Official Luthiers Forum!

My whole reason for joining this forum is to shamelessly glean all the information I can.
I intend to build an F style mandolin from scratch, and have no experience whatsoever.

So, my first question is;
Why isn't Spruce used for the backs of instruments when it is such a great tone wood for the fronts?
Is it just to save the good stuff for fronts?
Does the back need different structural qualities than the front?
I appreciate any help, and don't mind a little gigging in case it's a stupid question.

There was another thread recently addressing this. Some examples were pointed out that have been made.

I know that some classical makers have used spruce or cedar backs, but I think they all put a thin veneer of hardwood to protect the back. I think Contreras was well know for this on some guitars. One improtant reason to not use it for backs is that it is very fragile, and, if not veneered, would be attacked by belt buckles, buttons, etc.

I see. I have found two bookend sets of Sitka that are 1" thick and thought I would use one for the front and one for the back. If it's not advisable to use Spruce for a back, then I'll just save one set for my next mandolin.
You know, the one I build AFTER I screw up the first one.

I am certainly no expert , at the GAL convention last year a fellow had an "all doug fur" guitar.. it sounded remarkably good. the only practicle issue I can think of is the spruce may not take the abuse a maple back would...Jody

One of my customers, Jeff Sigurdson, is using spruce for backs and sides on his student flamencos. He says that the Canadian Cypress (yellow cedar) was a little too has=rsh sounding for him and felt that the spruce was giving him a better result for his build style. I am not sure that I would use it for steel string guitars but people have indeed done it. Are talking about Mandos or guitars here? I don't know of any mandolins that are built with spruce backs. I send a lot of spruce to Roger Siminoff and he has never asked for back and side stock, but I can ask him if he has heard of it being used before for mandos.

Shane

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Canada

I played an all spruce guitar built by John S Kinnard at Epic Guitars in Carlsbad Ca. It was wonderful.
It lasted in the shop about 2 weeks, so there certainly seems to be a market for them. The owner of the shop, Kevin, said there was a lot of interest in the guitar.



Here is the link.
http://www.johnkinnard.com/index.html#inv012071236

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"An adventure is only an inconvenience rightly considered. An inconvenience is an adventure wrongly considered." G. K. Chesterton.

As has been indicated, you can use spruce for the back if that's the sound your'e after. However, in general, the back has a bit different job than the top, and using a different wood can work out better.

One thing is that there just is not much energy in a plucked string, and you have to make the most of it. You want the top to be light, for the same reason you would not put a little engine in a Hummer; it won't move if it's too heavy. The top has to move to produce sound.

All of the energy that moves the back is 'stolen' from the top, in some sense; either through the air in the box or else through the motion of the sides. Generally speaking, the back is not going to be as effective at producing sound, partly because it is usually heavier than the top, and partly because of where it is. So it usually ends up being a good ides to limit the amount of energy the back can steal. One way to do that is to make the back heavy, so that most of the sound that hits it is reflected off, rahter than causing it to move.

A light weight back does tend to give a 'punchy' sound: it moves a lot on the string attack, and pumps a bunch of air through the soundhole. Flamencos use this, and other tricks, to get a sound that 'cuts' through the loud party atmosphere and the strident singing. Mahogany Dreads also make use of the 'whump' of a light weight back.

A light back tends to cut down on sustain in some ways, and may also favor a less 'complex' sound.

It's really hard to make broad generalizations, though. For one thing, there will always be counterexamples. BTW, I would not class a Doug fir back as one of those: Doug can be as dense as oak or rosewood. Anyway, this is a complex subject, as is much of string instrument acoustics; ultimately the best one can say is that there is genrally a reason behind tradition.

Not sure if mentioned in the above postings, but I recall a previous post of the opinion that the more species of wood used throughout the guitar, the "better" the sound--in the opinion of the poster.

Thanks everyone!
I figured there had to be a mechanocoustical reason for the different woods in the different places. Mr Carruth is very plain spoken about the dynamics of the box in motion. I believe I'll search out some maple for the back, and have two sets of tops to play with.
It is, however, intriguing that the flamencos use this idea for "punch". There's a certain "bark" I'm looking for in the mandolin, but it's too much hand carving at stake to experiment and find that punch does not equal bark.
Again, thanks to everyone. I feel like I've done the right thing by joining.