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I own several RCF ART series 312 speakers and am very pleased except for one minor thing. There is a noticeable hiss coming out of the horns. It's nothing major just getting on my nerves. When I'm doing a gig its not really audible and I dont think about it. When I'm home practicing, etc. it drives me crazy.
I've already unhooked everything to see where it originates from but cant find it. I hook the rcf's into an Allen and Heath ZED14 mixer if that helps. Could it be an electrical issue? The hiss varies in volume from room to room from venue to venue.
Thanks

I notice a hiss whenever the effects are way too high on the mixer. I run the effects through mixer channels. Try backing off the effects gains.

Hiss is floor or thermal noise. All amps, receivers radars have it when they are cranked full blown at max gain. Amps have a linear range at -3DB from low gain to -3DB at max gain where the signal is linear with no distortion. On either end there is distortion. Hiss at the lower end and audio clipping at the higher end. In the gain structure all stages have to be operating in this range and it is efficient to operate all in the middle of this range and add stages or power to obtain the audio level needed. Constant hiss indicates more stages or power is needed for a stage is being run at max or near floor level.

Yes if the EFX units are at max they cause floor noise. also.

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Alright well Karyoker just gave you the amazing technical answer that repeats and expands on the point that Angel was making but I'm guessing you didn't follow half of what he said. Ultimately what you've found is the noise that exists in any system. I'm not going to bore you with the technical explanations but here's the deal. As both Angel and Karyoker expressed in their own unique ways, you've got a component somewhere in your system that has it's output level (or input level on the console) set so high that you're actually picking up what is normally the in-audbile noise it produces. If you have any outboard effects units or dynamic processors (compressors, eq's, etc) start there, they are the most common cause. Try just unplugging them one at a time and see if the hiss goes away (or reduces greatly). Once you find it, then make sure that your send level from the board ot the effects is high enough (without going too high and into clipping) so that you can keep the output from the unit relatively low (around the middle or so of it's total output capability). This should lower your noise floor enough to get rid of the hiss.

Also, dirty channels on your console can cause this too. So if you don't find the issue in any outboard effects or compressors, try just muting individual channels until you find one that makes it go away. There's not much you can do if a channel strip itself is causing this, but at least you can identify it and mute it if you really need to.

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DJ Tony
Let It Rip Karaoke

Thanks for all the comments. As I stated earlier, I've unhooked everything going to the mixer except the one speaker and still have a noticeable hiss. The effects knob is muted, etc.

I know you will have tried changing speaker cables.
Try feeding your speakers from the Aux outputs from your desk.

are these active speakers? if so I had a similar prob. because the area was large and the volume required was quite low I would put one speaker a long way away from me..and plug it into the nearest socket...irritating hum. somone suggested I run an extension back to the same place as I was plugging all the rest of my equipment...bingo no hiss/hum at all. I has meant some extra mucking about at gigs running extension cables and taping them down but its worth it for clean sound

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I'll never plug anything again..

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A bad water pump....

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Just a thought... try turning the gain knobs on the mixer completely off with everything unplugged. You might just be overdriving one of the chanel preamps, maybe one that you're not even using.

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Nearly every amp has some hiss. Some more than others. Generally the more you turn the volume or gain up, the more hiss you will hear.

I've noticed that my Yamaha EMX512 has a noticeable hiss and I believe it uses a class H amp, it's VERY light. I have 3 different class AB amps that have less hiss than the EMX512.

I've read that many/most powered speakers have some hiss when they are turned up all the way. The only way I've been able to reduce hiss is to turn the main volume/gain down and then increase each individual channel volume/gain on the mixer. Turn up the main volume/gain and you will increase hiss. Using a powerful enough amp allows you to keep your main fader low while still having enough sound volume.