Measuring Noise/Sound Level

[kaiyoti]

I'm wondering what are the correct way to measure the sound levels in a given environment?

Long story short, I live in a condo that's currently being disrupted because a new neighboring building has HVAC on their rooftop (which is on the same level as my unit). We got a city inspector to come measure the noise to see if it's within city bylaws and first time around he measured 75dB average. He went back, and claims that the measurement was erroneous and needed to do it again. He comes back with a different colored device, another inspector with him, and in the same noise environment, measures only 68dB. On top of that they also subtracted 1~2 dB from 68dB to give us a measurement of around 67dB.

My neighbors and I both used smartphone apps and got closer to 75dB. I'm suspicious of foul play to ignore the noise problem.

Questions:
1. Are smart phone apps fairly accurate compared to sound meter devices? Just from a sample of 4 devices we all seem to get similar numbers.
2. Why did they subtract 1dB-2dB from the average?
3. The noise specialist said "1dB~2dB" our human ears can't detect the difference, is that true? Limit is 65dB, their "supposed" measurement is 68dB.
4. Can I set up my own measurement with a condenser microphone and laptop? Does anyone know any tools and software for this?

Any help would be great because this noise is making our properties uninhabitable and impossible to sell.

Paul

[BertKoor]

The only right way is to use a proper (hardware) SPL meter. You'd at least need to put the smartphone app readings next to a properly calibrated SPL meter to verify its readings. The same app on a different phone could differ some dB's.

But there are several ways tomeasure that, even the simple $30 SPL meters by RadioShack have some switches that influence the readings. The city bylaws should state how it should be measured, but I guess the law makers could be sloppy and not bother with technical details.

A difference of 1dB is noticable, 0.1dB is not. Still 1 dB is not very significant. In a real world scenario you'd see the needle of the SPL meter hover, and long-term averaging should take that out of the equasion.

But if the limit is set to 65dB and the officials measured 67dB after correction, then the outcome is still clearly something should be done about it, not?

[Hink]

I have a cheap SPL meter I got from Amazon, I actually am well versed in my city's now ordinance as I am always concerned that I might bother my neighbors. The fact is if the city is to measure it states it must be a calibrated/inspected/approved and not a cheap SPL meter from rat shack or amazon...still while it may not be accurate to .1db I do believe it's accurate enough for my purposes, in fact it's consistency I am more concerned with. However one issue is exactly what bertkoor talks about, it has a setting for "max/mim" so you can set it and come back to it...but the design is stupid, the switch clicks and not all that quiet. The switch is not really isolated in the construction from the mic and the result is a 6-9db boost in the reading when you push the button. For loud areas it's no big deal, for quiet using the max/min switch is useless. It has rubber strips on the side to hold it by which helps with handling noise, but even the slightest scrape of ones fingernails on the rest of the body of the unit can cause huge jumps. (I use one of those cheap 6" flexible pocket tripods because it has a mounting hole for tripods)

It's cheap enough that it is worth getting but I use it for 'ballpark' figures. In the question of whether or not the units on the roof are too loud the question maybe answered without such measuring. Often the measure is would a reasonable man find it disturbing (though they have db standards, said question might trump the readings if it is determined to be bothersome), 75db is pretty loud by "peaceful enjoyment of one's home" standards...in fact right now with my 7.0 surround my TV is only reading about 55 db, when I have music up to a point where talking over it is difficult it's around 75db.

[kaiyoti]

Thanks for the responses.

@BertKoor. Yes something is expected to be done about it, but it's most likely just wooden panels. There's another building that's being developed on the other side so really, it'll just bounce right back. My suspicion is that the city hired noise inspectors cheated us with the numbers considering the first measurement was significantly higher. I'll have a detailed look at the bylaw for how to accurately measure.

@Hink. Can you elaborate on this max/min control? What exactly is the purpose of this?

[Hink]

if you set it for max it records the highest level...so say you're at 50 db but there was a sound that was 70 it will stay at 70 until something higher pushes it higher and of course the same for the minimum control...you can only use one at a time, it does not record them individually. here is the one I got but I didn't pay that much (typical amazon, prices change all the time and often for the better)

[kaiyoti]

I was looking at that one initially but some poor reviews and most people seemed to just get them for kids. I'm picking up this http://www.amazon.com/American-Recorder ... chnologies since this is a Type 2, which is the standard provided by my city bylaw. Figured I could make use of it for building future silent PCs, may as well put in a bit more for decent one.