Output transducerFig.2.8:Diagram of Amp with Transducers In a public address system, the input and output transducers are of keyimportance. They input and output transducers are capable of convertingenergy from one form to another form. The input transducer, which is themicrophone is fed with mechanical sound energy which it converts intoelectrical energy, while the output transducer (loud speaker) on the otherhand converts electrical energy to mechanical sound energy.2.4.1Input Transducer (Microphones)A microphone operates by converting sound waves into mechanicalvibrations which in turn produce electrical energy. There are different typeof microphones which could be used as input transducers for a publicaddress system e.g. carbon microphone, crystal microphone, moving-coilmicrophone (dynamic), moving iron microphone etc. The most commonmicrophone is the moving coil microphone, in a moving coil microphone,20PRE AMPLIFIERPOWERAMPLIFIER
(as shown in fig…..), a small coil is attached to the center of a diaphragmthat is in a steady magnetic field, when sound waves cause the diaphragm tomove it vibrates the “small coil” thereby acquiring an induced electronicforce (e.m.f), due to electromagnetic inductions. A signal current isgenerated as the coil vibrates to and fro in the magnetic field.The change in the magnetic flux results into an equivalent change in electricflux hence the electromotive force produced in the coil is a resulting effectof the sound pressure is transferred to the amplifier stage of the PublicAddress System from which it is amplified to operate an output transducer.Fig. 2.9:Diagram of Moving Coil Microphone2.4.2Output Transducers (Loudspeakers)Output transducers are devices that can convert electrical energy intosound energy. A loudspeaker is am electro-acoustic device that converts21
electrical energy into sound energy, these devices are generally the converseof microphones. In a loudspeaker, the voice coil moves freely over but doesnot touch the permanent magnet pole. There are different types ofloudspeakers such as the moving coil, electro-acoustic and the subdivisions(woofers, mid-range speakers, tweeters). High fidelity systems makes use ofthe three speakers, the woofer, the mid-range and the tweeters, with threespeakers the incoming frequencies are split, the low frequencies (20 – 1000Hz) are handled by the woofer, the middle frequencies (800 - 10,000 Hz) arehandled by the mid-range speakers while the higher frequencies rangingfrom 3.5 – 20 KHz are handled by the tweeters. Public Address systemsmostly use the moving coil “horn type” loudspeaker due to its highefficiency. A cone-type loud speaker could also be used.Fig 2.1:Diagram of the Loudspeaker22
CHAPTER THREEDESIGN METHODOLOGY3.1Introduction This stereo amplifier uses low cost, and widely available components.
You've reached the end of your free preview.
Want to read all 58 pages?
- Spring '14