A Greek e-mag just published a lab-test of 16 commercial speaker cables.
Google translate link:
AVMentor Speaker Cable test - Google translate
Some vendors insisted that their speaker cables should be reviewed along with matching interconnects (i.e. from the same cable maker) to really shine.............
Google translate link:
AVMentor Speaker Cable test - Google translate
Some vendors insisted that their speaker cables should be reviewed along with matching interconnects (i.e. from the same cable maker) to really shine.............
That would put its impedance down to 35R. I think we can conclude that it is very unlikely to be 75R, so if it 'improves' SPDIF this either means that impedance doesn't matter at all on such short cable runs with such a robust system or that people are interpreting audible degradation as an improvement. Either case would be disconcerting to cable fans.
We are told <97pF/m; I assume that means not far below 97pF/m. We need to calculate from the stated capacitance which already includes the effect of the air.
The amount of air will also affect the (unstated) velocity factor. More air means higher velocity factor. So for a given capacitance more air means lower impedance.
The amount of air will also affect the (unstated) velocity factor. More air means higher velocity factor. So for a given capacitance more air means lower impedance.
Z= Sqrt(L/C) when R and G can be ignored
Decreasing C raises Z
If you look at Coaxial Cable Specifications Cables Chart - RF Cafe
97pF/m or about 30pF/ft is typical of 50R coax. 75R is around 65pF/m
Decreasing C raises Z
If you look at Coaxial Cable Specifications Cables Chart - RF Cafe
97pF/m or about 30pF/ft is typical of 50R coax. 75R is around 65pF/m
If we're keeping the geometry fixed and foaming the dielectric, yes, we are reducing C.
I was estimating the Z for a particular cable linked to by an earlier poster.
If other people want to estimate Z for quite a different cable then that is fine, but it would help if they said for which cable they are estimating Z. Otherwise people might assume they are merely getting wrong their calculation for the same cable as me.
If other people want to estimate Z for quite a different cable then that is fine, but it would help if they said for which cable they are estimating Z. Otherwise people might assume they are merely getting wrong their calculation for the same cable as me.
Yes, that what DF96 is saying. I'm just pointing out that the person who's disagreeing with him is holding geometry constant and lowering dielectric constant, which raises the characteristic impedance.
We are at cross purposes here.
If you do that and increase the centre conductor diameter to maintain capacitance (a strange goal), yes the impedance drops.
If you play with this tool Clemson Vehicular Electronics Laboratory: Transmission Line Impedance Calculator
Starting with Er of 2.1, shield radius 1.8mm, core 0.5mm, you get 91pF/m at 53R
Now add lots of air to go down to Er=1.3
Now we have 56pF/m, Zo=67R
To maintain the capacitance you have to fatten the core to 0.82mm radius.
Now you have Zo of 41R
The problem is that the dielectric is now < 1mm thick, so any flexing is likely to cause shorts through foam collapse.
For most interconnect applications, especially MM phono, low capacitance is a bonus
I can't claim to understand the "tool", but I had a look at R'
When frequency is set low the resistance seems to be quite high.
I can't see an allowance in the equations for the cross-sectional area of the shield.
It appears that skin depth has been taken account of, but I can't confirm that the values predicted fit with other methods of arriving at total "resistance".
When frequency is set low the resistance seems to be quite high.
I can't see an allowance in the equations for the cross-sectional area of the shield.
It appears that skin depth has been taken account of, but I can't confirm that the values predicted fit with other methods of arriving at total "resistance".
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