Mounting lasers on stage

[smokeAndMirrors]

I'm starting work on a new show with a band, and I want to have my lasers relatively low down (possibly near floor level). My tripod stand are minimum 1m high and because of the spatial constraints of small venues it may be hard to get the larger tripods in. Plus there's no way to mount a single laser on a tripod without it toppling (they're ~600mW RGBs, about 6kg). So I'm looking for a way to mount a laser quite close to the floor. A flight case won't work because I need to tilt the laser up at an angle (I considered putting a laser on top of an amp at one point but I'm guessing this is not so clever?).

So has anyone got some suggestions as to how to mount my fixtures?

[Jem]

Hi

It would be useful if you could give us some idea as to where in the world you are. The reason for this is because there are different laws depending on which country you are in.

For instance, if you are in the UK or the USA there is no way you would be able to use a floor mounted laser for a public show.

It may be useful to have a read at this article...

http://www.hse.gov.uk/pubns/priced/hsg195.pdf

Cheers

Jem

[smokeAndMirrors]

Hi

It would be useful if you could give us some idea as to where in the world you are. The reason for this is because there are different laws depending on which country you are in.

For instance, if you are in the UK or the USA there is no way you would be able to use a floor mounted laser for a public show.

It may be useful to have a read at this article...

http://www.hse.gov.uk/pubns/priced/hsg195.pdf

Cheers

Jem

Hi Jem,

Yeah I'm UK based. The document states

"In circumstances where access restriction is not possible, eg during deliberate audience scanning, safety assurance becomes more an issue of controlling beam hazard so that applicable exposure limits are not exceeded. The height of the scanning beams is particularly important, eg above audiences on a dance platform. A minimum height of 3 m above the highest dance platform is recommended."

As I said, I want to tilt the laser up and this will easily give 3m clearance. Also I've done my MPE calculations using software and I max out at a little less than 0.1*MPE, well within the exposure guidelines.

Unless I've missed something - which I probably have! - that should be sufficient?

[aclasers]

Depending on your projector you can secure it to box truss using doughty clamps,

As jem said, there is H&S issues first,

If the stage is high and projection zone can be in the saftey zone, and no perfomers etc etc.,

[norty303]

You can buy long G clamps, so you could use your tripod with a T bar (and counterweight on the other side if needed to balance) at minimum height and then extend the projector towards the floor on the long clamps.

I find they're useful when you have a truss flown quite high for lighting but you want your laser beams more perpendicular to the floor such as behind the DJ's head. saves on having extra stage clutter from tripods and risk of knocking from passing traffic upsetting carefully set up targets and the like.

[Doc]

Or use a tophat pole mount on your tripod.

http://www.djsupplies.co.uk/speaker-...35mm-463-p.asp

I would be very surprised if you could even see a beam that was 0.1 x MPE and unless your audience is *very* far away; that you would achieve that value with 600mW lasers.

[smokeAndMirrors]

Or use a tophat pole mount on your tripod.

http://www.djsupplies.co.uk/speaker-...35mm-463-p.asp

I can't see how the top hat helps unless I mount the laser upside down?

I would be very surprised if you could even see a beam that was 0.1 x MPE and unless your audience is *very* far away; that you would achieve that value with 600mW lasers.

LaserSafe PC tells me that for a scanning effect

Wavelength = 532nm (green, the most powerful diode in the box)
Exposure = 5s scan time (average)
Power = 0.6W
Beam diameter = 4mm
Divergence = 15mr (estimated)
Target dist = 5m (to audience)
Scan angle - 90 deg
Scan freq = 20kHz (I think it's actually 25)

the emission is 0.142*MPE

In practice, I'd not be getting peak power all the time, and the power of the blue and red are quite a bit lower, so unless I'm mistaken this is an upper bound and quite within the safe zone.

[mixedgas]

WARNING, you have one detail wrong on the maths.

Better divide that scan freq by 10. 20 kpps or 30 k pps is NOT 20 kilohertz, the best galvos can only do about 2500 hz sinusoid, and much less then that square wave. This is why we tell people to use a photodetector and a oscope to measure scan rates.

Steve

[buffo]

20 kpps is NOT 20 kilohertz

Exactly right!

To wit: 30Kpps = ~2500Hz small step bandwidth with *significant* distortion.

Smokeandmirrors:

Remember... The center circle of the ILDA test pattern is actually made up of 12 points which all lie *outside* of the center square. Yet on a properly tuned set of scanners, this appears as a smooth circle that lies *inside* the square. That's some serious position inaccuracy there, and even so the max frequency is only 2.5Khz. (12 points around = 1 cycle = 1 Hz for a small step signal, thus 30Kpps yields 2.5Khz.)

Or: Kpps speed divided by 12 = rough small signal bandwidth limit.

Adam

[smokeAndMirrors]

Ok, that's useful information. Figure is now 1.59*MPE for a line, .564*MPE for a circle. Care to be taken for sure.

But I'm still none the wiser as to how to mount the laser, which is the topic of the OP. And I seriously doubt that lasers can't be mounted on the floor; the Australian Pink Floyd for example:



(in the actual show I saw they were a bit lower).

[mixedgas]

In the US, if on stage, and you meet the 2 meters horizontal and 3 meters vertical beam placement rules,yes, you can mount on stage. 3 meters up from the highest audience accessable point. BTDTGtTS.

But they look at stabilty. And you need a signed waiver from everybody on stage stating they have been trained, and in some cases, dead man's switches, ie pressure sensitive floor mats for the performers to stand on. Its all about mechanical stability.

What we are cautioning you on is about position stability in a noisy, cluttered, vibration filled environment. Tripods often don't work there. Tripods with sandbags are often worse yet. Poles vibrate with huge amplitudes. You want scaffolds or half width scaffolds which is what Oz floyd uses.

Heck, I've done some stuff where half width scaffolding didn't work. If I can grab your mounting pole and shake it and move the beams around, you flunk. If the speakers shake your beams, even the dumbest promoter types will complain, as they want a crisp look.

Scaffolding that is tightly constructed and with locking wheels (better yet, NO wheels) is what you want for a first show. My projector has holes in the floor plate to lag screw it to the wood top on the scaffolding. Got a tee shirt for that one too. Assume you will be hit by 10,000 watts RMS of Bass. That is a typical rave.

steve

[Doc]

Pole mount works like this:




Your scan angle is probably going to be nearer 40 - 50° max and certainly not at 30kpps.

Any venue that allows you to mount your projectors below head height are leaving themselves open for a revoked entertainment license (at the very least).

More or less all the members of this forum perform safe and legal laser shows on a regular basis and to some; lasers have been their career for decades. Doubting their advice is in the same veign as doubting that the sun will set at the end of the day.

Advice is given freely and acurately until said advice is ditched as incorrect. Be in no doubt; the members that have tried to give advice to you in this thread are probably more qualified to do so than *anybody anywhere*

Download a copy of HSG(95), it's free now, read it, read it again, then come ask some more questions.

[Doc]

10,000 watts RMS of Bass. That is a typical rave.

steve

We were running 60k on Saturday. Whilst outside taking a smoke break, one of the DJs got some LF feedback going (the joys of vinyl). I was leaning against the building wall (brick), and felt the entire wall vibrating at about 8-10hz. All of the aluminium cladding on the upper half of the building started rattling so bad it sounded like it was going to fall off.

[norty303]

and felt the entire wall vibrating at about 8-10hz.

I would be very surprised if the system didn't have a high pass filter at around 30hz or higher unless it had dedicated infrabass cabs. Even then they're only good to 25hz or so. Technics typically cause feedback at 80hz and most engineers notch the EQ in advance. Oh, the joys that CD's and laptops have brought us (along with the ability to play shit quality mp3's)

[Doc]

I would be very surprised if the system didn't have a high pass filter at around 30hz or higher unless it had dedicated infrabass cabs. Even then they're only good to 25hz or so. Technics typically cause feedback at 80hz and most engineers notch the EQ in advance. Oh, the joys that CD's and laptops have brought us (along with the ability to play shit quality mp3's)

No, definately well sub bass. The system is newly installed and I thought at the time that it shouldn't have happened with the HP filter, I know 1200s normally suffer from that 80hz resonance (we get that bad at the Park Hall venue and have to tune it out with the parametric) but this was a vinyl resonance (must have been a dished or warped record). Scared the shit out of me from outside.

[smokeAndMirrors]

Thanks guys, don't mean to be arrogant. Your help is appreciated.

Question:

HSG95 says

"Therefore, if any reasonably foreseeable installation fault condition could cause an accessible emission in excess of the applicable MPE value (see Table 1), direct scanning of an audience or the public should not be permitted."

So how come anyone audience scans?

[Doc]

Thanks guys, don't mean to be arrogant. Your help is appreciated.

Question:

HSG95 says

"Therefore, if any reasonably foreseeable installation fault condition could cause an accessible emission in excess of the applicable MPE value (see Table 1), direct scanning of an audience or the public should not be permitted."

So how come anyone audience scans?

The interpretation of this rule to me, is that providing that your show meets MPE levels during the show; the only fault condition that is likely to change a calculation parameter is if your scanners stop or slow down to a point that increases emission exposure beyond safe levels.

Therefore to satisfy this rule we need to install scan fail protection if we're going to audience scan.

Scan fail protection kills the lasers if the galvo scan speed falls below a pre set level.

Thereby; the fault condition will not expose the audience to excess emmisions.

[mixedgas]

Thanks guys, don't mean to be arrogant. Your help is appreciated.

Question:

HSG95 says

"Therefore, if any reasonably foreseeable installation fault condition could cause an accessible emission in excess of the applicable MPE value (see Table 1), direct scanning of an audience or the public should not be permitted."

So how come anyone audience scans?

scan fail safeguards, dedicated MPE meters, time to plan and check each effect and the fact that if you don't in Europe you will have zero business.
You also have a different legal climate.

You can get away with perhaps 5-10x the MPE and be somewhat safe, recent studies have shown remarkably few injuries occur with laser shows, well, at least until the cheap chinese DPSS has came out, things like 500 mW pointers in the hands of audience members are starting to cause abberations, as well as a recent fool in Moscow who aimed 30-60 watts into a crowd. remember the MPe has a fudge factor built in, but there is not much reserve. (BTW, if a high power pointer shows up in a venue while you are there, confiscate it, or otherwise make it go away, because as the laserist, you are the liable person because you are the "expert".)

In fact there have been more injuries in the past 3 years then probably the whole total history of laser shows back into the 70s.


Lasers used to need a skilled technician just to get them fired up, and were a expensive art form. People who can market a expensive art form usually take care and have brains enough not to cause health issues for their clients. Now, due to weak enforcement of laws, plus Chinese advancements and advantages in copying technology, anybody can order anything out of a internet catalog, and not just lasers.

When I started, galvos were 3,000$ a set and not in stock, but custom made. A 5 mW hene was as much as 250-450$ used, and a 250 mW air cooled argon was 3500$ used. DPSS did not exist. And I could call the FDA and get a actual human expert on the phone to ask questions. If you asked the right questions, they came out and checked you out for safety.

Now so many people have lasers, there is no one with the qualifications to enforce the rules.

You are on the right path, and you are realizing the huge amount of responsibility you have. And you are asking questions, which is very good.
Use safety zones, put the hot stuff above the zero line, set the zero line at 3 meters up, and work from there. remember, the MPE x time = cumulative exposure, and there is a limit to cumulative exposure as well.

Good shows use bursts of scanning, positioned differently each time. This reduces cumulative MPE. Max MPE scans are often uncomfortable for the crowd, you will learn to back off some times.

Oh, and how do I, a American, get to see aud scanning? ILDA conferences, SELEM, and teh fact that Canada, is 250 miles AWAY.

ps, SINCE YOU ARE NEW AT THIS, LEARN WHAT A "SHOW RIDER" OR "TECHNICAL RIDER" IS, AND MAKE ONE UP. MAKE SURE IT PROTECTS YOU AND MAKE SURE YOU HAVE A "i GET PAID, SOMETHING, NO MATER WHAT " CLAUSE. TYPICALY YOU PRO RATE HIGHER FEES AS THE NIGHT PROGRESSES. we have discussed what should be in it, enough times here, and the UK guys can get specific.


***Bridge if your reading this, I'm sorry, but many of your competitors are not as ethical as you.

sTEVE

[smokeAndMirrors]

"Safety related control systems (SRCS), operating on scan failure detection, are also unlikely to turn off a high power laser in a time short enough to render it safe to view. See Appendix A for a definition of SRCS."

And if even a 5mW beam can be classified as harmful, there can hardly be a laser in the land safe for scanning.

[Doc]

"Safety related control systems (SRCS), operating on scan failure detection, are also unlikely to turn off a high power laser in a time short enough to render it safe to view. See Appendix A for a definition of SRCS."

And if even a 5mW beam can be classified as harmful, there can hardly be a laser in the land safe for scanning.

There have been changes in opinion on this matter specifically to the document the BSEN60825 document; on which HSG(95) is based. Due to the fact that diode pumped lasers can be shut down so quickly (a fact that now obviates the need for a safety shutter in some cases).

The key thing to consider especially when dealing with anything health & safety related (in the UK); is the phrase "so far as is reasonably practicable"

That is; if you find yourself in court, charged with injuring somebody; that question *will* be asked by the prosecution; did you do everything you could, so far as is reasonably practicable, to ensure the safety of yourself and others. If the answer is yes then you only have to worry about the civil case, if no; you could go to jail too.

In my day job in the construction industry I have to deal with this sort of stuff every day; risk assessments, method statements, personal protective equipment, measures to ensure the safety of staff and the general public. Much of this involves providing calculations for stress, ground compaction etc etc.

Fear makes me do these calculations correctly and keep a record of everything I do, the same has to apply for something that could destroy somebody's eyesight in a microsecond.

[danielbriggs]

Without meaning to threadjack;
Could I just ask recommendations of a half decent stand for my "Toblerone" rig?
I've seen these two; any preference?
http://www.dolphinmusic.co.uk/produc...ker-stand.html
http://www.djkit.com/product.php?id=2290&cat=278

I was planning to make a plate (from some really thick kitchen top laminated chipboard cut to the size of the base of the triangle), screw on some square section around the edges for location, and mount a top hat adapter on the base for mounting to the stand.
Can anyone advise on a better way to do this? I don't really want to mount the tophat adapter directly to the aluminium base...

Ta,
Dan

[mliptack]

And I seriously doubt that lasers can't be mounted on the floor; the Australian Pink Floyd for example:



(in the actual show I saw they were a bit lower).

Steve covered this topic already. The performers of course were trained with the safety of the lasers behind them as were the crew. (I should know, I worked on the lighting for that tour in the US)

Unfortunately, however, they have dropped the lasers from the show this year. I am unsure of the specifics, but it might be due to the Barco projector they fried with the laser.

[Doc]

Without meaning to threadjack;
Could I just ask recommendations of a half decent stand for my "Toblerone" rig?
I've seen these two; any preference?
http://www.dolphinmusic.co.uk/produc...ker-stand.html
http://www.djkit.com/product.php?id=2290&cat=278

I was planning to make a plate (from some really thick kitchen top laminated chipboard cut to the size of the base of the triangle), screw on some square section around the edges for location, and mount a top hat adapter on the base for mounting to the stand.
Can anyone advise on a better way to do this? I don't really want to mount the tophat adapter directly to the aluminium base...

Ta,
Dan

Hi Dan, the first of those two looks incredibly flimsy. You need something much more substantial.

I have two truss clamp positions on my RGB that I use where possible, but also use a tripod when it's the best option (bearing in mind what Steve said about vibration and movement; I would only use the tripod on a solid concrete stage).

I think Carl B uses the mounting method that you described but I have installed the top hat mount in to the chassis of the projector, and from memory your toblerone has an extremely solid frame so maybe that's an option?

[mliptack]

You know I have to wonder, what is the obsession of people using tripods?

Tripods always seem flimsy even more so when used improperly (legs not spread correctly, up too high, overweight to manufacturers suggestion etc.). Why don't we see more threaded pipe and pipe fittings in here? Using a 50 Lb threaded base and carying some various sized schedule 40 pipe you can make one hell of a projector stand, that could take almost any diode-based system.

50lb base: http://www.stagelightingstore.com/s.nl/it.A/id.1477/.f (this was a quick search, I am sure you could find one cheaper)
SCH40 pipe: Available at a home depot
SCH40 pipe fittings: Home depot

They actually sell a piece that is a flange with a threaded coupler. I cant find an image of one for the life of me. but using this you could screw the flange part into the bottom of your projector and then thread it directly on top of the pipe and base.

Of course if you already had a c-clamp or my personal favorite the mega claw http://www.thelightsource.com/products/7/view you dont even need the flange, just a pipe T at the top.

This is something else I have been meaning to throw onto the forums, and now is no better than any other - so here it goes. To those of you using C-Clamps to hold the weight of you projector. Keep in mind, while C-Clamps can surely hold quite a bit of weight, they are only made to hold the weight of the manufacturers heaviest fixture created.

[Doc]

I wouldn't call it an obsession, I prefer to use trussing where possible but sometimes it's not.

My projector weighs about 60lbs, my tripod is rated at 3 times that and has a rack and pinion winch that raises it to 10 feet. Even at maximum height it is rock solid and the legs have a spread of 6 feet. It's no lightweight itself though, but it will fit into a medium sized car and is a godsend at 5am when you are packing up.