Physics 1251 The Science and Technology of Musical Sound Unit 2 Session 14 MWF Human Perception: Loudness

Physics 1251 Unit 2 Session 14 Human Perception: Loudness

Foolscap Quiz:

A sound has an intensity of 0.005 W/m 2 . What is the Sound Intensity Level (SIL) in dB?

Pass the sheet to your left when you finish. Please do not use your notes. Thank you!

SIL = 10 Log ( I / I threshold ) SIL = 10 Log ( .005/ (1 x10 -12 )) SIL = 10 Log ( 5 x 10 9 ) = 97 dB.

Physics 1251 Unit 2 Session 14 Human Perception: Loudness

•

1′ Lecture:

Loudness is the magnitude of the sensation produced by a sound; the “amount” of sound.

• Loudness (in sone) is how many times larger (or smaller) the sensation is judged to be, relative to a tone of SIL=40 dB at 1000 Hz.

• Loudness Level (in phon) is equal to the SIL at 1000 Hz that produces the same magnitude of sensation.

Physics 1251 Unit 2 Session 14 Human Perception: Loudness

The Human Ear is a “non-linear Sensor”

Physics ⇒ Physiology ⇒ Perception

Physics 1251 Unit 2 Session 14 Human Perception: Loudness

• •

Human Aural Response:

But…

Intensity →

Vibration Recipe

Loudness

Intensity

Frequency →

Vibration recipe

Pitch

• Intensity

Vibration Recipe →

Frequency

Timbre

Physics 1251 Unit 2 Session 14 Human Perception: Loudness

“Resonant” Frequency vs Location on Basilar Membrane 20 kHz Range of Maximum Sensitivity 20 Hz

Physics 1251 Unit 2 Session 14 Human Perception: Loudness

The Density of Hair C

ells (HC) varies with distance from the stapes.

Fewer HC More HC Fewer HC

Physics 1251 Unit 2 Session 14 Human Perception: Loudness

Fletcher- Munson Diagram SIL (dB) Loudness (phon) 30 10 Frequency (Hz) Fletcher and Munson (1933) J. Acoust. Soc. Am. 5, 82-108

Physics 1251 Unit 2 Session 14 Human Perception: Loudness

80/20 The Fletcher-Munson Diagram is a plot of the SIL (in dB) versus frequency for the SIL required to produce an equal sensation as that produced at 1000 Hz. 80/20 The contours are of equal loudness level.

80/20 The unit of loudness level is the phon.

Physics 1251 Unit 2 Session 14 Human Perception: Loudness

Fletcher- Munson Diagram SIL (dB) 30 10 Frequency (Hz) Fletcher and Munson (1933) J. Acoust. Soc. Am. 5, 82-108

Physics 1251 Unit 2 Session 14 Human Perception: Loudness

Auditory Demonstration #6

Houstma and Rossing Institute for Perception Research (IPO) Einhoven, The Netherlands Track 17,18 & Acoustical Society of America Count the number of tones you that can hear at each of the following frequencies: 125, 250, 500, 1000, 2000, 4000, 8000 Hz.

Physics 1251 Unit 2 Session 14 Human Perception: Loudness

Using the Fletcher- Munson Diagram

Determine the SIL necessary to have a Loudness Level of 70 phon at 200 Hz, 2000 Hz and 10,000 Hz.

Physics 1251 Unit 2 Session 14 Human Perception: Loudness

Using the Fletcher- Munson Diagram Determine the SIL necessary to have a Loudness Level of 70 phon at 200 Hz, 2000 Hz and 10,000 Hz.

130 SIL (dB) 30 10 Frequency (Hz)

Physics 1251 Unit 2 Session 14 Human Perception: Loudness

Fletcher- Munson Diagram SIL (dB) 30 10 200 Hz—70 dB 2 kHz—70 dB 10 kHz—75 dB Equal Loudness (70 phon) Frequency (Hz) Fletcher and Munson (1933) J. Acoust. Soc. Am. 5, 82-108

Physics 1251 Unit 2 Session 14 Human Perception: Loudness

Using the Fletcher- Munson Diagram Using the F-M Diagram determine the Loudness Level of an 80 dB tone at 100 Hz, 400 Hz and 8000 Hz.

130 SIL (dB) 30 10 Frequency (Hz)

Physics 1251 Unit 2 Session 14 Human Perception: Loudness

Fletcher- Munson Diagram SIL (dB) 80 dB 73 phon 81 phon 72 phon 30 10 Loudness (phon) Frequency (Hz) Fletcher and Munson (1933) J. Acoust. Soc. Am. 5, 82-108

Physics 1251 Unit 2 Session 14 Human Perception: Loudness

Fletcher- Munson Diagram SIL (dB) 30 10 Frequency (Hz) Fletcher and Munson (1933) J. Acoust. Soc. Am. 5, 82-108

Physics 1251 Unit 2 Session 14 Human Perception: Loudness

Since the Loudness Level for a given frequency can be approximated by a linear function of the Intensity Level, Thus: LL ≈

A f

(SIL – SIL threshold ), 80/20 One of the settings of a Sound Level Meter (filter switch “A”) modifies the calibration of the instrument to account for the frequency dependence of human hearing.

80/20 The Sound Level is reported then as “dBA.”

Physics 1251 Unit 2 Session 14 Human Perception: Loudness

Sound Level Meter

•

Measures Sound Intensity Level (SIL) in dB

Physics 1251 Unit 2 Session 14 Human Perception: Loudness

Loudness

80/20 A subjective measure of the magnitude of auditory sensation is called Loudness and is measured in sone. In this system, one listens to two sounds and judges how much louder or softer a test sound is compared to the reference .

For example, a sound of 2 sone sounds twice as loud as a tone of 1 sone.

Physics 1251 Unit 2 Session 14 Human Perception: Loudness

Auditory Demonstration #7

Houstma and Rossing Institute for Perception Research (IPO) Einhoven, The Netherlands Track 19,20 & Acoustical Society of America Estimate how loud each of the sound samples is, compared to the reference sound sample. The reference is presented first along with the loudest and softest sounds.

Physics 1251 Unit 2 Session 14 Human Perception: Loudness

Loudness Scaling

Loudness L ∝∛ I

80/20 Thus, an eight (8) singer ensemble sounds about twice (2x) as loud as a soloist. Because

∛

8 = 2. Likewise, a choir of sixty-four (64) sounds about four (4x) times louder than a soloist.

∛

64 = 4.

Physics 1251 Unit 2 Session 14 Human Perception: Loudness

• • •

Summary:

Loudness is the magnitude of the sensation produced by a sound; it is measured in sone.

Loudness Level (in phon) is equal to the SIL at 1000 Hz that produces the same magnitude of sensation.

Loudness increases approximately with the cube root of intensity.

Physics 1251 Unit 2 Session 14 Human Perception: Loudness

•

Summary:

The loudness depends on frequency.

Physics 1251 Unit 2 Session 14 Human Perception: Loudness



Examination 1

Physics 1251.001 2003C Examination #1 35 30 25 20 15 10 5 0 F D C B A