Loudspeaker Attenuator

[Biskit]

In one of my venues we have a portable 'meeting room' type system consisting of a rack with mixer etc and a Sennheiser IEM transmitter unit fed from the mix output. The speakers are self-powered (internal re-chargeable battery) and each have a radio-mic receiver (picking up signal from the IEM transmitter) installed in a slot in the back, powered from the speaker battery. So with the exception of mains power into the mixer rack, no cables required whatsoever. Each cab has its own volume control, and you can even plug in a local mic on XLR for announcements in one area only.

 

Its a brilliant system, speakers charge overnight and will do a full day (unless you drive them really hard), sound perfectly acceptable for speach and background music and are not stupidly heavy either.

 

Annoyingly I can't remember the make of the cabs (think it begins with K?), perhaps someone else has come across these? Range is limited to whatever the radio-link will do, but I'm guessing you're outside so might be okay.

 

HTH

 

Ben.

[handyandi]

Seen the same thing done on a budget with lapel sennys TX/RX , & a couple of car batteries with an inverter feeding a crest 100V line amp powering some large horns. Not sure on the length of time the battery charge lasted but if you dont drive the system too hard may last quite a few hours.

[Charlie Jeal]

Ben,

 

Having read throught this thread a few times nowI have to agree that running 300m of speaker cable from 1 amp with attenuatorswill result in a huge drop in signal level to the boxes at the far end of the run. The only solutions I can offer are the following:

 

1. Stick with the powered boxes but run a 32A supply for them with say 6mm cross section mains cable that way you should end up with a lot less voltage drop at the end of the run.

 

2. Stick with the 16a mains feed and use unpowered boxes with a smallish switch mode psu amp(eg Crwon XTI1000) per pair of boxes to give you your level control per area as these can be a less sensitive to voltage fluctuation.

 

3. If you really dont want to run XLR signal cable to each station Handheld Audio hire out a Samson line level transmitter and reciever system which I've used on carnival parades which have a dj in the middle but the signal is then broadcast to every truck in the parade which has a smallish genny on board running the system for each truck. So what you could do then is use a a few smaller gennys spaced out to power your boxes and then relay the signal to them with the radio system and could still use your powered boxes and 16A cabling. As you would be relaying the audio signal via radio there would be no physical connection to cause groundloops between multiple mains supplies.

 

Charlie

[Dan Appleby]

Although in principle the high power 'L' pads seem like a very good idea - my experience of passive monitors fitted with these is that they are unfortunately not reliable.

Because of the power they might have to dissipate - they run hot, and as we all know heat is the enemy as far as reliability is concerned!

One poster mentioned mounting them in an ABS box - please don't, as they need to be ventilated to get rid of the heat. I can almost hear someone saying 'just where is that funny plastic burning smell coming from.......!'

 

Very good point. This is not 'rag your boxes and amps at full' solution.

 

We did some soak testing in the warehouse using a couple of prototypes before me made the remainder of the boxes using an 8 ohm dummy load on a QSC PL224 (740w)... If you run the amp at full whack (and have your l-pad turned down), even though most of the coil is being used - it gets VERY hot (120+ degrees). If you run your amps lower and therefore run your l-pad higher, then less of the coil is being used so more of the amp power is being run through less of the coil - it still gets VERY hot!

 

In reality we run these at relatively low output, the amps are run at about 30%, so the heat in the coil never becomes a problem - we have been using our boxes for about 2 years now and havn't had one go down on us yet :-)

 

If you need to run your speakers loud - find another way!

 

Peace

Dan.