Aeropanel acoustic absorber

[ralphs99]

I've built myself some acoustic absorbers. They help to control the sound being reflected off the rear wall behind the listening position.
The overall dimesions are 1m high, 1.2m wide and 160mm deep. It's a broadband design and is effective down to about 150Hz becoming acoustically transparent below 100Hz.
It looks very striking and suits a modern decor. It also works very well! For anyone that has a similar problem where they are forced to have their listening position close to the rear wall, an absorber of this type is very effective.

There's a lot more information on a new web page devoted to it. Check it out! http://www.aeronet.com.au/Aeropanel%20Absorber.htm


Cheers, Ralph.

[sdclc126]

A very nice blending of form and function - they would go nicely in most rooms I think - almost looks like a wall hanging, or a very large ventilation outlet!

How did you construct the wood panel - did you just route the slits in it? I'm thinking one could be very creative with something like this - maybe cover it wil perforated metal gratings, etc., which are available in lots of home decor-type finishes.

A lot of people probably would not know that these were part of a home audio system, until they asked.

[Tenson]

Ralph,

I very much like the design it reminds me of stuff done by "Recording Architecture". http://www.aaa-design.com/gallery/index.htm

It looks like it is a helmholtz slot absorber. I have to say though, I my calculations don't agree it will work down to 100Hz. More like 400Hz at most, bar a little bit passing straight through the panel and seeping round the side.

What is the width of the slots and the width of the gaps between the slots?

[richie00boy]

Looks good. I might have a bash someday as I find a lack of focus in sat in my sofa by the wall but it sounds good if I move forward a bit.

What precisely is acoustic foam? Is bonded acetate fibre (BAF wadding) any good?

[sqlkev]

Originally posted by richie00boy
Looks good. I might have a bash someday as I find a lack of focus in sat in my sofa by the wall but it sounds good if I move forward a bit.

What precisely is acoustic foam? Is bonded acetate fibre (BAF wadding) any good?

This is the exact problem that I'm having, I posted a thread about this a week ago, toeing in the speakers helped with the focus a bit more. But, I think I will try this panel as well.

Again, what exactly is the acoustic foam? Is it similar to eggcrate foam or those studio panel foam?

[ralphs99]

Hi sdclc,

Thanks for the compliment! The slots are simply routed with a CNC router. There's lots of creative possibilities available depending on your decor. I liked this approach for it's simplicity and the wood finish. The woodgrain looks a lot better in real life. The photo doesn't do the wood justice.

Hi Tenson,
Thanks for the link to the studio pictures. There's lots of cool ideas there!
It does look a bit like a Helmholtz slot resonator, but it's not, because it has no enclosure behind the panel. In order to resonate it would need to have an enclosed volume of air. My panel is just acoustic foam with a decorative cover.
I've made my estimations of the low frequency cut-off from manufacturer's data. I fully expect the panel to operate down to about 150Hz. Unfortunately I don't have a reverberation chamber to actually measure the performance of the panel! There's some more info about the expected performance on the web page. http://www.aeronet.com.au/Aeropanel%20Absorber.htm
There's 20mm of material between the slots BTW.

Hi Richie,
Sounds like you have exactly the same problem as I did. I'm sure you will find a big improvement in the imaging if you tame the reflection from the rear wall.
Acoustic foam is open-cell polyeurethane foam -ie the air bubbles in the material are open to one another. In a thin sheet it's possible to blow air through the material. Conversely, the stuff that goes into pillows is a closed-cell foam where each air bubble is distinct. It's more difficult to manufacture open-cell foam and it's not as common, so it's relatively expensive. The closed-cell foam is too resilient and doesn't dissipate sound energy very well, so it's not suitable as an acoustic absorber.
BAF wadding might be suitable if it was highly compacted and made thick enough (You'd probably need to squash half metre of BAF down to 50mm to get it dense enough). Fibreglass wool would be much better though. Unfortunately the glass fibres are a health hazard, hence the choice of foam.

Hi asqlkev,
Definitely experiment with something to quash the rear wall reflection. I simply used the bare foam to experiment with initially. Once you're confident that it helps, you can add a decorative cover later on. As I mentioned in the web page, the mix of absorbant material behind a partially reflective cover gives the best results. Just foam on it's own, makes the rear wall sound far too dead. Don't forget that it also needs to be as thick as possible to be absorbant to low frequencies.

Cheers, Ralph

[richie00boy]

Thanks a lot. Do you have any recommended brands or sources for this foam? Is the size of the slots anything to do with the frequency or is it just the thickness of the foam? If it's just the thickness is your 150Hz just taken from manufacturers data?

I was thinking about mounting a canvas artwork over some foam - would this work as well?

[ralphs99]

Hi Richie,
On this side of the world I used a foam manufactured by a New Zealand company called Latimer. I suggest you try google for some sources in the UK.
I just had a look and came up with http://www.studiospares.com/pl_65_65...INSULATION.htm & http://www.foamtechniques.co.uk/acoustic.htm

Studiospares seem to sell precut tiles and other specialised pieces. That's ok, but the tiles tend to be much more expensive. I'd try someone like Foam Techniques. You can probably buy 50mm acoustic foam by the metre from them. For an idea on price, a linear metre of 50mm foam costs about A$80 here.

The slots have little to do with the low frequency performance, it's the thickness that counts. I've estimated the low frequency performance from manufacture's data based on thinner materials. I suggest you have a look at my web page for more detail about this. http://www.aeronet.com.au/Aeropanel%20Absorber.htm

Canvas artwork is ok as long as it's a partially open weave and not fully covered with paint or other solid material. The requirement is to have enough open area for the sound to pass through, but not be fully absorbant. So the canvas idea will probably still need to have a partly solid material underneath it.

Cheers, Ralph

[richie00boy]

Originally posted by ralphs99
Canvas artwork is ok as long as it's a partially open weave and not fully covered with paint or other solid material. The requirement is to have enough open area for the sound to pass through, but not be fully absorbant. So the canvas idea will probably still need to have a partly solid material underneath it.

Thanks again. I'm not sure what you mean by that bit though, particularly about having something solid underneath. I was thinking of putting a canvas on a frame over some foam.

[Tenson]

Ahh okay Ralph, I see looking at the picture it is not 'boxed in'.

I would suggest that experimenting with the thickness of the panel on the front would get some good results. Using a thinner panel you can make it reflective at high frequencies and less at low frequencies. In most cases you want as much absorption as possible from about 200Hz downwards to get really tight bass.

I might try a panel 3mm thick rather than 9mm.

Also, apart from the reflected sound, the sound that goes through the slots will be diffused on its way out. The shape of the slots will alter that radiation pattern. I would suggest having circles so you get a 360degree radiation pattern, or putting the slots vertically so sound is radiated in a 180degree patters across the horizontal plane of the room where there are more objects to help diffuse it further.

Originally posted by richie00boy


Thanks again. I'm not sure what you mean by that bit though, particularly about having something solid underneath. I was thinking of putting a canvas on a frame over some foam.

I'd suggest using water based paint that soaks into the fabric or even ink. You want to avoid a paint that will 'gunk' up the fabric and block sound passing through.

Underneath you then might want a hard surface with lots of holes or slots in to stop the room being too dead from all the absorption. What about those sheets you get for radiator covers with all the patterns in them?