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Old 17th May 2006, 08:51 PM   #1
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Default Question on Piezo/Pioneer 8" FR Hookup...

I'm finishing up one of Godzilla's projects using the recommended drivers, and I had one question about the final hook up of the drivers. The Piezo has a 20 ohm resistor wired in parallel (across the tweeter terminals) and a 1.0 Uf Cap in series. This is really a hi pass filter and I was wondering how to hook the drivers up....series or parallel? I would think that the addition of the resistor would affect the overall system impedance. The Pioneer is nominally rated as an 8 ohm speaker.

Any suggestions appreiciated

Mike aka LowVoltage
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Old 17th May 2006, 10:35 PM   #2
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The way I understand it the resistor shows the amp a normal load. Since it’s for only the highest frequencies, having a load of 20 ohm is fine. In my first Pioneer/Piezo project I used a resistor of 8ohm. For that project the tweeter was facing forwards.

The resistor lowers the output of the tweeter. A 20ohm lowers the output less than an 8ohm. Facing forwards, I found the drivers integrated more smoothly using the 8ohm resistor… but for the rear facing tweeter the 20ohm resistor sounds better to me.

I hope you enjoy this project! I listen every day in my office to the pioneer/piezo.

http://www.zillaspeak.com/pioneerb20-piezo.asp

Peace,
Godzilla
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Old 18th May 2006, 07:45 AM   #3
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Default I assume then, that.....

I wire them in parallel, i.e (+) to (+) and (-) to (-).

And yes , it is a rear firing tweeter. I'm really sensitive to overly bright sounding systems.....no Klipsch horns here! Listening fatigue really sets in after prolonged periods.

The cab is a simple .67 ft3 BR. If it's to boomy, I'll simply seal it! The boxes will make good 'mules' to burn in some other speakers.

The only mods I plan are: modpodging the tweeter diaphragm, and using some duct seal on the basket/magnet of the Pioneer. And possibly using some modpodge on the whizzer only.

I will do NOTHING for two weeks , I want to bench mark them "as is"

I made similar changes to the little 4" Pioneer and immediately went to the "Full Monte"......and it was a success. However I don't know which changes had the greatest effect! I did use some homemade phase plugs on the 4" and since they are removable, it is really obvious how well they clarify and smooth out the top end of the little guys

Mike AKA LowVoltage
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Old 18th May 2006, 03:22 PM   #4
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>>> I wire them in parallel, i.e (+) to (+) and (-) to (-).

Yup.. plain and simple.

btw, i used an Lpad on the tweeter to adjust output. I can send you my wiring diagram tomorrow if i can find it. I think have it by the workbench.

http://www.partsexpress.com/pe/showd...number=260-255

Seems i didnt indicate the part... my bad.

It's not mandatory if you like the 1uf cap.. which i think will be just fine btw, but i wanted to be able to control things a bit more. Since setting it on the first day i havent changed it... yet.

Listening fatigue will NOT be a problem with these speakers. They are mellow and full sounding. Mine are sealed for cleanest clearest bass tho maybe not the deepest the B20's are capable of.

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Godzilla
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Old 19th May 2006, 03:29 PM   #5
Kensai is offline Kensai  United States
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Zilla,

I've got some old bookshelf cabinets with a cutout for an 8", a 4" and something smaller for tweeter. I'm thinking that this would be a perfect project to refurb them. I think I once calced their internal volume at about .88 cu ft. Do you think that will work for me if I stuff the living daylights out of them?

I'll just need to find a piezo that will fit the 4" opening and either seal up the tweeter opening or I could possibly retrofit an L-Pad into that opening. How necessary to you feel the L-Pad is? How far from the maximum level have you tuned yours? I'll be using an 8ohm resistor and a 1uF cap, but in use, the piezo's center will be no mor than 8"-10" from a carpeted floor (and could be swapped to only be 5"-6" from the floor if that might help tame them). The $15 or so for l-pads is actually kind of important for getting this budget shoehorned in with lesser things (you know, food, mortgage, that sort of thing).

I've been interested in the Pio FR for probably 3 years now but just never got off the couch with it, so to speak. This is inspiring . . .

Kensai
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Old 19th May 2006, 03:42 PM   #6
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Default Re: Question on Piezo/Pioneer 8" FR Hookup...

Quote:
Originally posted by LowVoltage
The Piezo has a 20 ohm resistor wired in parallel (across the tweeter terminals) and a 1.0 Uf Cap in series. This is really a hi pass filter and I was wondering how to hook the drivers up....series or parallel? I would think that the addition of the resistor would affect the overall system impedance. The Pioneer is nominally rated as an 8 ohm speaker.

I am not really an XO expert, and am probably in over my head here, but....

A dynamic driver is modeled more or less like a resistance, a piezo is more like a capacitance. The rules change. As I understand a piezo XO, the series cap sets the SPL (voltage divider with the driver) and the parallel resistor sets the XO point.

Bob
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Old 19th May 2006, 05:25 PM   #7
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Kensai .88 is perfect for a sealed Pioneer/Piezo!

If you plan to face the piezo forward my recomendation is an 8ohm resistor and a .47uf cap. The 1uf cap sounded too bright for me but you may prefer it. No Lpad needed here, IMO. Basically, you are playing the B20 full and blending the piezo just at the tippy top. The piezo will hiss and add some needed sparkle, tweet and fizz. It's all good. You will likey.

Facing the piezo to the rear i prefered a 20ohm resistor and 1uf cap... i turn the Lpad about three quarters full. Since facing the piezo to the rear was a variable i couldnt completely predict, the Lpad was necesarry for me.

http://www.zillaspeak.com/pioneerb20-piezo.asp

Your response with .88 will be like the blue line for the 26 liter cab. Just scroll down to the bottom chart. It will be a full sound for a pretty small cabinet with clean 'sealed cabinet' bass.

http://www.zillaspeak.com/ZillaSpeak...PioneerB20.asp

Sometimes when i find speakers at garage sales that have many holes in the front i simply go to home depot to have a new baffle cut and make new holes. Then i cover up the old front. This doubles up the front baffle which only seems to help. Just make sure the B20 has room behind it to breath.

Godzilla
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Old 19th May 2006, 06:05 PM   #8
Kensai is offline Kensai  United States
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Thanks 'Zilla. I appreciate the effort there. These things already have .47uF caps wired into their tweeter lines, so I can start there easily. And definitely the 8ohm resistor.

Now's I've got a newer set of these running in the living room (which is what I'm going to be comparing them with, of course). They seem to have a woofer that was idenical sounding but cosmetically different (white woofer instead of the gray from the older models), and had a black cab instead of charcoal one. They look nicer, but were basically the sames so they ended up in the living room. The woofer is running full range, and I've replaced the 4" mids with B&G Neo3PDRs (in surface mount faceplates), which I felt sounded best hooked to the tweeter line (.47uF, which I don't understand; on a 4ohm speaker, isn't that like a 85,000Hz cross? am I totally not getting anything from the Neo3s like that?).

Anyway, I guess I've been wanting to try to 1up what I've got in there already. If I use the Neo3s, I should go with like a 1uF cap since they are 4Ohm, right? Your calculations show at least similar bass response, but then again, I'm comparing that to what I'm hearing with them, in room, and since they're mounted in the outer-lower compartments of a huge oak entertainment center (has a bottom panel that's one piece, the full size of the thing, but held about 2" off the ground on 3 sides and open in the back) their bass is heavily reinforced. Then we'll see how it does through the mids and into the top end, comparitively.

And, as for mods, what do you suggest? Damping the basket? Coating the cone (just the whizzer, or the whole thing). Anyone tried modding these with phase plugs? That seems like it would certainly smooth things out a bit.

Kensai
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