100V LINE PA SYSTEM FOR FOOTBALL GROUND

[munga42]

I have been asked to have a look at the pa system we have at out local football ground. The issue I am having is the speakers are not in sync. Meaning when I play music it comes out of one speaker on the right floodlight and then there is a half to second delay on the speaker on the left floodlight. This makes it sound awful. I also tried adding another speaker at quite close prox to amp and im guessing as the cable is a shorter run it get the sound first. I have tried to break the speakers in to zone with little effect. Any help I would be very grateful.

 

MUNGA42

[Simon Lewis]

Hi Munga, and welcome to the Blue Room.

 

It's not too clear what your level of knowledge is, so forgive me if some of this is too basic...

 

A football pitch is about 100m long, so you'd expect around 120ms or so of delay between one speaker and the other, when listening close to one speaker.

If this is not the problem you are hearing, then is there a delay line in the system? Could this have been set incorrectly?

What sort of loudspeakers are in use, and are they low impedance or definitely 100V line? If they are 100V line, most systems won't sound too good with music!

 

I can say that unless you are using loudspeaker cables that are many miles in length, the electrical signal will arrive at all of the loudspeakers at the same time.

 

If you give us some more information, we'll see what we can do to help.

 

Simon

[Brian]

Hi and welcome to the Blue Room.

 

Before you make too many changes you ought to check that the system is only meant for incidental announcements and is not part of the grounds voice evacuation system. If it is then making any changes will have big implications on the grounds licence and insurance.

[paulears]

It might we worth walking around the edge and seeing if the delay goes the other way too. Is there a place where the same delay happens with the other tower.

 

Where you have a big space and a small number of loudspeakers, this is a very difficult problem to solve, as Bruce said above - it takes time for the sound to travel, and if people are hearing two separate signals arrive - then it will be different at every position. It's the same in big stadia too - they might have thousands of loudspeakers, each covering a very small area of the crowd - in an attempt to solve this one. With a couple of speakers on the floodlight poles, music is NEVER going to work well, and speech will be difficult - when the wind blows, even a carefully designed system goes t1ts up!

[TomHoward]

Old topic...

 

The problem mentioned above, covering an outdoor area, like a show ring, are there any particular methods or tricks to avoid the delays between sources?

Keeping horn clusters small and trying to cover one edge only?

Clustering more in fewer locations to reduce sources?

Live with the sound slapping around?

[dbuckley]

are there any particular methods or tricks to avoid the delays between sources?

 

Have the horns all face one way; In particular, don't have horns on a pole facing 180 degrees away from each other, as when the listener is between poles they hear two strong signals from opposite directions that are out of time. When the horns all face one way there is always a nearest speaker to the listener, and then further away speakers that are quieter. The ear hears the delays but it doesn't destroy the intelligibility.

[Owain]

Have the horns all face one way; In particular, don't have horns on a pole facing 180 degrees away from each other, as when the listener is between poles they hear two strong signals from opposite directions that are out of time.

Even worse, when standing next to the pole they may hear next to nothing directly from the speakers, but two or more indirect sounds reflected from buildings etc. which may be very different distances, and this delay times, from the listener.

 

 

Edinburgh Waverley's new PA/VA system cost about £20 million. Even after all that money there are still some dead spots on the platforms if you get the builder's temporary hoarding over WHSmiths between you and the column speaker which is the distance side of the concourse. A couple of steps in any direction makes a huge difference.