Fire in the Hole

[dswpro]

I played a gig last night in a new tavern with an outdoor stage. 10-20 feet from the stage on one side was a gas fire pit. Basically a brick box about 4x20 feet with lava rocks laying on gas jets. Gets chilly at night even in the summer so this is where folks smoking outside can congregate to keep warm. (You cannot smoke in bars anymore in Ohio). So I set my mixer on the far side of the fire pit.
During the night I was thinking the high end of my Otops were cutting in and out. Not really cutting as much as muffling.
Then I recalled a Rolling Stones concert a long time ago in the old Cleveland Stadium. I was on the upper deck a couple hundred yards from the stage. The wind in that stadium was notorious. They called the stadium the mistake on the lake because of how cold it was in winter with the wind whipping off lake Erie. Went through your bones. That day the wind was literally blowing the high frequencies out of the mix. Last night it seems the hot air rising from the fire pit was doing the same to my mix. Darnedest thing. Last time I'll use that mix position.

[Bill Fitzmaurice]

Fog can do some odd things with sound as well.

[byacey]

Real fog, or man-made stage fog?

[Bill Fitzmaurice]

Real fog, or man-made stage fog?

Real fog. I once did neighborhood measurements of environmental bleed through from a concert venue, and one foggy night distant levels were running 6 to 9dB higher than I'd normally measure based on the SPL at the FOH.

[CoronaOperator]

Real fog, or man-made stage fog?

Real fog. I once did neighborhood measurements of environmental bleed through from a concert venue, and one foggy night distant levels were running 6 to 9dB higher than I'd normally measure based on the SPL at the FOH.

That would be from the temperature inversion bouncing sound back to earth https://sites.google.com/site/kundapark ... bout-noise

I watched a documentary on how some battles (cannon, pre-radio) were lost or won depending on the weather and temperature inversions. Some units couldn't hear the commotion of battles taking place nearby due to being in an acoustic shadow, whereas other commanders could hear the commotion from 40-50 miles away and act accordingly.

[biggerrigger]

I have ran into this numerous times playing outdoors where even a small campfire is involved. It can have a very cool effect on most classic rock songs if enough adult beverages are added into the mix
Its a neat way to learn how the atmosphere around us effects sound waves. Try it sometime by placing a speaker on one side of a heat source and listen from the other side. Its a very cool effect.

[Bill Fitzmaurice]

Real fog, or man-made stage fog?

Real fog. I once did neighborhood measurements of environmental bleed through from a concert venue, and one foggy night distant levels were running 6 to 9dB higher than I'd normally measure based on the SPL at the FOH.

That would be from the temperature inversion bouncing sound back to earth https://sites.google.com/site/kundapark ... bout-noise

Probably not in this case, as even 100 feet out from the FOH the levels were much higher than normal. I attributed it to increased speed of sound in the very dense air.

[Bruce Weldy]

Probably not in this case, as even 100 feet out from the FOH the levels were much higher than normal. I attributed it to increased speed of sound in the very dense air.

Interesting. Last Thursday, I set up exactly the same as the Thursday before, ran the same song to check out the system - it didn't have the high-end that was there the week before. I dialed up about 3db of 5k and it came to life.

It was probably higher humidity than the time before. Could that affect certain frequencies more than other? It seems to me that denser air might be tougher on higher frequencies.....could that be the culprit?

[CoronaOperator]

That would be from the temperature inversion bouncing sound back to earth https://sites.google.com/site/kundapark ... bout-noise

Probably not in this case, as even 100 feet out from the FOH the levels were much higher than normal. I attributed it to increased speed of sound in the very dense air.

The inverse square law is independent of velocity, if the sound is louder at distance then the space that the sound is radiating into has gotten smaller. The boundary layer may of only been 30-40 feet high refracting sound back down. Then the sound would only drop by 3dB per doubling of distance instead of 6 as the space would essentially become an expanding cylinder as opposed to a sphere.

[byacey]

Probably not in this case, as even 100 feet out from the FOH the levels were much higher than normal. I attributed it to increased speed of sound in the very dense air.

That could well be. I've noted when the temperature drops around -40C that passing aircraft sound much closer / louder than normal on a clear day.

[Bruce Weldy]

I've noted when the temperature drops around -40C

Is that inside or outside of the igloo?

[Bill Fitzmaurice]

It was probably higher humidity than the time before. Could that affect certain frequencies more than other? It seems to me that denser air might be tougher on higher frequencies.....could that be the culprit?

Could be. In this particular case it seemed that the midrange was more prominent than usual. It would be interesting to test, but we'd probably have to rely on foggy Londoners to do so, as they have more of an opportunity. Maybe Seattle? This particular night had foggy humid conditions that I only saw once in over 300 concerts.

[CoronaOperator]

In this particular case it seemed that the midrange was more prominent than usual.

To me that seems to support the refraction theory as the index of refraction is dependent on frequency. Like light refracting thru a prism, your listening position happened to be in one of the color bands (midrange). If you moved further away did the lows start to become more prominent or maybe the lower frequencies may not of been refracted enough to bend back down to earth at all.

[Bruce Weldy]

In this particular case it seemed that the midrange was more prominent than usual.

To me that seems to support the refraction theory as the index of refraction is dependent on frequency. Like light refracting thru a prism, your listening position happened to be in one of the color bands (midrange). If you moved further away did the lows start to become more prominent or maybe the lower frequencies may not of been refracted enough to bend back down to earth at all.

That was Bill's quote, not mine. I didn't notice the mids being any more prominent. I only noticed the lack of highs in various positions - at FOH and walking the venue.

It's always interesting though....the stuff that changes even though you haven't touched a knob.

If we had played longer last Thursday night, we'd have been able to discuss how rain and 50mph winds affect sound. Fortunately, iPads with weather radar helped us make the decision to get the hell out about 45 minutes early. At least we got most of the gig in....the is the same event on the same week the we lost to a rainout last year.

[byacey]

Is that inside or outside of the igloo?

No, you only see igloos further north in the tundra where it gets cold. Because it's past the tree line, there isn't any wood available for building material.

Everyone around here has an ordinary log cabin.