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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => LAB Lounge => Topic started by: Bob Burke on July 08, 2014, 07:14:40 AM
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Another stupid question:
I'm using a QSC PLX1804 (550 @ 8 ohms/ 800 @ 4 ohms) with two Yamaha S115v's on channel 1, and two Peavey PR-12's on channel 2. The Yamahas are rated at Power handling 500 watts program, 1,000 watts peak, and the PR-12 are rated at 400 watts program/ 800 watts peak.
Since they are daisy-chained, two per channel, the amp is seeing a 4 ohm draw, correct? Mike Pyle, who sold me the QSC, said it was a great match for the Yamahas, which it is. My concern is for the Peaveys – I don't want to blow the tweeters (again*). I usually run the gain on channel 1 at about 1 O'clock, and the monitors at about noon. The LED cluster in the amp never shows clipping, it occasionally shows at the -10 dB meter mark. Are these levels safe for my speakers? We're never sick loud or anything, and only vocals and backing tracks through the system.
Is there a better way to do this, or should I get a separate amp to run the monitors?
* p.s. - Could I have blown the Peavey tweeters at that power level? I didn't think they were getting too much signal, but they were blown when the talking monkey at Guitar Satan "tested" them (with a 9-Volt battery across a 1/4" phone plug, which I understand will blow tweeters)
Thanks,
Bob
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Another stupid question:
I'm using a QSC PLX1804 (550 @ 8 ohms/ 800 @ 4 ohms) with two Yamaha S115v's on channel 1, and two Peavey PR-12's on channel 2. The Yamahas are rated at Power handling 500 watts program, 1,000 watts peak, and the PR-12 are rated at 400 watts program/ 800 watts peak.
Since they are daisy-chained, two per channel, the amp is seeing a 4 ohm draw, correct? Mike Pyle, who sold me the QSC, said it was a great match for the Yamahas, which it is. My concern is for the Peaveys – I don't want to blow the tweeters (again*). I usually run the gain on channel 1 at about 1 O'clock, and the monitors at about noon. The LED cluster in the amp never shows clipping, it occasionally shows at the -10 dB meter mark. Are these levels safe for my speakers? We're never sick loud or anything, and only vocals and backing tracks through the system.
Is there a better way to do this, or should I get a separate amp to run the monitors?
* p.s. - Could I have blown the Peavey tweeters at that power level? I didn't think they were getting too much signal, but they were blown when the talking monkey at Guitar Satan "tested" them (with a 9-Volt battery across a 1/4" phone plug, which I understand will blow tweeters)
Thanks,
Bob
The PR12 peaveys have a light bulb inside that is supposed to protect the tweeters. Are you sure the tweeter is blown and not just the bulb?
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Another stupid question:
I'm using a QSC PLX1804 (550 @ 8 ohms/ 800 @ 4 ohms) with two Yamaha S115v's on channel 1, and two Peavey PR-12's on channel 2. The Yamahas are rated at Power handling 500 watts program, 1,000 watts peak, and the PR-12 are rated at 400 watts program/ 800 watts peak.
Since they are daisy-chained, two per channel, the amp is seeing a 4 ohm draw, correct? Mike Pyle, who sold me the QSC, said it was a great match for the Yamahas, which it is. My concern is for the Peaveys – I don't want to blow the tweeters (again*). I usually run the gain on channel 1 at about 1 O'clock, and the monitors at about noon. The LED cluster in the amp never shows clipping, it occasionally shows at the -10 dB meter mark. Are these levels safe for my speakers? We're never sick loud or anything, and only vocals and backing tracks through the system.
Is there a better way to do this, or should I get a separate amp to run the monitors?
* p.s. - Could I have blown the Peavey tweeters at that power level? I didn't think they were getting too much signal, but they were blown when the talking monkey at Guitar Satan "tested" them (with a 9-Volt battery across a 1/4" phone plug, which I understand will blow tweeters)
Thanks,
Bob
the panel on the back that has the connectors has the crossover underneath it. Take that panel off and the light bulb is on the underside. The guy at guitar satan should have known that.
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Why would you expect them to know anything? Your only setting yourself up for disappointment.
Sent from my iPhone using Tapatalk
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The PR12 peaveys have a light bulb inside that is supposed to protect the tweeters. Are you sure the tweeter is blown and not just the bulb?
I probably should have checked that, but was afraid of voiding the warranty. The tech I took them to yesterday said it might just be the light bulb. Fingers crossed.
Any advice on the power vs. wattage?
Thanks.
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I would go a step further and ask what 1/4" jack attached to what. That type of test isn't reliable, and at the very least needs to be run with a tap of the leads attached directly to the compression driver.
Remove the back plate and check for a "bulb" safety device. If you find one take your meter and check for continuity. Open = bad, closed = good. If that's not enough then take the cabinets to a speaker shop that has a signal generator. Have them test through the crossover, and then through each driver.
400 watts isn't enough to kill those cabinets if you can keep them from clipping and the system is powered off and on properly. Keep in mind though that not enough power can be a worse condition than too much power. 2x times the long term rating is a good rule to follow.
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I probably should have checked that, but was afraid of voiding the warranty. The tech I took them to yesterday said it might just be the light bulb. Fingers crossed.
Any advice on the power vs. wattage?
Thanks.
those speakers are not as durable as the better peavey lines. When you take that back panel off you'll see that the components are tiny. I had one of mine blow a bulb. I would think that you would be hard pressed to hurt them on monitor duty, since feedback would be a problem before you overpowered them.
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I would go a step further and ask what 1/4" jack attached to what. That type of test isn't reliable, and at the very least needs to be run with a tap of the leads attached directly to the compression driver.
Remove the back plate and check for a "bulb" safety device. If you find one take your meter and check for continuity. Open = bad, closed = good. If that's not enough then take the cabinets to a speaker shop that has a signal generator. Have them test through the crossover, and then through each driver.
400 watts isn't enough to kill those cabinets if you can keep them from clipping and the system is powered off and on properly. Keep in mind though that not enough power can be a worse condition than too much power. 2x times the long term rating is a good rule to follow.
Bob,
The guy plugged a 1/4" cable right into the speaker input on the back of the speaker, then contacted the tip of the other end to the sleeve with the 9V poles. I later learned that you can test woofers that way, but never tweeters. I don't think they were blown at all when I brought them in (to return them) - I think this idiot did that.
I have them at the shop now.
The power thing - those PR-12 are getting 800 watts at 4 ohms, daisy-chained. I'm asking if it's safe to run them at 1/2 the amp level (400 watts?).
Thanks.
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The power thing - those PR-12 are getting 800 watts at 4 ohms, daisy-chained. I'm asking if it's safe to run them at 1/2 the amp level (400 watts?).
Thanks.
No, Bob L. is correct. You are sending enough power to generate 800 watts between TWO speakers, so they are getting 400 apiece. The "amp level" you are talking about actually just attenuates the input and does not limit the power output of the amp. No matter what you set the "amp level" at, you can still drive the amp to it's rated output and beyond if not careful.
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The power thing - those PR-12 are getting 800 watts at 4 ohms, daisy-chained.
No.. they aren't. The amp they're connected to is capable of delivering 800w but at -10db on the meters the speaker are only seeing 80w.
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Thanks guys. Pardon my ignorance. I'm just trying to get as much performance out of my liitle system without blowing anything up. ;D
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I had the PR12's in my dj rig with that same amp. 550 watts each in stereo 8ohms (crossed to subs at 90hz). I did drive them hard and had no issues at all. I know others have poo-pooed these cabs, but for the price and light weight, I found they're sound more than acceptable. I can see where using them for monitors might not engender the same love. Playing mp3's for a room full of drunks doesn't usually demand the same sq as a musician's monitor rig.
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The 400 watt power rating is for the entire speaker. However, the HF driver is rated at only 30 watts continuous. Under normal circumstances, the average power for musical programming has most of the energy in the lower frequencies. However, a quick high frequency feedback can deliver all of the amp's power to the HF driver. It doesn't take much for the HF driver to blow when that happens.
On the Peavey's, the protection circuit is usually a light bulb that begins to glow as the voltage increases. This is in a sense creating compression of the HF energy and can be quite audible. However, quick HF feedback will still blow the driver, and it's possible to blow the driver before the lamp goes in certain situations.
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Bob,
The guy plugged a 1/4" cable right into the speaker input on the back of the speaker, then contacted the tip of the other end to the sleeve with the 9V poles. I later learned that you can test woofers that way, but never tweeters. I don't think they were blown at all when I brought them in (to return them) - I think this idiot did that.
I have them at the shop now.
The power thing - those PR-12 are getting 800 watts at 4 ohms, daisy-chained. I'm asking if it's safe to run them at 1/2 the amp level (400 watts?).
Bob,
Running your amp at 1/2 level means you simply have more potential to clip your mixer and EQ, it does not limit the output power. 1/2 power is only a 3 dB reduction, start thinking in terms of dB and things will start making sense- it takes a 10 dB reduction (1/10th the power) to sound half as loud in the mid range where the HF driver operates.
The tweeter is protected by passive crossover which includes a capacitor which blocks DC battery current (and low frequency musical content), unless one flips the 9 volt over back and fourth, you won't even hear a "click" out of the tweeter assuming it or the protective light bulb are not blown.
A 9 volt battery (like you put in guitar pedals) used for a click test does not have enough current potential to blow out any PA compression driver, period. Even if it could deliver a full 9 volts (it can't) in to an 8 ohm load (9 x 9 =81/8), that would only be 10.1 watts.
Anyway, point the horns at your ears rather than your knees to avoid blowing the diaphragms or light bulbs after they are repaired ;).
Seriously, the picture you posted recently showed your mic (and therefore ear) position at least 6 dB off axis from your monitors, which requires 4 times the power to be heard at the same level if they were pointed at your ears. It's pretty easy to burn stuff up when you can't hear it.
Art
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Bob,
Running your amp at 1/2 level means you simply have more potential to clip your mixer and EQ, it does not limit the output power. 1/2 power is only a 3 dB reduction, start thinking in terms of dB and things will start making sense- it takes a 10 dB reduction (1/10th the power) to sound half as loud in the mid range where the HF driver operates.
The tweeter is protected by passive crossover which includes a capacitor which blocks DC battery current (and low frequency musical content), unless one flips the 9 volt over back and fourth, you won't even hear a "click" out of the tweeter assuming it or the protective light bulb are not blown.
A 9 volt battery (like you put in guitar pedals) used for a click test does not have enough current potential to blow out any PA compression driver, period. Even if it could deliver a full 9 volts (it can't) in to an 8 ohm load (9 x 9 =81/8), that would only be 10.1 watts.
Anyway, point the horns at your ears rather than your knees to avoid blowing the diaphragms or light bulbs after they are repaired ;).
Seriously, the picture you posted recently showed your mic (and therefore ear) position at least 6 dB off axis from your monitors, which requires 4 times the power to be heard at the same level if they were pointed at your ears. It's pretty easy to burn stuff up when you can't hear it.
Art
Thanks Art. I will be propping the monitors up next time. ;D
I still can't get my head around the "Running your amp at 1/2 level means you simply have more potential to clip your mixer and EQ, it does not limit the output power." thingy.
I'm so used to guitar amps, where the volume knob raises the level. So I should set my QSC higher to keep from clipping? I know this is common knowledge here and I'm being obtuse, but I just don't get it! >:(
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Thanks Art. I will be propping the monitors up next time. ;D
I still can't get my head around the "Running your amp at 1/2 level means you simply have more potential to clip your mixer and EQ, it does not limit the output power." thingy.
I'm so used to guitar amps, where the volume knob raises the level. So I should set my QSC higher to keep from clipping? I know this is common knowledge here and I'm being obtuse, but I just don't get it! >:(
Bob, the input level control on a power amp is an attenuator. When you turn it to the left, it increases the electrical resistance - the amp has the same output voltage potential, it will just take a hotter input signal to reach full output.
Guitar amps are different animals. You have control over actual gain at multiple stages within the amp. Power amps used in audio don't generally work that way.
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Seriously, the picture you posted recently showed your mic (and therefore ear) position at least 6 dB off axis from your monitors, which requires 4 times the power to be heard at the same level if they were pointed at your ears. It's pretty easy to burn stuff up when you can't hear it.
Never underestimate the power of even just a few degrees change in angle. I recently worked with a very diminutive female fiddle player who stood a few feet back from a monitor designed to be very close who went from politely repeatedly asking for her monitor to be turned up because it was shooting right over her head to "screaming" for us to turn it down when I place a 1" roll of console tape under the audience side.
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Thanks Tim. So, if my QSC is set at 12 O'clock (-10) it is putting out 1/2 of the rated power, regardless of the mixer output?
(http://i40.photobucket.com/albums/e222/DunnellonOnline/a3f0203f-b0dd-4f9b-9b4e-f6004add76b2.jpg) (http://s40.photobucket.com/user/DunnellonOnline/media/a3f0203f-b0dd-4f9b-9b4e-f6004add76b2.jpg.html)
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Never underestimate the power of even just a few degrees change in angle. I recently worked with a very diminutive female fiddle player who stood a few feet back from a monitor designed to be very close who went from politely repeatedly asking for her monitor to be turned up because it was shooting right over her head to "screaming" for us to turn it down when I place a 1" roll of console tape under the audience side.
Wow. I had no idea. I never knew monitors were that directional!
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Thanks Art. I will be propping the monitors up next time. ;D
I still can't get my head around the "Running your amp at 1/2 level means you simply have more potential to clip your mixer and EQ, it does not limit the output power." thingy.
I'm so used to guitar amps, where the volume knob raises the level. So I should set my QSC higher to keep from clipping? I know this is common knowledge here and I'm being obtuse, but I just don't get it! >:(
the setting on the volume knob on the amp has no affect on clipping. It is there to match the input of the amp with the output of whatever is driving the amp. The amp itself is at 100% at all times. If you turn the knob down on the amp, but turn the output up from the mixer, the music you hear remains the same. Just like if you were to turn your guitar amp down at the amp, but then turn the volume up on one of your pedals, the music is just as loud as before. A 1000 watt amps is a 1000 watt amp with the volume knob at 50% or at 100%. An amp can actually put out considerably more power than it's rating if you send it a hot enough signal(overdrive it), and that is where the danger is in tearing up speakers.
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the setting on the volume knob on the amp has no affect on clipping. It is there to match the input of the amp with the output of whatever is driving the amp. The amp itself is at 100% at all times. If you turn the knob down on the amp, but turn the output up from the mixer, the music you hear remains the same. Just like if you were to turn your guitar amp down at the amp, but then turn the volume up on one of your pedals, the music is just as loud as before. A 1000 watt amps is a 1000 watt amp with the volume knob at 50% or at 100%. An amp can actually put out considerably more power than it's rating if you send it a hot enough signal(overdrive it), and that is where the danger is in tearing up speakers.
David, I think it's starting to get into my thick head! I know it must be tedious for you guys answering these stupid questions, but this info is solid gold to me.
This is from the QSC manual - I didn't understand it before:
"The amplifier Gain control
should be in the upper half of its range to prevent input overload."
So I should be running my amp at 3 or 4 O'clock instead of 12? Or should I run it wide open and just keep my mixer from clipping? Which would result in the best sound?
Thanks.
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David, I think it's starting to get into my thick head! I know it must be tedious for you guys answering these stupid questions, but this info is solid gold to me.
This is from the QSC manual - I didn't understand it before:
"The amplifier Gain control
should be in the upper half of its range to prevent input overload."
So I should be running my amp at 3 or 4 O'clock instead of 12? Or should I run it wide open and just keep my mixer from clipping? Which would result in the best sound?
Thanks.
it's all a balancing act. The volume knob on the amp is to help balance everything. It's kinda like the problem that can happen on a mixer. You keep turning up separate channels until the overall level is too high, so then you back down the master. Before long all the channels are all the way up, and the master is all the way down, and all you hear is distortion. If anything in your signal chain is way high or way low, you might need to do some leveling. There is no correct setting for the volume control on the amp. If there was a correct setting, it would come set that way and there would be no knob. At any stage of your signal chain there is the possibility to overdrive and cause distortion. There are articles on balancing gain structure, but it isn't rocket science. An old rule of thumb was to have no channel fader higher than the master fader. Not a hard fast rule, but something to consider if anything anywhere is way high or way low.
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Thanks Tim. So, if my QSC is set at 12 O'clock (-10) it is putting out 1/2 of the rated power, regardless of the mixer output?
(http://i40.photobucket.com/albums/e222/DunnellonOnline/a3f0203f-b0dd-4f9b-9b4e-f6004add76b2.jpg) (http://s40.photobucket.com/user/DunnellonOnline/media/a3f0203f-b0dd-4f9b-9b4e-f6004add76b2.jpg.html)
No. It takes 10dB MORE signal to reach the same output voltage than if you had it wide open.
The knob DOES NOT CHANGE the amount of gain the amp has available (output voltage potential).
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Roger that. Thanks.
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Roger that. Thanks.
Post #13 may make more sense to you now, the input knobs attenuate by -10 dB (takes 10 times the input level to reach amp full power) at "noon", around 4 pm is -3 dB, where it takes double the input power to reach full output.
If you look at your console, you will see that it does not take much fader movement to equal those level changes. Start listening to the level changes as you move a fader or attenuator to get an idea of what is happening in terms of power.
Have Fun!
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Thanks Art and everyone who responded. I just had to unlearn some things I "knew". ;D
I'm getting much better sound now, and I owe it all to you guys.
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One feature of running the amp with the attenuators wide open is that someone cannot bump them up. Worse case is bumping down.
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One feature of running the amp with the attenuators wide open is that someone cannot bump them up. Worse case is bumping down.
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Rob,
I understand about bumping up, but I don't understand how bumping down is "worse".
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Because things will get quieter!
Steve.
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Rob,
I understand about bumping up, but I don't understand how bumping down is "worse".
He ment that if it get's "bumped down", the worse that can happen is it get's quiet.
Getting "bumped up" usually costs drivers.
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He ment that if it get's "bumped down", the worse that can happen is it get's quiet.
Getting "bumped up" usually costs drivers.
It could get worse than "just quieter" if the operator clips the board output trying to make up for the "quieter"....and introduces distortion into the equation. But no physical harm from bumping the amp down.
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Thanks for clearing that up guys.
My new mantra is:
I will not clip the board...I will not clip the board........ ;D