@jonhodgson

Interesting article and I can’t disagree with any of the theories, in particular the point that more arching of the top leads to a decrease in flexibility and loss of sound.  It’s a point well made and is accepted in the world of carved top instrument where people agree that a flatter arch gives a better sound.

The only weak point in the article is the lack of scientific data to allow it to be called a thesis, as it’s all opinion given from experience. Although this is valid up to a point some observational recorded data would help to give credibility, possibly using an oscilloscope to show sound wave patterns and frequency. I’ve seen these type of demonstrations and they are very effective in proving a point.

A few years ago there was a BBC 4 TV programme by Alan Yentob in which he investigated the history of guitars. One visit was to a US acoustic maker whose name I’ve forgotten. He demonstrated putting a small flame near the sound hole and  tapped the top above the X bracing. The flame blew out, which shows the desired effect ie pumping sound waves out. 

Some people like to “spring” the tone bars on carved instruments to counter the down push of the strings. This is only by 0.5mm or so at each end but it creates more movement in the top and more air pumping. Springing is where the gluing surface of the tone bar has a slight rocking action. I was very impressed with the pyramid acoustic bridge which Mark demonstrated on a video last year. It seems to be a similar idea as it’s flat bottomed and relies on gluing pressure to follow the top curve. I think the effect of this counters the upward pull of the strings, although I could be wrong.

The only weak point in the article is the lack of scientific data to allow it to be called a thesis,

That doesn't figure in the dictionary definition of "thesis".

Thanks for the other information.

@rocknroller912

Can you remember if the video where Mark showed the pyramid bridge was the one where he builds a bridge for an acoustic guitar? I have some chores to finish but I'd like to watch it later.

@jonhodgson

Thanks for making the point, always thought of a thesis as something presented for formal qualifications although I didn’t check the dictionary definition. I was just thinking back to my student days some of which were light years ago and some fairly recent, where work would be marked down if it didn’t include evidence.

@jonhodgson

Yes I think the video you mentioned is the one. It was about a year ago.

@rocknroller912 I have to confess I pondered about whether or not to use the term thesis, since my first thought when i hear the term is also an academic thesis, so I checked whether it would be appropriate

😉

@jonhodgson and Rocknroller912 

Definitely an interesting read and the author obviously has experience with 1000 guitars under his belt. My first acoustic is still on the drawing board so most of this is over the top of my head.

A couple of things I picked up on. I've drawn a smaller body than Mark's online course model and have gone with a shorter scale length (25"), I'm getting the impression that the shorter scale length might be a good thing.

Another thing is the x bracing being more towards 90° but not exactly 90° but with any explanation as to why. My drawn x braces cross at exactly 90°, not a good thing, but drawing on my past life experience as a design engineer it seemed like the right thing to do.

As for choice of wood, I'll take Mark's guidance on that.

When all's done and dusted, I'll have a guitar and only then we'll find out how it sounds.

@jonhodgson

Fair point about the use of the word “thesis” and in a sense the term is academic (pun intended). Obviously if someone has made 1000 guitars then he’s worth listening to but I think he could use some help to put his experience into words better. There’s a whole book worth of information that’s worth expanding.

@robin

My theory on bracing is that the standard X pattern and bracing sizes have been developed over a number of year by big manufacturers to give the best strength and flexibility, however using a different bracing angle just needs adjustments to the bracing stiffness or size and maybe a larger bridge plate.

I’ve banged on about violin making probably too much but it’s what I know. There is a book called “Secrets of Stradivari” by an Italian violin maker Sacconi in which he explains that the area behind the sound holes is known as the vibrating table, and this is where the action happens ie there has to be enough flexibility to allow the top to vibrate but enough strength to support the string pressure, so applying this to guitars the bracing pattern and size work in tandem to get a good outcome.

If you glue the bracing on unworked and dry clamp the top you will get an idea of how stiff it needs to be. Wouldn’t we all love to have Mark’s level of experience where you can just flex it in both hands and take a bit more off.

My perception is that classical guitars seem to have had rather more variation in bracing ideas (as in clearly different approaches to the layout rather than tweaks of the same basic arrangement) than steel string

https://www.thisisclassicalguitar.com/bracing-styles-for-classical-guitars/

@jonhodgson

Good research i didn’t know there are so many different types of classical bracing 

Wow, that’s a lot of info to digest but I really enjoyed reading these, cheers!

So many geometry variations, so many design philosophies, so many material choices. Yet so many companies and luthiers each following these different paths still all manage to produce wonderful, playable instruments. Could it be that there are many possible solutions to building a guitar and that the vast majority will work pretty well? There are lots of versions of this but it is worth remembering the maxim ‘don’t let the pursuit of perfection be the enemy of good’. In other words, don’t over think every little detail for fear of making a mistake when just getting on and trying something might teach you more than you can possibly imagine. If none of us were to make a guitar until we fully understood the science behind voicing soundboards, the effect on tone caused by reducing the X brace angle by 1.5° or the benefit of +0.5mm of tone bar spring then the spruce forests of this world could take a very long and deep breath, safe in the knowledge that we wouldn’t be bothering them any time soon!

@darrenking

I’m with you on this one. The persuit of perfection is very limiting and can absolutely paralyse builders. I’ve heard of people who are so frightened of making a mistake that they won’t build anything.

One year I was at the Cambridge Violin School run by Juliette Barker, a very respected maker who broke the stereotype and became one of the first women to train professionally. She commented that the day she made a perfect instrument would be the day to stop. The general opinion was that you have to make a lot of instruments to develop the skills, so mistakes are part of that process.

She commented that the day she made a perfect instrument would be the day to stop.

That’ll keep us all busy then!