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High Efficiency Tweeters

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    Posted: 29 Jul 2010 at 3:02am
What do others like to use for High Efficiency Tweeters?
I have used 2 inch paper cones, 1 inch mylar domes, and compression horns.
I do like my 1 inch mylar domes, very pleasing highs and good efficiency.
Compression horns were a little squaky and forced sounding.
I have some 12 inch woofers; 98db SPL 1w/1m, fs 20 Hz, 20 to 5500 Hz, ...
 
I am now wondering about piezo tweeters as they are not supposed to need crossovers.
I have read that putiing 10 ro 100 ohms in series helps smoothout frequency response and
protects against peaks causing burnouts.
Others say using a capacitor (a crossovrer) to limit the low end frequencies would keep out unwanted back EMF and frequency dependent phase anomalies.
Any ideas or experiences?
 
BAK
 
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 29 Jul 2010 at 5:58am
A 10 to 100 Ohm series resistor will suffice and the transducer IS its own capacitor that limits low end frequencies. Any back EMF is from inductance that it will only exhibit at ultrasonic frequencies and that would be countered by the series resistor (the load impedance will become negative but the resistor is in series - if worried start at 100 Ohms and work backwards - your ears guiding you)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote BAK Quote  Post ReplyReply Direct Link To This Post Posted: 30 Jul 2010 at 4:33am
Posted: Today at 12:58am By Graham Slee
A 10 to 100 Ohm series resistor will suffice and the transducer IS its own capacitor that limits low end frequencies. Any back EMF is from inductance that it will only exhibit at ultrasonic frequencies and that would be countered by the series resistor (the load impedance will become negative but the resistor is in series - if worried start at 100 Ohms and work backwards - your ears guiding you)

I have thought of using a 100 ohm pot like a level control in series with 2 piezo tweeters in parallel. I know that, by the basic physics of how piezo tweeters work, their impedance increases as frequency decreases just as a capacitor does. It would be handy if piezos were spec'd with a characteristic capacitance, not just a useful frequency range. I could make some empirical frequency and impedance tests. 

I have seen some spec'd with an effective impedance at a given frequency; that would allow me to reverse calculate the capacitance.

An empirical test would definitely be more accurate.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote BAK Quote  Post ReplyReply Direct Link To This Post Posted: 30 Jul 2010 at 5:10am
Posted: Today at 11:33pm By BAK
I have thought of using a 100 ohm pot like a level control in series with 2 piezo tweeters in parallel. I know that, by the basic physics of how piezo tweeters work, their impedance increases as frequency decreases just as a capacitor does. It would be handy if piezos were spec'd with a characteristic capacitance, not just a useful frequency range. I could make some empirical frequency and impedance tests. 
 
I just read the specs on the box of some; "typical impedance appears as .12 uf cap"
and "A 30 ohm series resistor is recommended to assure stability of extended range amplifiers and preclude hazard of amplifier damage"
and "range of 3500 to 25,000 Hz".
That would calculate to 379 ohms at the spec'd low end of useful range of 3500 Hz and 1327 ohms at 1000 Hz.
 
Maybe I should put the fixed 30 ohms in front of the 100 ohm pot for safety.
I dont want to damage my Dynaco ST-120. It is now 35 years old, 12 years since rebuild.
It does have an extended frequency range of 5 to 70,000 Hz, Original design was 5 to 100,000 Hz.


Edited by BAK - 28 Nov 2014 at 5:50pm
Bruce
AT-14SA, Pickering XV-15, Hana EL, Technics SL-1600MK2, Lautus, Majestic DAC, Technics SH-8055 spectrum analyzer, Eminence Beta8A custom cabs; Proprius & Reflex M or C, Enjoy Life your way!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote BAK Quote  Post ReplyReply Direct Link To This Post Posted: 28 Feb 2011 at 8:31pm
Update on the piezo tweeters crossovers. I used 22 ohms acroos the imput to the crossover for impedance stabilizing the amplifier, then 2 uF in series with 10 ohms in series with a 150 ohm pot (wired as a variable resistor) in series with the piezo. With the 150 ohm pot at 150 max it still does not attenuate enough.
I may try this pot wired as a pot next; as a voltage divider. I have a 500 ohm pot to use as well.
 L-Pads dont come higher than 16 ohms that I can find. I have seen 50, 100, and 1000 ohm L-Pads a long time ago for 70 volt systems.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote BAK Quote  Post ReplyReply Direct Link To This Post Posted: 28 Nov 2014 at 6:14pm
Originally posted by BAK BAK wrote:

Update on the piezo tweeters crossovers. I used 22 ohms acroos the imput to the crossover for impedance stabilizing the amplifier, then 2 uF in series with 10 ohms in series...


Update on the piezo tweeters crossovers. I used 22 ohms across the input to the crossover for impedance stabilizing the amplifier, then 2 uF polyester in series with 10 ohms in series with the piezo tweeter.
I found this connection to work the best.

The piezo tweeters sound great!
I have them paired with some 8 inch woofers that have the following specs:
- 97dB/1w sensitivity
- 35 Hz to 4700 Hz frequency response
- 8 ohms nominal / 6 ohm DC resistance
- 100 watt rms / 200 watt peak power (I won't be listening at that much power, but they won't be over-driven by my 60 watt rms per channel amplifier.)

I now have rich base, clear midrange voices, and clear highs... with no noticeable phase shift.


Edited by BAK - 28 Nov 2014 at 6:16pm
Bruce
AT-14SA, Pickering XV-15, Hana EL, Technics SL-1600MK2, Lautus, Majestic DAC, Technics SH-8055 spectrum analyzer, Eminence Beta8A custom cabs; Proprius & Reflex M or C, Enjoy Life your way!
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