physics of an effective public speaker

Physics of an Effective Public Speaker

PHYSICS 1204 / MUSIC 1466Dr. Selby

John ScrughamMay 10, 2012

Introduction

It was with delight that one who remembers Edward Everett in his robes of rhetorical splendor;

who recalls his full-blown, high-colored, double-flowered periods; the rich, resonant, grave, far-

reaching music of his speech, with just enough of nasal vibration to give the vocal sounding-board

its proper value in the harmonics of utterance.

-Oliver Wendell on American politician and legendary orator, Edward Everett’s 1887

speech at Cambridge (Fillebrown 10)

Although Oliver Wendell gave Edward Everett a verbose and positive review of his

speaking, Wendell, and even many scientists 1in 1887, did not completely understand the physics

of why Everett sounded so great. Wendell did notice the beautiful sounds that were coming from

Everett’s throat and mouth, but he used words such as harmonics, vibrations, and resonance that

were not well understood at the time. Within a few years of Everett’s speech though, our

understanding of sound and physics expand rapidly with the help of great breakthroughs such as

Wallace Sabine’s research on architectural acoustics (1895) and Lord Rayleigh’s book The

Theory of Sound (1894). Over the course of the next century, our understanding of physics and

sound continued to exponentially grow. Now we can fully explain the harmonics, vibrations, and

resonance of Everett’s voice. More than merely explaining the voice of a 19th century politician,

we have the power to manipulate the physics behind our voice so that we can become more

effective speakers.

While scientists have published research on speaking and physics, little research has been

published on the interplay between speaking and physics—i.e., how speakers can harness the

physics of their voices to become more effective speakers. I hope to provide that connection in

1 On the forefront of sound and physics research was Helmholtz’s published book On the Sensations of Tone as a Physiological Basis for the Theory of Music (1863).

Scrugham, The Physics of Good Public Speaking, p. 1

this paper. I will focus on two techniques—and the physics behind them—that effective speakers

can harness to deliver powerful speeches: you can achieve a heartier voice through vowel

darkening, pulling your larynx down, and by thickening your vocal chords; you can better project

you voice by tightening your vocal folds and by using belly breathing to achieve greater lung

volume.

Before delving in to the techniques that effective speakers employ, let’s look at how we

produce sound. The human instrument’s first part is the diaphragm which is a muscle under the

lungs that forces the lungs up and down: it is the driving force of the instrument. The lungs,

beyond giving us oxygen to sustain

life, serve as the energy source for

sound produce. The trachea and the

esophagus are tubes that connect the

lungs (energy source) to the vocal

folds (sound production) and have

little acoustic significance. Above

the esophagus, in the throat, lies the larynx which contains the vocal folds (Rossing 337-339).


Figure1: The mechanisms of human sound (Rossing 337)

The vocal folds are a muscular tissue that vibrates if we achieve the correct air pressure

and tension in the larynx. The vibration is

depicted in the graph on the next page

where the V-shaped opening opens and

closes rapidly in sound production. The V-

shaped area between the folds is called the

glottis (Rossing 339). The glottis is open

when we are breathing normally or when

we make open consonants such as “f” or “sh.” The glottis is closed in times like right before you

cough. Lastly, and most importantly, the glottis can rapidly open and close, which makes a

buzzing sound in your throat. This occurs when you speak vowels and voiced consonants. The

frequency of your voice is determined by the buzzing sound of the vocal folds (Wolfe).

However, we don’t talk in buzzes; we have the ability to speak smoothly. This is because

we have a filter above the vocal folds that is composed of the upper throat, mouth, tongue, lips,

and nasal cavity, which together round out the buzzing sound from the folds. All of these parts

come together as a “resonance chamber” and play an important role in creating good sound

(ibid). An example of a part not working correctly is when we have a stuffy nose. Our voice

changes because the resonance chamber is significantly decreased in size when mucus fills the

nasal cavity. Your voice is often flatter—or “nasally”.

Now that we understand how humans produce sound, let’s look in to some things that

you can do to become a better speaker. Namely, creating a heartier voice and projecting a louder

voice.

A Heartier Voice


Figure2: The vibration of the vocal folds (Wolfe)

A heartier voice is a voice that is deep, rich, and resonates well. Examples include the

voice of a sports announcers and good actors. You can obtain a heartier voice by using vowel

darkening to decrease your formant frequencies and by dropping your larynx to create a richer

and lower pitch. You should strive for a heartier voice for two reasons.

First, your voice often sounds deeper and richer to yourself than it does to other people,

so it may not be as deep and rich as you think it may be. In a study, participants listened to

recordings of themselves speaking and were asked to compare the recorded voice to the voice

that they believed to have. The subjects perceive their voice in the recording as being higher-

pitched and less rich, both undesirable traits of good voice (Lundh 25). We think that our voice is

deeper and richer than it actually is because when we talk, the eardrum, ossicles, and cochlea—

the places where sound is transferred from the sound air waves to electrical signals to the brain—

picks up on not only the sound outside (like they normally do) but also pick up on low-frequency

vibration through bone conduct (your check bones, skull, jaw) originating from your mouth and

throat (Wolfe). Our perceived voice is thus a combination of bone vibration and air vibration.

The second reason that you may want to gain a heartier voice is that there is a wealth of

research on the benefits of having a lower voice. For many years, men have dominated

leadership positions, so some scientist say that voices that sound more like a male leader (around

70-200 Hz) are perceived as being more effective (Campbell 160). While the discussion of why

deeper voices are perceived this way is outside the scope of this paper, the implications are that

by lowering your voice (in both pitch and tone quality) you can become a more effective

speaker. Men with lower-pitch voices are said to be stronger (Feinberg 562) and more socially

dominant (Gregory 525) and women are perceived to be socially dominant with deeper voices

(Borkowska, 2011).


Our actions reflect our perceptions of people with lower voices: we prefer people with

lower voices to be our team leader, CEO, and even president (Campbell, 1960) (Kloftstad, 2012).

In a recent study conducted by Casey Kloftstad, it was found that people vote more often for

candidates with deeper voices. The research team played recordings of a person saying, “I urge

you to vote for me this November” to participants. The team played two variations of this

recording: higher and lower pitched versions of the original statement. The lower pitched version

was shifted down about 20Hz and the higher pitched version shifted up 20Hz from the original.

The team asked the participants, “if [the two people in the recordings] were running against each

other in an election, which one would you vote for?” Male and female participants selected male

and female leaders with lower voices more often than the higher-pitched voices even though it

was the same person speaking in both recordings (Klofstad).

Perhaps the most famous story of a leader lowering and darkening her tone of voice is

that of Margaret Thatcher and her rise to prime ministry. Her advisors, particularly her political

strategist Gordon Reece, wanted to train her to speak in a heartier voice in order to increase her

chance of winning the elections (Dunbar). Reece and the rest of the advisors most likely wanted

to change Thatcher’s voice in lieu of the consistent, and sometimes harsh, criticism. One such

criticism was delivered by television critic Clive James’ in The Observer during the 1973

elections:

The hang-up [with Thatcher] has always been the voice. Not the timbre so much as, well, the tone

—the condescending explanatory whine which treats the squirming interlocutors as an eight-year-

old child with personality deficiencies…She sounded like a cat sliding down a blackboard (Clive).

Reece understood the need to change Thatcher’s voice, especially before the 1979 elections.

Luckily, Reece had a chance run-in with one of England’s best actors, Laurence Oliver, on a


train ride out of London. Reece asked if Oliver could help Thatcher to improve her vocal quality.

Oliver agreed to help and arranged lessons between Thatcher and his speech coach at the

National Theatre. After a year’s training, Thatcher lowered her voice by 46 Hz and darkened

many of her tones including her harsh, high shrills (Dunbar). It paid off. Not only did she win the

elections but critics also took a noticeable shift to enjoying her speaking. Charles Moore, the

author of Thatcher’s autobiography-in-process, noted that, “soon the hectoring tones of the

housewife gave way to softer notes and smoothness.”

So how exactly did Thatcher rid herself of the shrill and

high pitch of her voice? Let’s take a step back and look at how we

produce pitch, specifically vowel sounds. We have the ability to

make sound by vibrating the vocal folds so that they rapidly open

and close. The frequency at witch these folds vibrates determines

the pitch of the voice (Wolfe). The first sound spectrum that you

see on the right is a chart of the frequencies produced from the

vocal chords and their relative strength. As you may recall, the

“resonance chamber” above the larynx filters the buzzing sound

that is produced from the vocal chords. The amount and how it

filters depends on how you position each part of the chamber

(Rossing 340). For example, sing “ah.” Now, sing “ee.” Notice

how on the “ee,” you pull your tongue up, make your mouth smaller, and move your lips back.

The shape that your “resonance chamber” takes on the “ee” versus

the “ah” makes significantly different sounds because the intensity

of different harmonics differs with each shape. This is exemplified in the second graph. The


Figure 3: Filtering of vocal fold frequencies and the presence of formants (Selby Lecture 32, Slide

20)

shape of the “resonance chamber” resonates with some frequencies found in the first graph (high

peaks of resonance) and “filters” other frequencies that do not resonant well with that shape

(valleys between the high peaks). The frequencies that resonate the most (the peaks) for a certain

resonance chamber shape are called the formants. Lastly, the vowel sound that reaches an

audience carries the original frequencies produced by the vocal chords with the relative

intensities determined by the resonance chamber (third graph).

You can produce different sounds that have different formant frequencies as we saw in

“ah” versus an “ee.” In fact, all vowels have a different “frequency envelope”—or shape of

formants. Vowels with the first formant (the first peak of high resonant intensity) in the lower

frequency ranges are said to be darker vowels.

You don’t have to always use darker vowels to have a darker and richer timbre. To create

a darker, richer timbre, you can lower the frequency of your first formant artificially; this is

called vowel darkening (Selby Lecture 33). To do this, push your tongue back towards your

throat while still allowing air to come up from the vocal tract. Back vowels, or dark vowels, are

created this way (Lewis 47). The graph on the right

illustrates what happens if you were to darken an

“ah.” The first formant in a normal “ah” lies at 700

Hz as seen in the first chart. By pushing your tongue

further back when sounding the “ah,” you shift the

first formant down to 300 Hz as exemplified in the

second graph. Notice that the frequencies present

(represented by the vertical lines) remain the same in

both graphs. Thus, pitch remains constant, yet the tone quality changes. This occurs because with


Figure 4: Vowel darkening (Selby Lecture 33, Slide 19)

vowel darkening, we are not altering our vocal folds; rather, we are changing the shape of the

resonance chamber at the end of the human instrument.

The second way to create a heartier voice is to pull the larynx down. This lengthens the

vocal tract and widens the pharynx. Let’s first look at what happens when we lengthen the vocal

tract. As you may recall, the larynx (the voice box) holds the vocal folds and can move up and

down. When you lower your larynx, you lower the position of your vocal folds, lengthen the

pharynx (the area above the larynx), and subsequently lengthen your vocal tract (Wolfe). The

physics behind lower our voice by lengthening our vocal tract is as follows. Below is the

equation2 for a standing wave in an open-closed pipe3

Frequency=Velocity of Sound

4 Length

Velocity of Sound= 354 m/s at 37°C (which is the temperature of the air in our throats)

The average resting vocal tract length for an adult male is 16.9 cm.4 Using this as our length (L),

we can solve for the frequency that the resting larynx would naturally produce.

Frequency = 354 m /s

4 (.169)m=523.67Hz

Let’s say you drop you’re your larynx down 1 cm so that the total length of your vocal tract is

now 17.9 cm, what would happen to the frequency of your voice?

Frequency = 354 m /s

4 (.179)m=494.4Hz

The frequency of your voice dropped 29.3 Hz from 523 Hz to 494 Hz by lowering the larynx

1cm. Margaret Thatcher was able to lower her voice by 46Hz which means, if we hold all other

2 To simplify, I eliminated the modes from the equation, so that we can only solve for the fundamental frequency of the system. I understand that n=1,3,5,… (only odd modes present in this system).3 The human vocal tract is an open-closed pipe. The vocal folds start the closed open of the system and the moutt is the open side.4 Goldstein, U.G. (1980) An articulatory model for the vocal tracts of growing children. Ph.D. dissertation, Massachusetts Institute of Technology, Cambridge, MA.


factors constant, that through training, she was able to hold her larynx 1.9 cm lower than it was

before training (Dunbar)!

The second thing that lowering the larynx does is that it widens your pharynx. This

lowers your fourth formant frequency which creates richer sound. In a study, it was found that in

the production of vowels, better-than-normal male voices have a fourth formant that is lower

than worse-than-normal male voices. A better-than-normal (BNQ) voice was determined by a

group of linguistics PhD students on qualities such as richness of voice, strength of sound, and

resonance of the voice (Bele 570).To be an effective speaker, we should strive to lower our

fourth formant.

To achieve a lower fourth formant frequency, the pharynx has to be widened because it

naturally creates many high harmonics when vibrating with a small opening. When an average

male talks, the pharynx’s fourth formant resonates at 3,500 Hz (Bele 574). When we widen the

pharynx, longer wave lengths have the ability to form in that area, thus decreasing the frequency

and lowering the fourth formant. To support this claim, let’s look at the equation that drives this

assumption: velocity is proportional to frequency times wavelength, v = ƒ λ. When we widen our

pharynx, the wavelength (λ) increases. Since we aren’t changing the speed of our breath (v), in

order for the equation to stay balanced, the frequency (ƒ) must decrease proportionally to

wavelength. By widening the pharynx, we are able to drop the frequency of the fourth formant

by on average 200Hz (579), which contributes to darker and richer sounds, much like how vowel

darkening lowers the first formant frequency.

In the study though, the better voices had naturally wider pharynxes, but you can

artificially widen the pharynx by lowering your larynx. To widen your pharynx, you need to

achieve the same motion as if you were just about to swallow. When you are about to swallow,


you lower your larynx, which pulls down of the pharynx and widens it to let food down the

throat. Once you achieve the same action of swallowing, hold the larynx down but don’t

swallow. Now, produce sound with this set up and your fourth formant frequency will be lower

and your voice will sound richer.

Lastly, you can make your vocal chords thicker to create a heartier voice. Let’s look at

how vocal folds interact with air passing through your throat first. Looking at the chart below,

the folds on the left are the thick folds and the folds on the right are thin folds. The chart depicts

the first 3 steps in a cycle of the folds flipping up and down when producing sound. Notice how

the thick vocal folds close completely for

longer than for thin vocal folds. Because

the thick folds stay closed for longer than

they are open during the cycle, the sound

pressure created is non-sinusoidal5, and

thus produces a richer timbre (Rossing

384-386).

To achieve thick vocal folds, flex the folds so that the muscles contract and bulge (similar

to how your muscles flare up with flexing during lifting heavy objects). You will know that you

your vocal chords are thick when you feel significant vibration in the chest register. This is

called your “chest voice.”

A Louder Voice

5 Sinusoidal sound is a pure sound that comes from a sine wave. It has one tone with no other harmonics present. On the contrary, when air is passed across the thick vocal folds, the resulting pressure wave is a non-sinusoidal. High harmonics then capture the “roughness” that a non-sinusoidal wave has (such as a square wave or saw-toothed wave).


Figure5: Thick versus thin vocal chords in first 3 phases of vibration cycle (Rossing 387)

By projecting your voice, your audience will be able to more easily hear your message. If

an audience can hear and interpret the words of your message, you can be a more successful

speaker. To get a louder voice, you can use belly breathing and use a voice with strong high

harmonics.

Research has been conducted on the positives of speaking louder. Jean Krause wanted to

understand how a person can communicate as clearly as possible to people who are hearing

impaired. She analyzed how the volume of read statements affects listener comprehension. Two

groups of participants were set up: a reader and an audience member who was hearing impaired.

The readers were instructed to read ten sentences. The team then normalized the loudness of the

sentences of all of the readers and created a louder and softer version of the statement which was

15 dB apart. An audience member then listened to the recording and wrote down what they

heard. Krause found that the audience understood 53% of the words in the loud speech whereas

only 43% of the words in conversational speech were understood (Krause 2172). While the

hearing impaired may benefit more from louder speaking, the implication for regular speech is

that, in general, it’s easier better understand someone when you can hear all the words that they

are saying.

First, we can speak louder by speaking in a pitch with strong frequencies which our ears

are most sensitive to. The loudness perceived by the audience varies across frequencies. The

graph on the right shows that the

sensitivity of our hearing is poorest for

very low and very high frequency sound

(think about how hard it is to hear a dog

whistle). One line contour represents equal


Figure 6: Frequency and intensity of equal sensitivity sounds (Selby

loudness and frequency as perceived by the human ear. Let’s use the bottom contour (the solid

line above the dotted line) as an example. On the far left, the contour line lies at a frequency of

50 Hz and loudness of 80 dB which creates a sound as sensitive as 5000 Hz and loudness of

10dB which is the far right of the same contour line; a speaker can just as effectively yell (80 dB)

at 50 Hz as barely whispering (10 dB) at 5000 Hz (Rossing 108).

The volume that you choose to speak at is influenced by the frequency of your voice.

Choosing frequencies where our hearing is the most sensitive—1000 to 7000 Hz—will give the

speaker the greatest ability to produce a sound that has the most sensitivity to the audience’s ears

(Wolfe).

Although our ears are most sensitive at these ranges, humans cannot produce sound with

its fundamental frequency as high as 5000 Hz. Therefore, we must make sound with high

frequency 3rd and 4th formants to carry the sound far. We can produce high 3rd and 4th formants by

influencing the rate of glottal closure. When the V-shaped vocal folds shake faster, we can

produce higher harmonics that resonant in the vocal tract (Pinczower 447).

To increase the rate of your glottal closure, you can increase the tension of the vocal folds

so that when air goes by them, the speed at which they vibrate increases. When we increase the

tension, we increase the velocity that the glottal closure vibrates at as displayed in the following

equation:

V= √ Tμ

T = tensionμ = mass per unit length


Second, we can maximize the volume of our lungs to create louder sound. At normal

breathing, the sub glottal pressure6 is 100 N/m2, yet we have the ability to fill our lungs to exert

up to 10,000 N/m2 in pressure when the glottis is closed. There is a direct relation between sub

glottal pressure and the maximum loudness you can produce with that pressure, so the more

volume in our lungs, the more pressure we can

exert on the vocal folds and the louder we can

project our voice (Rossing 381).

So what techniques are there to get more

air in the lungs? Many singers use a technique

called belly breathing. They achieve higher lung

volume through belly breathing by lowering the

diaphragm and pulling out the walls of their

abdomen as shown in Figure 7. This creates a larger lung cavity to pull in air to the lungs

(Sunderg 284). Effective speakers have adapted the signer’s techniques of belly breathing to

ensure that they can project their voice during oration (Marshall).

Belly breathing is preferable over

chest breathing because it allows more air to

enter the lungs. In chest breathing, we elevate

our ribs to create more room in our lungs to

breathe in. This is called shallow breathing

because we only use the top part of our lungs to inhale and exhale the air that we need.

6 The pressure that our lungs exert on the glottal area (the area below our vocal folds) is called the sub glottal pressure.


Figure 7: A human cross-section of belly breathing (Rossing 380)

Figure 8: Lung volume modes (Rossing 382).

Figure 8 shows the potential volume that you can add to your lungs by using belly

breathing. The tidal volume is the volume during normal breathing and falls between 2,400 and

2,800 cm3; this is the volume fluctuation of our lungs when we chest breath. The inspiratory

reserve volume is the volume we can fit in to our lungs (Rossing 382). With belly breathing, we

can maximize our use of the inspiratory reserve volume which gives us on average 3000 cm3

more volume, nearly doubling the maximum volume that we can speak at from chest breathing

(Sundberg 290).

Conclusion7

We are able to be smarter about how we speak by understanding the underlying physics

of our voices. Because we know what makes sound, we can modify the mechanisms in a positive

way to create a voice that is both rich and loud, which is a voice that is more effective in

persuading individuals and getting them to trust you. Recall that you can achieve a heartier voice

through vowel darkening, pulling your larynx down, and by thickening your vocal chords; you

can project you voice better by tightening your vocal folds and by using belly breathing to

achieve greater lung volume. While I don’t promise that these tactics will lead you to presidency

or influence writers to publish wonderful prose about your speeches, I can ensure you that your

public speaking will greatly improve if you adapt and practice some of the tactics outlined.

7 In addition to my concluding remarks, I would also like to make it apparent of conflicting physics in the richer voice and louder voice production. I know that a higher frequency produces a louder sound and that getting a richer voice means making a lower sound. How can we get a higher and lower frequency at the same time? We can’t; it’s a trade-off between the two. One work around is to use the tactics of gaining a heartier voice and use a microphone to help you project your voice.


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physics of an effective public speaker

Education

good public

inspiratory

change thatchers

normal male

fourth formant

glottal closure

vowel darkening

vocal chords