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Documentation for Sub-Woofer Crossover |
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The circuit for the crossover came from the website of
Elliot Sound Products (Project 8). Ron Elliot's infor-
mation on Westhost.com is very clear and complete. I
did make a few minor changes to the circuit.
I used NE5534AN ICs, which are simply the single op-amp version of the 5532s. I doubled the value of the filter network resistors to lower the crossover center frequency to 150Hz. And, I added a couple of 4.7k resistors to the input to mix the left and right stereo channels to monaural. I did not have any 100-ohm resistors, so I substituted 51-ohms for the output resistors; and I powered the crossover with a +/- 12-volt wall-wart rather than the +/- 15-volt power supply designated in the system. None of these substitutions should affect the end result, except for the frequency and a slightly diminished headroom. Austin has extremely limited sources for electronic components, despite (inspite of?) its high-tech reputation, and if one wants components, they are available only in quantity. The only known local sources of components are Howard Electronics and Frys. |
Component value matching is very important in 3-pole
filters used in the crossover, and I bought 3 times the
number of resistors and capacitors in the filter trees so
I could select matching values (using an ohmmeter
and capacitance meter). Even so, I will install
standoffs on the 5-input version so I can more easily
adjust the high-pass roll-off frequencies to match each
other and the low-pass filter at -3db.
One of the more disturbing things about this project is distortion. Perhaps some came from the misalignment (time wise) of the two speaker systems. But upon looking at the outputs on a scope, there is a serious issue on the high-pass output around 60Hz. Although this is quite a bit down the rolloff, it is quite obvious, at least on the scope. (See Photos.) Another interesting observation is the phase shift around the center frequency, nearly 90-degrees. I connected a scope (x=high, y=low) to look at the phase relationship. (Also, see Photos.) Two points: it is on a breadboard for a reason, and I am learning about merging filter crossings. |