C-Extension Length?

[robobass]

How do you determine the length? In high school physics class I learned that the relationship between the C and E for the same string and tension should be 5/4, meaning the extension should be 25% of the length of original E. In practice, that seems to be too short. On my Pfretchner that percentage is something around 26.3% I suppose that clamping the string at the E would increase tension somewhat. Is that all that is at play here?
Wisdom from the Gods, please...
Robobass

[Mudfuzz]

Use a fret Calculator, double the string length so that your nut is the octave, then just count down in frets from the twelfth to C [8th] and there you are.

[arnoldschnitzer]

Originally Posted by Aaron Noguer

Use a fret Calculator, double the string length so that your nut is the octave, then just count down in frets from the twelfth to C [8th] and there you are.

I've tried this and it gets pretty close. But every string will intonate a little differently, and you need some adjustability in the extension's nut to get everything right. It's like bridge saddles which compensate on guitars and bass guitars. I use the rough formula of: string length divided by four, add about 1/4" (roughly 7mm). Also, turning the E latch into position tends to raise the pitch compared to fingering the note, so there's some fine tuning that needs to be done to get both C and E in tune.

[Mudfuzz]

Originally Posted by arnoldschnitzer

I've tried this and it gets pretty close. But every string will intonate a little differently, and you need some adjustability in the extension's nut to get everything right. It's like bridge saddles which compensate on guitars and bass guitars. I use the rough formula of: string length divided by four, add about 1/4" (roughly 7mm). Also, turning the E latch into position tends to raise the pitch compared to fingering the note, so there's some fine tuning that needs to be done to get both C and E in tune.

I kind’a figured that would be the case, intonation and compensation you can't get out of it can you?

[bassist14]

Originally Posted by KSB - Ken Smith

Try listening to a bass section playing an Ab in 1st pos/E-str and tell me how in-tune they are (or not?) as soon as they draw the Bow!

ken, you hit the nail right on the head...
just this ....ing Ab...
...most fun with only two basses playing mozart...