[martyo]

I have the 8033SII.

Thanks "bob".

[chargedmr2]

In case anyone is interested here is the unit that I will experiment with first, and hopefully keep if all goes well.

[Austin08]

Nice, it would be better if it has phase adjustment.

[Nuance]

I don't know if you can adjust the input level of your receiver with that, but it looks pretty nice.

[chargedmr2]

Austin08 - I figured I will try to adjust for phase issues in the crossover area by using the distance settings on the AVR.  Maybe it's more complex than this?

Nuance - were you thinking I might run into issues where the signal is clipped by the EQ or just that the signal from the AVR may not be strong enough for the EQ?

Actually, I keep going back and forth about what I want to try out, but will likely try more than one EQ in the end and stick with the best solution. 

I read an really interesting EQ myth document put together by Rane and it suggests that proper EQ requires more than just creating a flat response with a few filters (maybe the five filters of the PE17 is not enough for my situation)  Here is a quote from their site:

"MYTH #6: An ideal equalizer would add no phase shift when boosting or cutting.

Phase shift is not a bad word. It is the glue at the heart of what we do, holding everything together. That it has become a maligned term is most unfortunate. This belief stands in the way of people really understanding the requirements for room equalization.

The frequency response of most performing rooms looks like a heart attack victim's EKG results. Associated with each change in amplitude is a corresponding change in phase response. Describing them as unbelievably jagged is being conservative. Every time the amplitude changes so does the phase shift. In fact, it can be argued that phase shift is the stuff that causes amplitude changes. Amplitude, phase and time are all inextricably mixed by the physics of sound. One does not exist without the others.

An equalizer is a tool. A tool that allows you to correct for a room's anomalies. It must be capable of reproducing the exact opposite response of the one being connected. This requires precise correction at many neighboring points with the associated phase shift to correct for the room's opposing phase shift. It takes phase shift to fix phase shift. Simple as that.

One way people get into trouble when equalizing rooms is using the wrong type of equalizer. If an equalizer is not capable of adding the correct amount of phase shift, it will make equalizing much more difficult than it has to be. The popularity of the many constant-Q designs has come about because of this phenomenon. Equalizers that produce broad smooth curves for modest amounts of boost/cut make poor room equalizers, and good tone modifiers. They lack the ability to make amplitude and phase corrections close together. Lacking the ability to make many independent corrections with minimal interference to neighboring bands restricts their usage primarily to giving a shape to an overall response rather than correcting it. Serious correcting requires sharp constant-Q performance, among many other things.

Only by adding many precise, narrow phase shift and amplitude corrections do you truly start equalizing a system's blurred phase response. You do not do it with gentle smooth curves that lack the muscle to tame the peakedness of most rooms. Broad smooth curves do not allow you to correct for the existing phase shift. Its just that simple, you must pre-shape the signal in both amplitude and phase. And that requires narrow filters that preserve their bandwidths at all filter positions."

[Nuance]

chargedmr2,

What I meant was, if the subwoofer output on the receiver is set too high and clips, that clipped signal will be sent all the way down the chain to the subwoofers.  Not good.  The point of setting the input level of the receiver is to prevent this. 

I just PM'd you the process.

As to the phase topic, the article tidbits you quoted sound correct to me.  The nice thing about REW is it shows the phase changes when you apply EQ.  That's why I prefer to use it paired with something like the MiniDSP or Behringer 1124p or 2496; the options and features are almost limitless.

Edit: Others have expressed interest in how to set the input level of the receiver/preamp using the Behringer EQ's, so I will post the link here publicly.  Scroll down to the section that states "Setting The Input Levels On The BFD."

http://www.hometheatershack.com/forums/bfdguide/

The point of this is to prevent sending a clipped signal from the receiver to the subwoofers.  Once setting the input level is complete, you'd apply EQ.  After that is finished you'll likely need to raise the subwoofer output level because it'll be a lot quieter than what it was.  You need to use the gain knob on the subwoofer amp in order to do this; do notadjust the subwoofer output using the receiver or preamp, as you will be nullifying the process you just completed of setting the input level of the receiver/preamp.

[chargedmr2]

Nuance,

That's basically what I thought you were referring to and it does make good sense.  The Rane has an adjustable input and output that can be set via sliders.  After looking at the spec sheet, I don't think there will be concern over clipping the input.  Here is a link to the specs--let me know what you think: http://www.rane.com/pdf/old/pe17dat2.pdf

[Nuance]

^Sweet!  Keep us posted.

[chargedmr2]

My EQ should arrive on Friday, so it should be an interesting weekend!  I did mess around with Audyssey for automatically EQing the sub (but then disabling Audyssey for the mains).  I really did not like what it did.  It fixed some issues but created a curve that was overall unacceptable.

[chargedmr2]

I figured I'd post a brief update about the Rane EQ that I ended up purchasing.  First, I ended up with a damaged unit on the first time around, but the seller replaced it and all is well at this point.  The unit is fully analog, so the adjustments all take place via dials which makes precision a little difficult, but with patience it works quite well.  To make adjustments, I eliminated the room effects by looping the output of the unit back into the mic input of my extreranl soundcard.  I used this method to set each filter to the precise frequency needed.  After that I adjusted bandwidth and cut/boost according to the dials and did some measuring, followed by fine tuning.  I was able to produce a much better frequency response below 80Hz.

I did run into one problem, which has nothing to do with the EQ or the sub.  I was not able to eliminate my peak (fully) that occurs around 63Hz.  Turns out this is caused by my SongTowers, despite the fact that they are crossed over at 80Hz.  I still need to reduce this peak by about 5dbs, but am at a loss as to what, if anything, I can do.  I measured around my listening position, and also moved my STs within the limits I have and the peak remains.  Any ideas for a solution?  Large bass traps are not an option either.  Also, I'm not sure if running an EQ on the mains is a good idea.  I wish the crossover was steeper, as that might have been enough to further reduce the peak as the STs roll off to the sub.  I may just have to live with it for now. 

Otherwise, I find that the sound is definitely improved in the lower frequencies.  Overall, the bass is a little less boomy and doesn't appear to overtake/drown out upper frequencies as much as before.  Hard to explain really, but I like the changes as opposed to leaving the signal untreated.  And this EQ adds zero perceived noise to the signal and no issues with buzz/hum either. 

[fsimms]

I have two possible suggestions for the peak.  I am not sure how well the Master Set procedure works as even though I use it my self.  I haven’t taken the measurements to confirm their effect.  I know that subjectively it seems to work for me.  Speaker movements as small as ¼” in the placement of the speakers seem to have large effects on the peaks and dips.  I would think that getting the SongTowers as flat as they can be before you use your equalizer might be of benefit.  Looking at your pictures, the master set position should be near where your speakers already are.

http://www.audiocircle.com/index.php?topic=64320.0

http://www.audiocircle.com/index.php?topic=65908.0

Another possibility that you might try that would be easier would just be to plug up the bass ports on the SongTowers.  Just another guess.

Bob

Edit: Salk speakers are designed to sound great without toe in so the last master step procedure is probably not necessary.

[ricardojoa]

I figured I'd post a brief update about the Rane EQ that I ended up purchasing.  First, I ended up with a damaged unit on the first time around, but the seller replaced it and all is well at this point.  The unit is fully analog, so the adjustments all take place via dials which makes precision a little difficult, but with patience it works quite well.  To make adjustments, I eliminated the room effects by looping the output of the unit back into the mic input of my extreranl soundcard.  I used this method to set each filter to the precise frequency needed.  After that I adjusted bandwidth and cut/boost according to the dials and did some measuring, followed by fine tuning.  I was able to produce a much better frequency response below 80Hz.

I did run into one problem, which has nothing to do with the EQ or the sub.  I was not able to eliminate my peak (fully) that occurs around 63Hz.  Turns out this is caused by my SongTowers, despite the fact that they are crossed over at 80Hz.  I still need to reduce this peak by about 5dbs, but am at a loss as to what, if anything, I can do.  I measured around my listening position, and also moved my STs within the limits I have and the peak remains.  Any ideas for a solution?  Large bass traps are not an option either.  Also, I'm not sure if running an EQ on the mains is a good idea.  I wish the crossover was steeper, as that might have been enough to further reduce the peak as the STs roll off to the sub.  I may just have to live with it for now. 

Otherwise, I find that the sound is definitely improved in the lower frequencies.  Overall, the bass is a little less boomy and doesn't appear to overtake/drown out upper frequencies as much as before.  Hard to explain really, but I like the changes as opposed to leaving the signal untreated.  And this EQ adds zero perceived noise to the signal and no issues with buzz/hum either.

So you mean the peak is there when xover at 80hz and with not sub?

[Nuance]

So you mean the peak is there when xover at 80hz and with not sub?

Same question from me.  If the peak is being caused by the speakers it should go away (or at least be able to be EQ'd down) when crossed to the subs, unless you're still running them full range and you don't know it, or if the slope is not steep at all.  It is possible to run the mains full range and also add in the subs; I just don't recommend doing that with SongTower's.  Double check to ensure the high and low pass are actually in effect.

[chargedmr2]

Unfortunately the filters are in effect.  At first, when I began measuring and adjusting the EQ for the sub, I thought the EQ just wasn't cutting the frequency enough.  The peak did come down, but not by the amount that it should have based on the settings.  Further cutting made no difference.  This is when I measured the STs without the sub (with the 80hz crossover engaged-not full range) and found that they were the cause of the remaining peak.  The crossover has a common 12/24 slope, which I assume is fine in most situations, but it doesn't seem effective when you have a giant peak just 10-20Hz below the crossover point (if I remember correctly, this slope would be down 12db by 40Hz, but only around 3-6db between 60 and 70Hz). 

I'll try to post some graphs later to show what is happening visually. 

It's not an option at the moment, but in the future when I run a separate amp for the mains, would putting an inline crossover before the amp input be a bad idea for the mains.  I'm not sure if these would be transparent enough, or what a good one would even cost.  Just thinking out loud...

Edit to add: I just took a look at my Denon 3312's EQ options.  I didn't like what Audyssey did when I experimented with it a while back, plus I really don't want to EQ my mains.  I did notice, however, that there is an Audyssey setting for "manual" EQ.  Does anyone know what this function does?  I know that it allows me to cut and/or boost certain preset frequencies, but does this engage any other Audyssey based corrections?  It just so happens that one of the frequencies available for adjustment is 63Hz.  That is almost exactly where my peak occurs (63.4Hz).  Any thoughts as to whether this would be a good solution?  Are there any concerns that I should be aware of?  I'll try to dig up some info on Audyssey "manual" mode. 

[Nuance]

So you have a peak at 63Hz even with the subwoofer off when the crossover is set and engaged at 80Hz? How does that work?  It sounds like the crossover isn't working.

[ricardojoa]

try pluging the port of the mains to see if the ports are not causing a room mode.

[chargedmr2]

Ricardojoa- My STs are front ported, so it would be a bit unsightly to plug them.  I'll experiment to see what happens though. 

Nuance- Maybe something is up with the crossover, but I think the peak is just a room effect showing through.  If I'm understanding the way the crossover should be working, it means the mains begin to roll off at 80Hz.  The slope of the crossover is such that the mains should be down 12db by 40Hz.  Since the peak is at located between 63-70Hz, the mains are down by less than 6db at this point.  Thus, the peak is reduced by the crossover, but in this case, not by enough to eliminate it.  Am I thinking about this correctly?  Actually, the crossover, might be down 3db at 80Hz and then slopes further down from there, but I can't remember for sure.

At any rate, let me know what you think based on the graph below:

No Smoothing, top line has sub engaged, bottom line is just the ST's with the crossover set to 80Hz and engaged (unless something mysterious is happening).

[ricardojoa]

I see. You could still cover the ports for testing and eliminate all the possibilities. Keep in mind that though the fronts are HP, there would still be bass comming from the ports.

[TJHUB]

I see. You could still cover the ports for testing and eliminate all the possibilities. Keep in mind that though the fronts are HP, there would still be bass comming from the ports.

It's a room mode and messing with the ports will do nothing positive.  Besides, I'm fairly certain the ports are tuned far below the 63Hz area, so plugging them makes no sense. 

[Nuance]

The response is quite different between 60 and 80Hz when comparing each graph, so the crossover and subwoofer integration is working. Try reversing phase and see if anything happens (it'll likely effect nearer to 80Hz, but it's worth a shot). Is the slope adjustable?

Room modes can be EQ'd, so something is still amiss. Are you sure you're applying a 80Hz crossover and not a 60? What is the bandwidth of the cut filter you applied to the 63Hz peak?  I'd use a 24dB slope if you aren't already and I'd try reapplying the EQ cut after you've ensured the slope and crossover frequency. Setting the crossover alone doesn't mean peaks will automatically go away, but then you should be able to apply PEQ to the subwoofer at that frequency once the crossover transition is applied successfully.