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Old 04-27-2012, 07:52 AM #17
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Default Re: Does this look safe to you?

Quote:
Originally Posted by JLSE View Post
Blasting class 4 into a crowds eyes is not wise...

The Russian incident wasn't just any Class IV. It was a 40W+ KTP/YAG 'Laserscope' style setup running in Q-switched mode. See the problem? (no pun intended)

It's a rule that you never, never, under any circumstance, use a Q-switched or pulsed (such as CuBr) laser for crowd scanning, due to the high peak powers involved.

They were going to sky-scan with it originally, but adverse weather (strong wind and rain) meant they couldn't run the projector out in the rain.

Instead, the event organisers wheeled the unit on-stage and aimed it at the audience instead. Whoops, bad idea.

Audience scanning with projectors in excess of 10W CW is acceptable, in the hands of a trained and competent technician.

It isn't the power that does damage -- it's a combination of the MPE (maximum permissible exposure) and the laser type.

I'm not going to do a full write-up of MPE here(every laser 'enthusiast' or 'hobbyist' should understand this concept), but it's the maximum exposure your eyes can take before your retina goes up in smoke. It's a combination of scan speed (exposure time) and power density (how much light you get hit by).

Example: scanned fast enough, a 1W 445nm laser can be used to audience scan safely.

And then there's the laser type, and as I've said, with a Q-switched laser, the peak (instantaneous) power is often magnitudes higher than the average power. In that case, even scan duration won't save you.

The bottom line doesn't change, though: Class IV is safe. Bad practices are not.

Quote:
Originally Posted by bobhaha View Post
^Actually... that's wrong (to an extent). I've had a firework go off in my hand (it was pressure sensitive... I didn't light it and hold it) and as soon as the boom went off I was deaf in both ears for 5-6 hours.

All I heard was ringing, nothing else... just this annoying ringing sound.

But I highly doubt a speaker has the capacity to displace enough air in order to damage someones ears in the same fashion the firework did to me. But instant deafness is possible.
The firework would have well been in excess of 170dB SPL (given distance to your ears) , and well above the threshold of pain. If it were an actual explosion it could well have been even louder, depending on how close you were holding it.

To put things into perspective, that's at least twice as loud than a .22 handgun being fired at 1m from your body. The pressure differential between the two is a factor of 10.

We've all seen (or, at the very least, heard of) people using small arms (including larger cartridges such as the 7.62mm NATO rounds) without hearing protection. They don't go deaf instantly, even though the instantaneous sound pressure level is well above 130dBA, which is the threshold of pain (and possible damage).

As for a nightclub or pub band gig - the average 500W powered speaker that you'd find in smaller clubs can output up to 135dB SPL (on average) RMS, with 138dB peaks.

That's at a distance of 1m from the speaker. Move away further, and loudness drops off rapidly.

Take a bigger speaker -- for instance, the EAW LA460. The high-frequency section can do 130dB SPL long-term (RMS) at one meter.

That's not a lot of sound pressure, really. By the time you throw in some humans (and being bags of blood and water, they soak up sound like nothing else), you're looking at an average SPL of 100-110dBA. Which, in the grand scale of things, really isn't much.

Mind you, though, speakers can move enough air to cause serious damage (and by that, I mean burst eardrums). Dual 21" cone drivers can move a lot of air.

Quote:
Originally Posted by Cyparagon View Post
So... you'd leave if you saw a varianced laser, but you'd be fine with >120dB sound for example?
If you wanted to talk something a little bigger, say, a metal concert, then you're dealing with systems that can easily do 150dB SPL at close (<5m) range. But then again, these are massive flown line arrays with up to 20 boxes at a time.

120dB SPL RMS at the mix position (usually halfway down the venue) is not unheard of at larger rock/metal concerts.

There's a good reason why you're advised to bring a set of earplugs to a heavy metal concert. Most times you'll need 'em.

Digression: I don't know why everyone still thinks louder is better -- it's not. Beyond 100dB SPL your ears begin selectively shutting down (and your ears' frequency response goes out the window) and everything sounds like arse once you're missing a large chunk of information in the 2kHz range.

Anyway -- most times in a club, you'll be just fine. The normal rule-of-thumb is if you can feel pain, then it's too loud.

Another bit of perspective: I've had 126dB of speaker in my face before. Was putting up a measurement mic when a colleague accidentally hit the unmute button for the pink noise channel. Whoops. It hurts, but it's nothing permanent. 15 minutes later and everything feels normal again.

Quote:
Originally Posted by Benm View Post
One advantage is, at least, that you get the time to determine its painfully loud somewhere and then leave before any damage is done. When laser shows are painfully bright, you are probably too late.
Comparisons between light and sound are invalid because of the difference in the way our eyes and ears handle bright (or loud) things.

The threshold that is considered safe for sound pressure levels can be safely exceeded in certain circumstances for small amounts of time, with little chance of permanent damage. Of course, as was bobhaha's case, instant deafness is possible (and that's how flashbangs work), but in most cases, it only lasts for seconds to hours, depending on the intensity of the exposure.

The same cannot be said for the retina. Any damage beyond the threshold of pain is usually permanent.

Of course, long-term exposure to loud noises is not a good idea nonetheless. After all, 85dB SPL is the long-term damage threshold.



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Old 04-27-2012, 05:51 PM #18
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Default Re: Does this look safe to you?

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Originally Posted by CapeClover View Post
Personally I don;t feel lasers should be used for purposed such as this. They are scientific/medical devices, not entertainment toys. If I entered a club and saw one of these in operation I would leave immediately. I don't care how "safe" they claim it is. No amount of money is going to bring back my eyesight when I am blind.

I may be way off base regarding the safety issue. Perhaps I am overly cautious. But I am not about to put something as valuable my eyesight in the hands of some club.
Laser shows have been a well-respected form of entertainment almost from the moment they were first invented. I think that entertainment is easily as legitimate of a use for a laser as surgery or industrial cutting.

Regarding safety, cyparagon touches on something that has always bothered me about the idea of laser show safety: What is it that makes the lasers more dangerous than the extrememly high sound pressure levels generated by most large concert PAs? Is hearing less important than eyesight? I think the answer would vary depending on who you ask, but IMO they are equally important, but yet we never hear people bitching about sound levels like they do about laser beams touching people.

On the contrary, in the US there are some "professional laserists" who (mostly to protect their own interests) insist that lasers should be regulated like firearms and dynamite. Much of the time, if you read between the lines, you see that the only people who can easily pass the kind of tests and pay the kinds of fees they say should be involved in the process are them and other already established individuals, making their ideas equate to little more than attempts to limit competition.

All local regulations aside, the bottom line is that crowd-scanning MUST be done properly with the correct calculations done prior to an audience entering the venue in order to guarantee safety. One can further guarantee safety by increasing the divergence of the beam. Personally I never crowd scan because I don't feel that it's worth the effort in a sue-happy country like the US. It's not necessary for a show to have audience scanning in order to melt faces..
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Last edited by ElektroFreak; 05-02-2012 at 12:45 AM.
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Old 04-28-2012, 01:47 AM #19
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Default Re: Does this look safe to you?

Quote:
Originally Posted by bobhaha View Post
^Actually... that's wrong (to an extent). I've had a firework go off in my hand (it was pressure sensitive... I didn't light it and hold it) and as soon as the boom went off I was deaf in both ears for 5-6 hours.

All I heard was ringing, nothing else... just this annoying ringing sound.

But I highly doubt a speaker has the capacity to displace enough air in order to damage someones ears in the same fashion the firework did to me. But instant deafness is possible.
It IS possible indeed, in situations where a firework blows up at close range, or when you use a firearm close to your ear etc. For this to happen you are probably looking at 150 dB sound levels or over though.

A club sound system will not produce anything over 120 or so if you are standing straight in front of the speaker. Sticking around that area will cause hearing problems (both deafness and tinitus) in time, but should also be painful enough to make you budge before either takes permanent effect.
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Old 04-28-2012, 07:56 AM #20
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Default Re: Does this look safe to you?

Quote:
Originally Posted by ElektroFreak View Post
Laser shows have been a well-respected form of entertainment almost from the moment they were first invented. I think that entertainment is easily as legitimate of a use for a laser as surgery or industrial cutting.

Regarding safety, cyparagon touches on something that has always bothered me about the idea of laser show safety: What is it that makes the lasers more dangerous than the extrememly high sound pressure levels generated by most large concert PAs? Is hearing less important than eyesight? I think the answer would vary depending on who you ask, but IMO they are equally important, but yet we never hear people bitching about sound levels like they do about laser beams touching people.

On the contrary, in the US there are lots of "professional laserists" who (mostly to protect their own interests) insist that lasers should be regulated like firearms and dynamite. If you read between the lines you see that they only people who can easily pass the kind of tests and pay the kinds of fees they say should be involved in the process are them and other already established individuals, making their ideas equate to little more than attempts to limit competition.

All local regulations aside, the bottom line is that crowd-scanning MUST be done properly with the correct calculations done prior to an audience entering the venue in order to guarantee safety. One can further guarantee safety by increasing the divergence of the beam. Personally I never crowd scan because I don't feel that it's worth the effort in a sue-happy country like the US. It's not necessary for a show to have audience scanning in order to melt faces..
There are two very sound (no pun intended) reasons why lasers are regulated but big PAs aren't.

1. When was the last time you heard of permanent hearing damage at a concert? Exposure over time to loud noises will cause permanent hearing damage, yes. Short-term exposure, however, will not. In the past few decades there's never been any reports of anyone leaving a concert with permanent hearing damage.

2. The damage thresholds for the ear and the retina are different. It's a lot easier to damage the eye than it is to damage the ear.

Peaks of up to 160dB SPL are tolerable momentarily (ask anyone who's used a rifle without hearing protection before). If it continues to be that loud, you have time to put your hands over your ears. With a laser of sufficiently high power, your blink reflex won't react in time.

On the other hand, getting hit in the eye by 200mW is not that great of an idea. Also, do not forget that while the Inverse Square Law applies to large PA clusters, it does not apply to a tightly-collimated laser beam.

The bottom line is that even a (very) large PA can't do the sort of damage a misused 10W DPSS can.

Quote:
Originally Posted by Benm View Post
It IS possible indeed, in situations where a firework blows up at close range, or when you use a firearm close to your ear etc. For this to happen you are probably looking at 150 dB sound levels or over though.

A club sound system will not produce anything over 120 or so if you are standing straight in front of the speaker. Sticking around that area will cause hearing problems (both deafness and tinitus) in time, but should also be painful enough to make you budge before either takes permanent effect.
Wrong.

1. A .30-06 rifle can peak at up to 170dB SPL with the rifle shouldered. The pressure differential from an explosion (assuming that it actually creates a shockwave) can be up to 180 or so dB SPL.

2. This is an 'average' club speaker. If you're too lazy to click through, it's the JBL EON 515XT. It's a popular speaker with smaller clubs and touring DJs because it's so damn easy to use. It also sounds like arse, but that's another story.

If you read the spec sheet, you'll see that it can do 132dB SPL maximum. That's measured at 1m, by the way. Which, in most cases, is a typical distance for the closest audience members to a speaker.

120dB is more than enough to make you flinch and/or go and get earplugs, though.
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Old 04-28-2012, 05:19 PM #21
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Default Re: Does this look safe to you?

Quote:
Originally Posted by Oceansoul View Post
There are two very sound (no pun intended) reasons why lasers are regulated but big PAs aren't.

1. When was the last time you heard of permanent hearing damage at a concert? Exposure over time to loud noises will cause permanent hearing damage, yes. Short-term exposure, however, will not. In the past few decades there's never been any reports of anyone leaving a concert with permanent hearing damage.

2. The damage thresholds for the ear and the retina are different. It's a lot easier to damage the eye than it is to damage the ear.

Peaks of up to 160dB SPL are tolerable momentarily (ask anyone who's used a rifle without hearing protection before). If it continues to be that loud, you have time to put your hands over your ears. With a laser of sufficiently high power, your blink reflex won't react in time.

On the other hand, getting hit in the eye by 200mW is not that great of an idea. Also, do not forget that while the Inverse Square Law applies to large PA clusters, it does not apply to a tightly-collimated laser beam.

The bottom line is that even a (very) large PA can't do the sort of damage a misused 10W DPSS can.



Wrong.

1. A .30-06 rifle can peak at up to 170dB SPL with the rifle shouldered. The pressure differential from an explosion (assuming that it actually creates a shockwave) can be up to 180 or so dB SPL.

2. This is an 'average' club speaker. If you're too lazy to click through, it's the JBL EON 515XT. It's a popular speaker with smaller clubs and touring DJs because it's so damn easy to use. It also sounds like arse, but that's another story.

If you read the spec sheet, you'll see that it can do 132dB SPL maximum. That's measured at 1m, by the way. Which, in most cases, is a typical distance for the closest audience members to a speaker.

120dB is more than enough to make you flinch and/or go and get earplugs, though.
Lol... you're talking to someone who suffered permanent hearing damage at a Metallica concert. It was enough that I was medically discharged from the military because of it after only being in a few weeks. I actually had a medical entrance waiver revoked. It happened when I was 17, I left the concert and the hearing never fully returned to my right ear. It still hasn't. I joined the military awhile later and they passed me on a waiver. They revoked the waiver about 10 weeks later when someone decided that the condition would (or could) be degenerative, especially if I were in a combat situation.

So I'm thinking you're incorrect somewhere along the line.. I didn't actually read past where you tried to say that the experience I had as a teenager is impossible. I have no idea what the sound pressure levels were in there, but it hurt. I spent the last third of the concert sitting in my seat with my hands over my ears.. and I wasn't the only one.
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Last edited by ElektroFreak; 04-28-2012 at 05:29 PM.
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Old 04-29-2012, 05:05 AM #22
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Default Re: Does this look safe to you?

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Originally Posted by ElektroFreak View Post
Lol... you're talking to someone who suffered permanent hearing damage at a Metallica concert. It was enough that I was medically discharged from the military because of it after only being in a few weeks. I actually had a medical entrance waiver revoked. It happened when I was 17, I left the concert and the hearing never fully returned to my right ear. It still hasn't. I joined the military awhile later and they passed me on a waiver. They revoked the waiver about 10 weeks later when someone decided that the condition would (or could) be degenerative, especially if I were in a combat situation.

So I'm thinking you're incorrect somewhere along the line.. I didn't actually read past where you tried to say that the experience I had as a teenager is impossible. I have no idea what the sound pressure levels were in there, but it hurt. I spent the last third of the concert sitting in my seat with my hands over my ears.. and I wasn't the only one.
That's the point at which you do something about the problem. That may or may not include leaving.

I didn't say that damage was impossible -- I just said it was highly unlikely from short periods of exposure. Longer exposures are another issue altogether.

Now, staying in a 130dB+ environment (as you did at the concert) for an extended period of time is not a good idea.

You wouldn't stare down the barrel of a 10mW HeNe for a couple of minutes, right?
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Old 04-29-2012, 08:32 AM #23
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Default Re: Does this look safe to you?

Oh I agree that intelligent people should (and probably would) leave, but a 17 year old who just blew $300 in 1997 dollars for a pair of PIMP concert tickets for himself and a little bootylicious hottie?

Not so much..
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Old 04-29-2012, 11:30 AM #24
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Default Re: Does this look safe to you?

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Wrong.

1. A .30-06 rifle can peak at up to 170dB SPL with the rifle shouldered. The pressure differential from an explosion (assuming that it actually creates a shockwave) can be up to 180 or so dB SPL.

2. This is an 'average' club speaker. If you're too lazy to click through, it's the JBL EON 515XT. It's a popular speaker with smaller clubs and touring DJs because it's so damn easy to use. It also sounds like arse, but that's another story.

If you read the spec sheet, you'll see that it can do 132dB SPL maximum. That's measured at 1m, by the way. Which, in most cases, is a typical distance for the closest audience members to a speaker.

120dB is more than enough to make you flinch and/or go and get earplugs, though.
Well, let it be 132 dB at close range and maximum power, i guess it doesnt change the broad argument. The 120 dB i mentioned is more of a realistic maximum on a dancefloor - in case of a concert with the speakers standing on a stage and the audience right in front of them it can be more.

As for 160 dB, i'm sure in most cases you wouldn't be instantly deaf, but i wouldn't take the risk either
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Old 04-30-2012, 03:14 PM #25
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Default Re: Does this look safe to you?

I am the poor slob who was walking past a stack late one night (Late 1990s) when the idiot setting up the system dumped a 2 Khz sweep pulse/pseudo-sequenced noise tone into a 10+ kilowatt stack. My then employer (A laserist) swears he could here me scream over the stack. It took 20-30 minutes before I was "normal". I laying was on my side and screaming on the ground.

No permanent damage, but I hunted him down and started screaming at him, because he could clearly see me in front of the stack.

It was pointless, he was stone deaf. "Ah dude, what??"

He depended on thousands of dollars of instruments to keep his sound business running, as he could not hear. The test pulse was from a "delay mapper" used to line up array phases.

Since this was outside, and in a very large city, I'm sure the apartment dwellers nearby were not happy with speaker stacks tested on both sides of the river all night for two miles.

Before any one asks, each stack had its own 3 Phase generator. Event was for a predicted 200,000 people over 3 days.

I won't go into a concert, club, or rave without some ear protection, ever since. Hottie or not, its not worth it.

BTW, Guys, as you get older, you develop a deep notch at where the hotties screach... Protective Evolution at work? LOL!



Steve

Last edited by LSRFAQ; 04-30-2012 at 03:21 PM.
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Old 05-02-2012, 12:49 AM #26
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Default Re: Does this look safe to you?

Quote:
Originally Posted by LSRFAQ View Post
BTW, Guys, as you get older, you develop a deep notch at where the hotties screach... Protective Evolution at work? LOL!



Steve
Probably so lol! Mine's plenty deep... but it's selective too.
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