Wind

[tolley1466]

Okay, having an interesting conversation with a friend about the sound while Blur were on at Glastonbury (Apparently it was worse due to the wind? He was standing further back apparently)

 

Personally I think he's wrong, but I want to get my facts right first...

 

So, would the wind affect the quality of sound/throw from a speaker?

 

I did point out about the atmospheric changes that may have occurred...

[Rob_Beech]

Of course it does. If you have sound waves travelling in one direction and the wind blows them around then you'll lose ineligibility and lose the sound to a point.

 

People often (quite wrongly) say that line arrays suffer from wind problems more so than point source systems. This is not true technically but the overall effect can sometimes make it seem like it does.

 

As I'm sure you're aware, line sources use coupling to achieve a minimised loss of sound due to the inverse square law. As such, very often boxes achieve louder coherent results than they would if if was a curved array or a none coupling point source array. This means that when the wind blows then all this is lost and you tend to get issues further back as this coupled sound isn't getting to where it should be.

 

 

That all said, we certainly don't want to get into a debate about why a particular sound might not have been to yours or your friends liking. Perhaps you and/or your friend can design a better system next year.

[Killyp]

Perhaps another point against the 'line-arrays suffer from it more than other systems' argument is that line-arrays are usually seen in large-scale outdoor events where you would expect the mixture of large distances and wind to cause issues (as opposed to a nightclub - indoors and not exactly very windy).

 

Either way, there was a topic recently which deviated into a discussion about this at Glastonbury and the Funktion One rig they tried out a few years back.

[bruce]

So, would the wind affect the quality of sound/throw from a speaker?

Yes.

 

Trivial example. I live about a mile northeast of a railway station. When there is a gentle wind is from the southwest, I can clearly hear the platform announcements. When the wind is from another direction, I can't.

 

(and when there's a strong wind from the SW, I can't hear the annoucnements, cos the wind drowns them out!)

[slim_mcslim]

A couple of years ago a festival held on a beach for a popular tv channel that had line arrays provided by a company with similar initials to "sounds ###### everytime". the wind was so bad there that the sound was being blown directly from infront of arrays into town, leaving the promoters with two problems, unhappy audience on the beach who could hardly hear anything and an upset council in the town who were convinced that the PA was too loud as they could hear it clearly all day long.

 

The last mini festival we were involved with supplying PA to, despite strict noise monitoring on and off site, and the level only being 97db at foh, I could still hear when the bands went off and on at my house 3 miles away and nowhere near direct line of site, and that was entirely down to the wind carrying the sound. This was a small EV line array, that sounded good (if not slightly quiet) in the arena, and met all the Leq noise requirements at local residences.

 

P.

[Stan Hope-Streeter]

<... leaving the promoters with two problems, unhappy audience ... ... who could hardly hear anything and an upset council in the town who were convinced that the PA was too loud as they could hear it clearly all day long.

<br>

Whilst the wind can be a cause of this type of problem, it is more often caused by refraction effects due to the variation of air temperature with height. This is especially important when you have 50,000 dancing punters, each generating around 200W of heat, in front of the stage. The sound propagates in an upward curve instead of covering all the way to the back of the audience.

 

The reason line arrays are particularly badly affected by this is because they provide quite precise vertical coverage and therefore rely on very accurate aiming.

The people who use them generally have no fundamental understanding of acoustics. They think they only have to aim the arrays according to a computer spreadsheet provided by the speaker manufacturer. But array calculation software is designed by computer geeks, not acousticians. It is always based on the assumption that sound waves only travel in straight lines.

 

So they foolishly follow what they see on the screen, unaware that the array calculation results need to be modified, on the basis of expertise and experience, to suit the prevailing conditions.

 

This normally means tilting the coverage downwards, to compensate for the sound bending upwards. It is also wise to open out the beam for more vertical coverage. This is because changes in air temperature, or wind speed and direction, will have a similar effect to changing the tilt angle of the array. If the beam is too tight, a small change in angle will cause a large change in front-to-back audience coverage.

 

Late in the evening as things cool down, (and just when the headline act are going on stage) the upward refraction will gradually diminish. That's when you need to turn up the delays.

Oh, er, you mean the ones the array calculation software told you were not required, so you didn't install ? ....

 

A few hundred feet above the ground, there may be another layer of warmer air. This means the sound will eventually start to bend downwards, to come to earth a few miles away. Where the local residents will be presented with surprisingly high sound levels. If this is on the Continent, they will all sit in their gardens and enjoy a bit of background music. But in Britain, where The Power Of "NO" rules every aspect of daily life, they will call the police and the local council demanding an immediate end to this terrible outrage. So even if the sound levels in the audience are quiet, the Noise Police will make you turn it down even further. This is where you need to keep a very careful eye on the audience and be aware of the inherent danger in an angry crowd. You may be faced with having to turn it up to avoid a riot, in which case you need to cover yourself with a quickly scribbled risk assessment to avoid being held responsible for the massive fines the council will impose on the event for being 10dB over the general background noise, six miles away....

[tolley1466]

Thanks for the replies guys!

I've actually learn't something from this thread :)

 

Thanks again!