Mike's Oud Forums
Not logged in [Login - Register]
Go To Bottom

Printable Version  
Author: Subject: A simpe real world string measurement rig
rojaros
Oud Junkie
*****




Posts: 521
Registered: 7-9-2008
Member Is Offline

Mood: No Mood

[*] posted on 12-18-2014 at 01:14 AM
A simpe real world string measurement rig


In case anybody is interested in real world measurements of string tensions I present here a simple rig to do these measurements.

So the idea is to tune exactly the string I want to check at the required scale length which can be adjusted to need to exactly the pitch I want to use, then wait until it settles and re-tune as often as it needs to remain stable. Then switching on the scale and zeroing it I quickly release the violin peg and here is the actual tension at that pitch with that scale length. Very simple, cheap and quite precise.

[file]33727[/file]
View user's profile View All Posts By User
rojaros
Oud Junkie
*****




Posts: 521
Registered: 7-9-2008
Member Is Offline

Mood: No Mood

[*] posted on 12-18-2014 at 01:20 AM


Here a detail of the measurment side

[file]33729[/file]
View user's profile View All Posts By User
rojaros
Oud Junkie
*****




Posts: 521
Registered: 7-9-2008
Member Is Offline

Mood: No Mood

[*] posted on 12-18-2014 at 01:21 AM


And here a detail of the tuning peg and movable nut (scale length adjustment) side:

[file]33731[/file]
View user's profile View All Posts By User
journeyman
Oud Junkie
*****




Posts: 490
Registered: 12-28-2003
Location: Hamilton, Ontario
Member Is Offline

Mood: No Mood

[*] posted on 12-19-2014 at 01:26 PM


I'm afraid I don't understand. Why would you release the violin peg? Wouldn't that release the tension? Perhaps I'm not getting the whole picture of the apparatus. Do you have one end of the string attached to the peg and one to the scale?



http://jacobscattle.com/ instrumental roots/americana
View user's profile Visit user's homepage View All Posts By User
rojaros
Oud Junkie
*****




Posts: 521
Registered: 7-9-2008
Member Is Offline

Mood: No Mood

[*] posted on 12-19-2014 at 03:12 PM


Quote: Originally posted by journeyman  
I'm afraid I don't understand. Why would you release the violin peg? Wouldn't that release the tension? Perhaps I'm not getting the whole picture of the apparatus. Do you have one end of the string attached to the peg and one to the scale?


Well I'll try to explain.

The purpose of this post is to show you an easy method to determine the real string tension of given string set on a given oud scale length at any desired tuning. The oud, especially the more lightly built ones, is such a delicate instrument, that it is vital to have an idea what kind of string stress one is putting on!

So again how it works:
One string is attached to the scale, the other is wound around the peg. I bring the string up to pitch and tune it up again and again until it has really settled and stays in tune (tuner check!) When it has got stable I switch on the scale and it zeroes itself automatically. When I release the tension very quickly with the peg, it goes down to zero, which becomes the negative figure on the scale as much below zero as the tension of the string was.

It is not different from electronic kitchen scales: When you put a pot on a scale and press the tara button (or zero button) it shows you exactly zero with the pot on it and when you remove the pot it shows a negative number corresponding to the weight of the pot.

Why I do it that way? Because I cannot tune up the string fast enough before the auto off function of the scale kicks in ... hope I could explain it clearly enough.
View user's profile View All Posts By User
journeyman
Oud Junkie
*****




Posts: 490
Registered: 12-28-2003
Location: Hamilton, Ontario
Member Is Offline

Mood: No Mood

[*] posted on 12-19-2014 at 07:28 PM


Got it now. Thanks.



http://jacobscattle.com/ instrumental roots/americana
View user's profile Visit user's homepage View All Posts By User
alchemy
Oud Maniac
****




Posts: 57
Registered: 11-30-2014
Location: Buenos Aires, Argentina
Member Is Offline


[*] posted on 12-22-2014 at 05:19 PM


Very clever! What is the black thing that you use to tie the string to the scale?
View user's profile View All Posts By User
jdowning
Oud Junkie
*****




Posts: 3445
Registered: 8-2-2006
Location: Ontario, Canada
Member Is Offline

Mood: No Mood

[*] posted on 12-23-2014 at 04:57 AM


A simpler and more accurate set up would be to mount your rig almost vertically, eliminate the digital scale and tension the string with a 'dead weight' - weights added or subtracted in a small container suspended from the free end of the string. The weights can be any metal object handy from screwdrivers to metal washers. When the added weight results in the measured stable pitch required the container is removed and weighed to determine the string tension. No need to rush or mess around with quickly releasing pegs etc.

I have used this system successfully on my string test rig for the past 4 years now and obtain consistent measured results. When the string on the vertical rig is plucked to determine pitch it is necessary to first gently press the string against the lower nut with a fingernail to eliminate any possibility of 'buzzing' at the nut.
View user's profile View All Posts By User
rojaros
Oud Junkie
*****




Posts: 521
Registered: 7-9-2008
Member Is Offline

Mood: No Mood

[*] posted on 12-23-2014 at 08:22 AM



Thanks for the comments!

@alchemy: it's a guitar bone bead used to fasten the strings on a classical guitar that happened to hang on that used string.

@jdowning: as to the accuracy, every measurement is as accurate as the devices you use plus the care you put into the measurement. The scale I use seem to be pretty acurate within it's display range. I compared it to my electronic kitchen scale which is accurate to one gram.
As to convenience,I find the apparatus actually quite convenient. I can tune it up withe the peg quite quickly, and releasing is not a problem, it goes easily fast enough. That diesn't mean that other ways doing this kind of measurement are not at least as convenient as mine, or as precise as that one. But I would have to provide a hole lot of different small weights, keep track of which one is how much and what did I add and what do I have to remove etc. I like it quick and dirty... And no method releaves you from waiting until the string settles.
View user's profile View All Posts By User
fernandraynaud
Oud Junkie
*****




Posts: 1865
Registered: 7-25-2009
Location: San Francisco, California
Member Is Offline

Mood: m'Oudy

[*] posted on 12-23-2014 at 07:55 PM


@rojaros, I'm with you on this. Great apparatus. The electronic scales are excellent these days. Not for this application, but for $22 I got one that reads milligrams and is repeatable to within +/- 2 mg.

Both issues you mention are important, and come from experience. The auto-tare on these scales is excellent. You can let the system stabilize nicely and repeat tare zeroing. Huge time-saver when weighing out stuff in containers. The way all these scales save battery life, whether you like it or not, with a short time-out is a real practical headache. Having torn through every scale manual looking in vain for a way to extend the time-out, I think your solution is perfect.

@jdowning, hi! Hardcore as ever! Been a while. I love the image, adding objets cassées/trouvés to the basket! Maybe Go pebbles? Money? Merry Christmas! ;-)

View user's profile View All Posts By User
jdowning
Oud Junkie
*****




Posts: 3445
Registered: 8-2-2006
Location: Ontario, Canada
Member Is Offline

Mood: No Mood

[*] posted on 12-24-2014 at 05:41 AM


Hi fernandraynaud - welcome back to forum activity!

For information the attached image shows 'des objets trouvés' used for my last string test. The weight carrier is just a tin box with weight (mass) added to make a convenient approximate weight when empty together with a few makeshift lead weights so that I know roughly the weight initially applied (don't want to break anything prematurely through overloading). The fine tension adjustments are then made by adding/subtracting anything that comes to hand - old screws, nails, washers, money if you like etc. etc. No need to know the exact weight of the found material because once the desired tension has been achieved the whole bag of tricks is then 'weighed' on a digital scale to precisely and directly determine the load and hence string tension. Nothing could be simpler at minimal cost.
I happen to have some standard calibration masses, borrowed from another precision scale, so that the digital scale accuracy can be verified for local gravitational conditions - but usually this calibration has already been accurately set for even store bought digital scales
Christmas greetings to all.
View user's profile View All Posts By User
rojaros
Oud Junkie
*****




Posts: 521
Registered: 7-9-2008
Member Is Offline

Mood: No Mood

[*] posted on 12-24-2014 at 07:24 AM


Cool pic!
View user's profile View All Posts By User

  Go To Top

Powered by XMB
XMB Forum Software © 2001-2011 The XMB Group