Bad alternative tweeter wiring

[Bill Fitzmaurice]

In the diagram to the right, power has to make it through the entire length (down and back up) there is no 'shorter path.' so all piezo's have a chance at providing useful output.

I haven't dissected the diagram, and I won't, but the'path' makes no difference. You're equating mechanical functions to an electrical circuit. If electricity travelled through wire at the speed of sound there would be a slight possibilty of this scenario occurring, but not at its actual .7 x speed of light.
Suffice it to say that wired correctly all the tweeters in an array will receive the same voltage input. If tweeters are blowing based on their location in the array then the wiring is not correct.

[gdougherty]

If you intend to follow the right hand wiring scheme I would "replace" the green jumper with the recommended resistor ( 8 -10 ohms?)
* IF I ever get to the point of making a piezo array I 'll use a distributed buss ( like mentioned above, for the reasons listed above )

Is there any special reason to place it there rather than in-line mounted to somewhere in the back of the cab? I'd be worried about it rattling or something like that if it lived up in the horn path with the array. The array also isn't the full height of the OT12, so you'd be limited on places to mount it out of sight if you weren't using grills. As cool as the melded array looks I've been tempted to sand and finish it and leave the grills off. It would also give you a better line of sight to judge dispersion of the array when placing the speakers.

[Sydney]

That would be my preferred place ( for reasons I won't go into ) - But if it's not practical - AS along as the amp sees the resistance, Put it in either the red line or the black line that feeds the array - where ever you can.

[DaveK]

Shortest path to ground is a euphemism for least resistance path to ground. In the diagram shown, the acutal length of the wires makes no difference. The resistance from one end of the buss to the other should be a fraction of an ohm. Thus, every tweeter on the buss should be seeing the same voltage on the + terminal.

The only electrical explaination I think of (and this is a long shot) is that the impedence of piezos drops to almost nothing at very high frequencies (like 100kHz). If there was signal content there, and if the impedence of the peizo dropped low enough, the resistance of the wires and connections in the buss might become significant. Then more of the signal would flow through the piezos closest to the input connection.

[Bill Fitzmaurice]

Then more of the signal would flow through the piezos closest to the input connection.

Not with the resistance that even the smallest gauge of wire available would offer over that short a distance. Or even ten times that distance for that matter.

[jbell]

Last time I checked. A piezo horn was considered about a .15uf capacitor.

What's is a piezo's resistance? All of the above discussion, revolves around resistance, not capacitance.

[Bill Fitzmaurice]

What's is a piezo's resistance?

Immaterial, as it's impedance that matters. As is the case with all drivers a piezo's impedance varies with frequency, though being capacitive rather than inductive in nature it decreases as frequency increases. Within the audible bandwidth piezos show a minimum impedance of at least 20 ohms, so for a piece of wire to offer any meaningful insertion loss it would have to offer at least 2 ohms resistance. That would require 200 feet of 20ga. wire.

[Sydney]

gdougherty
I sent PM's to you and jbell , about this, and other topics etc. The Sent Box doesn't show the messages ever existed ( lost down the "memory hole" I guess

EDIT * Both PM came in

[Sydney]

I'm betting that the wiring change might suppress or eliminate both the distortion or the burnout problem... If not the resistor should.

As agreed the wiring is equal with AC @ lower frequency 20 - 20Khz.
As the frequency increases above 20khz, the subtle differences in the wiring have a different impact.
And for audio amplifiers as the frequency increases above 20khz, all amplifiers exhibit poor stability, increased distortion, and a propensity to oscillation - quickly.
Manufacturers who make amplifiers using Class D or Class H ( both of which use internal high speed switching ) do not specifically list warnings against capacitive loads. One of the problems of Class D, H and PWM circuits is suppression of the high frequency components generated, I don't know if they are more sensitive to load conditions and high frequency problems than Class A/B however, but no audio amp is immune
Without a high speed oscilloscope, available at the time of the "crime" it's hard say, but I suspect it's a high frequency problem.
Perhaps representatives of the amp manufacturers of Class D and H and other switching type amps will make specific recommendations on capacitive (multiple piezo ) loading if asked.

Slightly related on this page:
http://sound.westhost.com/faq.htm
Is detailed how to use a piezo tweeter to test for amplifier distortion