Official Luthiers Forum!

I have just built me first classical guitar with Sitka spruce top (Daniel Frederich 1971 plan) and I had a 25 foot radius on the top and I have noticed that this is a subtle doom behind the bridge but between the bridge and sound hole there is a slight concave. I am thinking the guitar humidity is too dry, but wanted to know how to trouble shoot the problem.Thanks, Paul

Hi Paul a sunken area in front of the bridge can indeed be symptomatic of a dry guitar.

Another test is to run your fingers along the fret ends. If they feel sharp or proud it's a sign of a dry guitar too. When a guitar dries out the neck wood(s) shrink but of course our frets don't so they start sticking out.

Another possibility is if pretty strict humidity control was observed or not while building the guitar. If not the kind of thing that you are seeing is possible too.

Don't know what would be a good building humidity range for your neck of the world my friend but here in Michigan I like 42 - 48% and of course determined and measured by a calibrated and reliable hygrometer.

If you need help rehumidifying the guitar please let me know and I can tell you of a fast and easy way to make that happen.

What tension strings are you using?
How tall (high) is the top of your saddle from the top?

How long has it been strung up?

This really is a normal reaction for all the string pull on the top.
You may see some of the brace(s) outline also.
telescopic figuring is what that is.

How thick was the top ?

How's it sound?

Mike

_________________
Mike Collins

Some people are of the opinion that the better classicals always do this. If you build so stiff to avoid this, you also miss the best outcome.

Firstly thanks All to your replies-very helpful. Given this was my first guitar I didn't have a humidity controlled workshop. I'm from New Zealand and my shop is in my Garage and we are just starting Summer. I haven't noticed any frets sticking out. It would be great to know some easy ways to humidity my guitar. In respect to string tension I have D'Addario J45 strings normal tension.The saddle is higher than I would like but I wanted to wait until I see whether I need to adjust the action. Intonation is very good apart from the G string which is a little sharp. Action is 4mm on the bass and 3 on the treble. It has been string for one week. The thickness of the top is about 2mm with 2.2mm closer to the fret board. The sound is F# for the sound box, and basses are well rounded and loud, but trebles are not as loud and don't 'sing' as much, with sustain less than I would like. Thanks Guys

I have measured too the height of the saddle from the top of the soundboard and it is 14mm-which thinking about it might be a contributor to the concave top assuming this may place more downward pressure on the soundboard. Is this correct and would it impact tone -I am more thinking about the lack of treble tone? Cheers Paul

many factors for the lack of treble.
The thin top.
bracing.
depth of body.
s.h. size.
get some better treble strings.
Hannabach , Saverez ,La Bella.(the Flamensco 820 trebles)
come to mind.
Use a med. tension treble set.
with the J45 basses.
High saddle height helps the basses sing.
So that may be a factor also.

And give the guitar time to settle in.
Which means -time for all the tensions put on the neck-top
settle in.

Mike

_________________
Mike Collins

Great thanks Mike for the advice. What would be 'normal for the saddle height from the top? Cheers Paul

A 2mm top with strings at 14mm seems a bit edgy to me. 11-12mm is a more typical string height.
What are heights of the fan braces?
If your worried and the frets are well dressed, maybe you can live with a lower action. At least until you see what the future holds

Thanks Dave I will try lowering the action and give the guitar time to settle in. The fan braces are a Daniel Frederich design so 10mm on both treble and bass outside braces, with 5 mm for the rest of the in between.

10mm is great for classicals.
What is the bridge made of ?
How wide is it?
How thick is it at the tie block?
How thick are the wings-the portions from the tieblock
to the ends of the bridge?


Mc

_________________
Mike Collins

Hi Mike-over the last few days I have hydrated my guitar using a damp sponge and no have a flat top again, so problem solved!! Thanks everyone for your help.cheers Paul