Transducers for Music Dr Ian Drumm www.aee.salford.ac.uk Student Area Undergraduate Username: Studen

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Transducers for MusicDr Ian Drummwww.aee.salford
.ac.uk - Student Area UndergraduateUsername
Students Password Module

• Aims
• To discuss bass response and distortion
• Learning Outcomes
• Bass Reflex
• Power Handling
• Crossovers

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How can we get more bass?
Consider Omni directional Source
move more air
Increase S? will increase moving mass reduce
high frequency response Increase u? will
require better suspension, motor, etc.
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Use Back Radiation?

• Will need phase inverter
• the transmission line enclosure
• the bass reflex enclosure
• the auxiliary bass radiator

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Bass Reflex Enclosure

• Tube
• End open to enclosure
• End open to listening space
• Helmholtz resonator
• Air in port Mass, Spring
• Second order resonant system
• Phase inversion above resonant frequency of port

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Problems with Bass Reflex

• At resonant frequency of port back load from
  port at speaker reduces response of speaker
• Below resonant frequency of port destructive
  interference because there is no phase inversion

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Tuning the Bass reflex Enclosure
k stiffness of air in port Scross-sectional
area of port leffective length of the port
including end corrections mmoving mass of port
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Bass Reflex Design Considerations

• Greater speaker displacements because less back
  load
• (except near port
  resonance)
• Prevent mid-frequencies through port
• Port kept reasonably small (gives air lump - LP
  filter)
• Turbulence at the port ends causing audible
  "chuffing" sounds, solution
• Port not too small
• Damping
• Ends profiled

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Efficiency of Typical Loudspeaker
Acoustic Power Electric Power
Very poor at low frequency Peaks at resonance
10 Operating range If you know efficiency, electrical power and
directivity then can find sound pressure level
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Distortion

• Power Compression temperature increases
  resistance hence lessens sensitivity (small)
• Cone Break Up standing waves in diaphragm

Cone break up
Normal
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Power Handling

• Input power speaker can take before unacceptable
  distortion

E.g. an 8? speaker rated at 35W has sensitivity
of 85dB/2.83V _at_ 1m
Maximum SPL is
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Crossovers
Remember mechanical impedance
Frequency dividing network -tweeter 3kHz -woofer
Analogous to electrical circuit
Capacitor (C) high frequencies low impedance
Inductor (L) low frequencies low impedance