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fEARful crossovers by greenboy
fEARful CHEAP BUT GOOD crossovers
Designs subject to revision ...
Don't be fooled by the fairly low parts count. To the neophyte this may seem to indicate 2nd or 3rd order slopes, but these networks are in fact tailored to driver-specific in-enclosure impedance and phase plots using a design technique I call Over-Damping, wherein value selections of primary and secondary components are radical compared to simplistic generic "textbook" selections. This provides steeper slopes at chosen thresholds and better off-axis summing. Textbook and generic design don't address specific drivers in actual enclosures.
Properly applied over-damping allows one to use beefier components while still keeping the build simple, the parts count low, and weight manageable. In the case of the fEARful, this is a better choice than using more components but of lesser power handling - both in terms of longevity and performance.
Over-damping could have been taken even further without destroying nice phase/time plots were one not concerned about nominal impedances presented to amplifiers when multiple cabs are used, ie: we want to keep cabs within safe 8-ohm ratings - or 4-ohm ratings for dual driver configurations. I have not ignored the "difficult load" issue so many designers sweep under the rug, nor have I had to de-rate enclosures to SIX ohms.
Linked Shopping Lists shown below are merely guidelines to assure proper values and ratings are known. Feel free to use like values from elsewhere as long as quality is assured.
Be aware that one merely need replicate the lowpass sections of 15/6 or 12/6 when doing crossovers for 15sub or 12sub if meant to be used as part of a 15/6 or 12/6 bass/keyboards/drums stack. For PA use an active crossover is recommended, set at a suitable lower frequency between 80 and 125 Hz.
fEARful 12/6 with Alpha6 or Alphalite6
This is the one to use if you WON'T be stacking with a 12sub or 15sub.
fEARful 12/6 with 6NM410 or 6ND410
This is the one to use if you later wish to stack with a 12sub or 15sub.
THREE 10.0O Erse 25w 5% Wirewound Resistor - 2 parallel on leg, 1 on shunt
THREE 7.5O Erse 25w 5% Wirewound Resistor parallel on leg
TWO 40.0O Erse 25w 5% Wirewound Resistor parallel on shunt
FOUR 6.0O Mills 50w 1% Non-Inductive Resistor - parallel on leg
TWO 75.0O Mills 50w 1% Non-Inductive Resistor - parallel on shunt
TWO 2.7mH Erse ESQ 16AWG .163O 500w Solid Core Inductor - coils paralleled to get 1.35mH value
high-pass for 3-way fEARfuls
To use an optional HF (high frequency) section comprised of compression driver and waveguide - aka "tweeter" - you will also need at least a partial crossover for it, something like this:
A high-pass filter is essentially half a crossover. The idea is to let the midrange driver (Alpha6A/Alphalite6A or 6ND410/6NM410) roll off naturally. The tweeter then just fills in the top of the spectrum. The difference in mid driver sensitivities and user tastes can be compensated for by using a variable L-pad.
The ASD1001 (cheapest reccomended compression driver for all but the 1515/66) is a PA-style compression driver that is quite a bit more capable than what's commonly found in bass cabs. And with a ~6.0K Hz third-order (18dB per octave) high pass filter, it's not being pushed hard at all in this application. The waveguides are constant-directivity devices, which means they don't beam the high frequencies - unlike most horns in bass cabs. The tonal balance stays fairly uniform across a 90-degree frontal arc so that nice, wide sweet spot characteristic of the fEARfuls can be extended up near the top of the spectrum. Also, the flare geometries of these waveguides means less of that boxy horn mouth distortion.
¤ highpass parts:or for 12/6 or 12/6cube with 18 Sound mid driver
Resistors take the energy that's been attenuated and convert it to HEAT. As such, it's good to have supporting standoffs at each end of them so they are not against the circuit board (nor should they be against each other). Cutting holes beneath each resistor network/bank aids free air passage so that thermal buildup is minimized. Make sure each hole is wider than the resistor network that sits above it so that hot air from beneath can easily escape around the sides. Thermal shedding is GOOD.
In spite of the unsuitability of variable L-pad use with midrange drivers, some companies take the tempting shortcut of putting these "attenuators" in their cabs' midrange circuits. But to pad properly in this most important voicing range, fixed resistor networks are much better. Read why here: I WANT TO BELIEVE (in variable L-pads on mid drivers) -- But I Can't.
Resistors can be arranged in parallel or in series to arrive at needed values and ratings. In some of these crossover plans you will need to place multiple resistors in parallel or series, into a network/bank, using wire to connect appropriately. On either the series leg or the parallel shunt the schematics show only a single element and the total value for that, but the text in the parts list details this. Arrangements and formulas:
Here's a handy series & parallel resistors/coils/caps calculator using those formulas to show how multiple components combine to values.
inductor spacing & orientation
Shown in the chart below, some possibilities of coil spacing and alignment and their effect on accurate audio performance. Don't be confused by the difference between solid-core and air-core designs. Though their shapes vary, what is important is the wire wrapping orientation.
In general, the spec'd parts are very stout compared to those found in commercially available crossovers and can handle anything you can throw at a fEARful over a very long duty life. But if you are paranoid, for longevity and increased performance when driving very powerful amplifiers hard - ones that can take a fEARful to the top of its output and beyond - you might want to substitute 14AWG solid core inductors and 16AWG air core inductors and 400 volt capacitors of the same essential values. Erse's site often shows upgrade substitutes for the components, but sometimes it misses them too. So do look at the indexes for each part type if you don't see one listed.
Also, BRAND NAME is not specifically important. What is important are ratings (voltage or wattage), values (mH, uF, ohms), tolerances (%), and type (solid core or air coil, cap type). If it's a quality line from a brand like Solen, Jantzen, Dayton, etc then it's fair game for use.
If I were to recommend higher-rated parts at all, it would be for dual-woofer systems with a lot of power amp behind them. If you don't want to substitute everything, the order of precedence for improvement would be to upgrade components that are inline to the driver. After that, look at the ones on shunts to ground if you really like throwing money at things. ; }
If it's likely you won't be using more than 300 or 400 watts into a single fEARful enclosure, you could drop back to 18AWG solid core coils on the lowpass, and 19AWG air coils on the highpass, and using PeX 250v caps instead of PulseX. This will shave your crossover cost. But realize that if you do get a substantially more powerful amp later you'll then have to do component upgrades to assure reliability. In my estimation lowballing is a mistake.
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