3 dB is a doubling of power, not perceived...generally 3dB is accepted as the smallest noticeable increase..lots claim to hear better, but don't have controlled tests. Trained ears can obviously do better than untrained ones, so bear in mind the 3 db description doesn't apply, they are not the "average" listener, due to being outside the norm.
if you wanna use a crossover cap on peizos a parallel resistor is necessary, or an L-pad, so as to present an 8 ohm load to the xover. This would be in addition to a series resistor which is recommended.
Essentially a parallel set of peizos, with a 20 ohm series resistor, wired past an L-pad, is the simplest.
Trimming the flanges of the peizos so they couple better has merit.
The peizo has a "falling" impedance curve...40-50 Ohms, say, at 2K, falling to perhaps 8 at 40 KHz. This leads many ignorant marketers to claim no crossover needed, and the peizo's bad rep. They produce energy all the way down to 800 Hz or so, in a bad fashion. My opinion calls for 6-7 KHz or even higher usage. I use half a dozen stacked in a vertical array, with the flanges trimmed. Amazing how good they CAN sound when used properly, especially at the price.
Using piezo tweeters wisely: a "how to" - AudioKarma.org Home Audio Stereo Discussion Forums
Lynn and Steve's Piezo page
Do this-stack VERTICALLY. I like them closer together.
Horrible idea, do not do this! Comb filtering Hell.
Why a series resistor? 8 ohms at 40 K divided by 6...equals freaking out amplifier. Not many ruggedized pro amps will handle a load like that, much less home stuff.
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