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Corner Bass Traps DIY (caution: picture load)

Audiolab 6000A Amplifier

Santy

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There is not an iota of doubt that room acoustics can be one of the cheapest and most ideal ways of improving the sound quality of a system. I wish to share some detailed information on how I made corner bass traps that works. It can be done by anyone who has time and inclination. Sorry for being too detailed in terms of WIP pics but I hope they help in explaining every step involved to anyone who wishes to try.

Materials used and approximate cost:
Rs. 4000 Rockwool Slabs (96 kg/m3, 2 x 4, 12 nos)
Rs. 700 Aluminium Frame
Rs. 600 Plywood + cutting labour
Rs. 300 Adhesives
Rs. 1600 Fabric
Rs. 300 L-angles, screws
Rs. 7500 Total
Tools: Drilling machine, hammer, arc saw, long scale, gloves, measuring tape, marker pen.

I had a space constraints on the front wall with the projector screen on it, so I could have a maximum face width of only 18.3 inches. Ideally it should be 22-24 inches or more. For same reason, I used thin (0.75) aluminium frame for maximum exposure of rockwool on the facing side. It can be 1 thick if you decide to follow this method so that its stronger. We can always have the enclosure fully made of ply.


Phase I - Frame
Aluminium L- section frames, cut to measurement. The height would be as per your requirement ideally full height of the room.



L- angles easily available in hardware stores.



Plywood 0.75. Cut to size by a carpenter using a saw machine.



We need to chop the sharp edges of the facing side to get right angled corners for the frame to fit.






Holes drilled on both the wood and metal. It is better to mark the holes with each angle in place since the hole location in them may vary piece to piece. Remember that you would need different drill bits for metal and wood.



Secure the angles using the drilling machine with screw bit. Use washers for added grip.



Screws for angle to wood and nut-bolt for angle to frame. As tight as you can.



Repeat it for all six sides.



The first casing is ready.



It may be wobbly but don't worry once the stuffing is done, it would become more rigid.



Now that you have tried the method, the remaining frames can be made quite faster. All four are now ready




Phase II Stuffing

The rockwool slabs. They are very itchy so ensure you are wearing gloves and full hand shirt, jeans and socks when you work with them.



This is how the slabs are cut. I have ensured zero wastage accordingly.



Now using a long wooden scale, mark the measurements. For cutting, if you have an electric knife it would be a lot easier. But a simple arc saw blade would also do the job as well. Cut the panels one or two deep at a time.





This task took quite a long time for me to complete. Quite messy too.



Now the square slabs are cut diagonally.



You can start placing them in the frame as and when you chop.



I suggest to work on all 4 frames simultaneously with equal distribution.



All slabs cut from squares are now used up.



Now take the smaller rectangular bits and place them side by side. It will form a square now.



Repeat the same procedure- ie cut diagonally. The two pieces together will form a triangle of same proportions.



Start stacking them in the frame as shown in the pic. You can alternate the smaller triangle position between left and right sides. Tuck the corners of the slab so that they fit into the frame.



When you add the last two slabs, you might have to compress the ones below to make room. This is important because it helps to grip the slabs in position and add to the strength of the frame.



There you go. The stuffing is complete.





I initially planned to wrap the frame using a steel mesh. I could not find one. I managed to get a plastic one but it was not flexible enough and was too fragile to stretch. So dropped the idea.



Phase III Fabric wrap

I decided to use two layers of fabric to eliminate even the slightest fear of hazard (though I believe rockwool is quite safe according to several experiments). Even if you use single layer, it should be fine. Choose the fabric carefully in that case.

The first layer was done with used bed spreads. The cloth must not be stretchable at the same time porous enough to allow some air if you blow through it. You need to get a strong glue for this task, like Fevikwik but thats expensive for large quantities. The same formula is available in hardware stores for much less. Cut the fabric as per measurements and start from the top. Place the cloth on the frame and allow few drops of adhesive to ooze inside, It will quickly dry and bond the fabric.



Complete the three sides.



Wrap the cloth and proceed to glue it longitudinally over the frame.
Now stretch the fabric and glue the other side of fabric over the frame. Do so 0.5 feet at a time. Stretch everytime to avoid wrinkles.





Now complete the other side of triangle. Stretch hard before pasting, to avoid slack in the fabric.



Repeat it for other panels.



Place a few drops of glue on other two lengths of frame to hold the fabric in place. Helps when you move it around.



Now all four panels are ready.



Time to grab a beer can!


Now for the final wrap. I bought suiting bit from a textile shop. It turned out to be slightly expensive. The color and tecture was very cool so I didnt mind.



For the glue, this time we will use Synthetic rubber Fevicol SR998 to be precise. Its good for cloth on cloth and cloth on wood. You can use gloves but later I moved to paint brush.



Apply the adhesive on *both* the sides to be glued together. Wait for a minute, once the wetness is gone, stick them together with pressure.



The fabric will hold due to the viscosity of the glue so you can continue the work without waiting for it to completely dry.



Continue the same along the length of the frame.



Keep stretching often to avoid wrinkles.



Apply on both the sides to be glued





You can now cut the excess fabric if any





One panel is now ready.



Complete the other panels



Job done. They look pretty cool.



I wanted to seal the ends with a acrylic panel but could not find one in reach. Alternatively, you can close it with another thin ply fully wrapped with the same fabric. It can be screwed into position. Since it is not visible, I did not bother much.



Now the panels are in place. Click to view large size.







I enjoyed DIYing this. :)

Coming up, impressions and measurements.
 

shafic

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Very nice DIY work Santy!! :clapping:

Very timely post for me. Gives me some ideas for my home set up.

regds,
shafic
 

magma

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Santy

a couple things more you need to know

the corner traps need to be put where the bass load

it is not neccesary they are the corners behind the speakers
it can be anywhere
A good lisntener can actaully move around and feel it

that is where a trap should be put

Also 1 foot vertex to base of 100 density rockwool will take care of 70HZ
50 Cycles ideally requires close to 2.25 feet

Yes the bass traps will make a differnce even if they are put in the wrong place
because you have raised the absorbtion coefficient in the room

However if you know where the bass loads
You can get away by using minmal trapping

Overtrapping or overdoing absorbers tends to kill hte midbass making the whole texture a bit wooly
You will loose the airiness in certain tracks

Anyway
I know very little about acoustics


this is nothing to take away from your effort

phenomenal JOB !!!
 

Thad E Ginathom

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Very nice. And an excellent HOWTO too.

The minimum-waste geometry is particularly clever :clapping:.

Same again for the back of the room?
 

rohigupt

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nice job done santy !
i too have unequal bass in the room, specially after adding 7060..

just a few questions.

1) where to buy rockwool in mumbai and which brand did u use.
2) how much diff. in sound is there after using these..
3) corner bass trap - triangular seems appropriate in corners..how about rectangular ones to hang on opposite wall..like picture frames.. will it work

cheers!
rohit
 

sidvee

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Excellent Job santy. Looking forward to before and after measurements, especially mid bass 60-120 hz.
Cheers,
Sid
 

hydrovac

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There is not an iota of doubt that room acoustics can be one of the cheapest and most ideal ways of improving the sound quality of a system. I wish to share some detailed information on how I made corner bass traps that works.
Great DIY stuff Santy!

I was curious, in a typical square/rectangular room, are you supposed to use bass traps for the entire height of the corners and where the walls meet the ceiling/floor and cover wall/ceiling (and possibly wall/floor) corner as well... or just the top and bottom?

On the other hand, there is an argument for covering the trihedral corners (where 2 walls meet the ceiling or floor), since these have generally the biggest bass buildups. Ive always seen super chunks taking up a lot of the corners up but I was just asking because, if I place 10cm thick and 60cm wide, straddling a corner vertically centered (no tri corner), down to about which frequency this construction could absorb? To 140, 110, 80 or 50Hz?

I tell you after building the first few traps and hearing the improvement myself, I have become addicted to building more and more bass traps/acoustic panels.
An accurate and well balanced room can be an acquired taste but once you get used to it you'll never go back.:D

Happy bass trap building!:)
 

Santy

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Thanks everyone!:)

@magma
I fully agree with your advice. I cannot conveniently place them in other corners due to space constraints but I can still try if I have to. I have seen studios giving priority to the rear corners of the console so I followed. And I have not done any calculation on absorption characteristics because honestly, I don't know how to. :D

I think we need to be careful with the placement at reflective spots (wall panels) but I believe one can never go wrong with the corners. Infact if someone decides to treat the room, the first target should be the corners. Tri-corners are worst places where the bottom end waves happily camp. Please correct me if I am wrong; IMO, there is no such thing as absorbing more than enough at a specific area of the room, as you need 100% absorption of targeted frequency band, ideally, though I understand that that too chunky or dense panels can start reflecting instead of absorbing. The key is to keep the liveliness of the room while treating it.

I for one am very happy with the room mod. It not only tightened up the bottom end but cleaned up the mids as well making it crisper and more coherent. For music, not much energy below 55Hz in my setup so not much worries there.. For HT, I have lost bass for sure. More than I expected. So I am pumping up the sub volume to match the SPL however, now there is no over-hang of bass and it is clearly evident. With still lot of headroom left, I could enjoy the brute force of the sub without getting nauseated by the bass bleed.

I am yet to listen critically but let me measure first!

@rohigupt
Check out indiamart for some dealers near your area. There are many. They wouldn't probably know that they are used for acoustic purpose too but it doesn't matter:eek:hyeah:. No particular brand but if you get branded one, its good for you. Difference in sound quality is more than significant. Rectangular panels do help for absorbing the mids and highs so they need to be placed carefully at reflective spots. I feel it may be better to use diffusers at first order reflection points and go for wall panels at secondary reflection points along with corner traps to keep the liveliness of the room. Again, I am a novice in this and you should seek opinion from experts in our forum.

@Thad
Thanks. For the rear I may go for small tri-corner traps.

@sidvee, docd and others
Sure will post the graphs and impresssions.

@hydrovac
I think you know better than me about the queries you posted:rolleyes:
The tri corners are worst affected in any rectangular/ square room. So if full height traps are difficult, tri-corner traps would help to tame all room modes. 10 cm rectangular panels in corners would also do well in terms of larger surface area and more air space behind them. I have seen many following this design. But I do not think they can manage anything lower than 125 Hz. Corners store more concentrated energy so it may be better to go for chunky design with atleast 24" face width. Again I do not know what density and thickness are needed for various frequencies. The triangular section makes the calculation complex. May be experts can chip in.

You are very right on the acoustics. No level of upgrades can achieve what cheap acoustic panels can do. Your ears quickly get tuned to listen to more of the speakers than the room.
 
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Thad E Ginathom

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I'm still curious as to how you arrived at the dimensions and did the geometry. Did you begin with working out the maximum number of triangles you get from the slabs?
 

himadri

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Very good job Santy
My experience with DIY corner chunk traps tightened up the lower mids and consequently allowed me more freedom to locate the listening position nearer to the back wall thus helping in 2 ways;
-increasing/optimizing the listening distance for better driver integration.
-get a warmer tone considering the ushers have a highly resolving tweeter/lighter tone.
Cheers
 

Santy

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Thanks guys

Thad,
First I had measured the height of the room.
For that height I calculated how many slabs I would need of 50mm thickness.
Added 4 slabs so that I can compress and stuff more of them.
Then you know how many triangles you can get from one slab.
Accordingly ordered for the required no. of slabs.
The dimensions of the bass trap was restricted to available space which matched with the standard slab specifications so I could manage with minimum wastage.
 

manoj.p

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Santy,

Nice and clean job. You have the measurement equipment, so please post some measurements, before and after. Will be fun.

Although, I am bit curious about using two center speakers. Any particular reason/benefit you are doing it?
 
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