Check your piezo's, Damp your cabs, Follow the plans!

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gdougherty
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Check your piezo's, Damp your cabs, Follow the plans!

#1 Post by gdougherty »

It's been said over and over around here, but it bears worth repeating.

I've built wedgehorns and T48's following the plans closely. I've had nothing but great comments about them (once I got the EQ on the wedgehorns dialed in) and been nothing short of amazed at how well they do what they do.

Recently I built 4 1xOT12's and I've been satisfied with them, though things just didn't seem right. By reasonably conservative calculations I'd expected them to each be the equal of my outgoing Peavey SP2x's, doubling my output capacity. They were not, and the EQ I needed to get them aproximately flat seemed excessive compared to the published charts. I'd expected they might not sound perfect without EQ but they sounded murky and unimpressive without it. I'd expected a few db here and there, but 200-500Hz was averaging 6db down and the 2.5K+ side was averaging 3db up. My RTA plot also showed a huge un-eq'able drop around 1.5K.

One item I neglected to complete was a small section of damping material directly behind the mounted 2512. I'd been a little scared of burning up the driver with the foam topper material I used elsewhere, so I opted to leave the portion behind the driver uncovered. Knowing what I'd learned about cabinet resonances from home audio it should have been a no-brainer that a flat surface directly behind a driver needs some sort of damping.

Within the past few weeks somebody posted about problems with a DR cab and Bill's response indicated reponse problems were possibly due to inadequate damping in the driver chamber. So I took the OT's home, pulled the back off one and added a piece of foam behind the driver. I also pulled the piezo's to check output levels and polarity. Turns out I had three near dead tweeters in my array. Fortunately, I had a bunch on hand so I tested a few more and replaced the driver elements. To be fair to piezo's it seems very possible that I blew them while running too much power through them because of my excessive EQ.

The result? I plugged it in this morning in parallel with my monitor at the board and was blown away. Ran some pink noise through it and checked it with my RTA. Response is now near flat without EQ and output is noticeably louder.

3 more to fix and I can't wait to take the full setup out again.

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vlad335
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#2 Post by vlad335 »

Thanks for your post.

After building two of Bill's designs, (Omnitops and Titan) I have a huge amount of respect for Bill and the amount of work that went into his plans. I'm sure he must have tinkered with alot of prototypes for each design and to me, that's a mind boggling amount of work.

What I know now is everything is there for the builder. Bill did all the work for us and any omission or deviation will most likely just hurt performance.

Take my OT-112's for instance. I used EVM-12S speakers because I already had them and just laid out for four 2512's and two 3015's at once. Besides being stupid heavy, they definately sound different than the OT-212's ( somewhat harsh ) and I'm sure that this will manifest itself in a negative way with high volume levels.
Currently running:
Four Titan 48's, Six Omnitop 12's, Two Wedgehorn 10's, Omni12 2-10

Also Built: Omni15 Tallboy, Omni10.5.

'The hardest material on earth is the human skull'. How do we know this? Try pounding a new idea into one.

bgavin
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Re: Check your piezo's, Damp your cabs, Follow the plans!

#3 Post by bgavin »

George, do you have any RTA plots from a pair of OT112 stacked, no EQ?
My biggest worry is that when I'm dead and gone, my wife will sell my toys for what I said I paid for them.

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brodave2
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Re: Check your piezo's, Damp your cabs, Follow the plans!

#4 Post by brodave2 »

To be fair to piezo's it seems very possible that I blew them while running too much power through them because of my excessive EQ.
I just built a pair of OT 2-12's, with the melded arrays, so that was 48 piezos. I tested a BUNCH of them to get 48 good ones. I think 10 were near dead, but the real shocker was, 1/3 of them had reversed polarity. There were so many with reversed polarity, that I made one bank out of them, 12, and just wired them backwards so they would play with proper polarity. It appears that the ones that have low output usually have a drop of glue holding the cone to the frame in one spot, and that can be fixed if you are careful.

bgavin
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Re: Check your piezo's, Damp your cabs, Follow the plans!

#5 Post by bgavin »

Last month I did a 24 hour show using DaveK's set of four DR200.
The truly amazing part was how wide the sound field was, as we walked the arc.
It literally extends to line of sight, and didn't cut off until we were just short of 90 degrees off axis.
As long as I could see the melded array, I heard plenty of highs.
My biggest worry is that when I'm dead and gone, my wife will sell my toys for what I said I paid for them.

mobetter
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Re: Check your piezo's, Damp your cabs, Follow the plans!

#6 Post by mobetter »

How do you test the polarity of the Piezo's?
T39 / OT12 Bass rig
2 T-48
4 DR250, 6 T-48 in the works

Gregory East
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Re: Check your piezo's, Damp your cabs, Follow the plans!

#7 Post by Gregory East »

Someone invented a setup with a resonating cardboard tube with the proper length for a designated freq that would give away an out of phase one in an instant. I forget the details.

Or you can play one "standard" one and see if the 2nd one next to it, wired parallel, makes it louder or quieter. Reverse the wiring if you suspect it's quiet and if it gets louder it's confirmed.

SeisTres
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Re: Check your piezo's, Damp your cabs, Follow the plans!

#8 Post by SeisTres »

brodave2 wrote: I just built a pair of OT 2-12's, with the melded arrays, so that was 48 piezos. I tested a BUNCH of them to get 48 good ones. I think 10 were near dead, but the real shocker was, 1/3 of them had reversed polarity. There were so many with reversed polarity, that I made one bank out of them, 12, and just wired them backwards so they would play with proper polarity. It appears that the ones that have low output usually have a drop of glue holding the cone to the frame in one spot, and that can be fixed if you are careful.
Wow, what brand are they? I ordered 50 from leland for my four melded arrays and I think I got one reversed, all working, and about 6 with low output. However, I did get about 12 with high output so it averaged out.
Built:6 t39, t18, 4 Jack10, 2 autotuba, 2 SLA,2 wedge, 2 TT, 2 Tritrix, curved sla, 2 otop212, 2 SLA pros, Ported 8" sub, 2 ported 210, dual ported 8" sub

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Zack Brock
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Re: Check your piezo's, Damp your cabs, Follow the plans!

#9 Post by Zack Brock »

Other than the polarity, I don't worry about it. All of the piezo arrays I've built have sounded very similar.
Zack Brock
Authorized Builder, Northeast Florida (Greater Jacksonville Area)
WavePulse Acoustics | zackbrock@macpulse.com | http://www.bestbasscabs.com/

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AntonZ
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Re: Check your piezo's, Damp your cabs, Follow the plans!

#10 Post by AntonZ »

mobetter wrote:How do you test the polarity of the Piezo's?
Afaik Rubicon was the first to build a piezo testing jig. I copied his idea when I had a batch of piezo's to test. See this thread for details.

Edit: it seems the thread that I linked to got culled. Here's some information anyway.

One known good piezo fixed to the jig. A second can be inserted into the cup, making contact with the copper wires that are in there.

Here's the jig in construction.
Image

Here's a piezo in the jig, playing along with the fixed pizzer. Note the old portable FM radio on the left. It is tuned between stations. The headphone out is connected to the jig input.
Image

I can switch the reference piezo on or off. Noise (source = FM radio tuned between stations) should sound very similar just louder when I engage the second piezo "in phase". If it gets softer instead, the second piezo is probably wired out of phase with the reference piezo. I can check that by flipping the nr 2 switch in "out of phase" position.
Image


(2 piezo's one cup - sorry got a bit carried away there)

All credits to Rubicon for the idea. I just copied.
Last edited by AntonZ on Tue Jan 11, 2011 6:11 pm, edited 2 times in total.

shane2943
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Re: Check your piezo's, Damp your cabs, Follow the plans!

#11 Post by shane2943 »

AntonZ wrote:See this thread for details.
Bad link.

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AntonZ
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Re: Check your piezo's, Damp your cabs, Follow the plans!

#12 Post by AntonZ »

Original thread got culled apparently. I added some information and snapshots to my original message instead. See above.

shane2943
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Re: Check your piezo's, Damp your cabs, Follow the plans!

#13 Post by shane2943 »

AntonZ wrote:
mobetter wrote:How do you test the polarity of the Piezo's?
Afaik Rubicon was the first to build a piezo testing jig. I copied his idea when I had a batch of piezo's to test. See this thread for details.

Edit: it seems the thread that I linked to got culled. Here's some information anyway.

One known good piezo fixed to the jig. A second can be inserted into the cup, making contact with the copper wires that are in there.

Here's the jig in construction.
Image

Here's a piezo in the jig, playing along with the fixed pizzer. Note the old portable FM radio on the left. It is tuned between stations. The headphone out is connected to the jig input.
Image

I can switch the reference piezo on or off. Noise (source = FM radio tuned between stations) should sound very similar just louder when I engage the second piezo "in phase". If it gets softer instead, the second piezo is probably wired out of phase with the reference piezo. I can check that by flipping the nr 2 switch in "out of phase" position.
Image


(2 piezo's one cup - sorry got a bit carried away there)

All credits to Rubicon for the idea. I just copied.
:loler:

Thanks for the info! Looks like a solid idea to that jig.

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fender3x
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Re: Check your piezo's, Damp your cabs, Follow the plans!

#14 Post by fender3x »

Thanks for the great testing ideas.
Last edited by fender3x on Mon Aug 08, 2022 10:54 am, edited 1 time in total.
One man's magic is another man's engineering. --Heinlein

1 x DR250
1 x T39
1 x Omni 10

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fender3x
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Re: Check your piezo's, Damp your cabs, Follow the plans!

#15 Post by fender3x »

Please ignore this post. It has an error in it.
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piezo_test_circuit.jpg
Last edited by fender3x on Wed Aug 10, 2022 5:49 pm, edited 4 times in total.

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