Entire front wall as bass trap vs corner bass traps - AVS Forum
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post #1 of 39 Old 05-23-2014, 12:23 AM - Thread Starter
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I am building out my front wall to place a large AT screen with my speakers behind it. I have about 18" worth of space behind the screen and I'm wondering if I should go ahead and fill that space with pink fluffy insulation cover or maybe uncovered with 6mil poly. I see lots of people doing the corner super chunk bass traps but my room is odd shaped with 2 doors that open into the screen wall preventing a corner trap placement. I've also been reading a lot about baffle walls and it appears that I don't have enough room lateral to the L/R mains to get a true baffle config. So, I started researching alternatives and it appears that deadening the front wall will help prevent SBIR and having that much real estate used as a bass trap should help with bass response as well.

Does this sound like a worth while treatment? If so what do people wrap their pink fluffy in the prevent fiberglass from getting all over the room? And lastly, should I use the 6mil poly here or go with a completely broadband absorber?
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post #2 of 39 Old 06-20-2014, 09:16 PM - Thread Starter
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Any suggestions here? I'm also very curious as to if the pink fluffy needs to be wrapped if its behind a curtain? And if so what would be the cheapest option for that?

Thanks
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post #3 of 39 Old 06-21-2014, 12:17 AM
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I would do it, without the 6 mil poly. Aside from helping with bass decay and boundary cancellations, the absorption will also minimize reflections from your surround speakers. You don't want to hear surround content coming at you from the wrong direction (in front of you), muddying the soundstage.

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post #4 of 39 Old 06-21-2014, 05:21 AM
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I would definitely do it, but it won't have the same effects as corner treatment. The reason corner treatment works well is because all room modes end in the corners and the sound pressure is the highest in the corners. See this for instance:

Intro to some room modes

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post #5 of 39 Old 06-21-2014, 06:14 AM
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Bob, as explained by Dr Floyd Toole in his room acoustic classes fiberglass is a good velocity absorber not a pressure absorber. Corner traps need to be membrane bass traps to be effective. His direct quote when asked the question was "Putting fiberglass in corners for bass trapping is a waste of fiberglass"

A well know theater designer specs a layer of compressed fiberglass, 5 mil poly and another layer of compressed fiberglass for the entire front wall turning it into a membrane trap.
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post #6 of 39 Old 06-21-2014, 08:45 AM
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I will be ordering a pair of MSR "Spring Traps" for my room though recommendation is for four........quite ingenious way to tame bass in a smaller package. From my understanding, Triad manufactures product for PMI ie. MSR.

An option for you to consider..........
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post #7 of 39 Old 06-22-2014, 12:06 AM - Thread Starter
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Doublewing, I thought your room was done? Are you having issues with your UXL's? I like those MSR traps but they are a little more $$$ than I'd like to spend. I was looking at some R30 batting sideways at 15" thick to try and deaden things up front, and just hoping it will somewhat help with bass given i don't really have any corners to put traps in.

Bigmouth, is there any use in trying to emulate that membrane trap? Do you see any use in the large pink fluffy trap or just a waste of time/fiberglass?
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post #8 of 39 Old 06-22-2014, 09:15 AM
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Quote:
Originally Posted by uopdrmark View Post
Doublewing, I thought your room was done? Are you having issues with your UXL's? I like those MSR traps but they are a little more $$$ than I'd like to spend. I was looking at some R30 batting sideways at 15" thick to try and deaden things up front, and just hoping it will somewhat help with bass given i don't really have any corners to put traps in.

Bigmouth, is there any use in trying to emulate that membrane trap? Do you see any use in the large pink fluffy trap or just a waste of time/fiberglass?
Is a theater ever done?

I was rushed to finish room due home being a "Tour Home" last year. I'll finish room up this Summer when my coffered ceiling project is complete. Wasn't able to finish ceiling before tour due to time constraints.

My four UXL's are fine.........80-90% of what you hear is room related. Like most who have a soundproofed, dampen room will have issues around 30 Hz or other frequencies due to room dimensions and modal interaction. Bass traps are used to help decay times in room since a well sealed room tends to keep LF energy in room.......my objective is to improve sound as best as I can with appropriate tools.

I know you are looking to go ported, but IMHO.....I refuse to give up below 15 Hz content........where the wow! factor lies. Four UXL's in my room deliver WOW! factor in spades!
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post #9 of 39 Old 06-22-2014, 12:41 PM
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You don't have to give up low SPL because you go ported. Porting low (below 20hz) often gives a huge SPL boost at port tune (below 20hz) compared to sealed and provided the tune is low enough (think 17hz, 16hz, 15hz, 14hz etc...) then you have usable real world output down to single digits with the right sub and box.

Bigger boxed have less fall off below port tune so that's a negative, but if you can hide behind a false screen wall and use the height to add some volume you can get a really nice big ported sub with output at 10hz.

Four UXL's are really nice subs. Those ported would be even nicer

Those subs are monsters either way, but they are scary when ported. Check this out:



There's plenty of exension IMO. The point where the ported and sub is equal is about 6.85hz. At 8hz there is more usable output on the ported.




If low extension is your game you just need to lower the tune a bit. Sure you give up some SPL in the meat of the bass band (30hz-60hz) but that is compared to a higher tune like 20hz or 25hz, not a sealed box. Compared to a sealed box the ported hangs with it for SPL no problem, and near port tune has a ton of power handling and output.

You could port at 12hz or 13hz even with those subs and get significant output at 6hz if you wanted it.

The shock factor and impressiveness of 13hz @125 db is a lot more impressive than 6hz at 90db IMO. By the time a low port tune sub drops in output compared to a sealed I think output on both is dropping off on most subs anyways so a proper port design is a great way to extend out your -3db bass shelf. If your sealed subs are down a bunch of db's anyways it's going to take EQ and a ton more wattage to bring that back up flat- that just puts a heavy load on your amp and driver unnecessarily IMO.

I've been playing with subs and sub ideas for my theater and I am totally stuck. I want Sealed but to get the output I want in my giant room I'd need so many of them and so many watts.

One idea I had was a front loaded or folded horn in my riser, two actually with two UXL 18" drivers and tuned for output to about 25hz to start. I'll lack that ultra low extension but I'll have plenty of output out of just 2 subs. And then later I can add some low tuned ported subs to fill in the bottom. 4 drivers should get me 130db's @20hz and also with usable output at 8hz of 105db. I can't figure out how to get that with Sealed subs.

If I go sealed I'd need to do like 4 subs like you, but then add something like 10 or 12 more cheaper subs like the Infinity 1260's around for a boost. The wow factor of a lot of drivers could be cool, and I could hide them in clever spots. I am just totally confused. I think I need to audition some sealed and ported and horns for some help, I wish I had attended one of the DIY audio guys get together events.
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post #10 of 39 Old 06-22-2014, 01:47 PM - Thread Starter
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I had planned on going sealed originally, then switched to ported because of the same thing you are talking about Mfusick. Ultimately, I ended up going back to sealed due to smaller footprint and being able to put 2 in the rear to even my response. Once I have them built and I can measure things I may end up switching to ported if I have the space where they sound best and only if I find the sealed lacking. After hearing DW's experience I'm thinking I may be fine with the 4 UXL's sealed.

Here's the latest build idea: Looking for design help on low profile UXL-18 build

I'm still wondering if it's worth loading the front wall with the pink fluffy. It looks like some say yes and a few say no. Just not sure what to do there?
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post #11 of 39 Old 06-22-2014, 02:36 PM
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Sealed boxes are way easier to make. They are easier to design and also build. They are also smaller. And the cost less to make because they need less materials. That's a bonus for sealed. Basically if you can live the with SPL of Sealed then that is the way to go.

My understanding of the options are basically:

IB sub: Cheapest drivers because IB subs tend to have smaller magnets which saves on cost. Great low end extension, great sound quality. Doesn't need a ton of power. Least amount of SPL output.

Sealed: Increase power handling and SPL compared to IB, great power handling. Good for small footprint enclosures. Excellent low end extension and sound quality. Expensive drivers and amps to get great results.

Ported: Bigger boxes, more expensive to build due to more materials needed. More SPL output than sealed at port tune, great power handling at port tune. Below port tune power handling and SPL drop off. More complicated to design properly. Increased efficiency.

Horns: Lowest distortion, most SPL output. Increased efficiency. Most expensive to build. Largest. Cost the most to build in materials used.

You can often make up for the lost SPL by going with sealed by using high end drivers and amps, which is required to get the output or the small footprint with great results.

I am toying with the idea of what if size totally didn't matter, and what if how complicated the build totally doesn't matter, and what if it took 5 or 6 sheets of wood to build and it didn't matter, and I wasn't looking to cheap out on the drivers or amps. What's the maximum I could achieve ? It seems like horns win hands down. I might do one each back corner, and two under the riser. But then again I might just go sealed and keep adding drivers over the years until I am happy. I think I am more confused now than when I started.

It seems like ported does get a bad reputation and most of that is due to the bigger size (a real problem for some) and the other part is bad designs. But the higher end ported builds by some of the pro's in the DIY forum that both designed them right, and used high quality drivers seem like the best. The output and extension is great.

How big is your room ?

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post #12 of 39 Old 06-22-2014, 02:40 PM
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As far as the front wall I would not do the whole thing a bass trap, I would just do the corners and see how it sounds and measure. Chances are you should be ok.

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post #13 of 39 Old 06-22-2014, 11:32 PM - Thread Starter
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My room is 4200ft^3. I would do normal corner traps except I really only have 1 corner due to 2 corners being covered by doors and the other is really a cutout into the room so there is no 90 degree angle more like two 135 degree corners. I was thinking the entire wall would also help to cancel out any SBIR issues a cut down on the crazy echo that already exists in there as is.

DW: At this point I'm kinda hoping for the end of my theater as I just can't wait to have 4 UXL's and some decent acoustics. After that I'm sure I'll tinker, but at least the big stuff will be done.
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post #14 of 39 Old 06-23-2014, 12:19 AM
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Originally Posted by uopdrmark View Post
I was thinking the entire wall would also help to cancel out any SBIR issues a cut down on the crazy echo that already exists in there as is.
I think the large surface area of the front wall will be more effective than corner traps. Aside from helping with long decay times and boundary cancellations, it will also prevent surround information from reflecting off the front wall.
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post #15 of 39 Old 06-23-2014, 05:11 AM
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Do the whole front wall. you really only want to hear the speakers not the reflections from the front of the room.
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post #16 of 39 Old 06-23-2014, 06:48 AM
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I'm confused I think, are we talking about absorption from reflections or bass trap for nodes?

I agree with Big(Jeff) that do whole wall so you only hear speakers; but you'll still want the corner traps too for bass. Your front wall shouldn't be bass only treatments though. You'll want to treat for higher frequencies too.
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post #17 of 39 Old 06-23-2014, 03:45 PM
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How do you suggest compressing the insulation? 4" compressed with mesh? Chicken wire or something of the like I would suspect. Compress to an inch?

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post #18 of 39 Old 06-23-2014, 04:03 PM
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Originally Posted by Mfusick View Post
I'm confused I think, are we talking about absorption from reflections or bass trap for nodes?

I agree with Big(Jeff) that do whole wall so you only hear speakers; but you'll still want the corner traps too for bass. Your front wall shouldn't be bass only treatments though. You'll want to treat for higher frequencies too.
So the front wall should absorb all frequencies... Like a black hole?

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post #19 of 39 Old 06-23-2014, 05:11 PM
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Quote:
Originally Posted by Mfusick View Post
You don't have to give up low SPL because you go ported. Porting low (below 20hz) often gives a huge SPL boost at port tune (below 20hz) compared to sealed and provided the tune is low enough (think 17hz, 16hz, 15hz, 14hz etc...) then you have usable real world output down to single digits with the right sub and box.

Bigger boxed have less fall off below port tune so that's a negative, but if you can hide behind a false screen wall and use the height to add some volume you can get a really nice big ported sub with output at 10hz.

Four UXL's are really nice subs. Those ported would be even nicer

Those subs are monsters either way, but they are scary when ported. Check this out:



There's plenty of exension IMO. The point where the ported and sub is equal is about 6.85hz. At 8hz there is more usable output on the ported.




If low extension is your game you just need to lower the tune a bit. Sure you give up some SPL in the meat of the bass band (30hz-60hz) but that is compared to a higher tune like 20hz or 25hz, not a sealed box. Compared to a sealed box the ported hangs with it for SPL no problem, and near port tune has a ton of power handling and output.

You could port at 12hz or 13hz even with those subs and get significant output at 6hz if you wanted it.

The shock factor and impressiveness of 13hz @125 db is a lot more impressive than 6hz at 90db IMO. By the time a low port tune sub drops in output compared to a sealed I think output on both is dropping off on most subs anyways so a proper port design is a great way to extend out your -3db bass shelf. If your sealed subs are down a bunch of db's anyways it's going to take EQ and a ton more wattage to bring that back up flat- that just puts a heavy load on your amp and driver unnecessarily IMO.

I've been playing with subs and sub ideas for my theater and I am totally stuck. I want Sealed but to get the output I want in my giant room I'd need so many of them and so many watts.

One idea I had was a front loaded or folded horn in my riser, two actually with two UXL 18" drivers and tuned for output to about 25hz to start. I'll lack that ultra low extension but I'll have plenty of output out of just 2 subs. And then later I can add some low tuned ported subs to fill in the bottom. 4 drivers should get me 130db's @20hz and also with usable output at 8hz of 105db. I can't figure out how to get that with Sealed subs.

If I go sealed I'd need to do like 4 subs like you, but then add something like 10 or 12 more cheaper subs like the Infinity 1260's around for a boost. The wow factor of a lot of drivers could be cool, and I could hide them in clever spots. I am just totally confused. I think I need to audition some sealed and ported and horns for some help, I wish I had attended one of the DIY audio guys get together events.

Ported will never, ever dig in single digits like multiple sealed. Your model doesn't show eq ability with sealed.........multiple sealed below any ported subs tune will kicks its butt period.

It's all about your goals......I'm flat down to 8 Hz and only -2db's at 5 Hz.......show me a ported sub that can do that with out being the size of an elephant!

My goal is flat to single digits.....so SPL above 115 db's is not an objective of mine. Small cabs placed around room does wonders.........hitting reference down to 5 Hz is
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post #20 of 39 Old 06-23-2014, 05:26 PM
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Quote:
Originally Posted by Mfusick View Post

If I go sealed I'd need to do like 4 subs like you, but then add something like 10 or 12 more cheaper subs like the Infinity 1260's around for a boost. The wow factor of a lot of drivers could be cool, and I could hide them in clever spots. I am just totally confused. I think I need to audition some sealed and ported and horns for some help, I wish I had attended one of the DIY audio guys get together events.

Re-think this idea......ie. adding 10-12 more less expensive subs. Granted, many multiples might help some, but those driver would be holding back the big guns. You are much better off going 6-8 UXL's IMHO.......much easier to integrate and maintain end goals. Just passing on same advice I received from an expert.
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post #21 of 39 Old 06-23-2014, 05:45 PM
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So the front wall should absorb all frequencies... Like a black hole?
The only thing you want to hear from your front wall is your speakers.
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post #22 of 39 Old 06-24-2014, 10:19 AM
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The only thing you want to hear from your front wall is your speakers.
Maybe, maybe not. The front wall is a reflection point for the surrounds, and maybe we should incorporate some diffusion on it. Personally I've never done it but if the front wall was tall and/or wide enough I could see myself speccing it in, much like I've designed hybrid solid/absorptive walls in larger spaces.

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post #23 of 39 Old 06-24-2014, 10:49 AM
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Maybe, maybe not. The front wall is a reflection point for the surrounds, and maybe we should incorporate some diffusion on it. Personally I've never done it but if the front wall was tall and/or wide enough I could see myself speccing it in, much like I've designed hybrid solid/absorptive walls in larger spaces.
really? I have always read that the only thing you should hear from the front wall was your speakers. Wouldn't it make more sense to have diffusion on the side or back walls ? I am not doubting you, just really curious the thinking.
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post #24 of 39 Old 06-24-2014, 01:28 PM
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The front wall is a reflection point for the surrounds, and maybe we should incorporate some diffusion on it. Personally I've never done it but if the front wall was tall and/or wide enough I could see myself speccing it in, much like I've designed hybrid solid/absorptive walls in larger spaces.
I tried experimenting with absorption on the front wall at the reflection points of all 4 surrounds. I liked it enough to add more absorption. Tried the same thing with diffusion; helped, but I preferred absorption.

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post #25 of 39 Old 06-24-2014, 03:41 PM
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So pink fluff across the front wall besides the corners would be ok?

Any certain type I need to look for?
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post #26 of 39 Old 06-25-2014, 09:29 AM
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Anyone that could help please?
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post #27 of 39 Old 06-25-2014, 09:41 AM
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I tried experimenting with absorption on the front wall at the reflection points of all 4 surrounds. I liked it enough to add more absorption. Tried the same thing with diffusion; helped, but I preferred absorption.
It's good to experiment of course.

I would expect each person's experience to differ depending on the speakers they are using, the angle at which the sound leaves the surround speaker and hits the front wall (and hence the spectral content of the reflection) and the distance from speaker to wall and wall to listener (hence level of reflection relative to direct sound).

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post #28 of 39 Old 06-25-2014, 10:39 AM
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Ported will never, ever dig in single digits like multiple sealed. Your model doesn't show eq ability with sealed.........multiple sealed below any ported subs tune will kicks its butt period.

It's all about your goals......I'm flat down to 8 Hz and only -2db's at 5 Hz.......show me a ported sub that can do that with out being the size of an elephant!

My goal is flat to single digits.....so SPL above 115 db's is not an objective of mine. Small cabs placed around room does wonders.........hitting reference down to 5 Hz is
If you ported at 11hz the point where sealed would be louder than ported is 4hz. You also don't need EQ boost in the single digits because of room gain. Your goal is flat response, not louder response. A UXL ported at 11hz would be flat to 6hz before any EQ by most definitions of "flat". A negative 3db bass shelf is way over there in single digit land and most importantly the ported sub has significantly more output at 10hz. Below this really is point of diminishing returns IMO, and I am not sure you could give a sealed sub enough EQ and watts to equal the ported SPL at 10hz anyways. Every time you boost EQ to bring up the low end extension of a sealed sub you need like twice as many watts or more, you will eventually hit a solid wall weather or not that is either mechanical or electrical in nature. Ported has better SPL and very good power handling at port tune, so you could actually apply a crap load of watts and even boost at 10hz and get even more output. But again the goal would be flat, not higher- so you want all frequencies to be the same. The main problem with ported is the subsonic filter for protection, if you really wanted to push it hard below port tune you risk damage to your driver. I doubt at that low there is any serious source material to do that, but it might be worth considering.

Both options are good. I agree with you and everything you say. I am leaning towards sealed myself simply because of simplicity and extension seems easier. But the big difference between the two systems is not that either wouldn't be flat from say 5hz to 19khz but that the ported system would go about 10db louder and still be flat. If you want a system that does 100 or 105db sealed makes sense. But if you want a system that will be flat at 120db you'll need to go ported. Different priorities.

-

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post #29 of 39 Old 06-25-2014, 08:28 PM
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If you ported at 11hz the point where sealed would be louder than ported is 4hz. You also don't need EQ boost in the single digits because of room gain. Your goal is flat response, not louder response. A UXL ported at 11hz would be flat to 6hz before any EQ by most definitions of "flat". A negative 3db bass shelf is way over there in single digit land and most importantly the ported sub has significantly more output at 10hz. Below this really is point of diminishing returns IMO, and I am not sure you could give a sealed sub enough EQ and watts to equal the ported SPL at 10hz anyways. Every time you boost EQ to bring up the low end extension of a sealed sub you need like twice as many watts or more, you will eventually hit a solid wall weather or not that is either mechanical or electrical in nature. Ported has better SPL and very good power handling at port tune, so you could actually apply a crap load of watts and even boost at 10hz and get even more output. But again the goal would be flat, not higher- so you want all frequencies to be the same. The main problem with ported is the subsonic filter for protection, if you really wanted to push it hard below port tune you risk damage to your driver. I doubt at that low there is any serious source material to do that, but it might be worth considering.

Both options are good. I agree with you and everything you say. I am leaning towards sealed myself simply because of simplicity and extension seems easier. But the big difference between the two systems is not that either wouldn't be flat from say 5hz to 19khz but that the ported system would go about 10db louder and still be flat. If you want a system that does 100 or 105db sealed makes sense. But if you want a system that will be flat at 120db you'll need to go ported. Different priorities.
This must be my biggest quote ever!

A ported sub tuned to 10-12 Hz.......well I can fit four sealed in the same space with better overall seat to seat FR........

I agree with a lot of your points, it's all about compromises......I'm ok with less output above 20 Hz as long as I'm flat down to 5-8 Hz at reference with no more than 1-2 db variance across seven seats. I've done that in my system and nobody has a clue where all four subs are ........the beauty of going multiple sealed.

If one is ok with giving up floor space, subs in full view, and wants to hit > 130 db's above 50 Hz ....well yeah.....ported is the way to go. My poor quad UXL's can only hit 126 db's.
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post #30 of 39 Old 06-26-2014, 05:24 AM
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Any suggestions here? I'm also very curious as to if the pink fluffy needs to be wrapped if its behind a curtain? And if so what would be the cheapest option for that?

Thanks
I am currently experimenting with a baffle wall and an AT screen. I had to cover the baffle wall with a black cloth because there was too much of light reflection from the baffle wall, causing a lack of contrast in the projected image. The baffle wall did not produce the sound I was seeking to achieve. I'll need a lot of help here. My HT is a 100% DIY project.
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