Hall AV equipment.

[maniac]

Finally, after a year of suggesting and this mornings assembly being a complete mess up, I've been given the go-ahead to order some kit to permanetly install in the Hall for assemblies.

 

At the moment we use a portable PA kit, laptop and lots of cables to make it all work. This has a lot of problems because bits get borrowed off the PA, cables go missing, kids play with the mixing desk when it's in storage behind the stage so it sometimes goes completely wrong when we've no idea what switch, button or cables been moved or unpluged - like this morning! The speakers are parmanently wired into the hall with 2 speakon connectors on the wall at the front where we hook it up.

 

What I've suggested is we buy a seperate power amp, DVD player, rack mounted PC with pull out keyboard and monitor, and small mixing desk to permanely wire in in a 19" wall mounted rack at the front of the hall (as that's where the speakers terminate) that way we know the kit will never be messed with as we will hold the keys for its use! Drama can still use their existing PA when required, as we will leave the speakon connectors in place and hopefully, if I can find the right sort of switch box, have it so you can change between the two.

 

So I'm looking for a professional speaker swich box which can be used to select between the permanetly wired in kit and the portable PA kit. It's pretty powerful stuff, so a normal domestic switch box is a no go. Anyone got any suggestions?

 

Mike.

Edited February 8, 2010 by maniac

[plexer]

Is there a projector in this mix as well either allready in place or going to be installed?

 

Do you have a control box solution for that as well so that they don't need the remote?

 

Ben

[maniac]

Is there a projector in this mix as well either allready in place or going to be installed?

 

Do you have a control box solution for that as well so that they don't need the remote?

 

Ben

 

Projector's already in place, that will be wired into the PC in the new rack, but also via a KVM switch they'll be a wall box next to outside the rack so the Dance teacher can still use her laptop, we'll make sure the KVM is switched over to the external connection when we leave the hall. We may possibly allow the dance teacher to use this kit once it's installed, but at the moment it's aimed at allowing assemblies to take place without all the drama that happens at the moment!

 

We will still use the remotes for turning the projector on, we have about 6 of them with various people around the school, so that's not really a problem. I just need to ensure the people that use the screen, projector and sound equipment can still use what they have, and my new installation can be totally seperate and only used for presentation evenings, assemblies etc.

 

I would like to dismantle what we have already and fix the whole lot in, but our Director of learning for Performing arts wants that PA to remain portable unfortunitely.

 

Mike.

[Andrew_C]

You could use any reasonable size switch, mounted on a plastic (or metal) patress plate. Unless the rig is huge, and run flat-out, then a 20A switch would be more than ample. Double throw-double pole is what you are after. The hot wire is switched, the cold can be commoned.

[mjs_mjs]

You normally wouldn't switch the output of an amp, usually you switch the signal before it hits the power amp. Using a switch in this way could damage the amp's.

 

Behringer do a nice and cheap line mixer which may be worth looking at.

[maniac]

You normally wouldn't switch the output of an amp, usually you switch the signal before it hits the power amp. Using a switch in this way could damage the amp's.

 

Behringer do a nice and cheap line mixer which may be worth looking at.

 

The thing is, I don't wany any of the equipment in the new rack to be left on or for it to be left open at all, but Performing arts need to be able to use their existing PA still with the same speakers that are already fitted, so each set needs it's own amp really.

 

It is really that bad to switch the output from power amps in this way, if so I might need to re-think my strategy?

 

The problem we have at the moment is too many people are using the PA equipment and not putting it away properly, stealing cables and leads or messing with the settings on the mixing desk that it's taking us an age in the mornings to set up a simple assembly and quite often it doesn't work properly or sound very good as a result because sometimes we've no idea what wire they've moved or what setting they've changed. As most of the people using it have no real idea how it works, they tend to just move every single dial when it doesn't work meaning the carefully worked out settings that I spent hours testing get all messed up.

 

The idea is seperate equipment which is permanely wired in and under lock and key to use for these events, and everyone else can carry on using what they do already. This way I know the hall will always be ready for an assembly or other event and I know bits aren't going to be stolen, borrowed or changed without me knowing.

[RinSewand]

How about getting some speakon sockets(a) and putting them on the side of the cabinet, with tails into the cabinet, put another set of sockets(b) facing into the cabinet with tails that go to your wall sockets, cable from your amp to speakon socket(b) for your use, when you leave, plug in the tails from (a) in instead... external people come in, plug in to the side of the cabinet through sockets(a), no switching needed (just make sure the ones on the wall already are glued in or boxed over or something to people don't get confused?)

 

Cheap solution

 

RwD

[nicholab]

Get a some nexo ps-15 speakers and a camco amps.

[maniac]

How about getting some speakon sockets(a) and putting them on the side of the cabinet, with tails into the cabinet, put another set of sockets(b) facing into the cabinet with tails that go to your wall sockets, cable from your amp to speakon socket(b) for your use, when you leave, plug in the tails from (a) in instead... external people come in, plug in to the side of the cabinet through sockets(a), no switching needed (just make sure the ones on the wall already are glued in or boxed over or something to people don't get confused?)

 

Cheap solution

 

RwD

 

That's a good idea, a little bit more complex than I had in mind, but would do the job. I was after a switch of some sort, but I've just been reading about power amps and switching speakers - it really isn't a good idea it transpires. Speakon connectors might be the best bet as they're easy and cheap to get hold of and wireup.

 

Mike.

[Andrew_C]

You normally wouldn't switch the output of an amp, usually you switch the signal before it hits the power amp. Using a switch in this way could damage the amp's. .

 

Oh rubbish. You MIGHT conceivably if the amp was running flat outand you switched to open circuit, but really!

[RinSewand]

Speakon connectors might be the best bet as they're easy and cheap to get hold of and wireup.

 

Yup - plus if they get smashed it's easy enough to buy another connector and solder it on. Patch panels gave me the idea...

[maniac]

Oh rubbish. You MIGHT conceivably if the amp was running flat outand you switched to open circuit, but really!

 

Actually there is some truth in his statement, but it seems to depend on the power amp.

 

Saying that, we would be in control of the switch, and would obviously make sure it is switched to the correct speakers before we turn it on, so might still opt for a switch of some sort. Just weighing up my options at the moment.

[Andrew_C]

Actually there is some truth in his statement, but it seems to depend on the power amp.

I'd be fascinated to know how! Please tell...

 

One problem with Speakons is that it ISN'T intuitive how to unplug them, especially the ring-locked type. I've had to replace several that have been ripped out by kids. They are however, by far the best, and only dedicated speaker connector. Excluding the execrable DIN.

Edited February 8, 2010 by Andrew_C

[nicholab]

I would have thought that kids should not be touching the PA in normal operation. Although by year 11 I was using a 40 channel desk and thousands of pounds worth of mics.

[maniac]

I'd be fascinated to know how! Please tell...

 

I can't find the site I was reading earlier, but essentially it's not the amps it can damage, but the speakers. Some cheaper amps don't sense whether there's speakers connected or not, and can apparently accumulate high charges inside capacitors inside them which can blow the speakers if they are suddenly connected while the amp is switched on. A lot of better amps will detect if the speakers are connected or not, and if they are plugged in while the amp is on have a sort of 'sort start' system so the speaker won't blow.

 

Saying that, according to what I was reading the risks are low and any decent brand of amp this will not be a problem, although speaker switch boxes aren't recommended on high output rigs by anyone, hence the reason I can't find any dedicated decent speaker switches. The speakers in our hall are 4 x 400w RMS output which is pretty powerful so I am warey about switching it.

 

I might have a totally different appraoch for this now, as it's now possible they may go for having all the PA kit permanetly installed so I may not have to buy new stuff, just put the equipment we have in a decent rack and wire it all up properly!

 

Please note I'm by no means an expert on PA equipment, Home audio yes, but this is different. I am probably the person who understands the most amongst the people emplyed at the school however, so naturally it's fallen to me to sort out which I don't really mind as it will make my life a lot easier.

 

Mike.

[BTCC_Fan]

If there is nothing wrong with existing kit why not permantly install into a lockable rack and provide training to people, with a sheet or something to sign when they get the key to use the kit each time. That way you know everyone should know how to use it and if its been messed about with you know who last used it.

 

Or if it needs to be/someone thinks it sholuld be portable then perhaps you could put all the kit such as amp, PC etc in a rack with a wheels on and a box on the wall to pluf vga and speaker cables into. Then loan out the rack out to people in a similar way to my first sugestion.

 

Edit : With box on wall for speakon cables and VGA people can use their own kit if they want to

[maniac]

Or if it needs to be/someone thinks it sholuld be portable then perhaps you could put all the kit such as amp, PC etc in a rack with a wheels on and a box on the wall to pluf vga and speaker cables into. Then loan out the rack out to people in a similar way to my first sugestion.

 

Edit : With box on wall for speakon cables and VGA people can use their own kit if they want to

 

That's how it's done now, but it's a complete nightmare as cables go missing left right and centre - this morning someone had stolen the extension lead so we had to find another one at short notice. It really doesn't work. Plus I don't want to be responsible for managing the loan of the rack. We have a Performing Arts technician who's supposed to look after the kit, but his time is split between Performing arts, Art and Design and photography so he can't manage the kit effectively and it ends up in a right old mess. He's also not that technically minded, and never has claimed to be - he just got lumbered with the PA kit as there was no one else to look after it.

 

I origenally suggested cannabalising what we have now into a permanent solution, but the Director of learning for Performing arts doesn't want me to touch the existing kit, although aknowledges something needs to change to make assemblies easier. I was just looking at the options available. I want to leave plugs on the wall so the existing kit can be wired up and used as it is now, but also have some permanently wired in kit that can be turned on at a moments notice and we know is going to work properly, rather than bodging wires together in a hurry to replace missing cables like we do at the moment. The problem with the portable kit is it's way OTT for assemblies, it's got a 16 channel mixer with only 2 stereo inputs and all the radio mic gear on it. I want to keep it simple, just one mic input and 3 or 4 stereo inputs on a small mixing desk we can clearly label so it's easy to use.

 

We have fitted speakers in the hall which are good and work well, so it was working out the most effective way to switch between the fixed installation or the portable kit that was proving to be a problem.

[Dos_Box]

CPC Have a huge selection of 19" mountable equipment. Try here: Your Search Results | CPC

[BTCC_Fan]

At my place we have a custom made ( I think) splitter box which takes the input from two mixers with a little flix switch to control which one goes to the amp. The amp is pretty much left on all the time.

 

A system that might work for you is to permantly install the kit needed to do assembellys and take the main speakon and VGA cables inside your rack and split/switch them there with one feed going to your kit and the second going outside box for everyone else to use. Then as long as you remeber to switch it all over to the cables for others to use you should be ok. If you don't want the amp on 24/7 then just put the amp on a seperate power socket with switch on the outside of your rack and put a big sign on saying its the amp and must be switched off.

 

Edit : http://www.radialeng.com/re-hotshot-abo.htm this looks like it might be able to allow you to use two mixers with one amp.

Edited February 8, 2010 by BTCC_Fan

[mjs_mjs]

Oh rubbish. You MIGHT conceivably if the amp was running flat outand you switched to open circuit, but really!

 

not rubbish - the class A amp i have connected up for my room cannot handle an 'open cuircuit' if i did it would be a huge waste of a decent amp. NOT all amps can cope with no loads, some have load resistors built in, some amps have advanced circuitry so that they ''know'' if these is nothing, some even adjust the input gain depending upon the loads impedance.

 

Actually there is some truth in his statement, but it seems to depend on the power amp.

 

Saying that, we would be in control of the switch, and would obviously make sure it is switched to the correct speakers before we turn it on, so might still opt for a switch of some sort. Just weighing up my options at the moment.

 

Amps should be turned off before this and also allow time for any residual currents in the voice coils to dissipate. The voice coil(s) are inductive so have a slight capacitance. amps have capacitors to store energy for long bursts and will continue to output signal after being turned off (some dont i know).

 

I'd be fascinated to know how! Please tell...

 

One problem with Speakons is that it ISN'T intuitive how to unplug them, especially the ring-locked type. I've had to replace several that have been ripped out by kids. They are however, by far the best, and only dedicated speaker connector. Excluding the execrable DIN.

 

that's the idea behind speakon, not easy to unplug unless you know how - like the powercons. anyone who is untrained in this simple task should not be doing it.

 

I would have thought that kids should not be touching the PA in normal operation. Although by year 11 I was using a 40 channel desk and thousands of pounds worth of mics.

 

Same here, i'm now 19 and have my own 32 channel rig, and work for the local council on a 32 channel rig i designed for them. When i was in year nine i was working on a 24 channel rig with about 8k's of radio mics, in ears and other bits and bobs. But by then i had learnt to read so new all the manuals inside out and could actually use the gear. (i was supervised at all times i must add).

 

I can't find the site I was reading earlier, but essentially it's not the amps it can damage, but the speakers. Some cheaper amps don't sense whether there's speakers connected or not, and can apparently accumulate high charges inside capacitors inside them which can blow the speakers if they are suddenly connected while the amp is switched on. A lot of better amps will detect if the speakers are connected or not, and if they are plugged in while the amp is on have a sort of 'sort start' system so the speaker won't blow.

 

Saying that, according to what I was reading the risks are low and any decent brand of amp this will not be a problem, although speaker switch boxes aren't recommended on high output rigs by anyone, hence the reason I can't find any dedicated decent speaker switches. The speakers in our hall are 4 x 400w RMS output which is pretty powerful so I am warey about switching it.

 

I might have a totally different appraoch for this now, as it's now possible they may go for having all the PA kit permanetly installed so I may not have to buy new stuff, just put the equipment we have in a decent rack and wire it all up properly!

 

Please note I'm by no means an expert on PA equipment, Home audio yes, but this is different. I am probably the person who understands the most amongst the people emplyed at the school however, so naturally it's fallen to me to sort out which I don't really mind as it will make my life a lot easier.

 

Mike.

 

In this situation what would be technically the best thing would be to have the amp perminantly installed and away from hands, then have the inputs for plugging things into. You could also put in a compressor/limiter to stop people overdriving the system. (very good idea if you let the space out).

 

It is a bad idea to switch anything above 20w. The voltages on my PA's hit 72V or higher... that can and will kill.

Someone else mentioned commoning the ground - also a bad idea incase someone uses a bridged amp.

 

the biggest fear i would have with this is switching the speakers while amps were on. And if there was signal, you could destroy a speaker. a speaker relies on being sent a smooth sine like signal, starting at 0 and ending at 0, 0 being pd across terminals. start that mid flow and you may cause the voice coil to distort. This would be an additive effect, distortion kills pa voice coils (but it can add to a guitars effect).