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If a guitar is tuned down 1/2 step, with .012 to .053 strings, how much will this decrease the total string tension. 25.2" scale.

Hope this helps…

https://www.daddario.com/pages/string-t ... calculator

Using the "G" Thang Guitar Design Tool, I initialized a new guitar design to a standard OM, which contains a conventional 0.012 - 0.053 string set. Setting the scale length to 25.2" and reading the total string tension from the Statistics Panel yielded 159.5lb. Dropping the pitch of each string in the design a half step, total string tension reported was 142.1lb.

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R.M. Mottola
LiutaioMottola.com

Author of the books Building the Steel String Acoustic Guitar, Practical Design of the Acoustic Guitar and Similar Instruments, and Mottola's Cyclopedic Dictionary of Lutherie Terms.

I don't check in here very often. If you need to contact me the best bet is via email through the contact page on my site.

I was going to post slides from the 2006 GAL conference. D'Addario's engineer gave a very good presentation on string theory explaining this but my images are too big for forum software (I could e-mail them too you). String tension varies with square of frequency, one semi tone is about a 5.9 percent change in frequency. Therefore the change is tension is 1/ (1.059)^2 or 89percent less. One full step is two semi tones so 79.5 percent.

Note that this agrees with what R.M. Motolla calculates by a different method.

Edit to add, your 25.2 inch scale affects things also. Tension varies with the square of lenght also and most tension charts (like D'Addario's) are published for 25.4 inch scale

Yep, that really helped. I determined that EJ-16 PB strings at standard tuning have almost the same tension as EJ-17 PB strings tuned down 1/2 step.
Thanks for the link.
James

Freeman, yes, that was an excellent presentation! Fan Tao, the guy that gave that presentation, was the principal engineer at D'Addario for many years. He is now retired. In addition to doing presentation like that he is one of the principals of the Oberlin Acoustics Workshops of the Violin Society of America. He was also a president of the VSA. In his position at D'Addario he was amazingly approachable and helpful over the years. He was the go to subject matter expert for questions about strings when I was editing the Questions Column of American Lutherie. I don't know how many times I had asked him for some technical information in preparation for my own experiments, only to receive extremely detailed responses, often accompanied by a box of strings to experiment with. He definitely went above and beyond when it came to technical support!

_________________
R.M. Mottola
LiutaioMottola.com

Author of the books Building the Steel String Acoustic Guitar, Practical Design of the Acoustic Guitar and Similar Instruments, and Mottola's Cyclopedic Dictionary of Lutherie Terms.

I don't check in here very often. If you need to contact me the best bet is via email through the contact page on my site.

I learned more string theory in that seminar than all the other reading I had been doing. I have photos of all the overhead slides that Tao used that day, I could e-mail the set to anyone interested (I don't think there are any copyrights on a public presentation). I'm also pretty sure the presentation was writen up in American Lutherie.

D'Addario's support of the lutherie community is one of the reasons that I use their strings almost exclusively,