I've seen photos where people had glues rose quartz crystals inside their amps for supposed benefits. It looks like madness to me but I don't like to completely discount things as nonsense until I've tried them so who knows, maybe this works.
For people that don't know, a piezoelectric crystal is a crystal that when physically "excited" (hit with something) produces a voltages. Or when a voltage is applied to them they vibrate. They are used in various applications from cigarette lighters to cooling/heating plates.
So it appears to me that if these rose quartz crystals are effecting the audio signals though a piezoelectric effect, then it should either be that the presence of a nearby electrical signal is causing the crystal to vibrate, or the presence of vibrations in the room/system are causing the crystal to produce a voltage. The latter seems very unlikely to me as I don't think the vibrations in the room would be strong enough to cause this effect but I'm no expert so who knows.
If the effect is being caused by a piezoelectric effect then it would seem logical that the same effect or an even more pronounced one could be gained from the application of some proper piezoelectric crystals like those found in piezoelectric transducers, peltier coolers or in some fag lighters.
I personally don't have time to strap fag lighters to my hi-fi so I'll leave that to someone else.
Joking aside, that's about all I can hypothesise on the subject but I'd be interested to hear other peoples thoughts or experiences.
