Help needed re: impedance resistor/cab setup

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davexpert

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Dec 25, 2013
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#1
Hello,

I was bored and decided to open up my "spare" 1x15 cab -- it was a Ampeg BA115 tilt back combo, but someone before me stripped out the amp portion; and now it's an empty cab.

The speaker is the original 4 ohm 15" speaker that came with it... and it has a piezo tweeter in it. However, the piezo is not hooked up ... and there's this resistor or capacitor or something dangling free in it. (See photo)
IMG_20161216_215027903.jpg

Dropbox - IMG_20161216_215027903.jpg

Can you help me understand what this would be for? Is it supposed to be there, or is it something someone added? And what would happen if I hooked it back up to the main driver? Would the impedance of the cab change?

Thanks! (And pardon my ignorance ... if it's not a resistor and something else, would love to know that too. ;))
 
Last edited:
#3
If there was really a piezo and not a small compression driver, the capacitor is being used to raise the basic crossover frequency of the tweeter. A piezo tweeter is different in that it is by itself a capacitive element with a first order rolloff of the lows. Adding the capacitor in series raises the crossover frequency. Often you will (also) find a small resistor (say between 4 and 10 ohms) in series with a piezo tweeter to isolate the effects of its capacitance from amplifiers that may be sensitive to capacitive loading.

If you are not using the tweeter, it is not necessary, nor does the tweeter affect the cabinet's nominal impedance.
 
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