By comparison, a 40w like the DSL40C is fairly on par in terms of volume as a 50w amp. Not a great deal of volume difference.
For whatever it is worth: there is not much perceived "loudness" between a 50w and a 100w either. A 100w is not twice as loud as a 50w. Quite the contrary, its only about 3dB on a normal day, which is very loud to our ears. I know this sounds COMPLETELY stupid but allow me to explain:
It takes 10x the amount of wattage to double the "loudness" humans would regularly hear. So if you want double the total volume of a 50w? Its gonna take 500w.
Here's a chart to help explain
View attachment 78234
Its quite believable that a 40w DSL kept up with or even possibly exceeded the Carvin 100w by a couple factors:
The Carvin full stack is dissipating its 100w capability across 8 12" speakers. That's really only giving a maximum of 12.5w per speaker, so even if they were 25w Greenbacks, they are operating at about 50% of their total capability. If they were something more standard like 65-75w speakers, now they are operating far less, about 1/5th of their capability.
Meanwhile the DSL40C
The DSL40C however was operating a single 75w speaker as you mentioned. So it was pushed around 53% of its capability.
All of this seems stupid still right? Well remember: you were in a small space and you still can only hear what your ears perceive by your surroundings. If this was outside in the open, the full stack Carvin would carry WAY farther than the DSL40C, which IS the reason stacks were invented in the first place: casting out to the crowd before PAs were really worth much more than just letting the singer be heard. But you were within a small area and distance doesnt play a factor: you're hearing it right in your face and having it bounced back at you immediately.
Hope this helps? Lol