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Author Topic: pas 2-18 subs  (Read 14533 times)

Greg g. Pierce

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pas 2-18 subs
« on: January 23, 2012, 08:20:22 pm »

Hello all, I have bought a pa system with pas cabinets, a pair of 2 - 18s and a pair of 2-15s/ 2" high horns. I am having trouble with the 18s. In three different shows we are getting a different speaker making a brrraaap noise at high volume only on kick beats bass gtr. We can run an ipod through the system with volume allmost too loud to stand, with no noise, sounds good at lower volume. The subs are being powered by an xls802 ea. I have been told this amp is not supposed to be run at 4 ohms, which is how the cabs are wired. Ive also been told we should be hitting the subs with 2400 watts, the 802 doesn't even list output at 4 ohms, but I was told its 2100 watts. So, my question is do we have too little power, or is running the amp at 4 ohms causing problems with the speakers. I want to fix this problem right, if I have to get new amps, I just need to stop getting speaker problems. The speakers are b52's rated at 1000w. Also speakers, whole system is being processed with a driverack pa.
I know you probably need more info. Let me know whats needed, I am ready for a cure.

Thanks for any help in advance.
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Tim Weaver

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Re: pas 2-18 subs
« Reply #1 on: January 23, 2012, 10:03:13 pm »

Hello all, I have bought a pa system with pas cabinets, a pair of 2 - 18s and a pair of 2-15s/ 2" high horns. I am having trouble with the 18s. In three different shows we are getting a different speaker making a brrraaap noise at high volume only on kick beats bass gtr. We can run an ipod through the system with volume allmost too loud to stand, with no noise, sounds good at lower volume. The subs are being powered by an xls802 ea. I have been told this amp is not supposed to be run at 4 ohms, which is how the cabs are wired. Ive also been told we should be hitting the subs with 2400 watts, the 802 doesn't even list output at 4 ohms, but I was told its 2100 watts. So, my question is do we have too little power, or is running the amp at 4 ohms causing problems with the speakers. I want to fix this problem right, if I have to get new amps, I just need to stop getting speaker problems. The speakers are b52's rated at 1000w. Also speakers, whole system is being processed with a driverack pa.
I know you probably need more info. Let me know whats needed, I am ready for a cure.

Thanks for any help in advance.


The cone is bottoming out. An uncompressed kick drum hit is entirely different than playing music from an ipod.

What kind of crossover are you using? Does it have a selectable high pass filter on the subs? If it is adjustable roll it up a little higher until the noise goes away.


The PAS rig won't be found on anybodies wanted list, but is still pretty good kit.
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Greg g. Pierce

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Re: pas 2-18 subs
« Reply #2 on: January 23, 2012, 10:17:29 pm »

Tim,
Thanks not many people know what the pas cabs are. I know they are old and out dated, but so am I. We are not playing big arenas or anything. We are a progressive country group playing for free for Relay for life shows, raising money for them. But we still like to kick it.
The system has a Driverack PA prcessor with the crossovers set, it also has a compressor/limiter and a few other processors in it, I'm sure your familiar with it. I am just trying to learn how to set this stuff. I was hoping there wasnt anything wrong with the speakers. Maybe something in the settings. As I understand the drpa can be manually set for crossover points for low/high on lows mids and highs. What crossover points would you think I should go to, if this is even anything you can suggest.
And THANK YOU for your information, I've been reading until my eyes are sore.

The cone is bottoming out. An uncompressed kick drum hit is entirely different than playing music from an ipod.

What kind of crossover are you using? Does it have a selectable high pass filter on the subs? If it is adjustable roll it up a little higher until the noise goes away.


The PAS rig won't be found on anybodies wanted list, but is still pretty good kit.
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duane massey

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Re: pas 2-18 subs
« Reply #3 on: January 23, 2012, 11:04:15 pm »

The amps should not be run bridged into a 4ohm load.
http://www.crownaudio.com/pdf/amps/139440.pdf

Get 1 bigger amp (QSC RMX5050, Crown XTi6002, etc) and dial the DRPA to eliminate the possibility of over-excursion. Also, experiment with comp/limiters on kick and bass.
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Duane Massey
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Tim Weaver

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Re: pas 2-18 subs
« Reply #4 on: January 23, 2012, 11:34:52 pm »

Tim,
Thanks not many people know what the pas cabs are. I know they are old and out dated, but so am I. We are not playing big arenas or anything. We are a progressive country group playing for free for Relay for life shows, raising money for them. But we still like to kick it.
The system has a Driverack PA prcessor with the crossovers set, it also has a compressor/limiter and a few other processors in it, I'm sure your familiar with it. I am just trying to learn how to set this stuff. I was hoping there wasnt anything wrong with the speakers. Maybe something in the settings. As I understand the drpa can be manually set for crossover points for low/high on lows mids and highs. What crossover points would you think I should go to, if this is even anything you can suggest.
And THANK YOU for your information, I've been reading until my eyes are sore.

I would probably start by running a hi pass filter on the subs at around 30 hertz. an 18db butterworth should do it. Then for the sub to top crossover point do a 12 db LR (linkwitz-reilly) on the subs at around 80 hertz low pass.

On the tops run a 18db butterworth hi pass set to 100 hertz.

Lets start there and see what happens. If your subs are still bottoming out (brapp, or clacking noise) then slide the 30 hertz hi pass up until it quits making bad noises. To set your mind at ease, you probably haven't damaged anything yet, but don't make it a habit or you will break something!


BTW, If you get new amps, come on back here and we'll help you set the limiters too.
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Tim Weaver

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Re: pas 2-18 subs
« Reply #5 on: January 23, 2012, 11:36:07 pm »

I would probably start by running a hi pass filter on the subs at around 30 hertz. an 18db butterworth should do it. Then for the sub to top crossover point do a 12 db LR (linkwitz-reilly) on the subs at around 80 hertz low pass.

On the tops run a 18db butterworth hi pass set to 100 hertz.

Lets start there and see what happens. If your subs are still bottoming out (brapp, or clacking noise) then slide the 30 hertz hi pass up until it quits making bad noises. To set your mind at ease, you probably haven't damaged anything yet, but don't make it a habit or you will break something!


BTW, If you get new amps, come on back here and we'll help you set the limiters too.

One more thing I forgot. The DRPA has some kind of "sub synth" type of a deal. Make sure thats turned off. That crap will lunch your drivers pretty quick...
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Greg g. Pierce

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Re: pas 2-18 subs
« Reply #6 on: January 24, 2012, 08:24:49 am »

The amps should not be run bridged into a 4ohm load.
http://www.crownaudio.com/pdf/amps/139440.pdf

Get 1 bigger amp (QSC RMX5050, Crown XTi6002, etc) and dial the DRPA to eliminate the possibility of over-excursion. Also, experiment with comp/limiters on kick and bass.
Thanks Duane, I looked that same thing up last night. The guy I bought the system from apparently didn't know what he was doing, well.. neither do I.. but I seen that. So I think I am going to set the crossover as Tim has told me to do, and get by for a month or two, we only play twice a month, then be looking for some other amps. I will just move the 802's up in the rack to tack the place of the peavey and Carvin, or use them on monitors. This guy told me the amps could even be ran down to 2 ohms and would put out 2100 watts bridged.
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Greg g. Pierce

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Re: pas 2-18 subs
« Reply #7 on: January 24, 2012, 08:28:26 am »

I would probably start by running a hi pass filter on the subs at around 30 hertz. an 18db butterworth should do it. Then for the sub to top crossover point do a 12 db LR (linkwitz-reilly) on the subs at around 80 hertz low pass.

On the tops run a 18db butterworth hi pass set to 100 hertz.

Lets start there and see what happens. If your subs are still bottoming out (brapp, or clacking noise) then slide the 30 hertz hi pass up until it quits making bad noises. To set your mind at ease, you probably haven't damaged anything yet, but don't make it a habit or you will break something!


BTW, If you get new amps, come on back here and we'll help you set the limiters too.
Tim, thanks for the specifics, thats what I needed, I see in the drpa the settings for the hi pass and the butterworth and linkwitz-reilly, didn't know what they were, and still am confused but I can deffinitely set those, I did see the sub synth also, I don't remember if it's on or not but I will turn it off and set crossover as you suggest tonight, I will give you a report back as to what the results are. I do feel much better. I was worried this was some problem that I could never find and just keep blowing speakers or amps. Thanks for the help guys!
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Mark Long

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Re: pas 2-18 subs
« Reply #8 on: January 24, 2012, 09:14:00 am »

I would probably start by running a hi pass filter on the subs at around 30 hertz. an 18db butterworth should do it. Then for the sub to top crossover point do a 12 db LR (linkwitz-reilly) on the subs at around 80 hertz low pass.

On the tops run a 18db butterworth hi pass set to 100 hertz.

Tim, can you go into a little detail on your choice of filters? I'm trying to understand the pros and cons of mixing different filter types and slopes at the XO point. Thanks for your input on this board!
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Tim Weaver

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Re: pas 2-18 subs
« Reply #9 on: January 24, 2012, 11:09:44 am »

Tim, can you go into a little detail on your choice of filters? I'm trying to understand the pros and cons of mixing different filter types and slopes at the XO point. Thanks for your input on this board!

My choice of filters are purely a guess. Although it's an educated guess based on my 18 years of dealing with poorly maintained club systems like the one the OP has.

These filters are what I choose as a "starting point" when I'm faced with a situation like above. I choose lower order filters because there is less phase shift. Therefor you have a better chance of at least passable summation at the actual XO point.

I also spread the XO point out a little (80'ish for the subs, 100 ish for the tops) because most subs have a rising response as you get to the XO region. 100 hz can be 10-12 db hotter than 40 hz. Spreading the ELECTRICAL crossover apart means that you ACOUSTICAL crossover gets closer to being right. Remember, what you see on that little screen is not what is happening acoustically. The freq response of your cabinets means your cabs will not follow that little line perfectly.

If after a listen (I have specific tracks that will highlight the XO regions I pick) I don't like what I hear, I'll move the XO points up or down based on what I hear. You can also mute a cabinet one at a time (ie mute the subs, then the tops) to hear if that nastiness is produced by one cab or the other, or if the nasties are produced only by the combo together.

If your punchy kick drum isn't happening, try flipping polarity on subs or tops to see if it comes back.

If male singers sound too chesty, move the tops XO point up until it subsides.

If there's clacking in the subs from the cones bottoming out (over excursion) move the hi pass on the subs up, or change to a steeper slope.

Keep listening and tweaking until you like what you get!
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Re: pas 2-18 subs
« Reply #9 on: January 24, 2012, 11:09:44 am »


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