Dual Opposed AV15H Subwoofer Build - Page 25 - AVS Forum
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post #721 of 802 Old 10-01-2010, 10:41 AM
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Originally Posted by tuxedocivic View Post

I've even been provided with measurements as proof. That graph Bosso has produced twice now is extremely convincing and I no doubt would hear that swing at 70hz.

Then you are getting the wrong information from the graph, and coming to the wrong conclusion.

It was not a horizontal dual against a vertical dual. It was two dual sub enclosures, with his top/bottom mounting. In the dipped graphs they were sitting next to one another on the floor. In the red trace one was placed on top of the other. The direction of the drivers had nothing to do with the change, or the dip. If anything at top firing driver would make this worse than it would have been in a normal enclosure. The tall virtual speaker that was created when the subs coupled is what changed the graph.

The point of the graph was to show that you can't fix a standing wave. This is a completely different topic, and has nothing to do with driver orientation, or any other room. If you are concluding the superiority of any enclosure based on that graph, you are doing a dis-service to yourself.
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post #722 of 802 Old 10-01-2010, 11:45 AM
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Originally Posted by soho54 View Post

If you are concluding the superiority of any enclosure based on that graph, you are doing a dis-service to yourself.

I'm not making a conclusion based on that graph, but I've given that graph some weight in my decision.

I knew how that graph was formed (side by side vs stacked). But what I can see happening is the cancellation caused by the horizontal proximity of the drivers. That is why I said I like the stacked configuration.
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post #723 of 802 Old 10-01-2010, 11:51 AM
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Originally Posted by tuxedocivic View Post

But what I can see happening is the cancellation caused by the horizontal proximity of the drivers.

Not sure what the conditions where for that graph, but.... Unless the measurements are repeated dozens of times for different listening positions and are consistent from position to position then that's _highly_ unlikely. It's far more likely that the drivers were interacting with the room differently in the two positions (moving a sub a couple of inches can make dramatic differences for a single location) and that the two positions were exciting different modes a the measuring point.
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post #724 of 802 Old 10-01-2010, 11:57 AM
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Originally Posted by tuxedocivic View Post

I knew how that graph was formed (side by side vs stacked). But what I can see happening is the cancellation caused by the horizontal proximity of the drivers. That is why I said I like the stacked configuration.

The cancellation was not caused by the horizontal proximity of the drivers.

The cancellation was caused by the distance to the ceiling from the floor/driver.

This adds no weight to the dual opposed enclosure debate one way or another.
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post #725 of 802 Old 10-01-2010, 12:35 PM
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We also see that PCB struggled with this frequency range on his setup.

My hypothesis: Having to opposing drivers near a reflective surface, a distance equal to approximately 1/4 wavelength from the driver to the reflective surface and back to the other driver causes a cancellation that can be measured at the LP.

Objective findings:

1. Laws of physics tell me this will happen, (1/2pi wave cancellation theory);
2. PCB's system measures dipping frequency response around 80hz;
3. Bosso's system measures before and after with dipping frequency response around 80hz corrected by stacking the drivers to be equal distance from nearby (1/8 wave length) reflective surfaces;
4. The dip can be corrected with EQ;
5. Ripple tank sims (up for debate whether this should be included).

Subjective findings:

1. Reports that other room modes may compensate the cancellation with reinforcement so it is possibly irrelevant;
2. The sub may be moved around the room to negate the effects;
3. Possible to not hear it.

Conclusion: The hypothesis is correct, however it is up to debate whether it is warranted to include the findings in a sub design when the benefits of the dual opposed design are accounted for or if the XO frequency is intended to be at or less than approximately 80hz. If the frequency range affected is to be considered, a dual opposed design may be viable with alternative placement techniques or opposing the drivers vertically.

That's what I'm seeing as an observer. Maybe it doesn't matter. But I believe it exists. Are there any other dual opposed systems that are well documented that you guys could point me towards? I'd like to read them.
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post #726 of 802 Old 10-01-2010, 12:50 PM
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Quote:
Originally Posted by tuxedocivic View Post

My hypothesis: Having to opposing drivers near a reflective surface, a distance equal to approximately 1/4 wavelength from the driver to the reflective surface and back to the other driver causes a cancellation that can be measured at the LP.

[...]

4. The dip can be corrected with EQ;

There goes your hypothesis: Unless you're EQing each driver separately, if the dip can be (significantly) corrected with EQ then it's not due to cancellation.
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post #727 of 802 Old 10-01-2010, 01:29 PM
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Ok, this is something I would not know. I thought I read that PCB was able to eq his dip, which I considered due to cancellation.

So why can't a cancellation be corrected with eq? This is something I know nothing about. A cancellation is never a 100% cancellation of the waves, because 100% of the wave would not be reflected. So why does eq not work.

PCB was able to successfully get a flat response at 120hz xo and eq. Or did he move around his subs or eq each driver separatly like scientest says would be required?
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post #728 of 802 Old 10-01-2010, 01:41 PM - Thread Starter
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Quote:
Originally Posted by tuxedocivic View Post

Ok, this is something I would not know. I thought I read that PCB was able to eq his dip, which I considered due to cancellation.

So why can't a cancellation be corrected with eq? This is something I know nothing about. A cancellation is never a 100% cancellation of the waves, because 100% of the wave would not be reflected. So why does eq not work.

PCB was able to successfully get a flat response at 120hz xo and eq. Or did he move around his subs or eq each driver separatly like scientest says would be required?

Actually, all I did to fix the dip was to play with the distance control setting in the AVR. Went from whatever Audyssey calculated (think it was 6 feet) to 13 feet, which, coincidentally enough, is the exact distance from the LP that the subs are.

Curious, would it add to the discussion at all if I measured the un-EQ'd response of the single sub in the corner of the room as is. Then took the same measurement but inverted the sub and placed it say on a couple 2x4's so that one driver was facing the floor (with about 3" clearance) and the other was facing the ceiling? Edit: Praying to God that the socket screws used will hold the bottom sub in place of course!

For the most part, I have zero idea what you guys are saying, but I don't think it would be difficult to measure the system in this manner outside of finding the time to do so!

 

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post #729 of 802 Old 10-01-2010, 01:41 PM
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Quote:
Originally Posted by tuxedocivic View Post

Ok, this is something I would not know. I thought I read that PCB was able to eq his dip, which I considered due to cancellation.

So why can't a cancellation be corrected with eq? This is something I know nothing about. A cancellation is never a 100% cancellation of the waves, because 100% of the wave would not be reflected. So why does eq not work?

You're right, it's not 100% cancellation since this is a 3D thing and not a 2D thing. That's why I wrote it can't be "significantly" altered by EQ. Some tangential wave may start to change the cancellation with lots of EQ, but mostly it's a loosing battle. Say you're adding 2X the power to the one wave front, while you're doing that you are also doing the same thing to the out of phase partner. Net result, they continue to cancel each other the same as before... Net result, you _might_ see a 2db or 3dB change, maybe even something more depending on the room, the frequency, the measuring location, etc. but you're not normally going to see a 9dB change or something bigger...

Edit: all that aside, I'd still bet the problem is room mode cancellation. Just not cancellation caused from having the drivers opposed...
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post #730 of 802 Old 10-01-2010, 01:54 PM
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Ok that makes sense how eq wouldn't work. So strike that from my list because now PBC has cleared that up for me, that eq did NOT fix his dip.

You say changing the distance setting on the AVR did I'm confused how this would fix a dip. The distance setting is for timing. Can someone explain how this would have changed a "room mode". Unless I'm wrong and this is like changing phase.
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post #731 of 802 Old 10-01-2010, 01:57 PM - Thread Starter
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Beats me, but as I changed the distance from 6db to 7db to 9db to 13 db the dip got better and better and better, and I'm sure I wasn't drinking while taking those measurements. Pretty sure anyhow.

 

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post #732 of 802 Old 10-01-2010, 02:01 PM
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Originally Posted by tuxedocivic View Post

You say changing the distance setting on the AVR did I'm confused how this would fix a dip. The distance setting is for timing. Can someone explain how this would have changed a "room mode". Unless I'm wrong and this is like changing phase.

Yeah, distance is the same as relative phase. However, for an AVR the distance setting may be done digitally and affect all frequencies equally. For an analog phase setting the phase will be centered on a frequency (or possibly multiple frequencies if the thing has multiple filters) and affect it the most.

Note that changing the distance like this won't change the null either _unless_ it is caused by interaction with a wave front from some other set of drivers in the room. IOW, for the cancellation to change like this by playing with distance we know it's not caused by the two drivers on the sub interacting with each other...
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post #733 of 802 Old 10-01-2010, 02:34 PM
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Originally Posted by scientest View Post

for the cancellation to change like this by playing with distance we know it's not caused by the two drivers on the sub interacting with each other...

This is correct. Finally some solid info I can rely on. Now we are left with only one example, Bosso's. I need to do more research then
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post #734 of 802 Old 10-01-2010, 04:22 PM
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Originally Posted by penngray View Post

Bosso, you are playing the world salad game.

Please explain your system in 95 and your system today. You will acknowledge that you used multiple subs to gain better response.

Placement, number of subs and EQ will dictate the response in room. Yes the red trace/gold trace difference is trivial in the REAL world. Again, your pendatic need for a flat response curve is not really a normal occurance for most. You will not hear that in a normal playback situation and you are going to have the XO and the mains blending in in most cases (You argue that PBC XOs high therefore the dip might be noticeable, well that is a problem with the main speakers and not the sub design). Hell, most people have a null in the 150 to 200Hz range because of their main speaker distance to the wall behind it with no treatments. There are nulls in the room, people need to realize that and decide to fix them or not....it does not take this back and forth to know that.

Nothing wrong with wanting incredible measurements but to think its a severe problem enough not to build a dual opposed sub is just crazy. That is the WHOLE discussion, someone is concerned about building a dual sub because of a possible dip in room.....sorry but there was not a need for 4 pages of back and forth on that sort of concern when we all know the benefits of that dual sub design outweights the dip created, we also know how to solve a dip in room. Again, solving it has nothing to do with building any sub box.

Sorry, but I must take issue with some of the ridiculous things in your post.

In '95 I built 2-10 cubes ported 1x18" boxes, 1 in each corner. The red trace is a single sealed sub in one corner of the same room with the same LP in each case.

Word salad game? Pedantic need for a flat response? No need for 4 pages of back and forth when "we all know..."?

I've played bass for 44 years. My first gig at 13 was as a studio session bassist for a country western single in a studio that was staffed by real engineers who wore white shirts and bow ties and smoked pipes.

From that experience to this day, not a single person in a single studio has ever let 22dB swings in the bass go as trivial. In fact, this is such an insane thought that I'm stunned to hear it from anyone with a straight face let alone as being preached from a mountain.

I'm not interested in what 'most people' do or don't do. I'm interested in results. When I see them, I try to pass on the method involved, especially when it's such a simple one as that being discussed here before yourself and LTD decided to make a baloney stew of it.

Please show us a source that describes 22dB swings in FR as 'trivial in the real world' because 'you will not hear that in a normal playback situation', besides yourself.

Really, what next?

I'll bow out here and stop wasting pages in this or any other thread, but, for the record, please stop telling others that 22dB swings in response are trivial in the 'real world' or any other world in the universe for that matter.

Bosso
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post #735 of 802 Old 10-01-2010, 04:49 PM
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bosso, don't bow out. it would suck if you left.

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post #736 of 802 Old 10-01-2010, 04:58 PM
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Quote:
Originally Posted by scientest View Post


Note that changing the distance like this won't change the null either _unless_ it is caused by interaction with a wave front from some other set of drivers in the room. IOW, for the cancellation to change like this by playing with distance we know it's not caused by the two drivers on the sub interacting with each other...

I haven't said that the interaction of the 2 drivers in the sub causes a problem, that was LTD's example of a 42" deep box, but, it should be noted that if digitally changing distance from one box to another shows significant improvement, it only makes sense that physically changing actual distance from the source to adjacent reflective surfaces can as well.

In both cases you're doing the same thing; changing wave interaction from a destructive (or, less constructive) interaction to a constructive (or more constructive) interaction.

My graph shows partial improvement by phase adjustment. That was the extent of reconciling mains to subs wave interaction. The rest was changing the physical position of drivers to room, which was easily accomplished with one sub and physically impossible with the other sub.

That was the only point I tried to make. Seems a simple enough point to me and it got good results with no effort.

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post #737 of 802 Old 10-01-2010, 05:40 PM
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"I haven't said that the interaction of the 2 drivers in the sub causes a problem, that was LTD's example of a 42" deep box"

i said that it causes some cancellation, but not as we might inuit, see #707.

"before yourself and LTD decided to make a baloney stew of it."

where did i make baloney stew?

"My graph shows partial improvement by phase adjustment."

which graphic had the phase adjustment?

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post #738 of 802 Old 10-05-2010, 05:25 AM - Thread Starter
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Quick Q, have noticed a slight hum coming from the subs and I believe it is the DCX causing it as the PB13 also hums now whereas when it's not connected via the DCX it does not hum.

Possible fixes? The hum on the AV's is pretty much not noticeable (probably because the fan on the QSC trumps it), but still want to nip it in the bud.

 

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Quote:
Originally Posted by penngray View Post

Bosso, you are playing the world salad game.

Please explain your system in 95 and your system today. You will acknowledge that you used multiple subs to gain better response.

Placement, number of subs and EQ will dictate the response in room. Yes the red trace/gold trace difference is trivial in the REAL world. Again, your pendatic need for a flat response curve is not really a normal occurance for most. You will not hear that in a normal playback situation and you are going to have the XO and the mains blending in in most cases (You argue that PBC XOs high therefore the dip might be noticeable, well that is a problem with the main speakers and not the sub design). Hell, most people have a null in the 150 to 200Hz range because of their main speaker distance to the wall behind it with no treatments. There are nulls in the room, people need to realize that and decide to fix them or not....it does not take this back and forth to know that.

Nothing wrong with wanting incredible measurements but to think its a severe problem enough not to build a dual opposed sub is just crazy. That is the WHOLE discussion, someone is concerned about building a dual sub because of a possible dip in room.....sorry but there was not a need for 4 pages of back and forth on that sort of concern when we all know the benefits of that dual sub design outweights the dip created, we also know how to solve a dip in room. Again, solving it has nothing to do with building any sub box.

I agree that it is not something that you will hear, but you clearly will be able to hear the difference between a system that is 22db down at 70hz vs a system that is flat at 70hz. You and Bosso are both talking about sub placement.
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Originally Posted by pbc View Post

Quick Q, have noticed a slight hum coming from the subs and I believe it is the DCX causing it as the PB13 also hums now whereas when it's not connected via the DCX it does not hum.

Possible fixes? The hum on the AV's is pretty much not noticeable (probably because the fan on the QSC trumps it), but still want to nip it in the bud.

This is cheap and it works. http://www.bhphotovideo.com/c/produc...liminator.html It also converts unbalanced to balanced.
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post #741 of 802 Old 10-05-2010, 06:18 AM
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You have used it?

For some stupid reason I have a new hum in my family room setup. I was changing some TV cables around in my close to add a new slingbox and now I have a hum that I can not solve

I was going to buy some Jensen transforms to place on my digital TV cables in my AV closet.

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Originally Posted by mjg100 View Post

I agree that it is not something that you will hear, but you clearly will be able to hear the difference between a system that is 22db down at 70hz vs a system that is flat at 70hz. You and Bosso are both talking about sub placement.

As I said I had a DEEP null in my HT room that could only be solved by a new sub. Sure I added the sub to fix the measurement but during any popular movie I can not tell you there was a null at 45Hz. No one would, I have left the sub off by accident and not cared one bit.

The only way to actually hear it is to run tests and that is not what Im talking about. During normal playbacks Nulls will not be noticed.

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post #743 of 802 Old 10-05-2010, 06:24 AM - Thread Starter
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This is cheap and it works. http://www.bhphotovideo.com/c/produc...liminator.html It also converts unbalanced to balanced.

Interesting. Will see if I can pick one up locally ...

 

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Quote:

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post #744 of 802 Old 10-05-2010, 07:04 AM
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pbc, don't you have a plasma ?

Did you inadvertantly plug the plasma into the same 120v line as the DCX possibly...
I had this same issue when I was rearranging behind my 65" to get my last LMS's back there and unplugged a bunch of stuff. Plugged the Plasma onto the same line as the DCX I think and got that buzz / hum - took me a while to figure it out....
Sometimes I can't keep it all straight - I got 4 power sources back there and that doesn't include the 3 x 30amp circuits for the Sub amps...
Sometimes I just wanna



Be sure to check that.....
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post #745 of 802 Old 10-05-2010, 07:39 AM
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Quote:
Originally Posted by bossobass View Post

but, it should be noted that if digitally changing distance from one box to another shows significant improvement, it only makes sense that physically changing actual distance from the source to adjacent reflective surfaces can as well.

In both cases you're doing the same thing; changing wave interaction from a destructive (or, less constructive) interaction to a constructive (or more constructive) interaction.

Well staying pedantic here.... Yes and no. Changing the physical distance of a sub from a reflective surface will change the primary modes that occur because of the resonances from the sub to the surface. IE; if the sub is farther away from the surface then the shortest wavelength it is reproducing there will be some resonant mode from the sub to the surface. So moving the sub around will change the frequency at which the primary modes are occurring. That may or may not affect some other problem frequency but, in particular, it won't any modes that the sub is exciting on any axis that did not change or any modes that are being excited indirectly, and you can't just say a previous destructive mode will go away, you may make it worse. In general, playing with electronic / filter created distance settings won't alter room mode interactions at all, the exception being that you create some reinforcing mode between two sets of drivers that in turn excites some room mode.

Any thoughts on my previous question to you about what you meant by the 1/8 wavelength interactions? I'm still not clear on what you were getting at...
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Quote:
Originally Posted by Warpdrv View Post

pbc, don't you have a plasma ?

Did you inadvertantly plug the plasma into the same 120v line as the DCX possibly...
I had this same issue when I was rearranging behind my 65" to get my last LMS's back there and unplugged a bunch of stuff. Plugged the Plasma onto the same line as the DCX I think and got that buzz / hum - took me a while to figure it out....
Sometimes I can't keep it all straight - I got 4 power sources back there and that doesn't include the 3 x 30amp circuits for the Sub amps...
Sometimes I just wanna

Be sure to check that.....


Yes, I have a Plasma. I believe the DCX, Plasma, AVR, bluray are plugged into my Panamax EX-5400 (or whatever it is) which his plugged into a 15amp circuit while the RMX is plugged into a separate 20amp circuit.

Been meaning to bring up another 20amp circuit but just haven't found the time.

I'll try connecting the DCX to the 20 amp circuit or alternatively a different socket (though I'm guessing the socket nearby runs on the same 15amp breaker) and see how that works before buying another doo-hickey.

 

My DIY Subs ... http://www.avsforum.com/avs-vb/showthread.php?t=1233892

Quote:

J Dunlavy:.. if you stop to think about it, no loudspeaker can sound more accurate than it measures.

 

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post #747 of 802 Old 12-09-2010, 05:56 AM - Thread Starter
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So I'm hoping to have more time over the holidays to play around with these. Have a Marantz AV7005 on the way as well to add to the mix, and want to try that MiniDSP thing I bought in lieu of the DCX (call me bored, besides, I hate the look of the DCX).

I relocated the fireplace switch from the front wall next to the fireplace, and finally patched up and repainted the front wall. May look at some acoustic panels on the front left and right of the TV as well (debating between trying DIY or not here).




So question, I still have my PB13 located nearfield but have it disconnected. I was planning on selling it to my brother, but it does sort of act as a "end table" right now and apparently isn't bothering my wife.

So now I'm wondering, should I try to integrate the PB13 with the two dual opposed sealed subs? What do you guys think?

Would it be better to do so with the PB13 in sealed mode, or a ported mode?

Just curious if anyone thinks this would be worth while, or would be a pain given I am crossing over my fronts at 120hz (and plan on trying 150 again) which may or may not be too high for the PB13? Given the smallish size of my room (12x17x9) I think in sealed mode the PB13 shouldn't have much difficulty keeping up given with 3 subs in that room I'll barely be using up much amp power? I know, this is immense overkill in my room, but hey, overkill is what we are all about isn't it?

Thoughts?
LL

 

My DIY Subs ... http://www.avsforum.com/avs-vb/showthread.php?t=1233892

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post #748 of 802 Old 12-09-2010, 07:14 AM
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I bought some ATS acoustic panels that I think are very nice...

The build quality is pretty good and simple. I would attempt to build these if I was you.... Its a piece of luan, (thin hardwood ply) for the back, then on the front you take 1x2 pine all the way around. The Pine has a 45 degree chamfer on one edge of the 1x2, staple or screw the pine on from the back of the luan. Then drop in your OC703 insulation and wrap with fabric - done...


The panels purchased come with these clips that make installation very nice easy and close to the wall....
You can buy these from ATS, and I highly suggest them.....
http://www.atsacoustics.com/item--ac...are--IK12.html


Chamfer bit


Here you can see the Chamfer look on the 2" thick panels...
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post #749 of 802 Old 12-09-2010, 07:46 AM
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"So now I'm wondering, should I try to integrate the PB13 with the two dual opposed sealed subs? What do you guys think?"

doesn't the pb13 have a low pass filter and phase control on the sub itself?

if so, and you could benefit from the extra spl or need to smooth out response around the room, why not give it a try? sealed mode might be easier because the raw frequency response rolloff will be closer to your main subs.

i'm interested to hear your thoughts on the minidsp when you get it integrated.

Listen. It's All Good.
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post #750 of 802 Old 12-09-2010, 08:25 AM
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An unrelated observation based on your picture. You should move your LCR speakers to the front edge of the subs and media center to avoid unwanted reflections.

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