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OT: how to log decibel readings over a period of days?

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  • OT: how to log decibel readings over a period of days?

    I've got a longstanding battle with the school next door that installed an extremely loud AC unit on their roof a few years back. The county environmental inspector won't come visit without me presenting a log of when its loud. But it varies. Oddly, it's often loudest in the late afternoon early evening after the kids are gone, I'm wondering if the janitors crank it up for some reason.

    Anyway, what I want is to create a database of readings, perhaps at 5 or 10 minute intervals, it doesn't even need to be calibrated dB, just a graph showing over the course of maybe 2 weeks the relative dB. I tried to find an Android app, thinking I could use an old phone just plugged in and sitting in a window. But the only one I found that could log and export was limited to 24 hrs. Is there a windows app that I could use with a mike? Any other genius solutions?

    FWIW, my goal is to get them to build a soundproofing wall around it to direct the noise up. I think they just dropped it on the roof and called it a day. Below was the view from my yard.



    view from Google Earth, it doesn't look like there's any noise abatement around it at all.

    Location: Jersey City NJ USA

  • #2
    While you are getting apps, get one that will show you the frequency distribution of the noise also.

    Reason being that reflecting sound works best for frequencies where the wavelength of the sound is considerably smaller than the height (in your case) of a potential reflector. Width may not be an issue.

    Sound propagation is approximately 1100 ft/sec. That means that 110 Hz has a 10 foot wavelength, and most practical reflectors will not affect it much, assuming the practical height is 8 or 10 feet tall. 1100 Hz will be well reflected, as will most down to the area of maybe 250 Hz, where it will begin to drop off in effectiveness.

    You want any suggested solution to be practical. In fact, you may want to avoid suggesting much, your task is to force the school folks to hire a noise consultant to solve the problem to get the noise down to whatever the County noise abatement regulations say. (which may not be very wonderful, by the way)

    But, you still probably want to know the spectrum, to see if you can even expect much help, and to get your own handle on what is going on, so the school folks cannot snow you with data as easily.

    As for the rest of it, why not just do repeated 24 hour checks, date them, and use the data like that?

    I assume you cannot do any sort of timed check, and if you did, you might miss a loud time anyway. I'd just download the 24 hour data and run it again the next day, until you have enough info.
    Last edited by J Tiers; 06-19-2018, 10:42 PM.
    CNC machines only go through the motions

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    • #3
      Thanks, I thought of resetting every 24, but it still seems like a pain. The sound is well above 1000hz, it sounds like someone leaning on a car horn a block away.
      Location: Jersey City NJ USA

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      • #4
        I used to work at an acoustics lab in a major university. We would get calls periodically to do measurements exactly like this. It was good money for starving grad students.

        To demonstrate your case, you will need environmental and/or equivalent continuous sound level measurements, Leq and/or Lden.
        https://www.bksv.com/media/doc/bo0051.pdf
        https://www.bksv.com/media/doc/br0139.pdf

        Basically, Lden sound level measurements are A-weighted sound levels (dBA) that are averaged and weighted by times of the day (loud night noises are weighted higher than loud daytime noises) and days of the week (daytime weekdays are allowed to be louder than daytime weekends). The weighting depends on the particular type of environment and regulations, and whether the sounds change quickly or slowly.

        To have your measurements hold up to any kind of scrutiny, you'll need a calibrated microphone attached to a Leq meter which automatically adjusts the dBA scale for time/day, along with certified technicians to demonstrate impartial operation. We would rent a Leq set up for 48 hours at a time from B&K, for around $4k in the early 1980s, then convert to Lden manually. The technology has certainly gotten cheaper and faster since, but because such equipment was paid for mainly by lawyers (on both sides), the price probably hasn't dropped.

        You can also look up Lden (day-evening-night) equivalent tests, and see if you can duplicate something like that protocol. The closer you can get to a standard community noise test the better chances you'll have to get the community engineers to pay attention to you.
        Last edited by DrMike; 06-19-2018, 10:57 PM.
        SE MI, USA

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        • #5
          Mike, that sounds really cool, but far above my pay grade and what I'm trying to accomplish! I just need to show a log to this lazy ass inspector who won't just come here some hot afternoon. My county is tiny, the 6th densest in the nation, he can't get more than a 20 minutes drive away from me! It's his job to do the serious dB readings.
          Location: Jersey City NJ USA

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          • #6
            If that's all you want/can/need to accomplish, then use the logging app to record the sound levels (you want them A-weighted, or in dBA, to adjust the frequency content to match what you can hear) over a 24-hour period from your location. No need to do this for several days in a row. Log during mid-week (either Tu, Wed or Th; Mon and Fri levels are always skewed) and then again on Sunday as a "control." If you have a choice with the app, set it to "slow" averaging to correctly capture the long-duration A/C noise (the "fast" setting, if there is one, is for impulsive noise, like car crashes or gun shots).

            As you are logging, you will absolutely need to note when the A/C compressor kicks on, when it turns off and any other unusual, loud noises (large trucks, low aircraft, trains, etc). When I did this for money, we always did it in a team of at least two, so someone was always awake to take these critical notes. If you take these notes during waking hours, it'll probably be fine for your purposes

            It's likely that your inspector will scoff at the method and equipment, but it might get him to do his job. Good luck.

            Also, be prepared to be a bit disappointed with the results. The noise, even though annoying and perceptible, may not look like much once it's weighted and logged at your location on the ground. Remember that the sound level dB scale is logarithmic, and large changes in sound pressure are small changes in sound level. Environmental noise is tricky and it's very difficult to accurately pick up background noise that is perfectly perceptible, regardless of pay grade or equipment costs.
            Last edited by DrMike; 06-20-2018, 06:47 AM.
            SE MI, USA

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            • #7
              Or you could do what the guy that lived next to a race track did. He put up big speakers and blasted them with classical music until they decided to negotiate. I had a noisy upstairs neighbor and one night I put on ear protection and cranked up the stereo for an hour or two. They got the message.

              You live next to a school. If you cause a noise complaint from the school the inspector will come right out and investigate. That opens the door for some negotiation.

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              • #8
                Originally posted by gellfex View Post
                Mike, that sounds really cool, but far above my pay grade and what I'm trying to accomplish! I just need to show a log to this lazy ass inspector who won't just come here some hot afternoon. ...
                I understand your frustration, but you may have already addressed the reason for that in your original post:
                Originally posted by gellfex View Post
                I've got a longstanding battle with the school next door that installed an extremely loud AC unit on their roof a few years back. The county environmental inspector won't come visit without me presenting a log of when its loud. But it varies. Oddly, it's often loudest in the late afternoon early evening after the kids are gone, I'm wondering if the janitors crank it up for some reason. ...
                Translation ...
                Inspector: So Mr. Gellfex, when do these noises occur?
                Gellfex: Well, it varies.

                He probably just wants to see a pattern to increases the odds that the noise will be present when he arrives.

                Originally posted by gellfex View Post
                ... My county is tiny, the 6th densest in the nation, he can't get more than a 20 minutes drive away from me! It's his job to do the serious dB readings.
                True, but he also works for all the other individuals calling in complaints.
                Location: Long Island, N.Y.

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                • #9
                  It is not completely unreasonable for the guy to want to know when this is happening. But he could also install recording gear on the roof of the school and figure it out for himself. You might consider asking who his boss is, and escalate. Ask them if they have the equipment to monitor this site, etc. It is not reasonable for you to have to spend a bunch of time on this, buy microphones, recorders, etc.

                  People who just call often get ignored. You gotta write.

                  The simple way for you to do the legwork is to record the audio continuously.

                  Logging the noise level, from afar, won't necessarily pinpoint the source. But the audio will confirm it. Once you have the audio you can convert it into a visual graph that shows when it is loud. You can extract examples of the noise. However, some other more nearby sounds may appear much louder on the graph.

                  Adding a visual to the audio may help your case. It'd be easy to take a photo of the school from the location of the recorder, and then merge that into a video. So it could be an unchanging youtube video of the school, with the audio, optionally with a timestamp. I doubt that will be necessary but if they continue to ignore you, it will help.

                  You won't have formal calibration, but you will have other reference noises in the recording. Trucks, birds, etc. Ideally you would have identifiable noise sources that are the same approximate distance as the a/c. Does the school have 'bells'? Those can be used to confirm the time - start of class, etc.

                  To record this you could use an inexpensive pocket recorder. Maybe you can borrow one from someone (from the school!). With the clock set correctly it will timestamp the recording. Another option is to use a PC or laptop. You don't need a good microphone. You can use the freely available Audacity to do the recording. Microphones work best when they have light of sight to the source. This is likely to be a pretty lousy and muddy recording.

                  The frequency will change the further away you are. So the true impact of the sound may not be obvious, as compared to the human ear. This is going to be a pretty lousy recording but it will pinpoint the time. Also, noise restrictions are more stringent at night. Something that may not be annoying during the day can be a real problem at 2am with the windows open.

                  Another option is for you to write a letter to the school board and the audio guy, Zoning Administrator, etc. Verbal calls mean nothing. You put it in writing, and stuff is much more likely to happen. Also, contact your Zoning Administrator. Again in writing. Email is fine, especially if you ask that it be considered as formal correspondence at the next meeting.

                  Also, don't waste any time on this delaying - on the writing. Schools move slowly due to funding, etc. The sooner you get serious the sooner it gets resolved. Maybe the hvac company promised some noise level, etc.

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                  • #10
                    Unless this is you it looks like you're not alone...https://en.seeclickfix.com/downtown_...se%20complaint
                    Len

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                    • #11
                      Originally posted by Glug View Post
                      The simple way for you to do the legwork is to record the audio continuously.
                      I think that's impractical to get a weeks worth of readings. My benchmark of what I want is my datalogging thermometer. You can set the data point time interval, record as long as you like, and then download it and either view it as a graph or import it into excel. At 5 minute intervals I can easily see the rise and fall of the room temp from the steam heat cycle.

                      QSIMDO,

                      No, that's not me! I've talked with other people who are fed up, and working different angles. What's intriguing me is this system is clearly not exactly like a normal window or house unit, where the compressor is either on or off. It can be on at various levels of noise. This is either using something like VFD controlled compressors, or has a series of compressors and kicks in more as needed.
                      Location: Jersey City NJ USA

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                      • #12
                        Try closing your window. Whichever one is yours.

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                        • #13
                          Originally posted by 3 Phase Lightbulb View Post
                          Try closing your window. Whichever one is yours.
                          [/IMG]
                          Actually, those are my tenants open. But it's not unreasonable to want a window open in the summer, or to be able to enjoy a pleasant summer dinner on the patio without having to shout to be heard.
                          Location: Jersey City NJ USA

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                          • #14
                            Originally posted by gellfex View Post
                            Actually, those are my tenants open. But it's not unreasonable to want a window open in the summer, or to be able to enjoy a pleasant summer dinner on the patio without having to shout to be heard.
                            Tough call. So you only hear the noise when you're outside?

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                            • #15
                              Originally posted by 3 Phase Lightbulb View Post
                              Tough call. So you only hear the noise when you're outside?
                              No, it's only unbearable outside.
                              Location: Jersey City NJ USA

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