Sound level meter help

[AnthonyR]

Hello all! I could really use some advice.

I am doing research at my university in Ecology where I will need to measure the sound eminatiing from a highway from various points. I have looked at a few sound level meters online, but I have no idea what I am looking for!

So, basically my question to you is this. If you were given the task of measuring the sound of a highway from various points (starting close, then moving away) what equipment would you use? I would need something that would ideally do these things:

1. Measure in more than one unit, but not necessarily all (i.e. frequency, hertz, Db, decibles, and whatever else there is)

2. Portable or easily set up/transported

3. Mic. Directionality (this is actually more of a question. Would Mic Directionality really affect results?)

Thanks for your time,
Anthony

[ulysses]

Most hand-held docimeters (I think that's the word) have a built-in calibrated omnidirectional microphone. A good one will allow you some control over various parameters including bandwidth, or at least let you choose from various "weighting" curves. "A-weighted" is the most common weighting curve, and it de-emphasizes low frequency information in accordance with the Fletcher-Munson curves, which correlate actual human hearing sensitivity with frequency. However, if it were me I would want the ability to measure SPL *unweighted* so I know exactly what's really there. It would be nice if the meter had the ability to measure individual narrow frequency bands too, but since I've never shopped for one of these meters I don't know how common that function is. Otherwise, you could build your own measurement system using a calibrated microphone, a bandpass filter, and an AC voltmeter (one that reads true RMS over a wide frequency range).

Even with an omnidirectional microphone, you will find that high-frequency response will vary with microphone position, and can drop off dramatically when the microphone is behind relatively modest barriers.

[rufus13]

With a traceable spl calibrator, you could set a reference into the spl meter, with an external output to a portable 24 bit audio recorder. Lots of recorders are stereo, so you could add descriptive commentary synchronized with the measuring channel.

The meter could be a Radio Shack spl meter, if budget is lacking. It has an rca jack for output. I use a General Radio Omni-Cal for a reference level/tones.

kk.

edit: With a recording of your reference tones/levels and a recording of the noise-of-interest, heavy analysis can be done with a computer.

You didn't tell us how critical the application is. If it has to stand up in court, better gear and a bit of certified training is in order. Think of it as technical sworn testimony, where the opposition will question your motivation, skills/training, and gear. For a paper, it'll be fine.

[tINY]

You may want a unit that logs average SPL over time and logs it.

Depending on temperature inversions, amount of traffic, type of traffic, relative humidity and so on, the sound level will vary a lot in a given location.

You should poke around the B&K site:

http://www.bksv.com/?ID=3950





-tINY