Chapter 3

Question 1

What is a decibel?

Answer 1

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

Question 2

The dB can be used to express ___________

Answer 2

voltage ratios

Question 3

What is the actual quantity of a decibel?

Answer 3

1/10 of a Bel

Question 4

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

Answer 4

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

Question 5

What is a Bel?

Answer 5

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

Question 6

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

Answer 6

dBu

Question 7

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

Answer 7

“unloaded

Question 8

How does one convert dbv to dbu?

Answer 8

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

Question 9

Power is proportional to _______ ______

Answer 9

voltage squared

Question 10

What is the formula for a bel?

Answer 10

Bel =log (P1+Po)

Question 11

True or False

“dB,” in itself, has no absolute value

Answer 11

True

Question 12

What does sound level mean?

Answer 12

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

Question 13

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

Answer 13

Because the number scaling is more natural.

Question 14

What does unloaded mean as in the case of dbu?

Answer 14

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

Question 15

What is dbm?

Answer 15

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

Question 16

What is sound power?

Answer 16

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

Question 17

What is sound pressure?

Answer 17

the level measured per unit area at a particular location

relative to the sound source.

Question 18

Typical line level XLR connector inputs

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

Answer 18

impedance equipment

Question 19

What is acoustic power is expressed in?

Answer 19

acoustic watts

Question 20

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

Answer 20

10

Question 21

What is Root Mean Square?

Answer 21

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

Question 22

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

Answer 22

specialized meter or detector circuit

Question 23

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

Answer 23

+4 dBm OR +8 dBm

Question 24

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

Answer 24

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

Question 25

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

Answer 25

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

Question 26

E=

Answer 26

√pz

Question 27

What is the 10 log equation of Acoustic power?

Answer 27

dB PWL= 10 log (P1/P0)

Question 28

What is volume in terms of audio equipment ?

Answer 28

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

Question 29

The lower the absolute sound levels involved (the | lower curves on the chart), ______________________________

Answer 29

the less sensitive we are to low frequencies.

Question 30

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

Answer 30

signal processor

Question 31

the phon, was coined to specify ________

Answer 31

loudness

Question 32

True or False | the ear is not linear guided

Answer 32

True

Question 33

Volume also refers to _____

Answer 33

cubic dimension of a space

Question 34

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

Answer 34

Alexander Graham Bell

Question 35

True or False | our ears' sensitivity is logarithmic

Answer 35

True

Question 36

What is gain?

Answer 36

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

Question 37

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

Answer 37

Two scientists, Fletcher and Munson,

Question 38

What is level?

Answer 38

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

Question 39

What is the dB equation?

Answer 39

dB= 10 log(P1/P2)

Question 40

Why was dBu was specified as a standard unit?

Answer 40

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

Question 41

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

Answer 41

proportional

Question 42

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

Answer 42

dBu

Question 43

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

Answer 43

Primarily because the number scaling is more natural

Question 44

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 _______________

Answer 44

a specific quantity

Question 45

What is the equation of power?

Answer 45

P= E^2 /R

Question 46

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

Answer 46

a 600 ohm telephone line

Question 47

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

Answer 47

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