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String height above the soundboard
http://www-.luthiersforum.com/forum/viewtopic.php?f=10128&t=49006		 Page 1 of 1
Author:  bcombs510 [ Wed Feb 15, 2017 9:46 am ]
Post subject:  String height above the soundboard
Hello,

I'm curious about the standard string height above the soundboard on a tenor uke. I went into the local guitar store and they heights were all over the place. I'm targeting 2.5-3mm at the 12th, but what should the fretboard thickness, bridge and saddle height be in order to get the "optimal" string height above the soundboard.

The reason I'm asking is the player is asking for maximum volume. If I understand string height above the soundboard correctly, too low can affect the volume / projection of the instrument. True? and if so, what's the magic number for a tenor? [:Y:]

This is the closest I've found on the forum:
viewtopic.php?f=10128&t=40808&hilit=string+height

Thanks!
Brad
Author:  Aaron O [ Fri Feb 17, 2017 3:58 am ]
Post subject:  Re: String height above the soundboard
I would imagine string height above the top is a result of other measurements such as Bridge thickness (1/4") & Fretboard thickness (.200") as opposed to a target number.
Author:  profchris [ Fri Feb 17, 2017 6:21 am ]
Post subject:  Re: String height above the soundboard
10-12mm is about right. Less than 6mm is likely to reduce volume, much more than 12mm can lead to soundboard distortion.

If you want maximum volume then building as light as possible is more important than bridge height. But light build and bracing means keeping your bridge height under 12mm to avoid distortion.

I find I can get a lot of projection (= perceived increase in volume) by putting an aggressive curve to the back. But in the end it's a uke, it has a small soundboard, so physics only lets you go so far.

Fretboard thickness doesn't matter much, because you adjust your neck angle to compensate, so decide on saddle height and work the geometry back from there.

If you're building with the neck and top in a dead flat line then the calculations are quite easy. 2.5mm at the 12th = 5mm at the bridge, so if you want 10mm string height at the saddle then the calculations are:

Thickness of fretboard + frets at 12th = 5mm (that's quite a chunky fretboard, so you could choose to angle the neck back to allow a thinner fretboard)

Saddle + bridge = 10mm
Saddle above bridge = 2mm
Bridge thickness =8 mm
Author:  bcombs510 [ Fri Feb 17, 2017 10:52 am ]
Post subject:  Re: String height above the soundboard
profchris wrote:
10-12mm is about right. Less than 6mm is likely to reduce volume, much more than 12mm can lead to soundboard distortion.

If you want maximum volume then building as light as possible is more important than bridge height. But light build and bracing means keeping your bridge height under 12mm to avoid distortion.

I find I can get a lot of projection (= perceived increase in volume) by putting an aggressive curve to the back. But in the end it's a uke, it has a small soundboard, so physics only lets you go so far.

Fretboard thickness doesn't matter much, because you adjust your neck angle to compensate, so decide on saddle height and work the geometry back from there.

If you're building with the neck and top in a dead flat line then the calculations are quite easy. 2.5mm at the 12th = 5mm at the bridge, so if you want 10mm string height at the saddle then the calculations are:

Thickness of fretboard + frets at 12th = 5mm (that's quite a chunky fretboard, so you could choose to angle the neck back to allow a thinner fretboard)

Saddle + bridge = 10mm
Saddle above bridge = 2mm
Bridge thickness =8 mm


Perfect. This is a great help, Chris!
Author:  bcombs510 [ Tue Apr 11, 2017 11:04 pm ]
Post subject:  Re: String height above the soundboard
profchris wrote:
10-12mm is about right. Less than 6mm is likely to reduce volume, much more than 12mm can lead to soundboard distortion.


Chris, I have a Uke here that is at 2mm at the 12th and about 10.5mm at the saddle. The player wants it to be closer to 3mm at the 12th, which is going to mean 12.5mm at the saddle. Am I asking for trouble if I make a new saddle that puts the strings at 12.5? Or is that close enough to be reasonable? Just looking for an opinion. Understood that you don't have all the details. :)

Brad



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Author:  profchris [ Wed Apr 12, 2017 5:02 am ]
Post subject:  Re: String height above the soundboard
bcombs510 wrote:
Chris, I have a Uke here that is at 2mm at the 12th and about 10.5mm at the saddle. The player wants it to be closer to 3mm at the 12th, which is going to mean 12.5mm at the saddle. Am I asking for trouble if I make a new saddle that puts the strings at 12.5? Or is that close enough to be reasonable? Just looking for an opinion. Understood that you don't have all the details. :)


That's probably OK if there is enough meat in the bridge to support the higher saddle. I'd say there are two main considerations, both based on the fact that the higher the saddle the greater the force trying to pull its top towards the nut:

1. Splitting the bridge over time. If the existing saddle is fairly low above the bridge and there's a decent depth to the slot, this should be fine.

2. Causing a dip in the top between the bridge and sound hole, again over time. This might be a concern on a very lightly built uke. If it's a Chinese-made factory brand (Kala, Ohana) it's likely to be built with quite a safety margin.

I'd expect a noticeable increase in volume and, if the uke is lightly built, possibly a "coarsening" of the sound if the higher saddle overdrives the top.

I think what I'd do is find a scrap of wood the right size and swap it for the saddle just to hear how the uke sounds and see if the top dipped or I lost confidence in the bridge slot holding up. If OK, make up a new saddle.

Or even better, persuade the player that 2.5mm at the 12th is what all the top players use!
Author:  bcombs510 [ Wed Apr 12, 2017 5:09 am ]
Post subject:  Re: String height above the soundboard
Perfect. Thanks! I'll talk it over with the player and run some tests. Appreciate the help!


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Author:  Aaron O [ Wed Apr 12, 2017 11:21 am ]
Post subject:  Re: String height above the soundboard
Even without all the details, your saddle slot should tell you how high you can go, if you go by the 50% rule - 50% of the saddle is in the bridge, or no more than 50% of the saddle is above the bridge.

If slot depth is an issue, you can always reslot. Especially if you're close, and there's ever a future UST to be installed.

You may also introduce intonation problems, since the strings now have farther to travel.

Splitting the bridge was just brought to my attention as one of the reasons to do a Turner Tilt-back Saddle. The others being intonation, break angle, UST installs, et al. If you had that, intonation and splitting the bridge is a non-issue. If you don't recutting the slot would bring you there, and take care of the slot depth.
Author:  bcombs510 [ Sun Apr 16, 2017 9:56 pm ]
Post subject:  String height above the soundboard
Thanks for all the help, Chris and Aaron.

I landed at 12.5 string height with a saddle that is 6.25 deep into the saddle and 6 above so the 50/50 (or less) ratio is intact. So I guess I have .5 mm of bridge material left in the bottom of the slot. :)

I'll check on the top over the next few days but I didn't see any issues with the top just after taking the strings to tension for the first time.

Really do appreciate the help!

Brad


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Author:  Aaron O [ Tue Apr 18, 2017 3:40 pm ]
Post subject:  Re: String height above the soundboard
Can't get much closer than that for % saddle depth. Seems you should be fine.
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