Two sirens wired in parallel are louder than when wired in series. Which wiring arrangement is louder?

• A. Series
• B. Both are equally loud
• C. None affect loudness
• D. Parallel

Answer: (D)

Loudness depends on how much electrical power is delivered to the sirens. When two identical sirens are connected in parallel, each one is connected directly across the same supply voltage, so both receive the full voltage and the total current drawn from the source doubles. That means more total power is delivered to the pair, making the combined sound louder.

If they’re wired in series, the same current flows through both, and the supply voltage is split between them. Each siren ends up with less voltage than the full supply, so each one produces less power, and the total acoustic output is reduced.

For two identical loads, parallel delivery can result in about four times the total power compared to series, which corresponds to a noticeable increase in loudness. So the parallel arrangement is louder.