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Saddle compensation for concert uke (Read 12245 times)
Likeke
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Saddle compensation for concert uke
Mar 26th, 2008 at 12:59pm
 
For the tenor the front of the saddle should be 17" plus 3/32".  Is the compensation for the concert uke the same, ie; 15" plus 3/32"?
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Don_Orgeman
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Re: Saddle compensation for concert uke
Reply #1 - Mar 27th, 2008 at 4:36am
 
Likeke:

The compensation will probably be a little less, but remember that the amount of compensation is an average for all of the strings, and as such is not accurate for each string.

David Hurd (Ukuleles By Kawika) has an interesting article on his web site that investigates compensation.  The article can be found at:

www.ukuleles.com/technology/compensate.html

I found your question interesting because I have just completed building a compensation jig similar to the one in the article, except I plan to attach my fretted tenor fingerboard (except for 1st and 11th frets) to the jig with carpet tape and building a 4 piece mini-bridge that I can slide forward or back to get an accurate measurement for each string.  I am building my uke for low G tuning using Aquila strings.

If you look at David's measurements you will notice that the C strings show a larger compensation than the other strings (I am presuming he was testing a high G set of strings).  If this measurement is correct, it might indicate that a high G saddle should have the high point at the neck side of the saddle for all of the strings except the C string, and the C string should have the high point at the tail side of the saddle to get a more accurate compensation.

I will let you know what I find when I am done (but it may be a while because I am waiting for Peterson to release version 2 of StroboSoft Deluxe).  I also have a set of Aquila high G tenor strings in my building kit, so I will probably test the high G set as well to see what I get.

Don
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Re: Saddle compensation for concert uke
Reply #2 - Mar 31st, 2008 at 10:54am
 
Hi Richard,
Good question, this brings up an important point.  As for most of building the answer is: it depends.  To feel confident in what you're doing, it is best to take the time to understand what you're trying to do.  What is compensation and why would it change?  

Here are some good articles on what String Compensation is:
http://www.classicalandflamencoguitars.com/Compensation4.htm
"The action can play a major part in how well a guitar plays in tune. This is mainly to do with the fact that the strings increase in tension as they are depressed onto the fretboard and between the frets. The greater the distance from the string to the fretboard, the greater the increase in tension. Keep in mind that the fret positions are based on a "perfect" model which does not include any increase in tension of the string."

"Again there are many factors that will come into play here, such as the end effects on the strings (end effect is caused by string stiffness, which makes the effective vibrating length of a string shorter than its actual measured length), inharmonicity (the successively greater sharpening of successive overtones caused by string stiffness) and the elasticity of the string and the increase in tension caused by depressing the string to the fingerboard."

http://www.windworld.com//tools/fretnot2.htm
"When you press the string of a fretted instrument down behind the fret, the string is stretched slightly in the process. This increases tension on the string and causes the pitch go a little sharp of what it would otherwise be. If you ignore this and make your fret placements based strictly on the mathematics of string lengths and scale factors, the fretted pitches will all be a little sharp of the ideal. "

http://members.shaw.ca/wilkatguitars/git_tips10.htm
"1.) The length of the instrument's strings will be greater than the actual scale length since the string must be raised above the fingerboard to avoid contact, and this normally requires the strings to be at a slight angle to the fingerboard as the string rises from the nut up to the top of the bridge.
2.) When you fret a note the string angle is increased, as the string is depressed, and the string is also slightly stretched. Naturally the higher up the fingerboard you go, the greater the clearance, and the greater the string string stretches by being depressed. "


As Don mentions Kawika Hurd explains how he determines the compensation for his instrument/string combo:
http://www.ukuleles.com/Technology/compensate.html


Some online scale calculators that give compensation AVERAGES:
http://www.stewmac.com/FretCalculator
http://www.13thfret.com/fretcalc.html

Don't let it overwhelm you, think of it as something you can fine-tune with each successive instrument.
Happy building!,
-Asa
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Don_Orgeman
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Re: Saddle compensation for concert uke
Reply #3 - Apr 8th, 2008 at 1:09pm
 
Likeke & Asa:

Well, I got done with testing the compensation for my tenor uke, and it has left me asking questions.  Here's what I did:

I built a 3" wide neck section with a scarf joint and made a peghead on one end.  After thinning the peghead to 9/16 inch, I mounted my tuning machines, and attached my Hana Lima pre-slotted fingerboard using double sided tape.  A little double sided tape on the nut and the base was done.  I cut 4 grooves in the bottom of a 1" by 3" piece of MDF to act as a string anchor point and mounted it about 2 1/2 inches behind the 17 inch scale length line with drywall screws.  I made a sliding bridge from another 1" by 3" piece of MDF, cut a saddle slot 1/4 from one edge, installed a corian bridge, and adjusted the jig to have the suggested 3/32 action.  I then slid the sliding bridge out and cut it into 4 pieces so I could adjiust each string individually.  The 3 little blocks are just ther to keep the strings in the right place.  Here are a couple of pictures of the jig:


...


...



Having completed the jig, I strung it up with a set of Aquila hig G strings and adjusted them in so they were pretty stable.  For tuning I used my Intelli IMT-500 tuner.  Here's the results I got:

A String      17 4/64 inches
E String      17 6/64 inches
G String     17 3/64 inches
C String     17 9/64 inches

This would indicate that a saddle at 90 degrees to the strings would be appropriate for a High G tenor uke, and some compensation can be accomplished by moving the high point to the front or back of the saddle to be more accurate if desired.

So, now I removed the High G string and installed a low G string instead.  Here is what I got:

Low G String      17 5/64 inch.

This would indicate that a square saddle would be even more apporpriate on a low G tenor uke.  I believe it is customary to use a slanted saddle when building a low G ukulele.  Are my measurements wrong?  What is going on?  I had hoped to perform these tests using StroboSoft's new version 2, but they haven't released the software yet, so I used my chromatic tuner for these tests, and some results might not be totally accurate.

PLEASE HELP!!!!!!



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Re: Saddle compensation for concert uke
Reply #4 - Apr 8th, 2008 at 1:58pm
 
Don thats cool!  Here's what I found.  I used the 17 and 3/32 additional setback to the front of the saddle slot on the tenor and slanted the saddle with no additional compensation.  For the low G tenor I used the angled saddle and placed it 17 3/32 to the center of the saddle slot. I had to file the saddle so that the low G and C strings were coming off the back edge of the saddle to get it properly intonated.
On my concert uke that I just finished I have the action set real low and used smaller frets.  I found it to be intonated just right with 15 and 1/16 compensation to the front of the saddle slot.  No messing with the saddle.  Seems less compensation is needed the lower the action.  I don't know how to explain your results nor do I know how to explain mine???  Good on you for trying to analyze this scientifically. ???
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Re: Saddle compensation for concert uke
Reply #5 - Apr 9th, 2008 at 4:03am
 
Hey Don,

That is really cool, the jig that you made.
Does that mean that when the saddle is square ( that is perpendicular ) to the strings, it is off at some of the strings?
I am a little confused ??? 
What are you testing at the different scale legnths?
Are you testing to get the optimal sound?
Do you think you could explain a little more?

Thanks
Bob 8)
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Re: Saddle compensation for concert uke
Reply #6 - Apr 9th, 2008 at 8:59am
 
Bob:

The jig is designed to test the compensation length needed for each string for a tenor uke with 17 inch scale length.  What you are testing is getting the open string note and the 12th fret note to be exactly equal but 1 octive apart.  If you place the saddle at exactly 17 inches the fretted note will most likely be sharp because of the stretching of the string in pushing it down to the fret.  So, moving the saddle away from the peghead lowers the fretted note and brings the open and fretted note closer together.  Its a matter of trial and error until you find the point where they match.  As you see from other comments, there are so many variables in type of strings and action height that all you can do is get a close approximation for the uke you are building.

This doesn't have anything to do with sound quality, just where the saddle should be located and should it be perpendicular to the strings or at a slight slant.  Asa did a great job of answering this post earlier -- reread his comments (and look at the links he provided) and they will help clear this up for you.  If not, send me an email or private note and I'll try to explain it more clearly.

Don
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Re: Saddle compensation for concert uke
Reply #7 - Apr 10th, 2008 at 5:40pm
 
Don (or anybody):
How perfect does the pitch have to be at the twelfth fret to consider it good intonation? My Kala tenor with aquila strings and low G is : G  +10
                                             C  +10
                                             E   0
                                              A   0

I will be stringing mine up tomorrow so I should have some idea where I stand by next week.

Bob
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Re: Saddle compensation for concert uke
Reply #8 - Apr 11th, 2008 at 9:32am
 
Bob:

Thanks for your uke info.

I have been playing around with this because I have decided to go with a Low G tenor uke on my current build and was unsure as to whether to use a slanted or square saddle.  The test was to try to answer that question with a simple test.

You are right, it probably doesn't make any real difference (square or slanted) as long as you are accurate in the bridge placement.  Your factory built uke with a square saddle is in good tune even though you switched to a low g string.  I have to admit that the jig I built is the result of being a retired engineer with time on my hands.

Don
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