1. Amplifiers and Speakers
Tufts University – ME 93 October 8, 2015

3. What is a speaker? http://animagraffs.com/loudspeaker/

4. What is a speaker?
A transducer converting electrical energy to acoustic energy just like an inverted dynamic mic

5. When is a speaker a mic?
A transducer converting electrical energy to acoustic energy just like an inverted dynamic mic

6. Signal Level Mic Level Preamp Line Level Power amp Speaker Level
5-50 mV
Preamp
Line
Level
50 mV – 2V
Power amp
Speaker
Level
50-100V

7. Signal Level - Voltage

8. What about Watts? P = E * I E I = R Watts measure Power (P)
Volts measure Voltage (E)
Amps measure Current (I)
Ohms measure Impedance (R)
P = E * I E R
I =
A microphone with a RMS voltage of: Volts
and an impedance of: Ohms
draws a current of: Amps
exerts an average power around: Watts

9. Signal Level - Watts

10. The Passive Speaker Cabinet
1 or more speakers
Crossover
Most be paired with an external amplifier
Dampening
The Cabinet
Grille
Port

11. Passive Crossovers
Amplifier

12. Active Crossovers
Amplifier
Amplifier
Amplifier

13. The Active Speaker Cabinet
1 or more speakers
Active crossover
Has it’s own amplifier(s)
Dampening
The Cabinet
Grille
Port

14. Speaker Specifications
Frequency Response
Power rating
dBSPL = 1 watt of 1 meter away
Impedance
Directionality and dispersion
coverage angle
Weight/Form Factor
Rigging components

15. Amplifier Specifications
Frequency Response
Power Rating
Dependent on impedance of the load
Bridging
Slew Rate
Damping Factor
Higher is better!
THD
Stereo 8 Ohms,
both channels driven……….240 W/ch
Stereo 4 Ohms,
both channels driven……….400 W/ch
Mono 8 Ohms,
Bridged………………..……800 W/ch

16. Impedance & Power 1 Znet =
Multiple loudspeakers will generally be connected in parallel
How do we calculate the impedance? 1
Znet = 1 Z1 1 Z2 1 Zn + +

17. Impedance & Power Only link speakers with the same impedance
divide Z by # of speakers or just keep dividing by 2 (conservative)

18. Parameters Passive Speakers Driver Attenuators Amplifiers
Input Sensitivity
Bridging
Filters

19. Best Practices Tweeters don’t like clipping
Woofers don’t like DC/over-excursion
Matching amplifers and speakers
Turn the amplifiers up so you don’t have to turn the mixer up

20. Next Steps
Speaker manufacturers close by
EAW
Bose
Genelec