Lesson 2: How Sound is Measured and Just What is Dynamic Range?

How can a sound system's dynamic range be increased?

- By increasing the maximum sound level capability - By making the environment quieter

What are the factors that will determine the headroom needed?

- The application - The available budget for amplifiers - The type of program material

Zero dBu is always ___.

0.775 V

The actual voltage chosen as a reference for 0 dB, 0 dBV is ___ .

1 V

The unit dBm expresses an electrical power level, and is always referenced to ____.

1 mW

What is usually an adequate amount of headroom for most sound reinforcement systems?

10 dB

When the loudness exceeds ___, most people become uncomfortable.

120 phons

For a musical application where high fidelity is the ultimate consideration, how much headroom should be allowed?

15 dB to 20 dB

Headroom, as a specification, says something about the ability of the sound system to adjust to varying voltage levels.

False

What problem(s) could one encounter if the dynamic range of the program material exceeds the dynamic range capability of the sound system?

I. Program peaks will be distorted due to clipping and/or loudspeaker break-up. II. Quiet passages will not be heard because they will be below the electrical acoustic noise floor.

What devices permit compression to be applied above a set threshold?

Limiters

A Bel is defined as the logarithm of an electrical, acoustic, or other power ratio.

True

Gain has several definitions. If not specified, gain is usually assumed to be transmission gain, which is the power increase of the signal, usually expressed in decibels.

True

The "u" in "dBu" stands for unloaded, a term engineers use to describe an output that works into no load.

True

The decibel always describes a ratio of two quantities.

True

What is the mathematical expression of the decibel?

dB = 10 log (P1 ÷ P2)

What is the equation used when a dB describes a sound pressure ratio?

dB spl = 20 log (P1 ÷ P0)

The difference in decibels between the loudest and quietest portion of a program indicates the ____.

dynamic range

The difference between the nominal and the highest (peak) levels in a program is the ___.

headroom

The difference between the nominal level and the noise floor represents the ___.

signal-to-noise ratio

? is the level measured per unit area at a particular location relative to the sound source.

Sound pressure