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Broadband bass trap with open frame: DIY build in UK
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Author:  endorka [ Tue Aug 06, 2019 2:50 am ]
Post subject:  Broadband bass trap with open frame: DIY build in UK

I found photos of a bass trap construction I undertook a few years ago and thought they might be useful. I built a lot of these of varying sizes, and they are pretty quick to make once you get in the way of it. The standard sized one was based around 1200x600x100mm Rockwool.

The calico is a bit translucent when stretched to cover, so the wood frame will show through a bit. I didn't like the look of this so covered the visible parts of the frame with standard grey gaffer tape, which was similar enough in colour to the Rockwool to give a uniform finish over the panel faces. You could probably achieve the same with a suitably drab coloured paint :-)

Materials were;

Rockwool RW5 1200 x 600 x 100mm
Kiln dried general purpose wood 2400 x 38 x 19 mm (from B&Q)
Calico 160cm wide (CALICO NATURAL) from Remnant Kings
Corner brackets from Screwfix
MSL Firecheck - fire retardant spray

In hindsight I've learned that Rockwool RW3 may have been a better choice than RW5 for basstraps, although at 100mm depth opinions differ. It's certainly been effective in use as is.

I've no idea how much benefit the open frame construction has in practice, but thought it may be worth building them such that as much absorptive surface as possible was presented.

Comments welcome!

Cheers,
Jennifer

First build the frame for the back of the trap. Upright posts from the same wood are attached with brackets;

Attachment:
20160821_134459.jpg


Attachment:
20160821_134505.jpg


Next staple the calico cover for the back face onto the frame;

Attachment:
20160821_133538.jpg


Trim Rockwool edges to fit with a sharp knife then put in frame. The rear face of the Rockwool doesn't need trimmed as it lies flat on the frame.

Attachment:
20160821_134420.jpg


Attach the top frame with four countersunk screws for a flush finish;

Attachment:
20160821_134407.jpg


Rear view of fully framed panel;

Attachment:
20160821_135505.jpg


Cover front and side with calico, stapling to back. I used something like "hospital corners" to get a smooth finish;

Attachment:
2019-08-05 17.03.09.jpg


Finished article;

Attachment:
2019-08-05 17.02.50.jpg

Author:  Soundman2020 [ Tue Aug 06, 2019 8:36 am ]
Post subject:  Re: Broadband bass trap with open frame: DIY build in UK

Welcome to the forum, Jennifer! :)

Very nice sequence of photos, too. Thanks for posting that!


- Stuart -

Author:  endorka [ Tue Aug 06, 2019 10:07 pm ]
Post subject:  Re: Broadband bass trap with open frame: DIY build in UK

Thanks Stuart. I've been reading posts here for a while, it's a very informative forum.

I came across it after reading posts by some people (including yourself and DanDan) on the Gearslutz acoustics forum.

Cheers!
Jennifer

Author:  DanDan [ Wed Aug 07, 2019 12:42 am ]
Post subject:  Re: Broadband bass trap with open frame: DIY build in UK

Hi Jennifer, welcome to a much cleaner forum. These look great. Many DIY traps end up a big iffy looking due to fabric choices and finishing details.
I used felt, doubled, but one can still see the dark fibre a bit, and it sags.
When I specify a very popular brand in white, I ask for a double wrap. This works well but it kinda rounds them off a little.
The future of DIY acoustics looks very bright IMO.....
I am very excited about the gradual appearance of Polyester batts. Autex, Caruso Isobond.
The material seems to have the best absorption coefficients at quite a low density and thus weight per batt.
It is certified fireproof and needs no fabric covering.
https://www.don-audio.com/acoustic-absorbers

DD

Author:  Soundman2020 [ Wed Aug 07, 2019 12:43 am ]
Post subject:  Re: Broadband bass trap with open frame: DIY build in UK

It's great that you found us here, and once again: Welcome!

It's always nice to have folks from other forums come on over where the water is warm, the science is good, and the advice makes sense ... :)

Dan is probably around somewhere here, and he'll probably drop in on your thread sooner or later. He no longer posts at GS for reasons that I'm hoping he'll be happy to share.

Anyway, one thing I liked about your absorber design is the clever use of the small metal angle brackets to keep the frame square and straight, and the "spacer" pieces that give the unit depth, as well as an air gap (where needed). Smart idea!

One suggestion I would add regarding the way the framing was visible through the fabric on early models: Try putting a layer of thin, cheap, black cloth with a fairly fine weave, on the frame first, before the final finish fabric goes on. That helps considerably to block light getting through, making the interior of the trap pretty much invisible.


- Stuart -

Author:  endorka [ Wed Aug 07, 2019 4:37 am ]
Post subject:  Re: Broadband bass trap with open frame: DIY build in UK

DanDan wrote:
The future of DIY acoustics looks very bright IMO.....
I am very excited about the gradual appearance of Polyester batts. Autex, Caruso Isobond.
The material seems to have the best absorption coefficients at quite a low density and thus weight per batt.
It is certified fireproof and needs no fabric covering.
https://www.don-audio.com/acoustic-absorbers


These look very useful indeed, have you tried any yet? Not having to cover them would be a huge time saver. It should be possible to design a very minimal frame if they are sufficiently rigid as well.

Cheers,
Jennifer

Author:  endorka [ Wed Aug 07, 2019 7:41 am ]
Post subject:  Re: Broadband bass trap with open frame: DIY build in UK

Soundman2020 wrote:
It's always nice to have folks from other forums come on over where the water is warm, the science is good, and the advice makes sense ... :)


Absolutely!

Re: the squareness, as well as the "getting it right" aspect, I use some of these as gobos so having them stable while upright was a requirement, and a good test of joinery skills :-)

Quote:
One suggestion I would add regarding the way the framing was visible through the fabric on early models: Try putting a layer of thin, cheap, black cloth with a fairly fine weave, on the frame first, before the final finish fabric goes on. That helps considerably to block light getting through, making the interior of the trap pretty much invisible.


Sounds like a good and fast plan, applying the tape took ages!

For two of the bass traps I stuck on some wrapping type paper with carpet glue to act as "foil face" and try for deeper frequency trapping where HF reflections weren't an issue. It was a real pain to get right though, for fear of having a partially stuck section of paper rattling and buzzing away like a kazoo, so I didn't do any more. Perhaps a section of card or somesuch over the front face would achieve similar without the hassle of glue.

Cheers,
Jennifer

Author:  endorka [ Tue Aug 20, 2019 9:01 am ]
Post subject:  Re: Broadband bass trap with open frame: DIY build in UK

Here's a temporary gobo panel adapter. It's constructed from an 18mm thick plywood rectangle that fits into the air gap in the frame at the back of the absorber.

Front absorptive side;

Attachment:
2019-08-19 23.30.21.jpg


Rear reflective side;

Attachment:
2019-08-19 23.29.53.jpg


Two brackets hold the plywood panel in place at the top;

Attachment:
2019-08-19 23.27.54.jpg


Attachment:
2019-08-19 23.28.56.jpg


Heavy duty velcro holds the plywood in place at the bottom of the frame. It's strong enough to hold the panel even with the gobo turned upside down - I wouldn't be doing this though, other than as a test :-)

The legs are shelf brackets with felt protector pads to keep wood floors in nice condition;

Attachment:
2019-08-19 23.27.08.jpg


The panel slides into place at the top, then drops down into the frame. Push the panel onto the velcro and it's secure. Gravity does an excellent job of keeping it there, 18mm thick plywood of that size is pretty heavy.

Attachment:
2019-08-19 23.28.40.jpg


Cheers,
Jennifer

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