2Music & Acoustics

Question 1

Define Acoustics

Answer 1

The science of the production, propagation & perception of sound

Question 2

A soundwave has longitudinal motion. What does this mean?

Answer 2

The movement of oscillation is parallel to the direction of movement overall

Question 3

The rate at which the crests or troughs of a wave pass a point is called what?;
This is measured in units of what?

Answer 3

Frequency;

Hertz

Question 4

The amount of energy used in terms of displacement from the centrepoint of peaks & troughs is called what?;
The perceived loudness of a sound is measured in units of what?

Answer 4

Amplitude;

Decibels

Question 5

A complex tone can be reduced to its sinusoidal components. What is the lowest of these components?;
Which number harmonic (or partial) is this?

Answer 5

Fundamental tone;

First

Question 6

What is the term for a complex tone which has a recurrent wave shape (repeated pattern) & an integer relationship between its components?;
Random looking wave shapes with no integer relationships (e.g. white noise) is called what?

Answer 6

Periodic (or harmonic);

Aperiodic (or anharmonic) - can’t multiply one frequency by another

Question 7

What determines Timbre (or characteristic) of a sound?

Answer 7

The various amplitudes of different overtones within a complex tone

Question 8

Which frequencies are emphasized on a power spectrum when a higher pitch is produced?

Answer 8

Lower frequencies (& vice versa)

Question 9

Explain the concept of Coupled Acoustics

Answer 9

A musical instrument has two vibrating devices where one generates the sound & the other amplifies it

Question 10

Give 3 examples of a Resonator

Answer 10

Hollow tube; air chamber; soundboard

Question 11

Any given resonator is likely to serve as a better what?

Answer 11

Conduit for certain frequencies than others

Question 12

It takes more energy or amplitude to perceive what?

Answer 12

Very low or very high frequencies (e.g. 100db to hear 20Hz or 80db at 20kHz)

Question 13

List some string instruments;

Answer 13

Bowed or plucked: Violin, viola, cello, double bass; plucked: guitar, harpsichord; struck: piano

Question 14

What does the fundamental frequency of string instruments depend on?;
What is the sound source?;
What is the sound modifier or resonator?

Answer 14

The mass per unit length, tension & length of the string;
The vibrating string;
The air contained within the body of the instrument & top plate; or soundboard on a piano

Question 15

How are Edge Tones created in woodwind instruments?;

How is the length of the resonator (air column) changed?

Answer 15

By blowing across a hole & onto a sharp edge (e.g. flute & recorder);
By means of finger holes

Question 16

How are Reed Tones produced?

Answer 16

By setting one reed (in clarinets or saxophones) or two reeds (oboes or bassoons) vibrating, which produces sound waves in adjacent air columns

Question 17

What is the sound source in brass instruments, such as trumpets, trombones & tubas?;
What does Embochure mean?
What do Valves or Sliding Tubes (in a trombone) do?

Answer 17

The player’s vibrating lips in the mouthpiece;
Shape & tension of the lips influence the vibration;
Change the length of the resonator

Question 18

With the exception of the xylophone, glockenspiel or marimba, what do most percussion instruments produce?

Answer 18

Non-periodic sounds

Question 19

What are Membranophones?

Answer 19

Instruments with vibrating membrane usually stretched over a frame of wood or metal; struck with a stick or hands

Question 20

What are Idiophones?

Answer 20

Instruments that produce sound by the vibration of their own material; doesn’t depend on membrane, string or air cavity (e.g. bell, gong, Jew’s harp, triangle)

Question 21

What is Direct sound?;

What is Reflected sound?

Answer 21

Travels directly from the source to the listener;

Reaches the listener by bouncing off one or more surfaces (e.g. walls, ceilings, pillars, etc)

Question 22

Define the Initial-Time-Delay-Gap (ITDG);

What is the optimal ITDG for concert halls?

Answer 22

The time at which the first reflection is heard after the direct sound;
Around 15 milliseconds

Question 23

What is the Clarity Index?

Answer 23

A measure of the ratio of early sound energy (from early reflections arriving within first 80ms of direct sound) to late sound energy (late reflections arriving after 80ms)

Question 24

Which shaped concert hall seems to be the preferred listening space?;
Why is this?

Answer 24

Shoe-box;
The narrow width of the hall allows for stronger lateral (side to side) reflections to compliment sounds coming from the stage (shorter time lag); but at the back under balconies no good as sound won’t reach

Question 25

Why are fan-shaped concert halls problematic?

Answer 25

Progressively widening curved walls towards the back diffuse many sounds away from the listener & sounds arrive at different time intervals (longer lag in middle); also reflected at an angle so sounds get lost

Question 26

Which shaped concert halls face similar problems to fan-shaped?

Answer 26

Horse-shoe, but more intimate with better ambience, so preferred

Question 27

What are Porous Absorbers?;

What are Resonant Absorbers?

Answer 27

Materials such as curtains, carpets & seats which tend to absorb higher frequencies;
Materials such as wood panels which may vibrate in sympathetic response to low frequencies

Question 28

How can Reverberation be defined?

Answer 28

The length of time for a sound to decay by 60 decibels

Question 29

What are advantages & disadvantages for reverberant performance spaces?;
What about dry performance spaces?

Answer 29

They reflect sound in many & varied ways; fuller sound; better for music, but long reverb time makes it difficult for musicians to hear each other & overall sound;
Better for speech as sound is clear & crisp, but sound is absorbed so it’s difficult for musicians to fill the space

Question 30

What is the frequency ratio for the pure tuned interval of Unison?;
Octave?;
Perfect fifth?;
Perfect fourth?

Answer 30

1: 1;
2: 1;
3: 2;
4: 3

Question 31

What is the frequency ratio for the pure tuned interval of 
Major sixth?;
Major third?;
Minor sixth?;
Minor third?

Answer 31

5: 3;
5: 4;
8: 5;
6: 5

Question 32

What did the Pythagorean Scale result from?;

What did the tuning system entail?

Answer 32

Attempts to create a scale based on the largest number of perfect (or beatless) fourths & fifths;
Tune each note relative to the first note of the scale; calculate ratios for adjacent pairs of notes

Question 33

What were the problems with the Pythagorean tuning?;

Answer 33

Discrepancy between tuning by fifths & tuning by octaves; same problem when tuning with Hertz; ugly sounding notes when trying to tune notes not belonging to home key; enharmonic notes such as F# & Gb would generate their own sound

Question 34

What was the discrepancy called when tuning by pure fifths didn’t match up with octaves in Pythagorean scale?

Answer 34

Pythagorean (or ditonic) comma

Question 35

If the main advantage of the Pythagorean scale was the emphasis on pure fourths & fifths, what were the disadvantages?

Answer 35

Poor tuning of major & minor thirds, problems with modulating music, transposition due to poor sounding black notes (distant from tonic)

Question 36

What did the Meantone Temperament attempt to address?;

What problems arose with this?

Answer 36

Pythagorean system by tuning by beatless thirds;
Beatless thirds led to poor sounding octaves; same problems with notes distant from tonic (poor sounding when modulating or transposing)

Question 37

What was the Just Intonation system based on?;

What were the issues with this system?

Answer 37

Frequency ratios for the pure triad 4:5:6;

Complex system; music again moves away from the notes of the home key so same issues of modulation & transposition

Question 38

Why is Equal Temperament the most convenient system still in most common use?

Answer 38

It divides the octave into 12 equal parts (same ratio of each pair of adjacent notes; octaves are beatless/pure; other intervals a little out of tune but distributed evenly); modulation & transposition to any key fully possible; convenient for large groups of musicians

Question 39

How many cents in equal tempered tuning make up an octave?;

How many cents make up a semitone?

Answer 39

1200 cents;

100 cents

Question 40

Choral conductors often prefer what to avoid a “flat” impression?;
What do violinists & other string players occasionally prefer to tune their instruments to?

Answer 40

A slightly raised major third;

Pythagorean fifths