Stage fog

[Brad361]

I know this has been discussed here before, but does anyone have a definitive answer as to why "fog" or "smoke" on stage, produced by a machine, affects wind instruments? Does it have to do with changing the density of the air? (I'm sure it does have an effect, I've experienced it).

I have a gig coming up at a place where we've had a problem with this in the past, I need a logical reason to tell the sound guy why to take it easy.

Thanks!

Brad
_________________
When asked if he always sounds great:
"I always try, but not always, because the horn is merciless, unpredictable and traitorous." - Arturo Sandoval

[kanemania]

Tell him that stage fog inflames the lingual papillae, making it impossible for you to play Motown covers.

[Dr. Manhattan]

Do you mean affects the instrument itself or the musician who is breathing in the stuff? If the latter....... Possibly something in the solution used to create the haze, fog, or smoke......
You can be allergic to what is used in the solution so your body releases histamines causing a wide variety of symptoms from teary eyes, scratchy throat and even your throat closing up. I've experienced my throat closing up to the point where I could barely breath.

Hope this is helpful.
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[cbtj51]

Fog vs Motown covers! I kinda remember something like that decades ago.
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[Don Herman rev2]

The speed of sound in air is related to density, which is impacted by humidity, and fog is humid... So the pitch changes. It is also affected by temperature, and fog tends to change the temp as well, so my guess would be those are the two main factors.
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[Brad361]

[Brad361]

[etc-etc]

Normally, the air inside of the trumpet is humid (at saturation / dew point) but the air outside is dry. This leads to difference in air densities that results in stronger reflection of sound back into the bell.

In presence of fog, the humidity both inside and outside of the bell is at saturation (for the respective temperatures which are similar). The decreased difference of air densities reduces the reflection of sound back into the horn. With less sound returned, standing wave needs more work to be sustained and thus the horn starts feeling stuffy.

[Danbassin]

Nice responses everyone!

The descriptions of the physics and acoustics above are dead-on. Additionally, every union contract I've seen for opera, pit, theater, etc. gigs that involve fog carry riders which seek to insure this stage effect neither impacts the health of the musicians nor the sound. Just putting it out there as information of a vital protection for our health and our art, and a safeguard which, if not in place, could allow for enthusiastic but uninformed stagehands/effects operators to seriously impact our livelihoods.

-DB
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[cheiden]

If stage fog is a health risk, I'm doomed. I've worked with three different children's musical theater groups and it's not at all uncommon to wind up in a pit completely filled with fog and zero visibility.
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[Brad361]

[american boy]

A number of years ago,Local 802 took up the issue of stage smoke,as it would work its way into the pit..I think ,if I remember correctly, they changed up the formula of how they made the stuff up,making it safe to be confronted with 8 times a week..I remember several shows where it was horrible; I think they still test it on occasion.

[mm55]

Humidity has quite a small effect on air density; humid air is ever so slightly less dense than dry air, but the difference is minuscule compared to the density differences caused by temperature differences. The effect of humidity on the speed of sound is likewise very small.

Stage fog (and meteorological fog, too), is more than humidity. Humidity is water vapor (gaseous H2O) in the air. Fog has minute droplets of liquid H2O suspended in air, which makes the foggy air denser. Stage fog can also have droplets of liquid glycerine (although there are quite a few varieties of stage fog). Some fog machines also chill the fog, making it still denser. If the fog stays close to the floor, or rolls off the stage into the pit, it's denser than the surrounding air.

As long as the fog is not inside the horn, its effect on the speed of sound inside the horn will be nil, as will the effect on pitch. It can certainly effect the acoustics of the foggy space, and how the horn interacts with that acoustic environment.

How long, I wondered, could this thing last? But the age of miracles hadn't passed.
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[Brad361]

[mm55]

You're fortunate if you have someone (such as a union) looking out for you with regards to possible health effects of inhaling stage fog. Some of that stuff can pretty nasty, even it's been approved as not being harmful, which always depends on it being used according to the instructions.

In plenty of amateur or local theatrical productions, as well as club dates, the person fogging the stage is not properly trained or competent, and sometimes bad chemicals are used, out of ignorance or penny-pinching.

If the pit fills up, it can make the orchestra sound bad, and it can be unpleasant for the musicians. When in doubt, you can ask to see the fog's material data safety sheet. If there's resistance to that, you may be in trouble.
_________________
'75 Bach Strad 180ML/37
'79 King Silver Flair
'07 Flip Oakes Wild Thing
'42 Selmer US
'90 Yamaha YTR6450S(C)
'12 Eastman ETR-540S (D/Eb)
'10 Carol CPT-300LR pkt
'89 Yamaha YCR2330S crnt
'13 CarolBrass CFL-6200-GSS-BG flg

[Brad361]

[etc-etc]

Fog (microscopic droplets of water suspended in the air) can be harmful depending on the composition of the droplets. For example, ultrasonic humidifiers that disperse cold fog are known to disperse bacteria and fungi from contaminated water tanks. Microdispersion of droplets enhances the absorption of contaminated material into lungs.

[trumpet.sanity]

Stage guys have told me "it's just water" and do not be worried about it.

That stuff smells nasty, and does a real job on my sinuses and I always have coughing fits after a show with that stuff.

I'm sure it's not a fatal dose of chemicals, but whatever is in that stuff can't be healthy.

How it effects playability and intonation, I don't know. I've never experienced problems in that respect. But man, that stuff is funky.

[dstdenis]

Apparently glycol is a commonly used ingredient in fog machines. Glycol can mess with nasal tissue, sinuses, etc., so the stage crew should take it easy with the effects if the fog machine uses it. No point in making the stage look cool if the cast, crew, musicians and audience keel over.
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[Brad361]

I forgot to mention: this particular sound guy is a lung cancer survivor who is now back to smoking...... Believe it or not. So I need to have reasons to tell him to back off on the fog that are related to the performance, because this guy obviously doesn't care much about health.

Brad
_________________
When asked if he always sounds great:
"I always try, but not always, because the horn is merciless, unpredictable and traitorous." - Arturo Sandoval