Questions and Problems

Author: N.H. Crowhurst

1. What are the natural limitations to obtaining a voice coil of specific resistance? If a voice coil, wound in 4 layers, has a resistance of 10 ohms, what would be the approximate resistance of a coil of the same dimensions, wound of a wire whose gage would permit 5 layers?

2. What is matching (a) as applied to microphones, (b) as applied to loudspeakers? If a loudspeaker has a voice-coil resistance of 8 ohms and an amplifier output needs a load of 5000 ohms, what transformer turns ratio is needed?

3. If the voice-coil resistance in Question 2 were 10 ohms instead of 8 ohms, what load would be provided for the amplifier by the same transformer?

4. What led to the use of multiple loudspeaker units to cover the audio range?

5. Why are dividing networks used with multiple loudspeaker systems? What might result from failure to use a suitable network?

6. Networks consisting of resistance and capacitance or resistance and inductance produce division of voltage or current according to frequency. Why cannot networks of these types be used to feed power to loudspeakers?

7. What is basic difference between networks in which the elements are (a) in series, (b) in parallel?

8. In the simplest type crossover, suppose the crossover frequency is 800 cycles. How much of the total amplifier power of 10 watts goes to each unit, when the frequency is (a) 400 cycles, (b) 800 cycles, (c) 1600 cycles?

9. What is the effect of using more inductors and capacitors in crossover networks? Explain how this difference in response is achieved.

10. What is meant by phasing? How would you tell if two loudspeaker units were connected to provide correct phasing?

11. What is resonance? State in which of the following it is a desirable feature, and in which it is undesirable: piano, microphone, violin, marimba, loudspeaker, organ pipe, flute, oboe, phonograph pickup.

12. A moving-iron loudspeaker, when compared with a moving-coil type, actually seemed louder, although its quality was poor, particularly in the bass. Explain this with reference to the effect of resonance.

13. Explain how a simple device can be used to obtain calibration of the particle velocity of air in sound wave. Does a Rayleigh disk discriminate between waves from the back or front? Is it uniformly sensitive to sound waves from all directions?

14. Is human hearing uniformly sensitive to all audible frequencies, and does its sensitivity to different frequencies depend on their intensity?