"Shh, No Talking" Home Theater... - Page 9

I hope the two subs fix your issue of uneven bass over your seating areas. Will cross my fingers for you.

That's great, ... two more tools in the quest.

Good lookin' out. Best of luck and keep us informed.

Looks great...and you say you're doing nothing??

The front wall looks good. That should really offer a significant improvement damping energy off the front wall. This, combined with the mains toe in, ... good stuff.

Good luck w/the subs, they look good,.. nice and beefy.

I'm sure there is a solution - you'll get there.

In regards to the consistency of your results - are you using a mic stand and a marked position? Is the mic placement exactly consistent - is what I'm trying to get at. A plumb bob hanging from the mic stand over a mark on the floor with the mic at a standard orientation and a measured height.

In regards to the room modes - I feel confident personally that they are at the heart of your problem. A suggestion I have read that you may not have tried: put one sub in a tricorner - as close as you can get - place the mic in the opposite tricorner - diagonally across the room (ceiling, not floor). Run a sweep. This will put you in a position to excite and measure all the room modes simultaneously. Then we can compare that to the free-space response of the sub (MFW?) and by subtraction, find the relative influence of each mode. Sound good?

Fred

I guess this is why IBs can be tough since you can't change placement....well, you could, but it is a bit more work. Do you have any graphs with just the MFWs and no IBs? You'll get this issue taken care of, but realize that every theater/room has different FR plots for each location. You can move your mic 1" and it can make a big difference.

Correct me if I'm wrong, please: the IB array is in the front (duh), and you've been working with the MFWs in the rear corners.

Is it possible to place the MFWs at the midpoint of the length of the room - along the side walls - just for testing? I have a hunch you'll see major improvement in the 60Hz problems with that arrangement. If not, can you post the graph of the normal arrangement with 90 degrees phase adjustment for the MFWs - all subs driven? (I may be barking up the wrong tree here, but I don't think so)

Fred

P.S. - look at this - put in your dimensions (as nearly as you can) in the add room tab - notice the strong modes near 60 Hz - then select the "floor" tab and position your ears in the first and second rows, watching the changes - it's kinda awesome. http://amroc.andymel.eu/

You'll sort this out to audibly be fantastic.

I know it's frustrating, I can see that. But surely there exists, in your current array of gear, a combination that gets you the response you want. Now, that said, I'd suggest bring more sources to the fight. If your mains are up to it, lower their lowest operating frequency perhaps down to 60hz. Measure the sum of the entire sub system, and manipulate the time alignment of the fronts to the mains, then bring in the rears at a varying amount of delay until the response appears the smoothest. Knock down the peaks, then manipulate the time alignment again and render the subsequent response to taste.

Sure, easier said then done, but the crossovers used between the subs and to the mains, isn't a brick wall either direction. So the mains extend downward to allow interaction,...smoothing etc out of band. So the response of several drivers over-laps, thus adding to the response smoothing of multiple sources.

So whether the subs a in the rear, or a bit forward toward the front, you'll get this.


Best of luck

Did you endeavor to level-match the MFWs with the IB? I'm not surprised that the IB has lots more output potential, but I think maybe you could be more effective with the filler subs with their gain cranked up a bit more. I make this assertion (guess) based on the relative levels of the graphs in post 254.

I'm not as well versed in this as a lot of people that have chimed in already, but I can only imagine your frustration.

With that said, have you taken any peak readings during any movies? I believe the PEAK, SUB, level is supposed to be 115 db. That's +10 db higher than the other channels peak value. I think it's been mentioned before that the sub channel is usually 10 db hot.

if I were in your shoes, I would start troubleshooting this systematically. You've got a couple extra subs that you can move around, so maybe disconnect all of your subs except one, and try moving it around. You'll need to "plug" your other subs somehow. Maybe put some foam over them to keep them from moving. You don't want them sucking energy out of your room. Try a sub crawl with that sub in the front row. Figure out where the "Best" place is for your sub, and then compare to where your IB is located. Maybe setup your room with the two subs in the "BEST" place with the IB disconnected and plugged, and compare to your results with all the subs running. This would at least ensure it's a location problem. Have you taken any measurements of the MFW's outside, perhaps? That would give you an idea of how they perform where modal issues are not a problem.

Also, have you double, triple, quadruple checked all of your wiring to make sure you don't have something out of phase? You don't have any low pass/highpass/bandpass filters inadvertently enabled? Are they all actually powered (again, if one is not it will will absorb energy from your room). You know your TT works well in the room, could you feed the wire from one of your IB's through the IB wall and drive your TT just to make sure everything is working well. Maybe try that with each IB sub?

I'm just throwing ideas out there that I would try if I was troubleshooting your problems.

Hang in there! You'll get it figured out!

It is easier to do a sub crawl by putting the sub at the LP and then just moving your ears to the best placement. You are more mobile than your subs. Check the DIY forum for more info on that.

+1

I suppose I was rambling a bit in my previous post, but absolutely. Put the sub in the front row in the spot you intend to use the most, and start crawling. However, another point is you can do this with multiple subs. So you might even try a sub crawl with the IB's running. Fire up the IB's, put 1 MFW in the front row, and start crawling around looking for a good response. Put your MFW there, then bring in the next one. Put it in the front row, crawl around again, and put it wherever you find the best response. Then you've optimized the placement with your IB's in place and working.

I'm rambling again, but my point is to start eliminating variables.

1) The first step I would take would be to make sure all the wiring is correct and to VERIFY that the IB's are all working and being driven in the proper phase.
2) Next I'd check to make sure the MFW's are working properly (polarity is correct, etc.).
3) Verify there are no inadvertent filters being added in the processing stream.
4) Then I might try a sub crawl with the IB's operating and one MFW in the "sweet spot."
4a) Put the sub in the best spot and recalibrate accordingly.
4b) Make sure nothing got worse after calibration
5) Repeat 4 for the next MFW.

Andreas had another good point with posting in the DIY speaker forum. There are some very knowledgeable people there.

Sorry for the rambling post. Feel free to ignore it

EDIT: I'm not trying to be condescending here, or point out the obvious, but you don't want to change more than one thing at a time. If you change the wiring and add two subs, then you don't know which caused the problem. At this point, you sort of need to be methodical about your approach to find what's been overlooked. I'm guilty of getting carried away with something like this!

JPA: I agree. Initially it seemed like something was very off with his subs because he was saying he wasn't getting much bass....which seems a little crazy with four 18s in an IB. I just don't get that at all. With these wacky FR, I have no idea what is going on especially with the MWFs not doing much....but I do agree that the MWFs need to be leveled to the IBs as far as output. You can't expect the MWFs to fill the IB's hole at 80db if they are only putting out 70db.

Please post in the DIY forum. They do FR plots all day long there and the guys know what they are doing. Dedicated theater builders is likely not the right forum.

(Still rooting for you Chris!)

Something may be amiss, I don't know. Maybe not.

I'd start from scratch

You will find a combination that will be fine, with the front IB, and with the filler subs.

Yes, you need to assure proper polarity/proper acoustic summing of the IB drivers. I took for granted that was done.

The above mentioned the DIY forum, yeah, they're good. The real problem solvers are at GearSlutz,...worldclass.


There are a handful of different ways to approach the system EQing, but stick with one and that way you'll find find the best combo of settings. Now, there are some combos of loudspeakers and rooms that are particularly problematic. That may or may not be your case.


I would turn all the speakers except the subs off. Always start with all subs same phase. Ideally, you need the ability to individually set levels, and EQ, of each sub (the IB's as a unit, then either the rears as a unit, or rears individually. Test each sub set individually, set levels and EQ, then reset with all subs running.

When EQing, only knock the peaks off, never boost nulls. Again, ideally each sub should have separate equalizers. But, what ever your capability is (in groups, more the better), EQ one sub, or sub group. Then, move on to the second sub with the first sub playing with its settings. Then, proceeding to the next group, while all previous are playing, etc, etc.

When complete, readjust relative level accordingly to mate with center channel (mains). Also, manipulate the entire group EQ as a whole to fine tune more. Also, without getting lost in your progress, try phase (or delay) adjustments to see if any further smoothing is achieved. Also, a final touch of experimenting with this adjustment can help localization issues. Experiment, carefully, with notes and don't lose your progress.

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Now, another approach is merely placing all subs in then locations, and prior to EQing each group, only try phase adjustment of each, seeing results immediately. Moving to next sub, etc. Then globally EQ the entire sub system as a unit.

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I'd think that carefully moving through one of these approaches, will get you a nice, listenable response curve. I wish you were closer, I'd drive over to help you out. I can appreciate your frustration. You'll get this.


Now, question; how many sub groups do you have the capability of controlling in time and frequency? What tools do you currently have?




Best of luck

Can you elaborate on how to do this?

Nothing fancy, polarity check w/battery one way, but that doesn't account for everything, so;

A nearfield mic, between each outside pair, and make sure they sum, then other outer pair, then last, assure both groups sum properly. like powered drivers when doubled, add approx 6dB


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So, prior to beginning the EQ'ing, everything ideally should sum positively (ie front IB, and back sealed individually, then both compared to front IB. Even though phase and time delay may be added later, beginning at the same acoustic polarity is typically the best starting point.

That makes sense. I'll add that to my bag of troubleshooting and setup goodies. Thanks for the tip!

Hey Chris, did you get to do any tweaking today?

If you haven't, or if it was fruitless, have a look at Dr. Geddes' approach to placing three subs. http://mehlau.net/audio/multisub_geddes/

Fred

Chris,
Any further attempts or questions?

I'd certainly be glad to help in any manner possible.