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[Matthias McCready]

So I am finding myself as the house engineer of a 1200 seat room these days.

Which has been a lot of fun with regular hours, and lots of time to really dive into mixes.

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One consistent problem I have been battling is humidity. I have talked to the facilities staff and I gather that the HVAC system does not address humidity level (or they don't have access to the computers that could modify that as it is underneath the user level).

Some weeks I have 85% humidity, and this week with a cold snap the humidity dropped down to 25%.

That there is change in the top end! 

If I remember correctly from my last systems deployment class it was stated that hot & wet or extremely cold & dry have less high frequency air loss, and thereby have more top end. 

Bob McCarthy's green box has a short paragraph on this on page 86, where he recommends using a HF filter; which makes sense.

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What I am trying to process through (finally a question!), is how I could make a standardized response to what is going on in the room?

I believe there are systems with processing that measure humidity (and to a lesser extent temperature) and make an adjustment. I don't have DSP that does that.

Obviously distance from box to seat makes a difference, and a 1200 seat space is a lot smaller than outdoor festival.

What is the correction those systems are making (is it simply a HF filter?)

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I am wanting to make myself a chart of humidity X = Filter Y.

I do have SMAART and a measurement mic with accurate top end, so I should probably start making some measurements with the different degrees of humidity.


Anything else I missing in thinking this through?

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Matthias

[Art Welter]

Some weeks I have 85% humidity, and this week with a cold snap the humidity dropped down to 25%.

What I am trying to process through (finally a question!), is how I could make a standardized response to what is going on in the room?

What is the correction those systems are making (is it simply a HF filter?)

---

I am wanting to make myself a chart of humidity X = Filter Y.

I do have SMAART and a measurement mic with accurate top end, so I should probably start making some measurements with the different degrees of humidity.


Anything else I missing in thinking this through?

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Matthias,

When I moved from Minnesota (Land of 10,000 Swamps) to the high, dry desert of New Mexico, thought I had lost my HF hearing ;^)
The difference in HF air attenuation with humidity vs. frequency can be huge:

http://www.sengpielaudio.com/calculator-air.htm

There is about a 5dB loss at 10kHz at 100 feet when humidity drops from 85% to 25%, and more at higher frequencies, near 9dB at 16kHz.

There is no simple fix to address the losses, as they are in addition to inverse distance loss. The longer the distance, the more HF boost required for less humidity- if you don't use separate coverage for each portion of the audience, you'll "fry" those up front with sizzle.

Art

[Brian Jojade]

As Art has said, there's no real 'fix' for this, other than have separate boxes covering different areas of seats that you can adjust.  Adjusting the entire system EQ to compensate for the back of the theater will massively mess with the sound in the front of the theater.

If you're using arrays, it may be possible for you to adjust the EQ curve for each box covering each area if you've got the equipment set up for that.

Note that with audio, it's pretty much IMPOSSIBLE for all sound to be completely equal in all spaces of the room.  As an engineer, your job is to make it suck as little as possible for as many seats as possible at the same time.

[Matthias McCready]

Matthias,

When I moved from Minnesota (Land of 10,000 Swamps) to the high, dry desert of New Mexico, thought I had lost my HF hearing ;^)
The difference in HF air attenuation with humidity vs. frequency can be huge:

http://www.sengpielaudio.com/calculator-air.htm

There is about a 5dB loss at 10kHz at 100 feet when humidity drops from 85% to 25%, and more at higher frequencies, near 9dB at 16kHz.

There is no simple fix to address the losses, as they are in addition to inverse distance loss. The longer the distance, the more HF boost required for less humidity- if you don't use separate coverage for each portion of the audience, you'll "fry" those up front with sizzle.

Art

Currently in Minnesota. 

I understand that this is something that occurs over distance and thereby cannot be perfectly rectified for every audience member; just as the sub(s) can only be perfectly in time for one person. Agreed this is a moving target.

Love the link, I will have to play with that some. Would be fun to make a spreadsheet that models this across many frequencies and distances. :-)

More so as I am in an installed space (with fixed seating and PA positions), my distances between boxes and heads is known factor. The variables here: Humidity and distance (closest seats to box and furthest seats from box).

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In two weeks I have a new rig being installed in the space, something that has been in works since before I took the position, L'Acoustics A15, and KS28's. Excited for the KS28's, and I will see how I like the constant curvature boxes once installed (mixed feelings on those). It is my understanding from talking with the integrator that I will have 1:1 box resolution.

So potentially in the future I could adjust individual boxes; however I feel like that is going deeper into the system settings than I should be, wearing the FOH hat. I think we have all come into "fix" a perfectly good PA where-someone found the system DSP and put in their preferred settings!

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Note that with audio, it's pretty much IMPOSSIBLE for all sound to be completely equal in all spaces of the room.  As an engineer, your job is to make it suck as little as possible for as many seats as possible at the same time.

So in this vein while it cannot be perfect for every seat, some compensation could potentially be helpful for most or all seats?

[Tim McCulloch]

BSS offered a meteorology probe for the FDS-388 so the system engineer wouldn't have to make real-time decisions about humidity and temps.  My personal approach is to compensate all PA zones the same - in theory the humidity is roughly the same everywhere.

[Chris Grimshaw]

BSS offered a meteorology probe for the FDS-388 so the system engineer wouldn't have to make real-time decisions about humidity and temps.  My personal approach is to compensate all PA zones the same - in theory the humidity is roughly the same everywhere.

Yes, but the effect of the humidity is greater at larger distances.


Chris

[Jason Raboin]

Once you get the A15 system you will have access to Network Manager.  Within each amp channel DSP is an air loss compensation filter, which can be applied to each zone without compromising phase.  If the designers were kind enough to give you a P1 processor to go with the system, you can get a USB temp and humidity sensor.  You can then use the Autoclimate feature to deal with your issue.  It has a simple GUI that is intended to be used during a show.

[Tim McCulloch]

Yes, but the effect of the humidity is greater at larger distances.


Chris

Yes, and so is general air absorption.  If you're compensating for long throw losses already then applying the low humidity compensation as a "global" change remains valid.

The biggest problem is that full compensation at 20% humidity and 150 - 200 ft throws is you'll run out of HF driver before you hit your compensation target.

Sometimes chasing the top octave to the last seats is a fool's errand.

[Chris Hindle]

Yes, and so is general air absorption.  If you're compensating for long throw losses already then applying the low humidity compensation as a "global" change remains valid.

The biggest problem is that full compensation at 20% humidity and 150 - 200 ft throws is you'll run out of HF driver before you hit your compensation target.

Sometimes chasing the top octave to the last seats is a fool's errand.

Isn't that what delay rings were invented for?
Chris.

[David Sturzenbecher]

Yes, and so is general air absorption.  If you're compensating for long throw losses already then applying the low humidity compensation as a "global" change remains valid.

The biggest problem is that full compensation at 20% humidity and 150 - 200 ft throws is you'll run out of HF driver before you hit your compensation target.

Sometimes chasing the top octave to the last seats is a fool's errand.

There is also the argument that if you are 200ft away at 20% humidity… it should sound somewhat relative to that.  Your mind is used to hearing HF loss over distance, and I have heard reports of systems sounding “unnatural” when the HF is boosted back so it sounds “in your face”.   Just another Sun-Aud-Con “it depends” situation.  There is also a potential for a middle ground for sure. Maybe a system at 200ft sounds like it’s at 100.


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