So what would happen to a brand-new guitar if you did the equivalent
of playing it for 24 hours a day for weeks or even several months? Could
you accelerate the aging process in just the right ways and get a broken-in
guitar right out of the box, so to speak? I have known several guitar
makers who have put new instruments next to stereo speakers, playing
music into the soundboxes for a week or two before shipping the guitars
to customers. Now there is an industrial-strength version of this technique
being used by Timbre Technologies, a company founded by luthier Michael
Tobias and SWR amplifier builder Steve Rabe.
Timbre Tech’s patented process involves clamping the guitar to a shaker
table, a kind of super–heavy-duty loudspeaker with a 7,500-watt amplifier
and a three-inch magnesium plate instead of a speaker cone, and vibrating
the whole thing at much higher forces than ordinary playing would produce.
The process takes about 45 minutes and is carefully monitored by acceleration
sensors attached to several points on the guitar. The strength of the
vibration is intense, much greater than that produced by playing the
guitar, and so the theory goes that 45 minutes on the table is equivalent
to several years of normal playing.
Upon hearing of this process, one of my first concerns was safety.
With such intense shaking, would glue joints fail? Would cracks appear
in the wood? Well, so far so good. Timbre Tech has done the shake on
30 or 40 guitars with no damage. As intense as the shaking is, the glue
joints shouldn’t be a problem, because a good glue line is stronger
than the surrounding wood. It’s probably not a good idea to shake an
already cracked guitar, but the process is not so strong as to damage
sound wood.
Once the guitar is clamped to the shaker table, the process begins
with a reading of the instrument’s frequency response. A reference accelerometer
is attached to the aluminum table, and it feeds into a computer that
flattens the frequency response of the system. Three accelerometers,
attached to the guitar with wax, monitor the frequency response of the
instrument at the peghead, bridge, and neck joint. The guitar is shaken
at a moderate rate with a full-range audio signal to record the "before"
response into the computer, and then the power is ramped up to full
intensity. After 45 minutes of shaking, the force is reduced and another
frequency response plot is captured. The "before" and "after" response
plots are then merged, and the graphical output shows only the change
that has taken place (see graph).
Does it work? Are the results predictable? Does the computer plot show
something relevant to how the guitar sounds after treatment?
To shed some light on these questions, we tested four guitars: a Sobell
owned by Henry Kaiser, a Taylor owned by Laurence Juber, a recent Gibson
Roy Smeck Radio Grande reissue owned by Jackson Browne, and a Martin
HD-28 loaned to us by the factory.
The Sobell is a stiff guitar design to begin with—-I describe it as
being 1/3 archtop and 2/3 flattop. Kaiser said he hoped it would come
out sounding as though Martin Simpson had been flailing away on it for
several years! The verdict? Kaiser gave the shaking a thumbs up. The
Sobell developed more low end, and the high end became more detailed
and open. The computer plot did not show radical changes, but the changes
did correspond with the audible results. The guitar gained nicely overall
and had the "played hard" factor that Kaiser had hoped it would develop.
My feeling was that the guitar felt more responsive to a lighter touch.
The Martin we tested is a scalloped-brace dreadnought with a fairly
loose top and lots of bottom end. It was passed around the office at
Acoustic Guitar so people could get used to its "before" sound—which
was found to be quite good right out of the box. It didn’t sound like
a guitar that particularly needed playing in.
The Martin changed more in terms of overall sensitivity than frequency
response, and that is admittedly a somewhat subjective view of it. Jeffrey
Pepper Rodgers and Dylan Schorer, working with engineer Steve Bird,
set up as controlled a recording test as was practical, and their report
is as follows:
"We recorded it before and after the shaking, with stereo mics in the
same position relative to the guitar, run through a mixing board set
flat and into a DAT machine. We used new strings (same brand!) both
times, and recorded the same series of songs, played as consistently
as possible. The difference between the before and after tapes is hard
to pinpoint and not necessarily consistent from song to song, but we
did feel that the guitar was ringing out more in the second session.
Even before the shaking, we had to set the mics to the highest bass
roll-off to get a decent sound; afterwards, if we had been trying to
get the best sound on tape (rather than to recreate the way we recorded
it the first time), we would have opted to move the mics further away
from the guitar to cut back the boom. The guitar sounded a bit bigger.
"Our ‘before’ and ‘after’ comparison is obviously subjective and fraught
with variables (the humidity, how hard the guitar was played during
the sessions, our expectations, our memories of what the guitar sounded
like before), but the bottom line is that this guitar did seem to be
opened up by shaking. Afterward, it seemed to make more sound with less
effort—a subtle but nice change."
These impressions of the HD-28 shake were very much in line with my
own. The guitar was loose and boomed out on the low end to begin with;
it did not sound like a typical new, stiff guitar. But what I noticed
was an increase in overall sensitivity. Nice old instruments sometimes
feel like they are playing themselves; it takes very little effort to
bring out a great sound. The shaking increased that factor in the Martin
just as it did in the Sobell; these were remarkably similar results
in two very different instruments.
The most dramatic change was in Laurence Juber’s Taylor 514, a small-bodied
cutaway with mahogany back and sides and a Sitka spruce top. Before
the shaking, Juber liked its balance—especially for recording—but felt
that it definitely sounded like a new guitar. Afterward, Juber says,
"It gained another octave of low-end tone, and the highs became much
more complex. My wife, Hope, noticed it immediately when I brought the
guitar home. It was like when an adolescent’s voice breaks and becomes
mature." Juber also reports that his use of the guitar in studio work
has greatly increased, as its sound is very mic-friendly. Also interesting
is that Juber feels that the guitar is continuing to mature more rapidly
than he would expect since the Timbre Tech treatment.
Finally, Jackson Browne’s comment on the shaking of his new Gibson
Roy Smeck was short and to the point: "Wow!" He elaborated that the
guitar now sounds much more like his vintage Smecks. Even the old ones
sound different from one another, but now the new one sounds as if it
has been played in. Browne now wants to try the shaking treatment on
a little-played 1935 Smeck.
Timbre Tech has also treated solid-body electric instruments, again
with interesting results. Aerosmith and Eddie Van Halen have recently
had instruments shaken, and Jerry Donahue reports spectacular results
on two of his Fender Custom Shop Telecasters. With solid-bodies, it
seems that the most dramatic results are with bass-wood–bodied instruments,
and run-of-the-mill new production guitars get more improvement than
instruments already judged to be excellent. The changes in solid-body
instruments would seem to indicate that it is not just simple flexural
patterns that open up with vibrational aging of guitars. Internal sonic
wave patterns in woods also change with shaking, whether done naturally
over time or accelerated on the shaker table.
Steve Rabe of Timbre Tech has been experimenting to see if it is possible
to "move" dead spots to less musically intrusive frequencies. By emphasizing
or de-emphasizing particular frequencies during the shaking treatment,
it might be possible to suppress wolf tones and bring life to the dead
spots. It might be further possible to program what kind of improvements
might be made to an instrument. For instance, by not exciting low frequencies
and concentrating the shaking in the mid- and upper frequencies, it
might be possible to balance out a too-boomy guitar.
I have talked to musicians who felt that guitars age according to how
they are played. An instrument strummed in open position will age one
way; the same guitar fingerpicked will turn out different. As far out
as this may seem on the face of it, it may just be true. Since the Chladni
patterns are frequency-specific for a certain size and thickness of
plate (think "top"), a musical style that emphasizes one key or frequency
range over another will excite a particular set of vibrational patterns.
Thus different vibration programming might age guitars according to
the music you want to play. Will that be the Doc Watson tone file or
the Reverend Gary Davis? Richard Thompson or Lightning Hopkins?
What about predictability? So far, the results on the guitars Timbre
Tech has shaken seem to indicate that the most noticeable results are
on newer, stiffer instruments—just the ones in need of the most aging.
There is not enough data yet to come to any conclusions about different
effects with the different woods commonly used on acoustic guitars.
We might expect, though, that the aging effects noted naturally might
just be accelerated with the shaker treatment—for instance, there might
be more opening up of a thicker spruce top than a thin cedar top.
The results heard by musicians and engineers seem to track fairly closely
with the computer frequency response charts made before and after treatment.
However, improvements in overall responsiveness do not show up so obviously
with current measurement techniques. Further testing using laboratory
mics with even more sophisticated computer programs may reveal the increase
in acoustical efficiency and sensitivity that all observers have felt
and heard. As in the rest of life, the right answers are right in front
of you if you ask the right questions.
Rabe is working with scientists at MIT to try to determine if there
are observable changes in the wood that has been shaken. Samples of
different woods will be shaken and compared with control samples of
matching cuts from the same planks left unshaken. Hopefully the combination
of acoustical testing along with electron microscope viewing of the
wood cells will result in documentation of what the musician’s ear knows.
For now, the ears have spoken: "This works."
Excerpted
from Acoustic
Guitar
magazine, February 1997, No.50
