high pass filter

1. You need to know the impedance, not the DC resistance, and you need to know it across the relevant range from about 200Hz down.

2. For 6dB rolloff, only a cap is needed. For 12dB, you will need a cap and a coil.

Kal

how would i measure that Kal? thanks for the help

Let's make this easy, for a ~4 ohm impedence at or around 80hz, you will need the following:

6db - 500uF cap
12db - 350uF cap, 11mH shunt coil

For ~8 ohm impedence:
6db - 250uF cap
12db - 175uF cap, 22mH shunt coil

These values will get you in the ballpark and most likely be just fine and fine tuning the values in relation to the exact impedence at 80hz will yield better results but in most likelyhood, your room acoustics will swamp any differences an exact impedence match would reveal.

Use ~100 volt non-polorized caps in the main feed and build an external crossover box...

Cheers

I really wonder if those numbers will be sufficient. Impedance varies greatly near resonance and is affected by enclosure loading. The rated 'nominal' impedance is estimated at 1Kohms but, in the bass, the difference can be huge.

You can measure it best with an impedance bridge or with an AC multimeter.

Kal

"Impedance varies greatly near resonance and is affected by enclosure loading. The rated 'nominal' impedance is estimated at 1Kohms but, in the bass, the difference can be huge." -Kr4

The impedance peak(s) at system resonance will cause a simple series capacitor or textbook L-C filter to exhibit non-textbook behavior. The problem is, the response is insufficiently suppressed at the resonant peak(s). Throwing a bigger capacitor at the problem just results in a deeper frequency response "saddle" above the peak.

The highpass filter should be optimized for that particular driver's frequency response and impedance curve, and doing so is largely a matter of trial and error, often calling for additional components in the circuit. Not saying it isn't worth taking a shot at, but this is one of those things that's more complicated than it appears at first glance, and the component cost to really do it right can be rather daunting.

A small, high-quality series capacitor in between the preamp and power amp is often a more elegant and cost-effective solution. Find out the power amp's input impedance, and calculate the capacitor value for the frequency you want using that number. You'll have to do some soldering involving RCA jacks and plugs, or balanced connectors, but you'll come out way ahead on parts cost for equivalent sound quality.

Imho, ime, ymmv, etc.

Duke
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