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Natural Science Forum / Physics / Acoustics / June 2006Dosimeters for police noise enforcement?
Speaking with some folks on a local noise ordinance enforcement issue, the question of police officers using sound level meters came up again. As I'm sure most of you have experienced sometimes, the locals don't like using SLM's for noise enforcement because the units and measurement procedures can be complex (and from my experience, even when police have been properly trained and are willing to use SLM's, the often still don't know what they're doing.) I've observed several municipalities that have absolute noise level limits (usually 65/55 or 55/54 day/night Lmax), but they also have "plainly audible" or noise nuisance type regulations that were added in response to concerns that cops can't/won't make noise measurements. While brainstorming ideas about making measurements easier on officers, I thought about using dosimeters as SLMs as backup for plainly audible-type ordinances. Basically, an officer would pick up a calibrated dosimeter (perhaps a Quest Q100 or similar)at the start of their shift) and sync the dosimeter clock with their watch. The meter would be set for 3 dB exchange rate and 1-sec datalogging. The office would put the meter in their pocket/belt/whatever, and the mic would be worn as specified by the manufacturer. When responding to a noise complaint, the officer can use his judgment in accordance to a plainly audible standard, but by (for example), standing quietly at a property line/standard distance/etc, the dosimeter will gather noise data from the event in question. The officers written log will have the time of the event, and when the officer's shift is over, the dosimeter data is downloaded to a PC for later comparison with the officer's logs and relevant absolute noise criteria. The largest problem that I can think of having to account for error caused by the diffraction/reflections from the wearers body. But they way I see it, it could still be used for exceptional exceedances. For example, if the dosimeter gave a value of 56 dBA for an event with a 55 dBA limit, I would say that the measurement is accurate enough to cite the offender. But if the event gave a value of 70 dBA for an event with a 55 dBA limit, the exceedance is will above the potential error. The advantage of this approach, from the perspective of a distrusting community and an overworked cop is that 1) it doesn't take a lot of effort or training on the cops' part to get data, 2) the data can't be easily tampered with, and 3) the community and the accused gets to see hard data to assuage bias concerns. Anyway, I can't believe that I'm the first to consider using dosimeters in this fashion, so I'm asking if anyone has tried (and had success) with this approach? If not, is there a good reason why this won't work that I'm missing? Thanks Herb There are a lot of police officers in relation to the number of noise complaints. Probably not practical for every officer to have a dosimeter. Perhaps for a few noise specialists. > Speaking with some folks on a local noise ordinance enforcement issue, > the question of police officers using sound level meters came up again. [quoted text clipped - 49 lines] > > Herb > There are a lot of police officers in relation to the number of noise > complaints. Probably not practical for every officer to have a dosimeter. > Perhaps for a few noise specialists. That's more of a policy issue, I'm wondering about the technical aspects (for example, would any of you guys find the data to be acceptable?). For the record, like you said, the intention isn't for every officer to have them, just a few who are focusing on quality-of-life issues. I'm just trying to simplify things for the cops, and I'm just trying to get some feedback. Thx Herb >> There are a lot of police officers in relation to the number of noise >> complaints. Probably not practical for every officer to have a [quoted text clipped - 8 lines] > just trying to simplify things for the cops, and I'm just trying to get > some feedback. I think the logistics would be quite challenging. Before the shift, you would have to make sure that the dosemeter clock was precisely synchronised with the officer's watch to identfy which samples represented the interfering noise, and also calibrate the dosemeter . Then after the shift, if there had been any noise issues, the calibration would need checking, the data downloading, and the relevant period identified by reference to the time noted by the officer. The accused would no doubt try to cast doubt on the correctess of the time synchronisation, i.e., what the measured level of the samples actually represented (could be someone talking next to the officer). It might be easier to have a cheap sound level meter that could be started and stopped manually, and read on the spot. That would also deal with sound levels lower than a dosemeter would do, and could be held away from the body to reduce reflections. It is possible to buy a sound level meter attachment for a PDA.  SignatureTony W My e-mail address has no hyphen - but please don't use it, reply to the group. > It might be easier to have a cheap sound level meter that could be started > and stopped manually, and read on the spot. That would also deal with sound > levels lower than a dosemeter would do, and could be held away from the body > to reduce reflections. It is possible to buy a sound level meter attachment > for a PDA. The biggest problems with SLM approach (based on my experience and conversations with police) are 1) it doesn't really work for intermittent noise sources that an officer may witness, but doesn't have time to whip out the meter (a passing boom car for example) 2) as easy as SLM measurements may be for you and me, I have been amazed at how often intelligent, but inexperienced, officers and city ordinance officials have screwed up the measurements when they have to do the setup themselves. For example, I was once helping out a big-city enforcement officer on a construction noise project. He made a measurement of a backhoe at 50 ft, and told me that he got a level of 130 dBA! I took a look at his meter (B&K 2231), turns out it was set to SEL... Simpler meters (like something from the Extech line) make it harder to screw up like that, but since they often only have slow/fast/max settings, they can be difficult for the layperson to use for intermittent sources. 3) SLM's are cumbersome, so a cop probably isn't going to carry it when he's walking the beat unless he's looking at a specific source. The nice thing about a dosimeter is that the cop can put it in his pocket or on his belt, and forget about it until the end of his shift. 4) durability - around here, I can pretty much guarantee that an SLM will get abused in normal use. This is a problem for dosimeters also, but IME, dosimeters can better handle getting dropped compared with most precision SLM's. You're correct when you say that the logistics could be challenging but the steps that you described (which I agree would be necessary) can be part of a standard daily procedure that doesn't require much thought. The measurement also doesn't require much though - just shut up and stand there for a few minutes, no need to boot up the SLM, check the Fast/Slow settings, etc. The high-noise floor of many dosimeters is something I haven't considered, but in my case, as long as it can get down to 40 dBA or so, it should be sufficient. Thanks for your input, as always, I'm open to ideas. Herb Here's a thought: Get rid of the time synchronization issue altogether by getting away from the sound level data and, instead, recording the actual sound. 1. Assuming a typical 12-hour shift, equip Officers with a 5 GB portable recorder. (Could be no bigger than an MP3 player. 5GB should be enough. At 16-bit, 44.1kHz, monaural, it's about 5MB per minute. 720 minutes in a 12-hour shift means you'd only need 3-4 GB of storage.) 2. Place a cal tone at the beginning of a shift. 3. Press "Record" when the shift begins. Note the time (by Officer's watch) of beginning of shift. 4. In the event of an "incident," the time should be noted by the officer. 5. A cal tone should be placed at the end of the recording. An event log can then be compared to the 12-hour recording by the sound technician. The compaint segments can be archived, the rest deleted. The recorder can be wiped clean for the next shift. The only drawback is that *everything* in a 12-hour shift would be recorded. I'm sure some cops wouldn't like that very much... Anyway, some thoughts... Best regards, Savant > Here's a thought: Get rid of the time synchronization issue altogether > by getting away from the sound level data and, instead, recording the > actual sound. [snip] > The only drawback is that *everything* in a 12-hour shift would be > recorded. I'm sure some cops wouldn't like that very much... Yeah, that was actually my first instinct since digital recorders like the M-Audio Microtrack 24/96 and the Edirol R-09 are small enough and cheap enough to make this practical. The problems are: 1. (like you said), the cops don't want their entire shift recorded, 2. The lawyers don't want the cops' entire shift recorded, and 3. Because of wiretapping laws (no recording without the informing all parties without a warrant), if the cop forgets to tell someone he has a recording device on him, he could be prosecuted. I, for one, am a big fan of using digital recordings for noise control since you can calculate any arbitrary metric (Lxx, C-wtd, A-wtd, etc) from the data without having to know ahead of time what metric you might want. Thanks for the suggestion. Herb If there was a market developed, I am sure the instrument companies could make specialty instruments for the application that in today's world also could include the ability to actually record the offending sound. I saw an article recently of a B&K meter set up especially for community noise problems. It was programmed so it could be left with a complaining resident who could push a button when the offending noise occurred. The meter would record the sound plus a period of some time before the button push along with measurements. This kind of technology could be built into the dosimeter sized housing. The main problem then could be as you pointed out the need for sufficient margin to overcome measurement errors due to microphone on the body etc. Having the sound recording could be very useful. >> It might be easier to have a cheap sound level meter that could be >> started [quoted text clipped - 51 lines] > > Herb > If there was a market developed, I am sure the instrument companies could > make specialty instruments for the application that in today's world also [quoted text clipped - 8 lines] > microphone on the body etc. Having the sound recording could be very > useful. Maybe I'll give a call to one of my Larson-Davis buddies. The problem I always run into when discussing these kinds of ideas with instrument companies is that the seem to not care about making instruments simpler, they always want to add more features (and complexities) so they can (IMO) lock in users and add more lines to their checklist. Worth a try tho'. Thanks. Herb Herb, There is a solution Take a look at ACO Pacific's SLARM(tm) http://www.acopacific.com/slarm.html This device may be used to monitor and even signal alerts as well as log the A,C or Z DBSPL levels over a week plus period timestamped in 1 second values And once set up password protections minimize mistakes The actual values and control may be monitored on a laptop or even a Pocket PC wired or wireless with Bluetooth or WiFi...or other technology. Both Indoor and Outdoor installations are possible. There are two thresholds - an ALERT level and then an ALARM Level which may be set by the user On the otherhand we have some installations which actually make sure alarm horns or other sounds are loud enough...I think 140 dBSPL @10 feet is loud enough to be heard>>>> Regards Noland Lewis > Speaking with some folks on a local noise ordinance enforcement issue, > the question of police officers using sound level meters came up again. [quoted text clipped - 49 lines] > > Herb > Herb, > There is a solution > Take a look at ACO Pacific's SLARM(tm) > http://www.acopacific.com/slarm.html [snip] Hi Noland, I've spoken with you a couple of times at various shows (Noise-Con 2005 Minneapolis and AES 2005 NYC come to mind) and I love the SLARM. Unfortunately this really isn't a stationary application, this is something that an police officer would carry on him to gather evidence on excessive noise sources that he might come across during his normal patrol (loud parties, noisy motorcycles, boom cars, etc). Last I spoke with you, you had demo units of the SLARM on display, but you indicated that it was still being developed. Is it in production yet? Herb |
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