Sheldon Brown's Wheelbuilding page links to the article: Check Spoke Tension by Ear. Obviously a tensiometer would be ideal, but Sheldon suggests that checking spoke tension by ear is a reasonable alternative. The article was written in 1987 and updated in 1997; are there any developments from the last 10 to 20 years that would invalidate the technique or require adaptation? For example, the article mentions that dished wheels require a different pitch on the left and right sides, but how great should this difference in pitch be? In general, how effective is tensioning by ear?
That depends on how good your ear is. If you can tune a stringed instrument effectively, then tensioning a wheel by ear is very effective. Identical spokes that have the same pitch when plucked should have the same tension within the margin of error for any tensiometer reading. The catch is you need a tensiometer to get the relative tone for the proper kg/f tension on the spokes, unless you have perfect pitch and can remember up to four different tones for a single wheelset.
How about this?
It is an iPhone based spoke tension gauge that uses sound to determine tension.
The method I use (still need to get a tension meter to verify) is as follows:
The formula for the connection between tension (KgF) to frequency is
f = 1/(2L)*sqrt(T/u) where L is the length of the spoke, T is the tension (in Newtons) and u is the linear density of the spoke. (http://en.wikipedia.org/wiki/Vibrating_string)
you can get the linear density by dividing the spoke mass by its length.
you can get the tension T by multiplying the KgF in 9.98 to get it in Newtons.
It is important to use all the length measures in meters and all the masses in Kg.
for example for 140 KgF and 260 mm spoke that weighs 6.5g you get the frequency to be (1/2*0.260)*sqrt(140*9.98/0.025)~450Hz which is approximately A4.
this results also correlates with John S. Allen's article http://www.bikexprt.com/bicycle/tension.htm.
If anyone gets to check this with a tension meter to confirm it would be helpful.