Bass/Treble tonal difference

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Bass/Treble tonal difference

Postby Shape note singer » Wed Jan 18, 2012 4:49 pm

Needing some advice here...

There is a marked difference in tone between the Bass and Treble bridges on an HD I bought used.
I've been playing some pieces that switch back and forth between the bridges, and the difference in sound is starting to make me crazy.

Notes on the treble bridge are nice, bright and sweet (3 strings per course).
Notes on the bass bridge are pinched, nasal and brassy (2 strings per course).
All the strings are at least 15 years old, and were quite corroded when I received the instrument.
(Lots of very gentle elbow grease removed the corrosion.)

Would replacing strings make any difference?
If so, would changing to one step lighter gauge for the majority of bass bridge strings improve the balance?

Is this difference in tone a symptom of some other problem? All joints are solid, no cracks, no evidence
that the bridges have shifted position. No buzzing. No rattles anywhere. Floating sound board.
Stays very nicely in tune and has been very stable over the few months I've had it.
It also has two small side bridges on the upper and lower left which sound just fine.

Anyone have advice on how I should approach this problem? ( Besides suggesting a new instrument ? :shock: )
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Re: Bass/Treble tonal difference

Postby mrchips » Wed Jan 18, 2012 8:48 pm

A total restringing wouldn't be out of the question considering the ones on it now were corroded. For a Hd to work right the mass of a string needs to be constant for the entire length of the string. Corosion will change that. Depending on how much steel turned to rust there could now be a difference in the string mass per inch.

Going to a lighter gauge will reduce the tension needed to get the same note. Changing the tension does have some effect on tonal qualities. There is also a tonal difference between a solid steel string, Prosper bronze wounds and brass wounds. The only way you will know if one of these chances the tone to your liking is to try one. I suggest doing only 2 or 3 courses to test things. You could also try moving the Bass bridge up to no more than a half inch from where it now sets too. On many HDs that will make a big difference in tone. There is no sweet spot for the bass bridge like there is for the treb as you only play the left side of the Bass. The only limiting factor is not getting too far from the bridge support under the top.
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Re: Bass/Treble tonal difference

Postby Shape note singer » Thu Jan 19, 2012 12:03 am

Thanks for your help. At least I know I won't cause any harm. :)

Restringing just a few courses to see if it improves things is good advice!
I'll give that a try first. I am reluctant to move the bridge unless there is a clear reason to do so.

Thanks, again!!
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Re: Bass/Treble tonal difference

Postby Shape note singer » Tue Mar 06, 2012 5:25 pm

Well, I have replaced all the strings along the bass bridge, with strings Of identical type and guage. Overall it sounds better, but there is still a tonal difference between notes played on the treble verses the bass bridge.

The next step is to experiment with the bridge placement. If the bridge had ever shifted position, I would guess it would have moved toward the center of the instrument, since the string pressure would push it that way. The bridge has clearly been in its present position for a long time!


Here's my question: Is there a clever way to know where the bracing is located beneath the sound board?????

It is a floating soundboard. I tried lightly tapping along the upper and lower edges from left to right. Some areas sound distinctly hollow, and others less so, but no clear location. There is a very narrow gap along the top and bottom edge of the sound board. I tried sliding a sheet of stiff paper into the gap, thinking it would hit the bracing, but a ledge runs all the way from side to side. Too bad those "stud-finder" tools only work on dry wall!

Any ideas?
Last edited by Shape note singer on Sat Mar 17, 2012 11:22 am, edited 1 time in total.
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Re: Bass/Treble tonal difference

Postby mrchips » Tue Mar 06, 2012 11:31 pm

Many Hds actually use a pair of braces under the bass bridge with the bridge positioned somewhere between them. Others use just one with the bridge either dead on top of it or of to one side or at a slope crossing over the brace.

Some stud finders will actually locate the braces as long as the top is in contact with them. They work by sending out some type of pulse causing the drywall to vibrate and where the drywall is over a stud it wont vibrate as much and the drop in signal indicates the stud. Those may work on a HD as brace dectors. The other type is basically a metal detector that picks up on the screws or nails. Those will NOT work on a HD as the brace inst attached with screws or nails.

Moving the brace will have some effect on the tone but it wont be much. The position of the braces divides the top into roughly 3 separate sections of vibration. There is some cross coupling but most of the tone is due to the shape and size of those sections. The major vibration as far as the bass bridge goes is the area between it and the treb bridge brace. The area to the right of it also plays a part. Stiffing up these areas with braces like inside a guitar will have dramatic effects on the sound but adding some is basically impossible on a finished HD so that's out. Thinning out a top to get less mas will also have pronounced effect on a top. Also not doable on a finished one within reason.

The only choices you have within reason is monkeying around with the bridge placement and different string gauges and materials. Going UP in gauge will require more tension to get the same note could cause structural problems if you go up more than 2 wire sizes. Going DOWN requites less tension for the same note. A tension change will have some effect on tonal quality but it could be so little its not worth doing.

The other approach is to try wounds and/or different materials like bronze or prosper bronze instead of steel. Phosphor bronze solids have a far lower breaking point than steel so dont be surprised if the same gauge bronze as a steel wire will pop before it comes up to tune. With wounds its NOT the overall diameter that determines the breaking point, its the core wire that's usually around .012 to .016 in diameter.

In either case if you start popping wires just go DOWN in size a couple steps and try again. As any string change is completely reversable with no harm that's probally your best choice of action.
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Re: Bass/Treble tonal difference

Postby Shape note singer » Wed Mar 07, 2012 12:22 am

Thanks for the advice. My latest brain storm is trying to use a tiny dental mirror to look through the sound hole, but there's not enough light. Almost think I should be able to see something in there!! Have decided I need one of those miniature led reading lights that I can actually lower inside. Hmmm... I'm sure there's some medical or dental device I could put to good use. :) might even try running a stud finder along the back of the instrument, but I don't expect that to work.

I guess the best approach is:
1- mark the existing position of the bridge.
2-keeping the orientation (slant) of the bridge exactly the same
3- minimally loosen strings/ move bridge 1/8th inch to the right/ tighten and re-tune.
4 -check tonal quality.
5-Sigh ;) and repeat....

until the bridge has been moved a total of a half inch (which is as far as I dare to go, unless I can determine the actual location of the bracing.). I do think I'll try to find some sort of tiny flexible light. If I can see that the interior bracing is in fact further to the right, I'll go as far as directly on top, but no further.

This seems like a reasonable plan, as it can be just as easily undone, as long as I approach it carefully and don't do anything foolish. Wish me luck. Think I'll put if off for a week until I'm sure I've thought it through. :)

Re stringing wasn't as hard as I thought it would be, thanks to those nice YouTube segments! I'm going to do the whole thing once I get this resolved.
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Re: Bass/Treble tonal difference

Postby Shape note singer » Thu Mar 29, 2012 10:37 pm

Just an up-date:

It took me long enough, but the full restringing is complete. Those auxiliary treble strings that go under the main treble bridge were tricky, but replaced those too. It helps to cover the sound board to prevent dents and scratches. (Thin cardboard or page protectors work well.) They don't call it spring steel for nothing!

I'm waiting for the new strings to settle in before making any real judgement here, but in general
the new strings sound REALLY GOOD! Causes me to question the general advice that strings don't need replacing unless they break.

Is there a recommended "string life " or expiration date? :?: What's your opinion?
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Re: Bass/Treble tonal difference

Postby CptCrunchie » Fri Apr 06, 2012 4:47 pm

I'm going to differ slightly with MrChips. I wouldn't move the bridge because there is no real reason to. While it will change tonal quality slightly, it won't change it near enough for what you have described. (A photo of it would also help greatly.) My thought is that the strings gauges may have been changed since it was built, likely for some unknown reason, and they used some where they should have used others. Who knows what has happened to it over the years.

Also, I recommend against buying a package of strings when you don't know how your HD was set up to begin with. Your string selections could turn the sound shrilly and tinny. Instead, I would start over with your string selection, one at a time.

First, you need to find out what your current string tensions are. To do this, pick a string and guess-timate what gauge it is.

Now go to http://wahiduddin.net/calc/calc_guitar_string.htm

Input your selected string's vibrating string length (VSL) and the note it is - like D-3. Start inputing various tensions until the box at the bottom shows around about what you think the string gauge is.

Do this for a few strings from each bridge to get an average tension.

Now that you know your average tension, start inputing your VSL's and notes into the calculator. It will give you the size you should be using for both base and treble. Now you have a more evenly balanced HD, and your tone will be what it was designed to be. Just be fore-warned, you may have a sow's ear or a pot of gold, but without knowing who built it, it's a crap-shoot.

The only place where there may be a slight difference in tension is in the lower base; some HD's are built that way. However, if you have 3 strings per course, I'm thinking the builder likely averaged the tensions.
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Re: Bass/Treble tonal difference

Postby CptCrunchie » Fri Apr 06, 2012 5:07 pm

String life is more complicated than replacing them when they break. How much do you play it? If often, you will likely want the best sound, so often is an option.

More importantly, are your strings coated or non-coated? WHat are they made of?

Mapes INT wire (most suppliers use Mapes) that typically comes in pre-packaged strings are triple tinned and polished, and other than a lemon-oil wiping every now and then, really only need replacing when they break. You can also get stainless steel, but I have very little experience with them. Roslau (used in many pianos and on some HD's) is non-coated and will tarnish, especially if you put your fingers on them. Phosphor-bronze and phosphor-bronze wound strings do tarnish, and should be replaced at regular intervals - again, depending on how much you play such that you'd want the best sound. I recommend twice a year.
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Re: Bass/Treble tonal difference

Postby Rahere » Fri Apr 06, 2012 6:43 pm

Heavier bracing on the bass will in any case darken the tone, and to some extent that's a useful asset as you can pass the dynamic of your playing from treble to bass and back again, using the different voices to develop the texture of the piece - we find lots of traces of this in Welsh music, and some of the hackbrett variations do the same.
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Re: Bass/Treble tonal difference

Postby Verduin » Mon Apr 09, 2012 9:57 am

I have a similar problem, with a 16/15 that I built...most of the notes are crystal clear and the bridges are in the right places, but on a few of my lower range treble strings I am getting a sort of nasal, metallic, kind of "mixed-note"-as-opposed to-pure note sound. The strings I used are from a pre-packaged 16/15 Folkcraft set of coils - I simply cut and used whatever gauge they did on their tuning diagram.
So...changing the gauge in these funny-sounding strings might help in getting a clearer sounding note? Would I go up, or down, in gauge?
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Re: Bass/Treble tonal difference

Postby Shape note singer » Tue Apr 10, 2012 5:48 pm

Well, I realize this is really basic stuff, but would those who have experience with this kindly
give a brief elemntary primer on the subject?

In the most general of terms,
:?: :?: What is the relationship between string length/ string gauge, for a given pitch. :?: :?:


QUESTION 1: Starting from its original position, suppose I move my bass bridge toward the center of my HD thus making the vibrating string length SHORTER.
If the string gauges remain the same, and each course is re-tuned to match the original pitch, the string tension goes:
UP, increasing the the tension across the instrument OR. DOWN, decreasing tension across the instrument?

QUESTION 2: Starting from its original position, suppose I move my bass bridge away from the center of my HD,
thus making the vibrating string length LONGER.
If the string gauges remain the same, and each course is re-tuned to the original pitch, the string tension goes:
UP , increasing the tension across the instrument. OR. DOWN, decreasing the tension across the instrument?

QUESTION 3: If string tension and string length remain constant (theoretically speaking),
changing to a THINNER string gauge would: RAISE the pitch. OR. LOWER the pitch?

QUESTION 4: If string tension and string length remain constant,
changing to a THICKER string gauge would: RAISE the pitch. OR. LOWER the pitch?

QUESTION 5: If pitch and string length remain constant,
changing to a THINNER string gauge would: REDUCE tension. OR. INCREASE tension?

QUESTION 6: If pitch and string length remain constant,
changing to a THICKER string gauge would. REDUCE tension. OR. INCREASE tension?

QUESTION 7: If a particular string snaps when you bring it up to desired pitch, you should try switching to a string:
One gauge THINNER OR. One gauge THICKER ?


Well, I guess we have a basic musical physics quiz here. Assuming everyone will give identical answers... :D
Thanks !
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