Mandolin project

[peter.coombe]

I have mostly been lurking the last few months, but have been busy in the workshop. Some might be interested in what has emerged. I hope someone finds this interesting because it has been a lot of typing because IE crashed on me, plus some other problems with broken links and previews on this site, and I lost the lot and had to retype GGRRR. Frustrating.

It all started at the National Folk Festival this year after a conversation with John (Woodrat). John picked up one of my mandolins and played a few chords and made some comment about what a fun instrument it was. Then he said what about falcate bracing a flattop mandolin? After all the excitement of the festival died down it got me thinking. Falcate bracing is designed to resist the twisting motion of a guitar bridge. It does not provide much lateral stiffness. That is provided by the bridge plate and the bridge. Now a mandolin has a floating bridge with no bridge plate, so the twisting force is on the tailblock, and the force on the bridge is downwards only. So the forces are different. Without a bridgeplate and glued bridge there is not going to be enough lateral stiffness, and not enough stiffness under the tailpiece. So without significant modifications to falcate bracing it won’t work in a mandolin. The top would collapse. So forget that idea for the time being. Back to the tried and proven X brace. X bracing works very well in my arch top mandolins. However, in a flattop it does not provide enough stiffness under the tailpiece, nor enough stiffness around the sound hole. A common structural failure problem in mandolins is the top folds in under the tailpiece, so that area needs to be reinforced. Flattop mandolins often fold in around the sound hole, so that problem also needs to be addressed. Graham McDonald has used a H brace to solve these problems, but I wanted to stick with an X brace. Off to the workshop to make an X braced prototype flattop mandolin top.
The approach was to use the plate tuning methods I use on my arch top mandolins and try and get patterns that looked familiar (and have a light and resonant top) , concentrating on the ring mode since that is the most important. At least then there was a fighting chance the thing will sound half decent. I have never much liked the sound of flattop mandolins, many of them just don’t sound clean to me. Some are just loud and obnoxious. Some of the old Gibson Army Navy flattops can sound sweet and clean, but the few I have seen are not very loud, and not many survive without signs of top collapse. It should be possible to design something that is loud and sounds good. After all, a flattop is lighter than a carved arch top, so it should be louder.

Eventually I came up with something I thought would work. But – need to stop for a moment and think about what we are doing here – what are the design aims?
(1) It must sound good
(2) It must be structurally sound
(3) It needs to be easy and cheaper to build than an arch top so I can sell them cheaper.
(4) Must look good

Addressing (3) – is a flattop so the top and back are much less work than an arch top, and there is less wood so the materials are cheaper. Back and sides can even be made from offcuts. Can keep the rosette simple and save hours of work. However there are marketing considerations, so retain the dovetail neck joint and varnish finish as well as retain the wood bindings. A varnish finish does also help with (4). Use a cheaper tailpiece and cheaper tuners. The tuners I chose are Rubner, made in Germany so are quality tuners, but I have found it is well worthwhile getting the Teflon bearings and buying direct from the factory. Case is made in China, but fits well.

I made a prototype to test if the criteria had been met. The prototype certainly sounded good enough, by far the best sounding flattop mandolin I have come across, so was very promising. That stimulated me to make another and another and so on, the usual story of continuous improvement. I think the design aims have been met. There has been no sign of any structural problems, and I have sold two for less than half the cost of one of my arch top mandolins. The most important thing is that the musicians seem to like them. They are louder, so make excellent session mandolins, and are attractive to learner musicians because they are a lot cheaper, but have the quality of sound and quality of construction of a handmade instrument. Hopefully they will sell once I get them in front of more musicians. I am very pleased with the sound. Not as refined as my arch top mandolins, but louder, huge ring and sustain, and nice clean sweet sound. Excellent value, or at least that is what I hope I can convince customers!

Here are some sound clips –
http://petercoombe.com/Flattop_sound/Beg_Si.mp3
http://petercoombe.com/Flattop_sound/Lord_Ic.mp3
http://petercoombe.com/Flattop_sound/S.mp3

The bracing pattern I have come up with is in the picture below. I call it “enhanced X bracing” because the X and cross piece north of the sound hole is reinforced with carbon fibre. The sound hole is reinforced similar to a guitar, and I have added two longitudinal braces from the tail block to the X to prevent top failure under the tailpiece. After 7 mandolins and one mandola what have I learned? Well, lighter is better for the top (oh what a surprise), and I like the sound of Myrtle or Blackwood. With Engelmann Spruce top and Engelmann braces I can get the weight of the top down to around 94gms. My arch top mandolin tops weight around 150gms so that is a massive difference. No wonder they are louder!

Picture of the bracing on the most recent instrument -

[peter.coombe]

Pictures of the actual instruments -

[Trevor Gore]

Good work, Peter! Thanks for sharing.

(BTW - At the risk of trying to teach my grandmother...dump IE and load up Firefox. Amazing how many problems seem to disappear...)

[ozwood]

Thanks Peter,

I really enjoyed reading that, I'd like to have a go at making a flat top mando one day.

They look great!

Cheers.

Paul.

[peter.coombe]

Thanks Trevor. Your book started this off.

One thing I forgot to mention -

One thing I learned from this is that the free plate tuning I use on my oval hole arch top mandolins works on these flattop mandolins as well. So I have been matching the ring mode of the back to the ring mode of the top, and the result is a nicely well balanced instrument. The first 2 were not well matched and ended up not being so well balanced. The free plate modal frequencies are in the lower range I get with my arch tops, so on average are lower, and the main air mode is about a semitone lower which makes it lower than the G string so I don't get the G string boom so common in the old Gibson arch top oval hole mandolins. Free plate tuning is about all we have with mandolins because even if I knew all about body modes and what to aim for, there is bugger all nothing I can do about it because once the box is closed there is no access. I have tried adding side mass on the outside, but it killed the tone, so they are probably about right anyway. I also tried a Padauk bridge and that killed the tone, so the bridge is Ebony 8-9gm. My modified Brekke bridges I use on the arch tops are around 11gm, a Loar type (usual standard bridge) mandolin bridge is around 18gm!

[P Bill]

Thanks Peter, interesting read.

[nnickusa]

You can pile everything I know about mandolins and modal whatevers on the head of a pin, and it won't fall off, but they sure do look nice

[peter.coombe]

You can pile everything I know about mandolins and modal whatevers on the head of a pin, and it won't fall off, but they sure do look nice

Well then design aim (4) has been satisfied.

Here are some pictures of the mandola. Soundclips here -
http://petercoombe.com/Flattop_sound/Mandola/Drover.mp3
http://petercoombe.com/Flattop_sound/Mandola/SW.mp3

[Paul B]

Thanks Peter, that was an interesting read.