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Would there be a noticeable difference between using 9400pF and 10000pF in the HRSCF? I have 2 4700pF silver mica caps to replace a 10000pF Radio Shack test cap. Should this be OK. I'll be using 470pF and 39pF caps with it. Thanks.
Joe
Follow Ups:
Hi All
I have just used the following in my 8 HRSCF for HF, MF and LF drivers in my Kef105's with external crossovers:
2off 4n7F Wima MP3 250V in parallel
1off 1n0F Wima MP3 250V and 100pF Wima FKP2 1000v in series (all from Farnell)
with
3off 12R Holco 1W 1% (lowest value available fro HiFi Collective)
as per HRSCF circuit layout. For wiring I used 75ohm satellite coax - without the shield...
The FKP2 are tiny and require placing vertically and a steady hand when soldering!
The sonic results are fantastic, easily the equivalent of removing the crossovers. For information I use a mix of QED and Audioquest cabling, a maximum of 1m to the Xover's, then 1m to each driver.
Thanks to Chris da Costa, bartc and Al Sekela for the inspiration !
A series R-C network looks like the capacitor at lower frequencies, with impedance inversely proportional to frequency, and the resistor at higher frequencies, with impedance independent of frequency.
The frequency where the capacitor impedance magnitude is equal to the resistance of the resistor is called the corner frequency. It is the frequency where R equals 1/(2*Pi*F*C), or,
F = 1/(2*Pi*R*C), where '*' indicates multiplication, 'Pi' is 3.14159..., R is in ohms, and C is in farads.
So the corner frequency at 10ohm and 10000uf is 1.6hz?
" " " " " 10ohm and 20uf is 796.2hz?
What does this mean that the filter is doing when placed across the speaker wires? What does the corner frequency have to do with filtering out the bad high frequencies? Did I miscalculate?
Edits: 03/05/09
I just calculated the frequency for 39pF (a value I have) and got 408 MHz. Did you convert to farads? This converter is helpful:
Ok I didn't convert from pico to micro before using the calculator I found on the internet.
What corner frequencies are we aiming for with these filters?
For R of 10 ohms and C of 0.01 microfarads (the Walker Audio High Definition Links recipe), the time constant is 0.1 microseconds. Invert this, divide by 2 and divide again by Pi.
The answer is 1.59 MHz.
I'd stay above half of this number to keep the filter out of the audio band.
What is the range of the audio band? 0-20kHz? These corner freqs are in Mhz.
1.59Mhz, 159Mhz and 1591Mhz for 0.01 uF, 0.001uF and 0.00001uF capacitors. or 10000pF, 100pF, and 10 pF, right?
What would cut off say from 300khz and up? What am I missing
What is the range of the audio band? 0-20kHz? These corner freqs are in Mhz.
1.59Mhz, 159Mhz and 1591Mhz for 0.01 uF, 0.001uF and 0.00001uF capacitors. or 10000pF, 100pF, and 10 pF, right?
What would cut off say from 300khz and up? What am I missing
With a first-order filter like the simple R-C, there is still some influence on the audio band with a filter corner two octaves above (80 KHz).
Remember the formula: corner frequency Fc = 1/(2*Pi*R*C).
You can use a larger capacitor with the ten ohm resistor to get to a 300 KHz corner: 0.053 microfarads, or use a combination of a larger resistor with a larger standard cap value, such as 11 ohms with a 0.047 microfarad cap.
So, at 10 ohm and 9900pF I have about 1.6 Mhz. Is that low enough? Can I go 15 ohm (1.07Mhz) on this leg but 10 ohm on the next two? If I need to keep the resitance the same, would 530Mhz then be high enough with 15 ohm and a 20pF cap? BillF
I've gone to 20 ohms without any trouble. You don't need to make all the stages have equal corner frequencies.
nt
It should work. But you have to have the 2 caps in parallel to one another (and both in series with the same resistor) to add the values that way. The values aren't all that precise in the end!
The other variable is the type of cap. Al Sekela wrote some posts on that, but generally he and I were using silver mica, which at that time he's found to sound best. He wrote something about types/sounds of caps recently, as I recall.
I guess my real question is how much difference there is between 9400pF and 10,000pF? I don't know what the formula is to calculate what frequencies are affected by each. Thanks.
Thanks. Now I'm waiting to see if anyone responds to the question below about whether to connect the filter from the small cap or large cap end!
Here's his answer in another post.
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