pit props

[daveh]

Hi,

Thanks for a great forum, i've spent ages looking through the archives and have learnt lots about resonator guitars.. but one element of their construction still eludes my understanding.

Anyway, I'm almost finished making a 'National' of my own. It's not a direct copy of any model, so I don't really know what it's gonna sound like. It's got a thick solid maple front with rippled solid walnut sides and back. The cone is a 9.5 inch national one and it's support-ring thing is maple ( laminated strips formed and turned ). The neck is mahogany with a slotted headstock and the body is four inches deep. Scale is 25" and the neck joins the body at the 12th fret. As far as I can make out the main (perhaps crucial) differences are:

The back is constructed with the standard acoustic style braces.

The neck is joined standard acoustic style using dovetail.

Would the absence of a ' neck stick' and pit props mean a significant loss of a resonator-guitar's characteristic tone ? does someone know the real purpose of pit props? I did read that they help prevent the back from vibrating.. should I add some from the cone ring to the back brace maybe?

thanks in advance

[LouisianaGrey]

Dave, I'd be inclined to do that if you haven't got a neck stick.

If you want my take on the philosophy of it here it is. Remember this is just one builder's opinion and others may well disagree:

These were originally metal-bodied instruments and thin metal bends easily so the bodies by themselves are not that good at resisting being folded up by string tension. The neck stick is essentially banjo technology, where you have the same sort of problem, and it means that you have a big chunk of stiff, straight wood holding the tuners and the tailpiece apart to resist lengthways tension. The soundwell is fixed to the neckstick to resist the strings pushing downwards on the bridge/cone assembly. Without these things I think the tops would cave in. I think the support posts under the neck stick in a metal bodied guitar have more to do with stopping the back from going out of shape than anything else, because it's a big area of thin metal and would bend pretty easily. Of course a wooden back doesn't have the same problem.

In the case of your guitar it sounds like you've got a thick top, which will help. Wood is much more resistant to bending than metal so it should help maintain the rigidity of the box. Support posts between the soundwell bottom and the back braces will help to resist the downward push of the strings on the soundwell by spreading the load across the whole of the back of the guitar. You will find this feature in many of the modern spider bridge guitars where, because of the way a spider bridge cone fits in the body, they tend not to use a neck stick of any kind. They usually have either a dovetail or bolt-on neck. Even the older-style construction ones with a full soundwell only used a very short neck stick that didn't extend as far as the tailpiece.

I used to make biscuit bridge guitars in a similar way to yours but although I still use dovetail necks I now fit a neck stick in brackets between the neck and tail blocks because of the reasons I've outlined. Like this:

This allows me to dispense with the support posts altogether and allows the back to vibrate more freely, which I think benefits the tone (I think tops moving are a bad thing, but backs moving are a good thing).

If you want to take a look at mine then it's www.petewoodmanguitars.com. I'm only across the water in the Isle of Man, so if you have any questions drop me an email.

[Alan]

I think that Donmos are done in a similarish way, the sides are thick and the neck is held in place with allen key bolts to a block. The neck stick the fits very tight against the ends of the body. 1 prop

www.donmo.com/

[daveh]

Many thanks for your help Pete. I'd love to get over to the Isle of man sometime, your site looks great.
I forgot to mention that I've put a hefty crossbrace under the top. It runs side to side under the upper frets to prevent any collapse due to string pressure. The fact that neck-sticks and pitprops might be a hangover from steel guitar construction had crossed my mind. My many google searches failed the locate any good interior pictures so your photos are much appreciated

From reading some reviews of copies of resonators, I noticed the reviewer felt that some of the factory's lack of attention to these constructional details was detrimental to the sound. I will probably go without any extra supports for the back. The neck is pretty chunky, the top quite solid. With the 15 -56 gauge strings, I plan on playing in standard tuning and both open D and G tunings, the thing shouldn't fold up (I hope).

Any thoughts on the merits of phosphor bronze versus nickel ?;