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HIS 140 - Amplifiers, Dampers, and Acoustic Plumbing
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  • 1. AMPLIFIERS, DAMPERS, & ACOUSTIC PLUMBING• Class A amplifier• It is a biased amplifier meaning that, even when no sound is present, electrical current is continuously flowing to the output transducer through the amplifier.• It is the most simple form of amplifier.
  • 2. AMPLIFIERS, DAMPERS, & ACOUSTIC PLUMBING• Class A amplifiers are very inefficient with their electrical current use.• Are most suitable for low power hearing instruments.
  • 3. AMPLIFIERS, DAMPERS, & ACOUSTIC PLUMBING• Class B Amplifiers Are more efficient because they separate the “work load” into two amplifiers. One amplifier is pushing the output transducer diaphragm while the other amplifier is pulling it.
  • 4. AMPLIFIERS, DAMPERS, & ACOUSTIC PLUMBINGClass B amplifiers are used most oftenwhere high output amplification isrequired. They are often referred toas push-pull amplifier circuits.
  • 5. AMPLIFIERS, DAMPERS, & ACOUSTIC PLUMBING• Class D amplifiers• Are smaller due to the amplifier being inside the same can as the output transducer/receiver.• Are more efficient with the electrical current, because they switch off and on at a rapid pulse rate.
  • 6. AMPLIFIERS, DAMPERS, & ACOUSTIC PLUMBING• Class D amplifiers are called “switching” amplifiers due to the rapid pulsed switching of current.• The are used in the output stage of today’s digital amplifiers.
  • 7. AMPLIFIERS, DAMPERS, & ACOUSTIC PLUMBING• Class H amplifiers Are class A amplifiers with a sliding bias for greater efficiency of current use. They are still less efficient than a class D amplifier.
  • 8. AMPLIFIERS, DAMPERS, & ACOUSTIC PLUMBING• Due to the sliding bias, the class H circuit has more distortion.• It is still less efficient with current use than a class D amplifier.
  • 9. AMPLIFIERS, DAMPERS, & ACOUSTIC PLUMBING• Compression amplifier Its basic operation is that when the sound input increases into the hearing instrument, the amount of amplification output decreases.
  • 10. AMPLIFIERS, DAMPERS, & ACOUSTIC PLUMBINGCompression amplifiers may also beknown as automatic gain control (AGC) orautomatic volume control (AVC).Compression amplification is fundamentalin the development of digital algorithms.
  • 11. AMPLIFIERS, DAMPERS, & ACOUSTIC PLUMBING• Digital Circuits/amplifiers Use many of the fundamental concepts of the analog hearing instruments; however, it must have an analog to digital converter on the input side of the digital amplifier.
  • 12. AMPLIFIERS, DAMPERS, & ACOUSTIC PLUMBINGThe A/D converter changes the analogelectrical voltage into a string of numbers.These numbers can then be manipulatedinto very discreet signal patterns.A digital to analog D/A convertor isnecessary to convert the signal into anoutput transducer.
  • 13. AMPLIFIERS, DAMPERS, & ACOUSTIC PLUMBING• Acoustic Dampers Are necessary to smooth the inherent electrical peaks of amplifiers and output transducers.
  • 14. AMPLIFIERS, DAMPERS, & ACOUSTIC PLUMBINGElectrical peaks create distortion andunstable frequencies. Unstablefrequencies are what make hearinginstruments “whistle”/feedback.
  • 15. AMPLIFIERS, DAMPERS, & ACOUSTIC PLUMBINGAcoustic dampers are most often made asfused mesh inside of a stainless steel ring.They may also be made from lamb’s wooland plastic foam.
  • 16. AMPLIFIERS, DAMPERS, & ACOUSTIC PLUMBINGDampers may be located/inserted into themicrophone or receiver opening of thetransducers; or somewhere within the“plumbing” i.e. earhook, tubing.
  • 17. AMPLIFIERS, DAMPERS, & ACOUSTIC PLUMBING• Acoustic couplers/”plumbing” Modify the amplified sound as it exits into the ear canal.
  • 18. AMPLIFIERS, DAMPERS, & ACOUSTIC PLUMBING• With various horn shapes of the couplings and damping, much of the frequency amplification can be modified before it exits into the ear canal.
  • 19. AMPLIFIERS, DAMPERS, & ACOUSTIC PLUMBING• Acoustic plumbing/coupling can be related to the various shapes of musical instruments in the creation of musical notes. This shaping of the acoustic coupling can modify the frequencies received at the eardrum.
  • 20. AMPLIFIERS, DAMPERS, & ACOUSTIC PLUMBING• Acoustic couplers include:1. Earhooks2. Earmolds3. Various tubing Note: We will learn more of the specific applications in future coursework.