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[Paul G. OBrien]

1. I see it's showing on the bottom right that the box tuning is 41.68 but my sub is tuned to 36 per the manual?

Well... I thought I read in your earlier thread about upgrading these boxes that the port was 8" diameter and 4.5" long.. was that right? And I think we figured the box was about 7.5cu ft internal after factoring in the volume displaced by the port, driver, and the foam cube?

2. I looked at your filters and see you have a high pass set at 37Hz with a BW 24? These subs were bottoming out before hitting the limiters with a low corner of 45Hz, will flattening the 80Hz and 120Hz bumps, which aren't necessary it seems, keep them from bottoming out while I boost the 40Hz you did?

Yes get rid of those boosts and definitely put in a low cut filter, again I have to point you back to the earlier graph showing cone excursion, it is at a maximum right around 60-70hz so it is those frequencies not the lower tones near box tuning that will cause the most cone deflection. You can see this yourself with a tone generator, drive the subs with a relatively low signal level and watch the cone move.

I really wish I had a SMAART system to measure this system as I'm positive that the peavey preset is for a newer version of the SP series.

  Do you have a measurement mic? If so download a copy of REW(free) and do some measurements.. http://www.roomeqwizard.com/

I moved the X-Over point to 95Hz for the sub, they've always sounded better there, to me, than higher. That also takes the 120Hz bump out of the equation, well mostly. What I found interesting is even with the 95Hz X-Over point and the tops muted, when I put a 250Hz sine wave thru the system, it's still fairly audible in the subs? The upper X-Over slope is a LR24, shouldn't that be all but killing the 250Hz tone? Isn't 250Hz an octave and a half higher than 95Hz? If that's correct then the signal reduction should be near 36dB an octave and a half higher, correct? The more I learn, the more I have questions...

Yeah I have a set of powered subs with a non adjustable 120hz crossover and they sound a bit muddy, I definitely like them better when externally processed with a 80-90hz crossover. And yeah with the tops muted you will hear lots of content well outside the passband, these filters aren't brick walls but that is OK.. don't let that bother you too much.. steeper filters have their pitfalls too.

[chuck clark]

Hi Allen!  Your in good company- Einstein once said "the larger the island of knowledge -the longer the shoreline of wonder."

If I recall from lots of experimenting in the eighties with a huge "Pile O Peavey" PA  we settled on a ratio of at least 2 subs for each top. 3 is even better if you like big low end, so you need to get another pair of subs.
   The 250 hz thing I've noticed also. Think "loudness curves". The fact is, as much as engineers like to talk about "flat" response, the human ear is not flat at all.  We are much more sensitive to 250 hz than 90 hz so even though it is many db down in response it will still appear to be there if other program material is not present to "mask" it.  uh-oh, there's ANOTHER fact about human hearing that lots of "soundguys" are oblivious to. 
  So:  1. your intuitive setting of the limiter just below the clip point of the amps is correct no matter what the charts say.  2. I always found the lower xover point to sound better also. In fact I've gone even lower to 80 hz. The SP-2 tops will handle down to 60 hz pretty well so no issues there.  3. Yes, flatten those bumps in eq @ 80 and 120.  In fact I've had a 6db dip at 120 really help in cleaning up a "bonky" sounding kick drum before.  4. Theory is the best place to start but good sounding results trumps theory no matter how many questions it raises or how many times it sends the engineers back to the drawing board. Lol  5. lastly, as an almost exact copy of a Crest amp the GPS is indeed a wonderful amp, but the PLX 3402 is no slouch either. I would expect any differences between the two (other than weight) to be nit picking.
Have a super day!
Chuck

[AllenDeneau]

Well... I thought I read in your earlier thread about upgrading these boxes that the port was 8" diameter and 4.5" long.. was that right? And I think we figured the box was about 7.5cu ft internal after factoring in the volume displaced by the port, driver, and the foam cube?

It was discussed but I didn't do it. I don't get to use this system much so I couldn't see spending the money to upgrade them yet. I'd love to explore it again though, the biggest issue I have is truly understanding what's happening within them and knowing what to do and what not to do. The subs are completely stock currently.

Yes get rid of those boosts and definitely put in a low cut filter, again I have to point you back to the earlier graph showing cone excursion, it is at a maximum right around 60-70hz so it is those frequencies not the lower tones near box tuning that will cause the most cone deflection. You can see this yourself with a tone generator, drive the subs with a relatively low signal level and watch the cone move.

I did kill those boosts. Will your boost and high pass filter suggestion stay the same with a different box tuning frequency? With the Peavey VSX I have a HPF 6 and a HPF 12 with Q adjustment. I have the VSX GUI interface but I've been warned that what the software shows is not always completely accurate, a reason for them abandoning it. Anyway, I set the HPF12 at 40Hz with a Q of .75 and it shows my -6dB is right at 30Hz, I'm thinking I need to move it up a bit? It seems that all the boosting is happening below my -10dB point of 38Hz, is that correct?

 

Do you have a measurement mic? If so download a copy of REW(free) and do some measurements.. http://www.roomeqwizard.com/

Sadly no, I sold it with my DRPA and never replaced it. Need to soon.

Yeah I have a set of powered subs with a non adjustable 120hz crossover and they sound a bit muddy, I definitely like them better when externally processed with a 80-90hz crossover. And yeah with the tops muted you will hear lots of content well outside the passband, these filters aren't brick walls but that is OK.. don't let that bother you too much.. steeper filters have their pitfalls too.

I guess I never really paid any attention to it before, weird. Would there be any benefit or protection offered if I added a LPF to the subs passband?

[AllenDeneau]

Hi Allen!  Your in good company- Einstein once said "the larger the island of knowledge -the longer the shoreline of wonder."

If I recall from lots of experimenting in the eighties with a huge "Pile O Peavey" PA  we settled on a ratio of at least 2 subs for each top. 3 is even better if you like big low end, so you need to get another pair of subs.
   The 250 hz thing I've noticed also. Think "loudness curves". The fact is, as much as engineers like to talk about "flat" response, the human ear is not flat at all.  We are much more sensitive to 250 hz than 90 hz so even though it is many db down in response it will still appear to be there if other program material is not present to "mask" it.  uh-oh, there's ANOTHER fact about human hearing that lots of "soundguys" are oblivious to. 
  So:  1. your intuitive setting of the limiter just below the clip point of the amps is correct no matter what the charts say.  2. I always found the lower xover point to sound better also. In fact I've gone even lower to 80 hz. The SP-2 tops will handle down to 60 hz pretty well so no issues there.  3. Yes, flatten those bumps in eq @ 80 and 120.  In fact I've had a 6db dip at 120 really help in cleaning up a "bonky" sounding kick drum before.  4. Theory is the best place to start but good sounding results trumps theory no matter how many questions it raises or how many times it sends the engineers back to the drawing board. Lol  5. lastly, as an almost exact copy of a Crest amp the GPS is indeed a wonderful amp, but the PLX 3402 is no slouch either. I would expect any differences between the two (other than weight) to be nit picking.
Have a super day!
Chuck

Hi Chuck, thanks for the response. Wish I could speak as eloquently as Einstein.

Yeah I agree that it takes a big low to high ratio with these for sure. I do own 6 of these subs fortunately.

Yeah the 250 thing was weird but none the less, a learning opportunity.

Can you talk more about the limiters? It sure seems my subs are coming apart far before reaching the limiter threshold. Is my math correct? I believe it is but mistakes can easily happen.

I too have run these with a much lower x-over point and liked it, I was really just trying to give the preset a chance to see if it sounded better or worse than what I dialed in before. The biggest problem with dropping my x-over point any lower right now is, I run out of eq filters to smooth out the SP2. I'm currently running the system bi-amped and with each passband I only have 5 filters. To get the horns smooth and the boxiness out of the SP2 I've used all 5, very creatively I must add, lol.

Yeah, the 100-160 area can so quickly just get overwhelming IMO.

I don't mind the practice and going back to the drawing board as long as I'm actually learning along the way and not just taking stabs in the dark.

I really did love those GPS amps, everything but the weight. I didn't think it's the PLX causing the issue, unless I run it into clipping. Maybe this is all just due to my ear being refined over the years with bigger and more capable systems I'm hearing and working with.

Any more insight you can offer would be much appreciated.

Thanks.

[Paul G. OBrien]

Will your boost and high pass filter suggestion stay the same with a different box tuning frequency?

The net internal box volume and port dimensions determine the box tuning so yeah the processing will be different if we aren't using the correct figures for the calculations.

I set the HPF12 at 40Hz with a Q of .75 and it shows my -6dB is right at 30Hz, I'm thinking I need to move it up a bit? It seems that all the boosting is happening below my -10dB point of 38Hz, is that correct?

No it's centered at 40hz.
 

Would there be any benefit or protection offered if I added a LPF to the subs passband?

That is what the crossover does, it puts a lowpass on the subs and a highpass on the tops.

[AllenDeneau]

The net internal box volume and port dimensions determine the box tuning so yeah the processing will be different if we aren't using the correct figures for the calculations.

How close do you think I can get estimating by taking the physical dimensions of the box, subtracting .75" per side for material thickness? There's not a ton of bracing within the box if I recall correctly. It has a small upside down U shaped structure in the bottom to hold the speaker pole. Maybe these pics help?

No it's centered at 40hz.

Ok, still learning how all the math and science works, gets a bit confusing.

 

That is what the crossover does, it puts a lowpass on the subs and a highpass on the tops.

Right, I was just wondering if my subs could operate more efficiently if I added another LPF thru the EQ settings to help filter stray signal, kind of just thinking out loud really.

[Paul G. OBrien]

How close do you think I can get estimating by taking the physical dimensions of the box, subtracting .75" per side for material thickness?

That will do it but 30 seconds with a tape measure once the driver is out and you have the numbers you need.

Right, I was just wondering if my subs could operate more efficiently if I added another LPF thru the EQ settings to help filter stray signal, kind of just thinking out loud really.

No.. it'll just mess up phase at the crossover, the fewer number of filters you can use to do a job the better in that regard.

[chuck clark]

Hi Chuck, thanks for the response. Wish I could speak as eloquently as Einstein.

Yeah I agree that it takes a big low to high ratio with these for sure. I do own 6 of these subs fortunately.

Yeah the 250 thing was weird but none the less, a learning opportunity.

Can you talk more about the limiters? It sure seems my subs are coming apart far before reaching the limiter threshold. Is my math correct? I believe it is but mistakes can easily happen.

I too have run these with a much lower x-over point and liked it, I was really just trying to give the preset a chance to see if it sounded better or worse than what I dialed in before. The biggest problem with dropping my x-over point any lower right now is, I run out of eq filters to smooth out the SP2. I'm currently running the system bi-amped and with each passband I only have 5 filters. To get the horns smooth and the boxiness out of the SP2 I've used all 5, very creatively I must add, lol.

Yeah, the 100-160 area can so quickly just get overwhelming IMO.

I don't mind the practice and going back to the drawing board as long as I'm actually learning along the way and not just taking stabs in the dark.

I really did love those GPS amps, everything but the weight. I didn't think it's the PLX causing the issue, unless I run it into clipping. Maybe this is all just due to my ear being refined over the years with bigger and more capable systems I'm hearing and working with.

Any more insight you can offer would be much appreciated.

Thanks.

If your subs are "coming apart" before hitting the limiter threshold they are most likely hitting the limits of their linear excursion.  Are you familiar w/ the theile small parameter -X-max?  Here's an interesting bit of info for you:  Since the area of the moving piston of the cone remains constant, the only way to reproduce lower (longer wavelength) tones at equal volume to higher (shorter wavelength) tones is through increased excursion. To reproduce equal volume an octave lower requires 4X the excursion for a given cone size. One reason bass reflex designs are so popular is they help limit this excursion by loading the pressure energy off the backside of the cone in with the pressure from the front side. This reaches it's peak effect at the tuned frequency of the box/port/driver unit. This additional cone excursion controlling output is welcome and sounds pretty great, but.....Warning!  Exactly 1 octave BELOW the tuned frequency that helpful back pressure wave is now 180 degrees out of phase and UNloads the cone allowing for crazy flopping back and forth and even bottoming of the voice coil against the backplate of the poor driver. Can you say major failure mode? Sure, I knew you could. Lol, thus the popularity and real necessity for a carefully set high pass filter about 1/2 octave below the tuned frequency of hard driven
bass reflex boxes.  Especially older relatively short x-maxx drivers like old Peavey speakers.  While Black Widows had a robust magnet/ voice coil assembly they were a bit late to the deep x-maxx thing.  So you might want to try a new set of lo-rider's which have about double the x-maxx of the old style Black Widows.
Hope this helps you out!
Chuck

[AllenDeneau]

That will do it but 30 seconds with a tape measure once the driver is out and you have the numbers you need.

True. I'll see if I can get into one sometime soon and get some numbers.

No.. it'll just mess up phase at the crossover, the fewer number of filters you can use to do a job the better in that regard.

Yeah, makes sense.

[AllenDeneau]

If your subs are "coming apart" before hitting the limiter threshold they are most likely hitting the limits of their linear excursion.  Are you familiar w/ the theile small parameter -X-max?  Here's an interesting bit of info for you:  Since the area of the moving piston of the cone remains constant, the only way to reproduce lower (longer wavelength) tones at equal volume to higher (shorter wavelength) tones is through increased excursion. To reproduce equal volume an octave lower requires 4X the excursion for a given cone size. One reason bass reflex designs are so popular is they help limit this excursion by loading the pressure energy off the backside of the cone in with the pressure from the front side. This reaches it's peak effect at the tuned frequency of the box/port/driver unit. This additional cone excursion controlling output is welcome and sounds pretty great, but.....Warning!  Exactly 1 octave BELOW the tuned frequency that helpful back pressure wave is now 180 degrees out of phase and UNloads the cone allowing for crazy flopping back and forth and even bottoming of the voice coil against the backplate of the poor driver. Can you say major failure mode? Sure, I knew you could. Lol, thus the popularity and real necessity for a carefully set high pass filter about 1/2 octave below the tuned frequency of hard driven
bass reflex boxes.  Especially older relatively short x-maxx drivers like old Peavey speakers.  While Black Widows had a robust magnet/ voice coil assembly they were a bit late to the deep x-maxx thing.  So you might want to try a new set of lo-rider's which have about double the x-maxx of the old style Black Widows.
Hope this helps you out!
Chuck

Thanks Chuck, I didn't know it took 4x the excursion to go an octave lower, interesting.

I definitely understand that the bottoming out is happening when they're moving further than their capable of and at a higher amplitude. What's got me perplexed is, as I see it anyway, I've got one or more of 3 things happening.

1. My DSP settings aren't correct
2. I've got the DSp settings correct however the action of the VSX26 DSP unit isn't as precise as needed
3. My VSX26 is malfunctioning.

Those may not be correct assumptions or there may be others and more but from what I understand, which seems like nothings some days, those are the 3 most plausible issues.

The VSX26 has RMS limiting so I understand that with a very quick spike in output the limiter won't protect the driver such as a brick wall limiter. However, with the high pass filter set, as well as a steep roll off on the low corner point of the X-Over for the subs, at the correct frequency, shouldn't that limit the mechanical excursion of the driver keeping it from bottoming out? Going back to my above three theories that if I'm set with the correct numbers nothing lower than what my sub should be able to handle should come thru correct?

Here's something I'm unsure of: If my RMS limiter is set correctly and judiciously, should I ever see the clip lights on my amps IF the increase in amplitude is gradual?

I know I'm missing some information and understanding so please bear with me. I have a Peavey VSX26 running into PLX 3402's. I have the clip limiter engaged on all amps. So if my RMS limiters are set correctly, I should never see the clip light on the amp should I? Here's the info about the PLX clip limiter switch

"When the audio signal drives the
amp's output circuit beyond its power
capability, it clips, flattening the peaks
of the waveform. The clip limiter
detects this and quickly reduces the
gain to minimize the amount of
overdrive. To preserve as much of the
program dynamics as possible, limiting
occurs only during actual clipping."

I think I may be starting to understand why I'm seeing the clip lights EVEN with proper DSP settings. My VSX does RMS limiting and the limiter is set for 350w RMS to match my subs power handling capability. While RMS limiting will keep the music program from constantly driving the amps to clip, thus RMS, since I don't have brick wall limiting and if I'm near the or even in the RMS limiters, a peak may quickly come thru sending more voltage than the amp input can handle therefore causing the clip light to engage on the amp. Is that close to what's happening?

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