Piezo Tweeter enhancement?

[jackfish]

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 . 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:

8 ohm 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 8 ohm driver?

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?

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:

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

2.Coat the paper cone with one coat of damar

3.Remove ‘pooling’ of damar with a tissue

4.Let dry overnight

5.Reattach horn

An application of rope caulk to the back and sides of the horn helps to deaden any plastic sound.

http://www.melhuish.org/audio/images/diy35-2.jpg

I would put the driver and ‘crossover’ circuit in a small box to be placed on top of the Large Advent cabinet and wire in parallel to the Large Advent terminal posts. One could put the driver and ‘crossover’ circuit in the cabinet and perhaps wire it to the Advent tweeter, but I wouldn't know the best placement for it on the baffle.

Anybody tried this or have any observations about the described setup?

[jackfish]

OK, I wasn't sure if there would be any interest. However, I think that those who are also interested in the Dahlquist DQ-10 might have some insight into this kind of modification. The DQ-10 used a piezo super tweeter to take the highest frequencies. Could someone who understands crossover schematics please describe the crossover for the Super Tweeter for the Dahlquist DQ-10?

http://www.diyhifi.org/forums/files/dq10xo_277.jpg

It looks like they use a 30 ohm 5 watt resistor, but what would those components provide for the roll off?

[jackfish]

Well, after some research I am ready to try my experiment. I purchased two CTS KSN-1005A piezo tweeters, two 20 ohm 20 watt resistors, pairs of a variety of caps; 1.0uF, 0.68uF, 0.47uF, 0.33uF, 0.22uF, and 0.10uF, 4 ounces of Dammar varnish, and some ACE Hardware rope caulk. I have a bunch of 3/4" MDF left over from making my FleXy Table.

I will varnish the piezo's cone element and apply rope caulk to the sides and back of the horn. The resistor will be soldered across the piezo's terminals. I have made a pair of small boxes out of 3/4" MDF just big enough to put the piezos in, the back remains open so I can get at the capacitors. I will then experiment with various attenuations provided by the capacitors wired to the positive terminal of the piezo. I bought an extra pair of 0.33uF to go with the 1.0uF for 1.33uF. I think 1.5uF will let too much of the piezo through. I can try some other combos to get intermediate values. The supertweeter system is then just wired to the speaker terminals of the Large Advent. I will also try the piezo facing forward and backwards on top of Large Advent cabinet. There is some suggestion that facing backwards might improve the sound.

We will see if this will add some pizzazz to the New Large Advent without harming the overall sound quality and report back with my findings. Total cost is under $50.

[Carlspeak]

Attached is the super tweeter portion of the schematic you provided.

It's a 3rd order circuit with a 16 ohm effect L-pad ahead of it.

Crossover point is very high I suspect.

It's all about the music

Carl

Carl's Custom Loudspeakers

[jackfish]

Yeah it looks like it would be 16 to 18 kHz. I think the solution I'm exploring will demand experimentation and listening to the piezo in various positional and attenuation modes. It may be a bust but it should be fun listening critically in my exploration. Thanks.

[Guest crusty]

I tried this method many years ago on a pair of large Advents.

Using a short length of pvc tubing (4 inches) 2 inch dia. mounted in a nicely made wooden saddle. But instead of a Piezo, I used a small automotive type tweeter (stick anywhere design).

I mounted the tweeter in the end of the pvc tube, the tube I had covered with wood grain shelf liner with adhesive backing (contact paper). For the hookup I used a 3uf cap and a small 8 0hm L pad (volume control) mounted at the back of the tube.

I hooked this directly to the input terminals on the back of the speaker. Being able to adjust the level of output with the L pad, made it easy to balance the sound.

The finished product had a livelier sound then the original and added spaciousness to the overall sound.

[2Turbos]

I tried this method many years ago on a pair of large Advents.

Using a short length of pvc tubing (4 inches) 2 inch dia. mounted in a nicely made wooden saddle. But instead of a Piezo, I used a small automotive type tweeter (stick anywhere design).

I mounted the tweeter in the end of the pvc tube, the tube I had covered with wood grain shelf liner with adhesive backing (contact paper). For the hookup I used a 3uf cap and a small 8 0hm L pad (volume control) mounted at the back of the tube.

I hooked this directly to the input terminals on the back of the speaker. Being able to adjust the level of output with the L pad, made it easy to balance the sound.

The finished product had a livelier sound then the original and added spaciousness to the overall sound.

Back in the "Day", 1975, we tried this(add piezos) to extend the highs. Like others have reported, it takes a bit of "tuning" to get it right. I had them on my large Advents but removed them after a period of time deciding that they sounded better without the HF enhancement.

You know, speaker performance is a very subjective thing. An audio engineer from Bose told me many years ago that there is as much variety in human hearing as in human voices for example, except each has two ears so the factor has to be multipled by two. For this reason a single speaker design will not please all.

Good luck with your piezo project, I had fun doing mine back then!