How to Tell if an Exhaust is Too Loud

by Steven Douglas

Automobiles often play a big role in producing noise pollution. Engines and exhaust systems can be noisy machines, but cars can get even louder when people install aftermarket exhaust systems to get better engine performance, or they allow their mufflers to become worn out and ineffective in quieting their engine's exhaust. Fortunately, most jurisdictions have a set decibel (dB) requirement that regulates the maximum allowable nose that may be produced by a vehicle. A simple test with an easily-found dB meter is all that is required to tell if your exhaust is too loud.

Step 1

Purchase, rent or borrow a decibel meter when you are ready to test your vehicle. They are inexpensive, and widely available from electronics dealers because they have many additional uses besides automobile testing. Read the instruction booklet or set up procedures so that you are acquainted with the specific model device you will be using.

Step 2

Check with your local police department, or Motor Vehicle Administration to determine what the maximum legal level of noise emitted from a vehicle is for your area or state is. For example, the California Highway Patrol specifies a maximum limit of 95 decibels measured no more than 20 inches away from the exhaust pipe, while the engine is running between 3,000 RPM and 5,000 RPM (revolutions per minute).

Step 3

Park your vehicle after it has been warmed up, and leave the engine running. Chose a quiet location, away from traffic and set the parking brake. The chosen location should be an open area, where sound does not reverberate (such as in a garage or other enclosure).

Step 4

Turn on the dB meter, using the power button. The device will start to immediately pick up ambient sound as it is received. Most units use an LCD display to convey this information to you, although some have an analog dial with a needle.

Step 5

Calibrate the unit by selecting the "Manual Ranging" setting. This will require that you press the button, or select the switch labeled "Manual". The unit will display "Hi" or "Low" meaning that the sound received is above or below the current range of dB being displayed. Press the "Range" button and select the appropriate range dB to test for. Most units test for 40-to-70 dB, or 60-to-90 dB, or 80-to-110 dB, or 100-to-130 dB.

Step 6

Hold the microphone of the meter toward the exhaust of your car, and with the engine idling, place the unit on the ground approximately 20 inches from the tail end of the exhaust pipe opening. Press the "Max Hold" button on the unit.

Step 7

Sit in your vehicle, and rev the engine (with the transmission still in "neutral") to approximate highway speed, or 3,000 rpm if you have a tachometer-equipped vehicle. Maintain that engine speed for 10 seconds. Allow the engine to idle briefly, then turn the engine off.

Step 8

Pick up the dB meter. View the measurement that is displayed on the dB meter. If the reading indicates higher than the maximum allowable dB limit as stipulated by your local police department or Motor Vehicle Administration, then your exhaust is too loud. Take appropriate measures to have your exhaust noise muffled.

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