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Yes, that's correct, but

206.228.220.39

Maxamillion

In Reply to: RE: I'm easily confused.... posted by rwiley on April 25, 2010 at 21:51:56

only well above the corner frequencies of both capacitors. There is a frequency dependence that needs to be taken into account. That is why I measured 32 ohms in my test setup (in the post above) instead of the calculated 25.5 ohms (51/2) - the 0.39uF cap still had a significant impedance to the test signal at the 10kHz test frequency. At a higher frequency it would have measured 25.5ohms.
What that shows is that the impedance will vary non linearly with frequency in a multiple parallel RC network - at audio frequencies it will be very large, then it will decrease to that of the resistor in series with the largest cap in the filter as the largest cap passes its corner frequency. Impedance should be stable for a range of frequencies, then it will begin to decrease non-linearly as the second cap begins to pass the RF, then it will decrease again as the third cap begins to pass the RF signal, and so on. Add to that the fact that somewhere in there the caps will reach their resonant frequency and the impedance will then increase again. It becomes quite complicated to figure out what impedance the filter is presenting at any particular frequency.
All that said, folks here do report good results with the parallel networks, so maybe sometimes we can analyze ourselves to death. It's the age-old struggle between the theorist and the experimentalist - and the best approach probably lies somewhere in the middle...

Edits: 04/26/10

Follow Ups:

I've had good results with... - rwiley 08:00:30 04/26/10 (1)
RC filters using the following values: .1uf + .012uf in series with a single 10R resistor. It will be interesting to hear the results of your experiments with values "theoretically" matching the characteristic impedance of your speaker cables.

BTW...the resistor values in the following link seem incorrectly sized "if" the goal was to have an R(eq) of 10R.
- http://alanmaherdesigns.com/Documents/HRSCF%20Project%20rev- (Open in New Window)
- RE: I've had good results with... - Maxamillion 13:31:47 04/26/10 (0)
  I wouldn't say they are "incorrect", but the impedance will be lower than 10ohms and as low as 3.33ohms at some frequencies. If that works, then it's fine, but if you need 10ohms at all frequencies it is not fine.
Without the theory, in practice - bartc 06:15:09 04/26/10 (3)
I've been testing over years both single and multiple R-C arrays. I can tell you unequivocally that the multiple R-C arrays do work better.

Second, I've also compared the multiple R-C array to the multicap R-C and the multiple array still sounds better.

Also, I've used Al's R-C-R formula too in my multiple array filters, but only in my AC filtering system, which uses safety rated X and Y caps. Yes, this works better there, but I have no idea if it works as well on the speaker cables as I have not yet tried it there.
- Thanks, Bart. Have you tried... - Maxamillion 07:35:05 04/26/10 (2)
  Have you tried using separate cascaded RF-friendly capacitors in parallel with only one resistor for the lot? For example, .01uF +.001 uF +.0001uF silver mica in series with one 10ohm resistor. In that way you would get the benefits of cascaded caps (shifting resonance to a higher frequency) but still keep the impedance constant.
  - Yes, Max, I tried that too - bartc 07:41:29 04/26/10 (1)
    On both speaker cabling and on AC filters. It does not work as well as the R-C or R-C-R multiple arrays.
    
    You are welcome to try these recipes sequentially yourself. I did it by simply using wirenuts to tie the pieces together, including lead wires until I found the best formulae. This makes it cheap and easy to try out the combos to your heart's content.
    
    Then I solder those final versions, which sounds better yet, as it doesn't engage the metal in the wirenuts (which may be ferrous).
    - I will try multiple combos - Maxamillion 08:30:32 04/26/10 (0)
      I have an array of silver mica values on order, and I already have .01uF and .001uF Multicaps on hand. I have lots of different values of PRP resistors, and I just ordered some 71ohm Texas Components TX2575 Z-foil resistors as well, to match the characteristic impedance of my speaker cables. Texas Components will make any value of resistor you want at no extra cost, but the resistors are pricy (~$10 each), so multiple parallel arrays can get $$$ fast!
      The Z-foil resistors are especially well-suited to this job as they have a very low self-inductance. I measured a 100ohm PRP resistor at 10kHz and found 3.3uH of inductance, meaning the 100ohm PRP thus has a -3dB point of only 4.8MHZ. Since I'll be using a value of 71ohm, this could be a significant issue.
      I'll post my results when I'm done - it will take 2 weeks for me to get the TX2575 resistors.
      
      Edits: 04/26/10

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