Would you mind taking a look at a few graphs for me and tell me if they're odd? - Page 2 - AVS Forum
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post #31 of 42 Old 09-03-2012, 01:10 AM - Thread Starter
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Thank you all for taking the time to respond. I have not done much more since last week, I've been busy renovation my bedroom and closet. I decided to come back down tonight to play around and did find something interesting. After I did the following test, I guess since the MFW's can't compete with the IB's, they actually won't do much good. I decided to unhook my IB's and run my MFW's only to see what results came of that. I found that with both MFW's in the front of the room, I got similar results (as compared to the IB's alone) only with about 7-8db less output. Now, if I have one MFW in front and the other right behind the rear center seat with the driver firing against the seat, I got MUCH better results in the back row except for a small sharp null at 30hz. My front row still had a huge 60hz rise but was smoother going up to it. Bottom line is that because the MFW's can't put out what the IB's can, it seems that they won't be much help in my situation.

Just to verify, the the subs are level matched. If I play the IB's alone vs the MFW's alone, they both show 75db on my meter while using the receivers' test tone. I don't know why MFW's alone test at about 7-8db lower than the IB's alone

Also, all polarity seems fine, nothing out of wack.

Here is a graph comparing the IB's (with and without the rear MFW's) along with the MFW's alone. The red lines show the IB's alone vs the IB's with the MFW's in the rear, you can see that the MFW's helped slightly, by only by a few db. The blue lines show the MFW's (both up front vs one up front and one in the rear), what a difference! All FR's are of the rear row where I have that large 30hz mountain.

mfwvsibrearrow.jpg


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post #32 of 42 Old 09-09-2012, 10:47 PM - Thread Starter
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So, while I'm awaiting some feedback on my most recent graph, I would like to post a question that I have been thinking about lately.

First, lets take the front row for instance. I'm pretty flat up to about 60hz and I have level matched my sub output to that of my mains, but why oh why is there almost no bass present? I really feel almost no low end in the front row. Same goes for the back row if I EQ out the huge 30hz mountain. Why does it seem like I would have to seriously crank either the AVR volume or the gain on the EP4000 / sub gain in the AVR to get decent results?

It's been bothering me because I read about other folks buying regular box subs (granted they can be pretty massive like the Seaton Submersive, and others in that range) and they seem to rock the house of said purchaser! But why do I feel like I really need to crank it up to ear piercing levels to enjoy the LFE part of my system? I guess I need to take some SPL reading during some scenes that I'm familiar with and see what you guys think of my current levels. If I play The Incredible Hulk at my comfortable but still kind of loud volume, there is almost no bass in the front row. I guess bottom line is that at the volume I listen at, the bass is almost non existent. I feel that I should still have the bass "rumble" even at lower volumes.. What's wrong with this? rolleyes.gif


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post #33 of 42 Old 09-10-2012, 07:30 AM
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If you were originally used to hearing that peak that was so prominent, It is certainly going to sound a little different. Maybe try boosting the subs to about 3 db's hot and see if that helps at all. I sometimes even end up 5-8db's hot depending on the movie content and up to 10db's hot with music.

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post #34 of 42 Old 09-10-2012, 07:47 AM
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Chris,

Did you ever try what I suggested with the MFWs in the back of the room at the 1/4 wall points, with cones pointing toward the bass traps, Eq.2 out of the picture, and delay/phase equal to the front subs?

What seat are all these latest graphs taken at?

Do you have the capability to measure delay with REW (run a loopback on one channel)?

It makes sense that the two 15" MFWs cannot keep up with the quad 18" IB array, and 7-8dB would be about right, but you can be fooled by dB readings with pink noise because the meter will only read the SPL of the largest peak, essentially. So if you have a big peak in one freq band, it will be the determining factor in 'calibration' SPL.

The reason why a flatter freq response seems 'dead' is because you are used to huge peaks in your response, with the power and ringing that comes along with them. The presentation will simply be different with a flat freq response. Also, much of what is 'felt' is due to sympathetic vibration of seating and the floor (if it is a suspended floor). If you were exciting a resonance with the peaks in one of your chair's frames, and that disappeared, you would be left wondering what happened to the bass.....

Here's what I recommend:

Looks like you have seen if you have any polarity problems. Double check again with an alkaline battery.

Take the BFD and the EQ.2 out of the signal chain. Run straight from the receiver to the Behringer amp, with whatever DI box you may have (or none). By the way, how do you go from the Marantz to the amplifier? The Behringer is XLR or 1/4" TRS input only. Please tell me you are not using cheater plugs, and have something like a Samson S-Convert in line. Set both EP4000 gains as equal. To make sure, run a 60Hz tone and measure ACV across the terminals, the voltage should be the same. Are both the MFWs and the IB array the same impedance? This could get important.

Set SW delay and SW level on the Marantz to zeroes. Set the crossover as high as it goes (prob 200Hz). Unplug your mains and surrounds. We are looking only at the LFE channel here, we will integrate later. Eliminate as many variables as you can right now. It can get as complicated as you want later.

Once you have taken those devices and variables out of the chain, run loopback compared sweeps of the IB alone, then the MFWs alone. Do the results agree with the real distances the subs are away from the LP? They should. If not, find the problem.

Then, run sweeps with the MFWs off, and the IB on at a 'normal' level using the Behringer gain controls. Then with MFWs on, and IBs off. Measure distortion with the MFWs only and see what your limits for distortion are, and note that gain level.

Run sweeps with the IB on at normal, and the MFWs turned down, and keep running sweeps until you either get an improved freq response or run into the MFWs max level that you reached before by looking at the Behringer' gain knob.

I know this is essentially 'starting from scratch'. But I think many here are assuming almost everything is already correct. I still think this is a simple room mode issue that can be helped with proper subwoofer setup.

JSS
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post #35 of 42 Old 09-14-2012, 05:59 AM - Thread Starter
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Thanks a lot for your reply max, here's what I tried today...

I took out the BFD and the EQ.2 and I am going from my AVR to the EP4000 via "Monster" rca > 1/4" cable, no adapter plugs. I believe that both sets of subs are running at 2 ohms. I also level matched the IB's to the MFW's via receiver test tones and SPL meter. I checked a few other things and decided to do a little more testing today without the mains in the mix and set the crossover to 250hz and I made a startling discovery!! If I put one MFW in each rear corner firing into the corner bass trap, my rear row is IMPRESSIVELY improved! Take a look! Bue is IB's alone and Red is with the MFW's in the corners.

rearrownew.jpg

I tried the MFW's in all other spots back there before and nothing had a change like this did, but today I WILL try those other spots again just to confirm that firing INTO the corner actually does the trick!

The front row has a change as well, in a good/bad way I suppose. What do you think?

frontrownew.jpg

Now another funny thing, this is all with no EQ inline, just rca from AVR to EP4000. If I add the BFD inline and deactivate all EQ functions, I get a few db rise over the whole graph, is this normal?

frontrowbfdinline.jpg

rearrowbfdinline.jpg


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post #36 of 42 Old 09-14-2012, 07:31 AM
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Tremendous results!

Here is a sketch of what I was advising (I hope the picture is accurate as to seating positions):



You can see the modes at 31Hz, 63Hz, 94Hz, and 126Hz. This is only the room's length axis. I am not taking into account tangential or oblique modes.

If your front and rear subs are the same polarity (I assume this is so), you have tamed the 31Hz mode on the rear row. The incredible increase from 40Hz-90Hz I am chalking up to nearfield response of the back MFWs, since you level-matched them to the IB array (from which row?). You cannot cancel the 63Hz mode, and that 's why you still have a peak in the front row at 63Hz. You have a lot of tangential mode activity in the 70-100Hz region, and that makes things a little inconvenient.

About the BFD, it is 'taking' an unbalanced line level source (receiver) and then boosting up to pro level XLR for the output. IT may not be the same as the boost applied on the rear panel of the EP4000. That explains that discrepancy.

I say you have made terrific strides forward. Here's what I recommend:

1. Decide whether or not you want 2 rows of good sound, or one row of excellent sound and another row of whatever is left.

2. The only adjustments you need to make are to the EP4000's gain controls. Keep measuring and playing with gains until you have a good compromise of freq response between the rows, and either EQ for one row preferentially, or for the best compromise between the two. You must understand, that your back row is already 95% of the way there. That back row is the ENVY of most here at AVS, including me.

3. Figure out with distortion testing if your IB will need a highpass (it may not, with receiver and amp rolloffs). You can do this with Soho54's Audio Test DVD and REW's Spectrum function.

4. Integrate your mains/surrounds and enjoy!

Congrats on the improvement. I would put the MFWs firing into the bass traps with the cones 2.5' from each corner to cancel width modes.


JSS

PS - WORD OF WARNING - You have Audyssey MultEQXT with Dynamic EQ on your receiver. I assume it was off when you did all the measurements, or else most of the measurements above may include EQ already, and you are not seeing the IB and MFW's true response. Remember that Audyssey can inordinately boost the lowest frequencies, requiring you to use a highpass (EQ.2), or you will overdrive your IB. I like Audyssey, but it has some caveats. I would see how Audyssey handles the freq response you have, and maybe you will not even need the BFD. To place more emphasis on one row over another, simply measure more spots in one row vs another in the Audyssey setup.
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post #37 of 42 Old 09-14-2012, 08:55 AM
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Much good advice given.

I'm glad to see some results, I still don't understand everything you've performed (i.e., what have you EQ'd and what you haven't).

Yes, Audyssey can add some un-warranted manipulation, and ideally I'd not even use it. Your IB doesn't need a high pass, powered off one half an EP4K. Ideally, you can power two four ohm IB3-18 drivers in series off each side of an EP4K. Even at those levels (225w/per driver), you needn't be concerned with a high pass.

Again, as I've said, I believe there may be much more boundary interaction, both constructive and destructive, influencing things than modal issues.



IMO

1.) physically place and experiment with response, each location utilize polarity reversals to establish causal relationship, get things as tidy as you can by only these means first.

2.) manual EQ'ing, in freq domain globally, ... and time domain as a group (ie rear subs as a group)

3.) if you want to, see what Audyssey does to the final subsequent response.


I'm not contradicting anyone, merely offering a simplistic hierarchy of tending to things. Take good notes, this isn't a trivial setup,...somewhat akin to setting up an Indy car, get the car close, then slowly tweak better and better, hoping not to go in the wrong direction. But, if so, you merely revert back to a baseline w/your notes,...then proceed again.


Best of luck Chris

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post #38 of 42 Old 09-16-2012, 03:46 PM
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That's looking more normal. Try putting a highQ -10db 60hz filter on the MFW's in the back or vice-versa with the IB and see if the 60hz in the front and back row change. It's gotta do something... I would think. eek.gif

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post #39 of 42 Old 09-17-2012, 05:58 PM - Thread Starter
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Thank you for all of the suggestions guys! Let me try and answer a few more of your recent questions...

Max, the level matching was measured at both rows, give or take a db or two between the two sets of drivers so they are pretty close to each other. On the same note as the picture you posted, I did a little bit of testing with mic placement. In the front row, I get the 60hz peak across all three seats, at the ground and at the ceiing. This tells me that the 60hz peak is definitely length related, correct? I acknowledged the info on the BFD, thanks smile.gif

I woud also like both rows to be good, at least in the low end, 30hz and below, I went with the IB's for that reason and I want everyone to feel what it's all about. I understand I won't get both rows identical but if I can tame the large peaks and have both rows within 5db of each other, I'm sure I can live with that, but then again, is that asking too much? I'm also not sure how to use the Spectrum function yet, actually never heard of it so I'm not sure how to detect distortion with that. And then there is integrating the mains... as soon as I plug those back in, bring on the cancelations once again. I have some serious tweaking there, but I guess when I'm happy with the subs only, I'll come back to you guys for help on implementing the mains smile.gif

Lastly, Audyssey was not enabled during testing smile.gif.

FOH, I'm not sure what you mean by this...

"Again, as I've said, I believe there may be much more boundary interaction, both constructive and destructive, influencing things than modal issues."

Then this...

"manual EQ'ing, in freq domain globally, ... and time domain as a group (ie rear subs as a group)"

I think I can time domain EQ only the rear subs (MFW's) via phase adjustment on the eq.2 box, but when I hook up the eq.2 box, I get a signal drop of a few db over the entire LF spectrum, I have to boost my gain on the EP4000 to cure that even though I don't like the idea. Regardless, time domain EQ would be phase adjustment, correct?

And speaking of location placement testing, I did a little more last night... I ended up trying to cancel the 60hz peak in the front row by placing one MFW on either side of the rear row firing at the IB's and it actually helped quite a bit but kind of reversed the results from having them in the back. So, I put one MFW at the side of the rear row and kept the other firing at one of the rear corners, decent compromise, but could be better. I'm thinking if I can pick up two more MFW's, I can have two firing at the corners to help the back row and then have two firing toward the front to help with the 60hz peak in the front row, am I thinking this correctly?

BassThat, I was about to tell you that I can only EQ the whole system as one or EQ the MFW's alone via the eq.2 box, but then, I technically could run from the AVR sub out, split that sub signal and run one line to the BFD and then to the IB side of the amp and the other sub out straight to the MFW side of the amp or to the eq.2 and THEN to the MFW side of the amp. If I do that, I can EQ for the IB's alone and or the MFW's alone, but., I'm not a fan of the eq.2 box yet so I would rather not use it.

Holy cow that was a finger full. I hope you understand it redface.gif


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post #40 of 42 Old 09-17-2012, 06:06 PM - Thread Starter
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Ah crap, you know what I just realized? By taking the MFW's out of the rear corners and fining them at the front, it didn't help with the front row, it just brought it back to when the MFW's were not in the rear corners, duh:rolleyes:

Well, now that my excitement is gone, what now? mad.gif


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post #41 of 42 Old 09-17-2012, 06:06 PM - Thread Starter
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Now why does my front row get so excited at 60hz with the MFW's at the rear corners?


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post #42 of 42 Old 09-17-2012, 07:27 PM - Thread Starter
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Ladies and gentlemen, I have some VERY good results from tonight! As I mentioned in my earlier post, as soon as I add my mains to the mix, the freq response goes bonkers! So, I decided to play with crossovers and sub distance. After about a half hour of playing around, I came to a very acceptable setting! X-Over at 60hz and sub distance at, wait for it...... 1ft !!!

I went from this (60hz x-over and true speaker distance)...

allat60hzxoverandtruedistancenofmod.jpg

To this just by dropping the subwoofer distance in the AVR down to 1 ft!!!

alltogether60hzxoversubdistance1ft.jpg

My only concern is with the MFW's... I had to turn them up about 5-6db higher than the IB's to get this flat... I'm worried about over excursion of the MFW's at lower freq. I decided to add in a 30hz FMOD for the MFW's and this is what happened...

alltogether60hzxoversubdistance1ft30hzfmodadded.jpg

WTF?


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