Gibilisco - Acoustics, Audio, And High Fidelity

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Gibilisco - Acoustics, Audio, And High Fidelity - Quiz


Questions and Answers
  • 1. 

    A young person can hear sounds at frequencies as high as approximately which of thefollowing?

    • A.

      20 Hz

    • B.

      20 kHz

    • C.

      20 MHz

    • D.

      20 GHz

    Correct Answer
    B. 20 kHz
    Explanation
    A young person can hear sounds at frequencies as high as approximately 20 kHz. This is because the human hearing range typically extends from 20 Hz to 20 kHz. Frequencies below 20 Hz are considered infrasound, while frequencies above 20 kHz are considered ultrasound. As people age, their ability to hear high frequencies decreases, which is why younger individuals have a higher upper limit for hearing.

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  • 2. 

    Electromagnetic interference to a hi-fi amplifier can occur in the presence of

    • A.

      A nearby radio broadcast station.

    • B.

      Improperly designed receiving antennas.

    • C.

      Excessive utility voltage.

    • D.

      Improper balance between the left and right channels.

    Correct Answer
    A. A nearby radio broadcast station.
    Explanation
    Electromagnetic interference can occur in a hi-fi amplifier in the presence of a nearby radio broadcast station. Radio broadcast stations emit strong electromagnetic signals that can interfere with the amplifier's circuitry and cause distortion or noise in the audio output. This interference can be particularly problematic if the amplifier is not properly shielded or if the radio station operates on a frequency that is close to the amplifier's operating frequency. Therefore, the presence of a nearby radio broadcast station is a likely cause of electromagnetic interference in a hi-fi amplifier.

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  • 3. 

    The midrange audio frequencies

    • A.

      Are exactly halfway between the lowest and highest audible frequencies.

    • B.

      Represent sounds whose volume levels are not too loud or too soft.

    • C.

      Are above the treble range but below the bass range.

    • D.

      None of the above are true.

    Correct Answer
    D. None of the above are true.
    Explanation
    The correct answer is "None of the above are true" because the statement in the question is incorrect. The midrange audio frequencies are not necessarily exactly halfway between the lowest and highest audible frequencies. They can vary depending on the specific audio system and the frequencies being considered. Additionally, the midrange frequencies do not necessarily represent sounds with a specific volume level, and they are not limited to a specific range between treble and bass frequencies.

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  • 4. 

    In the acoustical design of a room intended for a home audio system,

    • A.

      The use of small speakers can minimize distortion.

    • B.

      Reflection of sound waves from walls should be minimized.

    • C.

      The walls should all intersect at perfect 90° angles.

    • D.

      Wooden furniture, without upholstery, should be used.

    Correct Answer
    B. Reflection of sound waves from walls should be minimized.
    Explanation
    In the acoustical design of a room intended for a home audio system, it is important to minimize the reflection of sound waves from walls. Reflections can cause interference and create unwanted echoes or reverberation, leading to distortion in the sound. By minimizing reflection, the room can have better sound quality and clarity. This can be achieved through the use of sound-absorbing materials on the walls, such as acoustic panels or foam, which help to absorb and dissipate sound waves rather than reflecting them back into the room.

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  • 5. 

    A change of +10 dB in an audio signal represents

    • A.

      A doubling of acoustic power.

    • B.

      A threefold increase in acoustic power.

    • C.

      A tenfold increase in acoustic power.

    • D.

      No change in acoustic power, but a change in frequency.

    Correct Answer
    C. A tenfold increase in acoustic power.
    Explanation
    A change of +10 dB in an audio signal represents a tenfold increase in acoustic power. The decibel (dB) scale is logarithmic, meaning that each 10 dB increase represents a tenfold increase in power. Therefore, a change of +10 dB indicates that the power of the audio signal has increased ten times compared to its original level.

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  • 6. 

    What is the frequency of an acoustic disturbance whose wavelength is 120 mm in air?

    • A.

      279 Hz

    • B.

      2.79 kHz

    • C.

      35.8 Hz

    • D.

      358 Hz

    Correct Answer
    B. 2.79 kHz
    Explanation
    The frequency of an acoustic disturbance is determined by the speed of sound and the wavelength. In this case, the wavelength is given as 120 mm. To find the frequency, we can use the formula: frequency = speed of sound / wavelength. The speed of sound in air is approximately 343 m/s. Converting the wavelength to meters (120 mm = 0.12 m), we can calculate the frequency as 343 / 0.12 = 2858.33 Hz, which can be rounded to 2.86 kHz. Therefore, the correct answer is 2.79 kHz.

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  • 7. 

    What is the frequency of a sound wave that propagates at a speed of 1100 ft/s?

    • A.

      33.5 Hz

    • B.

      335 Hz

    • C.

      3.35 kHz

    • D.

      Forget it! The frequency of a sound wave is independent of the propagation speed.

    Correct Answer
    D. Forget it! The frequency of a sound wave is independent of the propagation speed.
    Explanation
    The correct answer is "Forget it! The frequency of a sound wave is independent of the propagation speed." This answer is correct because the frequency of a sound wave is determined by the source of the wave, not by the speed at which it propagates. The frequency of a sound wave refers to the number of complete cycles of the wave that occur in one second. It is determined by the vibrating object or source that creates the sound wave, and it remains constant regardless of the speed at which the wave travels through a medium.

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  • 8. 

    The relative phase of two acoustic waves from the same source at the same time, one wavedirect and one wave reflected from a wall, can affect

    • A.

      The positions of antinodes and nodes.

    • B.

      The perceived frequency.

    • C.

      The positions of antinodes and nodes, and the perceived frequency.

    • D.

      Neither the positions of the antinodes and nodes, nor the perceived frequency.

    Correct Answer
    A. The positions of antinodes and nodes.
    Explanation
    When two acoustic waves from the same source reach a point at the same time, their relative phase can affect the positions of antinodes and nodes. The phase difference between the two waves determines whether they will reinforce or cancel each other out at specific points in space. This results in the formation of antinodes (points of maximum amplitude) and nodes (points of zero amplitude) at different locations. The perceived frequency, on the other hand, is determined solely by the source frequency and is not affected by the relative phase of the waves. Therefore, the correct answer is that the relative phase affects the positions of antinodes and nodes, but not the perceived frequency.

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  • 9. 

    In an acoustic sine wave,

    • A.

      The frequency and phase are identical.

    • B.

      The sound power is inversely proportional to the frequency.

    • C.

      The sound power is directly proportional to the frequency.

    • D.

      All of the sound power is concentrated at a single frequency.

    Correct Answer
    D. All of the sound power is concentrated at a single frequency.
    Explanation
    An acoustic sine wave refers to a pure tone with a single frequency and no harmonics. In this case, "all of the sound power is concentrated at a single frequency" means that the entire energy of the wave is focused on one specific frequency. This is because a sine wave has no other frequencies present, so all the power is dedicated to that single frequency.

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  • 10. 

    Vinyl disks are

    • A.

      Susceptible to physical damage.

    • B.

      Useful primarily in high-power sound systems.

    • C.

      Digital media.

    • D.

      Preferred for off-the-air sound recording.

    Correct Answer
    A. Susceptible to physical damage.
    Explanation
    Vinyl disks are susceptible to physical damage because they are made of a fragile material that can easily be scratched or warped. Unlike digital media, which can be easily stored and accessed without physical contact, vinyl disks require careful handling to avoid any damage that could affect the sound quality. Additionally, vinyl disks are not preferred for off-the-air sound recording as they are prone to picking up background noise and interference. Therefore, the correct answer is that vinyl disks are susceptible to physical damage.

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  • 11. 

    If an amplifier introduces severe distortion in the waveforms of input signals, then thatamplifier is

    • A.

      Not delivering enough power.

    • B.

      Operating at the wrong frequency.

    • C.

      Operating in a nonlinear fashion.

    • D.

      Being underdriven.

    Correct Answer
    C. Operating in a nonlinear fashion.
    Explanation
    When an amplifier introduces severe distortion in the waveforms of input signals, it means that the output signal is not an exact replica of the input signal. This indicates that the amplifier is operating in a nonlinear fashion. In a linear amplifier, the output signal would be a scaled version of the input signal, but in a nonlinear amplifier, the output signal is distorted and contains additional harmonics. Therefore, the correct answer is that the amplifier is operating in a nonlinear fashion.

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  • 12. 

    Suppose a 10-W amplifier is used with speakers designed for a 100-W amplifier. Which ofthe following statements is true?

    • A.

      The speakers are capable of handling the amplifier output.

    • B.

      The amplifier might be damaged by the speakers.

    • C.

      Electromagnetic interference is more likely to occur than would be the case if the speakers were designed for a 10-W amplifier.

    • D.

      The speakers are likely to produce excessive distortion.

    Correct Answer
    A. The speakers are capable of handling the amplifier output.
    Explanation
    The speakers are capable of handling the amplifier output because the speakers are designed for a 100-W amplifier, and the amplifier being used is only 10-W. Therefore, the speakers are not being pushed to their maximum capacity and can handle the output of the amplifier without any issues.

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  • 13. 

    Which of the following frequencies cannot be received by an AM/FM tuner?

    • A.

      830 kHz

    • B.

      95.7 kHz

    • C.

      90.1 MHz

    • D.

      107.3 MHz

    Correct Answer
    B. 95.7 kHz
  • 14. 

    Which of the following statements about woofers is true?

    • A.

      They are especially useful for reproducing the sounds of barking dogs.

    • B.

      They are designed to handle short, intense bursts of sound.

    • C.

      They should not be used with graphic equalizers.

    • D.

      They are specifically designed to reproduce low-frequency sounds.

    Correct Answer
    D. They are specifically designed to reproduce low-frequency sounds.
    Explanation
    Woofers are a type of speaker that is specifically designed to reproduce low-frequency sounds. They are larger and have a greater cone area compared to other speakers, allowing them to move more air and produce deeper bass tones. Woofers are commonly used in audio systems to enhance the low-frequency response and provide a more balanced sound reproduction. They are not designed for reproducing the sounds of barking dogs specifically, nor are they limited to handling short, intense bursts of sound. There is no information provided about their compatibility with graphic equalizers.

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  • 15. 

    Suppose you have an amateur radio station and its transmitter causes EMI to your hi-fisystem. Which of the following would almost certainly not help?

    • A.

      Build a new transmitter that works on the same frequencies with the same power output as your existing transmitter.

    • B.

      Reduce the transmitter output power.

    • C.

      Install shielded speaker wires in the hi-fi system, and be sure the system is well grounded.

    • D.

      Move the amateur radio transmitting antenna to a location farther away from the hi-fi system.

    Correct Answer
    A. Build a new transmitter that works on the same frequencies with the same power output as your existing transmitter.
    Explanation
    Building a new transmitter that works on the same frequencies with the same power output as the existing transmitter would not help reduce the EMI caused to the hi-fi system. This is because the EMI is caused by the transmitter itself, regardless of the frequency or power output. The other options, such as reducing the transmitter output power, installing shielded speaker wires, and moving the transmitting antenna farther away, can all help mitigate the EMI and improve the performance of the hi-fi system.

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  • 16. 

    In an analog audio tape recorder/player, the recording head

    • A.

      Converts sound waves to radio signals.

    • B.

      Converts sound waves to fluctuating electric current.

    • C.

      Converts AF current to a fluctuating magnetic field.

    • D.

      Converts dc to AF current.

    Correct Answer
    B. Converts sound waves to fluctuating electric current.
    Explanation
    The recording head in an analog audio tape recorder/player is responsible for converting sound waves into fluctuating electric current. This is achieved through the use of a transducer, which converts the mechanical vibrations of the sound waves into electrical signals. These electrical signals are then recorded onto the magnetic tape in the form of varying magnetic fields. When the tape is played back, the recording head reads the magnetic fields and converts them back into electric current, which is then amplified and sent to the speakers to produce sound.

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  • 17. 

    A rack-mounted hi-fi system

    • A.

      Can save floor space.

    • B.

      Is more susceptible to EMI than a compact system.

    • C.

      Is cheaper than a compact system.

    • D.

      Is designed especially for use with vinyl disks and turntables.

    Correct Answer
    A. Can save floor space.
    Explanation
    A rack-mounted hi-fi system can save floor space because it is designed to be mounted on a rack or shelf, allowing it to be elevated off the floor and freeing up valuable space. This is particularly beneficial in smaller living areas or rooms where space is limited.

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  • 18. 

    An audio mixer

    • A.

      Cannot match impedances among interconnected components.

    • B.

      Cannot increase the audio output of an amplifier.

    • C.

      Eliminates EMI problems in all but the worst cases.

    • D.

      Allows a microphone to be used as a speaker.

    Correct Answer
    C. Eliminates EMI problems in all but the worst cases.
    Explanation
    An audio mixer is a device used to combine and adjust the levels of multiple audio signals. It does not have the ability to match impedances among interconnected components, as this is typically done using impedance matching transformers or other specialized equipment. Additionally, an audio mixer does not increase the audio output of an amplifier, as its main function is to control and balance the levels of different audio sources. While an audio mixer can help reduce electromagnetic interference (EMI) in most cases, it may not completely eliminate EMI in the worst scenarios. Therefore, the correct answer is that an audio mixer eliminates EMI problems in all but the worst cases.

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  • 19. 

    Which of the following devices or circuits ordinarily employs D/A conversion?

    • A.

      A portable CD player

    • B.

      A turntable for use with vinyl disks

    • C.

      An analog audio tape recording/playback system

    • D.

      An RC tone control

    Correct Answer
    A. A portable CD player
    Explanation
    A portable CD player ordinarily employs D/A conversion because it needs to convert the digital audio data stored on the CD into analog signals that can be played through speakers or headphones. The D/A converter in the CD player takes the digital information and converts it into analog signals that can be amplified and heard as sound.

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  • 20. 

    Which of the following is an advantage of digital audio over analog audio?

    • A.

      Digital media can be used to record and play back audio at higher frequencies than can analog media.

    • B.

      Multigeneration copies of digital audio programs can be made without degradation in fidelity, but this is not true of analog audio programs.

    • C.

      Digital audio is compatible with vinyl disks and old-fashioned reel-to-reel and cassette tape, but analog audio is not.

    • D.

      There are no genuine advantages of digital audio over analog audio. In fact, analog audio is superior to digital audio in every respect.

    Correct Answer
    C. Digital audio is compatible with vinyl disks and old-fashioned reel-to-reel and cassette tape, but analog audio is not.
    Explanation
    Analog audio is not compatible with vinyl disks and old-fashioned reel-to-reel and cassette tape, whereas digital audio is. This means that digital audio can be easily transferred and played on various devices and formats, providing more flexibility and convenience for users.

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