Lecture Notes

October 8th - Speaker design, Amplifier architecture
Considerations of passive speaker construction
-review of transducer principles
-speakers are microphones too!
-passive crossovers are made of speaker level LPF, HPF & BP filters
-active crossover are just line-level LPF, HPF & BP filters
-audio is AC; what happens when DC hits a speaker?
-materials and physics of a speaker
-cabinet construction
-form factor, aesthetics and resonance are all concerns
-porting vs. sealed enclosures
-how do we control vibrations
-active or “powered” speakers have amplifiers, filters and some DSP built-in
Power amplification
-observe the scale between microphone preamps and power amplifiers
-bridging vs. stereo
Specifications relevant to amplifiers and speakers
-impedance and ohms law review
-power (watts)
-current (amps)
-slew rate
-amplifiers/speakers and dBSPL
-measured as 1 watt 1 meter away from the source
Matching amplifiers & speakers
-why we use amplifiers with higher power ratings than the speakers
-so we don’t have to push the amplifier too hard
-common variables on power amplifiers
-’sensitivity’ controls
-why we turn them all the way up
-so we don’t clip coming out of the mixer
-when we don’t
-when they’re amplifying excessive noise
-to remove frequencies that aren’t going to be reproduced by the speaker
-IE: HPF at 50 Hz on a small box
Practical Speaker Setups
 Near-field monitors
o equilateral triangle!
o sounds great for one person, ok for the rest
 Small sound reinforcement
o needs to sound great for a small room full of people, without being too
 Large sound reinforcement
o needs to sound great for a large group of people
Line arrays vs. Point source
o Line arrays do a good job of distributing great sound across a large area
and distance, but you need A LOT of them.
o Point source do a good job of distributing great sound across a small area
and you only need a few to do the job right
Next Steps:
So you want to work at Bose, EAW, Genelec?
Designing, measuring and marketing the next revolution in headphones could be cool!