In Reply to: Re: Throwing in a small question along side Eriks. posted by Erik Johansson on June 14, 2002 at 03:13:25:
For acoustic damping material, use R13 fiberglass insulation. I don't know if you have this designation in Sweden, but you can just find some that's 5-6cm thick. Put it on the bottom, back and the side nearest the port.About the piezo, I don't recommend adding series resistance, at least not the series value that is shown by CTS as a protection device. By the time you get even close to damaging the tweeter, you've long ago destroyed the woofer/midrange. So it isn't necessary.
I used to install a very small value resistor in series, but I used it as a fuse and not as a current limiting device. And I was concerned about oscillation when I first considered using them too.
But after nearly 30 years of experience, I can assure you that these are unwarranted measures.
The kinds of circuits that encourage oscillation are unsuitable for use with piezo devices even with the resistor installed. Notice the previous post called "Don't go into clipping and check for back-EMF", where Andy reports that his piezo tweeters "buzz" (oscillate) even with the so-called protective resistors installed.
For those kinds of systems, there is no set of passive values that will solve the problem without excessive rolloff of the top octave. If you try to isolate other components in the system, you'll find that they must be attenuated too much to be of any value. So for these kinds of systems, the use of piezo's is really not an option and consideration of passive (resistor) solutions is not recommended.
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