There have been many experiments down to accelerate the breaking in process, in an attempt to give a new guitar that well-worn vintage sound. The idea of subjecting the instrument to high decibel sympathetic vibration whether placed near a speaker or other methods, hasn't produced any sort of conclusive results that these methods are indeed effective...and I for one am skeptical.

I think the best way to break in a new guitar is to play it often and play it as loudly as you can without breaking strings or creating buzzes. The direct vibration within the body as a result of playing it, tends to be more effective than any of these other methods.

There is no quick "vintage sound magic bullet" that will make a new guitar sound 40+ years old, in a matter of days, weeks, or even months. You buy a new guitar for the way it sounds NOW. You play it faithfully as often as you can - perhaps a couple of hours a day everyday for the first couple of months - and if its a quality instrument (or a "good one") you should notice an improvement in its tone and projection.

Of course it varies from make/model/manufacturer as to how long this break in period will take for the guitar to open up. I have found the new, higher end Martins will start opening up in a shorter period of time (2-4 months) and others like Collings can take a year or longer. But getting something that sounds just dandy now, is the way to go, knowing that it will only sound better as time goes on. If it doesn't open up and sound better to you after say a year of ownership and constant playing, think about selling it and finding something better not necessarily more expense just better.