1. Electroacoustics
Prof. Andrzej Dobrucki, PhD Maurycy Kin and Prof. Krzysztof Opieliński
The chair of Acoustics and Multimedia,
Wrocław University of Science and Technology

2. The plan of lectures Human auditory system Speech
Mechanical vibration of one- and multi degrees of freedom
Propagation of acoustic and ultrasonic waves
Quantities characterizing acoustic field in an open space
Quantities characterizing acoustic field in rooms
Test no. 1 (April, 10th)

3. The plan of lectures (cont.)
8. Basic acoustical systems. Electrical, mechanical and acoustic analogies
Electro-acoustic chain. Transmission of audio signals
Principles of operation of electro-acoustical transducers
11. Microphones and loudspeakers
12. Loudspeaker systems and earphones
13. Psychoacoustics
14. Ultrasonic transducers
15. Test no. 2 (June, 12th)

4. The graduating rules
Tests will contain 3 questions for describe from the topics given by the lecturers
Both tests must be positively graded
For those who will not have a success with tests the only one additional test is provided
The associated form is a laboratory which must be also positively graded

5. Human auditory system
Peripheries (the ear)
Central auditory system

6. The ear
Inner ear = cochlea + 3 semicircular canals

7. Outer ear Pinna Canal Eardrum
Length of ear canal 2.6 cm, diameter 0.7 cm, volume 1 ccm

8. Functions of outer ear Localization of the sound source
Protection of eardrum
Amplification of sound (selective)
Localization – shape of pinna (HRTF)
Protection – ear canal
Amplification – resonances of the canal: 1st at 2600 – 3000 Hz
Eardrum surface 85 qmm, thickness 0.1 mm, mass 14 mg

9. Middle ear Middle-ear cavity Ossicular chain (malleus, incus, stapes)
Muscles (stapedius muscle, tensor tympani muscle)
Eustachian tube
Ossicular chain: the smallest bones in the human
Malleus: 23 mg, incus – 25 mg, stapes – 3 mg

10. Middle ear
Protecton against high sound level: stapedial effect The eardrum becomes more rigid because of action of tensor tympani muscles and stapedius muscle. Time of response: 150 ms, time of relaxation: 1.5 s. Level of reaction SPL=85 dB

11. Functions of middle ear
Fitting of acoustical impedance
Protection against high sound level
Equalization of static pressures between outer and middle ear
The equalization is provided by Eustachian tube. However, it has the time constant. When the static pressure changes rapidly, e.g. During take off or landing of the plane, the equalization cannot appear immediately. We feel unpleasant pressure in the ear and the sound perception becomes worse.

12. Fitting of acoustical impedance
Effect of lever
Effect of piston
Effect of lever – transmission coefficient 1.3 to 3
Effect of piston –

13. Fitting of acoustical impedance
Effect of lever – transmission coefficient 1.3 to 3
Effect of piston –

14. Protection against high levels of sound
stapedial effect:
the eardrum becomes more rigid because of action of tensor tympani muscles and stapedius muscle
- time of response: 150 ms, time of relaxation: 1.5 s, level of reaction SPL=85 dB

15. Equalization of static pressures
It is provided by Eustachian tube. However, it has the time constant. When the static pressure changes rapidly, e.g. during take off or landing of the plane, the equalization cannot appear immediately. We feel unpleasant pressure inside the ear and the sound perception becomes worse for a moment.

16. Inner ear Semicircural canals (equilibrium sensor)
Cochlea and auditory nerve

17. Cochlea

18. Cochlea

19. Cochlear canal

20. Cochlea
The space between oval and round window is filled by perylimpha – rigid fluid,
- Scala media are filled by endolimpfa.
The concentration of ion of Na (sodium) and K (potassium) is different than in perylimpha, and potential of endolimpha is then ca. +90 mV.
- Basilar membrane lies on the bone shelf

21. Organ of Corti Hair cells –
Inner (IHC) 1 line, 3500, hairs – convert mechanical vibrations on electrical impulses
Outer (OHC) 30000, 5 lines, hairs (stereocilia) each – provide feedback between the central auditory system and ear

22. Organ of Corti Hair cells –
Inner (IHC) 1 line, 3500, hairs – convert mechanical vibrations on electrical impulses
Outer (OHC) 30000, 5 lines, hairs (stereocilia) each – provide feedback between the central auditory system and ear

23. Organ of Corti

24. Organ of Corti

25. Movement of basilar membrane
Maximum of displacement depends on frequency

26. Hearing cells
Normal
Damaged

27. Ascending auditory pathway
DCN –dorsal cochlear nucleus, VCN – ventral c.n., SOC – superior olivary complex,
IC – inferior colliculus, LL – lateral lemniscus, MGB – medial geniculate body
The monaural informations – black lines, the binaural ones – gray.

28. Descending auditory pathway
LAT, MED. – lateral and medial periolivary nuclei
OHC – outer hair cells, RAD – radial fibers, CN – cochlear nucleus

29. Selectivity of hearing
The selectivity of basilar membare is lower than whole selectivity. The selectivity increases because of neurons activity as well as the cental auditory system

30. Auditory area
Normal

31. Hearing loss
With hearing loss

32. Types of hearing impairments
Conductive hearing loss
Sensorineural hearing loss
Sensorineural (extracochlear)
Mixed hearing loss

33. literature
B. C. J. Moore – An introduction to psychology of hearing, Academic press, Cambridge, 1996
H. Dilon – Hearing aids, Boomerang press, Thieme, 2005