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Piezo Tweeter enhancement?

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The New Large Advent has a reported frequency response of 33Hz to 17,000Hz +/- 3dB. I thought I might try to extend the high frequency of the Large Advent by adding a Radio Shack Piezo Tweeter 40-1218 http://support.radioshack.com/support_audio/doc63/63021.pdf or the Motorola/CTS KSN-1005 (4kHz-27kHz). Although no crossover is needed and this driver supposedly does not significantly affect the impedence of the speaker it is wired to, I found the following ‘crossover’ circuit and modifications to the driver that is said to eliminate its "spitty and lispy" fatiguing harshness:

1. 8 ohm/20 watt resistor across the piezo terminals (Radio Shack part # 271-120, $1.49 each) What affect does this resistor have? Does it make the piezo an appear to the system as an 8 ohm driver?

2. 0.47 uf capacitor wired in series (Hovland, $1.50 each from Madisound) I assume this only allows frequencies above 15,000 Hz (based on 12dB filter parameters) go to the piezo tweeter?

3. Application of damar varnish on the piezo’s cone element is said to add refinement to the sound and almost completely reduce the fatiging sibilance:

a. Remove the three screws from the back of the piezo

b.Coat the paper cone with one coat of damar

c.Remove ‘pooling’ of damar with a tissue

d.Let dry overnight

e.Reattach horn

4. An application of rope caulk to the back and sides of the horn helps to deaden any plastic sound. (See attachment)

The heralded Dahlquist DQ-10 used a KSN-1005 piezo for the highest frequencies and essentially the Large Advent woofer for the lowest. Any ideas how to integrate a piezo into the Large Advent to take frequencies above 17,000 Hz? What capacitor would give a roll off of 17,000 Hz? If using the above ‘crossover’ circuit how would one wire this to the Large Advent tweeter?


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