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April 27, 2012 American University, Washington, DC
12th Annual New Millennium Conference
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THE WHISPERING GALLERY: STATUARY HALL UNVEILED
Xholina Nano
American University
4400 Massachusetts Ave. NW, Washington, DC. 20016-8058, xn1023a@american.edu
Abstract — Completed in 1807, Statuary Hall is one of the
most historic chambers in the U.S. Capitol. Also known as
the Old Hall, the impressive two-story, semicircular room
was the meeting hall for the U.S. House of Representatives
for nearly 50 years. Modeling an ancient amphitheater,
Statuary Hall was one of the earliest examples of Greek
architecture in America. The Hall was damaged when
British troops burned the Capitol in 1814 and was later
rebuilt to its current state. The Hall presented acoustical
obstacles that made conducting business difficult. The
elliptical shape of the room and smooth curved wooden
ceilings contributed to the interesting sound effects and
large echoes. It has been stated many times that
conversations of those standing in a far corner could be
heard by others standing in the opposite corner. The science
behind this sound effect can be explained by wave motion.
Sound waves are reflected, refracted, and brought to a focus
leaving the audience in the Hall experiencing a cacophony
of sounds. A number of unsuccessful attempts to improve the
acoustics in the Hall included hanging draperies and
reversing the seating arrangement. This paper will explore
the physics of sound waves and the architecture of Statuary
Hall as it relates to acoustics.
Index Terms — Absorption, longitudinal waves, reflection,
reverberation, sound waves.
INTRODUCTION
Acoustics can have a dramatic impact on the way sounds
travel through a room. The shape of a roomcan facilitate the
transfer of even the softest of sounds from one end to
another. Bystanders in Statuary Hall experience an
acoustical anomaly in which conversations are reflected
along the surface of the elliptical ceiling and clearly heard
on the opposite ends of the room. This effect has been
present since it was built and played a large role in its future.
HISTORY
Statuary Hall has played a large role in the history of the
Capitol and in shaping history for future generations.
President Monroe appointed Charles Bulfinch as architect of
the Capitol in 1818 to replace Benjamin Henry Latrobe.
Bulfinch rebuilt Statuary Hall between 1815 and 1819,
which was originally designed by Latrobe [1]. The Hall
remains a symbol for the country and a national landmark.
As the Hall of the House, it was home of many important
events. In 1824 the Hall served as the Chamber where the
Marquis de Lafayette became the first foreign citizen to
address Congress. Former Presidents James Madison, James
Monroe, John Quincy Adams, Andrew Jackson, and Millard
Fillmore all were inaugurated at the Hall [2]. John Quincy
Adams has long been associated with the Hall and it was
where the House of Representatives elected him President.
After his presidency, Adams served as a Member in the Hall
for almost two decades before suffering from a stroke in
1848. He died soon after the stroke and today there lies a
brass plaque in remembrance of Adams marking where his
desk was once located in the Hall (Figure 1). Many
FIGURE 1 [3]
PLAQUE OF JOHN QUINCY ADAMS AT STATUARY HALL
historians believe that during session Adams would put his
head down on his desk and would be able to hear the
conversation of others standing on the other side of the Hall.
Today, Capitol Hill tour guides will point to the spot of
Adam’s deskand proceed to demonstrate the Hall's acoustics
and its advantages for eavesdropping. Skeptics, on the other
hand, argue that Adams could not have possibly discovered
the acoustical anomaly since the Hall’s interior design was
different from its current form.
The poor acoustics in the Hall made it difficult to
conduct business. The domed ceiling contributed to this, and
draperies were hung in an attempt to muffle echoes. After
many failed attempts to reduce the echo effect, the only
solution was to build an entirely new Hall, one in which
debates could be easily understood [4]. In 1850, a new Hall
was authorized to be built as an addition to the Capitol
building. The House of Representatives was moved into its
present location in the new House wing in 1857.
Once members of the House moved into their new
chambers the fate of the Old Hall remained uncertain. One
popular suggestion proposed to use the Hall as an art gallery.
In 1864, Congress passed legislation sponsored by
Representative Justin Morrill to invite each state to

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April 27, 2012 American University, Washington, DC
12th Annual New Millennium Conference
33
contribute statues of prominent citizens for permanent
display in the room. The law led to the renaming of the Hall
to the National Statuary Hall. By 1971 all 50 states had
contributed at least one statue, and by 1990 all but five states
had contributed two statues [5]. Artistic works intended for
the Capitol extensions were put on exhibit; among these was
a model for the Statue of Freedom, which rests atop the
Capitol Dome. The legislation also provided for the
replacement of the Hall’s floor, which was leveled and
covered with the marble tile [6]. The floor modification,
along with the replacement of the original painted wooden
ceiling, eliminated some of the echoes that earlier plagued
the room. Though the modifications were somewhat
successful in reducing the excess noise in the Hall, there
remained issues related to echoes in the Hall.
Today Statuary Hall is one of the most popular rooms in
the Capitol. It is visited by thousands of tourists each day
and continues to be used for ceremonial occasions. Special
events held in the room include activities honoring foreign
dignitaries and presidential luncheons. The Hall serves as an
icon of American government and known throughout U.S.
history for its attributes and flaws. Its architectural design
plays a role in its unusually acoustic properties.
ARCHITECTURAL DESIGN
In Statuary Hall, the acoustic anomaly is most largely due to
its architectural design. The Hall is an early example of
Greek revival architecture in America. The shape and form
was adopted from ancient Greek amphitheaters for the new
legislative chamber, with a lantern in the ceiling to admit
light during late sessions [7]. However, The Hall had one
infamous flaw. As Members addressed the House, the sound
of their voices echoed through the Hall. The high curved,
smooth wooden ceiling prompted a cacophony of sounds.
FIGURE 2 [8]
PRESENT DAY STATUARY HALL
Every noise reverberated several times throughout the room
creating echoes, and conversations occurring across the
room could be heard with alarming clarity, disrupting the
conduct of business.
The great Hall experienced structural modifications
throughout its history. While most wall surfaces were made
out of painted plaster, the low gallery walls and pilasters
were composed of sandstone. Around the room's perimeter
stand colossal columns of variegated Breccia marble
quarried along the Potomac River. The Corinthian capitals of
white marble were carved in Carrara, Italy. The chamber
floor is laid with black and white marble tiles; the black
marble was purchased specifically for the chamber, while
the white marble was scrap material from the Capitol
extension project, which included the new House of
Representatives [9]. Later additions made in 1901, including
a fireproof cast ceiling and a marble floor, eliminated most
echoes. However, some very interesting acoustical effects
can still be demonstrated today and explained by the ways
that sound travels through the Hall.
PHYSICS OF WAVES
In order to better understand the Hall’s special acoustical
effects, it is necessary to understand the properties of sound
waves. The world is full of examples demonstrating wave
motion. One encounters waves of different types every day.
This paper focuses specifically on the notion that sound is a
wave while also acknowledging other types of waves. Sound
waves will be explored in greater detail in a subsequent
section. Besides sound waves, one experiences radio and TV
waves, water waves, waves in microwave ovens, and even
earthquake waves. In each case, some sort of vibratory
motion causes a wave.
FIGURE 3 [10]
PAINTING OF THE OLD HOUSE

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April 27, 2012 American University, Washington, DC
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Types of Waves
A wave is a disturbance that travels through a medium by
virtue of the elastic properties of that substance. A medium
refers to a substance or material that carries the wave, such
as air or water. Transverse and longitudinal waves are two
types of waves. Transverse waves describe a motion where
the direction of the pulse is at right angles to the direction of
wave speed. Longitudinal waves are waves in which motion
travels along the direction of the wave rather than right
angles to it [11]. To help conceptualize the differences
among types of waves it is best to use the example of the
motion of waves within a rope and Slinky. When a rope is
attached to a doorknob and moved up and down, a transverse
wave similar to the second wave shown in Figure 4 is
created. The disturbance caused by the up and down motion
creates high and low points within the wavelength. The
distance between the top of one crest to the top on the next is
the length of the wavelength. Wavelength in a transverse
wave is illustrated in the bottom of Figure 4. The crests are
the highest point in the rope is and the trough is the lowest
point below the equilibrium position [12]. There are also
places along the rope where it is not displaced from its
equilibrium position, referred to as nodes. Some examples of
transverse waves include a violin string, or a string in a
piano.
The top half of Figure 4 illustrates a Slinky being forced
back and forth in the same horizontal direction. By pulling it
out straight and then hitting the end, its motion will result in
a pulse moving along it to the doorknob. The back and forth
motion produce a pulse different from moving the rope up
and down. The force of motion given disturbs the first coil;
which pushes the second coil and displaces it from its
equilibrium position. The coils continue to push or pull on
each other, which then is displaced them from their
equilibrium position. In Figure 4 the top image of the slinky
illustrates areas of compression, areas of tightening, and
rarefaction, regions where the coils are farther apart that
usual. The result is a disturbance that moves down the
Slinky and identified as a longitudinal wave. It is
characteristic that the disturbance in is in the direction the
wave is traveling in for longitudinal waves. This paper
focuses on sound as the most important example of
longitudinal waves.
Compressions and rarefactions are analogous to crests
and troughs in transverse waves, as seen on top of Figure 4.
The number of compressions, or rarefactions, that pass a
given point per second is the frequency of the wave. A
measured threshold of hearing at a specified frequency,
expressed in decibels relative to specified standard of normal
hearing. The frequencies audible to the human ear range
from approximately 20 – 20,000 hertz (Hz) [13]. When the
sound falls out of this range it is not audible and will not be
detected by the human ear. The frequencies of waves are
dependent on how many oscillations a wave experiences per
second.
Figure 4 [14]
PARTS OF LONGITUDINAL AND TRANSVERSE WAVES
Simple harmonic motion is a periodic motion in which
the restoring force is proportional to the displacement. This
motion repeats itself in time. A sine wave experiences
simple harmonic motion in which a small section of it is
repeated over and over. This concept helps explain how the
period and frequency of a wave are derived. The period is
the time it takes to make one oscillation. The disturbance of
repetition is known as the wavelength of the wave, which is
usually designated by a lowercase Greek lambda, 𝜆 [15].
The wavelength of a transverse wave can be measured from
the maximum of one crest to the next, or from a minimum of
a trough to the next; refer to the illustration on the bottomof
Figure 5. The wavelength and frequency are inversely
related, the higher the frequency, the shorter the wavelength.
The distance from the equilibrium position to the maximum
of a crest is called the amplitude of the wave. Another
important property of the transverse, or sine, wave is the
number of crests (or troughs) that pass a given point per
second; this number is referred to as the frequency of the
wave and is usually designated by ƒ. Frequency properties
are important when discussing sound.
Sound
Sound is a wave created by a vibrating object that
propagates through a medium from one location to another.
The medium that transmits it is commonly air. A sound
wave moves through air as a result of the motion of the air
molecules. When one talks, vocal cords exert a force on the
air molecules next to them. As a result, molecules are
displaced from their equilibrium, or normal position. The air
molecules, in turn, exert a force on the air molecules next to
them. A push, or pull force, displaces neighboring air
molecules. The disruption causes an acceleration or air
molecules in an outward direction fromthe source. The push
and pull motions continue all the way to the receiver [16].

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April 27, 2012 American University, Washington, DC
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Since the medium for sound waves in this example is air, the
formula for the velocity of sound is measured to be 340m/s.
(1)
The significance of the wavelength formula is that it allows
to solve for a missing value of frequency or wavelength
since v is already known. The formula also shows the
inverse relationship between wavelength and frequency and
how it relates to sound waves.
EFFECTS OF SOUND
In the case of Statuary Hall, members of Congress who were
holding session there in the 1800s were dissatisfied with
acoustics of the structure. One explanation relates its
structural design and the methods which this might influence
the interactions with sound waves. When a sound wave is
produced from a source, just as the conversations between
members of Congress, it is scattered. The scattering effect
distributes the sound wave almost like a ripple effect when
dropping a stone in a body of water. The wave spreads out in
all directions until it hits an obstacle.
Reflection of Sound
The ripple effect demonstrates the direction and motion of
waves and can also be used to visualize the effects of sound
reflection. If there is no obstacle in the path of the wave then
the wave will continue to travel away fromthe source. When
an object oscillates in water it produces constant waves that
travel in ripples towards the edge of the water, as illustrated
in Figure 5. When a sound wave encounters an obstacle,
such as a wall, floor, or a ceiling, part of the wave is
deflected from its original course. When sound waves
encountersuch an obstacle, it could be reflected or absorbed.
If the source of the sound were in midair without any solid
surfaces nearby, then it would be difficult to communicate at
distances greater than a few meters [17]. For Example,
members of Congress might hold their sessions outside
instead of the Hall. It would be necessary to talk much
louder outside in order to be heard by others, and it would
make personal conversations not as audible to others.
Usually members of Congress hold sessions inside where
their feet are on the ground, there is a ceiling and there are
walls all around. The sound reflected from hard surfaces
then reinforces the sound, making it easier for Congressmen
to hear at much greater distances.
If the source of sound is completely surrounded by hard
walls as in a room, then the reflections may become
extremely troublesome, as the return of a sound wave froma
surface is disruptive to meetings. Such is the case of Statuary
Hall, where each syllable could be heard several times and in
extreme cases the meaning of phrases was completely lost.
In effect, the problem of architectural acoustics made it
intolerable to carry Congress’ daily business. One of the
keys to good architectural acoustics is the balance between
getting enough reflections from the walls to keep the sound
level up, while at the same time not producing blurring of
the sounds because of excessive reverberation.
FIGURE 5 [18]
THE RIPPLE EFFECT DEMONSTRATED IN WATER
Reverberation and Obstacles
The presence of walls creates an enclosed space around the
sound wave source and changes the character of a sound
field. The enclosed volume of air becomes a system that is
excited with moving air molecules while the sound source is
emitting. Enclosures, particularly those that are used as large
halls, have linear dimensions that are significantly larger
than the wavelength of sound waves, even for low
frequencies. If the obstacle is very large compared with the
wavelength, very seldom for sound, half of this scattered
wave spreads out, and the other half is concentrated behind
the obstacle. If the obstacle is very small compared with the
wavelength, often for sound waves, then the entire scattered
wave is sent out uniformly in all directions [19]. In these
types of scattered wave the vibration dies away if it does not
hit an obstacle.
With speech, characteristic vibrations arise in the air of
the room at frequencies corresponding to the component
frequencies of the source. When a wave strikes a body in its
path, a scattered wave spreads out from the obstacle in all
directions [20]. Reverberation is the persistence of sound
after the source has stopped emitting, and is caused by
multiple reflections of the sound within a closed space. It
consists of multiple, blended sounds caused by reflections
from walls, ceilings and other structures which do not absorb
sound
As waves hit a hard, smooth surface, the waves are
reflected. Obstacles affect the path of sound waves after its
reflection. The wave that encounters the boundary, or
incident wave, is reflected. The incident and reflected wave

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April 27, 2012 American University, Washington, DC
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create a scissor like effect when they intersect, as illustrated
in Figure 5. The intersection of sound waves along the
medium constitutes a projection of the incident and reflected
waves.
FIGURE 5 [21]
SOUND BEING REFLECTED ON A BARRIER
The ear has the ability to receive sequences of sound
impulses and sum their energy, provided that the interval
between the impulses does not exceed minimum delay time.
A person can often perceive a time delay between the
production of a sound and the arrival of a reflection of that
sound off a distant barrier. If the intervals are greater than
the minimum delay, then there is a gap between the signals
and the ear identifies the reflection as a distinct echo, which
is particularly noticeable when the level of the reflection is
comparable with the level of the basic signal [22]. The
degree of sound amplification depends on the absorption of
energy at the boundaries of the enclosure.
The level of sound amplification within Statuary Hall
creates speech that sounds livelier and in other areas where
the same conditions apply, music can become more full. A
noticeably long reverberation renders speech less
intelligible. The preferred reverberation time range for a
space intended for speech is 1.0 second, or less. As the
reverberation time becomes longer than that, it becomes
increasingly difficult to understand speech. In this case, the
sound of quality becomes lessened. When the reverb time is
long enough, it not only masks the next syllable, but it can
mask the next word. The loudness of sound, in certain
conditions, is increased by virtue of the normal modes of
vibration of the air contained in the enclosure. Contrary to
experience in unconfined space, the increase in loudness is
particularly noticeable by listeners fairly remote from the
sound source. One method of reducing this loudness is to
increase absorption in the Hall.
Absorption
Sound waves have unique effects on the surface of materials
when a wave impinges on it. Different materials react
differently to sound, depending on their structure. This
allows a reduction in the amount of sound energy reflected.
The introduction of an absorbent material into the surfaces
of a room will reduce the sound pressure level, or physical
intensity of the sound, in that room by not reflecting all of
the sound energy striking the room's surfaces. The effect of
absorption reduces the final sound level in the room. For
example, nonporous materials yield slightly to the vibrations
of sound waves, since they are never perfectly rigid. Porous
materials also allow some air to penetrate below the surface,
producing an additional effective motion of the surface. The
reaction of different materials to sound is dependent on that
material’s absorption coefficient. It is a measure of the
sound-absorbing ability of a surface and defined as the
fraction of incident sound energy absorbed. The values of
the sound-absorption coefficient usually range from 0.01 for
marble slate to almost 1.0 for long absorbing wedges often
used in anechoic rooms. The reaction is expressed as a ratio
between pressure at the surface and the normal velocity of
the surface [23].
The absorption coefficient can be mathematically
presented as follows:
(2)
Where:
 α is the sound absorption coefficient
 IR is the intensity of the reflected sound
 II is the intensity of the source sound
Absorption coefficient ( α ) for some common materials can
be found in the table below:
TABLE I [24]
THE SOUND ABSORPTION COEFFICIENT OF MATERIALS

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April 27, 2012 American University, Washington, DC
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All materials in an enclosure will absorb and reflect
sound. A fraction of the incident energy is absorbed and the
balance is reflected. A perfectly hard surface will reflect
back all of the energy. In the case of Statuary Hall, the hard
materials it was made out of added to the reverberations and
contributed to the line of echoes heard.
Echo, Echo
An echo is due to the reflection of sound waves. A reflected
wave is perpendicular to the incident waves as a result of the
law of reflection for sound waves, and illustrated in Figure
6. The law states that the incident angle will always be equal
to the reflected angle when a wave is reflected from a
barrier. A spherical surface, for example, does not reflect
sound to a point, even though all waves head towards the
same region [25]. Usually an echo is a strong reflected sound
that is sufficiently delayed from the direct sound, the
original sound wave. If a sound wave returns within 1-10
seconds, the human ear is incapable of distinguishing it from
the original one. In cases which sound requires 1-20 seconds
to reach the reflecting surface and the same time to return, it
can be heard as a separate entity rather than as a continuation
of the original sound [26]. The properties of reflection help
to understand how echoes work.
Reflected sounds help create a sense of fullness in a
room; however, it is not always desirable. Fortunately, high-
frequency waves are easy to dampen because of their high
level of activity. High-frequency sound waves tend to
bounce around, similar to light waves, on reflective surfaces.
Such surfaces, for instance mirrors or windows, add to the
echoes. One solution is to cover themwith blinds or curtains
to dampen the effect. Dampening the effect was one of the
methods employed by the staff at Statuary Hall. They hung
draperies and added more materials that would assist in
reducing the effects of reverberation and added more
absorbing material. Ultimately these efforts proved
unsuccessful and a new House of Representatives was built.
These acoustical effects were not only present in Statuary
Hall, but also studied elsewhere.
Whispering-Gallery Effect
Nobel Prize winner and physicist, Lord Rayleigh explained
the efficient propagation of sound waves around the inside
dome of St. Paul’s Cathedral in London in the late 19th
century, offering an explanation for the whispering-gallery
effect. Between the speaker and listener multiple paths exist,
each having a unique number of reflections off the surface of
the dome. When the travel time of the sound is similar,
constructive interference and amplification takes place [27].
Constructive interference describes a phenomenon in which
the interference of two or more waves of equal frequency
and phase produce a single amplitude. The amplitude will be
equal to the sum of the amplitudes of the individual waves.
An audible sound will travel around the inside of the dome
with exceptionally low attenuation, or weaker in intensity
form the original sound. The sound waves traveled around
the gallery in a narrow belt guided by the circular walls.
Therefore less reduction of sound intensity by various means
such as air, humidity, and porous materials, is experienced.
Whispering-gallery modes, numerous patterns of wave
motion or vibration, depend only very slightly on its ability
transmit sound. The explanation of the whispering-gallery
effect is rooted in the principle of the succession of
reflections, which is largely influenced by the Hall’s
architecture.
SOUND FIELDS AND ARCHITECTURE
Sound reflected from walls generates a reverberant field that
is time dependent. Reverberant field refers to the region in a
room where the reflected sound dominates, as opposed to the
region close to the noise source where the direct sound
dominates. When the source suddenly ceases, a sound field
persists for a certain time interval. The residual acoustic
energy constitutes the reverberant field, or the sound that
reaches a listener in a typical auditorium. The region in a
room where the reflected sound dominates describes the
effect of a reverberant field [28]. Two broad categories
classify reverberant field: the direct (free filed) sound and
indirect (reverberant) sound. The amount of acoustic energy
reaching the listener’s ear by any single reflected path will
be less than that of the direct sound. The differences in
reflection are illustrated in Figure 6. The result is greater
divergence, and all reflected sound undergoes an energy
decreases due to absorption of even the most ideal reflectors.
FIGURE 6 [29]
REFLECTION OF SOUND IN AN AMPITHETER
Individual vibrations, which make up the reverberation,
may decay at different rates. The dissimilar decay rates
result from the fact that the sound absorptive properties of
various areas of the surface forming the boundaries of the
enclosure may be very different from one another [30]. As a
result, the sound field becomes uneven. The response
characteristic of an air space, like that of any other vibratory
system, depends on the dimensions of Statuary Hall.

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April 27, 2012 American University, Washington, DC
12th Annual New Millennium Conference
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SUMMARY
The whispering-gallery effect at Statuary Hall is one that
many physicists explore in depth. The idea that a
whispering-gallery effect is produced at the great Hall is
supported by physics concepts such as reflection,
reverberation, echoes, and absorption. Ultimately, Statuary
Hall is an example of poor acoustical design. The structure
attributed to the intensified sound level and echoes made
everyday business hard to conduct. Currently Congress
members enjoy a new Hall with the proper acoustics.
Statuary Hall remains as one of the most historic sites in the
Nation’s Capital.
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[4] 24, Feb. 2012 http://www.aoc.gov/cc/capitol.
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[17] Stobart, H., & Kruth,P. Sound. UnitedKingdomat the
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water.jpg
[19] Morse, M. P., Vibration and Sound. American Institute of
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http://learningsparkle.blogspot.com/2009/04/waves.html.
[22] Ref. 10
[23] Ref. 9
[24] 22, Feb. 2012 http://www.engineeringtoolbox.com/accoustic-
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[25] Rossing, M. The Science of Sound. 3rd
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[26] The Columbia Electronic Encyclopedia. 2007, Columbia
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[27] Bannister, Peter R.VLF/ LF/ MF Whispering Gallery
Propagation Studies. U.S. Navy Publication. 9 Sep. 1981.
[28] Raichel, D. The Science andApplications of Acoustics: Modern
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[29] 23, Feb. 2012 http://www9.dw-
world.de/rtc/infotheque/sound_processors/REVERB1.gif.
[30] Ref. 10.