Temperature compensation

Steve Anderson

Steve Anderson

Freshman
May 2, 2011
52
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6
Sydney, Australia
So there're quite a few processors out there that, when setting delay times, one can enter a temperature into to set delay times by distance.

Are there any that actually do a live adjustment corresponding to a temperature sensor input?

Or is it not worth the hassle?
 
Re: Temperature compensation

Having set up a number of systems using the EAW UX8800 processor in varying climate conditions, I can attest to the importance of regularly updating the temperature *and* humidity settings in the processor. It made a world of difference when I had to optimize a system in the middle of a hot summer night. Humidity changed by about 60% from start to finish. Here's some great info to contemplate:
http://rane.com/pdf/ranenotes/Enviromental_Effects_on_the_Speed_of_Sound.pdf
 
Re: Temperature compensation

Steve Anderson said:
So there're quite a few processors out there that, when setting delay times, one can enter a temperature into to set delay times by distance.

Are there any that actually do a live adjustment corresponding to a temperature sensor input?

Or is it not worth the hassle?
Click to expand...
As Arthur pointed out, temperature and humidity both affect the speed of sound.
The problem with a temperature sensor is placement, stratification of temperature can be rather extreme between audience level and up where the sound is traveling.
The stratification will cause the sound to travel in an arc, further changing time of flight.
As well as time problems there is HF absorption rate of change going on.

To stay on top of the changes you could update delay times and EQ using Smaart or other programs that can derive time of flight, but multiple mic locations have to be used, and the further they are out of reach of the crowd, the less valid they will be for the various locations.
 
Re: Temperature compensation

Art Welter said:
As Arthur pointed out, temperature and humidity both affect the speed of sound.
Click to expand...

While this is true, the effect that humidity has on the speed of sound is so small you can basically forget about it. The speed of sound changes about 1 m/sec from 0 to 100% humidity, nearly the same effect as a 1 degree celsius change in temperature. The reason you care about the humidity is to account for HF air absorption.
 
Re: Temperature compensation

Are we talking about setting up delay stacks and delaying to the backline or are we talking about the phase and frequency things that happen with the climate conditions? In my experience there is a wide range of times that will work with backline and speaker stack delay. I am familiar with the rane paper Arthur mentioned and it has more to do with phase and frequency changes due to absorbtion and speed of sound changes if I remember correctly. It is more of an EQ thing rather than a case of cabinets drifting out of alignment with the backline.

As far as delaying to backline the reality of the beast is not near as complicated to set up as many people think. Calculations will get you in the ball park but actual listening is really easy and there is a range of several milliseconds that works just fine. In the case of delaying to the backline you are listening for the speakers to disappear. A drum kit works wonders to set up the delay time. It is almost like focusing a camera lens. As you change the delay time the sound will appear to stop coming out of the speakers and seem to all emanate from the kit itself. There is a range of over 10 milliseconds or more that is ideal. I have never tried to see how far that range is but I can promise it is over 10 milliseconds. When setting up delay stacks it is the same thing. When you no longer hear the delay speakers and only appear to hear the source you are done.

Temperature and humidity do change things but I have never had the cabinets come out of the useable delay range. The big thing I have always noticed is the frequency change which is not subtle.
 
Re: Temperature compensation

Scott Helmke said:
Wind will generally have a much bigger effect on delay times than temperature or humidity.
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And how do you adjust for that?

One of the keys to reducing wind effects is to use less sources of sound. The interference between multiple boxes sounds like it is "blowing around" more.
 
Re: Temperature compensation

Bennett Prescott said:
The reason you care about the humidity is to account for HF air absorption.
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Absolutely. The big "take home principles" from that Rane paper I mentioned as it relates to sound system optimization:

1. Relative humidity between 10 and 40 % are particularly absorptive of the HF from about 2000 Hz and up.
2. Be very careful with narrow band filters (1/10th octave or narrower) under changing environmental conditions. The frequencies of the problems you're "attempting" to correct may shift.
 
Re: Temperature compensation

Scott Helmke said:
Wind will generally have a much bigger effect on delay times than temperature or humidity.
Click to expand...

However, larger indoor venues still have issues with temperature and fluctuations (typically between setup/soundcheck and showtime) and whilst there are air currents moving around, wind isn't nearly such a problem.

Dave Rat had some interesting stuff in his blog about this a couple of years back.
 
Re: Temperature compensation

There is also debate about mixing on risers vs. floor level for some of these same reasons. Heat from the bodies causes the sound to rise up away from the people. So beyond air absorption and the fun stuff associated with climate, your measurements need to be relative to the listening audience. Many people refer to an RTA that has a target response lined out on it. The measurement mic doesn't move, so it can get a fairly relative idea of whats changing. As for delay times for climate? I wouldn't worry as much about it. The effect on a systems EQ response in air is another beast and it wouldn't hurt to be on top of it.
 
Re: Temperature compensation

Stuart Høgg said:
However, larger indoor venues still have issues with temperature and fluctuations (typically between setup/soundcheck and showtime) and whilst there are air currents moving around, wind isn't nearly such a problem.
Click to expand...

True, wind is rarely a problem indoors, but you might want to check on the nosebleed seats and turn up the delays a bit after the air handling fans get cranked up. That variety of "wind" can still cause problems.
 
Re: Temperature compensation

Steve Anderson said:
Or is it not worth the hassle?
Click to expand...

It really depends on the event. In an arena with decent HVAC, its fairly irrelevant, because temperature will stay fairly constant. Humidity may not, but equally its going to change during the event more than in the time between load in and doors, so then it becomes about your ability to adjust live, and whether you want to do that.

Where it plays a much bigger role though is in outdoor shows in certain areas. Ive done many a summer outdoor show where you load in at 9am, which means that time alignment happens at about 1pm or so (after lunch of course!), but the show doesn't start proper (after openere) until 9pm. In these situations, the temperatures can change by as much as 20 degrees between alignment and show. However, you need big distances to make an appreciable difference. over 100m, a 20 degree temperature difference is roughly equal to a 10ms difference in delay time. But arguably, in a distributed large format system, all that really does is shift the point of alignment. Since there will almost certainly be a point where the sources are coherent, it will just be 4m further away....

So in short, for most touring applications, its not worth it.

But it is certainly worth understanding the effects...
 
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