TOA bs-1030 Mode D'Emploi
TOA Electronics Speaker Guide
Audio Basics
18
Sensitivity Ratings and the Decibel
A speaker’s sensitivity is the on-axis loudness (dB SPL) measured at a specific distance that
results from applying a specific amount of power (i.e., 1 W @ 1 m). The output level of the
speaker at different power levels and distances can be calculated from this figure. For example:
If a speaker’s sensitivity is rated at 96 dB SPL with a 1 W input measured at 1 m from the
speaker, then doubling the power to 2 W raises the output 3 dB to 99 dB SPL at 1 m. Doubling
the power again to 4 W produces 102 dB SPL. For a discussion and examples of how to use
sensitivity ratings, see Chapter 5: Using Speaker Specifications.
results from applying a specific amount of power (i.e., 1 W @ 1 m). The output level of the
speaker at different power levels and distances can be calculated from this figure. For example:
If a speaker’s sensitivity is rated at 96 dB SPL with a 1 W input measured at 1 m from the
speaker, then doubling the power to 2 W raises the output 3 dB to 99 dB SPL at 1 m. Doubling
the power again to 4 W produces 102 dB SPL. For a discussion and examples of how to use
sensitivity ratings, see Chapter 5: Using Speaker Specifications.
Attenuation over Distance: Inverse Square Law
The inverse square law describes how sound attenuates over distance. It states that volume
(SPL) decreases 6 dB each time the distance from the sound source is doubled. This is due to
the diffusion of sound radiating from the sound source over a spherical area. As the radius of a
sphere is doubled, its surface area quadruples, effectively dividing the acoustical power by
four. This is consistent with the discussion above of power, volume, and the decibel: dividing
the power by 2 results in a 3 dB decrease in volume; dividing by 4 results in a 6 dB decrease.
(SPL) decreases 6 dB each time the distance from the sound source is doubled. This is due to
the diffusion of sound radiating from the sound source over a spherical area. As the radius of a
sphere is doubled, its surface area quadruples, effectively dividing the acoustical power by
four. This is consistent with the discussion above of power, volume, and the decibel: dividing
the power by 2 results in a 3 dB decrease in volume; dividing by 4 results in a 6 dB decrease.
For the mathematically minded: The following equation converts a change in distance to a
change in level for a spherically radiating source: level change in dB = 20 * log (D1/D2), where
D1 is the original distance and D2 is the new distance.
change in level for a spherically radiating source: level change in dB = 20 * log (D1/D2), where
D1 is the original distance and D2 is the new distance.
Speech Intelligibility, Acoustics, and Psychoacoustics
Speech intelligibility refers to the degree a listener can understand spoken words in a particular
space. It is important to clearly hear and differentiate consonant sounds. The two basic parameters
affecting intelligibility are the smoothness of the system frequency response curve in the
speech range (about 350 Hz – 5 kHz) and the effective signal-to-noise ratio of the system (noise
can include echoes, reverberation, distortion, and even out-of-band signals such as excessive
bass). Good frequency response depends on selecting high-quality speaker components and
locating and aiming them correctly. The following sections on masking effects and reverberation
cover some often overlooked factors that affect achieving a good signal-to-noise ratio.
space. It is important to clearly hear and differentiate consonant sounds. The two basic parameters
affecting intelligibility are the smoothness of the system frequency response curve in the
speech range (about 350 Hz – 5 kHz) and the effective signal-to-noise ratio of the system (noise
can include echoes, reverberation, distortion, and even out-of-band signals such as excessive
bass). Good frequency response depends on selecting high-quality speaker components and
locating and aiming them correctly. The following sections on masking effects and reverberation
cover some often overlooked factors that affect achieving a good signal-to-noise ratio.