ACOUSTIC AMPLIFICATION, PT. 1 BY LARRY FISHMAN
When the PG editors asked me if I would be interested in writing a quarterly column
on acoustic guitar amplification,
my immediate thought was, this
sounds fun, but another commitment is clearly not something I
need at this point in time. The
more I thought about it though,
the more the idea began to
appeal to me. Since I have been
designing and manufacturing
acoustic amplification gear for
over 30 years, writing a column
would give me a perfect excuse
to actually sit down, reflect on,
and catalogue my thoughts on
the subject.
A quick look at today’s guitar
market shows that acoustic guitars are still outselling electric
guitars, and that roughly half
of the acoustics being sold have
pickup systems already installed
by the manufacturer. The number of acoustic-specific amplification products—pickups,
This 1933 National Duolian represents an early effort to mechanically
amplify an acoustic guitar. A 9 1/2"-diameter aluminum cone—the
Duolian’s resonator—acts like a speaker, enriching the sound of the
vibrating strings by increasing their volume and adding complex
overtones.
Once you grasp the
basic mechanics of
an acoustic guitar,
you’ll see why many
types of pickups can
be used to sense its
complex vibrational
characteristics.
preamps, effects pedals, and
amplifiers—that are available
are at an all-time high. It’s very
clear that a large number of
players are focusing on amplifying their acoustics, but with all
the available choices, deciding
on what works best for you can
be a little daunting. In an effort
to help you select the best gear
for your needs, I’ll first cover a
few amplification fundamentals
and then dig into some details
in each product category. So
let’s get right to it, we have a lot
of ground to cover!
Why amplify in the first
place? After all, an acoustic
guitar is already an amplifier of sorts—it’s a mechanical
amplifier. The source of an
acoustic guitar’s sound is the
vibrating strings. But when
you think about it, without
some sort of amplification, the
amount of air that the strings
can push around is quite small.
Additionally, the vibrating
motion of the string is sinusoidal in nature, and the resulting
sound it creates by itself is a
fairly pure tone. While certainly a pretty sound, it’s not really
that interesting on its own.
The roles the top of the
instrument and the sound
chamber play in enhancing
the string vibration are huge!
They add more volume by
pushing a larger amount of
air, and they create sonic complexity by adding resonances
and overtones to the sound
of the vibrating string. Taken
together, the result is a louder
and richer set of sounds that
are able to project into a room.
This is why each individual
instrument has its own unique
and characteristic tone.
Before we decide the best
way to further amplify this
sound by adding pickups or
microphones and amplifiers,
it is important to understand
the physical operation of the
existing mechanical amplifier.
Now please stay with me on
this—it will be important to
understand this later when you
are deciding on a system for
your instrument. Once you
grasp the basic mechanics of an
acoustic guitar, you’ll see why
many types of pickups can be
used to sense its complex vibrational characteristics.
I like to look at it like
this: First, when the string
is plucked, it creates a string
excitation force (SEF) at the
saddle. This force is dynamic
in nature, in that it changes
or pumps in relation to the
pulling and relaxing of the
string—the string vibration.
This ever-changing SEF is then
transferred through the saddle
to the bridge, which responds
in a very interesting way.
Third, the moving string
support—in this case the
bridge—alters the initial vibration pattern of the string due
to something we call mechanical admittance. The result is a
more complex and interesting
overall tone shape.
Before I wrap it up, I’d like to
leave you with a simple assignment: Determine what your
own guitar really sounds like by
having a friend play it for you.
If you do this and are surprised
that your guitar actually sounds
brighter than you expected, don’t
feel bad—it’s a very common
misconception. Because you
are always sitting or standing
behind your instrument while
you are playing it, and because
the higher frequencies are very
directional and project away
from you, you’re simply not
getting the whole picture!
That’s it for now. I’ll be
back in a few issues, and that’s
when we’ll start looking at the
theory of operation for some
of the most popular categories
of gear.
LARRY FISHMAN holds
more than 30 patents in
transducer and musical
instrument design. He is
president and founder
of Fishman Transducers,
which he began in his
garage in 1981. In the early ’90s, he
also co-founded and managed Parker
Guitars (which was later sold to U.S.
Music Corp.) with his friend Ken Parker.
