Questions for the moonlight luthiers that lurk in these forums

aja

QUESTION NUMBER 1:

How exactly is an acoustic steel string guitar's top attached to the sides? Is it press fitted or glued? Is the binding (if any) also glued?
What I am getting at here, is how the top is mounted in order to allow it to oscillate with the vibrations of the strings.

I understand that Mevryn Davis tries to free up the top as much as possible in order to allow maximum amplitude of vibration. (Unless I'm mistaken)

Would a more flexible mounting allow greater sound amplitudes (volumes) to be reached or will it lead to loss of lower frequency response?

QUESTION NUMBER 2:

How does the soundhole affect the range of frequencies the body will produce? Is there a way to predict the type of sound you can expect by looking at the soundhole size, shape and placement?

Thanks for taking the time to read this ?

Wizard

I'll offer answers from my non-guitar background.
May be wrong ... so use with care.

1) The soundboard of a guitar acts in a similar way to the skin on a drum.
A force sets it into motion ... and it creates sound by moving air.
The sound energy is transferred from the strings to the soundboard via the bridge.
As with a drum skin, the entire integrity is affected by its attachment at the sides ... so I would guess the connection of the top to the sides has to be VERY firm.
(imagine a drum skin loosely attached to its rim !!)

2) I would guess that the guitar body acts a Hermholtz resonator in similar way to a xylophone resonator.
The guitar body is used to give extra resonance to the lower frequencies.
The higher frequencies are reflected quite well by the soundboard itself.
The body is often tuned to about 100Hz.

A bigger hole leads to a higher resonant frequency.
So ... I would guess that fiddling with the hole size will affect the bass response.
Making it smaller would give extra emphasis to even lower frequencies ... making it bigger would eventually lose all bass response.

Round shapes have proven to be optimal ... non-circular shapes amplify "wolf" harmonics (with oval and square shapes being particularly bad).
I once made a marimba with square cross-section resonators - it sounded terrible.

I don't think placement is very important.
Bass tones are fairly directionless ... which is why the placement of sub-woofer loudspeakers is not critical.
Also explains why some guitars can even have their sound holes on the side.
The entire body of air inside the cavity is resonating ... so the tone is not affected by the hole position, but by the volume of air and the size of the hole.

Bob-Dubery

aja wrote: QUESTION NUMBER 1:

How exactly is an acoustic steel string guitar's top attached to the sides? Is it press fitted or glued? Is the binding (if any) also glued?
What I am getting at here, is how the top is mounted in order to allow it to oscillate with the vibrations of the strings.

There are usually linings inside the guitar. Strips of wood, usually cut to make it easier to follow the curves of the shape. Top and sides are actually fastened to the linings rather than directly to each other.

That's for most guitars, but not all. Ovations and the like may be different, as will the Smoothtalker.

I understand that Mevryn Davis tries to free up the top as much as possible in order to allow maximum amplitude of vibration. (Unless I'm mistaken)

Yes. But his design is completely different. He frees the top up by having very light bracing. Because his construction takes nearly all stresses off of the top he doesn't have to have any bracing for reinforcement. He braces for tone only. I think that he glues the top directly to the sides, but the sides are like 3/4 of an inch thick. The back of the Smoothtalker is bolted on (literally) rather than glued.

I can't help you with the rest.

AlanRatcliffe

aja wrote: How exactly is an acoustic steel string guitar's top attached to the sides? Is it press fitted or glued? Is the binding (if any) also glued?

Glued via the kerfed lining as bob said.

how the top is mounted in order to allow it to oscillate with the vibrations of the strings.

The top itself flexes (the classic vibrating "elastic plate") - there is no vibration at the edges. Some interesting info:
http://www.phys.unsw.edu.au/music/guitar/guitarchladni.html
http://www.phys.unsw.edu.au/music/guitaracoustics/construction.html

Would a more flexible mounting allow greater sound amplitudes (volumes) to be reached or will it lead to loss of lower frequency response?

But what would you do about the force of the strings pulling the top upwards?

How does the soundhole affect the range of frequencies the body will produce? Is there a way to predict the type of sound you can expect by looking at the soundhole size, shape and placement?

http://www.phys.unsw.edu.au/jw/Helmholtz.html

In fact, just go to http://www.phys.unsw.edu.au/music/guitar/guitarintro.html and follow all the links - excellent site.

Gearhead

Recommended reading for math nerds that like guitars: "Left Brain Lutherie" by David C. Hurd. I can borrow you my copy, will bring it to Andy's 2moro night. Can't say that I've gotten my head around all of it, but have no time now anyway.

djpauw

The other guys said pretty much everything I would have said, except for the following:

PLACEMENT of the soundhole plays a role also (duh). Obviously you have seen guitars with a "traditional" placement of the soundhole which can be described as centered I suppose. And then you would probably have seen some guitars with soundholes in the upper bout almost next to the connection of the neck to the body. Sometimes there are multiple smaller holes making up the soundhole as an entity.

This last configuration is often claimed to produce more acoustic volume, however no formal study has been done on this as far as I am aware. It does however lower the Helmholtz resonance slightly, which produces a little more bass from a smaller bodied guitar (relatively speaking).

Just my 2c.

What are you planning to build?

Gearhead

djpauw wrote: What are you planning to build?

I think he's not concerned with building as much as with his guit having a funny looking soundhole. It does sound great though...

aja

Thanks for all the replies! Very interesting stuff ?

Thanks gearhead haha! Funny looking? Don't start with me, Tom V. ?
Sorry I couldn't make the second workshop, looked like fun :'(