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Author Topic: Basic PA Setup Questons  (Read 428 times)

Mark Monson

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Basic PA Setup Questons
« on: December 07, 2018, 04:00:01 pm »

Following advice received in this forum, my band has just purchased a dbx venue 360 and M32 mixer.  I want to set up our system right and I have a few basic questions.  We are running a tri-amp system with Peavey QW4 over JTR orbit shifters.

1.  I read online that the QW4 should be crossed over at 1.6K,  but it sounds better when I set it at 1.2K as is the internal passive X-over.  The subs are x-over at 100hz.  Am I correct going with my ears?  The RTA made greater corrections when it was crossed at 1.6K, than when it was crossed at 1.2k.
2.  The subharmonic synth sounds good with recorded music, but it makes live sound muddy.  Any suggestions on improving sound, or should I not use it?
3.  Should I use the time delay?  Peavey says 0 highs,  0.34 lows, I can't find the JTR number on the website, but another thread said 0.6ms
4.  I have read that after using the RTA to flatten the response curve, I should set the EQ on the DSP by listening to recorded music and setting to taste.  It sounds best when I modify the DJ setting.  Should I do this on the DSP or with the LR EQ on the M32?

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Mal Brown

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Re: Basic PA Setup Questons
« Reply #1 on: December 07, 2018, 07:01:13 pm »

The OS is a horn of some length (which I do not know...). The other bands need to be delayed by something like 1ms per foot horn length to compensate.

As far as the 1.2 vs 1.6 goes, maybe you should hit the rig with smart ?
« Last Edit: December 08, 2018, 06:35:56 pm by Mal Brown »
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Fb Gorge Sound and Light
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Tim Halligan

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Re: Basic PA Setup Questons
« Reply #2 on: December 07, 2018, 07:14:14 pm »

I like the Dave Rat method - although it's not proprietary...most mixers would follow the same steps.

Look, learn, and inwardly digest: https://www.youtube.com/watch?v=cU9BmupC62c

If nothing else, bypass the subharmonic synth.

Additionally, if someone offers to sell you a Sonic Maximiser - shoot them.

If you actually buy a Sonic Maximiser - shoot yourself.

Cheers,
Tim
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Jeremy Young

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Re: Basic PA Setup Questons
« Reply #3 on: December 07, 2018, 07:37:13 pm »

The JTR Orbit Shifter Pro has a 9' long horn path, so presuming the cabinets are in roughly the same vertical domain you'd need to delay the mid/highs somewhere around 8ms and you may or may not need to invert the polarity for maximum summation in the crossover range.

Crossing over the horn in a cabinet at a lower frequency may sound good at low levels, but it also means you're asking the diaphragm to move more (excursion) to handle those lower frequencies and it might not sound very nice (distortion) when you get to "full tilt boogie".  A worst case scenario is that the diaphragms can bottom out against the phase plug and suffer catastrophic failure. 

However, if that's the frequency used in the factory crossover it's probably not too dangerous for the driver but we don't know what slope that passive crossover  network is at below that frequency, nor what the slope of your driverack crossover is.  Even with the same crossover starting frequency, different slopes will allow varying amounts of energy below that frequency into the driver.  Remember to think of it as more than just the crossover number, but the entire response even out-of-band. 

How loud were your tests when you determined that it sounded better with a lower crossover frequency?

Unless there will never be an open microphone on any of your channels, don't use the subharmonic synthesizer.  It might sound OK as an insert on a playback channel, but it sounds very unnatural on a voice and since it's in your system processor you can't control which channels are affected by it.  I'm not sure why DBX still puts those in there... maybe their marketing team is paid by the number of bullet point features a product has?  Just kidding, sort of.

Don't forget to walk around when critical listening.  Sometimes you can go quite far down the rabbit hole trying to get perfect response in one location on-axis but it might sound worse off-axis.  Play some music, walk behind the rig and around, crouch down low and stand up high.  Any changes you make, try to A/B them from multiple listening positions.  Also try not to listen to the same album or producer exclusively or you might just be adjusting for what they heard on their studio monitors if your taste is different than theirs.

Good luck with the new rig!
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Douglas R. Allen

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Re: Basic PA Setup Questons
« Reply #4 on: December 08, 2018, 04:01:38 pm »

Following advice received in this forum, my band has just purchased a dbx venue 360 and M32 mixer.  I want to set up our system right and I have a few basic questions.  We are running a tri-amp system with Peavey QW4 over JTR orbit shifters.

1.  I read online that the QW4 should be crossed over at 1.6K,  but it sounds better when I set it at 1.2K as is the internal passive X-over.  The subs are x-over at 100hz.  Am I correct going with my ears?  The RTA made greater corrections when it was crossed at 1.6K, than when it was crossed at 1.2k.
2.  The subharmonic synth sounds good with recorded music, but it makes live sound muddy.  Any suggestions on improving sound, or should I not use it?
3.  Should I use the time delay?  Peavey says 0 highs,  0.34 lows, I can't find the JTR number on the website, but another thread said 0.6ms
4.  I have read that after using the RTA to flatten the response curve, I should set the EQ on the DSP by listening to recorded music and setting to taste.  It sounds best when I modify the DJ setting.  Should I do this on the DSP or with the LR EQ on the M32?

It could be the 1.2k lower passive crossover point is to roll off more high end information making it to the woofers than bringing more low end into the horns frequency range.  A passive crossover may simply let too much high end into the woofers so in the passive one they dropped the crossover point down some to accounted for that.  More than likely there is some padding and passive EQ in the passive horn section that may roll more low end out of the horn than one may think. An active crossover may take more of the highs out so this 1.6k crossover point could very well be correct. The QW4 has a 44xt horn driver if I remember right so it is pretty robust. I had a QW1 system and I seem to remember a 1.2k crossover point with the 44xt horn but I'll have to look around to be sure.
   In auto eq systems a lot of eq around rgw crossover point could be the eq trying to correct time alignment problems between the horn and woofer. I used to see a big boost just below the crossover frequency and a big cut above it. ( or the reverse , it depends )  The higher you go in frequency the smaller the wavelength and more the woofer handles the upper range. With the woofer being out .34ms I could see this to some degree. The longer the wavelength the easier it is to get 2 drivers within a 1/4 wavelength or closer. Set your crossover point to 1.6k.  Do a auto eq. Then add the .34ms of delay to the woofer section and do it again. Do you notice less eq changes going on now?  Without proper delay the bad sound you hear may be the misalignment between horn and woofer. Also your levels you set between the woofer and horn may be off some.  In a 3 way system and no proper system to set levels ( like smaart ) I always run the subs first. Then bring in the mids and last the horns with music I know well.  In the passive crossover they did as best as they could to blend the drivers in the box. If the horns are a little loud in your triamp setup you may be just annoyed with the horn "sound" more than the crossover point.

I wanted to add that the QW4 , if I remember right , uses CD type horns. CD Horn eq is required in the horns bandpass to make them "sound" right. Be sure to use the correct CD horn eq type in your horn section when your triamping or the horns will sound very bad....

Kindest Regards;
Douglas R. Allen
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Douglas R. Allen

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Re: Basic PA Setup Questons
« Reply #5 on: December 08, 2018, 04:18:41 pm »

Following advice received in this forum, my band has just purchased a dbx venue 360 and M32 mixer.  I want to set up our system right and I have a few basic questions.  We are running a tri-amp system with Peavey QW4 over JTR orbit shifters.

1.  I read online that the QW4 should be crossed over at 1.6K,  but it sounds better when I set it at 1.2K as is the internal passive X-over.  The subs are x-over at 100hz.  Am I correct going with my ears?  The RTA made greater corrections when it was crossed at 1.6K, than when it was crossed at 1.2k.
2.  The subharmonic synth sounds good with recorded music, but it makes live sound muddy.  Any suggestions on improving sound, or should I not use it?
3.  Should I use the time delay?  Peavey says 0 highs,  0.34 lows, I can't find the JTR number on the website, but another thread said 0.6ms
4.  I have read that after using the RTA to flatten the response curve, I should set the EQ on the DSP by listening to recorded music and setting to taste.  It sounds best when I modify the DJ setting.  Should I do this on the DSP or with the LR EQ on the M32?

Cd horn eq primer.   https://peavey.com/support/technotes/processors/crossover101_c.cfm

Douglas R. Allen
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Don Boomer

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Re: Basic PA Setup Questons
« Reply #6 on: December 08, 2018, 06:37:53 pm »

As part of the team that created the factory presets for the Peavey dsp, I would recommend trying to duplicate the factory numbers as closly as possible. Remember, those values are for the electrical part of the crossover and when added to the actual speaker box create an acoustical crossover that may not seem to directly relate to those values. Donít count on your ears to roll your own as you will likely not get the best performance from the box.

ThAt said, QW4s were designed to be used without a subwoofer. Crossing to a sub at 100 Hz essentially means one of the 15Ē woofers is essentially not being used so you are effectively dragging around  dead woofer. A better way to go for most users would be to use the subs in aux fed configuration.   https://peavey.com/support/technotes/concepts/AUX_SUBs.pdf

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Don Boomer
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