introduction to acoustics dr inż. michał bujacz bujaczm@p.lodz.pl visitng hours: tuesday...
Post on 29-Dec-2015
217 Views
Preview:
TRANSCRIPT
Introduction to Acoustics
dr inż. Michał Bujaczbujaczm@p.lodz.pl
Visitng hours:
tuesday 15:00-16:00
wednesday 10:00-11:00
„Lodex” 207
Acoustics[gr. akoustikós ‘related to hearing’]
field of physics and engineering that deals with the study of all mechanical waves in gases, liquids, and solids including topics such as vibration, sound, ultrasound and infrasound
http://www.physics.byu.edu/2
Sound
„phys. mechanical disturbance in a compressive medium capable of inducing an auditory sensation, as well as the auditory sensation itself” (Encyklopedia PWN)
3
Longitudinal wave (wzdłużna)
Particles oscillate in the direction of wave propagation.
Areas of increased and decreased pressure.
http://www.physics.byu.edu/
What’s the range of movement of the air particles moved by sound?
0.008nm to 0.1 mm
4
Physics vs. perception
Physical definitions:
- Intensity (natężenie) or
amplitude (amplituda)
- Frequency (częstotliwość)
- Spectrum (widmo)
- Speed (prędkość)
Psychoacustic definitions:
- Loudness (głośność)
- Pitch/tone (wysokość/ton)
- Tembre (barwa)
6
Intensity of soundIntensity = the amount of energy passing through an area in time
224 m
W
r
PI
http://hyperphysics.phy-astr.gsu.edu
How does amplitude change with distance?
22 ~~~ ApEP
rrIA
1~
1~~
28
Measures of sound level
Pressure (rms)
from 0.00002 N/m2 (threshold of hearing)
to 20 N/m (threshold of pain)
atmospheric pressure
100000 N/m2
9
Decibel scaleRatio of power:
Ratio of amplitude:
dB power ratio amplitude ratio
60 1 000 000 1 000
50 100 000 316.2
40 10 000 100
30 1 000 31.62
20 100 10
10 10 3.162
6 3.98 2
3 2 1.414
0 1 1
-3 0.5 0.7071
-6 0.251 0.5
-10 0.1 0.3162
-20 0.01 0.1
-30 0.001 0.03162
-40 0.000 1 0.01
0
110log10P
PLdB
20
21
10log10A
ALdB
0
110log20A
ALdB
10
Confusing „sound levels”Sound Power Level (SWL)
- energy emitted by sound source per second (cause)
Sound Pressure Level (SPL)
- pressure (amplitude) changes at receiver (effect)
Sound Intensity Level (SIL)
- energy delivered to receiver area per second (effect)
μPa200 p 212
0 mW10P
11
Audio frequency ranges
Tones Examples
Low bass: 20 – 80 Hz
Lowest two octaves. Explosions, storms, lowest church organ notes
Upper bass: 80 – 320 Hz
3th – 4th octavesDrums, bass, cellos, wind instruments
Lower mid: 320 – 2560 Hz
5th – 7th octavesMost instruments and human speech
Upper mid: 2560 – 5120 Hz
8th octaveHighest notes on most instruments, whistles, most sensitive perception range
High/treble: 5120 Hz – 20000 Hz
9th -10th octavePercussion (hi-hat, cymbal), higher harmonics of sounds, noise
15
Musical tone (pitch)
Musical scales
– divided into octaves (intervals), e.g. C (dur)
A4 = 440Hz
Psychoacoustic scales
– Mel or Barkhttp://www.sfu.ca/
17
Tembre/qualitySet of features distinguishing sounds of the same base frequency on different instruments
Spectrum dependent (harmonics and noise) and transients (sudden changes)
Described semantically (np.brightness, warmth, coarsness, clarity)
23
top related