BillFitzmaurice.info

... even though it's not, really...

Suppose I wanted to pad down a piezo array passively, and had a compelling reason to do so. This will be an off-reservation application, and it would require too much across-the-board EQ to do this (it needs a 10-12db pad, really). How might I go about doing that? On a compression driver, you'd use an L-Pad, but that supposedly doesn't work with the piezo array. Can I add or change a resistor somewhere in the filter to accomplish this, or perhaps would the whole filter have to be rebuilt?

I don't want to dive too deeply into what the project is, for fear that the usual "don't do that" responses will flood the thread.... there is a good reason I want to do this. If it won't work, it won't work, and I can figure something else out... it just wouldn't be as cost effective as what I have in mind.

BE

Now I (and I'd imagine everyone else) are interested in what you have going on! Spill the beans!

My initial thought was that you obviously still want some HF, just not a lot.

So rather than passively, if you biamped and dropped the gain on the HF by as many dB as required, would that achieve your goal?

Change the wiring from two banks in series to four or more.

Bill Fitzmaurice wrote:Change the wiring from two banks in series to four or more.

Would I be correct in assuming that each time I double the number of banks, I reduce sensitivity by 6db, or would it be 3?

ncgrove wrote:Now I (and I'd imagine everyone else) are interested in what you have going on! Spill the beans!

Grant Bunter wrote:My initial thought was that you obviously still want some HF, just not a lot.
So rather than passively, if you biamped and dropped the gain on the HF by as many dB as required, would that achieve your goal?

Basically I'm building some frankencabs with parts I have on the shelf from various projects to generate some extra income. They're going to be either sold outright or installed somewhere, so biamping won't do... but there is an extreme sensitivity differential between the array and the woofer section.

The cabs sound pretty good with some extreme EQ adjustments, but I need to get the HF and LF sections more matched for them to be practical.

i found this

L-Pads don't work on piezo tweeters as they act mostly as capacitors and not resistors. To reduce the output you need a capacitor in series. Dunno which tweeter the MBE series uses but a "typical" high quality one is a KSN1025B which has a capacitance of 0.3uf so a 0.3uf capacitor in series will reduce the output by 6db . You can also increase the quality of its sound (and increase its life) by using a resistor across it to form a true piezo compatible crossover.

With the 0.3uf capacitor in series, a 75 ohm 10 watt resistor across the piezo will give you a 3.5KHz 6db/octave crossover.

Personally I'd start with a 1uf capacitor in series, with a 47 ohm 10 watt resistor across the piezo for a -2.3db pad and 3.4KHz crossover. I've done that to smooth out a few piezo equipped monitors with good results

here

http://www.talkbass.com/forum/f15/paddi ... er-869182/

BrentEvans wrote: Basically I'm building some frankencabs with parts I have on the shelf from various projects to generate some extra income. They're going to be either sold outright or installed somewhere, so biamping won't do... but there is an extreme sensitivity differential between the array and the woofer section.

The cabs sound pretty good with some extreme EQ adjustments, but I need to get the HF and LF sections more matched for them to be practical.

Cool, no worries, was just a thought...

BrentEvans wrote: Would I be correct in assuming that each time I double the number of banks, I reduce sensitivity by 6db, or would it be 3?

3dB. But if you don't need to keep up with the sensitivity of a DR, Jack or Otop you also don't need to use near as many tweeters. That's why the W6 uses only four.

i found this



Quote:
L-Pads don't work on piezo tweeters as they act mostly as capacitors and not resistors. To reduce the output you need a capacitor in series. Dunno which tweeter the MBE series uses but a "typical" high quality one is a KSN1025B which has a capacitance of 0.3uf so a 0.3uf capacitor in series will reduce the output by 6db . You can also increase the quality of its sound (and increase its life) by using a resistor across it to form a true piezo compatible crossover.

With the 0.3uf capacitor in series, a 75 ohm 10 watt resistor across the piezo will give you a 3.5KHz 6db/octave crossover.

Personally I'd start with a 1uf capacitor in series, with a 47 ohm 10 watt resistor across the piezo for a -2.3db pad and 3.4KHz crossover. I've done that to smooth out a few piezo equipped monitors with good results

That will not work with the piezo HP filter that we use.

Bill Fitzmaurice wrote: 3dB. But if you don't need to keep up with the sensitivity of a DR, Jack or Otop you also don't need to use near as many tweeters. That's why the W6 uses only four.

Very true.. but the arrays are already built, and the vertical dispersion of the longer array is valuable for what these cabs would be used for (spot monitors). Plus... the whole point of this project is to sell the stuff I have on hand for as much as I can get out of it, and build something useful (like some titans!)

I Like It ....

BrentEvans wrote:frankencabs

Its always educational for me reading about this sort of stuff. I made numerous abominations in my early teens, before i could drive around and make loud noises from all types of weird and wonderful cabs.

I once hooked up a 10 inch very cheap auto subwoofer driver into the top of a 30litre plastic bucket as it offered the correct volume according to the t/s parameters Surprisingly enough it worked pretty well apart from the flexing bucket chewing up all the power.