Enhanced Ion Tweeter

1
Enhanced Ion Tweeter

• Our Team Members
• Rob Alejnikov
• Mark Blattner
• Colin Joye
• Our Advisor
• Dr. Robert Caverly

2
Project Objectives

• What did we do?
• Created an audio transducer that offers the same
  frequency content in all directions.
• Concentrated on high frequencies since they tend
  to beam the most.
• How we did it The Ion flame
• What is it?
• Voltage -- flame size -- sound
• Existing devices use vacuum tubes, creating
  excessive heat
• Goal
• Raise power efficiency
• Decrease unit cost

3
Presentation Objectives

• Intro, Audio Subsystem Rob
• High Voltage Generation Mark
• Results and Conclusions Colin

4
The Audio Subsystem

• Need
• Ion tweeter cannot implement low frequencies --
  Filter
• Output of source device (CD, cassette) up to 1 V
  power rail modulation requires 30 V -- Gain
• Design Criteria
• Flat frequency response for high audio
  frequencies
• Sufficient gain on signal passed to high voltage
  circuit

5
The Audio Subsystem

• 3-stage implementation
• Buffer for high input impedance
• Low Pass
• High Pass
• Performance measures
• Cutoff at 4 kHz and 40 kHz
• Total gain factor up to 60

6
High Voltage Circuit Operation

• Generates high voltage necessary for Corona
  Discharge
• Major Components
• Power MOSFET
• MOSFET Gate Driver
• Coil
• Uses Resonant Properties of Coil to produce High
  Voltages
• Self-Oscillating nature of circuit provides
  resilience to environmental changes

7
Coil Implementations

• Keys to producing High Voltage
• Resonant Frequency between 3MHz and 8MHz to avoid
  audible hiss and limitations of technology
• High Quality Factor (Q) causes near open circuit
• Low DC resistance

8
Coil Implementations

• 10 Coils Built and Tested
• Built with Varying Specs
• Dimension, wire gauge, and number
  of turns
• Coil Chosen
• 16 Gauge Wire
• 45 Turns
• 5 MHz Resonance
• D3 H2.5

9
Field Effect Transistor (FET)

• FET rapidly switches a small current in the coil.
• Optimal FET
• High Voltage handling
• 500 volts
• High Transconductance
• Greater current in coil
• Low Gate Capacitance
• Reduces stress on Gate Driver

10
Interface Methods

• Numerous Approaches Tried and Tested
• Pulse Width Modulation (PWM) via Gate Driver
• Power Rail Modulation via Audio Transformer
• Ground Rail Modulation via Audio Transformer
• Faraday Shield Modulation

11
Interface Methods

• Decided on Power Rail Modulation
• PWM unable to obtain clean waveforms and
  oscillations
• Faraday Shield requires very High Voltages

12
Noise versus Coil Frequency

• Flame Flicker Noise present up to 3MHz, as noted
  by Siegfried Klein in 1956.
• This noise is virtually inaudible 7MHz and up.
• At 30MHz, the flame has a different appearance
  and no noise.

13
Testing

• Power Efficiency Test
• Tube-based
• 114W at 1cm flame height.
• FET-based
• 67W at 1cm flame height.
• 40 Power savings

14
Unit Cost

• Unit Cost (45 savings)
• FET 48.46 (to us), 65.44 (industry)
• Tube 120.53
• Total man-hours
• 750 man-hours
• Estimated industry cost
• 45,270

15
Recommendations

• For Increased Linearity
• Pulse Width modulation of the FET.
• Requires high speed, high precision circuitry.
• Requires virtually zero extra power.
• Occupies almost no space.
• Faraday Shield Modulation.
• Affects the voltage gradient directly.
• Requires high voltage audio.
• Increase operation frequency
• Increase flame power

16
In Conclusion

• Special Thanks to
• Texas Instruments (gate drivers)
• BGR-WYK Distributors (ST FETs)
• International Rectifier (FETs)
• Fairchild Semiconductors (FETs)
• Alpha Industries (diodes)
• Join us for a demo in CEER 210.
• Questions????