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RE: crossover question?

Posted by kurt s on July 4, 2007 at 21:46:18

In Reply to: crossover question? posted by steverw on July 3, 2007 at 13:03:56:

>>The full-range driver is 12 ohms 98dB eff., the tweeter is 6 ohms 101 dB eff. The goal is to let the drivers do most of the rolling off and avoid cross-overs, but I need at least to use a series cap to shift up the fill-in curve for the tweeter. Right now I have 0.175 uF caps, nothing else.

Here's my question: which output tap of the amp should I use, 8 ohm or 16 ohm? Should I add any more components to my "network" to balance out these dissimilar drivers?

From listening to both taps, the 16-ohm tap has more "air", but sounds flat. The 8 ohm tap has that "in the room" presence and wide/deep soundstage, but the cymbals and drum slaps are muted.

I've tried different cap values on the tweeter, but have found that if I go much higher the tweeter begins to color the full-range driver too much.

Will I need to go to a higher-order crossover? Any suggestions for on-line resources where I can read about this?
>>

I would probably add a series resistor with the tweeter to add impedance to the top end and reduce output since its a more efficient tweeter than the full range driver. Try 3 - 6 ohms series in there. Then I would be tempted to add an inductor in series with the full range driver to roll it off more at 12 KHz, getting this driver out of the way in the highs. I would not try to drop the tweeter crossover too low from what you are experiencing. Keep it high with a small cap, but also make sure the output is not overbearing (add that resistance) and probably add that rolloff to the fullranger.

Much of what you might be hearing is a dissimilarity in impedance and output and crossover all at once between these two drivers. They are not real "similar" in many ways. So you need to try to make them separate a little and make them as similar as you can. That to me means making the impedance about the same, the output about the same, and not sharing too much of the same frequency coverage.

If this "1st order crossover fails", I would go to second order. The tweeter would then need a proper series cap plus resistor plus shunt inductor. The full ranger would then need a series inductor plus shunt capacitor, all crossing over at around 12 KHz or a little lower, like 10 KHz.

You would need to have a computer program to design such a filter with some accuracy unless you're good at circuit analysis and math.

After you are done with the crossover and listening overall for frequency accuracy at the lower 8 ohm impedance, then you can try 16 ohms.

You may have to iterate a few times to get it decent. Without measurement tools and computer circuit analysis software, it's a bit like searching in the dark hoping you hit the needle in a haystack. Sorry about that, but it's true.

Kurt

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