More mandolin thoughts - the end result

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peter.coombe
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More mandolin thoughts - the end result

Post by peter.coombe » Mon Nov 23, 2020 11:13 pm

Some time ago I posted some mandolin thoughts about how I was using the principles outlined in the Gore/Gilet books to improve the sound of my flat top mandolins. A quick summary - I found that the main back mode of my flat top mandolins was 3 semitones below that of the main top mode. This matched what I measured in a vintage Gibson Army Navy mandolin (pancake mandolin). Mandolins vibrate like guitars, so the obvious thing was to make the back stiffer so as to raise the main back mode. That I did, and the sound improved significantly.

Now the first two mandolins I made with stiff backs are now prototypes, used to prove the concept. I have not been idle, but have been working to try and develop this further. Rather than use a pancake type of mandolin, I switched to what I call my "Classical Flattop" model. This has the same body size and shape as a vintage Lyon and Healy style C mandolin, and has been the best sounding of all my flat top mandolins. It is different from anything anyone else has built in the mandolin world, braced similar to a guitar. The only real difference from a guitar is that it does not have tone bar braces but has two braces from the tailblock to the X brace to resist the rotational force from the string tension on the tailpiece. The X braces have carbon fiber tow on their tops which makes a very strong top because the tow is about 10mm from the axis of bending, and the force is downwards pulling on the CF tow. The fingerboard extends over the sound hole (similar to the Lyon and Healey mandolins) which has the effect of lowering the main air mode to about 1/2 semitone below the G string (lowest note). That gets the main air mode out of the way.

Anyway to cut a long story short I have made 8 of these mandolins to date and have sold 7, so the players have noticed, which is very important. The 8th I am keeping for myself and is the subject of this post. All these mandolins have the same characteristics in terms of sound - unusually clean and clear sound for a flat top mandolin, and very even across the strings and up the neck. I thought the best sounding ones were the ones with Tiger Myrtle back and sides. Myrtle is the most dense of the back woods I used, so maybe the good sound is due to it being more on the dead back end of the live back/dead back spectrum. So why not make something with a really dead back. I have some Macassar Ebony that I purchased 25 years ago and have not been game to use it until now. So I made this mandolin as an experiment. Red Spruce top, Macassar Ebony back and sides, Brazilian Mahogany neck, Blood Wood bindings. The back has 3 hefty braces of Douglas Fir (Oregon). I used Douglas Fir because it is stiffer and heavier than Spruce. The weight does not matter because this is meant to be a really dead back mandolin. The top weight was 75gm, the back was 220gm, so a really big difference. What happens when the back is heavy and stiff. Everything changes. All the modal frequencies go up. The main top mode node moves out so it sits just about right on the rim. The ring node of the main back mode on the back shrinks in diameter. All this means nearly all the sound is coming from the top, so it is a bit like a classical guitar. The frequencies actually overlap the lower end of what I measure in my arch top mandolins which would explain why these things sound so good.

So, the result. The Ebony mandolin is an amazing sounding mandolin. In my opinion the best flat top mandolin I have made to date, and I find it difficult to imagine a flat top mandolin could sound any better than this one. I have not come across any flat top mandolin that sounds even close. I am keeping it, it stays right here, and another one is almost finished. Only problem is these are rare woods, pretty much now wood unobtainium so I can only make a limited number of these. The Bloodwood bindings were difficult and the subject of some bad language, but the red bindings against the black Ebony just looks stunning.

Sound clips
http://petercoombe.com/Sound/classical- ... hiquin.mp3
http://petercoombe.com/Sound/classical- ... npipe7.mp3
http://petercoombe.com/Sound/classical- ... /begsi.mp3
http://petercoombe.com/Sound/classical- ... ellows.mp3

Pics
Attachments
front.JPG
front-closeup.JPG
back.JPG
back-closeup.JPG
side.JPG
headstock.JPG
tuners.JPG
Peter Coombe - mandolin, mandola and guitar maker
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Dave M
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Re: More mandolin thoughts - the end result

Post by Dave M » Tue Nov 24, 2020 3:42 am

Peter that is good stuff. Have you come across any commercial mandolins with these characteristics?

It is certainly a very handsome looking instrument.

Making and selling 7 mandolins plus the eighth since you last wrote means you really have been busy!

When you say braced like a guitar it sounds like you mean an x brace...? Any chance of a pic of the top bracing?
Presumably one could drop the main air freq by using a smaller soundhole if you didn't want such a severe overhang?

Cheers Dave
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GregL
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Re: More mandolin thoughts - the end result

Post by GregL » Tue Nov 24, 2020 4:42 am

Hi Peter,
That looks fantastic!
If Ebony works, what about gidgee? (It is rare, but not (yet) unobtanium?)
Thanks,
GregL.


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Re: More mandolin thoughts - the end result

Post by kiwigeo » Tue Nov 24, 2020 8:47 am

Nice work Professor Coombe... :D
Martin

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peter.coombe
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Re: More mandolin thoughts - the end result

Post by peter.coombe » Tue Nov 24, 2020 9:19 am

I do have enough Gidgee for one of these mandolins, so that is on the to do list. Gidgee has the same problem as Ebony, rare to find pieces wide enough. I have plenty more Ebony, but would have to make a 3 or 4 piece back. Certainly you could drop the main air mode by using a smaller sound hole, but it would look odd and be difficult to adjust. As for commercial mandolins, nothing even comes close.

Picture of the bracing (not this mandolin, but is the same).
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Peter Coombe - mandolin, mandola and guitar maker
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Re: More mandolin thoughts - the end result

Post by GregL » Tue Nov 24, 2020 11:08 am

Hi Peter,
In terms of an "un-live" back, a 3 or 4-piece gidgee back would not be a problem? Maybe the "aesthetics" of a 4-piece back could be a "feature"? (A 4-piece ringed gidgee back would be nice!)
Thanks,
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Re: More mandolin thoughts - the end result

Post by Dave M » Thu Nov 26, 2020 7:03 am

Thanks for the image Peter. It does look like a lot of bracing for a small top but I know nothing about mandolins - though I am planning to try one soon so your work is going to be useful. Dave
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Re: More mandolin thoughts - the end result

Post by simonm » Fri Nov 27, 2020 9:35 pm

I wonder would a laminated back of some kind do the trick. You would obviously have to figure out a marketing angle to make it "premium" instead of "plywood" bit it might be worth a shot. e.g "double back, triple back, special re-inforced back" .

Great to hear of the success. :cl

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peter.coombe
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Re: More mandolin thoughts - the end result

Post by peter.coombe » Sat Nov 28, 2020 10:01 am

Of course a 3 or 4 piece back would work, but it is additional work, and I am not sure how the customers would see it. I did make a mandolin with a BRW back, and it sounded quite nice, slightly louder and brighter than the Ebony, but lacked something and I always went back to the Ebony mandolin. A laminated back may also work, and that is something I have thought about, but have not tried it yet. I have not been able to get the main back mode 4 semitones above the main top mode yet, but the closer I get the better they seem to sound, but the differences are small. The closest so far have been 3 & 1/2 semitones with a Myrtle back 3.5mm thick, and the Ebony mandolin is also at 3 & 1/2. There is a limit to how thick I can go because it gets difficult to implement the induced arch on the back. The Ebony back is 3mm thick, and it is really stiff. In the first one I made the main top mode was only 1 semitone above the main top mode, and sounded much better than the previous mandolins where it was 3 semitones below, so most of the improvements don't need the extreme stiff and heavy back, you just need to get the main back mode above the main top mode. However, for that last bit of improvement an extreme stiff and heavy back does seem to help. The disadvantage is that the instrument is heavier, and players do notice the extra weight.
Peter Coombe - mandolin, mandola and guitar maker
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Re: More mandolin thoughts - the end result

Post by Lillian » Mon Nov 30, 2020 3:16 am

Peter, that is just gorgeous and it sounds wonderful. It sounds like a dream.
Well done sir.

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peter.coombe
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Re: More mandolin thoughts - the end result

Post by peter.coombe » Tue Dec 01, 2020 2:40 pm

Well I have just strung up a new Tiger Myrtle and the second Ebony mandolin in the last few days. The Myrtle is a step below both Ebony mandolins in sound, although the back weight is about the same. I said I could not imagine any flat top mandolin sounding any better, well it is time to eat my words. I think I might be keeping this new Ebony mandolin instead, I keep coming back to it. The only difference is the back is slightly thicker (3.1mm) and the top is half of an expensive Adi guitar top from Allied Lutherie and bookmatched, instead of some left over bits of Adi Spruce. I guess I must have learned something, although I am not quite sure what. They measure very similar. They are so new I have not taken any pics yet.
Peter Coombe - mandolin, mandola and guitar maker
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Re: More mandolin thoughts - the end result

Post by Dave M » Wed Dec 02, 2020 3:43 am

Peter you are pushing more and more towards my next project being a mandolin! Dave
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peter.coombe
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Re: More mandolin thoughts - the end result

Post by peter.coombe » Fri Dec 25, 2020 9:09 pm

Here are some more pictures of the recently completed mandolins. The BRW and the Tiger Myrtle have already sold, the first and second Ebony mandolins I have not offered for sale (yet) because I am still trying to decide which one to keep. The Tiger Myrtle has arrived with it's new owner just in time for Christmas in the USA.
Attachments
Ebony front.JPG
Front view of the Ebony mandolin
Ebony.JPG
Macassar Ebony
Tiger Myrtle.JPG
Tiger Myrtle
BRW.JPG
Brazilian Rosewood
Peter Coombe - mandolin, mandola and guitar maker
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