High Pass Fullrange question

[Anchan]

When attempting to high pass a set of full range speakers, the math on a first order filter is quite easy. But what to choose for the "R"? Do I choose the nominal impedance of the speaker, lets say 8 ohms? Or do I use the "R" at the given frequency I am trying to cross at?

For example, if I am attempting to create a high pass filter at 80Hz for instance, most full range drivers at this particular frequency have an impedance of at least 50ohms. At 50 ohms, and with a crossover at 80Hz, I would need a 40uF cap. But if I use the nominal 8 Ohms in the calculation, I would need a 250uF cap. Which calculation would you use in designing? Of course I would probably get a few caps, and see what sounds best, but I am looking for the technical answer. Thanks

[planet10]

I'd put the cap in front of the amplifier & use the input R of the amp.

dave

[chrisb]

Originally Posted by planet10

I'd put the cap in front of the amplifier & use the input R of the amp.

dave

TLS.org | Passive Line-Level Crossover

[hm]

Hello Anchan,
both won´t work acousticly good, without
measurement, Impedance, it is very difficult.
Better take a active sub with active sat crossover,
500 µF in best quality are more expensive.

[chris661]

The problem with first order crossovers is that they take such a long time to get any significant attenuation that you can end up with peaks in the response corresponding to impedance peaks of the driver.

Have a read of the crossovers section of the articles on Rod Elliott's website.

Chris

[fakamada]

Very good method is to maintain first order but also use a shunt resistor to strongly reduce output gain at resonance. In my open baffles I cross to woofers at about 200hz. I'm using 90uF capacitor and additional 50ohm resistor beetween + and - of the fullranger (Sonido SFR175 Alnico). Works really great. IMHO no need for 2nd order filter.

[phivates]

Thanks for the reminder. I've had some success on tweeters but I haven't checked it out on a FR.

[pforeman]

Originally Posted by planet10

I'd put the cap in front of the amplifier & use the input R of the amp.

dave

Use the imput impedance of your amp. Then place the cap in series with the output jack of your preamplifer, or if using an amplifier with a volume control place the cap in series with the input after the volume control.
Paul