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Hi all,
I've been doing sound for bands over ten years. I've done festivals for crowds over a couple of thousands with no problems. I usually run a triamped system with the correct amp power/speaker (PGM) combination with muliple enclosures to achieve the SPL I need without distorting or clipping the amps. But the few times I've done sound for DJs, something always go wrong. Last night all my diaphrams on my FOH blew, but the monitors which I ran full-range didn't. I used a Driverack for limiting on my FOH and the preamps on my mixer weren't distorting. The club owner wants to continue to do business but over time I'll lose money.
Questions:
1. When a DJ "scratches" is this distortion destroying my speakers?
2. I'll start running fullrange for the tops (highs/mids) but will more distortion be introduced since I get a cleaner sound with less power triamped?
Follow Ups:
I wouldn't say that a DJ scratching is literally destroying your system as it's only the sound being played forwards and backwards in quick succession, but there is validity in the idea. Having a compressor or limiter of some sort is a good option. I run a compression plugin sometimes with my setup (I'm a DJ/turntablist) because the dynamics of a scratch can be really intense. The sound goes from zero to redline in an instant and for some reason has an effect on the signal levels. I think it's kind of like when you run a sine wave sweep through a full frequency spectrum and some frequencies are more prevalent or louder than others. Also, a lot of DJs don't take the time to understand the system that they're playing on or the concept of adjusting gain properly to avoid clipping and distortion.
I needed to insert a limiter for his incoming signal on my mixer. This shall be a common practice for me dealing with DJs. Even though I initially get a unity gain signal from them (on their mixer and mine), they sometimes lie and turn up instead of letting me turn them up (at least the ones I've dealt with) and I still may get a distorted signal because of the "scratching". In the future, I will try to get a unity signal from them "scratching" and also reset the Driverack.
I had the output limiters on the Driverack setup for bands and thought it would protect my speakers. But the previous gig with this rig was an outside concert and highs are absorbed quicker in air than mids and lows. So more highs are needed. Left unchanged, it was after the horns went out I notice on the Driverack, with this type of music, more output was coming from the highs. That explains the thyristor in the circuit shutting the horns off instead of the amp going thermal, especially when he started "scratching" which you described as going "zero to redline" (6-10dB). My high amp has more power than I need, which was dialed back at 1 o'clock, didn't go into protect mode because of headroom.
Thanks for your input.
Ya know those driveracks can lose their settings right?
Its possible the xover point on the drive rack was lost and you dumped
a full range signal into those compression drivers
I hope you have a series capacitor at bare minimum to keep a full range
signal being dumped into them by accident
Fusing them also helps
Like a 3/4amp slow blo buss fuse in series
Ive heard of those digtal xover units doing that
Hard to say....
The driverack kept its settings but was baffling to me was during the show one of the four enclosures the high frequency was still working. But the next day I checked all the enclosures in full range and biamp mode and they all worked. So that kills the amp protection mode theory.
The enclosures are Peavey SP1Gs which I switched out the phone plugs for speakons and had a toggle mounted for fullrange or biamp operation like on their DTH series. These speakers have the original SoundGuard HF protection (a thyristor in the circuit board) and has not been modified.
Again, I've used these cabs for about 10 years (7 after being modified) and they have never let me down.
Ah there is the probable culprit
You heated the circuit and the thermal protection kicked in on the
compression drivers with the passive xover circuit
Good thing
:)
Try using more compression and set your limiter threshold so it
kicks in sooner
If your really pushing that thing at high output try a 10:1 ratio
and make sure you limit it as well
I think you're right.
Thank you.
I did live sound re-enforcement for over twenty years on my rig and as house tech at several venues. Whenever a DJ wanted to plug into my system I would ask him to keep a 'handle' on his levels. Invariably all the DJs would keep turning it up as the night grooved on and I would constantly have to clamp down on the trim in his inputs on the mixer.
I realize things have changed with the gear as much of it is digitally controlled and processed to the nines but some things still hold true. If he is clipping the trim on the console or any input, the resulting signal will send a nasty spike into your compression drivers and even if the input to the driver is within acceptable limits it will damage the diaphragms or trip the breakers/fuses.
I suggest you monitor the input or place a compressor/limiter on the DJs feed before it enters your gear. BTW: Never, ever use slow-blow fuses on loudspeakers. By the time they blow the damage is already done. Slow blow fuses are for power supplies, period.
Hope I helped
They can also be distorting the output of their DJ mixer, while you are showing unity gain on yours. That could be it. You could be running out of headroom on your amps.
Certain Pioneer mixers, notoriously the DJM-600, had very little headroom, probably because the innards are digital. This is a problem when DJs are used to analog mixers that don't immediately turn into fuzzboxes if the red LEDs start flashing.
I always tell them to keep the signal they're sending me green or no more than unity and I'll turn them up if more volume is needed. But I noticed when they "scratch" the volume is much louder.
By the way, I checked all my speakers this evening and the drivers are all functioning thank God. They are 2" exit drivers. I think the high amp went into protection mode but I didn't notice the LED indictor so I'll get it checked out.
What drivers are you using?, I hope 2" throat drivers, as they
will handle much more power. I could see that the "scatching" would
send all kinds of high freq's to the horns, I think I would use
a really good x-over or limiter to filter that somehow.
The Peavey SP1G have a 1.6 throat with a 4" VC and 8 ohms (80 watts Cont./160 watts PGM). The amp I use is a Soundtech PS802 which is 400W @ 4 ohms per channel. Two cabs per channel total 4 ohms and I usually dial the volume on the amp at about 1 o'clock.
Ditch the Soundtechs. Buy some used Crown MAs in good shape. Buy more amp than what you need so that you have at least 3dB or more headroom. Or, buy some of the Crest amps and keep the money all in Hartley's pocket.
The amps on this rig I used were (1) Soundtech PS802 (400w @ 4 ohms/ch) for the highs, (1) QSC PLX3402 (1100w @ 4 ohms/ch) for the mids to power (4) SP1Gs and (2) Yorkville A4.4s (1100w/ch) to power (4) 2x18" subs.
I think the amps are fine but I need to set the compression ratio higher and the limiting lower for DJs to keep the HF circuit in the speakers from going thermal like smcdonie said. I checked but didn't change the settings on the Driverack. Throughout the years it has worked flawlessly for doing sound for live bands at festivals (50Hz-16kHz,+/-3dB), but todays Hip Hop music has very rumbly lows (20-30 Hz) and clacky highs (16kHz and above) maybe fine for home and car systems but this compressed music at levels of bands are dangerous to speakers so more limiting and filtering is needed.
But thank you.
Remember that harder compression can add distortion. if you have a threshold that is too low.
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