dB meter for the car

I am adding sound deadening to my car and bought a dB meter to gauge its effects. The first step is to calibrate the meter using a 94dB 1mhz sound source. I was rather hoping new tech would come calibrated. I don’t work in the machine shop any longer and am trying to think of where I could locate one.


“1mhz” must be a typo. I presume you mean 1 kHz; i.e. 1000 Hz. There are probably smart phone applications that measure sound pressure level. I bought my sound pressure meter years ago from Radio Shack, inexpensive, and is upposedly already calibrated.

Thanks… yes kHz, sorry. I was sort of assuming, since it says to calibrate the unit right after explaining how the buttons work, it may not be calibrated.

I may have the same unit you have, but wasn’t sure of its reading so bought this $30 unit. I assume it’ll be OK for comparison readings, but I wanted reasonably accurate actual readings. Maybe I can decorrode the old unit.

I have the free version of the “dB Meter” app on my iPhone. Plenty accurate for judging the effectiveness of adding sound deadening material.

I saw that online and tried it. The 74dB part had me wondering. I was curious how I’d know it was that dB without another accurate meter.

It’s the old puzzle, how do you get the ladder out of the rafters?

Sorry, 94dB… and tried it by sounding it thru my head phones.

Who cares about calibration? You’re looking for changes, right? Not absolute levels. If you see a 4 dB improvement, that’s what’s important, not the starting and ending values.


True, but I was interested in comparing to factory values also. Yes, I could compare it to what the old meter read… probably close enough.

Hmm… maybe my stereo dude will have something to compare it to, here or at the main shop.

But factory values for a car in motion depend greatly on the tires and road surface, so comparing them to what you get will be tough.

Where do you get factory values? Or do you mean road test values from magazine tests?

True. I have factory tires (5K miles) but I can’t duplicate the road surface. Yes, the dB levels are online and are EU speced. They can’t be accurate for every car assembled, but seem reasonably competent as a guide.

There’s an increase in dB with the seats removed. (They are probably 80% of the rear dampening in this car.) At 70, the chart says 68.3 dB (gets louder with speed), but I’m pretty sure over 70dB seatless. Applying 1/2" insulating foam dropped it to speech level. I’m wanting reasonably accurate reads on future stages.

Anecdotally, after quieting the car, I had to fix a small rattle in the trunk mounted amp, and when I turn on the AC fan, a soft whoosh (tire noise) comes in from the rear air vent. Those were inaudible before. The automatic stereo volume can keep up with road noise; no more cranking it up 5 notches to hear commentary.

Hopefully it wouldn’t take long to calibrate at 94dB, about an hour is what a few charts say is the maximum allowable time of exposure at the noise level.

True. The calibration is safe (plugged into the calibration machine’s port)… and takes about 15 seconds, if it weren’t. We had a machine where I used to work, but that was 20 years ago.

You’d think OSHA would have helped, but they said to buy the calibration machine. At work we had to send that machine to a standards company every 3 years… even the $1600 machine “went off”. :crazy_face: