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Old 26th December 2012, 09:37 PM   #1
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Default Crossover adjustment/re-engineering

I'm working away on one of my first speaker rebuilds right now and am at a point of dealing with crossovers. The original speakers (stereo pair) each had two woofers and two tweeters in a vertical array. All the drivers are 16ohm but are wired in parallel so the crossover deals with an 8ohm load.

I'm planning on building new boxes for the speakers as the old ones are 1970's construction with cheap particle board and no bracing. My desire would be to separate them into one woofer and one tweeter per box, giving me four speakers in total, but my worry is that I'm not terribly well versed in crossover design just yet and would botch something up in the process. I trust where the crossover point and slope is on the original crossover, so is it possible to easily reverse engineer the current crossover while turning the loads from 8ohm to 16ohm?
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Old 26th December 2012, 10:06 PM   #2
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double all inductor values, halve all capacitor values...,but if the drivers are old, you'd be better off to run an impedance plot of the drivers and re-calculate from that
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Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
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Old 10th March 2013, 01:16 AM   #3
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So I've finally measured and drawn up the old circuit. I just wanted to get input and fully understand what's going on here. I believe there's an L-pad in the circuit, along with a signal LED? I'd like to know what xover frequency the crossover is currently at. Also with all the extra stuff in the circuit, I'd like to keep the L-pad, not sure if the fuse is needed, but I see no point in keeping the LED. Can I drop the LED in the new crossover without adjusting anything else? Is the fuse really needed?

So with everything going on here is it as simple as doubling the inductance and halving the capacitor values?

Also, the drivers are old, but I'm not skilled enough to accurately re-measure the resistance and re-calculate everything. Any tutorials on how to do that for next time?
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Last edited by stochastic; 10th March 2013 at 01:19 AM.
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Old 10th March 2013, 01:52 AM   #4
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You are lucky, it's a 3 component crossover.
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Old 10th March 2013, 04:25 AM   #5
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I don't see how luck has anything to do with the project at hand. Can you help me answer any of the questions I posed?
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Old 10th March 2013, 04:44 AM   #6
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What's the purpose of doing so ? If you need four speakers....well...make a working one.
The bobbin before the woofer should be half...more or less.
So the capacitor before the tweeter; the inductance after it...should be doubled !?

I would rework it by adding a new 8Ω tweeter only. Two tweeters are bad.
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Old 10th March 2013, 05:39 AM   #7
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Pico I'm not sure what you're saying, would you mind writing complete sentences?
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Old 10th March 2013, 10:27 AM   #8
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Hi,
I'm not really 'into the thing' but I just swap various parts from the
garbage sack
So: you could end in doing whatever you do !
To see what happens by changing the value of the components in the crossover circuitation, see also in the 'tools' section in Strassacker: Lautsprecher - Boxen - Selbstbau, just to get the ratio ( crossover calculator)
You'll see that for the tweeter, the capacitor value diminishes as the Z rises;
and for a woofer you'll need 'less' inductance for half Z .

For the tweeter, why don't you try a modern and powerful ( 10 W) model
maybe you can try a waveguide to help it in the lower region, it also helps in making crossover easy ( sometimes ... )
As I said, it's better a single source, specially for the treble
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Old 10th March 2013, 11:49 AM   #9
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Pico, I only plan on having one tweeter per box. The diagram is of the old crossover where there were two speakers in each box. I'm looking to transfer the same crossover slopes and features to the new box.

I've attached a pic of the new box so you can see there will only be one of each speaker in each box.

The online calculators really only get me so far as I'm not sure how things like the L-Pad will interact with the filters, and I'm not sure what the exact knee of the current filters are (I see that the woofer is a single order and the tweeter is a double order, but I don't know where the knee is). Really, I'm just doubling the resistance load on each channel but would like to keep the crossover the same.
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Old 10th March 2013, 12:16 PM   #10
system7 is offline system7  United Kingdom
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If I haven't lost my touch, the conversion is as follows. You would actually use preferred values like 3.3uF. It'll make little difference.

Regular sort of simple crossover. The bass will roll off gently and overlap with the tweeter quite a lot. Quite how well it works depends on the woofer rolling off naturally and smoothly.

Be interesting to know more about the drivers.
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File Type: jpg 2_Way_Conversion_16ohm.JPG (29.7 KB, 64 views)
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