Simple Modifications To Acoustic Guitars

BigBear
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Wed Mar 06, 2013 7:26 pm

Dermot- I'm in full agreement with the other posters here. With an electric guitar, like my Les Paul, there are thousands of after market products I can slap on if I wanted to. And there wil be a noticeable sound difference. Change the pick-ups for example and you can go from a mellow bluesy sound to screaming hard rock with a "hot" pickup.

But acoustics make their sounds because of the way they are built. Other than strings what is really to change? An ivory nut or saddle versus Tusq? Tuners maybe. Every acoustic guitar has a sound, good or bad, that the builder put into it. It's what makes each guitar unique. Like Dennis said let Bob Taylor or Chris Martin mess with the sound and if we like it we'll buy it. But enormous research and experimentation has gone into those their various models and I really doubt I can change them for the better.

I have tried the coated D'Addarios you mention. I love D'Addarios in general and these were pretty good strings but they aren't nearly as bright as Elixir Nano PB and the Elixir seem to wear much better. Maybe a little tougher coating. If I put on non-coated strings I always use D'Addario PB and have for years.

Cheers my friend!! :cheer:


cosmicmechanic
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Wed Mar 06, 2013 9:05 pm

neverfoundthetime wrote:
... I'd rather drop it from off my shoulder strap like I did with my heavy 12 string the other day (first time in 25 years)! Damned thing came loose at the button hole and dropped on the bottom edge of the guitar ...
Chris, run, don't walk, to the nearest beer store ... I heartily endorse the following method, works like a charm (hic !) :blink:



wrench
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Wed Mar 06, 2013 9:15 pm

thereshopeyet wrote:
Wrench Wrote:
I consider the O-Port a troubleshooting tool at best. An acoustic guitar can only benefit from it if there is something causing an imbalance in the tonal range. I find this to be the case more because of environmental factors than issues with the instrument. By the way, a cylinder made from posterboard will do the same thing as the O-Port, with the added advantage that you don't mind cutting it, and its mass is lower than the O-Port. These devices alter the Helmholtz frequency of your guitar's body.

I won't bother to go into the science here, but a good guitar in a matching acoustic environment does not need an O-Port.
Thanks for your interesting comments regarding the O Port.
If you have any further suggestions or links regarding the science and matching acoustic environments please post :ohmy:

Wrench Wrote:
Fret leveling and crowning, a well-fitted bone or TUSQ saddle, a nut with correctly profiled string slots, and proper action settings are all simple, and very effective, modifications
Thanks for the heads up on these fundamental adjustments.
It's taking me a long time to understand the mechanics of the acoustic guitar but am getting there slowly.
I was looking at saddle adjustments last week. I don't know the difference in terms of sound with respect to bone or TUSQ
other than both materials get good reviews.

Dermot
Dermot, the natural, or resonant, sound of a guitar is the result of a huge number of variables, but the most fundamental among them are the natural frequencies of the main air, the top, and the back of the guitar. My own research adds one more - the neck. This gets dicey because the neck, the top, and the main air frequencies are pretty close to each other in many guitars, mainly dreadnoughts with a one-piece mahogany necks. The main air frequency is also known as the Helmholtz Frequency, and is essentially the natural frequency of the air inside the guitar body. The dicey part comes in because these frequencies can change slightly because of humidity or anything else that changes the mass of the top or back. When these frequencies become mathematically related, the guitar will sound funky. Perhaps you've noticed a guitar that sems to have a beat or undulation in its decay after an open strum, or a wolf note, where some note, usually a low G, is very loud but has no sustain. These guitars need a tuning of the tops and backs, which I just love doing. It's very simple and very complicated all at the same time. It really isn't very difficult though, and if you want to experiment a little, take some coins of various sizes and tape them one at a time to your bridge and see if you can hear a difference.

By the way, I see many more of these types of problems in dreadnoughts. In small waisted guitars, the main air frequency is higher, and therefore further from the top's frequency. Before going any further, I will say you can make a substantial difference in a guitar's sound with a shockingly small mass change, sometimes as small as just a couple of grams. A minor change like a set of dressy bridge pins can alter a guitar's tone somewhat, but not because of the material, it's because of the mass change, which causes a change in natural frequency. If the new frequency gets related to the others, the sound will change, and if it does not relate, there will be no difference in sound. This is why the reports of tonal changes from bridge pins are so inconsistent.

Wiley mentioned he maybe picked up some sustain by using the O-Port. Again, it was probably the mass increase that led to this. Sustain is the result of impedence matching in the transfer of energy from the string to the saddle. If there is low sustain, impedences are closely matched. For long sustain, impedences must be mis-matched, resulting in more time required to transfer the energy.

Whenever I hear a guitar that sounds bad, I play it in a different room or outdoors to eliminate the possibility of furniture absorbing certain frequencies or voicing its own resonances through the guitar. I had an extreme case of this in my own house that caused me to nearly dispose of a perfectly good guitar until I realized it was sitting in a stand untouched - and it was rattling! All by itself. And I couldn't hear it make a low G note. Turned out to be an end table in the room, so I always check the environment. I'll even do a spectrum analysis of the room without the guitar in it just to see what the natural acoustics are. As I found out, they can be devastating to acoustic guitar sound quality.

I spent most of the last three years analyzing guitar sound and learned quite a bit about them along the way. To read more about the physics of acoustic guitars, I recommend Googling Alan Carruth. He was doing spectrum analysis on guitars long before I got into it, and has written a few very good papers. He is an active, current, and teaching luthier in New England.

Bone and TUSQ saddles both sound good, as they have identical densities and sonic properties below 1KHz, but TUSQ also can pass some higher overtones that bone doesn't. This makes TUSQ sound a little brighter. And I like the EXP strings, too. They sound great, and seem to have a softer or smoother feel to them. I think they squeak a little less than their uncoated counterparts.


wiley
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Thu Mar 07, 2013 8:57 am



wrench
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Thu Mar 07, 2013 8:58 pm

Wiley, changing the saddle gives the biggest bang for the buck. I have research that shows high quality nuts will improve tone and harmonics to the degree that I think it's woth doing. Many experts will disagree with this on the premise that the nut becomes ineffective when fretting. I do not agree with this. Results with pins vary wildly because of the effect of mass change. The other physical properties of pin material don't affect tone, at least not that I could detect.

Of the materials you listed, I'm afraid I never tested ivory, so I can't comment. Ebony, or any other wood, will have a natural frequency too low to work well throughout the entire frequency range of the guitar. This will soften the tone of your guitar. Hard plastic and micarta have the right frequency response, but lack the density of TUSQ and bone. This means they will sound OK, but will limit the volume of the instrument. I also find these materials stifle harmonics quite a bit. From a workability standpoint I prefer bone over TUSQ. Tusq is brittle, and it contains glass, so it is brutal to steel cutting tools. It wipes out anything sharp nearly instantly. I use abrasives mostly on TUSQ, and use steel tools as little as possible. Bone, on the other hand, is very good to work with, except for the odor. I never used the dried bone you mentioned, but of the other two, I can see no difference in either sound or workability.

So I'm generally using bone or TUSQ for saddles, and which one I use depends on what the player wants from the saddle change. On Seagulls, bone flattens the tone a lot more than I expected. It seems to me that most guitars sound best with the material with which they were originally equipped (except for plastic). A guitar that sounds somewhat bright with plastic or bone gets too harsh with TUSQ. If you replace a plastic or micarta saddle, you will be surely notice the increase in volume. Spectrograms reveal the sound levels are nearly double that of plastic.

I don't consider the guitar's tonewoods when selecting saddle material. I do, however, consider the guitar's natural voicing through spectrum analysis. If the instrument has a lot of high quality high order overtones, then TUSQ's extended frequency range will bring out the bright best in it. If you want to tone it down a little, bone will attenuate those high order overtones. If the guitar's overtones get unruly, I'd stick with bone. An "unruly" overtone usually comes from something wrong in the instrument. It amazes me how many crappy saddle slots there are in the world, and they can give rise to some very bad sounds. I think Yamaha guitars are generally a great value, but they are the source of most of these crappy slots. A Yamaha with a re-machined saddle slot and a well-fit bone saddle sounds dramatically better than it did originally. Spectrum analysis is valuable for determining if higher order overtones are indeed overtones or the sound of a defect.

For instruments of the caliber you listed, I would get a stack of saddle blanks and start off with bone in the Gibby and TUSQ in the Tacoma. YMMV. And make sure the bottom of the saddle is square and flat, the bottom of the slot is flat, and the saddle fits the slot tightly enough that it cannot lean. I'd REALLY like to hear that Tacoma some day.


wiley
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Thu Mar 07, 2013 10:22 pm



thereshopeyet
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Thu Mar 07, 2013 11:02 pm

Wrench Wrote:
For long sustain, impedences must be mis-matched, resulting in more time required to transfer the energy.
Thanks for taking the time and touching on you findings.

In electrical cable, (RF cable) the characteristic impedance must match the load impedance to maximize the transferred signal.
If impedance mismatching occurs then signal loss occurs due to signal reflections going back along the cable interfering with the original signal.

I don't really know much about the materials and their responses to vibration and conversion of the material vibration to audible frequencies but
I assume it's a similar scenario to the one you mention where the two materials have characteristics that resonate differently resulting in sustain due to material differences such as flexibility, density etc, which I suppose might be referred to as impedance as it's a combination of different forms of resistance.

It does reflect that each instruments unique properties are as unique as the tree that was used to build it.
The addition of mass or changes to the guitar materials must have a knock on effect whether audible or not.
It certainly make things interesting.

I can understand now more than ever that a guitars just what it's been designed to sound like, anything else
added or taken away is just an experiment that could totally change it.

it's a bit like art, it's down to the eye of the beholder .... the ear of the beholder.... I suppose !

Thanks again Wrench

Dermot


thereshopeyet
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Fri Mar 08, 2013 1:38 pm

Some bridge pins have the slot cut to the pin skirt
and some slots are cut through the skirt.

Is this important or is it just when the slot stops at the skirt of the pin
it means there's more pin available on top to aid pin removal.

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wrench
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Fri Mar 08, 2013 7:30 pm

The slots cut through the skirt allow more room for the string, especially the larger strings, often allowing the pin to enter the hole farther. My personal preference for pins is tapering the hole to match the pin taper, and not using the slot at all. I slot the bridge for the string to pass through. What I get out of this is very easy removal of the pin at string change, less chewing of the bridgeplate by the string ball, and maximized break angle of the string over the back side of the saddle.

You are spot on with impedence, but in a guitar you want mis-match. Matched impedence would cause the energy to transfer too quickly resulting in loud notes of short sustain. In all honesty, impedence is one of those properties that eludes a clear scientific explanation by me and many other people who study the physics of acoustic guitars. Intonation would be another, which to understand thoroughly requires a working knowledge of string theory, and lots, lots, lots, lots of math.

In mechanical engineering, resonance is something to avoid. In electrical engineering, matched impedence is something to be sought, and an acoustic guitar makes its living doing the exact opposite of both!

Wiley - the anticipation of that Tacoma must be maddening. I know it's making me edgy! :blink:


thereshopeyet
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Sat Mar 09, 2013 9:00 am

Wrench

That's an interesting method, slotting the bridge, I think I can understand why the pin will remove easier
because it's not jammed against the string.

I assume then you would need a different slot width for each string ?

I did notice that some bridge pins are supplied with no slot, so they probably go into a slotted bridge ?
The purpose of the skirt then is?

I've been looking at intonation of an acoustic guitar again too.
When I think I'm beginning to understand how to carve a saddle from a blank something always comes up that
throws my understanding of the process. Basically each string needs of a certain length to be in tune.
From what I've picked up there's an element of trial and error and experience of the trial and error involved to get it right.


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