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Old 27th August 2005, 08:00 AM   #11
AndrewT is online now AndrewT  Scotland
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Hi Cv,
thanks for the confidence " go with direct drive".
But how do you find the safe drive parameters without risking damaging the tweeters?
The tweeter system appears to be a 4ohms impedance with an 4ohm resistor in series.
Is the 4ohm resistor there primarily to adjust the volume to match other 8ohm speakers?
or
Is the 4ohm resistor there to adjust the phase angle and give the drive amp an easier job?
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Old 27th August 2005, 09:18 AM   #12
CV is offline CV
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Allo Andrew,

Well, I'm just guessing here - hard to say without seeing an exact schematic etc, but I'd expect the thing would be a capacitive load, so by sacrificing sensitivity etc we can add the 4ohms to make it more like a resistive load. Which is pretty much what you said :-)

I guess the best thing to do is actually measure the voltage across and current thru across the piezo element at various frequencies while driving normally, ie through the x/o. Then you should get an idea of what the thing really needs and what the EQ requirements might be.

I know it's messy but I suspect that if you were to EQ in your direct drive amp you would find that much less power was required, which should really ease the amp design.

Hope this is of help.

Wish I could find a pair of these things somewhere... then again, probably easier to buy the piezo film (I found a source a while ago) and roll me own...

cheers
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Old 27th August 2005, 11:06 AM   #13
AndrewT is online now AndrewT  Scotland
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Hi,
the peizo dome encloses a volume of pressurised gas. It may be that prodution of this and coping with warranties thereafter that convinced Audax to abandon production. They are there to make money out of their customers after all. If it was economic I would expect HD3p availability to be ongoing.

Q. Can this piezo element drive a small HF horn? Is there enough drive power to get it to work effectively?
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Old 27th August 2005, 11:25 AM   #14
CV is offline CV
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Hi again,
Yeah, I suspected they had too many problems with the dome losing pressure and decided it was a warranty timebomb? Who knows...

As for the horn idea, no idea, but you'd need an elliptical throat there; if you had the capability to make something suitable, you could probably make your own HD3Ps :-)

Cheers
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Old 27th August 2005, 11:33 AM   #15
AndrewT is online now AndrewT  Scotland
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Hi,
I could easily turn a wood horn for treble with undersized throat and then hand finish the throat section out to elliptical merging into circular over the first 10mm to 20mm or so.

Q. wood (would) the throat need to be elliptical if it simply formed a front chamber with 1 to 2 throat to Sd ratio? Would that need more driving power?

Even with a dismantled HD3p laid out in front of me could I even imagine the production tools and jigs needed to make and assemble that piezo system.
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Old 27th August 2005, 12:26 PM   #16
CV is offline CV
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Hi again,
Really have no idea if the horn would work at all.
What are you trying to achieve anyway? If it's more low end, it *might* be worth pursuing, but if it's more efficiency, I think it's a misadventure.

Also, if you're going to use a compression chamber, you'll need a phase plug.

What with the superb frequency response and waterfall, whacking the thing on anything other than a well designed, true elliptical horn is probably going to do more harm than good.

Not that I want to discourage you from expermentation, and these are just my guesses anyway...

Cheers
cv
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Old 28th August 2005, 07:00 AM   #17
Luke is offline Luke  New Zealand
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Does any one know if the gold foil on these drivers can be replaced as a spare part? My cat got to one of mine and it has a big scratch through it.
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Old 28th August 2005, 11:38 AM   #18
AndrewT is online now AndrewT  Scotland
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Hi,
I would think that the gold foil is plated onto the piezo element and forms the electrode that charges up one face of the piezo element. The back face will similarly have a conductive surface but it might be aluminium to save weight.

It might be gold leaf, but I would NOT try to burnish on a patch for fear of damaging the piezo element.
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Old 2nd December 2008, 07:26 AM   #19
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Default Audax HD3P - Tweeter Replacement

So has anyone found a direct replacement?
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