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

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)

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)

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

Human auditory system Peripheries (the ear) Central auditory system

The ear Inner ear = cochlea + 3 semicircular canals

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

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

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

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

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.

Fitting of acoustical impedance Effect of lever Effect of piston Effect of lever – transmission coefficient 1.3 to 3 Effect of piston – 15 - 30

Fitting of acoustical impedance Effect of lever – transmission coefficient 1.3 to 3 Effect of piston – 15 - 30

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

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.

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

Cochlea

Cochlea

Cochlear canal

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

Organ of Corti Hair cells – Inner (IHC) 1 line, 3500, 30-60 hairs – convert mechanical vibrations on electrical impulses Outer (OHC) 30000, 5 lines, 100-140 hairs (stereocilia) each – provide feedback between the central auditory system and ear

Organ of Corti Hair cells – Inner (IHC) 1 line, 3500, 30-60 hairs – convert mechanical vibrations on electrical impulses Outer (OHC) 30000, 5 lines, 100-140 hairs (stereocilia) each – provide feedback between the central auditory system and ear

Organ of Corti

Organ of Corti

Movement of basilar membrane Maximum of displacement depends on frequency

Hearing cells Normal Damaged

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.

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

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

Auditory area Normal

Hearing loss With hearing loss

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

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