Is It So Hard To Mic A Piano?
By Charles Helpinstill
For Worship Magazine, Nov/Dec 2003 Issue
Today's larger sanctuaries, and the
growing trend to include contemporary music in worship services
have caused piano amplification to become a problem for many
churches. In order to fill the larger spaces of new churches,
it has become necessary to make the piano louder than its own
acoustic power. This situation with regard to keyboard amplification
parallels the problems encountered in the Concert Sound industry
in the early '70's, when the first generation of piano superstars
(Elton John, Billy Joel, Leon Russell, etc.) appeared on stage,
all wanting to use acoustic grand pianos in the midst of highly
amplified rock bands. The piano amplifier solutions to their
dilemma are still available, but first let's take a look at the
A Piano is a Distributed Sound Source.
Unlike vocals, horns or electric instruments
like guitars played through amplifiers, the piano does not have
a focused, single point for obvious mic placement that will enable
us to hear the piano clearer. Pianos generate their considerable
sound energy over a large area (the soundboard) that effectively
couples the vibrations of thin strings to the surrounding air,
without any one spot ever being that loud. Pianos also present
an additional problem of having the low notes originate on one
end, and the high notes on the other.
The First Approach: Acoustic Microphones
For solo piano performances, or a singer being accompanied by
only the piano, a mic can get the piano into the sound system
with limited gain before feedback, but if anything else is going
on onstage, it's not much help. The human voice is capable of
producing 110-db sound pressure levels directly in front of the
mouth. There is no spot on a piano with SPL over 95, even when
it's played hard. When the ambient SPL on stage during a Contemporary
Worship group performance is in the 100-db range, a regular microphone
close to the piano isn't amplifying the piano; it's a room mic!
Using more than one mic to try to compensate for the high note-low
note problem just compounds the problem, and additionally can
introduce phase-cancellation effects that produce dead zones
on the keyboard. Placing a mic on a boom stand inside the center
of the piano with the lid open, or laying a vocal-type mic on
a cloth inside the piano with the lid closed are common ways
of approaching the problem, but are of little benefit in an ensemble
Improvement No. 1: Pressure Zone
Closing the lid on a grand piano can
help a little, by somewhat limiting the surrounding instruments'
bleed-through into the piano mic. Unfortunately, regular mics
then just hear the sound of the piano trapped in a closed space,
and reflecting off the inside of the lid. A PZM attached to the
underside of the lid can eliminate part of the problem, because
its design cancels the effect of the reflecting surface, and
eliminates some of the boxiness in the sound. Very little improvement
will be noted in the gain-before-feedback problem, however, because
it is still a microphone coupled to the air around the piano.
Improvement No. 2: Vibration Transducers
Piezoelectric transducers such as those
available from Barcus-Berry and many other companies attach to
the soundboard, and offer an intermediate improvement to the
gain-before-feedback ratio. They are also very simple to attach.
Their main drawback comes from their sound source: the wood of
the piano. This naturally results in a somewhat "wooden"
sound, which may require a lot of equalization to be suitable.
They also may lack some of the attack, or "punch,"
because the transients and high frequencies are stifled as the
sound travels through the wood. The isolation from other instruments
is moderately improved over mics, but the soundboard of the piano
is just as effective at catching surrounding sounds as it is
at being the keyboard amplifier, and these outside sounds are
sometimes picked up by the transducer.
Improvement No. 3: String Sensing
Although it's not obvious to the casual
observer, the entire sound we recognize as the piano is contained
in the string vibrations. Aside from the obvious note definition,
the impact of the hammers striking starts the string moving,
and that sound is registered in the strings. The characteristic
wooden warmth of this acoustic instrument is also present in
the strings, since they are connected to the sounding board through
the bridge, and reflect this resonance. If it were possible to
produce an electric signal that was an exact analog to this string
vibration, and then translate this signal through amplifiers
to speaker movements, we would hear the piano exactly as we do
through the air, but without any chance of feedback or bleed-through.
Fortunately, systems have been designed that do exactly that,
and were first used in the early Seventies by the rock superstars
Electrostatic piano pickups were the first detachable systems
to monitor the string movements, but proved to be problematic
in practice and were discontinued. The Helpinstill Piano Sensor,
a magnetic system, is the only string sensing pickup currently
on the market. It operates on the same principle as an electric
guitar pickup, and dominated the concert-sound scene in the Seventies
and Eighties. Although the company ceased production in 1985,
the resurgence of interest by churches caused Helpinstill to
start up again in 2001, and the product is once again available
through the company's website (www.helpinstill.com). The benefits
of using this type of system include a totally isolated piano
channel for recording or amplification, total elimination of
feedback, and a clarity of sound that results from taking the
piano sound from its original source.
Installing a string-sensing pickup such as a Helpinstill involves
a little more care than placing a mic on a stand, since it is
necessary for each string to be sensed for every note to be heard,
but it is proving to be worth it in churches that strive for
a state-of-the-art approach to their piano sound.
No matter what your solution is, hopefully
this article has brought you closer to getting the beautiful,
rich sound you want out of the instrument, to compliment and
augment the worship experience in your church.
Charles Helpinstill has been granted
five U. S. patents in the field of piano amplification, and since
1972 has been considered one of the world's leading authorities
in the field.