A Weighty Subject

[yellowesty]

I recently received my copies of the Gore/Gilet guitar books (fantastic!!!) and in Volume 1; Design, they discuss adding weight to the sides of the guitar to move the node line of the main top resonance out to near the edge of the top plate. The Chladni patterns (page 1-87, with weight and without) are impressive. With the weights, the radiating area is substantially greater; without the weights, the area outside the node line is actually cancelling some of the top's radiation.

They use two weights (~8 oz. each) fastened to blocks of wood glued to the inside of the lower bout at its widest point.

Has anyone here tried anything like this? And?

As an aside, I have a Pono 0040-VS (ebony s/b) which is remarkably loud for its size and I wonder how much its heavy sides contribute to that.

[Rodger Knox]

Trevor's books have been out for a while now, and quite a few builders, myself included, are using techniques from The Book. I have not used side weights, but I do make the linings extra heavy.

[Alan Carruth]

It works as advertised, but there's no free lunch. Guitars like that are moved a little closer to the 'banjo' end of the 'piano to banjo continuum'.

[Trevor Gore]

Originally Posted by Alan Carruth

It works as advertised....

Yes, it really does! "As advertised" is "The effect acoustically is to give the guitar a more solid, weighty, sound, increasing the general volume but favouring the lower frequencies by increasing the level of a note’s first partial. This can be observed using a spectrograph. Projection is also increased. On steel string guitars the added mass also adds more sparkle and shimmer into the high frequencies without adding harshness, which is a nice side effect".

Originally Posted by Alan Carruth

Guitars like that are moved a little closer to the 'banjo' end of the 'piano to banjo continuum'.

Well, I've done a good many now and have never heard that effect. In fact, I hear the opposite; movement towards the "piano" end. As the side mass increases and the T(1,1)2 node line moves outboard, the effective mass of the top increases and that lowers its resonant frequency, i.e. the T(1,1)2 drops. This is consistent with a "darker" sound; the more solid sound I mentioned above.

Originally Posted by Alan Carruth

...but there's no free lunch.

I think it's the nearest thing to a free lunch you'll ever find in guitar building!

I came a across this effect when I was making Chladni patterns with the guitar body in a building mould. I then replicated it by sticking 50c coins all around the outside of another guitar and got a similar effect. One things was clear though. You need a really solid attachment of the mass to the sides. If you don't achieve that you just have another mass swinging around in its own time.

It's also a very low risk thing to try if you are building. If you don't like the effect you can take the mass out and you're left with just a couple of over-size side stiffeners that have very little acoustical effect.

I'll stick a link to an anecdote in another post, just in case those sorts of links aren't allowed.

[Trevor Gore]

...and here's the link to the anecdote.

[McCawber]

Many years ago Augie LoPrinzi told me he kept the sides of his guitars a fill 1/8 inch thick because he thought the extra weight improved the sound. I couldn't argue - my Augustino AR-70 was a killer guitar. I was nuts to let it go.

[Jim.S]

I use it, last one I used about 6.5oz per side. As has been pointed out you do get a benefit by moving the node. It's main use for me is to drop the T(1,1)2 down to lay between the fret board notes, as I use CF on my bracing I can't just go in and tune down by lowering brace height so the side mass works well for me.