These are notoriously inaccurate. To get accurate decibel readings, the mic must be calibrated to absolute known levels (something your App can't do). The App's are basically just comparing relative sounds (this sound is more prominent than this other one, and therefore must be louder... after establishing some relative baseline). Real decibel measuring equipment is very expensive and requires re-calibration routinely. So, measuring 80db could easily be in a swing of +/- 10db's (or more).
> 150dB: Jet take-off at 25 meters (eardrum rupture)
That's not quite accurate. Long term exposure could lead to damage over time, but for comparison a shotgun is typically measured at 165db when it's up against your shoulder and face. Yes, you wear hearing protection (nick-named "ears" if you are a frequent shooter) but your eardrumps aren't rupturing immediately if you take them off.
> What shocked me was the volume of the PA system
Yes, it's loud -- by design. The PA system is not there just to provide something to listen to in case you are bored. In a best case scenario, it's there for the usual "buckle-up" talk and for the pilot to give a greeting. In the worst case scenario, it's there for emergency instructions (a time when panic and passenger noises are likely to get quite loud on their own).
From the referenced study: "The measurements were conducted in a diffuse sound field at a reverberant noise chamber at the NIOSH acoustic testing laboratory. The diffuse sound field ensured that the location and size of the smartphones did not influence the results of the study. "
Having done sound testing extensively, you can be sure in an airplane positioning and sound source and sound type can drastically impact your measurements. Multiple reflections can re-enforce, or reduce the measured level. The type of sound measured is very important as well.
He's not measuring pink noise on the airplane, what the measured level of a particular sound is, needs to be normalized to really understand what effects it will have on you.
I'm sure in a good test setup the smartphone can get you pretty darned close. I'm more concerned with this guy's test setup than the equipment used.
Is a db meter on an iPhone really inaccurate? This recent article from the National Institute for Occupational Safety and Health suggests otherwise:
> for A-weighted sound level measurements three apps had mean differences within ± 2dBA of the reference measurements. For un-weighted sound level measurements three apps had mean differences within the ± 2 dB of the reference measurement. Since national standards and occupational guidelines specify that type 2 sound measurement instruments have an accuracy of ± 2dBA, some of the above-mentioned apps could potentially be used in the occupational setting
±2dBA would already be much more precise than what you'd need to assess if a certain sound pressure level can be endured for an extended period of time safely, or not.
To put it in numbers: ±3dB is doubling/halving of Power, but humans typically perceive a change of ±10dB as doubling/halving of "Volume". Also the damaging effects of noise typically scale as double-the-power, half-the time.
And personally I'd rather not be in the situation where I'd ponder if the damage to my hearing is double or half what it should be if my iPhone app were accurate: I'd rather have it show numbers that are 20dB below this level, so that I can be assured of no significant damage at all!
Probably worth noting that shooting without "ears" can still leave you basically unable to hear anything for a good while depending on the firearm, shooting environment, etc. It's not an instant ear-bleeding rupture but it's still VERY loud and will cause significant hearing loss with little repetition.
Side note: I'm always curious how soldiers/SWAT/HRT/etc. are able to hold normal volume conversations. If they're wearing ear-protection, how do they listen for potential threats and assailants? If not, how do they not shout all day long every day?
I would guess that they use more expensive hearing protection systems with an active electronic system to pass through sounds at a comfortable level, attenuate louder and potentially damaging noises, and possibly even amplify quiet sounds.
The technology would be similar to that used in hearing aids and noise-cancelling headphones. But it is also probably an order of magnitude or two more expensive just because the primary customers are tax-funded.
Without electronics, I could also conceive of an earplug with a winding channel bored through it, past flaps that can block the channel by moving too far in either direction and forming a seal with the outer wall of the channel. Sound energy above a certain level would push the flaps closed as the air vibrated, and would thus attenuate louder sounds to a greater extent than quieter ones. If the flaps were tuned to different sound energies, the loudest sounds would push closed the most flaps.
That would require some precise machining to fit inside the outer ear canal. The electronic filter might actually be cheaper.
Usually the ear protection used just has a simple narrow channel. This is effective in attenuating loud sounds without impacting quieter sounds as much. The name brand I'm most familiar with are the SureFire Sonic Defenders. They're in-ear, not very visible without the retention cord attached unless you're specifically looking for them.
Those look a bit bulky for use by police or military in the field. You would need to miniaturize down to an in-ear version. Then you need to add very generous padding in your procurement contract.
If an over-the-ear tech is available for civilians for $70, I would guess that an in-ear police/military version is $850, with an upsell option to integrate with your existing radio communications system for only $1150 per pair. I'd also call it "active hearing protection system" and never, ever refer to them as "earplugs".
That's comparable with a good hearing aid, only because the health insurance payments system is superficially similar to government procurement contracting with respect to profiteering middlemen.
Again, this is only a guess, made without supporting data by someone who owns a foil hat.
> Soldiers can adjust the rocker with a quick "click" depending on the amount of protection they need. When it's in the open or "weapons fire" position, sound can travel through the sound channel filter into the ear.
> For noisy environments that don't require an acute listening capability, such as around helicopters, troop carriers or generators, the rocker can be switched to the closed or "constant protection" position.
There's also larger over-ear kinds that are integrated with comms:
For those hitting the paywall on the the first link, the in-ear protection resembles 3M Ultrafit earplugs, with a hole bored through the center. The rocker switch may be lengthening or diverting the pass-through channel, like the rotary valves on a tuba or French horn. A longer or narrower channel would provide more attenuation of all sounds. It may also simply be closing and opening the channel.
They don't seem to have variable attenuation based on the acoustic energy, though. If the soldiers find them to be acceptable everyday gear at all, there would certainly be funding available to engineer improved internals.
The over-ear comms-integrated rig is priced at double my estimate for what an in-ear version might sell for, which tells me that I was probably underestimating.
Most of the hearing protection I've used when shooting seemed designed to disrupt the sound wave move than actually reduce it.
You can achieve reasonable short-term protection by holding your hands flat over your ears. It doesn't reduce the subjective volume, but it does [anecdotally] prevent subsequent symptoms that indicate temporary or long-term damage has occurred.
> You can achieve reasonable short-term protection by holding your hands flat over your ears.
Not flat... that won't do much. They must be cupped... basically you make a letter "C" with your hands then old that up to your ear with your side of your palm (pinky side) resting on your temple.
This will deflect the sound wave around your ear. Old-school artillery trick.
I often take issue with the "pilot greeting". Many pilots just ramble on and on. Often on and off throughout the entire flight. I really don't care nor do I want that blaring in my ears. I don't understand why airlines think this is a good idea.
I would assume that a large amount of the public actually feels comforted knowing that there's a real human up in the room with all the buttons making sure the airplane stays in the air. Given, I'd doubt very many of those people are engineers, so I'd assume the HN crowd would mostly consist of people that just want to put on headphones and only be contacted if there's some sort of "exception" thrown at some point in the flight.
My biggest question is how much training airlines give pilots about exactly what to say on these updates - on a recent flight, the pilot said that a critical system in the plane went from "too broken to take off" to "yep, that looks fine" with a couple of restarts just before we left the gate. I'm sure he did everything per spec, but I'm not sure how helpful it is to tell everyone that they are riding on equipment that's only legal because the turn-it-off-and-on-again principle isn't just for IT.
I was delayed for 6 hours once because a part was broken and they were searching for a new one. They couldn't find a new one and 'cleaned' the old one and said we'll see how it works. Just what I wanted to hear. That we were going to see how it works over the Atlantic.
Different strokes, I suppose. If the pilot is saying something interesting I'd otherwise miss ("look out your left for a cool view of xxx), I'm happy to hear it. I also prefer to hear status updates during the flight.
The PA system is not there just to provide something to listen to in case you are bored.
Yeah, but there's no reason for the people operating the PA to blast our ears for mundane drivel. I was on a flight last weekend where, because I was right next to a speaker, I had to cover my ears for 5 minutes while the flight attendant droned on about non-emergency stuff. It was so loud it hurt my ears. I already have tinnitus, so I don't need any more hearing loss.
The PA system is used to announce to the cabin non-trivial details: emergency exits, how the safety features of the airplane work, what is expected of passengers during the flight, flight times, expected turbulence, late arrivals, etc. These are not "mundane" details.
As well as stuff like how much drinks cost, what you might see out the left side of the plane, where to find a catalog of ridiculous items you would never buy, etc.
I thought the point of the high volume was to get thru to the people who were ignoring it because they already know the message.
The point isn't to not do the presentation, the point is to acknowledge that most people ignoring it don't need it and hence there isn't a need to YELL IT SO LOUD OVER THE PA THAT EVERYONE IS AT RISK OF HEARING DAMAGE.
165 db LCpk is a good estimate for the muzzle blast 1 m in front of the barrel of a shotgun. However, outdoors, it's going to be closer to 140-150 measured at the shooter's head. There is a significant asymmetry in how the muzzle blast propagates.
The only thing it's an indication of is the App feels the PA is louder than the other ambient noise in the cabin... which in order to be an effective PA, it must be.
The number it assigns it might as well of been made up... or put on some App-specific scale like 1-10, 10 being "we think this is really loud".
> and opened the decibel meter on my iPhone
These are notoriously inaccurate. To get accurate decibel readings, the mic must be calibrated to absolute known levels (something your App can't do). The App's are basically just comparing relative sounds (this sound is more prominent than this other one, and therefore must be louder... after establishing some relative baseline). Real decibel measuring equipment is very expensive and requires re-calibration routinely. So, measuring 80db could easily be in a swing of +/- 10db's (or more).
> 150dB: Jet take-off at 25 meters (eardrum rupture)
That's not quite accurate. Long term exposure could lead to damage over time, but for comparison a shotgun is typically measured at 165db when it's up against your shoulder and face. Yes, you wear hearing protection (nick-named "ears" if you are a frequent shooter) but your eardrumps aren't rupturing immediately if you take them off.
> What shocked me was the volume of the PA system
Yes, it's loud -- by design. The PA system is not there just to provide something to listen to in case you are bored. In a best case scenario, it's there for the usual "buckle-up" talk and for the pilot to give a greeting. In the worst case scenario, it's there for emergency instructions (a time when panic and passenger noises are likely to get quite loud on their own).