Another DIY Basstrap project

[F5D]

This is how I just spent my summer holiday...

I finally decided to build my own bass traps after I found out how much it would cost to order proper bass traps from USA.

The biggest problem was to find proper wool for the traps. Because I live in Finland, the choice was Paroc rock wool. I chose FPS14 wool (66kg/m^3) which should be good enough for bass absorption. I bought 20 pieces (1200x600x50 mm) of the wool which was enough for building 4 corner traps and 3 basic flat traps (2x 6" thick and 1x 4" thick).

I used polyester cotton and felting to avoid rock wool dust and fibers from escaping the traps. The traps were finally coated with simple white fabric.

I decided to post some pictures of the project so here they are:

DIY Basstraps, 2007

I have not yet tested these in action but I guess there should be a very high probability that these traps will work. I will move to a new apartment in August and will install the traps there among other acoustic panels. I will report then how they work.

[Analogue Vanity]

nice work. lots of work though.

[Glenn Kuras]

wow you did a great job on them. nice work. thumbsup

Glenn

[willsing]

Those are some sweet looking traps though. I have read that if you can provide a space between the trap and the wall of at least 4 inches, they'll soak up the standing waves more effectively. Assuming you have some sort of permeable shell on the outside of those babies, they should work well in this regard AFAIK.
Will

[Cojo]

Nice!

[frank lyon]

nice work!

[Sayat Nova]

I will be treating my own personal studio soon, and this is really helpful to see. Thank you for the post and for sharing.

Cheers...:-)

[F5D]

Thank you everybody for the comments. I also want to thank other gearslutz members for sharing your knowledge and pictures of building basstraps. And sorry Glenn if my traps look too similar to what you're selling. I would have bought the traps from you but as we know, the shipping costs to Europe are very high.

I searched information about basstraps for several months before starting my own project. 2 very important things about the basstraps are imo that 1) you use (rock)wool which has high density (48kg/m^3 or more) and 2) you seal the basstraps well by using proper fabrics that no harmful wool dust or fibers can enter the room air. Building the wooden frames is very easy if you have done such a work earlier.

The most difficult part when assembling the traps imo was attaching the final fabric coating. It's easier if you have a friend to help you but it can also be done alone. I did almost everything alone. However, moving the traps alone at the end of the project became harder because 1 corner trap (which I built) for example weights at least 22kg when filled with rockwool and is big anyway (about 122 x 63 x 35 cm). Just staple one end of the fabric and start rotating the trap and try to keep the fabric tight. There are several ways to handle the seams. I didn't plan them much beforehand. I didn't care too much about the back or bottom of the traps because they cannot be seen when the traps are installed so I just tried to make the front and top (and sides) of the traps to look nice. The white fabric which I used was quite ruffled but I managed to tighten it so much that it looks totally straight.

I decided to build a back-sealed enclosure for the corner traps because it was easy to do . It shouldn't affect the absorbtion levels much either because when the trap is placed in a corner, the sound cannot really know whether it's reflecting from the room wall or the bass trap enclosure. The enclosure material is only 11mm thick so the trap goes pretty close to the wall. You may have to use little stands for the corner traps if you have baseboards in your room.

Btw, I built these traps mainly for bass absorbtion. I will also install some foam based absorbers for high frequencies.

I will post the results and some pictures of my new studio room in early September.

[Glenn Kuras]

Originally Posted by F5D

I would have bought the traps from you but as we know, the shipping costs to Europe are very high.

September.

No problem at all, just glad you treated your room. But hey if you ever want to get MANY boxes you would be amazed how low the shipping really is.

Glenn

[boojum]

Originally Posted by F5D

I have not yet tested these in action but I guess there should be a very high probability that these traps will work. I will move to a new apartment in August and will install the traps there among other acoustic panels. I will report then how they work.

Way cool. Good job! You did a very nice job, or, as the Finns say, "Sisu!"

[F5D]

Originally Posted by boojum

Way cool. Good job! You did a very nice job, or, as the Finns say, "Sisu!"

Thanks! And yeah, I guess, you must have "sisu" to start building your own basstraps!

[nandoanalog]

Nice! Today I also started doing some traps. Acoustics rule

[F5D]

Ok, finally I moved to a new place and installed the traps and some foam. I have foam on the back wall too.

The walls are concrete so the room is more sensitive to standing waves and it shows when you move around the room but wihtout the traps the situation would be alot worse. The frequency response is quite good and neutral at the listening point. The room doesn't decay much in the higher frequencies and at first it felt very weird. As a result, the stereo image and depth are alot better and accurate. I still attenuate 130hz and 350hz a little with a software eq in logic and all system sounds go thru that master eq. Anyway, I am quite happy now. The sound quality is good and the traps look ok.

[Darm]

Very nice, and that Andromeda is AWESOME!
Can you share some of your music? I would love to hear that synth workin'

[Glenn Kuras]

Originally Posted by F5D

Ok, finally I moved to a new place and installed the traps and some foam. I have foam on the back wall too.

The walls are concrete so the room is more sensitive to standing waves and it shows when you move around the room but wihtout the traps the situation would be alot worse. The frequency response is quite good and neutral at the listening point. The room doesn't decay much in the higher frequencies and at first it felt very weird. As a result, the stereo image and depth are alot better and accurate. I still attenuate 130hz and 350hz a little with a software eq in logic and all system sounds go thru that master eq. Anyway, I am quite happy now. The sound quality is good and the traps look ok.

Looks great and the set up looks right also. Can't see back of room but I am sure you did it right.

Glenn

[F5D]

Thanks for the comments. I have 2 pieces of 1m^2 foam on the back wall above my couch and they should abrosb above 300-400hz very well. Btw, the name of my couch is NEVE! I just had to purchase it when I saw it in a local furniture shop!

I had to put all my DIY absorbers against the front wall because of the shape of the room. One of the back corners of this room leads to kitchen and the other corner to my bedroom so I cannot block them and it's impossible to put my traps in my kitchen and bedroom.

I put the absorbers against the front wall without any air gap because I want to block as much noise as possible going thru the wall to my neighbour. I'm not sure whether it makes much difference but I also tried the abosrbers with a 2" air gap and didn't notice any difference in the sound so I just pushed them back against the wall. The absorber in the middle has a 1.5" airgap on the back inside the frame. The other 2 don't have any air gap but have 3x 2" rockwool layers instead of 2.

This project was very interesting and I learned alot. Altough the result with the traps may not be as good in this room as it could be in another room without concrete walls, the sound is still alot better than it was in my earlier apartment with 2 foam pieces on the walls. Especially everything above 500hz is now much clearer and accurate. The bass works too after using Eiosis Air eq to slightly attenuate a couple of frequencies. I don't boost any frequencies, just attenuate 2-4dB at the worst peaks. Without the traps I guess it would be a total disaster.

One thing I couldn't do in this room was to treat the first reflection points on the side walls. On the left side I have a window so I just use a heavy curtain which is located on the first reflection point. At least I don't hear much sound coming from that direction. On the right side I don't have a wall at all but a short (3 meters) corridor to my front door so it's also impossible to put anything there but it doesn't seem to be a problem either.

[nicolasmasset]

I think I'm going to copy your design, thanks mate!

[F5D]

Originally Posted by nicolasmasset

I think I'm going to copy your design, thanks mate!

Great, good luck! I have made some arrangements in the room. The whole system is rotated 90 degrees left now and I will get a second pair of monitors soon. I just yesterday decided to build a couple of traps more (for early reflections on both sides). I get more echoes now compared to the arrangement shown in the pictures but overall the bass response is alot better because the room is longer in the current listening direction. I just need to improve the acoustic treatment a little to get rid of the new high frequency echoes.

Btw, I made a webpage for easier viewing of the pics: DIY Basstraps, 2007

[nicolasmasset]

Nice, care to share what dimensions the triangles are? Are they 600mm each side?
And should I leave the back open or close em with wooden panels like you did..?

[undertone]

Originally Posted by F5D

Btw, I made a webpage for easier viewing of the pics: DIY Basstraps, 2007

Thanks for sharing! BTW: I see the pix in Safari, but not in Firefox (on a Mac).

[Colonel Blues]

thumbsup Nice job ! very clean !thumbsup

[springer]

Forgive me F5d but where is the necessary "space" in between the wool barrier and the enclosure? After reading F. Alton Everett book I made DIY's for my theater that work really nice but the proper operation of them depends upon an airtight space within the trap. Otherwise it isn't really a trap but just a giant reflector for many freqs.
I am not criticising just curious if there is a real basis for your design...

[nicolasmasset]

Originally Posted by springer

Forgive me F5d but where is the necessary "space" in between the wool barrier and the enclosure? After reading F. Alton Everett book I made DIY's for my theater that work really nice but the proper operation of them depends upon an airtight space within the trap. Otherwise it isn't really a trap but just a giant reflector for many freqs.
I am not criticising just curious if there is a real basis for your design...

Can you elaborate where the space should be? The poster's traps are not enclosed front or back, so where should that space need to be? Between the side panels of wood? I'm curious cause I'm going to start building my own traps soon..

[Tomer1]

If I recall correctly Harvey's designed are sealed not broadband hens the need for air tight construction.
This is not the case with broadband design.

[nicolasmasset]

Originally Posted by Tomer1

If I recall correctly Harvey's designed are sealed not broadband hens the need for air tight construction.
This is not the case with broadband design.

Ok that's what I thought! So unsealed for broadband, but sealed with wood in front, then air and then fibre for more focused frequency absorption! Can you ever over absorb a room? Is it ok to put absorber after absorber on an 18ft front and rear wall?

[F5D]

I built the corner traps using a sealed back because it was easy to do and it does not matter when the traps are in the corner. They are not a tuned design but broadband absorbers, like any realtraps or GIK products. I could have made the back open but I didn't. The air would reflect from the corner wall behind the trap anyway and the air does not know whether it is reflecting from the wall or the enclosure of the trap. Of course the trap does not work if you cannot put it far enough in the corner. The easiest way to build corner traps is to just put wool triangles on top of each other in a corner and cover them with a fabric.

Regarding the flat traps I built, one of them has about 3cm of free space behind the trap, the other two don't have but this should not be a problem. Anyway, the larger air gap you can make behind the trap, the more effective it will be at low frequencies.

Next I am going to build 120cm x 120cm x 10cm traps for my early reflection points at sides. To answer the question about my corner trap size, I cut 120cm x 60cm wool panels to 8 parts each. The front of the corner trap is about 60cm wide.

[Tomer1]

Originally Posted by nicolasmasset

but sealed with wood in front, then air and then fibre for more focused frequency absorption!

Varying the spacing between wood slats,thickenss of the slots, thickness of absorption,gas flow resistense of the absorbent matirial of choice and overall depth of the device will vary the Focal frequency,Q factor and absorbent coeficient.

Originally Posted by nicolasmasset

Can you ever over absorb a room

Sure you can, Thats the main "problem" with thin open cell foam absorbers, They have high absorbment efficiency in the upper freq range but lack completly in the low and low mid freq. ,
Covering of too much surface area using this type of matirials will result in over absorbtion which will result in very uneven reverb time between low and high freq and will coused your monitors playing in the room sound like you rolled off the highs and boosted the lows.

[nicolasmasset]

What about the thickness of the fibre? I just rang up the rockwool company over here and they told me they could get 70kg/m3 traps in 3cm - 4cm - 5cm - 6cm - 7,5cm ... thickness. Why would I need to get thicker traps like F5D is doing if a thin one has the same density?

Is the 70kg/m3 the way to go, or is 45kg/m3 better?

[F5D]

Originally Posted by nicolasmasset

What about the thickness of the fibre? I just rang up the rockwool company over here and they told me they could get 70kg/m3 traps in 3cm - 4cm - 5cm - 6cm - 7,5cm ... thickness. Why would I need to get thicker traps like F5D is doing if a thin one has the same density?

Is the 70kg/m3 the way to go, or is 45kg/m3 better?

Well, the density tells how many kilograms there is wool if you cut a m^3 (1m x 1m x 1m) piece of it. The thicker the absorber is, the better it works at low frequencies because there is more mass and the wool will have more distance from the wall. For high frequencies, above ~ 400hz, it does not matter much which of those panels you choose from but for low frequencies, I suggest 10 - 15 cm thickness. Wool having density of 48kg/m^3 or more is good. I used wool that has a thickness of 66kg/m^3 and the wool plates are 5cm thick each.

I suggest that you read some of the longer threads where Ethan and Glenn tell the secrets of these things.

[nicolasmasset]

Originally Posted by F5D

Well, the density tells how many kilograms there is wool if you cut a m^3 (1m x 1m x 1m) piece of it. The thicker the absorber is, the better it works at low frequencies because there is more mass and the wool will have more distance from the wall. For high frequencies, above ~ 400hz, it does not matter much which of those panels you choose from but for low frequencies, I suggest 10 - 15 cm thickness. Wool having density of 48kg/m^3 or more is good. I used wool that has a thickness of 66kg/m^3 and the wool plates are 5cm thick each.

I suggest that you read some of the longer threads where Ethan and Glenn tell the secrets of these things.

Thanks, I'll try and find those threads, it's not easy in the jungle of the acoustics forum!
I just rang rockwool again and the guy told me a layer of 2cm 90kg/m3 combined with a layer of 4cm 70kg/m3 would be a good deal. The 70kg in front and the 90 in back. So the sound goes through a more gentle absorption first and then the bass gets halted even further in the back. Total of 6cm. Sounds good?