simple summing resistance q

hello, i am building this
http://www.forsselltech.com/8chsum_2.pdf

(its an 8 channel to 2 channel passive summing bus)

question is if i went to 10 channels (or 16) would i want to keep the resistance at the summing node the same by chaning the resistor values (currently each channel has a 5k hot and 5k cold) or keep them at 5k reguardless of how many channels i add.

i guess i don't know how to think about it... input channels need to see 5k or the output impedence is a function of these 5k parallel resistors.

help
thanks

anyone

Leave at 5K until you get around 100 inputs.

Maybe this should be for the Drwing board... How does Fred calculate the approx input impedance at 5.7kOhms?

I suppose 5k in series with the parallel of the other seven 5k resistors:
Z = 5k + (5k / 7) = 5714
This is the impedance with respect to ground, right?

Is this the usual parameter (given by manufacturers, for example) or usually impedance is calculated between hot and cold? This way the impedance should double, am I correct?

Thanks,
Frank

> Z = 5k + (5k / 7) = 5714

Yes. Or for the balanced case, twice that.

Assuming that each source Z is <<R, and that the load is >>R/N, where R is the mix resistor(s) and N is the number of inputs.

And in general, for N greater than "a few", the impedance seen by each source is just slightly higher than its mix resistor(s). Since most sources don't much care if the load is 13.3K (4-in) or 11.4K (8-in) or 10.1K (100-in), it's all the same.

Many thanks PRR,
I'm wondering based on what parameters Fred chose to use 5k instead of another value?

Frank