1. Microphones Design and Application Huber Ch. 4 (Eargle Ch. 3)

2. Huber’s Rules There are no rules, only guidelines. The overall sound of an audio signal is no better than the weakest link in the signal path. Whenever possible, use the “Good Rule.”

3. Microphone Design Transducer Dynamic mics Ribbon mics Condenser mics

4. Dynamic Electromagnetic induction Stiff Mylar diaphragm Voice coil Magnetic field Analogous current Voltage depends on speed of coil Hum-bucking coil

5. Ribbon Electromagnetic induction Diaphragm: extremely thin aluminum ribbon (corrugated) Older designs typically large Small output signal

6. Condenser Condenser is an old term for capacitor. Electrostatic principle Two very thin plates--one fixed and one movable. Capacitor Capacitance changes as distance between plates change. Requires electrical power.

7. Condenser (2) Plates of capacitor are connected to DC power source (usually 48v) Electrical charge determined by eq. Q = CV (Q is charge, C is capacitance, and V is voltage) Polarizing voltage (+/-)

8. Condenser (3) C is inversely proportional to plate distance. Plate distance is inversely proportional to Sound Pressure. C and V are inversely proportional. V inversely proportional to Sound Pressure.

9. Condenser (4) To read the voltage, use a resistor (large value) in the circuit. Voltage across resistor is output signal Extremely high impedance - preamp circuit (also needs power) Placed in mic body FET / Tube

10. Electret Electret-condenser Polarizing charge permanent No external power needed. Impedance change still needs power - usually a battery.

11. Other types Loose particle carbon Experimental/Other (electronic, magnetostriction, optical, thermal) Piezoelectric