Difference between 1mfd and .68 mfd on 1st order crossover?

[Ken L]

I'm looking at some configurations on crossovers in the Madisound Fostex .pdf files.

one is using a .68 mfd cap and the other a 1 mfd cap.

I am wondering what frequencies the different caps affect and in what way?

Thanks

Ken L

 

[tiroth]

Well, f=1/(2*PI*r*c) so if all else is the same, the smaller cap will have a 47% higher corner frequency.

 

[purplepeople]

Or assuming that one of the frequencies is 3kHz, the other will be -47% or +47%, or ~2kHz or 4.5kHz. Sounds like your typical two or three-way XO points.

🙂enen.

 

[Ken L]

I'm trying to understand

What effect is the 1 mfd cap having here?

http://www.madisound.com/imgs/208ez_encl.pdf

In terms of what is it doing, my understanding is that is putting a first order slope on the woofer?

If so where does it start the slope?


And if you were to change this cap out for a .68 mfd, then that would bring the tweeter in 47% higher??


Thanks

Ken L

 

[purplepeople]

I believe it's acting as a high pass filter for the tweeter. But assuming that the tweeter is a nomimal 8R, I get nearly 20kHz as the corner frequency. With a 6 dB roll-off, we get -12 dB at 5kHz and -18dB at 2.5kHz so I'm guessing that it supports the FE208 very well.

🙂ensen.

 

[planet10]

Originally posted by purplepeople I believe it's acting as a high pass filter for the tweeter. But assuming that the tweeter is a nomimal 8R, I get nearly 20kHz as the corner frequency.

That is indeed the situation... i can't find T900A specs, but if the others are indicitive, they are much more efficient than the 208, so by XOing so high they also get attenuation.

dave

 

[Ken L]

Thanks

Ken L