The document provides an overview of loudspeakers, including their history, basic design, acoustic wave propagation, impedance, power, sensitivity, distortion, frequency response, speaker positioning, and some studio classics. It discusses how a loudspeaker works based on the voice coil and magnet creating a magnetic field. Impedance is described as the opposition to electric current flow and how manufacturers specify nominal impedance. Crossovers are explained as either passive or active systems to separate signal frequencies sent to individual drivers. Common studio monitors are also highlighted.

1. Loudspeakers
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2. Agenda
1. History
2. Basic Design
3. Acoustic Wave Propagation
4. Impedance
5. Power
6. Sensitivity
7. Distortion
8. Frequency Response
9. Speaker Positioning
10. Studio Classics
11. References

3. History

4. Alexander Graham Bell Oliver Lodge
History

5. Basic Design

6. Basic Design
Components
Gasket
Dust Cap
Cone Spider Basket Top Plate
Voice Coil
Core Magnet
Back Plate

7. Basic Design
Components
A loudspeaker works on the basis that like charges repel
and opposite charges attract and when current flows
through a conductor, a magnetic field is produced around
it. There are two important components in a speaker that
cause movement:

8. Basic Design
The Voice Coil and Magnet
Voice Coil
MagnetCore

9. Basic Design
Components
The voice coil and a magnet.
The voice coil is a long winding piece of copper than is
rapped around a circular drum called a core.
The voice coil is suspended above the centre of a large
magnet with the end of the voice coil attached to terminals on
the basket.

10. Basic Design
The Voice Coil

11. How Stuff Works Deconstructed - How Speakers Work
Basic Design
The Voice Coil

12. Acoustic Wave Propagation

13. Uniform PipeDiaphragm at rest
Pressure is uniform
everywhere in the
pipe
Pressure
Distance
P0
Acoustic Wave Propagation

14. Diaphragm
moves
forward
Pressure increases in
front of the moving
diaphragm
Pressure
Distance
P0
Acoustic Wave Propagation

15. Acoustic wave
propagates away from
diaphragm at speed of
sound, even though the
diaphragm has stopped.
Pressure
Distance
P0
X=ct
c
Acoustic Wave Propagation

16. The job of a loudspeaker is to set up vibrations in the air which are acoustic
representations of the waveforms of the electrical signals that are being supplied
to the input terminals.
A loudspeaker is therefore an electro-mechanic-acoustic transducer.
Acoustic Wave Propagation

17. Impedance

18. Impedance
It is an electrical measurement of a loudspeaker's resistance; its opposition to the flow of electric current
(the audio signals) from your amplifier through your speaker cables to the speaker drivers and the fine wire
in the driver voice coils.
Similar to the way water pressure (voltage) forces the water (current) through a hose. If you have a narrow
hose (a high impedance), not as much water (current) flows. Use a larger diameter hose (lower resistance)
and more water (current) flows.

19. Impedance
Acoustic Impedance
Acoustic impedance can be thought of as a quantity that expresses how difficult the air is to move.
A low value of impedance tells us that the air moves easily in response to an applied pressure (low
pressure, high velocity), and a high value of impedance tells us that it is hard to move (high pressure,
low velocity).

20. Impedance
Mechanical Impedance
Mechanical impedance is directly equivalent to acoustic impedance, but with pressure replaced by
force (pressure is force per unit area)
A low value of impedance tells us that the current moves easily whereas a high impedance restricts
the flow of current to the speaker.

21. Impedance
Manufacturers Specification
We measure impedance in "ohms," named after
George Ohm, the German physicist.
Manufacturers of loudspeakers give us a nominal
impedance of 4,6,8 ohms as this is the dominant
characteristic.

22. Impedance
1. Electrical impedance is the reluctance for alternating current to flow in a
voice coil.
2. Mechanical impedance is the physical opposition of the speaker cone or
diaphragm to move.
3. Acoustic radiation impedance which refers to how efficiently the speaker
moves air.

23. Power

24. Power
Manufacturers Specification
Power is just the maximum power a loudspeaker can theoretically handle without damage.
Rather more important to those doing live sound than studio sound.

25. Sensitivity

26. Sensitivity
Speaker sensitivity is a measurement of the amount of sound output derived from a speaker
with one watt of power input from an amplifier.

27. Sensitivity
Measuring Sensitivity
1 Meter
1 Watt
(2.83 volts)
Speaker sensitivity will generally be given as a SPL measurement taken at 1 meter on axis with a 2.83 volt input (1 watt @ 8 ohms).
dB SPL Meter
Speaker
Reference
Microphone

28. Sensitivity
Loudspeaker Specification

29. Distortion
Total Harmonic Distortion

30. Distortion
Total Harmonic Distortion
When an audio signal is passed through a component, unwanted harmonic
frequencies that were not present in the input signal are generated and added
to the original signal producing what is known as harmonic distortion.

31. Distortion
Total Harmonic Distortion
THD is typically given as a percentage (1%THD).
Distortion in frequencies away from those most sensitive to our ears (~1kHz)
will be not nearly as evident to the listener as distortion in frequencies that
are.
This means that 1% THD could “sound” much less distorted than 0.01% if the
distortion occurred “favourably”.

32. Distortion
Manufacturers Specification
With the speaker outputting 90dB @ 1 meter THD =
2nd harmonic
3rd harmonic

33. Frequency Response

34. Frequency Response
Manufacturers Specification
Often, Manufacturers give frequency
response simply as two extreme high
and low frequencies.

35. Frequency Response
A simple claim of frequency response that cites two frequency extremes
unqualified by a dB specification (as with the specification given regarding
sensitivity) is meaningless.
It may mean that although the speaker responds at 40Hz (the cone moves a bit,
perhaps) nothing will be audible because the speaker's response at 40 Hz is at -
30 dB and inaudible!

36. Frequency Response
On the other hand, if the frequency response is given as 40Hz - 24kHz +/- 3dB,
this indicates that every tone that emerges from speaker will be within 3 dB of
the entire frequency range.
However, manufacturers often use different methods of measuring frequency
response, because there are still no universally accepted standards.

37. Crossovers

38. Crossovers
There are two kinds of crossover: passive and active.
Crossovers separate the signal into component frequencies which are routed to individual
drivers.
Separating the frequencies allows the drivers to be more efficient and protects them from
being overdriven.

39. Crossovers
However they are implemented, crossovers have the same basic job to do. The
audio spectrum must be split up into two, three or (rarely) four bands, with
appropriate crossover frequencies and filter slopes so that they recombine
properly in the air in front of the loudspeaker. The roll-off rates must be fast
enough to avoid exciting response inaccuracies that occur outside the intended
frequency range of the unit; for example the bass filter output must drop fast
enough as frequency increases to avoid exciting the resonance of the mid-
frequency drive unit.

40. Crossovers
Passive
Amplifier
Passive
Crossover
Input
HF
LF
Passive crossovers deal with the signal after it has left a single power amplifier,
and must therefore be able to handle large voltages and currents.
Cabinet

41. Crossovers
Active
Amplifier
Active
Crossover
Input
HF
LFAmplifier
An active crossover uses a separate power amplifier for each driver unit, and the division of
the audio spectrum is done before these amplifiers, using circuitry working at preamp signal
levels.
Cabinet

42. Crossovers
filters
{
{
{
Crossover
region
LF pass band HF pass bandknee
crossover point
crossover frequency
dB
Hz
Crossovers
filters

43. Speaker Positioning

44. 90
90
1.5m - 3m
50cm 50cm
50cm50cm
Mixing/Listening Position ‘Sweet Spot’
30˚ 30˚

45. Speaker Positioning
Speaker placement depends greatly on the room geometry.
For example, a rectangular room will require different
placement from a room with more complex floor plan.
Exact placement depends on room acoustics, speaker type,
and listener preference.
They should be placed no less that 50cm from a boundary
wall (especially from a rear wall if the speakers are rear
ported)

46. In their 1980 paper, Davis and Davis specified that
there should be “. . . an effectively anechoic path
between the monitor loudspeakers and the mixer’s
ears.”
Davis, D. and C. Davis, Sound System Engineering, 2nd ed., Howard W. Sams, pp. 168–169, 1987.
Speaker Positioning

47. The front speakers (particularly the tweeters) should
also be placed at approximately ear level when
seated and aimed at the listening position.
Speaker Positioning

48. Speakers placed too wide will loose their centre
image.
Speaker Positioning

49. Studio Classics

50. The first “compact” monitor to see
widespread use in recording studios
was the JBL 4311, a 3-way design
introduced in the late 1960s.
Studio Classics

51. Auratone “cube,” has a single 5-inch
speaker.
Studio Classics

52. Yamaha NS -10M
Studio Classics

53. Loudspeaker Specification
Do I have stands? These will prevent bass from leaking out.
Is my amplifier good enough or is it a weak link in the chain?
Perhaps the most important factor of the quality of the speaker?
Am I happy to have a crossover frequency in such a noticable frequency band?
Does the impedance match with my amplifier?
Is this large enough to move the air in front of my speaker?

54. References
Books
Self, D., “Audio Engineering Explained”, Focal Press, 2010, U.S
Everest, Alton F. & Polmann Ken C., “Master Handbook of Acoustics”, Fifth Edition. Mc Graw Hill, New York
Dickason, V., “Loudspeaker Design Cookbook, Audio Amateur Press, 2006, U.S
Borwick, J., “Loudspeaker and Headphone Design, Focal Press, 2001. U.S
Toole, F.,” Sound Reproduction. Loudspeakers and Rooms”, Focal Press, 2008, U.S
Davis, G & Jones, R., “The Sound Reinforcement Handbook”, Hal Leonard Publishing, 1989, U.S
Ballou, G. “Electroacoustic Devices: Microphones & Loudspeakers”, Focal Press, 2009, U.S
Web
Rybak, James P, “Oliver Lodge: Almost the Father of Radio”, http://www.antiquewireless.org/otb/lodge1102.htm(accessed Feb 2012)
Understanding Loudspeaker Sensitivity http://www.goodsound.com/features/2008_02_01.htm
Total Harmonic Distortion http://www.bcae1.com/thd.htm
What Is THD? http://stereos.about.com/od/stereoscience/qt/whatisTHD.htm
Loudspeaker Specification Explained http://www.hifipage.com/loudspeaker-specifications-explained-11/
Speaker Impedance and Ohmshttp://www.ecoustics.com/electronics/products/articles/556241.html
Historic Timeline http://www.emolabs.com/images/timeline.swf
Good Reference, Brain Knave, Electronic Musician, 2001. http://www.drbraukmann.com/DESN385/reading/StudioMonitorsArticle.pdf

55. References (cont)
Video and Animation
How Stuff Works Videos Deconstructed How Speakers Work, You Tube http://www.youtube.com/watch?v=3qA5315XTb8
(accessed, Feb 2012)
Woofer Animation. You Tube http://www.youtube.com/watch?v=3ZQqCyRQFB4 (accessed, Feb 2012)
Papers
Toole, F.E., “Loudspeakers and Rooms for Stereophonic Sound Reproduction,” Proc. AES. 8th Intl. Conf., Washington, D.C., pp.
71–91, 1990.
Davis, D. and C. Davis, Sound System Engineering, 2nd ed., Howard W. Sams, pp. 168–169, 1987.