I've been wondering recently about which factors in the making of a CBG contribute to it having good sustain.
My top guesses are:
- The rigidity of the soundboard
- The rigidity of the neck
- The material of the nut and bridge (and also how accurately the slots are cut)
- How the strings are anchored to the guitar
Of my recent builds, this one has the best sustain:
So, to go through the list,
- The soundboard is sapele (African mahogany-like hardwood), with bracing inside and a plate under the bridge, it feels extremely solid to the touch
- The neck is sapele, with an oak fretboard, this was the last guitar I made without my current heel design, and there is a recess in the part of the neck running through the box to accommodate the lid and bracing/ The neck is secured by a total of 5 wood screws through the bottom of the box
- The nut is bone, and the bridge is a thin strip of bone on top of a shaped piece of oak. The bridge is sanded to a point so the strings rest on a surface no larger than 1mm. The nut slots are sloped downwards towards the headstock, and again the string contacts only a very small area
- The strings are anchored through a piece of sapele, passing through metal bike spoke nipples which are there for grounding. The tailpiece is fixed with 4 wood screws (to the box, not the neck)
My thinking is that the rigidity of the soundboard is probably the biggest factor in the sustain, as all of the other aspects are effectively the same as on all my other builds. I found this one to be very quiet acoustically, so on my other home made box builds (using spruce, a much lighter wood) I was a little more sparing with the bracing. They were far louder, by didn't have quite as much sustain.
If anyone has any of their own experiences or knowledge to share about sustain, I'd love to hear them!
Let the discussion commence!
Replies
you can't really compare solid body sustain and hollow body sustain.
Build your acoustic guitars like a factory acoustic guitars. Build very light, as little bracing and glue as possible sand the sound board to the thickness you want not what the box gives you. Don't let the neck touch the sound board. Make sure the box is sealed.
Good answers and a good review for me.
Interesting topic. My latest build using stiff koa wood for the top is not real loud but has great sustain. The bamboo body is very heavy with a bolt on neck. I think I understand why a little better now.
Fazool, from the Acoustic Guitar Forum who has an engineering background had this to say about sustain…
“It's actually an extremely complex engineering topic that can be simplified into a very basic concept. That means it can be summarized easily, but not quantified easily.
Sustain is the ability to keep vibrating. The only one single thing that stops a vibrating body (assuming no mass and no friction) is the damping of the system.
So, sustain is achieved by eliminating vibration damping.
Think of damping as analogous to "friction" for vibration.
Damping is to vibration as friction is to sliding
If you can minimize damping, you will maximize sustain.
Typically damping effects come from (here's the complex part) structural shapes, inherent material properties, mechanical interfaces (neck joints etc.)
The single most important thing is the inherent damping of the material. For example, if you made a guitar body out of nerf sponge rubber, it would absorb and dampen all the vibration and you would get no sustain.
If you have a very hard material with no damping, you would get significant sustain.
Large masses also contribute to sustain because they are not easily "moved" by the vibrating forces. The string vibration isn't lost trying to accelerate a huge mass.
So, the main things that contribute to sustain are these:
1. Material's inherent damping (hard wood vs. soft foam)
2. Mechanical interfaces (neck joints, saddle/bridge)
3. Mass (weight at anchor points)
This assumes you don't have extraneous flaws like loose nut slots, buzzing, etc that cause mechanical interference.
The other issue is the neck joint stiffness. This will absolutely affect sustain by introducing damping at a non-solid joint, however the joint solidity will have no effect on the natural frequency. Again, it may appear related but it is the effect and not the cause.”
Hi All,
I like this information. I think it needs to be further developed into a set of "best practice guidelines".
Here's my first attempt...
Item 1, Material's inherent damping (hard wood vs. soft foam):
This makes sense, as I have noticed better sustain in hardwood necks verses softwood necks. I have also seen better sustain in laminated necks with a solid hardwood core. Cherry is a relatively soft hardwood compared to beech wood, and in the necks I've made with the solid beech wood core, the sustain is better and the sound (IMHO) is "sweeter" (sounds better) as compared to my laminated necks made just out of cherry slats.
I think this also applies to bridge and nut materials -- the harder the better.
Item 2, Mechanical interface between neck & body:
I assume you want a tight fit and as wide an area of contact as is possible. I wonder if this means a permanent, wide spread glue joint is better than a "spotty" joint secured by a few wood screws or similar fasteners? I guess that if the screws are properly spaced and the two pieces of wood fit well together, there shouldn't be that much difference. Perhaps doing both (glue and secure with fasteners) would be best as the shank of the faster should carry the vibrations of the neck to the sound box (or neck extension) across the interface boundary better. Can anyone comment on their experiences with this question?
I also assume you'd get better sustain if the materials you are joining are the same wood or similar hardness. So, maybe joining a hardwood neck to a softwood sound box might not provide as much sustain as if both were made of hardwood.
Also, minimizing the number of joints (mechanical interfaces) makes sense.
Item 2, Mechanical interface between Saddle/Bridge:
This interface includes a string-to-saddle interface, then a saddle-to-bridge interface, and a bridge-to-soundboard interface (and maybe soundboard-to-air) interface. It seems obvious to me that we should try to minimize the number of mechanical interfaces to help improve sustain. So, maybe a single piece bridge would be better than a two piece bridge and saddle. Also, adding a shim under the bridge to raise the string action (something I often have done) might not be such a good idea from a best possible sustain point of view.
Item 3, Mass (weight at anchor points):
I'm not quite sure I know what this means. Would heavier tuning machines and a heavier tail-piece anchored in heavier (denser, harder wood) improve sustain? Perhaps, but I don't have any experience to backup the idea. Maybe some experiments are in order. Can anyone recommend some heavy guitar tuners? Maybe a set of bass tuners in one instrument verses a standard set of guitar tuners in two other wise identical instruments. Then, maybe using an even harder/denser wood for the headstock and as the underlying block of wood that backs up the tail-side of the sound box (into which a heavier duty tail piece is anchored). Anyone have experience with this?
-Rand.
That's great Tom, thanks for posting it!
My fist build is a solid body. The type of wood you use there will effect the sustain as well. I used pine. Lots of twang but not so good on sustain.
Well.Thanks for the responses. This makes total sense to me now. My spruce top builds have exactly the same soundhole configuration but are far louder. This must be because of the lighter wood and less bracing. Don't gt me wrong, the sustain is still OK, just much longer on the sapele one.
Next project might have to be a solidbody... although I may need to buy a router.
Thanks again!
It's all energy man. It can't just be created out of nothing. Some (a whole bunch actually) is stored in the string tension, but you don't get that back until you break or loosen the string.
Otherwise it's only the kinetic energy you impart to the string to get it moving - this is transferred into the bridge, the top, the air in and around the top... And it leaves the string. There are elec/magnetic devices you can use to 'bow' the string and contribute more energy, but otherwise it's going to slow and stop, and the sooner the top absorbs energy from the string (=volume) the sooner the string will come to rest.
This is the whole idea behind the wiz bang four grand carbon fibre resos, that the stiffest body possible will steal the least energy from the cone
The guitar and all lutes are quite inefficient in terms of the amount of music they can make from a given amount of energy, certainly compared to violins and the like, imagine if you put a post in to get the back singing as well, the note would decay almost immediately
Nice looking build there.
Sustain and acoustic volume are mutually exclusive. The best sustain will be a solid body. The best acoustic body will be thin topped w/ light bracing. I tend to make mine with a thru neck and like the thicker tops for amplified pickups because it gives much better sustain, and is easier for me to make.
On the one you have pictured, bigger sound hole(s) will let out more acoustic volume.
Many more experienced builders will weigh in for you.