Re: Busy Wood / Stable Wood

alcarruth wrote:
What Dorgan said.

There _is_ scientific proof that instruments change when they're
played. Carleen Hutchins published measurements years ago in the
'Journal' of the Catgut Acoustical Society. She looked at the
vibrations of new violas and then checked them out again at a later
date, after they had been played. Some were played 'naturally', and
some were driven with sound from a radio, but all showed the same sorts
of changes.

I've measured the same thing on guitars. I've looked at guitars that
I've made when they're fresh off the bench, and tracked some for
several years in the hands of good, and busy, players. I've also
measured the same sorts of changes in new and old guitars of similar
construction and wood types; not as good as tracking the same
instrument over time, but the results are consistent.

What happens is that the top, in particular, 'loosens up'. It moves
more, and pumps more air. This mainly effects the low and mid range
tone directly, but it also 'puts a floor' under the sound of the
guitar. The 'main air' and 'main top' resonant peaks in the output
spectrum tend to become broader and taller over time. I don't think
this has as much to do with glue or finish as it does with wood:
violins use hide glue, most guitars these days are put together with
aliphatic, and we see the same sorts of changes. Ditto finish: I've
seen these changes in instruments that were finished with everything
from French polish and varnish through nitro and epoxy. The finish
makes a bit of difference, but you can attribute that pretty much to
the thickness of the film and the hardness of the material.

Generally speaking, guitars that have narrow 'main air' and main wood'
peaks don't sound as good to most people. The 'air' peak fills in the
fundamentals of the lower notes, and the 'top' peak does much the same
in the mid range. In particular, a narrow 'main top' peak in the output
is often associated with a 'thin', 'harsh' or 'brash' tone, while
instruments with a broader peak tend to sound 'fuller' or 'more solid'.
As far as I can tell, all guitars change in the same way when they're
'played in'. This means that it's not always an improvement: if the
guitar sounded 'full' and 'bassy' to begin with there's a good
liklihood that it will end up 'tubby' or 'fuzzy' sounding.

Most of the change in properties seems to happen fairly soon after the
guitar is strung up and played for the first time. The rate of change
slows down, and almost all of it seems to take place in the first
month. However, things we hear often don't line up with measurements;
sometimes you can hear stuff that's hard to measure, for example. In
this case it seems to work the other way often enough: there has to be
a certain amount of change before you notice it, and that can take a
while. The result is that the time at which the guitar sounds 'played
in' can come up long after that first stringing up, and seem relatively
sudden. It all depends in the end on how the particular guitar works.

So, to comment on the original post; while there are changes that
happen in wood simply with the passage of time, most of those don't do
much to effect the tone. Instruments that I've made, and ones I've
heard, that were made of old wood, generally did not sound 'played in'
right out of the box. Old wood can make great instruments; it tends to
be a little less dense and a lot more stable than freshly cut, and
those are big benefits, but you still have to play the guitar.

Alan Carruth / Luthier

Thanks for weighing in, Al. I was hoping to see you give your input on this. It's one of my favorite topics to regularly come up here. Logically and experientially, I'm in agreement with you all the way through. I'm interested what methods and types of measurement you've done/are doing. And, what can you tell me about what the violin researchers (like Carleen Hutchins) have measured/studied in the same area? Over the years, I've had some opportunity to study a few materials engineering problems; although they had to do with structures rather than tonewoods. The combination makes a fascinating topic. And, I don't seem to be having much luck in googling scholarly articles that have to do with variations in the plasticity of tonewoods. Although, I probably should let it go and just devote more time to playing the darned guitar.

Regards,

Jeff Holston
.

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