Muffler NOISE Level Metering - what to use and where to use it?
 

I want to do some db testing on exhaust noise levels.

What do you track guys with noise restrictions use to test the sound levels and where do you position the equipment in proximity to the car?

Were is our resident mad scientist (or just experimenter) when we need him?

"HEY JACK!"

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What you need to find out is where the "sound booth" is located at your local track. That is what you are trying to keep from triggering so that is what you need to replicate.

Radio Shack has hand held DB meters for sale relatively cheap

position the meter's sensor wherever the track you are concerned about does...

visit the track and find out -- and ESPECIALLY note the presence of trees, bushes, tall grass, concrete, etc. anywhere nearby - behind the car form the meter too. Some things will reflect certain frequencies and others will attenuate them.

see if they use A or C weighting on the meter (a bias towards certain freq.s)

Radio Shack is the bottom for the meters. Industrial supply houses will have better ones -- due to OSHA regs. OSHA has helped bring down prices on meters. You don't need to worry about the next level up which is a lab grade meter or a spectrum analyzer.

But a spectrum analyzer could be made for cheap using a calibrated mic. and a PC with some fast data acq. software. ...

Radio Shack? Never thought of that, they must have a lot more stuff than that phone booth sized (now there's an expression with no future) store looks to hold.
What is the difference in quality between Radio Shack units and Industrial Supply units? Significant? Reproducible? Accurate to +/- what?
I wonder if ther is an ASTM for gaging sound levels, I'll have to look into that .......

that's hard to say -- but I'd for sure try the $40 RS unit first before counting out a couple of Benjies for the other...

Brian - I'm about to install a couple of Ben's race cans on my car. Might be fun to see how loud those are also... :>)

Looks like I'll give the Radio Shack unit a go and see how reproduceable it is.
Mike - difinitely. Let me know when you get them and we'll do a test.

I bought a DB meter at some point. But of course the only meter that counts is the one that's going to get you a black flag.

I'd find out the approximate setup at the track (or testing facility) and try to reproduce it. You'll at least be able to get a ballpark idea of the difference specific modifications will make.

What I want to do is not track related.
I have several different mufflers for my car and I need a way to quantify the noise level of each, using stock as the baseline.
I would like the gage to be as accurate as possible for a reasonable price. I know nothing about db meters so education is needed on what is available, calibration, etc.
It seems reasonable that the reading should be taken X distance from the exit vector of the tail pipe in order to thwart any muffling due to outlet configuration. Readings would also be taken X feet directly in front of, inside, and behind the car.

Jack, where did you purchase your meter and are you happy with it?

there's some stuff online about specs, like 45 degree off the pipe at some bla bla radius, 3 or four feet. Radio shack meters work well and for testing, I mean I'm sure you know keep everything the same for all tests, except the car/muffler. I have one from radio shack and tested ben's mufflers more than once. They work fine. A tripod helps for positioning, and masking tape on the pavement for lines/measurements. I don't know if that's worth .02 but it's what I did, worked well.

Stereo stores - higher end ones - used to carry an affordable spectrum analyzer with a calibrated mic. You might look around for that. You still need to decide on A or C weighting, and pay attention to the background and foreground where you test the car.* If you want to come close to a human's perception you'll need to put the mic 5.5 ft. off the ground on a tripod.

* The degree of attenuation for different auditory spectra of several different environmnets (conifers, deciduous woodland) has been worked out already, bu tI advise you avoid that entire issue by ensuiring that pavement or low grass is the only thing around.

The Radio Shack meter is fairly accurate and comes in both analog or digital. I use it once a year or so to calibrate my home theater speakers. With the digital, I adjust the scale(60-120dB) and it reads in A or C weighting.

http://www.radioshack.com/product/index.jsp?productId=2103667&cp=&sr=1&origkw=sound+ level&kw=sound+level&parentPage=search

Thanks for the link and info.
I had looked up model 33-4050, the digital version did not come up.
The testing will be done in a controlled environment - my driveway. Ha!

should be easy to replicate!

Another vote for the Radio Shack meter. I've owned the analog one for a number of years, and it's a great tool/toy. Just used it the other day to check out the noise-level in an airplane cockpit. I got in trouble once, though, when the wife came around the corner and saw me metering our toddler in meltdown mode....

You probably don't want any walls or structures to bounce and elevate sound. Is there an open parking lot close?

My yard is an acre lot and the neighbor's homes are even further away. Should be a good "real world" testing area. We shall see .........