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audio and sound reinforcement > Chapter 3 > Flashcards

Chapter 3 Flashcards

1
Q

What is a decibel?

A

The dB always describes a ratio of two quantities… quantities that are most often related to power.

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2
Q

The dB can be used to express ___________

A

voltage ratios

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3
Q

What is the actual quantity of a decibel?

A

1/10 of a Bel

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4
Q

What is the ratio, in dB, of 2 watts to 1 watt?

A 
dB = 10 • log (P1+P0)
=10 • log (2+ 1)
=10 • log 2
=10 • .301
=3.01 or 3
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5
Q

What is a Bel?

A

the logarithm of an electrical, acoustic, or other power ratio

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6
Q

____ is a more appropriate term for expressing output or input voltage.

A

dBu

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7
Q

What does the “u” in “dBu” thus stands for ?

A

“unloaded

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8
Q

How does one convert dbv to dbu?

A

you can convert dBV to dBu (or dBm across 600 ohms) by adding 2.2 dB to whatever dBV value you have.

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9
Q

Power is proportional to _______ ______

A

voltage squared

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10
Q

What is the formula for a bel?

A

Bel =log (P1+Po)

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11
Q

True or False

“dB,” in itself, has no absolute value

A

True

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12
Q

What does sound level mean?

A

refers to the sound pressure level, although it may refer to sound power.

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13
Q

Why is decibel is more convenient to use in sound systems?

A

Because the number scaling is more natural.

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14
Q

What does unloaded mean as in the case of dbu?

A

“unloaded,” a term engineers use to describe an output which works into no load (an open circuit) or an insignificant load

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15
Q

What is dbm?

A

an electrical power level, and is always referenced to 1 milliwatt

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16
Q

What is sound power?

A

the total sound energy radiated by a loudspeaker (or other device) in all directions.

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17
Q

What is sound pressure?

A

the level measured per unit area at a particular location

relative to the sound source.

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18
Q

Typical line level XLR connector inputs

and outputs are intended for use with low or high ________________.

A

impedance equipment

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19
Q

What is acoustic power is expressed in?

A

acoustic watts

20
Q

When fed 100 watts into a loudspeaker, it might generate as little as ___watts acoustic power

A

10

21
Q

What is Root Mean Square?

A

a mathematical expression used in audio to describe the level of a signal

22
Q

For an aperiodic signal such as speech or music, the rms value can only be measured using a __________________________________

A

specialized meter or detector circuit

23
Q

Older low impedance equipment was sensitive to power, XLR connector nominal levels were often specified as “____” or “____”

A

+4 dBm OR +8 dBm

24
Q

What do you use acoustic power and dB PWL to calculate?

A

when calculating the reverb time of an enclosed space, or the efficiency of a loudspeaker system

25
Q

What is the most important use of Root Mean Square (RMS) ?

A

describing the energy of a complex waveform or a sine wave.

26
Q

E=

A

√pz

27
Q

What is the 10 log equation of Acoustic power?

A

dB PWL= 10 log (P1/P0)

28
Q

What is volume in terms of audio equipment ?

A

Defined as power level, in terms of audio equipment, then, if
you turn up the volume, you are increasing the power.

29
Q

The lower the absolute sound levels involved (the

lower curves on the chart), ______________________________

A

the less sensitive we are to low frequencies.

30
Q

The audio level in a __________, for example, may be expressed in dBm, which is referenced to 1 milliwatt

A

signal processor

31
Q

the phon, was coined to specify ________

A

loudness

32
Q

True or False

the ear is not linear guided

A

True

33
Q

Volume also refers to _____

A

cubic dimension of a space

34
Q

What is the name of the individual whom Bel was named after?

A

Alexander Graham Bell

35
Q

True or False

our ears’ sensitivity is logarithmic

A

True

36
Q

What is gain?

A

it is usually assumed to be transmission gain, which is the power increase of a signal, usually expressed in dB

37
Q

Who were the two scientist who described the phenomenon demonstrating that human hearing itself does not have flat frequency response?

A

Two scientists, Fletcher and Munson,

38
Q

What is level?

A

defined as the magnitude of a quantity in relation to an arbitrary reference value.

39
Q

What is the dB equation?

A

dB= 10 log(P1/P2)

40
Q

Why was dBu was specified as a standard unit?

A

In order to avoid confusion with another voltage-related dB unit, the dBV

41
Q

Power is _ _ _ _ _ _ _ _ to voltage squared

A

proportional

42
Q

_____ is a more appropriate term for expressing output or input voltage

A

dBu

43
Q

Why is a decibel is more convenient to use in sound systems?

A

Primarily because the number scaling is more natural

44
Q

when a standard reference value is used for “0 dB,” then any number of dB above or below that implied or stated
zero reference may be used to describe _______________

A

a specific quantity

45
Q

What is the equation of power?

A

P= E^2 /R

46
Q

What was the typical circuit in which dBm was measured when the term was first devised ?

A

a 600 ohm telephone line

47
Q

What is the ratio, in dB, of 100 watts to 10 watts?

A 
dB = 10 • log (P1+PO)
= 10 • log (100+10)
= 10 • log 10
= 10· 1
= 10

audio and sound reinforcement (5 decks)

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