The cheap violin is apparently so difficult to play that it results in at least twice as many musical "errors", mostly intonation, compared to the others. This is a give away.
It was a giveaway long ago in that BBC Test from the 70s I mentioned as well. Even if you couldn't guess 3 out 3 of the 4 back then, you could still guess the 3rd one by deduction for that exact same reason. And it is quite simple - it is exactly what you say. Many new violins are simply more difficult to play. Breaking in a violin is much harder than breaking in a pair of speakers or large headphones. Some will tell you takes a 100 years plus...
And for that reason often with brand new instruments you will hear the signs of a subtle struggle - scrapes and squeaks, uncertain shifts, etc that you are not going to get as often on old instruments.
Anyone who has enjoyed this thread might want to take the time to listen to that old BBC program I heard fresh on the FM radio all those years ago. The only link I can find is poor quality MP3, but still good enough to hear what we are talking about.
http://abcviolins.com.au/bbc-radio
I don't think I am going to spoil it by telling you the new violin in that BBC test was number 3. But just listen for the struggle involved and you can tell - forget about the actual sound! By the way, the sound I got on the original FM broadcast was miles ahead of this MP3. I suppose that is another thread - the golden years of pure analogue FM.
Mind you, regarding new violins, there was a wonderful maker in Australia called Cedric Clarke. He was originally a maker, then repaired instruments only for many years based out of his home in northern Sydney. You could say that he, myself and my Mum became friends because we always seemed to be there - if it were not for repairs or new strings it was that very convoluted search for the next violin upgrade (yep, no different at all to audio equipment I'm afraid).
He moved to southern NSW some years ago and began making them again. Of course, having known him for 20 years by now I couldn't resist being first in line to try one out (he'd made a batch of two). I was a bit nervous trying them out - not from a playing or performance point of view but because his reputation preceded him. So many people I knew in professional circles had always said such wonderful things about him that I was really nervous I would be disappointed. I needn't have worried though. He had always said to me that a good violin is always going to sound good right from the get go. If it doesn't, it is doomed to be a bad one forever. But a good one, he said, would sound great from the word go and just get better and better.
Suffice to say those two were amongst the best violins I had ever played - period - and at the absolute top echelon of new ones. He did not disappoint me at all. I took the two instruments with me back to Sydney, played them in for a week then at his request took them to Christopher Kimber's house so he could have a go of them. I don't know what happened to them but I guess they did the pro rounds of the Clarke fan club.
My only "regret" was that his output would remain forever low. He repaired instruments only for so many years and not long after we last met he passed away. A few years later at the shop of a mutual acquaintance I knew well, I saw his very last instrument. It was reminiscent of the very last Strads. A perfect, exquisite body but a very sorry scroll carved by an obviously frail person. But it sounded just as good as the ones I played when he was - workmanship wise - still in his prime.
I could probably write a book of Cedric Clarke anecdotes. He was one of those blokes that was at the same time very serious and very funny. I believe he was the 20th century Aussie answer to Stradavari.