Acoustics and noise control: An automobile horn measured at approximately 1.5 m (typical roadside proximity) produces a sound pressure level closest to which value in decibels (dB)?

Introduction / Context:
Decibel scales are logarithmic and crucial for evaluating community noise, occupational exposure, and environmental impact. An automobile horn is a familiar source used to benchmark perceived loudness. At short distances along the near field-to-far field transition (around 1.5 m), its sound pressure level provides a practical reference for noise assessment.

Given Data / Assumptions:

• Source: typical passenger vehicle horn, not specialized emergency sirens.
• Measurement distance: ~1.5 m from the horn outlet.
• Quiet background assumed so the reading largely reflects the horn.

Concept / Approach:
Common horns produce levels on the order of 85–100 dB at a few meters. Occupational guidelines associate 85–90 dB with loud traffic and 100+ dB with jackhammers or very close proximity to sirens. Values like 150 dB or 180 dB are extreme and associated with explosives or aircraft at very short distances, far beyond typical vehicle horns. Therefore, ~90 dB at 1.5 m is a realistic and widely cited ballpark figure.

Step-by-Step Solution:
Consider practical SPL ranges: horns are loud but non-damaging at brief exposure outdoors.Eliminate unrealistic extremes (150–180 dB) for standard automobile horns.Select the plausible value near common references: 90 dB.

Verification / Alternative check:
Municipal noise codes and automotive specifications often cite horn sound levels near 100 dB at standardized test distances; adjusting for 1.5 m leaves a reading near the lower end of that range, about 90 dB, depending on exact horn construction and directionality.

Why Other Options Are Wrong:
120 dB: More typical of sirens or very close proximity to very loud sources.150 dB / 180 dB: Associated with shock waves, explosions, or rocket launches, not street horns.

Common Pitfalls:

• Confusing horn levels with emergency sirens.
• Ignoring distance attenuation; small changes in distance can shift dB significantly.

Final Answer:
90