1. How Things Work! Brendan Barber
Headphones
How Things Work!
Brendan Barber

2. Transducer Technology
Outline:
History
Early Development
Modern Design
Transducer Technology
(Audio Drivers)
Moving Coil (Dynamic)
Planar Magnetic
Electrostatic
Balanced Armature
Summary

3. History: Early Development
Originated in 1910 and developed by Nathaniel Baldwin
Developed as only way to listen to electrical audio signals
First versions had no padding and poor sound quality
Often had impedance of ohm

4. History: Modern Design
John C. Koss created the first stereo headphones and the consumer market was born
1958
Stax developed the first electrostatic “earspearker”
1960
Yamaha built upon the dynamic and electrostatic drivers and created the first planar magnetic driver
1976
Earbuds/IEM’s become mainstream
2000

5. Types of Audio Drivers
Currently there are 5 main designs in consumer products:
Dynamic (Moving Coil)
Planar Magnetic
Electrostatic
Balanced Armature
Magnetostriction (Bone Conduction)

6. Moving Coil (Dynamic) Driver
Most common type of driver
Consists of a stationary magnet and voice coil attached to a light weight diaphragm
Varying current from the audio signal is passed through the voice coil and creates a varying magnetic field
Varying magnetic field reacts with static field causing a force

7. Moving Coil (Dynamic) Driver

8. Moving Coil (Dynamic) Driver
Can be manufactured very cheaply
Easy to drive
Light weight
Depending on design has very good low end response
Benefits
Diaphragm being pushed and pulled creates distortion
Non-linear distortion (worse at higher volumes)
Sound produced as spherical wave
Draw Backs

9. Planar Magnetic Work on a similar principle to dynamic driver
Two magnets push and pull a diaphragm which has an embedded “wire”
Requires larger magnets as the as the force is applied across the whole diaphragm
The whole diaphragm responding to the input signal leads to tight and powerful bass

10. Planar Magnetic

11. Planar Magnetic Much lower distortion compared to dynamic drivers
Fast transient response
Flat frequency response = better bass
Benefits
Expensive to manufacture
Hard to drive i.e. signal needs amplification
Heavy
Draw Backs

12. Electrostatic
By far the most expensive driver type (some costing as much as $50,000)
A thin electrically charged film is suspended between two perforated plates (electrodes)
Electrical signal is applied to the plates and depending on polarity moves the diaphragm
A special amplifier is required in order for the signal to deflect the membrane

13. Electrostatic

14. Electrostatic Near flaw-less detail
Fastest transient response of any driver
Sound is produced as a plane wave
Benefits
Very expensive
Require high voltage for operation (100V-1kV)
Heavy
Draw Backs

15. Summary There are many designs for audio transducers
All drivers use varying magnetic fields to generate sound
While each driver has pros and cons ultimately cost has played the greatest factor in adoption.

16. References
work-page-3
english.pdf

17. Sennheiser HD 800

18. Audeze LCD-4

19. Stax SR-009

20. Shure SE 84