piezo super tweeter

[operaman]

I want to install a Goldwood GT-1005 Piezo Super Tweeter on my 3-way. Is it best in parallel with an existing Polk SL5000 Soft Dome Tweeter w/ a low cutoff @ 5000Hz or across the 3-way's input? I want a 8500Hz low cutoff for the piezo. I'm not sure what size series cap that will do the trick? Do I also need a series resistor before the piezo in either case?

 

[j_garcia]

What is the issue you are trying to address? It isn't exactly as simple as what you're suggesting.

 

[operaman]

I've used piezos in the past by simply going across speaker inputs and have liked the results, but unlike the past I'm modifying a more expensive speaker and I'd like to do it the right way.

 

[j_garcia]

There is no "right way" of modding a speaker in this manner - you are talking about a design change and are in uncharted territory. To achieve your goals, you'll just have to experiment, but modding the x-over in the manner you are talking about will require some gear to figure out what affect you are actually having on the tweeter and for proper blending of the piezo to the tweeter.

People I've seen in the past modding Polks upgrade the x-over and replace the tweeters with newer ones. These are documented retrofits with carefully selected components that were validated with proper testing.

 

[KenM10759]

We're all different so in my case I consider my time to have some value. That means I'd just shop for some speakers that are designed to give me what I want right out of the box.

What model Polk are the speakers? This could easily be a case of gilding the lily.

 

[TLS Guy]

I want to install a Goldwood GT-1005 Piezo Super Tweeter on my 3-way. Is it best in parallel with an existing Polk SL5000 Soft Dome Tweeter w/ a low cutoff @ 5000Hz or across the 3-way's input? I want a 8500Hz low cutoff for the piezo. I'm not sure what size series cap that will do the trick? Do I also need a series resistor before the piezo in either case?

There are a number of issues with Piezo tweeters. First the manufacturers provide no specs. Piezo tweeters are sensitive and loud and need attenuation. Without crossover they are harsh and burn out. The are a high capacitance load and can blow amps without a network. They are high impedance, so you have to drop it with a shunt resistor if you don't want to spend a fortune on caps.

Here is a generic piezo crossover.

The 22 ohm shunt resistor lowers the impedance. The cap which is calculated by the above formula. This goes ahead of the shunt and will give you a first order crossover, down to the tweeters natural crossover and add an extra order below that point.

Now the tweeter will still probably play too loud. If so place a 0.15 mfd cap between the 22 ohm shunt resistor and the tweeter. Now place an additional resistor between the cap and the tweeter. This resistor will need to be between 8 and 100 ohms. I have crossed piezos a number of times. This resistor most often has to be between 30 and 50 ohms.

You will need to arm yourself with a number of 10 watt wire wound resistors of varying values and do careful listening.

At the end of this you may well find you don't like it.

I have calculated you series cap ahead of the 22 ohm resistor and for 5 K it is 1.4 mfd. Now I think for a super tweeter 5 K is too low. 10K is considered optimal for a super tweeter to pull up he high end of a tweeter. Remember this is a first order filter until the piezos natural crossover, so I would use a 0.7 mfd cap to use this device as a super tweeter.

Darn I could see my circuit as I wrote it and in the edit, but it did not go into the post. Any how you need a 1.4 or 0.7 mfd cap in series. I would use 0.7 mfd and then a 22 ohm 10 watt wire wound resistor in parallel across the tweeter. If it is too loud then place another 0.15 mfd cap and a 30 ohm resistor between the 22 ohm resistor and the tweeter.

 

[JohnnieB]