I wholeheartedly agree with the general 'run of opinion' in this thread.

Amplification should be only be used to balance the sound levels of the instruments thus achieving the required 'sound picture' and to enable delivery of this 'sound' at only such levels as are necessary for it to be clearly heard by all (...save the deaf :o) at all points round the dance floor/concert hall.
In smaller venues, provided the instrument balance is right, there is very often no need for amplification at all, save perhaps with a larger band there may be a need for low level amplification for the caller.

Ceilidhs, Barn Dances and the like, are (or should be) great social occasions where people not only dance, but also engage in conversation. Sound levels should be set so as to afford the opportunity to be heard without having to shout. If the music is too loud this will significantly reduce the overall enjoyment of the evening for many and may well persuade some not to come again.

If you allow the initial levels to be set too high, background noise from 'conversation', (by now most likely shouting), also means that the caller feels he cannot be heard and will either turn up his mike or end up shouting into it .... or in the worst case, doing both!

As any good teacher knows, if you have to shout, you have lost the battle and the only way the general noise level goes, is up.

Noise induced hearing loss is far more common than many might suppose particularly amongst musicians, older folks with a history noisy jobs and, sadly, far too many youngsters. This degenerative condition also has a fairly common, but there is a less well known, side effect called Hyperacusis. This is a lowered tolerance to loud sounds which causes a jangling effect in the ears, much like a split in a speaker cone, while higher levels of sound cause real physical discomfort, a distinct loss of enjoyment of the music and for musicians a lowering of concentration levels. In bad cases you can almost lose the will to live.
If you are in the audience and the band is too loud, at least you can 'vote with your feet' but if you are in the band you are stuck with it.
To be fair, I must declare an interest here as I left half my hearing down coal mines, and suffer from significant intolerance of loud sounds.... my own concertina, strangely, seems to be exempt btw :o)

This same 'noise snowball' effect also occurs in totally unamplified sessions.
For some strange reason, many folks seem hell-bent on thrashing the guts out of their instrument to gain the maximum possible volume (and speed... but that is another story...) Session etiquette is a whole separate issue, but six melodeons, a similar number each of concertinas and fiddles an accordion and a whole assortment of other instruments all in full flight in a low ceilinged bar you could not swing a cat in, would give your average local environmental health noise monitoring technicians a dicky-fit.

I would make a plea for folks to concentrate more on the content of the music and to play quieter, in many cases slower, and also consider that they are not duty bound to play, or attempt to play, every single tune throughout the session.

So speaks the reactionary (and deaf) 'old fart'.

Seriously though, I hope I am not considered too much of a kill-joy. Quite the reverse I hope. I firmly believe that cutting back a bit on the volume will increase the everyone's enjoyment of such occasions rather than take away from it

Regards

Dave