your amp.

Your new amp will probably be putting out 50 watts at a minimum, probably more.
 

Torren61

Member
Messages
2,035
I wouldn't push that cab with more than about 15 watts if you plan on actually cranking your amp.

Your new amp will probably be putting out 50 watts at a minimum, probably more.
Thanks. I have another head being built rated at 15watts.
 

Trebor Renkluaf

I was hit by a parked car, what's your excuse?
Gold Supporting Member
Messages
13,679
I understand the wattage rating will be twice the lowest rated speaker. 30 watts. Correct??
Correct.

What is the wattage limit I an throw at this cab?
30. Now many will say Alnico Blues are conservatively rated at 15 watts and can easily handle more so you might be able to push the cabinet with more than just 30 watts. An AC30 is rated at 30 watts and contains a pair of Alnico Blues.
 

FourT6and2

Member
Messages
2,109
30 watts will blow one of those speakers after a while. Your cab should be rated for twice the output of your amp. If you have a 50-watt amp, your cab should be at least 100 watts. If you have a 15 watt amp, your cab should be be at least 30. If you have a 30 watt amp, your cab should be at least 60.

I mean, you don't have to follow these rules. But you'll eventually blow a speaker if you don't.
 

Torren61

Member
Messages
2,035
I emailed Celestion about the speaker wattage question. They emailed back and said the maximum wattage I could throw at that cab is 30 watts.
 

FourT6and2

Member
Messages
2,109
I emailed Celestion about the speaker wattage question. They emailed back and said the maximum wattage I could throw at that cab is 30 watts.
Right. But a 30-watt tube amp puts out more than 30 watts... That's why a good rule of thumb is to make sure your cab can handle double your amp's power rating. But do whatever makes you happy.
 

Silent Sound

Member
Messages
5,123
No one can say anything for sure. Yes a 30 watt tube amp CAN (not will) put out more than 30 watts. There are different ways of measuring output power, so not all 30 watts are equal. A 30 watt amp is supposedly measured at such because 30 watts is the point at which the amp starts to distort and no longer puts out a clean signal. But how much clipping is okay? Tube amps generally distort somewhat at all levels, which is usually what people like about them. Tube amps also tend to compress a good bit near their output limits, raising the RMS a lot more than the peak output. But is the amp or the speaker rated at RMS or Peak output? If so, at which frequency was that measure measurement taken? Beyond that, there are about a million different ways of building a 30 watt amp, and not all will actually clip at max output (which is how you usually get more than the listed wattage out of an amp). Some stay clean until the end. Some amps rated at 30 watts may not even be able to put out a full 30 watts (because they may not be true 30 watt amps, but rather rounded up to 30 for marketing reasons). Also Celestion, and many other brands, tend to rate their speakers pretty conservatively, as previously stated. So a 15 watt speaker may be able to handle 30 watts on it's own. Two 15 watt speakers may be able to handle 60 watts.

But wait, there's more! What type of sound wave are we even talking about here? A sine wave? Cause a square wave will often blow a speaker at below it's rated wattage! That's right, you can blow a 100 watt speaker with a 25 watt amp if you're pushing it with a tight square wave at the right frequency long enough! Solid state amps tend to clip a lot harder than tube amps. That's why in the hi-fi world, they generally recommend you use an amp with twice the power rating of the speaker, which is backwards from what most guitarists will tell you! But some guitar pedals (especially fuzz pedals) can output square waves on you, meaning just because you're not using a SS power amp doesn't mean you're in the clear here!

As for the power of your amp, you can't tell the wattage of an amp by just listing the power tubes and OT. If the OT was rated at 50 watts, you're not likely to get more than 50 watts of clean power out of the OT. But that doesn't mean the amp's max output will always be 50 watts, even with a pair of EL34's. There's a lot of stuff that goes into determining how much power an amp can output. Post a schematic with some voltage readout points or at least the transformer model numbers (PT and OT) and we can make a better guess (that's if someone here is willing to do the math for you). But the best way to determine output wattage is to get the amp up on a O-scope, plug it into the proper power resistor, and feed it with a smooth 1kHz sine wave from a signal generator just below the point of the onset of distortion (of course, that point is up for debate as well).

Plus, keep in mind that most people don't crank their amps up to 10, because most amps sound terrible there. So it's not always a terrible idea to pair lower powered speakers with higher powered amps so long as you're the kind of person who can resist getting drunk and cranking everything cause it seems like a good idea at the time.

My point being, don't rely on magic formulas. No one can say for sure if your amp would be safe or not be. There are just way too many variables to consider. Some people came up with some rules of thumb a good while back (like only using speaker with double the rating of the amp) not because they knew what they were talking about, but because they knew that hardly anyone knows what their talking about when it comes to this stuff. It's kind of the wild west with a mix of engineers, accountants, and marketers all throwing around a bunch of different numbers to describe what they believe to be the same things. Add to that dangerous cocktail a bunch of guitarists, who are generally overly opinionated and woefully uneducated on stuff like this (being one, I have first hand knowledge of this:D), and you'll wind up with a bunch of threads with more arguments than information. Hence why this question keeps getting brought back up, and no answers ever seem to stick. In any case, good luck!
 

Torren61

Member
Messages
2,035
Right. But a 30-watt tube amp puts out more than 30 watts... That's why a good rule of thumb is to make sure your cab can handle double your amp's power rating. But do whatever makes you happy.
I'm not arguing with you. I merely related what was Celestion's answer to my email question. I generally try to do what makes me happy. :rockin
 

MikeMcK

Gold Supporting Member
Messages
5,281
Right. But a 30-watt tube amp puts out more than 30 watts... That's why a good rule of thumb is to make sure your cab can handle double your amp's power rating. But do whatever makes you happy.
Yes, especially if the modded amp puts out what the original Traynor BassMaster did. I know this firsthand... I fried a 65W speaker with a YBA-1 (nominally 45W) with the volume less than halfway up. Pete Traynor was well-known for using conservative power ratings.
 

Torren61

Member
Messages
2,035
No one can say anything for sure. Yes a 30 watt tube amp CAN (not will) put out more than 30 watts. There are different ways of measuring output power, so not all 30 watts are equal. A 30 watt amp is supposedly measured at such because 30 watts is the point at which the amp starts to distort and no longer puts out a clean signal. But how much clipping is okay? Tube amps generally distort somewhat at all levels, which is usually what people like about them. Tube amps also tend to compress a good bit near their output limits, raising the RMS a lot more than the peak output. But is the amp or the speaker rated at RMS or Peak output? If so, at which frequency was that measure measurement taken? Beyond that, there are about a million different ways of building a 30 watt amp, and not all will actually clip at max output (which is how you usually get more than the listed wattage out of an amp). Some stay clean until the end. Some amps rated at 30 watts may not even be able to put out a full 30 watts (because they may not be true 30 watt amps, but rather rounded up to 30 for marketing reasons). Also Celestion, and many other brands, tend to rate their speakers pretty conservatively, as previously stated. So a 15 watt speaker may be able to handle 30 watts on it's own. Two 15 watt speakers may be able to handle 60 watts.

But wait, there's more! What type of sound wave are we even talking about here? A sine wave? Cause a square wave will often blow a speaker at below it's rated wattage! That's right, you can blow a 100 watt speaker with a 25 watt amp if you're pushing it with a tight square wave at the right frequency long enough! Solid state amps tend to clip a lot harder than tube amps. That's why in the hi-fi world, they generally recommend you use an amp with twice the power rating of the speaker, which is backwards from what most guitarists will tell you! But some guitar pedals (especially fuzz pedals) can output square waves on you, meaning just because you're not using a SS power amp doesn't mean you're in the clear here!

As for the power of your amp, you can't tell the wattage of an amp by just listing the power tubes and OT. If the OT was rated at 50 watts, you're not likely to get more than 50 watts of clean power out of the OT. But that doesn't mean the amp's max output will always be 50 watts, even with a pair of EL34's. There's a lot of stuff that goes into determining how much power an amp can output. Post a schematic with some voltage readout points or at least the transformer model numbers (PT and OT) and we can make a better guess (that's if someone here is willing to do the math for you). But the best way to determine output wattage is to get the amp up on a O-scope, plug it into the proper power resistor, and feed it with a smooth 1kHz sine wave from a signal generator just below the point of the onset of distortion (of course, that point is up for debate as well).

Plus, keep in mind that most people don't crank their amps up to 10, because most amps sound terrible there. So it's not always a terrible idea to pair lower powered speakers with higher powered amps so long as you're the kind of person who can resist getting drunk and cranking everything cause it seems like a good idea at the time.

My point being, don't rely on magic formulas. No one can say for sure if your amp would be safe or not be. There are just way too many variables to consider. Some people came up with some rules of thumb a good while back (like only using speaker with double the rating of the amp) not because they knew what they were talking about, but because they knew that hardly anyone knows what their talking about when it comes to this stuff. It's kind of the wild west with a mix of engineers, accountants, and marketers all throwing around a bunch of different numbers to describe what they believe to be the same things. Add to that dangerous cocktail a bunch of guitarists, who are generally overly opinionated and woefully uneducated on stuff like this (being one, I have first hand knowledge of this:D), and you'll wind up with a bunch of threads with more arguments than information. Hence why this question keeps getting brought back up, and no answers ever seem to stick. In any case, good luck!
Thanks for that post. Lot of info in there. It's pretty much what I figured. I doubt if I'd ever crank the EL34 amp loud enough to push 50 watts out of it.

If my hours keep going the way they are now, I'll have a Silent Sister isolation cab as another over time trophy.
 

71strat

Member
Messages
9,291
I like all the Speaker capacity I can get vs amp.

Even though frequency response ect must be taken into account, its still IMHO/YMMV a good rule of thumb to go by. Ive been using that theory since 1973.

I also like 0 speaker breakup, and I like to know that generally the speakers can take most anything I can throw at them, for hours on end... DIMED. Even though I may never dime my amp. I also have an amp that has some of the best natural OD there is. A Metro LTD ED GMP45 Head x all nos glass x 2 x 1 x 12 Celestion Creams. It has unreal OD cranked. To get the OD it has to be cranked, as it is Very Clean very high up the dial. Kills my Blackfaced/ODS mod nos tubes x 69 Dual Showman for Cleans. Metro's not as loud, but the cleans have more harmonics.

I also usually estimate the amp wattage at full output, and then pick my speakers from there. I figure my Metro is 50-55 watts cranked, and use a minimum of 180 watts RMS worth of speakers. Metro says the amp is 38 watts RMS. Sometimes/I was using 2 Hemp Coned JBL E120s which are 300 watt each, and 103db for my Metro, and a 69 Dual Showman. Some tube amps are also capable of more than 2x their RMS. Solid tate I believe does not react in the same way, but as was said, it throws Square Waves, and even a 10 watt amp can blow a 300 watt E120 in some cases. I believe SVR blew EV10ms which are 300 watts in his souped up 85 watt Super Reverb. So he was blowing 1200 watts worth of speakers with a 130-150 watt PEAK ( Generous ) amp. At 130 watts Peak Amp vs 1200 worth of speakers, and still capable of blowing speakers should say something. That's around 9 Times ( 1170 + 30 left over ) more speaker capacity vs Amp/Peak.

I generally like 3+ x RMS worth of Speaker vs Amp at estimated PEAK output..50 PEAK amp gets at least 150 watts worth of speakers. That's just my take. Everyone has their preference. But if I cant dime my Amp/Speakers for long periods of time, while also using OD ect. Its useless for me.

Also you cant go by the #s on the Volume control, to judge output. Volume Tapers/Amp Breakup on the dial vary greatly.
 
Last edited:




Trending Topics

Top