Red gum
- peter.coombe
- Blackwood
- Posts: 670
- Joined: Fri Oct 15, 2010 2:52 pm
- Location: Bega, NSW
- Contact:
Red gum
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.
Peter Coombe - mandolin, mandola and guitar maker
http://www.petercoombe.com
http://www.petercoombe.com
Re: Red gum
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.
Martin
-
- Blackwood
- Posts: 777
- Joined: Tue Aug 27, 2013 6:36 pm
- Location: North East Victoria
Re: Red gum
My experience with the sound absorbtion qualities of red gum is that I wouldn't use it for anything much,especially an instrument.-Ross
"Everything I say on the topic is based solely upon inexperience and assumption!"
- peter.coombe
- Blackwood
- Posts: 670
- Joined: Fri Oct 15, 2010 2:52 pm
- Location: Bega, NSW
- Contact:
Re: Red gum
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.
Peter Coombe - mandolin, mandola and guitar maker
http://www.petercoombe.com
http://www.petercoombe.com
Re: Red gum
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.
Martin
- peter.coombe
- Blackwood
- Posts: 670
- Joined: Fri Oct 15, 2010 2:52 pm
- Location: Bega, NSW
- Contact:
Re: Red gum
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.
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.
Peter Coombe - mandolin, mandola and guitar maker
http://www.petercoombe.com
http://www.petercoombe.com
- Trevor Gore
- Blackwood
- Posts: 1531
- Joined: Mon Jun 20, 2011 8:11 pm
Re: Red gum
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.
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.
Fine classical and steel string guitars
Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.
Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.
- peter.coombe
- Blackwood
- Posts: 670
- Joined: Fri Oct 15, 2010 2:52 pm
- Location: Bega, NSW
- Contact:
Re: Red gum
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 - mandolin, mandola and guitar maker
http://www.petercoombe.com
http://www.petercoombe.com
- peter.coombe
- Blackwood
- Posts: 670
- Joined: Fri Oct 15, 2010 2:52 pm
- Location: Bega, NSW
- Contact:
Re: Red gum
Not too shabby under varnish. I am happy with this. Will continue, more later.
Peter Coombe - mandolin, mandola and guitar maker
http://www.petercoombe.com
http://www.petercoombe.com
- Mark McLean
- Blackwood
- Posts: 893
- Joined: Thu Apr 10, 2008 2:03 pm
- Location: Sydney
Re: Red gum
That does have a lot of life to it!
If it sounds as good as it looks.............
This is tantalizing.
If it sounds as good as it looks.............
This is tantalizing.
- Trevor Gore
- Blackwood
- Posts: 1531
- Joined: Mon Jun 20, 2011 8:11 pm
Re: Red gum
Yep, that looks fine. Gerard would have been using nitro over a grain filler, which may well look different from an (oil?) varnish.
Fine classical and steel string guitars
Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.
Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.
- peter.coombe
- Blackwood
- Posts: 670
- Joined: Fri Oct 15, 2010 2:52 pm
- Location: Bega, NSW
- Contact:
Re: Red gum
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.
Peter Coombe - mandolin, mandola and guitar maker
http://www.petercoombe.com
http://www.petercoombe.com
Re: Red gum
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.
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.
Bruce Mc.
- WJ Guitars
- Blackwood
- Posts: 183
- Joined: Thu Jan 26, 2017 4:28 pm
- Location: Sutherland NSW
- Contact:
Re: Red gum
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
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
- Blackwood
- Posts: 670
- Joined: Fri Oct 15, 2010 2:52 pm
- Location: Bega, NSW
- Contact:
Re: Red gum
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.
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.
Peter Coombe - mandolin, mandola and guitar maker
http://www.petercoombe.com
http://www.petercoombe.com
-
- Blackwood
- Posts: 777
- Joined: Tue Aug 27, 2013 6:36 pm
- Location: North East Victoria
Re: Red gum
..a custom build for a bloke with a beer gut and a skinny wife?-Rback inverted to concave
"Everything I say on the topic is based solely upon inexperience and assumption!"
Who is online
Users browsing this forum: Andos and 40 guests