Replies to This Discussion

Permalink Reply by Jim Woods on May 6, 2014 at 7:25am

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.

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Permalink Reply by The Phrygian Kid on May 6, 2014 at 8:55am

I concur.

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

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Permalink Reply by Richey Kay on May 6, 2014 at 7:58pm

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!

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Permalink Reply by Cause the Blue rat on May 6, 2014 at 11:27pm

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.

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Permalink Reply by Primitive Acoustics on May 7, 2014 at 1:27pm

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.”

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Permalink Reply by Richey Kay on May 10, 2014 at 8:08pm

That's great Tom, thanks for posting it!

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Permalink Reply by Rand Moore on May 11, 2014 at 8:54pm

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.

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Permalink Reply by Uncle John on May 11, 2014 at 10:33am

Good answers and a good review for me.

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Permalink Reply by The Phrygian Kid on May 12, 2014 at 3:51pm

Sorry, you have it completely arse about IMHO. See the first two answers here, they're from the guys who've built a substantial volume of quality instruments. The solid body built from the less resonant 'dead' wood will in fact sustain BETTER than the other, not worse. Try to understand, the resonance/volume and the sustain are tradeoffs. Ps rand. There is therefore no 'best practice'.. It's all swings and roundabouts mate.

Cheap Chinese strings are undoubtedly crap, but of the quality brands daddario, dean markley, etc etc just grabs the ones that's priced right, they're all about equally good.

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Permalink Reply by Jim_N on May 13, 2014 at 1:24pm

"The solid body built from the less resonant 'dead' wood will in fact sustain BETTER than the other, not worse." ~The Phrygian Kid

I'm a believer. Following Fender's and others' leads using softwood solid bodies, I've built several using pine/redwood/etc. (occasionally in combination), and I've been very happy with the sustain.

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Permalink Reply by jim on May 13, 2014 at 3:25pm

I believe that would depend more on the specific piece of wood and how the guitar is made.  BINGO!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

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Permalink Reply by RTZGUITARS on May 15, 2014 at 1:25pm

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.  

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