What actually determines volume power? Is it watts?

Hello dman777.  By now, you have waded through a lot of anwers to your question. They are all pretty good. Let's talk first about speaker sensitivity. A speaker rated at 84 db (we assume the ratings are honest) will play 6 db softer than a speaker rated at 90 db. It will take four times the power to drive the 84 db rated speaker to the same volume (loudness?) in the same room. A 94 db rated speaker would need only one tenth the power to play the same loudness as the 84 db rated speaker.

The advertisements don't tell you that, but it's true. Do you have some input device with meters on it to indicate the strength of the output signal. Watch the needles dance. A 10 db increase calls for ten times the power from an amp. A 20 db increase call for 100 (Yikes!) times the power from the amp. Amps that double their output power into four ohms verses what they put out at eight ohms have pretty hefty power supplies. A two ohm rating at four times the power output indicates a really strong power supply. Check the ratings of tube amps verses solid state amps. Also look at the distortion percentages at rated power. Tube amps are often rated with maximim power at 10% (harmonic) distortion. Solid state amps are often rated a so much power at 1% distortion. Tube amps can seldom double their output power into a 4 ohm load verses an 8 ohm load. All of this means that when the drum goes BOOM! an amp is called upon to put out a lot of juice in a hurry! Can the amp do it? You want an amp that never has to sweat. An amp rated at 100 watts that has to put our 150 on occasion (not even a 3db difference in apparent loudness) will sound less pleasant than the same input with the same speakers in the same room, with a 200 watt rated amp and not have a problem at all. The more efficient your speakers are, the happier your amp will be. I hope this helped. Enjoy the music!

@baconboy 

Bryston offers many different colors/finishes on their faceplates, although they are the same design.

Regards,

barts

@dman777 you’ve sparked one of the best threads I’ve seen in a long time with many members taking deep dives into watts / amperage / speaker relationship.  A lot of members took a lot of time to delve into the topic and provided a lot of great advice and guidance.  I’d echo what others already have form a speaker / amp pairing.  Gaining Volume from an Amp relative to your speakers is more complex than just looking at the speaker sensitivity rating and the watts rating on the amp.  Improving performance / volume with your current speakers is more complex than manufacture #’s on an amp and or speakers. As many have referenced, having visibility to your set up would really open up the type of detailed advice that could be provided, not just your speakers but everything in the chain.  Gain values apply to DAC’s, Streamers, CD players, Turntables and that impacts the volume knob on your Yamaha Reciever.  
 

Best analogy I’ve seen when talking about amplifier performance and the ability for an amp to drive a set of speakers is that to an engine, not all Horsepower is created equal, following that logic, not all Watts are created equal.  For an engine, torque plays a huge role in performance of the HP that an engine produces, where and when the torque and HP shows up in the RPM range of the engine plays a huge role in how the performance of the engine translates to the performance of the car.  It’s the same for an amplifier, not all watts are created equally.  In SS amps, so much of the control of the speaker has to do with the amps ability to control the woofer, drivers and as many others have referenced, deal with the wide variation of impedance requirements.  A large power supply coupled with the proper design / implementation is what allows the combination of amperage and watts that drive speakers to effortless volume.  Having a reserve of power to then drive watts / amperage is what gives an amp headroom.  When you pair an amp with speakers you need to understand what type of car you are dropping the engine into.  You wouldn’t drop a race car engine in a Ford Super Duty 350 and you wouldn’t drop a diesel 6.7 liter V8 into a Toyota Camry.  Same principles apply when pairing an amp with speakers.  You need the right combo of watts / amperage, one without the other however won’t get you to fully realize a speakers full potential.  An amp with a lower wattage rating but a higher amperage rating, power supply that can deliver more current will almost always drive speakers to higher levels than an amp that has a higher watts rating but lacks the power supply to deliver amperage / current.  Again though, grab a pair of high efficiency speakers and hook them up to high amp / watt Coda or Krell amps and you won’t get past turning your equipment on and you could have music playing rather loudly with the volume dial at zero, create as many problems as not having enough watts / power.  
 

Thanks for starting the thread, it generated a ton of thoughtful, insightful replies within the Gon community, good luck. 

For what it  might be worth and given that our systems are VERY different, here is my experience.  I have a 75W tube amp (ARC Ref75se using 8 ohm tap) driving speakers with a nominal  impedance of 8 ohms and a sensitivity of 91db-listening room (and 89db anechoic chamber).  I have never seen the meters on the amp ever go higher than 5-10W.  I usually listen with the volume setting on my preamp (0-103) (ARC Ref6) between 3 and 26, background and dedicated listening when I want to blown away so that nothing else exists.  I have very "transparent" (NOT the brand) cables.  Anything louder borders on painful and I am afraid of blowing something out.  There is no where in this system to adjust the gain.  I wish there was because I'd like to use less attenuation of the volume.

With respect to volume, lots more in the signal path matters. I do not stream. Source: caching server with its own internal SSD, Macbook pro running JRiver Media Center, hi-res files on computer or external SSD, and embarrassed to reveal you tube.   I run only NOS (no over sampling, all processing is disabled in JRiver except volume leveling and PEQ - parametric equalizer).  Volumes for each source are different.  All sources run without attenuation.

Conclusion, to echo what many others have suggested: this needs a systems approach.  The best solution to OP's original question would be found in the synergy of the individual components of the system as a whole.  And for ultimate endgame satisfaction the solution must include the often forgotten details that matter like the room's dynamics and the listener's hearing, sonic & music genre preferences.  It has taken a long time to sort through all this for myself.

SPL which answered all my questions (and is fun to play with) Toptes TS-501B from Amazon for less than $30.

Happy listening dear friends, Leon AKA Timbrehead

I agree with the comments that there is an equation here: amplifier output / speaker efficiency, and that speaker efficiency usually matters more. 

My Altec 604Cs are 101db, 16 ohms. That’s way more efficient than most stuff being made today.