Must speakers have certain volume to sound convincing ?

...since the dust is being knocked off this ancient argument....*G*

Not a single mention of ribbons or AMT's, which I suppose one could place in the 'planar' column in a stretch.  Or my preference for a 'well-done' omni, which IMHO actually reproduces the 'original environment', but that starts an entirely different 'discussion' that can also go on forever, much like cables 'flavours', tube vs. solid state, TT/arm/cart combinations, etc.  It reminds me of boxers vs. briefs vs. none at the end of the day.....

There is no 'perfect reproducer', and all the 'upstream' hardware is flawed in some fashion.  'Perfection' existed at the moment of creation of the music itself, and everything deteriorates beyond that in the capture and reproduction of that moment.  We simply exhibit our tastes, preferences, and budget in the pursuit of one's goal to hear that moment, be it aria or zydeco.

And then there's the differences in the original instruments that created the music in the first place.  Stradivarius vs. 'student' violin, the latter in the proper hands can be made to sound wonderful despite it's shortcomings I suspect.  Much like us, different 'voices', subject to skill and combination.

I tire of the argument, another endless 'tail chase'.  Enjoy what you have, pursue what you must.....;)

Play on....

...and going back to the original query by the OP....

How loud is loud?  When the sheetrock cracks?  When the neighbors give up banging on the door and call the cops?  When the cannons in the 1812 ov bust the windows?  When you ears begin to leak?  When you can smell the voice coils give it up?

MHO, for what it's worth, nil or not...

Floyd in concert, loud enough.
Smashing Pumpkins, same venue, way too much.
I wear hearing protection when setting up the active eq on my system, just because white noise is irritating at high db's.
I take them to concerts (yes, I get stared at...).  Not because of the band...because of US.  That racket we make when a set concludes freaks my ears out.  WE are Too Loud.
I used to take them to audio shows when I used to bother to go.  Saved my ears for what I wanted to hear.  'Selective listening' in action....*G*

geoffkait, Absolutely.  And then it was subject to the space it was in, how it was set within it, the materials within that space, the equipment combination....were there others in the room (audio show 'extravaganzas'), what was being played, any predispositions you may or not have held at that given time....
inna's 'processing of perceptions' seems rather apt to moi'.  I'm sure we as a group could essentially agree when a 'system' behind a curtain sounds like pounded poop.  It's when we reach the 'extremes' of our selection of equipment and the above variables I've noted that we launch into our perceptions of what we're hearing....this 'n that nuance, shortfalls, strident, 'forward', 'restrained'...we begin to parse ourselves into our subjective perceptions of what and how is happening to our ears, inside our heads.  And 2psyop is right in that respect....we listen with our brains, or what's left of them, given modern uncivilization and the daily dose of it.  We'll agree on some aspects, argue endlessly on others of what we 'hear'.
And then there's our 'listening systems', the ones our DNA has gifted or cursed us with.  I find it fascinating that there are people who apparently relate what they hear as colors....I can't do that.  My spouse says I can't hear her at all, but that may just be 'selective' on my part. *L*
I know my hearing is faulty, due to age and abuse.  I have mild tinnitus, which I only have full awareness of when I go to bed.
As for what's in my skull...having had an MRI recently of it, I can verify that at least there's something in there.  I got a cd of the imagery as proof of some content.  Function?  Well, there's something else we could argue about...;)
My personal 'system' can't be regarded as 'high end'.  I don't have the budget to pursue such, and frankly I'm not interested in the pursuit of it anymore.  I do know what I like to listen to, and have my own thoughts as to how to attain that, given the space I have to work with.  Within that envelope, I listen to what I like to spend the time doing so.
In some respects, IMHO, we're alike in that pursuit. *S*
It should be the music that's important.  The 'how' to do so is up to the individual to decide what limits to set, where one can 'stop' and be satisfied with that....

...and then there's the aesthetic approach...;)

Agreed, dl.  Sheer volume/db's and the pursuit of more of it in the final analysis is ultimately silly.  Rock concert levels in your living room or wherever is OK, but isn't what one would normally do, daily....IMHO...

Louder does have certain effects on nuance, but one's perception and processing of what's occurring (or seems to be)....should remain...'stable', still 'perceivable'....hmm, 'uniform'....
I appreciate the 'venue appropriate' thought; chamber music vs. small club jazz vs.*insert your favorite here*.  It's a judgement call as to the appropo, but a nice view to take...
Sounds like your line conditioner was your best investment....although the Thiels' + Classe' sounds like a promising match....

Enjoy.....play loud...;) *L*

Yeah, subs 'liven up' low volumes, even with larger speakers as mains.  Bass comes down to moving lots of n2o2co2ar about, and one can't seem to get it to move enough. *G*