ELEC-E5650 Electroacoustics, Lecture 1
Part 2: Introduction to electroacoustics
Ilkka Huhtakallio
Department of Signal Processing and Acoustics
Aalto University School of Electrical Engineering
2016/02/25
Introduction to Electroacoustics
Electroacoustics...
is a branch of acoustical engineering
combines the knowledge of acoustics, mechanics and
electronics
deals with design of transducers that executes the conversion
between mechanical or acoustical vibration and electrical
signal
deals with the applications using the electoacoustic
transducers
ELEC-E5650 Electroacoustics, Lecture 1
Ilkka Huhtakallio
Aalto SPA
2/19
2016/02/25
ELEC-E5650
Transducer
General description of a device that transforms input energy
to output energy
Typically the output energy is in another form, but related to
the input.
Prefix specifies the type of transduction,
i.e. electoacoustic transducer converts electrical energy to
acoustical energy, and vica versa.
Passive transducer:
Output energy is derived entirely from the input energy
Active transducer:
Output energy is derived partly from other sources than the
input energy
ELEC-E5650 Electroacoustics, Lecture 1
Ilkka Huhtakallio
Aalto SPA
3/19
2016/02/25
ELEC-E5650
Transducers in different applications, bands and
mediums
Audio range
Microphones
Ultrasonics
Loudspeaker
Therapy
Headphones
Welding
Buzzers / beepers
Cleaning
Imaging
Signal processing & electronics
(oscillators, filters)
Chemistry (catalysis, mixing)
ELEC-E5650 Electroacoustics, Lecture 1
Ilkka Huhtakallio
Aalto SPA
4/19
2016/02/25
ELEC-E5650
Transducers in different applications, bands and
mediums
Underwater acoustics
Hydrophones for wide
bandwidth listening
Sonar / echo sounding
(narrow band)
Solids
Actuators
Accelerometer
Strain-gauges
ELEC-E5650 Electroacoustics, Lecture 1
Ilkka Huhtakallio
Aalto SPA
5/19
2016/02/25
ELEC-E5650
Electroacoustic devices in audio band
Electroacoustic devices plays a key role in modern society by
transmitting information
Communication
Entertainment
Signaling
Alarm
ELEC-E5650 Electroacoustics, Lecture 1
Ilkka Huhtakallio
Aalto SPA
6/19
2016/02/25
ELEC-E5650
Microphones applications
Music recording studios
Research
Broadcast
SPL meters / loggers
Portable recording
Active noise control
Sound reinforcement / PA
Laptops / tablets
Video conferencing
churches, stadiums,
festivals, clubs
public transport, public
spaces
Telecommunication
Cars
Hear through, augmented
reality
Hearing aids
Surveillance
Signaling and alarm
Acoustical measurements
ELEC-E5650 Electroacoustics, Lecture 1
Ilkka Huhtakallio
Aalto SPA
7/19
2016/02/25
ELEC-E5650
Loudspeakers applications
Music recording and
mastering studios
Broadcast
Hi-Fi system
TV’s & home theaters
Movie theaters
Personal audio (BF)
Portable audio
Laptops / tablets
Video conferencing
Telecommunication
Cars
Research
Active noise control
Sound masking
Sound reinforcement / PA
churches, stadiums,
festivals, clubs
public transport, public
spaces
Surveillance
Signaling and alarm
ELEC-E5650 Electroacoustics, Lecture 1
Ilkka Huhtakallio
Aalto SPA
8/19
2016/02/25
ELEC-E5650
Headphone applications
Music recording and
mastering studios
Research
Noise cancellation
Broadcast
Hi-Fi system
Personal audio
Movies
Telecommunication
Hear through, Augmented
reality, virtual reality
Hearing aids
ELEC-E5650 Electroacoustics, Lecture 1
Ilkka Huhtakallio
Aalto SPA
9/19
2016/02/25
ELEC-E5650
Electroacoustic systems
System is an assembly of one or more transducers with other
parts (such as enclosures, baffles, electronics, amplifiers)
Passive system operates only with the input energy for which the
output is related
Active system has an external energy source from where at least
part of the output energy is coming
ELEC-E5650 Electroacoustics, Lecture 1
Ilkka Huhtakallio
Aalto SPA
10/19
2016/02/25
ELEC-E5650
Signals chain in electroacoustic system
Microphone
preamplifier
Mixing
console
A/D
converter
(digitizer)
Digital signal
Data storage
processing
and/or
Data reduction
Transmission
and coding
= microphone
= loudspeaker
(a)
Reception
and/or
Data retrieval
Decoder
Digital signal
processing
Room
correction
D/A
converter
Power
amplifier
(b)
Figure: Systems and sub-systems involved in a) recording and b)
reproducing the sound field. (Adapted from Kleiner)
ELEC-E5650 Electroacoustics, Lecture 1
Ilkka Huhtakallio
Aalto SPA
11/19
2016/02/25
ELEC-E5650
Linearity of a system
“For perfect reproduction from a loud speaker two requirements
must be met: (1) a current of a given frequency must produce
sound of that frequency and that frequency only; and (2) the power
radiated in the form of sound must be proportional to the square of
the current independent of frequency. This assumes that the
available current is an exact reproduction of the pressure of sound
applied to the microphone” (Hanna & Slepian, 1924)
If these two requirements are not met, the system is nonlinear and
reproduction is distorted.
Hanna, C.R. and Slepian, J., 1924. The function and design of horns for loud
speakers. American Institute of Electrical Engineers, Transactions of the, 43,
pp.393-411.
ELEC-E5650 Electroacoustics, Lecture 1
Ilkka Huhtakallio
Aalto SPA
12/19
2016/02/25
ELEC-E5650
Linearity
Any practical system will have some nonlinearity.
Three types of signal degradation affecting electroacoustic
systems are
1. Linear distortion
2. Nonlinear distortion
3. Irregular distortion
ELEC-E5650 Electroacoustics, Lecture 1
Ilkka Huhtakallio
Aalto SPA
13/19
2016/02/25
ELEC-E5650
1) Linear distortion
Linear distortion is unevenness of frequency response (magnitude
and/or phase). It can be corrected by some degree by using
equalization.
Level
Peak
Lref
Lref – 3dB
Ripple
Flat
Low-frequency
cutoff
Rise
Dip
fl
Roll-off
High-frequency
cutoff
Passband
fref
fu
Frequency
Figure: Magnitude response an electroacoustic system.
ELEC-E5650 Electroacoustics, Lecture 1
Ilkka Huhtakallio
Aalto SPA
(Adapted from Kleiner)
14/19
2016/02/25
ELEC-E5650
2) Nonlinear distortion
Nonlinear distortion is characterized by introduction of new
spectral components at frequencies that are related to the input
frequencies.
Hard to compensate with processing.
Various types of nonlinear distortion occurs in electoacoustic
systems
ELEC-E5650 Electroacoustics, Lecture 1
Ilkka Huhtakallio
Aalto SPA
15/19
2016/02/25
ELEC-E5650
Level
Harmonic distortion
0
(a)
f1
2f1
Fundamental
3f1
4f1 and so on
Frequency
(linear scale)
Harmonic distortion
(both even and odd
harmonics shown here)
Figure: Harmonic distortion (Adapted from Kleiner)
ELEC-E5650 Electroacoustics, Lecture 1
Ilkka Huhtakallio
Aalto SPA
16/19
2016/02/25
ELEC-E5650
Intermodulation distortion
Level
Intermodulation distortion
(sidebands)
0 f1
f2
f2 – f1 f2 + f1
(b)
Low-frequency
component
High-frequency
component
2f2 Frequency
(linear scale)
Harmonic to f2
Figure: Intermodulation distortion (Adapted from Kleiner)
ELEC-E5650 Electroacoustics, Lecture 1
Ilkka Huhtakallio
Aalto SPA
17/19
2016/02/25
ELEC-E5650
3) Irregular distortion
New spectral components at high frequencies, whose occurrence
might be shorter than the period of the stimulus signal.
Might occur as a noise, rattling, rubbing, buzzing, clicking etc.
ELEC-E5650 Electroacoustics, Lecture 1
Ilkka Huhtakallio
Aalto SPA
18/19
2016/02/25
ELEC-E5650
Designing an electroacoustic system
The design should meet the requirements of the target
application.
Wide variety of the applications has wide variety off requirements,
and there is no single solution to all.
Some requirements for the same application may be more strict
than others, and balance between the compromises has to be
found to found to fulfill the requirements.
ELEC-E5650 Electroacoustics, Lecture 1
Ilkka Huhtakallio
Aalto SPA
19/19
2016/02/25
ELEC-E5650