13-06-2013, 01:59 PM
Power Amplifiers and Loudspeakers
Power Amplifiers.ppt (Size: 75.5 KB / Downloads: 136)
Power Amplifiers
An amplifier is an electronic device which transforms small voltages and currents into large ones.
Ratings
Wattage
Generally speaking more is better
Not all manufactures measure power ratings the same way. You must be comparing apples with apples
Peak – the maximum power the amp can ever output
Continuous – the maximum power the amp can output without clipping
RMS – Root-Mean-Squared. 0.707 peak power.
Correlates well to the real work done by the amp
Total Harmonic Distortion
THD
Measurement of the % of unwanted harmonics added to the original signal
Usually ranges from less than 0.1% to 0.25%
The lower the better. 0.1% is typically the highest professional grade used
Output impedance and loading
The engineers who designed the amplifier are assuming a load (impedance)
The load the amp is looking for will usually be labeled on the back of the amp or in the book
If the impedance is lower than expected, the amount of current the amp will be asked to supply will increase and could damage the unit
V=IR
Remember parallel and series circuits
Loudspeakers
A loudspeaker consists of one or more Drivers mounted in an Enclosure
Dynamic cone driver
The most common style of driver used theatrically or in live musical performance
Dynamic Cone Driver
The louder the volume the speaker is called upon to produce, the more current the amplifier supplies and the longer the back-and-forth motion performed by the voice coil / cone assembly
High frequency sounds – rapidly vibrating cones
Cones must be very light in order to move very quickly
Very small gauge wire in voice coil – susceptible to heat build-up
Tweeter
Low frequency sounds – require a great deal of air to move
Cones must be very large to push great quantities of air
Weight is not an issue because of the low frequencies
Larger gauge wire in the voice coil can take more heat
Woofer
Enclosures
Fancy term for a box
A great deal of engineering goes into these “boxes”
The cone pushes air in both directions. It is important to consider what happens to the sound coming from the “back” of the speaker
Cross-over networks
Electronic circuit designed to filter out some frequencies and allow others to pass
Used to ensure that a driver receives only the frequencies that it was designed to reproduce
High frequencies go to tweeters
Middle frequencies go to mid-range speakers
Low frequencies go to woofers
Very low frequencies go to sub-woofers
Cross-over networks can be located:
After the amplifier and before the speaker
One amp provides power for multiple drivers
Before the amplifier
One amp provides power for one range of frequencies. A second amp provides power for a different range of frequencies…