The 'double the wattage on the cab' rule.

[What?]

Here's a potentially face-palm question (to which I feel I already know the answer) in the form of a hypothetical.

Say an amp is producing a clean sound that is measured at 100dB, then an OD pedal is used to change the sound to more of a sine wave feel, but it still measures @ 100dB. Is this new pedal produced OD sine sound stressing the speaker more than the clean sound, despite both measuring at 100dB?

Maybe someone here knows how that is actually measured? And I think you likely mean changing the sound to more of a square wave.

 

[Nose4Noise]

Maybe someone here knows how that is actually measured? And I think you likely mean changing the sound to more of a square wave.

I warned you about face palm potential!

 

[What?]

I warned you about face palm potential!

It's an interesting question any way. And I guess one of the fancy modern digital scopes could be used for running an integration function for comparing power with a clean signal vs. a distorted signal.

 

[PelliX]

Maybe someone here knows how that is actually measured? And I think you likely mean changing the sound to more of a square wave.

The RMS of a given signal?

The RMS (Root Mean Square) value is calculated by squaring the values, taking the average of the squared values, and then taking the square root of the average.

Root mean square - Wikipedia

en.wikipedia.org

It's an interesting question any way. And I guess one of the fancy modern digital scopes could be used for running an integration function for comparing power with a clean signal vs. a distorted signal.

Yup, most certainly.

Incidentally:

Power Handling: All you need to know! - Celestion

What you should know about speaker power handling before you upgrade your speakers...

celestion.com

They used to have a better article on this, maybe I can dig that out later.

 

[What?]

The RMS of a given signal?

The RMS of a given signal?

The RMS (Root Mean Square) value is calculated by squaring the values, taking the average of the squared values, and then taking the square root of the average.

How do you practically do an RMS calculation for a complex signal though? The only way I can see is sampling the signal (at how many points for acceptable accuracy?) for calculating RMS. See graphical method:

https://www.electronics-tutorials.ws/accircuits/rms-voltage.html

 

[PelliX]

The only way I can see is sampling the signal (at how many points for acceptable accuracy?)

Yes, that's effectively how it works. Now if you have a decent-y multimeter (think Fluke, Keysight, etc) it will do that for you with a given resolution - this works pretty well IME for simple signals. A decent digital oscilloscope will be able to do this with much higher sample rates and thus more accuracy. Generally this comes paired with more tuning options and so on, allowing for complex signal analysis. In theory one could also log the data at a fairly high resolution to a computer and calculate from there, of course. While I've never done an RMS calcuation that way, I once had to decode an RF signal pattern from a controller unit for a lighting system. Eventually after a little ATmega fun and various libraries I gave up on that front as the codes exceeded the usable buffer on that. I attached an RF receiver module to a soundcard and snagged the data as audio that way. Then I proceeded to stretch the audio to a humanly hearable speed and sat there writing out morse code with headphones on. Thank God it wasn't tri-state or anything. Sorry for going off on a tangent there...

 

[What?]

Yes, that's effectively how it works. Now if you have a decent-y multimeter (think Fluke, Keysight, etc) it will do that for you with a given resolution - this works pretty well IME for simple signals. A decent digital oscilloscope will be able to do this with much higher sample rates and thus more accuracy. Generally this comes paired with more tuning options and so on, allowing for complex signal analysis. In theory one could also log the data at a fairly high resolution to a computer and calculate from there, of course. While I've never done an RMS calcuation that way, I once had to decode an RF signal pattern from a controller unit for a lighting system. Eventually after a little ATmega fun and various libraries I gave up on that front as the codes exceeded the usable buffer on that. I attached an RF receiver module to a soundcard and snagged the data as audio that way. Then I proceeded to stretch the audio to a humanly hearable speed and sat there writing out morse code with headphones on. Thank God it wasn't tri-state or anything. Sorry for going off on a tangent there...

Seems like a low buck way to do that would be to tap the speaker output for for a line out and run an integration function for those signals (a script in a daw), but I wouldn't be sure about the accuracy of the ratio of the tapped signal to the the speaker output. I guess if you can accurately measure the resistors being used for the line out that should be good enough?

 

[PelliX]

but I wouldn't be sure about the accuracy of the ratio of the tapped signal to the the speaker output.

Exactly. You can hang a nice digital scope or logger on the line/whatever output, no prob, but impedance is a lot more complex than DC resistance here. You could also send a few steady test signals through and calibrate your calculations accordingly before going to the complex stuff. I mean, technically you could just use a two channel scope and hook it up to the speaker output. It should generally be in the range of MOhms or more tip to tip, so not much of a problem there. Provided its got the "brains", it can tell you what you want to know.

 

[guitarbilly74]

I've heard of this rule but I've been running 4x12 with 25w Greenbacks with 100w Super Leads for a long time without issues.

I think if there is any "rule" I've learned about tube rigs over the years is that they're not as fragile as some seem to believe they are.

Obviously you should do basic maintenance like proper bias, matching impedance correctly, using quality cables etc

But other than that, a good tube amp or quad of Celestion speakers can take a lot of punishment without problems.