Amplifiers and SpeakersTufts University – ME 93October 8, 2015

What is a speaker?

http://animagraffs.com/loudspeaker/

What is a speaker?

When is a speaker a mic?

Signal Level

Mic Level5-50 mV

Line Level

50 mV – 2V

Speaker Level50-100V

Preamp Poweramp

Signal Level - Voltage

What about Watts?Watts measure Power (P)Volts measure Voltage (E)Amps measure Current (I)

Ohms measure Impedance (R)

P = E * I

I =

ER

A microphone with a RMS voltage of: 0.05 Volts and an impedance of: 200 Ohms

draws a current of: 0.0025 Amps

exerts an average power around: 0.0000125 Watts

Signal Level - Watts

The Passive Speaker Cabinet• 1 or more speakers• Crossover• Most be paired with

an external amplifier• Dampening• The Cabinet

• Grille• Port

Passive Crossovers

Amplifier

Active Crossovers

Amplifier

Amplifier

Amplifier

The Active Speaker Cabinet• 1 or more speakers• Active crossover• Has it’s own amplifier(s)• Dampening• The Cabinet

• Grille• Port

Speaker Specifications• Frequency Response• Power rating• dBSPL = 1 watt of power @ 1 meter away

• Impedance• Directionality and dispersion• coverage angle

• Weight/Form Factor• Rigging components

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

Impedance & Power• Multiple loudspeakers will generally be

connected in parallel• How do we calculate the impedance?

Znet

=

11Z1

1Z2

1Zn

+ +

Impedance & PowerOnly link speakers with the same impedance• divide Z by # of speakers or just keep

dividing by 2 (conservative)

ParametersPassive Speakers• Driver Attenuators

Amplifiers• Input Sensitivity• Bridging• Filters

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

Next Steps• Speaker manufacturers close by• EAW• Bose• Genelec