VSX Software

A forum for discussing the VSX and share settings
simplicity
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Re: VSX Software

Post by simplicity » Tue Apr 07, 2015 1:18 pm

Thanks Marty, that paper on programming a QW system was absolutely informative. Some of the principles I already knew of and some were totally new however, I've never done much design of that depth but I want to learn more for sure.

Not to sidetrack but I have a question regarding my old SP system that lends itself to this discussion if you don't mind.

You spoke of the generalization of "factory presets" and how they are a good starting point but not the end all be all, I agree.

My system is SP2G's over matching era SP118's. I downloaded the SP2/SP118 preset for my VSX and I've come to the conclusion that the preset is for a newer version of the SP series. My SP118 manual has a -3dB point of 48Hz and a -10dB point of 38Hz with a box tuning of 36Hz.

The sub is powered by a QSC PLX 3402 rated for 700 watts at 8 ohms, my subs are rated for 350/700/1700. I have the limiters set, but that's another post to be sure they're right.

The Peavey preset for the SP2/SP118 shows a low corner frequency of 40Hz Bes 24 and the upper corner at 135Hz LR 24. The PEQ shows 4.5dB boost at 80Hz with a Q of .7 and 3.5dB boost at 120Hz Q .6.

With those settings and limiters set, I hear the coils bottoming out before the system is even pushed, unless I'm missing something, I believe the low corner is just too low, correct?

Here's a question specifically relating to your paper, is this true for ALL Bessel filters "For our purposes the Bessel
filters have been “normalized” for the X-Over frequency to be defined as the -3 dB down points"
or just for that teaching exercise?

The Peavey preset says to use a Bes24 low corner filter, so therefore if the Bessel filters are defined as the low corner at the -3dB point, my VSX setting should be 45Hz correct?

Also the PEQ suggestions have me baffled a bit, especially after reading your paper. If we look at the amplitude response published of my SP118, it shows fairly flat from approximately 65Hz to 95Hz with a deep slope sub 60Hz. The highest amplitude looks to be around 80Hz but then the preset is also boosting 80Hz by 4.5dB. Again, I don't have a SMAART rig and just looking at the information and listening to the system, I'm certain the preset is for a different version of the SP series, no biggie.

I've found, over the years, that my subs sound best crossed over much lower than the 135Hz preset, typically I cross them over around 90 Hz so from there to 60Hz or so I'm showing a fairly flat measurement, as per the manual.

Ok all that to ask, can 8Hz be that big of a difference in a X-over point? I'm assuming so and that's probably the reason I'm hearing them bottom out without really being pushed.

Can the big 80Hz boost also be causing them to bottom out since my subs already peak at 80Hz?

Thanks Marty, I always appreciate you taking toe time to share the knowledge. Seems the more I learn the more questions I have...

One last thing, can you check my math for my sub limiter settings? With the result I got, my subs are over driven far before the limiter threshold it sounds.

here's my math:
20log (((SQRT(Watts x Resistance))/Gain)/.775)
20log (((SQRT(350 x 8 ))/40/).775)
20log((SQRT(2800)/40/).775)
20log((52.915)/40)/.775)
20log((1.323)/.775)
20log(1.71)
4.65

So according to the math, assuming it's correct my limiter should be set to start engaging at 4.65dB input. Ok that's fine except by the time they engage I'm bottoming out the driver and the clip light on the 3402 is lighting. That's putting music thru a board and the main outs just tickling the 0dB light.

I've found that to keep the subs from distorting and bottoming out my limiter needs to be set at -4dB.

So here are the questions I have regarding the setting of the limiters.

1. When RMS limiters are set (properly) should you see the clip light on the amps if you're staying under 0dB on the board and the channel isn't above 0dB as well?
2. Am I misinterpreting the math and the 4.65 number means a reduction in gain rather than the actual dB setting? My VSX says it has +24dBu outputs so I'm taking the math I've done to represent the actual output level rather than a reduction of 4.65dB, is that correct thinking?
3. Is my math correct?

Thanks. I know I'm sporadic on here but being a freelance guy, I get on everybody else's gear and don't get much opportunity to really dive into tuning s system and I'll learn from the help of many of you all, including Semperfi Steve, but then it'll be a long time until I can use it and I tend to forget or need more gaps filled in with my knowledge.
Allen D.

Marty McCann
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Joined: Mon Oct 27, 2008 3:50 pm

Re: VSX Software

Post by Marty McCann » Tue Apr 14, 2015 1:04 am

Hello,

I have just spent a week at the Ground Zero Blues Club here in Clarksdale Mississippi (93 hours in 8 days). So I am brain exhausted. If I don't answer by say Wednesday, send it again as a PM. I will answer and repost it.

Time for bed after I type up my work invoice.

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