# How much can be gained by bass traps?



## grn1969c10

I just opened a box of Roxul 60 and wanted to see how it affects the room response before deciding on how to install it. I took a baseline measure with no EQ which is dark blue. I then placed 4 sheets in the left front corner from floor to ceiling - two thick and two high. I placed the other two in the right front corner - two deep, but only half height on the wall. The next measurement is purple. There is some improvement I think, but not earth shattering.









Any suggestions on how to optimize the thickness and placement of the traps based on the room response would be great. I'll see if I can't find the layout of my room and post it. The room node analysis is based off of a rectangular room assumption ignoring the open kitchen.


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## OvalNut

Thanks for the testing. Try doing before and after waterfall charts in addition to the frequency response. A big benefit of bass traps is the reduction of low end ringing, and the waterfall charts will show that.

Thanks!


Tim
:drive:


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## grn1969c10

These waterfalls come from the previous before and after graph I posted. I can see a slight reduction at 19Hz and maybe some at 70Hz. I bought a BFD and it is capable of providing significant improvement to the frequency response, but I was applying filters with all the precision of a sledgehammer. With so much EQ, my max spl was greatly reduced and the ringing was excessive. I was hoping some traps in the corners would have a similar positive impact on the room response so I could apply less aggressive EQ.

Perhaps I should mention this room has nine windows in it with metal venetian blinds. What wall isn't covered by windows, is wood paneling with no drywall backing. If you push on the paneling it flexes quite easily between the studs.


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## bpape

A few things....

First, while corners are great for overall control, there are a lot of other places that will address specific issues. Corners are not a be all, end all solution.

Second, get the speakers out of the corners. You're maximally exciting the room modes.

Third, you'll need more coverage than just 1.5 corners. Also, you don't say how thick each of the panels is so it's hard to say what the effective range would be. Regardless, you're not impacting below 20Hz - that's likely a difference in mic position or something else in the room being different.

Fourth - play with subwoofer position. You can drastically impact frequency response with small movements of the sub AND with changes in the seating position.

Lastly - Having the width of the room being exactly double the room height, you're going to have overlapping room modes so some of that will need to be dealt with via a combination of some of the above.

Bryan


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## grn1969c10

Hi Brian,



> Corners are not a be all, end all solution


The room has so many windows and openings into other rooms that design (thickness, framing, placement etc.) is difficult for me to visualize. The front corners are the easiest place for me to add bulky material as they are virtually empty with about 26" diagonal clearance between window sills on adjacent walls. 



> there are a lot of other places that will address specific issues


Thats why I posted some REW measurements. Hopefully specific issues can be identified and alternate treatments suggested.



> Second, get the speakers out of the corners.


Already done. I need to update the room schematic. The CSX-15 is sitting left of the TV now and the mains are just outboard like bookends. That places the mains about 4 1/2' from the left and right corners and centered between the left and right double wide windows with about 1' behind them.



> Third, you'll need more coverage than just 1.5 corners. Also, you don't say how thick each of the panels is so it's hard to say what the effective range would be.


I have a second box of Roxul 60 (48" x 24" x 2") I haven't opened yet. That should be enough to treat the front wall (I hope!) I just opened one box and stacked the pieces in the corners to see what would happen.



> Regardless, you're not impacting below 20Hz - that's likely a difference in mic position or something else in the room being different.


My bass output drops like a rock at 40Hz. I'm fighting a losing battle just trying to get decent response to 25Hz. Oddly enough, I thought the waterfall showed a little less ringing at 19Hz. Though in the overall scheme of things that might be irrelevent.



> Fourth - play with subwoofer position. You can drastically impact frequency response with small movements of the sub AND with changes in the seating position.


I have experimented with moving the sub all over the place. The benefits have been quite small. Its current position just left of the TV seemed to limit the effect of a 32Hz null that showed up when the sub was nearer the corner of the room. The 60-80Hz range showed little variation. The couch has been moved two feet closer to the TV. I'm new enough at this that my testing technique changes every week or so. (Hopefully for the better.) Becasue of this, I don't attempt to compare with older test results much and try to establish a new baseline measurement before investigating changes in placement, settings, treatments, etc.



> Lastly - Having the width of the room being exactly double the room height, you're going to have overlapping room modes so some of that will need to be dealt with via a combination of some of the above.


Most room mode calculators predict problems at 70Hz from room width and room height. Not bad considering the room has a lot of open back wall which the calculators can't factor in. I definitely measured a big nasty at about 68Hz. Hopefully the absorption material can be optimized to squash this frequency. 70Hz has a quarter wave of about 4 feet, I think. I certainly can't place traps four feet from the walls! I can cover both front corners from floor to ceiling though. I can go 4" thick, 6", or even solid triangles filling the corner - whatever would be most effective. Distance between windows is well under two feet which might limit what I can do to the side walls.

I hope you don't mind all of the quotes. I type slowly and think even slower so it helps me keep my thoughts organized!


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## bpape

OK. If you want it to be pretty effective into the subwoofer range deep - you'll want to go 6" thick. 

As for dealing with the width/height thing, you can do that potentially by using 6" panels over the seating position. 

Dropping off under 40, don't know but my gut is that the sub just doesn't reach that low in the same power level as above that. Can't say for sure but $399 for a 15" sub at retail doesn't leave much money when you compare it to known drivers that do go down that low that cost that much just for a driver. Not trying to take a swipe at it, just trying to be realistic.

Bryan


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## grn1969c10

Thanks Bryan, I have been trying to find out the optimum thickness to make the traps. I will look into going six inch thick and from floor to ceiling.

I don't know if buying the Cadence sub was a good idea or not. It's a budget box and they do not publish any type of FR curve for it. The money saved compared to a MFW-15 has already been dumped into a BFD, cabling, and two boxes of fiberglass. I would like to think a lesser sub with some room treatment and EQ would sound as good as a better sub stuck in a bad room. I do know my old 12" JBL sub exhibits similar response from 40 to 200Hz indicating the room may be a significant source of my troubles. The JBL fell off so hard at 40Hz that some forum members questioned if I even had a sub when I posted a "sub response graph". :hide:


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## bpape

Overall sound quality, absolutely. Below 40hz, likely not. You said you were looking for good response down to 25hz and doing so for HT. That just takes a driver that will move some serious air, do so at higher volume levels, and do so without compression or breakup. An EQ won't fix rolled off response - unless you want to shelve it down from 40Hz up to make it flatter and then just push it harder.

If you're going to go 6" thick - you can make solid trianglar 17x17x24" chunk absorbers that will work even better with the same amount of material.

Bryan


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## grn1969c10

I started working on the bass traps today. My lack of woodworking skills is becoming painfully obvious. I raided my dads garage for scrap wood and had him cut me some pieces to work with. I tried gluing some pieces together - It's cold in the garage and it took over two hours before the wood glue even began to set. Tomorrow I'll see if my design concept will work.


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## grn1969c10

I got one trap made with three to go. I made a light frame to hold the fiberglass but I didn't anticipate the pressure it would exert on the frame due to tight tolerances. It bulged outward like a pear in the middle! I managed to bind it with some cheap plastic packing rope to cinch in the middle. I wrapped it with a layer of batting and I have some cotton cloth to cover it with eventually. I'll try to take a few pictures today.


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## grn1969c10

The pictures are quite ugly and thats with me staying out of them! They're good enough to see how I'm cutting the two inch roxul 60. I get 10 and 2/3 wedges from each sheet and 64 wedges per box of six sheets. The wedges have a 24" face and are 6" thick. (Trapezoid, 24" x 8.5" x 12" x 8.5")


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## grn1969c10

Here you can see the frames I made. My dad ripped a board into a bunch of 45 degree strips that I used to strengthen the frame and to provide a lip in the front to lock the wedges in place. The grain on the side pieces is different because I used all the scrap wood I could find in dads garage. The pieces with the horizontal pattern flex more than the ones with vertical cuts. 


























As I filled the frame with fiberglass it began to pooch a bit in the middle!


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## grn1969c10

I tried to tie the trap with cord to pull the sides in and get it a little closer to square. The cord looks like its going to show through the fabric. I've already wrapped it with batting now and probably won't redo it.









I notched the corners of the frame enough to give the cord a lower profile in the second trap I built and added some foam strips to the edges. Hopefully the cord will disappear under the fabric and won't be as obnoxious.


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## grn1969c10

Well, this is all I have completed today. I grossly underestimated the batting that I would use and need to buy some more. I will wait until all four are complete before I cover them in the final cloth. I haven't decided yet on what to use for feet. I need something that will bias them to lean back into the wall as I made them to be easily portable and don't have any positive attachment to the wall.


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## chas

Hi Matt....looking good - and they should look great once you get the fabric on them!


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## eugovector

Looking very nice. Can't wait to see the finished product.


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## grn1969c10

I got all four built except for the final muslin covering. They're in both front corners floor to ceiling. The benefits seem to be depressingly slim. I'm having a hard time getting motivated to even finish the covers.

After two and a half months of learning to use REW, buying BFD, building traps, etc, I'm coming to the conclusion that my CSX-15 is no better than the standard fare from circuit city. It can crank out some serious boom as long as you don't ask it to go below 35hz. Yeah, whatever. I was frustrated and deleted all the graphs from this last week. I'll redo before and after graphs and post them monday or tuesday.

I was hoping to participate in the Home Theater Shack Cash Giveaway which could have helped pay for the Roxul 60, but that's not going to happen either. :sad2:


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## bpape

Don't get discouraged. While bass control isn't going to perform miracles and add 2 more octaves to a sub's performance, it will still provide excellent benefits in terms of decay time control, tightness of bass/lower mids, improved dialog clarity, etc. 

Bryan


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## grn1969c10

I procrastinated posting for a while because I don't like the results. I have retested three different times and with minor variations due to mic placement, fridge humming, or whatever, the results are pretty much typical.

Waterfall 
- No traps in the room.








Waterfall 
- Both front corners trapped w/ 6" Roxul 60.








Graph 
- Light Green, No Traps
- Dark Green, With Traps








It's interesting to note the changes are from 55hz and up. I played with sub location again and found consistent and predictable variation in the same frequency range. I can't for the life of me figure out how to affect the low end. I'll post that comparison in the REW forum.


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## Guest

I'm also interested in adding corner wedge corner traps. I'm trying to decide whether I should go floor to ceiling or somewhere in between. Is the benefit as simple as go up 1/2 way to the ceiling and see 1/2 the benefit?


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## bpape

From a decay time standpoint - yes - it's pretty much that simple. From a frequency response perspective, you may get what you need with the top half or the bottom half or the middle half - or you may not.

Bryan


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## Guest

bpape said:


> From a decay time standpoint - yes - it's pretty much that simple. From a frequency response perspective, you may get what you need with the top half or the bottom half or the middle half - or you may not.
> 
> Bryan


Thanks Bryan, understanding your first sentence is easy, the second, not so much 

Is there a "simple" way to determine how much up the corner I need to go?


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## bpape

Not really - sorry. The best way to see what you're going to get from a FR standpoint is to take 2 pcs of 2' 703 or something similar and tape them together. Make 2 of these. Temp mount these in the upper corners and measure, lower corners then measure, etc. That'll tell you what if anything is giong to be helped by corners from a purely FR standpoing.

From a decay time standpoint, almost certainly, 2 full floor to ceiling corners is minimal to even approach a proper decay time in the bass region.

Bryan


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## Guest

bpape said:


> Not really - sorry. The best way to see what you're going to get from a FR standpoint is to take 2 pcs of 2' 703 or something similar and tape them together. Make 2 of these. Temp mount these in the upper corners and measure, lower corners then measure, etc. That'll tell you what if anything is giong to be helped by corners from a purely FR standpoing.
> 
> From a decay time standpoint, almost certainly, 2 full floor to ceiling corners is minimal to even approach a proper decay time in the bass region.
> 
> Bryan


I understand. Finally, being on a budget, the only option I have is DIY. I've been struggling to find local dealers of the 703 product or it's equivalents. Can you recommend someone who sells the boards?


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## grn1969c10

I used Roxul Rockboard 60 from ats-acoustics which sells on fleabay. The stuff is similar density to OC 705. It was 118 + 45 shipping for two boxes (12 sheets). The live cashback I used rebated most of the shipping cost back to me, which was nice. Nine sheets of it were used in my project.


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## Guest

grn1969c10 said:


> I used Roxul Rockboard 60 from ats-acoustics which sells on fleabay. The stuff is similar density to OC 705. It was 118 + 45 shipping for two boxes (12 sheets). The live cashback I used rebated most of the shipping cost back to me, which was nice. Nine sheets of it were used in my project.


Thanks for the feedback. I was wondering if I could use the cashback going via ebay, for some reason I thought it was only for electronics.

Thanks.


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## red12ax7

I know this is an old thread (google is your friend), but thank you so much for this thread and the trouble you went through to confirm my suspicions. I have a home recording studio with some standard 2" Owens Corning homemade panels on the wall, and it seems to work just fine. You saved me a lot of work, and a lot of arguing with the wife. Thanks. I`ve noticed a few proprietors on the net preaching bass traps, but for the length you`ve gone, and for that little a difference, I`ll use my "bass trap" money for a new Strat or something.:bigsmile:


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