Online Test: Comparison of back-woods on steelstring guitars
 

Hey folks,

as some of you may know, I am studying guitar making in Markneukirchen/Germany.
This semester I am writing a theoretical thesis about the influence of different back-woods on guitars.
The big difference between my work and previous works is that I am testing all backs with one top.
To realize this I built a jig to screw on tops and backs.
Here is a picture of the jig
https://farm5.staticflickr.com/4559/...765c6a71_k.jpg

To find out the true differences between different species, I made a blind listening test that is now online.
Here is the link to the survey:
https://www.umfrageonline.com/s/ac688bf

I would appreciate if you could do the survey.
Thanks, Max

That's a cool experiment! Tony Yamamoto did a similar experiment but with exchangeable tops instead.

How are you keeping the way you brace the backs "constant"? Maybe another point of experimentation could be using the same back/sides of similar properties (ideally sister sets) but bracing them differently :)

Thank you, Marcus.

I tested the deflection of the backs and worked them to the same stiffness, then I routed the profile on the braces and I made some templates for the scalloping. This is probably not the same crossgrain stiffness at the end, but it would be the same procedure than I would do on a "real" back.

When I built the jig my first idea was to voice the top on the jig with strings on and then build the guitar. I tried it on one guitar and wrote my last theoretical thesis about this but it is not the same sound on the jig than on the real guitar.

I was planning on doing something similar, not quite as robust clamping though.

So you said that the finished guitar does not sound like the parts assembled on your jig, how was it different if you don't mind my asking?



What, finished the listening and I can't get the result till next year? :(

Hi Fred, I am sorry that you have to wait until next year but due to the fact that it is for my studies I am going to wait as long as I can before closing the survey and starting analyzing the results. So I have more people making the survey and we can get a better result.

When making the test with the top/back on the jig compared to the real guitar I noticed that it always sounds brighter and much more sterile on the jig than on the finished guitar. So it sounds more natural and wooden when finished. I am pretty sure that it is because of the higher stiffness and weight that the jig has compared to my normal rim. The weight of the rim on the jig is with 1200g much heavier than the rim for the real guitar with 630g.

The following picture shows the FFT graph of both (the jig and the finished guitar). As you can see there are a lot of differences even in the main resonances. The red one is the real guitar and the black one is the top and back on the jig.

https://farm5.staticflickr.com/4571/...482cd97f_c.jpgVergleich Semesterarbeit by Max Spohn, auf Flickr

I hope that this answers your question a little bit. If not enough please let me know.

Interesting experiment! Any chance you could record some simple and slow arpeggios with the different backs? That could help reduce variations in playing/performance and might make comparisons a bit easier (at least for my ears). Also, is there any way to do the fft on the finished guitar and still have the jig attached? I've been building with heavy sides in recent years and the additional weight seems to have quite an impact on various resonant frequencies. Cool work though and that's great that it's something you can study in an official setting!

Mike

Just whining about getting to the end and not even knowing what the prize is. It is ok, I understood why. Thanks for the info on the test setup. I have the Gore a d Gilet books and they predict a change with the different mass but it is good to know how others have found the change.

I want to do something similar, I am thinking of using plastic bolts and nuts to reduce the weight. I have built guitars with spruce back and sides so spruce or poplar sides might be an option. Depending on how work goes I might have some extra time this winter and this is something I have wanted to do for a while.

J Condino does something similar with the mandolins he builds, but only the back is removable. That allows him to fine tune the bracing. He essentially puts a lining on the outside of the sides, and uses small screws to attach the back. When he's satisfied with the tone, he routes off the exterior lining and attaches the back normally.

Hey Mike, thank you. I am sorry but unfortunately it is not possible to make more records.
It is not possible to make the fft on the finished guitar with the jig because the jig is the whole rim and the neck, so it is not just the plywood piece around the sides. My rims are also pretty heavy so I thought that even more weight can't be that big of a difference but I was wrong.
I will make some fft's of the different backs too. I will post them here as soon as I can make them.

Hey Fred, I will give you the final result as soon as I finished it ;)
The weight of the sides makes a huge difference. If your sides are pretty weak but heavy they can start to resonate a lot!
Try it! I am interested if it works. There are a few people that have already tried something similar. Look in the latest Orfeo magazine, there you can find Greg Byers version.

Hey Rodger, thanks for letting me know. That is a really good idea. I assume that he is building archtop mandolins with removable bridges? Because it is a pain to make a clean finish when the bridge is already on.