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I'm new to high-efficiency speakers, and to learn about them I'm experimenting. I have a full-range (to 12K, anyway) 10" driver in an enclosure, and a standalone Fostex tweeter, and I'm wondering what is the right way to connect them to the amplifier (8W 300B SET).
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?
Follow Ups:
> > 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
Kurt: Thanks! I really appreciate your taking the time to respond.
Do you know of any free or low-cost circuit simulators?
I've been considering buying one of those USB oscilloscopes; any experience with any of them?
Thanks again
-stevew
> Do you know of any free or low-cost circuit simulators?
I've been considering buying one of those USB oscilloscopes; any experience with any of them? <
I don't know of a really low priced circuit simulator, but I use the lowest packaged "Electronics Workbench" on my home PC. It was somewhere around $200 about 10 years ago, and still loads and runs on Windows Vista.
I don't know anything about USB oscilloscopes. I have a 30 year old 5 MHz Heathkit scope I built way back when I was in high school and it still does a decent job of troubleshooting and measuring "good enough" type things. (Can't see high MHz oscillations, though, unfortunately.)
To measure frequency response coming out a horn driver you can actually get by with using a $40 SPL meter at http://store.acousticsounds.com/category.cfm?sct=equipment&id=62 along with a decent sinewave or function generator. You have to measure manually point by point at low SPL levels (like around 70 dB, C-weighted) and you want to plot on log paper to see what's going on with amplitude (dB) vs frequency (Hz). To do this every driver needs to be measured independently at close proximity (about 12" away from the driver) and you'll get +/- a couple dB accuracy which to most of us is again "good enough" to see what's going on and if we're in the ballpark.
The key to this is that we know where we are "in the ballpark" or not, and measure differences from there when we make a change. Then we use our ears to evaluate the effect of that change for the better or worse. With these two things going on we can zero in on a pretty good overall solution.
If you have really super high-end tools, you can get many more points and just see traces sweep across a screen and see many other parameters as well. And better simulators, the kind most people never heard of, can also interpolate impedance measurements and SPL output measurements of raw drivers and integrate that into an overall response, including the crossover components.
But I have been able to get by with just a sinewave signal generator and that SPL meter to see enough to know the effects of single driver outputs with the crossovers I used. People don't think it'll work, but it does. It's not perfectly accurate, but in the near field and with proper interpretation, you can get by.
Kurt
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