Please check out my final circuit X/O with piezo - diyAudio
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Old 26th February 2013, 12:24 AM   #1
krafty is offline krafty  Brazil
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Default Please check out my final circuit X/O with piezo

Ok, after reading a lot, everything is almost set.

After reading that piezo needs different treatment, I went on how to crossover my midbass with a piezo, I decided to follow some suggestions from the POINTED OUT ARTICLE.
Click the image to open in full size.

When I first went for my crossover values in HERE, I was told to go with the following circuit:
Click the image to open in full size.



And I was also told (before I realized I had a piezo) that I needed to attenuate my tweeter by 22dB because it seems like the woofer would be 96dB SPL while the tweeter 108dB. So someone told me to calculte an L-Pad in HERE and what I got was:

Click the image to open in full size.

To complicate more, the tweeter box says:

- Always use a 4.7uF/100V polyester capacitor.

Resistor usage table:

Resistor / Sensitivity (2,83 to 1m) / Power Range on 4 Ohms

No Resistor / 108dB / 40W RMS
15 Ohms / 105dB / 60W RMS
18 Ohms / 100dB / 75W RMS
22 Ohms / 97dB / 100W RMS

The label in tweeter box suggests the mentioned capacitor in series with a resistor.

The big question is... alright, I've made an effort... is there any failing thought in the first circuit?
My goal is to level the piezo with the midbass and crossover at 6000Hz/12dB.

Last edited by krafty; 26th February 2013 at 01:00 AM.
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Old 26th February 2013, 02:56 AM   #2
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96-108 = -12
It's going to be approximate anyway, the best way is to set up the crossover outside the box the first time you wire it up so it's easy to change parts, & use a variable resistor for R2 (in the first diagram) to tweak for the level that you like....
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Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
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Old 26th February 2013, 09:33 AM   #3
krafty is offline krafty  Brazil
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Well, turns out that the midbass is actually 86dB SPL, and not 96. So it's really 22dB.

I am confused about R1 (first diag). It DOESN`T DO attenuation, does it?
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Old 27th February 2013, 01:07 AM   #4
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thinking about it , it makes more sense to make R1 variable, take the tap to C2 from the wiper, & it will do attenuation (replace with fixed resistors after you've found the best setting)

The purpose of R1 is to make the Piezo look like a conventional tweeter to the crossover (C1). A Piezo is electrically a capacitor, hence the need for the different treatment
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Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
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Old 27th February 2013, 02:23 PM   #5
krafty is offline krafty  Brazil
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Quote:
thinking about it , it makes more sense to make R1 variable, take the tap to C2 from the wiper, & it will do attenuation (replace with fixed resistors after you've found the best setting)
Can you rephase this. What do you mean make R1 variable, did you mean using something like a potentiometer? I'm not familiar with expressions take the tap to C2 from the wiper. What does that exactly mean?
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Old 27th February 2013, 10:39 PM   #6
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re:"did you mean using something like a potentiometer?" - yes. The wiper is the variable part of the pot, connect C2 to that.
Potentiometers (Beginners' Guide to Pots)
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Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
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Old 28th February 2013, 12:57 AM   #7
krafty is offline krafty  Brazil
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Would it be something like this:

Click the image to open in full size.

If so, what would be the value for P1.
Also, are the other components subject to change?
Isn't it enough to make an adjustment with the pot and leave like that?
Do I need to find the "right" attenuation by listening?
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Old 28th February 2013, 01:49 AM   #8
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Yes, use the original R1 value, 22 ohms.
You can leave the pot, but over time they oxidise & become scratchy & unreliable, better to replace with fixed resistors after you've got the balance you like
Re: listening - it's your ears you have to satisfy....
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Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
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Old 20th February 2014, 10:05 PM   #9
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Krafty, did you build it, did it work?

I'm building something similar and would be interested in your results.
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Old 30th March 2014, 07:40 PM   #10
krafty is offline krafty  Brazil
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Hi nickparsons101,

Yes, I finished today ONE module. Well, I did not use the potentiometer. I used the circuit with fixed resistors in their respective values.

The treble was completely suffocated. I shortwired the C1 and P1 junction directly to the tweeter positive (+) and it gave the best result. (Kind of not too bright, but acceptable). I may replace C2 and R2 with a 4,7uF capacitor just for protection in there. I wonder why the necessity of R2 in the end of this story...

Looks like R1 is the real deal on this story. So my preference is in between 15 Ohms and 30 Ohms for R1. I still want to give a shot on these values to see if the sound is better. L1 is working nicely, the sound is very different on another box that is bare.

I must confess I am almost throwing my towel: building and testing this it's very time consuming.
It took me months to find some motivation to keep going on and on.

I have considered acquiring this set...
Genius

Last edited by krafty; 30th March 2014 at 07:43 PM.
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