A general discussion about volume

[Wrnchbndr]

Can we discuss the subject of output level vs volume. Specifically, I have a project in mind to build an amplifier with multiple output tube sections that is along the lines of an article that I read from Mesa Boogie. Lets say that I have a 12 watt amplifier running EL84s and then I add an additional output tube section running 6V6s with a potential for 25 watts. Does my existing 12 watt out essentially become sonically invisible or does it add an appreciable flavor and/or level of volume? The idea is that I can switch the 6V6s into standby when desired. I suppose I could do the same with the EL84s. For that matter, I could add another output section with 6L6s. Each output section would utilize its own OT. I know that the thing would weigh a ton but I actually have the OTs sitting around doing nothing along with some overkill PTs.

...maybe in a combo configuration with 2 12s (open back) and 1 10" (enclosed) speaker...
...on wheels...

This question is from a conversation I had some time ago where it was mentioned that power needed to be doubled to appreciate any increase in volume -- myth or fact???

Thoughts for discussion???

[loudthud]

Do you intend to electrically combine the outputs of the OTs or just have each one drive it's own speaker? If, for instance, the 6V6 section was on and you switched the EL84 on and off, I think it would be audible but alot would depend on the relative drive levels of each section. Even at clean levels of both outputs, one section will emphasize frequencies that the other doesn't so each will add it's own flavor.

[Wilder Amplification]

It won't get drowned out if you run a speaker with a -3dB lower sensitivity rating on the 25 watt amp. Since 25 is double the power of 12 watts (OK 1 watt more but that won't matter) and double the power = +3dB more perceivable volume, running a speaker with 3dB less sensitivity would be the sonic equivalent of dropping your output power by 1/2.

Also, 10x the power increases acoustic volume by a factor of 10dB. A 10dB difference in SPL level is what the human ear perceives as being double or 1/2 the loudness.

[Joey Voltage]

This question is from a conversation I had some time ago where it was mentioned that power needed to be doubled to appreciate any increase in volume -- myth or fact???

Thoughts for discussion???

Fact. I think Jon gave a good explaination, it's also the same reason why you wouldn't expect half the volume from a 50W amp when comparing it to a 100W. a 10W amp would have half the percieved volume of a 100W amp because we percieve changes in sound pressure logarythmically.

[Wrnchbndr]

Thanks for confirming my suspicions. It is an odd phenominon but I've seen this first hand when running a pair of Princeton Chorus amps as stereo. One would naturally think that this would be twice as loud but it isn't.

The intent here is to achieve different flavors of tone. I think I'll stick to the addition of a pair of 6V6s rather than get overly stupid with a concept that may become complicated. For the moment, I'm considering using a common phase inverter, and individual OTs driving their own speakers but its perfectly feasible to control both the B+ and the speaker switching with a rotary switch as long as the OTs are multitap.

Thanks. I'll dig up this post again as I proceed.