Worst case scenario of using two subs that are not identical - Page 2 - AVS Forum
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post #31 of 50 Old 06-29-2014, 07:33 PM
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Quote:
Originally Posted by craig john View Post
The "division of workload" is handled by "gain-matching" the subs. If they're gain-matched they all have EXACTLY the same workload, but only if they are also sent EXACTLY the same signal, i.e., if they are all sent EXACTLY the same EQ'd signal. IOW, they NEED to be EQ'd as a combined system in order to have an equal division of workload.
I agree that the subs need to be eqd as a combined system, but since each one will have peaks at different frequencies. there is nothing served by giving them power that they don't need at frequencies where their sensitivity peaks.

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Originally Posted by craig john View Post
You don't accomplish that by EQ'ing them separately.
Remember that I recommended EQing them separately and then Eqing them as an ensemble.

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Originally Posted by craig john View Post
What happens when one sub has a peak that offsets a null from the other sub? If you EQ down the peak, you're left with the null... that had already been corrected.
That's not how peaks and nulls work. It takes less energy to fill a null because a null represents a lack of energy. The purpose of having multiple subs in different places in the room is to avoid having a null in the one and only source.


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Originally Posted by craig john View Post
What are you going to do then? EQ the combined response by adding a boost to bring up the null?
The general rule is don't eq nulls period. It can take nearly infinite energy to fill in a suck out. If you have a bad suck out move the subs around until it goes away.

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Originally Posted by craig john View Post
That makes no sense at all. Better to measure the combined response and apply just one offsetting EQ to the combined response.
I have never said that eqing the whole ensemble is a bad idea. Go back and look at my last post - I said eq the whole ensemble once you get as good as you can by eqing individual speakers.

If you don't want to read what I wrote and complain about what I didn't write, fuggedaboutit.
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post #32 of 50 Old 06-29-2014, 08:29 PM
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arnky in one statement you said it does not take much to fill a null and a statement or two later you said a null can take a lot of energy. This needs more explanation.

I like EQ'ing sub as one since they work in the room as one unit. Between flattening the response, boosting and cutting in the setup, then re-EQ'ing the subs, it is possible to eat up a lot of headroom. I would much prefer picking a 3-5 db +/- response and live with it than extensive EQ'ing. Don't get me wrong, I am not saying EQ should not be used. I like cutting one or two peak and maybe a boost under 60-70 Hz and if more EQ is needed, time to reposition the subs.

EQ'ing is not the holy grail in my setup, MCACC standing wave funciton addressing issues in the room does a lot to correct the bass in the room. Addressing standing waves is just as important as EQ IMHO.

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post #33 of 50 Old 06-29-2014, 09:07 PM
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Originally Posted by arnyk View Post
...fuggedaboutit.
Consider it forgotten.

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post #34 of 50 Old 06-30-2014, 06:38 AM
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Quote:
Originally Posted by Ovation View Post
I'm about to pull the trigger on a new sub (SVS PB-2000) and I'm planning to move my old sub to the living room. The new one will greatly outclass the old one (at least, it should) but I've been reading a lot about dual subs smoothing out bass and I wonder if it's worth trying them both at the same time (the living room doesn't really need a sub, it's just the only place to put the old one if I don't keep it in the "cave").

I will not be overdriving the subs, so I guess my only concern is whether there is a chance that I could damage my older sub by running it with the new one (if the SQ is no good, that'll make the final decision easy). I currently have a Boston Acoustics PV900 (had it for ten years and it has served me well enough). I usually listen at -20 to -15dB from reference (very occasionally, in an empty house, at -10dB) and my room is about 2200 cubic feet.

If the consensus is that I could damage my PV900, then I won't bother with the experiment (it's in perfect working order at the moment so I don't want to "throw it away" on an experiment).
You dont have anything to worry about. I drive dual subs of two different types.My receiver has two seperate sub outputs, and play from the same signal. Audyssey will ask you to adjust your sub to 75 dcb's, if you don't have Audyssey, get a spl meter and adjust. If anything they will work the same, with a fuller range. That SVS is a great sub...try out their wizard set up feature on their web site to properly set up crossover from your mains. I believe that you will enjoy having both running together...
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post #35 of 50 Old 06-30-2014, 09:35 AM
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Quote:
Originally Posted by Ovation View Post
Radio Shack analogue SPL

The Radio Shack analog meter needs a LOT of correction at low frequencies... I forget the exact amount, but it was something like +5 or +7 dB at 25 Hz if I recall correctly. I'll try to remember to post correction values... have them on the other computer.

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Originally Posted by Ovation View Post
I did come across something elsewhere where someone combined a PB-2000 (classic corner placement) with a much less powerful PSW110 (Polk?) (in a "near field" placement--though I'm not sure how "near-field") and he posted REW generated graphs (no EQ applied) that looked rather good (he seemed astonished at the result). Is there any chance that such a near field placement would be beneficial if the main goal with the second, smaller sub, was to counteract nulls rather than add output (I'm guessing a near field placement would allow a lower gain setting--less danger of overdriving the smaller sub or limiting the larger one as described above in a post)? I know that trying it out will reveal that, but it would require a degree of effort regarding furniture placement that I might want to avoid if this idea is without merit. Thoughts?
There are 2 things at work when you talk about a near-field subwoofer and 2 subs at the same time.


1) 2 subs together perform like a single sub placed half-way between the 2 subwoofers (sort of, corner or wall gain can be pretty different depending on where the 2 subs are placed so each sub is going to have a wide range of possible operation profiles so averaging those will CHANGE how the 2 subs work-out when used together... for example, 2 subs placed in opposing corners of a room so that the centerline between the 2 subs is a diagonal line... in that case there will be corner reinforcement of both subs. If the midpoint between the 2 subs falls right on the listening seat, that would be equivalent to a single near-field sub BUT the 2 subs will have corner reinforcement that a single nearfield sub would not have.


2) Nearfield subs tend to measure (from the listening seat) similarly to anechoic measurements of the sub (because the room dimension effects tend to be pushed to the background when your measurement point is just a couple of feet from the physical subwoofer.


If you combine a nearfield sub with a more distant sub with a little or a lot of boundary reinforcement, you'll get an end result that has some characteristics of each sub measured alone. Nearfield subs can be problematic though. Sometimes they excite the furniture so much it feels like you're getting a massage during high energy moments... it's interesting at first, but tends to get annoying over time. So like every other placement option, nearfield placement isn't automatically perfect, but it CAN be, at least, an interesting option. It can be tricky to measure a nearfield sub though - the nearby furniture can have unexpected influences on the measurements to the point that the measurements can change significantly with just small changes in the microphone setup (angle, height, centering on 1 ear or half-way between 2 ears, etc.). If you measure the sub nearfield in an empty room... that's easier (but still sensitive to microphone orientation differences). Adding furniture adds a variable that affects measurements. Because of that you may have to fiddle around a bit with microphone placement until you get measurements that kind of correlate with what you hear--not something that's necessarily easy to do, unfortunately. Resonances in the furniture itself can make the measurements different that what you hear.

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post #36 of 50 Old 06-30-2014, 10:53 AM - Thread Starter
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I have the corrected calibration file for my meter already loaded into REW (but I'm sure the correction values will be useful to have as a back up). The near field option gives me three placement options for the smaller sub, instead of two. It should be arriving sometime in the next couple of hours, so in a few days I'll be able to experiment. If I do go near field, it will be directly to my left (in the place of the small table I currently have there to hold all my remotes). That may well be too close to the MLP. My other options are on either end of a couch that is along the long wall (not facing the screen, but 90 degrees away--kids usually lie down on that couch to watch). I'm a bit hesitant about either of those options, as the couch already receives a lot more impact than the MLP even with the smaller sub alone. Perhaps having two will help tame that effect, though. I foresee a long day of experimenting. Fortunately, the house will be empty (wife and kids and mother in law are going on a two week road trip).
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post #37 of 50 Old 06-30-2014, 11:41 AM - Thread Starter
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PB-2000 is in the house! Purolator guy was kind enough to help carry it into the basement (he was happy I went to the truck to help him carry it to the door). Serious setting up will have to wait for later in the week, though I may well be tempted to just plug it in where the old sub is now, run Anti-mode on it (15 mins from start to finish) and run it alone. Sadly, work beckons, so I'll have to wait until later tonight or tomorrow.
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post #38 of 50 Old 07-05-2014, 05:30 AM - Thread Starter
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Now that everything works together, I was able to make an initial set of measurements with the SVS PB-2000. I measured it from the three places it can fit (its size limits my choices--there is one more place I could try but it will require a lot of moving of other things--may try this tomorrow).

I set the measurements from 10hz to 150hz. My AVR crossover is at 80hz. I tried the SVS in the three spots it can currently fit (left corner, 1/4 from that corner towards centre of wall and 1/3 from that corner towards centre of wall). I made measurements with the SVS alone and re-ran all the measurements with the SVS + my old sub (Boston Acoustics PV900). I also measured the SVS alone and the SVS + PV900 with the Antimode 8033 set to bypass (no EQ) and set to its EQ for the PV900 (just to see the difference). I measured each combination with and without my bass traps (SVS alone, SVS + PV900 x 3 places for the SVS--the PV900 is now sitting next to the MLP and remained in place--will have to measure it in different places as well, eventually, but time and space are at a premium today (space will remain so, but time will be freer in the next few days). Lastly, I measured with front L/R with SVS alone and with SVS+900 (each with 8033 set for PV900's old settings). I can't change the 8033 until the new mic arrives (searched in vain for the one that came with it, so I got a longer one to give me more measurement options in terms of placement).

Initial impressions and findings:

One--I have a massive hump at 20.48hz (according the REW moveable vertical axis line). About 18dB from the target horizontal level of 75dB across the range. Nearly perfect bell shape that starts climbing dramatically from 31hz and curves down to about 17hz (those two points measure at 75dB). This hump remains pretty constant in each of the three places I put the SVS.

Two--SVS alone has a very deep null around 43hz. Very slight (very) lessening of the depth of the null as the sub moves towards the centre of the front wall. SVS + PV900 eliminates the null almost completely (in all situations, with or without EQ, wherever SVS is placed). Given the Antimode does not attack dips (nor should it attack this null), the PV900 acts as a useful form of null killer. Good to know.

Three--when I ran the mains with the subs, REW revealed another deep null centred at about 73hz. Moving my speakers back about a foot removed that serious null (I had them well out in the room as they are rear ported and I did not like them too close to the rear wall--still a lot of space to spare though). Without REW, never would have known it was there. All is not perfect, as the one deep null was replaced by a more shallow (yet still fairly deep) dip at about 69hz and another dip at about 92hz where response was response was reasonably flat before. May choose to go back to original speaker spots after some more listening. Will also try setting the Xover to 100hz (not necessarily ideal overall, I guess, but if it helps diminish the effects of the nulls at either speaker position, maybe).

Four--my traps don't do much below 80hz, but they do fix a somewhat nasty dip at 100hz quite well (REW thus showed me what I suspected--the traps work well enough for what they cost in time and effort but things could be better--unfortunately, no room for more traps at this time).

Well, that's about it for now (took about four hours to do that much and I have actual work to attend to). I will try a few more things soon (SVS in the one other spot available, with and w/o PV900--maybe put the PV900 at that spot first as it's easier to move than the SVS). But the real tweaking will begin when I can re-run the 8033.


General impressions of the SVS compared to my old sub:

Given that most music does not really go below 30hz or so (and it's measuring reasonably flat above 30hz), with music, it is an improvement over my PV900, but a fairly subtle one at my MLP. More subtle than I was expecting (so either my PV900 is better than I thought or my expectations were exaggerated). Will need more time to evaluate it on that score. With movies with strong LFE, it's no contest (though the very strong hump centred at 20hz is clearly influencing that impression--I look forward to revisiting this comparison after the hump is tamed by the 8033--something the 8033 is clearly designed to do). The best result, by ear, I'm currently getting is using both subs (clearly benefiting from the "null fix" provided by the PV900), but it's not as clear or articulate as I'd like. Again, looking forward to running the 8033 as that EQ made my PV900, in its previous location and alone, notably clearer and more articulate.

Pinkish trace is the SVS + PV900 and the blueish trace is the SVS alone. Measurements made with RS analogue (classic) SPL meter, Edirol UA-3FX USB sound card, MacBook Pro running Mavericks 10.9.4 and REW beta 21.
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post #39 of 50 Old 07-05-2014, 05:32 AM - Thread Starter
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Question regarding measurements above. Assuming the 8033 tames the giant peak, do I just raise the volume on the SVS to lift the (presumably flatter) curve output? In other words, is the giant hump messing with the readings about the output across the 10-150hz range I specified in REW?

Also, what, if anything, can I conclude from the fact that below 31hz or so, the giant peaks are practically identical? I think it means my PV900 just isn't doing much of anything below that frequency, but I'm not sure. I also hope it means that having the PV900 away from walls and corners (and right next to me) will keep it safe from trying to match the SVS at low frequencies and thus not be overdriven. Again, pure speculation and I have no physics background, so maybe I'm out to lunch. Thoughts?
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post #40 of 50 Old 07-05-2014, 09:57 AM
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Quote:
Originally Posted by Ovation View Post
One--I have a massive hump at 20.48hz (according the REW moveable vertical axis line).
Could that be a room mode?

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Originally Posted by Ovation View Post
The best result, by ear, I'm currently getting is using both subs (clearly benefiting from the "null fix" provided by the PV900), but it's not as clear or articulate as I'd like.
One thing I recently did was, after applying the Geddes method for place and tuning my subs, was to remeasure to minimize distortion as measured by REW. That is, looking at the Distortion tab in REW.

What I found was that things became much more articulate as I reduced the distortion. I'm too embarrassed to say what it started at but getting it to less than 5% made a big difference in clarity.
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post #41 of 50 Old 07-05-2014, 10:49 AM - Thread Starter
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Originally Posted by artur9 View Post
Could that be a room mode?


One thing I recently did was, after applying the Geddes method for place and tuning my subs, was to remeasure to minimize distortion as measured by REW. That is, looking at the Distortion tab in REW.

What I found was that things became much more articulate as I reduced the distortion. I'm too embarrassed to say what it started at but getting it to less than 5% made a big difference in clarity.
I will look at distortion measurements when I get a chance. As far as the giant peak, someone suggested it could be an artifact of my using the RS analogue SPL meter with the calibration file, though it would seem more likely if I wasn't getting any signal at that frequency from the sub itself and the correction file would be "filling in the empty space" (if I understood the explanation correctly). I doubt that a corner placed PB-2000 is lacking output at 20hz, though. In any event, I have a far more accurate mic on the way (should arrive Monday) and I will re-run all the scenarios. I am curious, though, about what could be causing such a massive peak and, if it's real, I very much hope the Anti-mode 8033 I have on hand can fix it.

ETA: found a room mode calculator (in meters--did a conversion, so things might be slightly off) and it shows a mode at 22hz in a purely rectangular room. Mine is mostly rectangular (two short walls and one long wall are straight, the second long wall is not, so width varies by up to 1.5 feet). Given my irregular wall and not quite precise measurement inputs for the calculator, the peak certainly code be a mode. If so, let's hope the Anti-mode 8033 lives up to its name.

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post #42 of 50 Old 07-05-2014, 11:35 AM
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Corner placement is "best" if you want to excite the biggest hump on the PRIMARY modes.....which is why most people place a SW somewhat AWAY from the Corner, so THAT mode isn't the ONLY bass frequency they hear.

A room needs to be quite LARGE to support sub-30-Hz frequencies. For 20.5 Hz room mode, the lowest (100) mode is only excited when one of the room dimensions is 27.625-ft:
http://www.marktaw.com/recording/Aco...WaveCalcu.html
Fol. similar calculator helps to explain the various room modes...but it's only in Metric:
http://www.sengpielaudio.com/calculator-roommodes.htm


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post #43 of 50 Old 07-05-2014, 11:46 AM - Thread Starter
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Quote:
Originally Posted by holl_ands View Post
Corner placement is "best" if you want to excite the biggest hump on the PRIMARY modes.....which is why most people place a SW somewhat AWAY from the Corner, so THAT mode isn't the ONLY bass frequency they hear.

A room needs to be quite LARGE to support sub-30-Hz frequencies. For 20.5 Hz room mode, the lowest (100) mode is only excited when one of the room dimensions is 27.625-ft:
http://www.marktaw.com/recording/Aco...WaveCalcu.html
Fol. similar calculator helps to explain the various room modes...but it's only in Metric:
http://www.sengpielaudio.com/calculator-roommodes.htm
The second calculator is what I used. My room is roughly 26 feet long (an inch or two shy), so allowing for A)inaccuracies inherent in using the RS analogue SPL and B)my less than precise conversions to metric (I rounded to one decimal place for convenience), could we call 22.3hz (calculator) and 20.48 (my REW result) "close enough"?
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post #44 of 50 Old 07-06-2014, 04:13 AM
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Corner placement in large room can lead to a very good room response. Spreading the subs out as far as possible can give a very even response for most of the room. I use 4 subs corner loaded. two of the sub are 20 ft. from the MLP. Max spl was not less at the MLP when compared to nearfield placement.

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post #45 of 50 Old 07-06-2014, 01:25 PM
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Quote:
Originally Posted by Ovation View Post
The second calculator is what I used. My room is roughly 26 feet long (an inch or two shy), so allowing for A)inaccuracies inherent in using the RS analogue SPL and B)my less than precise conversions to metric (I rounded to one decimal place for convenience), could we call 22.3hz (calculator) and 20.48 (my REW result) "close enough"?
May need to be corrected for the Speed of Sound....which depends on Temperature and Humidity (but NOT Air Pressure, e.g. High and Low Pressure weather systems)....which explains why Organ tuning varies from Winter to Summer:
http://www.mh-audio.nl/sg.asp
http://www.sengpielaudio.com/calculator-airpressure.htm


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post #46 of 50 Old 07-07-2014, 05:40 PM - Thread Starter
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Well, after a long session of measurements (few different placements, new sub w/o EQ, new sub w/EQ, new and old sub w/o EQ, new and old w/EQ--in all cases, EQ is Antimode 8033C), I have finally reached a point where I can now test to see if the graph, which looks good, equals good SQ. Attached is a (red) trace of the two subs w/EQ (it was taken at a bit higher volume setting on the AVR, so ignore the apparent large boost in output--REW puts the difference of each trace at 7dB (red one is higher) vs. a green trace of the PB-2000 with no EQ. About to put some real world sound to test the results.
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post #47 of 50 Old 07-10-2014, 03:45 PM
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Originally Posted by Murbella7 View Post
I run two subs, each totally different in size, design and response.
The main unit is an 18" JBL infinite enclosure, which covers the range from xover (lets be generous and say 100Hz) to around 16Hz +- 3Db.
The front array are 3 very large JBL studio monitors, which have a fabulous low response in their own right.
The side and rear surrounds are also JBL studio monitors, but smaller (and full range).
.
What are the large and smaller JBL monitors?? I am using a couple of JBL L200 home built monitors for left and right front channels and an 18 inch JBL in an 8 cu ft ported enclosure at the rear of the room.

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post #48 of 50 Old 07-10-2014, 05:45 PM
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What are the large and smaller JBL monitors?? I am using a couple of JBL L200 home built monitors for left and right front channels and an 18 inch JBL in an 8 cu ft ported enclosure at the rear of the room.
My speaker setup is as follows....
L&R - JBL 4333A 3-way near-field monitors
Centre - JBL 4315 4-way near-field monitor (this one was salvaged undamaged from a studio fire, it's mate was lost).
Surround - JBL 4301 2-way broadcast monitors
Back surround - Advent hi-fi bookshelf pair
Front height - Wharfedale Brick's (not much bigger than a house brick but incredible sounding tiny things now just coasting in this role)
Sub1 - JBL JRX118 Musicians Sub
Sub2 - DIY 15" folded horn (with a small peak at 45Hz)
Coming - Klipsch sides - RS 62II or RS 52II (for 11.2 setup)
Room is 7.2m x 5.1m (we view down the long axis).
Main seating pair is about 4m from screen (I like to be immersed in the scene)
A 2-seat lounge is behind the front pair on a riser
Lighting is side scones with IR remote dimming
Walls are have heavy sound insulation
Room entry via double doors (2nd used for wide access as necessary)
The doors are standard internal off-the-shelf things but I added heavy sound proofing to them on the theatre side and commercial housing expansion joint strips that scrub the floor for sound seals on the bottom edge.
I will soon be adding wireless remote scene/mood lighting and can't wait for the home version of Atmos to come.

Hope that is enough
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post #49 of 50 Old 07-10-2014, 05:50 PM
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Quote:
Originally Posted by Ovation View Post
Well, after a long session of measurements (few different placements, new sub w/o EQ, new sub w/EQ, new and old sub w/o EQ, new and old w/EQ--in all cases, EQ is Antimode 8033C), I have finally reached a point where I can now test to see if the graph, which looks good, equals good SQ. Attached is a (red) trace of the two subs w/EQ (it was taken at a bit higher volume setting on the AVR, so ignore the apparent large boost in output--REW puts the difference of each trace at 7dB (red one is higher) vs. a green trace of the PB-2000 with no EQ. About to put some real world sound to test the results.
After running Audyssey in my room, everything sounds so good.

I just don't get that some folk need to measure and set things within a micron of their capabilities (well in fact I used to but no longer).

Once you turn up the volume and your concentration goes to the moving image, supported by the enveloping sound of a great 11.2 system, you (almost) never hear the (almost irrelevant) deficiencies and discrepancies.

So set it once, turn it on, turn it up, sit back and enjoy.
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post #50 of 50 Old 07-10-2014, 08:04 PM - Thread Starter
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Have watched a few movies (Avengers and a couple of other superhero movies on Blu-ray) and played some bass heavy tunes in the last couple of days. System sounds better than ever. Think I'm done tweaking for now.
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