BroadBand Bass Trap's Build

**terry j** · **03-20-09, 02:10 AM**

excellent work, will bookmark for when I can get around to it myself.

question/comment time, they must weigh a fair bit, as it is only for diffusion/scattering, how feasible would it be to use esky type foam?

**cinema mad** · **03-20-09, 06:24 AM**

Hi Robbo, Thanks for the Questions...
The 15mm 90 degree folds are to allow for spot welds or riveting (prototype) the top and bottom peaces to the sides and the 90 degree fold's along the lengths allow for the wells and veins to be held in place /add to the look & give much needed rigidity..

It will become more clear to understand as I start to post the Assembly of the components...

Cheers....

**cinema mad** · **03-20-09, 06:37 AM**

Quote:

terry j wrote:

excellent work, will bookmark for when I can get around to it myself.

question/comment time, they must weigh a fair bit, as it is only for diffusion/scattering, how feasible would it be to use esky type foam?

Hi Terry, Thanks for your complement and questions..

This Abffusor will be very lite due to the choice of components used as compared to wood an the like..

With this type of Acoustic panel esky foam wont work because it wont absorb any frequancy's which is A critical feature of this 2in1 panel, If you just want Diffusion then Esky foam may work for lowering the weight but would be hard to get A nice finnish...

Cheers....

**Prof.** · **03-20-09, 06:34 PM**

Quote:

cinema mad wrote:

Hi Prof, Good to hear from you mate..
The Frame of the Abffusors will be fabricated/constructed of 100% 1-1.5mm mild steel sheet to keep the weight down as opposed to 20mm wood, The frame will contain 16 folds total to add to the rigidity and all precession lazer cut.. Also there will be some pattern in the side of the frame to further reduce the weight but not sure what at this stage....

Cheers...

Wow!! Jason..that sounds like one fancy, complicated and expensive frame..
I'll be very interested to see how that turns out..

**shift9999** · **03-21-09, 11:53 PM**

Cant wait to see the end results

**cinema mad** · **03-22-09, 06:14 AM**

Well I have fabricated the first set of Prototype frame Using 1mm sheet panel steel (cold rollled), Going to get them folded tomorrow..

These peices were only cut with my angel grinder & A very thin cutting wheel using A Wooden straight Edge as A fence guide... Once I assemble this prototype Panel and check for fit I will then move on to the next stage and have A few frames fabricated "cut and folded" and some form of pattern cut out in the sides to further reduce the total weight, then all that will be left is final assembley by me....

The camera make's them look warpted but trust me they are stright...

Cheers.....

**cinema mad** · **03-22-09, 06:26 AM**

The Net weight of this Acoustic panel will only be between 12 to 13.5Kg max...

Cheers....

**Prof.** · **03-22-09, 07:03 PM**

Very neat job Jason..
How did you manage to fold the edges over so neatly by hand?
Whenever I've tried to do that, they always come out uneven..

**cinema mad** · **03-23-09, 11:16 AM**

Hi Prof, The answer to your question is easy, In that picture they had'nt been folded yet

...

I am getting A metal fab place to fold the first set and will pick the frames up later today..
I know someone with A folding machine who owns A panel & paint repair shop so I will be hitting him up to bend the rest..

Cheers...

**cinema mad** · **03-23-09, 11:56 AM**

The biggest issue I had with this type of acoustic panel was finding A suitable membrane substrait to work the way I needed IE: reflect/diffuse down to the Diffusion limit of the QRD's 945hz-708 and below that point allow for absorbtion...

The simple answer to that problem is Kraft paper would'nt give optimum results also to fined acoustic coefficient data on A plastic membrane substrait to suit the above is far and few between....

After more research inc talking to Bryan Pape (thanks Bryan) I have found A way around this issue with A little design change using plywood as the membrane with A small air gap that will still work very well...

I should point out that the absorbtion performance of this diffusor/absorber panel will never perform as well as A 4"-6" thick fiberglass based panel but that was not my main goal/intention with this build.....

Cheers....

**Prof.** · **03-23-09, 07:22 PM**

Quote:

cinema mad wrote:

Hi Prof, The answer to your question is easy, In that picture they had'nt been folded yet

...

LOL!! I noticed that the long panels had the corners cut, ready for folding and the smaller panels looked like they had been folded, but it was obviously just the line marks on the panel..
I think I need a new pair of glasses!!.

**cinema mad** · **03-26-09, 08:31 AM**

Been A bit slow coming together I had A lot of trouble finding the Very thin PLY wood used for the membrane & to form the wells also absorb at the right freq which is obviously critical but I have it now

..

I have the Frame folded and just needs to be filed/cleaned up and then ready for paint or powder coat..

I have cut some of the vains and done A ruff fit tonight, Hopefully I will start Assembly in the next couple of days

...

Cheers....

**Lonely Raven** · **03-26-09, 10:24 AM**

Great start!

...waiting to see what you use for spacers.

**Prof.** · **03-26-09, 07:18 PM**

What type of timber supplier did you find for the 3mm. ply?
I haven't seen any 3mm. ply for years..these days it's all 3mm.MDF..

**robbo266317** · **03-26-09, 07:29 PM**

They occasionally have it at bunnings here in Ncle.

**Prof.** · **03-26-09, 07:42 PM**

I looked for it at Bunnings in Adelaide, but they only have it in 4.5mm..

**cinema mad** · **03-26-09, 09:41 PM**

Hi Prof its not 3mm ply 3mm is to thick for the membrane used with this Abffusor and wont work right, FWIW its thinner than that try 2mm...

Cheers...

**cinema mad** · **03-26-09, 09:43 PM**

Quote:

Lonely Raven wrote:

Great start!

...waiting to see what you use for spacers.

Thanks mate...

Cheers...

**Prof.** · **03-27-09, 06:52 PM**

Quote:

cinema mad wrote:

Hi Prof its not 3mm ply 3mm is to thick for the membrane used with this Abffusor and wont work right, FWIW its thinner than that try 2mm...

Cheers...

Wow!! I didn't think that it was even made that thin..

But why use ply?..There are other materials that are more stable than ply and cut more cleanly, like Styrene (not foam) or Acrylic..both are available in 2mm. thickness..

**Lonely Raven** · **03-27-09, 07:11 PM**

Both Styrene and Acrylic would cost much more than 2mm ply me thinks.

Though colored or even clear acrylic would sure look neat!

**Prof.** · **03-27-09, 07:27 PM**

You're probably right Raven..but it would give the panels a very nice appearance and a very smooth surface area..

**cinema mad** · **03-28-09, 07:59 AM**

Hi prof, Ply wood cuts very cleanly if you use the right tool with the right blade

.. I use A special 30deg Laminate blade 180mm x 60teeth cuts All PLY perfectly no chiping perfectly clean cuts

... I will post A picture of the clean cuts and blade needed...

No its not that easy you just cant use any old substrait, remember I needed A membrane with A curtain mass to meet A transmission loss at A fairly high mid frequency IE: Membrane stops reflecting/diffusing at 700- 900hz so below 750-900hz the membrane allows high freq sound to passes through to be absorbed...

There is A mathematical formula to work out the mass of A said substrait ,the math formula is also in the Master Handbook of Acoustics(4th edition) ..

So The reason I used thin 2mm ply wood is because it closely meets the criteria/mass required and with A small set air gap between the back of the ply and ultratel fiberglass(705) & applied attached in A certain way to the Vains as not to make the 2mm ply any more rigid in any way, the thin ply will transmit/pass the sound through at A mid frequency, which is what it needs to do...

Hope this helps Cheers....

**cinema mad** · **03-28-09, 08:53 AM**

Some pictures of the clean cut 5mm and 2mm ply, straight off the saw not sanded, this blade does an amazing job cutting ply...

Cheers....

**Lonely Raven** · **03-28-09, 12:01 PM**

Sorry, I didn't notice any saw or blade...I was admiring the warm and sunny background...it's about to hit freezing and start to snow here Chicago today.

**Prof.** · **03-28-09, 07:44 PM**

Quote:

cinema mad wrote:

Hi prof, Ply wood cuts very cleanly if you use the right tool with the right blade

.. I use A special 30deg Laminate blade 180mm x 60teeth cuts All PLY perfectly no chiping perfectly clean cuts

... I will post A picture of the clean cuts and blade needed...

Ah..yes..Having the right blade would make all the difference..
I used to work for a furniture manufacturer.. many years ago..and I remember they used a special blade for cutting laminate..The edges were so cleanly cut that you could cut your finger on them if you weren't careful..

I can't believe how critical these membranes have to be to perform correctly..

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