2Music & Acoustics Flashcards
Define Acoustics
The science of the production, propagation & perception of sound
A soundwave has longitudinal motion. What does this mean?
The movement of oscillation is parallel to the direction of movement overall
The rate at which the crests or troughs of a wave pass a point is called what?;
This is measured in units of what?
Frequency;
Hertz
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?
Amplitude;
Decibels
A complex tone can be reduced to its sinusoidal components. What is the lowest of these components?;
Which number harmonic (or partial) is this?
Fundamental tone;
First
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?
Periodic (or harmonic);
Aperiodic (or anharmonic) - can’t multiply one frequency by another
What determines Timbre (or characteristic) of a sound?
The various amplitudes of different overtones within a complex tone
Which frequencies are emphasized on a power spectrum when a higher pitch is produced?
Lower frequencies (& vice versa)
Explain the concept of Coupled Acoustics
A musical instrument has two vibrating devices where one generates the sound & the other amplifies it
Give 3 examples of a Resonator
Hollow tube; air chamber; soundboard
Any given resonator is likely to serve as a better what?
Conduit for certain frequencies than others
It takes more energy or amplitude to perceive what?
Very low or very high frequencies (e.g. 100db to hear 20Hz or 80db at 20kHz)
List some string instruments;
Bowed or plucked: Violin, viola, cello, double bass; plucked: guitar, harpsichord; struck: piano
What does the fundamental frequency of string instruments depend on?;
What is the sound source?;
What is the sound modifier or resonator?
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
How are Edge Tones created in woodwind instruments?;
How is the length of the resonator (air column) changed?
By blowing across a hole & onto a sharp edge (e.g. flute & recorder);
By means of finger holes
How are Reed Tones produced?
By setting one reed (in clarinets or saxophones) or two reeds (oboes or bassoons) vibrating, which produces sound waves in adjacent air columns
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?
The player’s vibrating lips in the mouthpiece;
Shape & tension of the lips influence the vibration;
Change the length of the resonator
With the exception of the xylophone, glockenspiel or marimba, what do most percussion instruments produce?
Non-periodic sounds
What are Membranophones?
Instruments with vibrating membrane usually stretched over a frame of wood or metal; struck with a stick or hands
What are Idiophones?
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)
What is Direct sound?;
What is Reflected sound?
Travels directly from the source to the listener;
Reaches the listener by bouncing off one or more surfaces (e.g. walls, ceilings, pillars, etc)
Define the Initial-Time-Delay-Gap (ITDG);
What is the optimal ITDG for concert halls?
The time at which the first reflection is heard after the direct sound;
Around 15 milliseconds
What is the Clarity Index?
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)
Which shaped concert hall seems to be the preferred listening space?;
Why is this?
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
Why are fan-shaped concert halls problematic?
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
Which shaped concert halls face similar problems to fan-shaped?
Horse-shoe, but more intimate with better ambience, so preferred
What are Porous Absorbers?;
What are Resonant Absorbers?
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
How can Reverberation be defined?
The length of time for a sound to decay by 60 decibels
What are advantages & disadvantages for reverberant performance spaces?;
What about dry performance spaces?
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
What is the frequency ratio for the pure tuned interval of Unison?;
Octave?;
Perfect fifth?;
Perfect fourth?
1: 1;
2: 1;
3: 2;
4: 3
What is the frequency ratio for the pure tuned interval of Major sixth?; Major third?; Minor sixth?; Minor third?
5: 3;
5: 4;
8: 5;
6: 5
What did the Pythagorean Scale result from?;
What did the tuning system entail?
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
What were the problems with the Pythagorean tuning?;
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
What was the discrepancy called when tuning by pure fifths didn’t match up with octaves in Pythagorean scale?
Pythagorean (or ditonic) comma
If the main advantage of the Pythagorean scale was the emphasis on pure fourths & fifths, what were the disadvantages?
Poor tuning of major & minor thirds, problems with modulating music, transposition due to poor sounding black notes (distant from tonic)
What did the Meantone Temperament attempt to address?;
What problems arose with this?
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)
What was the Just Intonation system based on?;
What were the issues with this system?
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
Why is Equal Temperament the most convenient system still in most common use?
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
How many cents in equal tempered tuning make up an octave?;
How many cents make up a semitone?
1200 cents;
100 cents
Choral conductors often prefer what to avoid a “flat” impression?;
What do violinists & other string players occasionally prefer to tune their instruments to?
A slightly raised major third;
Pythagorean fifths
