# Advice Needed: Making the Best of a Bad Situation



## TDO (Mar 8, 2011)

I understand that I am breaking nearly every "General No-No for Good Sound", but at the time I set this room up, I knew nothing about room acoustics and designed it more for general purpose use rather than a dedicated home theater.
With that said, I am looking for advice on the things which I _can_ do to help this 'bad' room sounds its best.

To save money, these will be DIY renovations, but I am willing to spend whatever it takes to get it right. In short, if it will make it sound better, I'm willing do give it a shot. :T

Hopefully the following information will help you understand exactly what I am dealing with. Please let me know if you'd like anything additional...


*Room Dimensions* (ModeCalc output below)
23' x ~14' x 7' = 2254 cu. ft. (to drywall ceiling)
23' x ~14' x 8' = 2576 cu. ft. (to floor above)


*Room Construction*
This is a basement room, so it is entirely under ground.
The walls on the left, right, and rear are exterior and consist of 1/2" drywall directly on top of 1/4" wood paneling, then 1/2" air gap, the 8-12" cement foundation, and dirt).
The front wall is just 1/2" dry wall over 2x4's filled with paper backed R13.
The ceiling consists of 1/2" drywall, directly on top of 1/4" acoustic tile, which is then spaced of the floor joist by 1/4" strips of wood.
There is no insulation between the ceiling and the floor above, making for a 12" air gap.
The floor is covered with carpet pad and carpet, (nothing fancy).


*Room Usage*
50% Music, 50% Movies


*5.1 Setup* (crossed over at 80 Hz)
Receiver: Yamaha RX-V661
Fronts: PSB Imagine B's
Center: PSB Imagine C
Rears: PSB Imagine S's
Sub-woofer: Velodyne DLS-3750R


*Floor Plan*
View attachment 30321




*Google Sketchup Model* (<-----click to download)



*Room Photos* (orange dots indicate 1st reflection points)
(below) mic position used during REW sweeps (primary listening position)







(below) view from primary listening position















































































*REW Graphs*
These were all taken from the prime listening position, room as is, no treatment.






















*ModeCalc* (2 dimensions of ceiling shown; 7' to drywall, 8' to floor above)






























*Game Plan* (thusfar)
1. Relocate sub-woofer.
2. Treat the SBIR issues by isolating and decoupling the speakers from the cabinet as much as possible.
3. Treat first reflection points, (right wall, rear wall, ceiling, left wall if needed).
4. Install bass absorption where possible.

Again, any and all advice is welcomed. Please let me know what you suggest. Thanks.


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## TDO (Mar 8, 2011)

I have made some adjustments and wanted to make an update.

Things I did in order:
1. Found the best location for the sub woofer. (now by couch in front of right speaker, facing pool table)
2. Found the best phase setting at that location. (was 0, now 90)
3. Found the best crossover point on my receiver. (was 80, now 60)
4. Found the best positioning for my monitors. (were centered, now toward the inside edge slightly toed in)

Here are the results:







Initial sweep, and one after the changes.








3 sweeps after changes were made. (sub only, monitors only, and then both together)








Waterfall after changes were made. (all speakers)


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## bpape (Sep 14, 2006)

Nice job. This is a perfect example of what can be done with a little time and care (and no money) to improve things purely by getting the best possible positioning. A very nice touch (and one often forgotten) by moving the xover to the problem null and then adjusting phase to minimize it). And, you didn't even move the seating which I'm sure would lead to even more gains but not really feasible.

Things to consider...

- Fill the cavity around the speakers with insulation and cover with a grille for looks to avoid the cavity resonance.

- Right wall by cabinet needs a panel of probably at least 3" thickness to deal with reflections and with remaining SBIR issues.

- General reflection control panels as possible on the side walls.

- Rear: This one is tough as we don't want the back completely dead but that's where you have available corners. You also would want to address directly behind you with something thick to help with the quick reflections as well as the bass buildup. Probably an either/or would be best. If you can pull the seating forward even a few inches, you could do something at the floor to help a bit with the bass buildup and be out of sight.

- Front left corner and right front corner where the wall bumps out would be good places for chunk style absorbers to help with decay times.

- If you're up for it, cut holes in the drywall ceiling and blow in insulation then re-patch the holes. Right now, the ceiling cavity is acting like a drum with it's own resonances. By filling it, you'll damp that resonance as well as allowing that thick cavity to act more like a panel resonator and absorb some bottom end ringing.

Bryan


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## TDO (Mar 8, 2011)

bpape said:


> Nice job....A very nice touch (and one often forgotten) by moving the xover to the problem null and then adjusting phase to minimize it).


Thanks Bryan. You made the process sound a lot more methodical than it was, believe me. 
I was just trying random things, running tests, and analyzing. If it made an improvement, I kept it; if not, it got tossed out. I may have had a little luck on my side, but am pretty pleased with how things turned out. 
So, I'm assuming we lock these changes in and move on to the next phase then?

Btw, this whole room analysis/'sound engineering' thing is VERY cool and a lot of fun...I'm loving it!


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## bpape (Sep 14, 2006)

I think you've done about all you can do with what you can move. 

Time to treat it the best you can. The big thing we need to address is that broader dip in the mid 100's

Bryan


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## TDO (Mar 8, 2011)

*Treating the Ceiling*



bpape said:


> If you're up for it, cut holes in the drywall ceiling and blow in insulation then re-patch the holes. Right now, the ceiling cavity is acting like a drum with it's own resonances. By filling it, you'll damp that resonance as well as allowing that thick cavity to act more like a panel resonator and absorb some bottom end ringing.





bpape said:


> The big thing we need to address is that broader dip in the mid 100's


I've been looking over the room modes with the ceiling set at 8', which is the measurement to the floor above. I see a 141.25 in the height column which I assume is contributing to the big dip. Would insulating the ceiling help that then?

At what frequency does drywall become reflective? In other words, approximately which frequencies are going through into the ceiling dead space that I need to trap?

To answer your question, I don't mind tearing into the ceiling. Aside from helping with in room resonance, it will also help isolate the room from the upstairs.
Is the blow-in adequate and do I fill the whole cavity from top to bottom the best I can?


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## bpape (Sep 14, 2006)

The drywall is actually your hard boundary - though some frequencies are still passing through they're lower mostly. Insulating the ceiling will help stop resonances and ringing and give you a little more reduction in decay times in the bottom end. Not likely going to fix the mid 100 dip.

Bryan


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## TDO (Mar 8, 2011)

*Speaker Isolation*



bpape said:


> - Fill the cavity around the speakers with insulation and cover with a grille for looks to avoid the cavity resonance.


This is my #1 concern and have been thinking about it for a while. I'm happy to hear you suggest what you did, the question is, which insulation, and how thick? A local supplier has endless amounts of Roxul RHT80, but can order in whatever I need.


*
Below is a mock-up of what I'm thinking, let me know what you think and/or what you'd change.*
Green: Roxul 2" RHT80 (I have a case at my house I can experiment with)
Gray: Fabric to cover insulation
Black: 1/4" black rubber (leftover from my gym floor)

















This would be the left speaker box, and the whole thing would be self supported, (no glue), and slide into the wood shelf opening. As shown the back is 6" thick, left side is 4" thick, right side is 2" thick, (_the wall edge is thicker because the speakers are now toward the inside of the shelf_); all of which can change of course..

If you want to download the 3D version you can do so here. (<---Google Sketchup Model)

Is RHT80 okay to use? Is there something better?
How thick to I want this stuff? 
With the speaker centered side to side, I have 5" of clearance on each side, 3" on top, and 10" in the back. Of course I need a little room for wires and hands. I will do one for the center as well. 
Thoughts?


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## bpape (Sep 14, 2006)

The 80 will be fine. Do as much to fill all of the gaps as is practical. The more you fill the better off you'll be.

Bryan


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## TDO (Mar 8, 2011)

bpape said:


> The 80 will be fine. Do as much to fill all of the gaps as is practical. The more you fill the better off you'll be.
> Bryan


So no fear of making that box too dead or absorbent?

One thing I should mention, is that all 3 front speakers are rear ported with the following response:

Bookshelf: On Axis @ 0° ±3dB 52-23,000Hz
Center: On Axis @ 0° ±3dB 47-23,000Hz

The ports are all blocked right now, as having them open showed poor results.

Does that change anything?


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## bpape (Sep 14, 2006)

Port tunings will be below the xover frequency so that's not really an issue. I wouldn't completely block them air tight as the compliance of the woofer isn't designed for a sealed box. 

Can't make the box too dead. The idea is to effectively make it non-existent.

Bryan


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## TDO (Mar 8, 2011)

bpape said:


> Port tunings will be below the xover frequency so that's not really an issue. I wouldn't completely block them air tight as the compliance of the woofer isn't designed for a sealed box.


K, so now I'm confused. The center came with a port plug, and you can get them for the bookshelf's, which I did. From what I have read on these speakers, a lot of people are plugging the ports due to an overly warm sound (SBIR related I'm sure). Are you saying not to use them? They are an airtight fit, and can't see a way to use them where they wouldn't be.

As far as the port tuning being below the xover point...
With my system setup as it is currently, (with the tweaks from last night), you can definitely tell a difference when the ports are open and when they are plugged; both audibly and graphically. Is something wrong with my crossover then? It is currently set to 60 but it doesn't seem to be shutting the speakers down below that point.

*Here is a sweep that shows what I'm talking about. Notice the red line (ports plugged, monitors only, sub turned off).*








Does that look right?


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## bpape (Sep 14, 2006)

If the plugs are factory supplied, you'll be fine. They're likely foam and 'lossy' type that still allow a little air movement. Go ahead and plug them.

Remember that a xover isn't a brick wall. If it's a 12db/octave slope, it's only down 12db from 60-30Hz. You'll still have some overlap.


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## TDO (Mar 8, 2011)

bpape said:


> If the plugs are factory supplied, you'll be fine. They're likely foam and 'lossy' type that still allow a little air movement. Go ahead and plug them.


The plugs were shipped by the place I bought them, not factory per se. I'll look at them closer when I get home, but they seemed to be made out of vinyl or rubber and very air tight. This whole thing has got me a little worried. Can it damage them if they are air tight?



bpape said:


> Remember that a xover isn't a brick wall. If it's a 12db/octave slope, it's only down 12db from 60-30Hz. You'll still have some overlap.


True, however.... unless I'm reading it wrong, I see the sub starting to fade at the 60 Hz mark like I'd expect, but the monitors seem to be holding strong all the way down to 30 Hz or so. As long as that seems normal to you, I'm happy.


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## bpape (Sep 14, 2006)

What xover are you using? The one in the receiver/processor or the one on the sub? Should be using the one on the receiver and disable the one on the sub or turn it as high as possible. Also, make sure that your mains are set to SMALL in the receiver/processor.

Bryan


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## TDO (Mar 8, 2011)

bpape said:


> What xover are you using? The one in the receiver/processor or the one on the sub? Should be using the one on the receiver and disable the one on the sub or turn it as high as possible. Also, make sure that your mains are set to SMALL in the receiver/processor.


It's set up just as you described. I'm not sure what's going on there, but maybe it's the room that's making it extend like that.


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## TDO (Mar 8, 2011)

*Speaker Isolation*

Man, I'm staring to feel like John "Hannibal" Smith....someone pass me a cigar. 


Preliminary Results, as I just have the left box done, but it looks like it's working.

*photo of the isolation box on the left channel*









*and here is the before and after comparison*
the before was just the left channel, no sub; the after was just the left channel, no sub, but in the box









Hopefully things continue like this after I get the other one done.


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## TDO (Mar 8, 2011)

bpape said:


> If the plugs are factory supplied, you'll be fine. They're likely foam and 'lossy' type that still allow a little air movement. Go ahead and plug them.


*Here is what the plugs look like....*









They are just rubber from what I can tell. Should I not use them? They help the response, but I don't want to damage the speakers.


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## bpape (Sep 14, 2006)

Yup. That's good. Now if you get something on that close right wall, it should help more.

I would find some foam and make your own plugs to try. They'll damp the port but without sealing the cabinet. You can even try just getting some quilt batting and fill it with that - don't pack it tight though.

Bryan


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## TDO (Mar 8, 2011)

bpape said:


> Yup. That's good. Now if you get something on that close right wall, it should help more.


Is the RHT80 okay for that as well, or is it too dense for such a shallow reflection? Anything better?
How thick of a panel and how much air behind? (if any)

The problem I'm going to run into there is that the wall is so close to the speaker, a thick/spaced panel will start to intrude into the speakers space.

What if I were to cut a hole in the drywall and counter sink the panel so it is flush with the wall? 
It can be as thick as I want and will have plenty of air behind it.

*This picture shows the wall with a section cut out that will be replaced with the panel*


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## bpape (Sep 14, 2006)

2" will probably work but with a standard stud wall you have room for 3-4". BTW, you need to do the same thing to the sub cabinet spaces as the mains.

Bryan


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## TDO (Mar 8, 2011)

bpape said:


> 2" will probably work but with a standard stud wall you have room for 3-4". BTW, you need to do the same thing to the sub cabinet spaces as the mains.


The sub is now moved out of the cabinet, so those space will most likely turn into storage areas.

Btw, did you see the edits to my last post? I don't know if I got them in in time and was wondering what your thoughts were on the countersink idea and if RHT80 is okay to use right there. That whole corner is dead space, the only reason it is there is to wall in a drain pipe. I could even stuff the entire thing full of pink fluffy stuff and make it into a huge bass trap. It is approximately 13"x5'.


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## bpape (Sep 14, 2006)

Sry. The 80 is a little dense. Even just fluffy fiberglass will work. R-13 would fit perfectly. Recessing it is fine.

If the sub is out of there, I'd fill that with 80 and just make it another bass absorber in that nice little tri-corner.

Bryan


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## TDO (Mar 8, 2011)

bpape said:


> Sry. The 80 is a little dense. Even just fluffy fiberglass will work. R-13 would fit perfectly. Recessing it is fine.
> Bryan


I should explain that walled in corner a bit. The only reason it is there is to wall in a drainage pipe, so the entire thing is dead space (13" wide x 5' deep x 8' high). 

What if I were to fill the hole thing with pink fluffy stuff? I could cut rectangular access ports all over to the let the sound in. The ports would then be covered with fabric to keep the insulation in, so it would look like a series of counter sunk panels.
*
Here is an illustration of what I mean*
(pink is fluffy insulation, black is fabric access ports)


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## bpape (Sep 14, 2006)

Given the limitations on space for broadband bass control, I think that would be an excellent idea.


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## TDO (Mar 8, 2011)

K, it's a plan, but before I begin...

Does the insulation need to go all the way back to the rear of the cabinet? Which is preferred?
Are the access ports needed, or will the sound go through the drywall as is?

(I'm looking for the best performance possible, but don't want to waste effort or materials)


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## bpape (Sep 14, 2006)

The deeper you take it back, the lower it's going to absorb.

The access ports are needed to make it broadband vs a membrane.


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## TDO (Mar 8, 2011)

Is all R-30 the same?
My supplier carries CertaPro Commercial AcoustaTherm Batts but can't see the density anywhere.
Will that work for the corner fill?


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## bpape (Sep 14, 2006)

R-30 would have to be compressed quite a bit. You can use just standard R-13 in this application.

Bryan


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## TDO (Mar 8, 2011)

bpape said:


> R-30 would have to be compressed quite a bit. You can use just standard R-13 in this application.
> 
> Bryan


I'm not sure what you mean by compressed. The cavity is 13" wide 8 feet high, and 5 feet deep.
My plan is to cut the bats lengthwise make 4'x1' pieces. Stacking 2 on top of each other will make and 8'x1' piece which should cover the rear of the cavity. Then just put row after row working back toward the couch.

Something like this...








Please let me know if this is a dumb idea, or if I'm thinking about this the wrong way.


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## bpape (Sep 14, 2006)

Nope. You're right. Wasn't remembering it was that deep.

Carry on!


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## TDO (Mar 8, 2011)

And that Certainteed stuff will work?


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## bpape (Sep 14, 2006)

Yup. Just either get the unfaced or use it with the paper not exposed to the room so it won't reflect higher frequencies.


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## TDO (Mar 8, 2011)

K, I picked up the unfaced, now I have to figure out how to put it in without it settling.

My original plan is giving me headaches. Is it okay to stack like so, or will it compress under its own weight?...


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## bpape (Sep 14, 2006)

Stacking will be MUCH easier. Yes - it will compress a little bit but not a ton


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## TDO (Mar 8, 2011)

*Setbacks*

So my initial jubilation and luck ran out this weekend. :crying:

It started out great. I tore into that empty space, packed the back corner from floor to ceiling and did a test sweep. Sure enough, things improved. Feeling motivated and with great expectations, I cut the rest of the openings and packed the remainder of the dead space. Upon retesting, however, things didn't improve at all, and even got slightly worse is spots. Talk about a bummer! All that material and effort for nothing.

How can this be I wonder? I thought that a giant cube of insulation would _have_ to make things noticeably better. Right?

My next thought was to put up more treatment, but where? I have an extra sheet of RHT80, so I decided to span that back corner with it to see what effect it would have on things. Again, worse.....worse?! How can it get worse?

Long story short, are setbacks like this normal? What do you do about them? I'd love to tear the room apart and pack every square inch with insulation, but if it is going to make things worse, I hardly see the point. :help:


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## bpape (Sep 14, 2006)

Just remember that there's more to 'improving' than purely frequency response. Even if you lost a db or 2 here or there, you will have made big improvements in getting the decay time under control.


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## TDO (Mar 8, 2011)

*So What's next.*

True. I forgot about the decay. I'll just keep pressing on and hope for the best.



So, in your opinion, what is next on the list of priorities in the room?

Also, what's the best way to treat the corners in that room, 24" x 17" x 17" superchunks? Is the RHT80 okay to use for those, or would the pink fluffy stuff be better? If the RHT80 is preferred, I can start cutting and stacking tonight. That stuff is a lot easier to move around, so I can do a little experimenting as well.

*example area for superchunk*


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## bpape (Sep 14, 2006)

The 80 will be fine for chunks. 

If you want to find out what happened, you can have someone hold plywood over the openings you cut in the side (other than the one beside the speaker) and see how much you have to cover or which you have to cover to undo any changes in response. Then you can make an assessment as to whether it's worth covering or not.


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## TDO (Mar 8, 2011)

So is the next step is to chunk every corner I can, or should I be a little more systematic to my approach?


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## bpape (Sep 14, 2006)

Those will help with decay times.

I would also consider some thick panels centered behind the seating on the far rear wall. Those may also impact bass response.


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## TDO (Mar 8, 2011)

Thick meaning 4" panels RHT80 panels with as much air gap as I can afford?

Space is limited, but I may be able to pull the couch out a bit. I'll also experiment with sandwiching some boards behind the couch itself.


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## bpape (Sep 14, 2006)

Or even 6" panels with a couple inch gap if you can swing it.


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## TDO (Mar 8, 2011)

That may be a little tight but I'll see what is practical and do what I can.

I know there has been discussion on this, but say I have 6" to work with, would I rather go?
a) 6" panel w/ no air gap
b) 4" panel w/ 2" air gap
c) 3" panel w/ 3" air gap


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## bpape (Sep 14, 2006)

a or b. Little difference in performance between the 2.


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## TDO (Mar 8, 2011)

Something like this? 
Keeping symmetry, this is about the best I can come up with. 


*2' x 2' panels in between column chunks*


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## bpape (Sep 14, 2006)

That'll work


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## TDO (Mar 8, 2011)

*On Panels...*

*On Fabric...*
Could you briefly describe the "breath test"; how much air transmission are we looking for here exactly?

Is there anyone that does custom fabric printing, (pre-printed or custom), that I could then use to cover the panels?

*On Frame...*
On a 4" thick panel, what type of a performance difference can I expect having the sides open to the air vs. having a solid wood frame which covers the sides? Both front and back will be open in both cases.


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## bpape (Sep 14, 2006)

All you're looking for is something that will pass air relatively easily. It's not like you're putting speakers behind it. If you hold it tight to your mouth and blow through it, are you busting a kidney?  If so, it's not good. If it's not too bad, you're fine.

We can do the printing on cloth. It's our Art Panel process but without the panel

On a 2x4' panel, you have 8 sq ft in front. If you left the sides open completely, you'd add another 4 sq ft of absorption. Without a frame, you'll have a hard time making it nice and sharp on the edges but it will work. A good compromise is to make the frame and then use a router or jig saw to cut large openings in the sides, top and bottom. Best of both worlds. Probably 2 extra Sq Ft of absorption exposed but still a nice sharp frame to hold corners and not crush the core when you stretch the cloth.


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## TDO (Mar 8, 2011)

bpape said:


> We can do the printing on cloth. It's our Art Panel process but without the panel


I don't see a price on your site for just the fabric. Link?


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## bpape (Sep 14, 2006)

It's not something we advertise. You can call the 800 number and Christina can go through the options with you.


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## TDO (Mar 8, 2011)

*Ceiling Idea*

In regards to the ceiling first reflection point...

Since my ceiling in only 7' high, mounting a panel might make my taller guests duck to get by. Instead, I was thinking about cutting a rectangle into the sheetrock and putting a panel in it's place. Essentially this would just be counter sinking the panel flush with the ceiling.

Would this work okay?
Would I want to use RHT80 for the panel or something else?
Do I want to fill the space above it with the fluffy pink stuff or leave the 12" airspace?


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## bpape (Sep 14, 2006)

That's doable and standard fluffy would be fine. Just understand this will compromise your isolation somewhat.


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## TDO (Mar 8, 2011)

bpape said:


> That's doable and standard fluffy would be fine. Just understand this will compromise your isolation somewhat.


Meaning it will be louder for the floor above? Hey, as long as it improves the listening experience for those _in _the room right? 

Expanding on this concept...
If I were to make a 2'-3' border around the entire ceiling perimeter for broadband/bass absorption, what kind of results could I expect? Obviously it would be a lot of work so I want to make sure it's worth it.

If I did this, which would net the best results performance wise:
a) Just RHT80, if so, how thick?
b) Just fluffy pink stuff, if so, how thick?
c) Sound board under fluffy pink stuff, if so, how thick on each?

As a reminder I have about 12"-14" of dead space above the drywall ceiling. 
(I could put in the blow-in while I had it open as well.)


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## bpape (Sep 14, 2006)

I don't know that you need all of that. Maybe just 2' across the front and rear walls. Standard fluffy will be fine. R-30 with a paper facing will keep things in place and minimize higher frequency absorption.


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## TDO (Mar 8, 2011)

bpape said:


> I don't know that you need all of that. Maybe just 2' across the front and rear walls. Standard fluffy will be fine. R-30 with a paper facing will keep things in place and minimize higher frequency absorption.


We want to minimize HF absorption? Why so?


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## bpape (Sep 14, 2006)

No point taking more high frequency energy out of the room than you have to. Curtains, people, furniture, carpet already do HF only absorbing.

Plus you'll have plenty more with the reflection panels and the other corner absorbers.


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## TDO (Mar 8, 2011)

bpape said:


> Port tunings will be below the xover frequency so that's not really an issue. I wouldn't completely block them air tight as the compliance of the woofer isn't designed for a sealed box.
> 
> Can't make the box too dead. The idea is to effectively make it non-existent.
> 
> Bryan


Are all foam plugs created the same, or do you have some you recommend? I've decided I need some.
Frequency response without them is horrible where they are sitting and with them I am getting an odd tight/distressed sound when it hits certain low frequencies at loud volumes; (I verified this today at my local audio shop). I think the foam ones may be a good compromise.


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## bpape (Sep 14, 2006)

Nothing special. You just need something that will damp the port yet still not seal the box air tight. Easiest way is to get some poly batting and put some in the ports - just don't pack it really tight.


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