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Author Topic: Restoring old peecker sound PA equipment. Need help.  (Read 7745 times)

Eugen Jeličić

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Re: Restoring old peecker sound PA equipment. Need help.
« Reply #10 on: August 16, 2014, 02:17:26 pm »

550 real watts is probably plenty for that type of speaker. Xmax is only 4.5mm, so if you see the cone move more than 9mm peak to peak (only 3/8 inch), it is exceeding it's linear range, more power would just increase distortion.

Doubling Xmax allows 6 dB more output (but also requires at least 6 dB more power), the better Italian PA woofers are now in the 15mm Xmax range, and there are some woofers with even double that Xmax now!

Well to be honest when i ran them at the amps maximum of 550w they worked very well. Sounded fantastic. Nice, warm, powerfull but still precise and punchy. So the reality is it's probably not worth forcing them more then that. If the drivers we are talking about are L18 P540's. And that's the only part i'm still not sure about. Because if they are not there are a few RCF drivers that look the same like mine but have 700w RMS handling capacity and 1400 program. And if i have one of those drivers then it's worth getting a more powerfull amp. But i can't believe it's so hard to indentify a driver :/

One more question. I'm a 100% sure that 12's in my mid-hi speakers are RCF L12-544K. They have a RMS handling capacity of 300w and AES handling capacity of 400w. That means i can feel safe running them under a 450w load? Because in the case of connecting 2 of those in parralel on one of my big amps each one would be able to get 450w if i push the amp to it's max. Those drivers should be able to take that power right?
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Art Welter

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Re: Restoring old peecker sound PA equipment. Need help.
« Reply #11 on: August 16, 2014, 03:50:39 pm »

I'm a 100% sure that 12's in my mid-hi speakers are RCF L12-544K. They have a RMS handling capacity of 300w and AES handling capacity of 400w. That means i can feel safe running them under a 450w load?
Eugen,

The speaker presents a "load" to the amp. The amp can deliver more power than it's rating if clipped in to that load, as much as double if hard clipped.
The older AES signal used in the RCF rating has a 6 dB crest factor, which is less than most music, which generally has more like 12 dB crest factor (which is the crest factor in the new AES signal  :'().  Assuming you are not clipping the amp, and not running unusually compressed music, 450 watt peaks will not be a problem at all, as the average power the load must dissipate is probably only 1/10th that around 45 watts.

That said, with some electronic dance music, the crest factor below 100 Hz may be as little as 3 dB, same as a sine wave- with that type of signal the AES rating could be more than the woofer may handle.

Art
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Eugen Jeličić

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Re: Restoring old peecker sound PA equipment. Need help.
« Reply #12 on: August 16, 2014, 04:11:51 pm »

Eugen,

The speaker presents a "load" to the amp. The amp can deliver more power than it's rating if clipped in to that load, as much as double if hard clipped.
The older AES signal used in the RCF rating has a 6 dB crest factor, which is less than most music, which generally has more like 12 dB crest factor (which is the crest factor in the new AES signal  :'().  Assuming you are not clipping the amp, and not running unusually compressed music, 450 watt peaks will not be a problem at all, as the average power the load must dissipate is probably only 1/10th that around 45 watts.

That said, with some electronic dance music, the crest factor below 100 Hz may be as little as 3 dB, same as a sine wave- with that type of signal the AES rating could be more than the woofer may handle.

Art

So crest factor is basically saying how much louder are the peaks in comparison with the song's average right? So by the new AES rating the 544K would be rated as an even more powerfull speaker?

So i'm going to rent my system in in about 14 days. I allready made a deal. I found a missing module for my amp so the system i'm going to be bringing is:

4x900w @4ohm (about 550 @ 8ohm) + 4x500 @4 ohm (about 300 @ 8 ohm) 

Those amps are going to be running my 4 woofers and 2 (12 + horn) RCF speakers.
I was thinking about the best way to hook it all up and i'm really not sure. I might connect my 4 woofers directly to big amps so they can get up to 550w (they are 8 ohm speakers) because i know they work fantastic with that power. Since i don't know witch exact RCF drivers they are i don't want to take any risks.
And then connect each 12+horn speaker to my 2x500 amp in bridge mode. So in birdge it's a 1000w @ 8ohm amp. Witch means it can give my 12+horn speakers up to a 1000w. I would then put those amps at 45% power and leave it like that. Do you think that is the best solution?
« Last Edit: August 16, 2014, 04:14:17 pm by Eugen Jeličić »
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Art Welter

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Re: Restoring old peecker sound PA equipment. Need help.
« Reply #13 on: August 16, 2014, 04:59:42 pm »

1)So crest factor is basically saying how much louder are the peaks in comparison with the song's average right?
2) So by the new AES rating the 544K would be rated as an even more powerfull speaker?
3) I would then put those amps at 45% power and leave it like that. Do you think that is the best solution?
1) Yes.
2) Yes.
3) A 50% reduction is -3dB. Reducing the amp input does nothing to protect speakers, one simply can turn up the source by +3dB (note how little a change that is on a fader) and the amp puts out the same power. Turning down the amps also makes it easier to clip the system upstream, which can tend to roast HF drivers, as clipping increases upper harmonics.

Short of having limiters that have separate peak and RMS settings set specifically for the driver's capabilities, the only safe solution is turning down the source material if you see any clipping. And as mentioned before, with the right (or wrong) type of music, even without clipping, your amps potentially have enough power to fry the sub's voice coils.

Dance music has changed since 1997...
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Eugen Jeličić

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Re: Restoring old peecker sound PA equipment. Need help.
« Reply #14 on: August 16, 2014, 09:09:35 pm »

1) Yes.
2) Yes.
3) A 50% reduction is -3dB. Reducing the amp input does nothing to protect speakers, one simply can turn up the source by +3dB (note how little a change that is on a fader) and the amp puts out the same power. Turning down the amps also makes it easier to clip the system upstream, which can tend to roast HF drivers, as clipping increases upper harmonics.

Short of having limiters that have separate peak and RMS settings set specifically for the driver's capabilities, the only safe solution is turning down the source material if you see any clipping. And as mentioned before, with the right (or wrong) type of music, even without clipping, your amps potentially have enough power to fry the sub's voice coils.

Dance music has changed since 1997...

When i sayed 45% i meant. I put my woofer amps at the max output and the mid-hi amps at 45% and then WATCH the signal. Of course if the signal hits +3dB i might fry my 12's but that should not happen.
Basically i want to use the system as much as i can. It's going to be in a closed club full of people. And there is going to be a DJ playing comercial electronic music. I'm going to need as much power as i can get.

EDIT: I'm going to be there watching the system all the time and the DJ is going to be plugged into my mixer so i have tone control. In case i see clipping i can turn down fast. The problem is.If i conenct my 2x 12+horn speakers into my 2x500 amps (bridge) the amp is going to be capable of outputing 1000w into each speaker before it clips. So clipping is not the problem i might have. The danger i want to avoid is destroying my speakers by giving them too much healthy power. If they are 300w RMS rated by the old standard. Lets say that is 800w program power by todays standard. (And that's optimistic) they won't be able to handle that much or more.

Let me put it this way. Let's say i'm connecting those speakers to an amp that can putput 3000w into an 8ohm speaker. I want the amp to give them about 450w. Maybe a little more at the peaks but that's it. Amp clipping is not what i'm going to be afraid of in that case. But overpowering the speaker is going to be a fear. How do i solve this?
« Last Edit: August 16, 2014, 09:15:06 pm by Eugen Jeličić »
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Art Welter

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Re: Restoring old peecker sound PA equipment. Need help.
« Reply #15 on: August 17, 2014, 05:05:28 pm »

But overpowering the speaker is going to be a fear. How do i solve this?
Alcohol can be used to overcome fears ;^).
Limiters that have separate peak and RMS settings set specifically for the driver's capabilities can eliminate their being overpowered.
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Eugen Jeličić

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Re: Restoring old peecker sound PA equipment. Need help.
« Reply #16 on: August 18, 2014, 10:39:41 am »

Alcohol can be used to overcome fears ;^).
Limiters that have separate peak and RMS settings set specifically for the driver's capabilities can eliminate their being overpowered.

So there is no way to know when i'm going to blow my speaker with too much power other then listening to it and praying for the voicecoil no to melt?
Considering i don't have those types of limiters.
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Art Welter

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Re: Restoring old peecker sound PA equipment. Need help.
« Reply #17 on: August 18, 2014, 01:33:04 pm »

So there is no way to know when i'm going to blow my speaker with too much power other then listening to it and praying for the voicecoil no to melt?
With experience, you can learn to recognize distortion, which generally precedes blown drivers by a good margin, though it may be hard to recognize when playing music which already has a lot of distortion in the recording. Comparing the output of good isolation headphones at a lower level to the speaker sound makes it easier to hear if the speakers are being overdriven.

Drivers also tend to suffer thermal compression, as the voice coils heat up, their impedance rises, and amps deliver less power in to a higher impedance.
If you notice increases in mixer level don't result in similar SPL increases, it means the voice coils are getting hot, and when too hot for too long, they burn.
An SPL meter is helpful, if you know the system can only do "X" clean  level when it's cool, don't expect it to do any more when it's hot. You can switch between "A" and "C" (or flat) scale to see whether the level above 1000 Hz is increasing more than below.

Unfortunately, DJs  often start out near "full tilt" and then try to increase the level from there, as their hearing threshold goes up, the speakers are capable of progressively less output, which is why re-cone companies stay in business  ;).


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Eugen Jeličić

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Re: Restoring old peecker sound PA equipment. Need help.
« Reply #18 on: August 18, 2014, 02:24:19 pm »

With experience, you can learn to recognize distortion, which generally precedes blown drivers by a good margin, though it may be hard to recognize when playing music which already has a lot of distortion in the recording. Comparing the output of good isolation headphones at a lower level to the speaker sound makes it easier to hear if the speakers are being overdriven.

Drivers also tend to suffer thermal compression, as the voice coils heat up, their impedance rises, and amps deliver less power in to a higher impedance.
If you notice increases in mixer level don't result in similar SPL increases, it means the voice coils are getting hot, and when too hot for too long, they burn.
An SPL meter is helpful, if you know the system can only do "X" clean  level when it's cool, don't expect it to do any more when it's hot. You can switch between "A" and "C" (or flat) scale to see whether the level above 1000 Hz is increasing more than below.

Unfortunately, DJs  often start out near "full tilt" and then try to increase the level from there, as their hearing threshold goes up, the speakers are capable of progressively less output, which is why re-cone companies stay in business  ;).

Well thet is some very usefull info there :) Thank you very much.
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