Red gum

[peter.coombe]

Has anyone tried red gum (i.e. river red gum) as a back and side wood? Only thing I can find after a bit of a hunt around is it is too heavy, splits easily. I am looking around for an Ebony substitute for mandolin backs that is more sustainable and not nose bleed expensive. So, Ebony is heavier and also splits easily but sounds really great so that too heavy stuff is rubbish. The principle is to make a dead back so heavy = good, so tick. I do have a piece I bought 20 years ago and have just made into a back and cut some sides. It bends easily so another tick. It has relatively high internal damping (so does Ebony) and for a dead back that is probably another tick. It also is commonly highly figured, readily available and finishes beautifully, so more ticks. It actually is a very good substitute for bloodwood bindings. Bloodwood is a nightmare to bend so I think I will use it for bindings when the red colour works. It does tend to have gum veins and borer holes and being a Eucalyptus is not very stable so some crosses there. However, for a dead back it might be the ants pants. Won't know for sure until I string it up. Will report here again when it gets the strings on. In the meantime I would interested if anyone has used it.

[kiwigeo]

I've got a couple of back and side sets that have been sitting on my shelves for 20 years now. The grain in the stuff is about as rogue as you can get and I don't look forward to running plane over it. I may be pleasantly surprised when I finally come to use the stuff but right now these sets dont incite a great desire to turn them into an instrument.

[blackalex1952]

My experience with the sound absorbtion qualities of red gum is that I wouldn't use it for anything much,especially an instrument.-Ross

[peter.coombe]

This is where I have problems with explanations. What is meant by "sound absorbtion qualities". A piece of wood has mass, stiffness and Q (amount of internal damping, high Q has less damping). High Q (e.g. rosewood) woods ring on for a long time, low Q woods have a shorter ring. So I assume you mean it has a low Q? Comparing an Ebony back I have with the Red Gum back it has slightly less mass, less stiffness along the grain and about the same Q (it rings on for about the same length of time). The Chladni pattern that shows it is mostly only bending along the grain has a lower frequency, but other frequencies are not that much different from the other backs I have. Nothing really unusual about it. That can be corrected with a brace, but I don't know if that is really necessary. So, just from the physical properties I can't see why Red Gum would be all that much different from Ebony. Jarrah also has high mass and internal damping and there is nothing wrong with Jarrah as a back and side wood in terms of sound, I used it many years ago with success. A high Q wood does not necessarily sound "better". Different, but not necessarily better. I am predicting a warmer sound, so am using a stiff piece of Red Spruce for the top, same as the Ebony mandolins I made. This is a dead back system so the back is not contributing much to the sound any way, so i can't see any reason why it won't work. We shall see in a few weeks.

[kiwigeo]

Where you want to minimize "leakage" of string energy from the top down the sides red gum would be the ticket. Not so good if you're after a live back. My main reservations would be it's density and the difficulty working the stuff.

[peter.coombe]

Martin, you probably did not read my mandolin thoughts thread. I have been making flat top mandolins with dead backs for around 2 years. You can make a dead back by more hefty bracing, making the back thicker, using more dense wood, or laminating. I was mostly making the backs thicker. Why? They sound better than a live back mandolin. Around 6 months ago I decided to go to extremes and make a back from Ebony and use really hefty bracing. Bingo! The sound is way better than any of the others I had made. I made another one and the sound is even better, would challenge any of my arch top mandolins in tone and is louder because the top is lighter. So, the more I shut the back up the better the sound. What actually happens, and you can see it in the Chladni patterns, is like a see saw. The top is about 1/3 the weight of the back so the fulcrum of the see saw is moved so that the top moves much more than the back. The energy is the same, and obeys the basic physics law of everything has an equal and opposite reaction. The node of the main top mode moves out so it sits right on top of the ribs. So the whole top is vibrating and the ribs are not. The effect is the same as adding mass to the ribs of a guitar, only it is even more effective. The tone is unlike any other flat top mandolin I have come across, and they are loud with an enormous dynamic range.

So, after all that. I want a dead back, a live back just does not have the sound. So, I do want something that is really dense. As for workability Red Gum is way easier than Ebony or Gidgee. Gidgee is heavier but it is brittle and hard as, and not readily available quarter sawn in the sizes I need. Making the center join is a challenge, and it is not the easiest wood to bend. Ditto for Ebony, but Gidgee is worse. Red Gum is a breeze in comparison, although I think I would avoid the widly figured pieces.

I am not getting what I wanted here. I really wanted practical experience with Red Gum, but so far no one has used it so it is all just speculation.

[Trevor Gore]

Give Gerard a call.

iirc, what he told me was a) it is not very stable in guitar sized panels, so prone to cracking and b) whilst the grain in most woods is enhanced with finish, in red gum any figure seems to disappear under finish. But best to check with Gerard as I have one set, but have not built anything with it and probably won't.

[peter.coombe]

Thank you Trevor. I never used it until now because the one piece I purchased twisted and cupped badly, but I am not so concerned about that in a flat top mandolin and for bindings it should not matter. So far so good and it has been though some big humidity changes with the braces on. Will try a bit of shellac and varnish on scrap and see what happens

[peter.coombe]

Not too shabby under varnish. I am happy with this. Will continue, more later.

[Mark McLean]

That does have a lot of life to it!

If it sounds as good as it looks.............

This is tantalizing.

[Trevor Gore]

Not too shabby under varnish.

Yep, that looks fine. Gerard would have been using nitro over a grain filler, which may well look different from an (oil?) varnish.

[peter.coombe]

That is shellac, followed by Aquacoat pore filler, followed by varnish. The varnish is Target Coatings EM2000, which is an oil varnish in a water emulsion, so it is a water based finish but does not have any of the blue tinge you can see on darker woods that many of the water based finishes have. I like it, no need to wear PPE if brushed on, or worry about weather conditions, and I especially like the way it ages.

[Bruce McC]

Peter
I have neither experience with river red gum nor mandolins but I have found your posts
very informative. Thank you for your time and effort.

[WJ Guitars]

Peter, I also find your information and comments are interesting especially when your are testing out other alternatives of timbers on your mandolins. I noted that your want the back to be dead and not live to improve the sound quality.

Side tracking, would a carbon fiber mesh back construction achieve similar sound control results? I 'm not sure whether a carbon fiber mesh finish on the back of a mandolin would be visually acceptable. However, I have seen some McPherson acoustic guitars on his website that are completely made out of carbon fiber mesh.

Looking forward to seeing the Red Gum mandolin result.

Regards
Wayne
https://wjguitars.wixsite.com/mysite-1

[peter.coombe]

Carbon fiber has a very high stiffness to weight ratio, which is good for the top, but that is not what I want for the back, it needs to be heavy. Remember the see saw analogy. The top needs to be as light as possible, so a carbon fiber lattice bracing might be worth a try, but I would not use it on the back. Problem is, getting the carbon fiber lattice right so it sounds good is tricky. Others have tried, but the result has been very loud and obnoxious sounding mandolins because the lattice is too stiff. I think it is possible, but would involve a lot of experimentation and hence a lot of time.

There are other woods that may be worth a try. We have a lot of native dense woods available. Many are too small a tree to get the size needed, but I have tried Jarrah and grey ironbark. Jarrah was successful, but is a bear to bend. The ironbark was a disaster so won't use that again. Very loud and course sounding, and the back inverted to concave and then popped back out again.

[blackalex1952]

back inverted to concave

..a custom build for a bloke with a beer gut and a skinny wife?-R

[peter.coombe]

Well the red gum mandolin is finally finished. Took a while because I ran out of bridges and Vern Brekke is having problems at the moment with the CNC he was using so had to wait for a bridge. Was well worth the wait. All the nay sayers on red gum now need to eat their words. This is the best sounding of this style of mandolin I have made so far, but it is not the loudest. In comparison to my Ebony mandolin it has more depth of tone and overall sounds more refined, but the Ebony mandolin is louder. Lovely beautiful sounding instrument. Very pleasing and a big surprise bearing in mind all the negative comments I found for red gum as a tonewood.

Here are some pictures of the bracing and the finished instrument. I have not done any sound clips yet due to my left middle finger having an argument with the bandsaw and the bandsaw won. However, was not too serious and is now not far off being ready to play mandolin again. The red gum is not very stiff along the grain so I added some 5mm strips of indian rosewood to stiffen it up a bit. Seems to have worked. Thickness is 3.4mm and weight is 212gm, so not as heavy as the ebony even though it is thicker. So, red gum has beaten BRW, EIR, sassafras, blackwood, myrtle, rock maple and red ironwood. So, not so shabby. The red ironwood has just been strung up, so is early days yet, but is no match for the red gum mandolin, and red gum is a heck of a lot easier to work with. It is common as mud, but not around here because it does not grow here. Main problem is getting a clear piece that is dry and quarter sawn and with a bit of figure. It is pretty rough stuff, full of gum veins and worm holes, but the sound is great, and commonly highly figured. Whether it would work in other instruments I have no idea. Unfortunately some years ago I sold the rest of the plank where this wood came from because I thought it was too unstable for an arch top mandolin and I would never use it. Bugger.

Woods are Red Spruce top from RC Tonewoods, red gum back and sides, Mahogany neck, Macassar Ebony fingerboard, Indian Rosewood bindings, and ebony bridge and headstock overlay. The fingerboad dots are opal.

[WJ Guitars]

Excellent result Pete. When you are able I would like to here a sound sample.

Wayne

[lamanoditrento]

I look forward to building with my red gum set with that review. Actually, I was anyway just because of the figure and colour. Now more so

[peter.coombe]

Here are some sound samples -
http://petercoombe.com/Pictures/for-sal ... hiquin.mp3
http://petercoombe.com/Pictures/for-sal ... rnpipe.mp3
http://petercoombe.com/Pictures/for-sal ... 69/bsa.mp3

This is the first of this style of mandolin where I have managed to get the main top mode and main back mode 4 semitones apart. All 3 modes are also between notes, so I nailed it this time, and that is one reason why it sounds so good. The whole thing is a bit counter intuitive, but makes sense if you follow the Gore/Gilet books. Red gum is heavy, floppy and the tap tone is more thunk than diiinnngg. The vast majority of guitar makers would say avoid from those properties, but for a dead back system that is exactly what is needed. It probably would be a poor choice for a live back system, however. As for the stability problem, apparently it is slightly more dimensionally stable than BRW, but that is not very reassuring since BRW splits if you look at it wrong.

Yesterday I had an interesting day with the red ironwood mandolin. It sounded somewhat bland and a bit thin in comparison, but the main back mode was 4 & 1/2 semitones above the main top mode. So I stuck a bit of blue tack on the back. Significant improvement in the sound, and when I measured it the main back mode had dropped 1/2 semitone. I added more blue tack and the sound got worse. A bit of head scratching how to make it permanent because internal access is difficult. Anyway I tried a round file stuck through the end pin hole and filed down the middle brace on the back until the main back mode dropped 1/2 semitone. Had the same effect as the blue tack, and is now quite a nice sounding instrument, very clean and clear sounding, but I still prefer the red gum mandolin, but the difference is now very much smaller. Red ironwood is heavier than red gum, but is a lot stiffer and rings almost like rosewood. I had great hopes for it because of the density, but probably won't use it again. It ain't easy to bend.

So what does all this mean? It just confirms that the principles in the Gore/Gilet books can be applied very successfully to flat top mandolins. They are really no different from guitars, just the frequencies are about an octave higher.

[colburge]

Beautiful Mandolin Peter, and lots of interesting and useful information in your posts.

Col

[Semmens Guitars]

I have built a number of guitars with Red Gum. I have always used an epoxy finish to strengthen the timber to stop it from cracking as I do with Jarrah. The pieces I used have been dried for 20 years and had no cracks in it at all. I laminate the sides now but on a few we bent them and they bent really well with no cracking anywhere.

All the guitars sounded great but had a none live back as the timber is quite heavy and dense.

The pieces I have used have looked beautiful under finish but yes some of the figure disappears a little.

[peter.coombe]

Following on from this, I have made 2 more Red Gum mandolins, and they all sounded very similar. So the first Red Gum mandolin was not a fluke. All 3 sold quickly. I had some left over Jarrah from a bed I made around 30 years ago so thought I would give that a go. I made 2 Jarrah mandolins 27 years ago and they are both still going strong, but I stopped using it because although they sounded great, potential customers were complaining about the weight. With a flat top mandolin, the weight is not so much an issue. It is now finished and the sound is great. i had a hard time choosing what I prefer, the Red Gum or the Jarrah mandolin. The sounds are different, but at about the same level. The Jarrah mandolin sounds more like my Ebony mandolin, but cleaner. The Red Gum is a tad sweeter, but does not ring so strongly and is not as loud. In the end I decided I preferred the Jarrah, and after it has settled down I can't put it down. So I now have a worthy Ebony substitute, and am sniffing around for more Jarrah. At least it is far easier to find clean Jarrah than clean Red Gum. I don't like paying for splits, worm holes and resin deposits.

I would be interested in any comments about Jarrah from anyone who has used it. Certainly works with mandolins, but I would be a but concerned about movement in bigger instruments.

Here is the Jarrah mandolin

back.JPG (77.08 KiB) Viewed 33991 times

front.JPG (85.15 KiB) Viewed 33991 times

[nkforster]

I've used jarrah, but it is laminated - veneer. But if you're going for a dead back, this approach may well work for you. There are a few new quirks to using veneer but it does allow you access to beautiful woods you might not otherwise consider because of stability issues.

[Semmens Guitars]

The first pic is some Regum Back and Sides. It Is also Laminated Back and Sides.

I have been using Jarrah in the Guitar Making School but we always pit a layer of epoxy over it to sure up any cracks and make it stable. I also use Jarrah Veneers for Back and Sides. Looks Beautiful!!