Help with saddle placement

[Shane Woonton]

Hi guys,

I feel a bit silly asking this question, since I have Trevor's books and have read the intonation section ( a few times). But...

Most of the less complex intonation fixes in the books require either a test rig to determine the correct string length or the ability to test the placement of the saddle on the guitar, prior to routing the saddle slot (such as the "intonator" from Stewmac). I don't have the spare time or resources right now to build a test rig and I don't have the intonator.

I'm ready to place the bridge on my latest build. It's 24.9" (632.4mm) scale length. I'd like to move the nut toward the saddle by 1.5mm (one of Trevor's simple approaches) to improve the intonation, but I need to know how much compensation to allow such that I should be able to fine tune within the bridge thickness. The Stewmac fret calculator suggests 2.2mm (+/- 0.5mm) for high E and 5.3mm (+/- 0.5mm) for low E to front edge of the saddle. The saddles I have are between 3.5mm and 4mm thick.

If I understand correctly I need to remove any nut compensation from the saddle end. So that would bring saddle compensation back to 0.7mm to 3.8mm. I should also add I assume the Stewmac numbers will assume a medium action. I will use a relatively low action (1.7mm to 2.3mm) and light gauge strings so I understand I may need to reduce those numbers a little further.

So (finally) to my question - where would you place the front edge of the saddle?

Cheers,

Shane

[Trevor Gore]

Shane, by light gauge are you talking 12-53 or lighter?

[Shane Woonton]

Hi Trevor,

They are 11 - 52's

Cheers,

Shane

[Trevor Gore]

OK, Shane. I dug out some very old programming (shows how often I set up with 11s!) and worked out the following, after making a few assumptions about your set-up. For 1.5mm shift of the nut towards the first fret the string lengths measured from the shifted nut to the saddle breakpoint should be:

E 633.5
A 631.9
D 631.4
G 630.8
B 631.6
e 630.6

So if you set the front edge of the saddle at 630mm from the shifted nut, everything should fit on a 5mm wide saddle with no slant on it. I'll let you work out the slant if you want to use a thinner saddle.

Have to say, though, that I've never done an acoustic set-up even remotely like this, so I proffer the usual disclaimers! (and you might be well down on volume).

[Shane Woonton]

Thanks Trevor. Really appreciate it!

The usual disclaimers understood and accepted. I will build a test rig in the near future but right now my 6MO baby is keeping building time to a bare minimum!

Do you say I could be down on volume just because I'm using 11's on a short-scale? I have built lightly in the hope of compensating for that. We'll see how it goes.

Cheers,

Shane

[Trevor Gore]

I will build a test rig in the near future...

If you have a Strat style guitar with adjustable saddles and a bit of imagination you can use it as a proto-test rig...

Do you say I could be down on volume just because I'm using 11's on a short-scale?

The energy embodied in a vibrating string is directly proportional to the string mass and proportional to the plucking amplitude squared. So using lighter strings, a short scale length and a low action limits the power in your "engine" (the string) quite a lot.

The drop in tension (which sets your static design criteria) due to using your 11s compared to "standard" 12s is ~7% which is about 0.4mm on your brace heights on a X-braced guitar to meet the same deflection criteria.

This is one of the cases where the "standard" solution (12-53 or 12-54) has evolved because it sits in a sweet spot of playability and volume and the possibilities either side drop away quite quickly due to compromising either the volume or playability.

That's not to say don't do it; just be aware of what you're up against.

[Shane Woonton]

Thanks Trevor. Makes perfect sense. I'll let you know how this one sounds once it is strung up.

Cheers,

Shane