BroadBand Bass Trap's Build

**cinema mad** · **03-28-09, 09:05 PM**

Quote:

Lonely Raven wrote:

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.

Hi Eric,
Yes it is often sunny here in the state of "Victoria" Australia and else where in Australia inc the state of SA where Prof lives, A little to sunny as it hardly ever rains thats why my back yard looks A bit like A Dusty Desert

it has'nt always been that way here but we are in A drought.... It does snow but only up in the High country never down in the flat plains...

Do you prefer Sun or Snow Eric ? I would gladly swap some sunny weather for some snow LOL...

Cheers mate...

**Prof.** · **03-28-09, 09:51 PM**

Quote:

cinema mad wrote:

Do you prefer Sun or Snow Eric ? I would gladly swap some sunny weather for some snow LOL...

Me too!!

**Lonely Raven** · **03-29-09, 02:35 AM**

I'm a cool weather person, but this 35 degree sideways rain and 30MPH winds just peel the life out of you.

Chicago is funny, we can have weather change so drastically in one day, that we've had T-shirts and shorts on at noon, and snow that same night! Honestly, I'm really tired of it...but I have family here.

Oh, back on subject, I did manage to hang the *heavy* 4" deep QRD on my back wall as you suggested. I have one hanging, and the other the stain is drying.

Yeah, I know they are MDF, but I figured I'd stain them a warm cherry red to match the oak stair treads I turned into flutter breakers. So I have one 4" QRD and one "stair tred" QRD up on the wall, and I'm working out an aesthetically pleasing layout to hang the rest of them. Photos to come later. Right now, I'm much more interested in your project!

**cinema mad** · **04-03-09, 06:11 AM**

Tonight I Glued & fitted the Veins of the Abffusor into place and Dry fitted the thin ply that form the wells... I am about to start fitting the ply permanetly to form the wells, Its going to be A very tedious job clamping each set of Veins untill the Ply is set permanently in place.....

Cheers....

**robbo266317** · **04-03-09, 09:27 AM**

That is so much effort.

I cant wait to hear what difference it makes.

**Prof.** · **04-03-09, 06:30 PM**

I admire your persistence Jason..I think I would have given up long ago..

**cinema mad** · **04-04-09, 01:20 AM**

Quote:

robbo266317 wrote:

That is so much effort.

I cant wait to hear what difference it makes.

Yes it is A huge effort to make this Abffusor, 88 components in all to make just one, and I still have 2 more to build

....

You can only assembel A little at A time in A curtan sequance so it is long and tedious...
It took 6 hours just to set 7 wells in place

...
Cheers....

**cinema mad** · **04-04-09, 01:32 AM**

Quote:

Prof. wrote:

I admire your persistence Jason..I think I would have given up long ago..

Thanks Prof, The way I look at it is To do it your self saves big $$$$ and the performance is often better than what you can buy for A reasonable price, For instance the RPG Diffractal is over $2000au A piece in Australia (making these nested Diffusors next), RealTraps Diffusor/Abffusor is $1400au & mine will outperform this Diffusor and cost one third as much.. So you see what I mean by the Huge savings if you can DIY, But I understand not everyone can...

Cheers....

**robbo266317** · **04-04-09, 02:41 AM**

Now I know why the hardware store didn't have any clamps left....

**Prof.** · **04-04-09, 06:54 PM**

Out of curiosity..who sells these RPG Diffractal's and diffusers in Australia.?
I've never seen them listed anywhere..

**cinema mad** · **04-05-09, 04:14 AM**

Hi Prof, The Australian RPG Distributor is Melbourne based Acoustic Vision...

Cheers....

**Prof.** · **04-05-09, 07:27 PM**

Thanks jason..

I had a look at their website...Some very interesting materials they carry..
I was most surprised to see they have GOM.! I didn't think it was available in Australia..
Something to keep in mind, should I ever re-build my theatre..

**cinema mad** · **04-07-09, 03:23 AM**

Getting close now to finnishing the first/Prototype Abffusor..
There is A fair amount of 2"705 being used for Absorbtion about 1200mmx1200mm sheet..

Because most of the wells being so deep I used my Wagner spray gun with A Matte Black Water based paint To paint the Abffusor, Making sure as to apply A very thin coat to the Actual membrane itself....

Just need to finnish up putting the Fiberglass in the back and closing it in with Muslin cloth then fitting the external metal frame after its painted....

I believe the total weight should be no more than 15Kg but I will check for sure once assembled

Cheers....

**Lonely Raven** · **04-07-09, 10:27 AM**

That looks fantastic after being painted black! Such a Pro looking job!

I picked up a cheap ($32 USD) HVLP spray gun somewhere many years ago...and never got it working right. The other day I took it apart and put it together again, which gave me a better idea of how it works (I've never used one before). It was a life saver for spraying the Warm Cherry stain on my two diffusers:

Not nearly as pro looking as yours, but they seem to do their job!

Now, after seeing yours, and reading your design thoughts...yours totally make sense! So the thickness and density of the parts were chosen so there would be a specific frequency that would pass through the paneling material and be absorbed, correct? And everything above the "cut off" would be then be diffused as normal. Clever!

And here, I was just going to stuff some 2" between my diffusers and the wallboard since mine are "floating" off the wall, suspended by some 2" X 2" I cut from some larger pieces of scrap. LOL

**Prof.** · **04-07-09, 07:17 PM**

Very nice job jason..

I love the little poser in the background..

**cinema mad** · **04-16-09, 10:57 AM**

Looking good Eric, I like the way you have your diffusors layed out also the cherry stain looks very nice

..

I replied to your post in my Mealstrom Subwoofer thread over at the AVS forum about your Diffusors and room acoustics, did you see it ??...

Yes you are spot on with your thoughts about the Abffusors and how they work....

Cheers....

**cinema mad** · **04-16-09, 11:17 AM**

Had A chance to install the Rigid fiberglass/ absorbtion membrane inc setting the pre determined air gap between the Back of the ply & front of fiberglass ...

The ultratel Fiberglass was cut A little to big and hangs out A bit but I dont mined the Muslin keeps it set in place and stops the glass fibers becoming airborn...

The reason I chose Muslin as opposed to Ply is because,
1: so the Absorbtion cf of the Abffusor will be higher due to the open back
2: Keep the weight down

....

Couple of pictures of the SLOW progress Just need to Paint the steel frame and rivet it together

Cheers....

**cinema mad** · **04-26-09, 07:06 AM**

Well I Spray painted the metal outer frame matt black using A new product: Dulux Quit Rust Water Based Gloss Enamel with Urethane but the paint did'nt stick

...

Initally I was very happy with the way the outer frame came up straight off the spray gun (3 coats)
I left it for 6 days to dry but the paint didn't stick, thus wasted my time...

This paint is A Primer and paint in one with 7 years of protection to all metal surfaces..

When I first opened the one LT can of Matt black paint it had seperated as expected so I went to stir it but the primer down the bottom of the can was rock hard and near impossible to mix..
I went back to Bunnings and showed the guy who sold it to me, he then checked 2 other cans off the shelf but they were all the same so he attempted to mixed all three cans on there electric mixer and tipped all three cans into one and gave me that..

But obviously half of the primer was left in the bottom of the can's due to not mixing in with the paint, So there's your problem

Before painting I preped the 1mm cold rolled steel by bead blasting with Glass beads then whiped over throughly with prepsol, This is the class 1 standard to prepair the metal surface and remove scale for painting and what Dulux recommends...

I am going to get A price on powder coating

and attempt to get my $32 clams back off bunnings...

Check out the paint job...

Cheers...

**Prof.** · **04-26-09, 08:45 PM**

That looks nice Jason..It's a pity that the paint didn't stick..
You certainly did all the right preparation..
A "one off" powder coated job probably won't be cheap, but it will give a nice professional finish to the frames..

**cinema mad** · **04-26-09, 11:27 PM**

Actualy to get the metal frame powder coated costs around $50 in satin black so not to bad, I have to build 2 more of these Abffusors 3 total for my back wall so $150 for powder coating...

As they say you learn by your mistakes,

Cheers....

**cinema mad** · **04-27-09, 11:03 AM**

I draged my first Abffusor into my theatre and placed it in the middle of the back wall while I watched The Day The Earth Stood Still on Blu-Ray to see how it performed..

To tell you the truth I could'nt really notice much differance But once I build the other 2 and place them all against the rear wall mid hight with 6" thick bass traps under neath and QRD flutter Echo tiles placed Horizontaly on top of the Abffusors I am sure it will aid in the Acoustic performance of my theatre...

My standard room Dimentions are very good (R Walker BBC/ Pass) no integer multipule within 5% Pass according to the room mode calc, I am Thinking of trying/striving with help from Acoustisofts RplusD Modal Analyzer For Dolby's optimum ratios for film & music room/ an RT60 of 242ms...
Is this worth trying for??

Absorbtion to Achieve ITU/EBU Control Room Recommended 198ms RT60:443 Sabins

To help with Room modes I Have been looking at using A Helmholtz Resonator Mainly because They can be tuned for very low room modes & I can use my front Riser as the chamber and have A very low Q thus larger bandwidth:

According to the Room Mode Calc My room modes Dominate between 30Hz to 118Hz :
I will be taking realtime measurments to get A more precise idea of the modes..

The most dominant are: Axial 30.2Hz, Axial 47.1Hz 35.8%)

Tangential 55.9Hz 15.7%) Axial 70.6Hz 14.1%) Tangential 76.6Hz 7.8%

This is what I have come up with :
Helmholtz Dimentions: H:40cm W:130cm D:120cm
Specs:
Port length: 2cm
Port Diameter: 100cm
Volume:624lt
F res: 67.83
Q: .79
Bandwidth: 85.64Hz
F low:25.01Hz
F high 110.65Hz

Any advice and Suggestions would be greatly Appreciated..

Some pics of the Abffusor in the theatre

Cheers....

**thewire** · **04-27-09, 05:03 PM**

Quote:

cinema mad wrote:

My standard room Dimentions are very good (R Walker BBC/ Pass) no integer multipule within 5% Pass according to the room mode calc, I am Thinking of trying/striving with help from Acoustisofts RplusD Modal Analyzer For Dolby's optimum ratios for film & music room/ an RT60 of 242ms...
Is this worth trying for??

242ms is low for a listening room but it can depend on the speakers, source, and at what volume level you are listening to. For very high quality sources such as blu-ray I think that a lower RT60 would be good to shoot for, but your ears must tell you what sounds right. You might have a conversation with someone in the room and see if it is comfortable since your room dimentions effecting <200 Hz is in good shape. I have found that maintaining a balance of symmetry is very critical. If you decide to use Helmholtz Resonators (usually in rooms +30' or so in a direction I think) it can be helpful to have two instead of one. They sometimes take some trial and error to get right more than most treatments. I like the new treatments.

**cinema mad** · **04-27-09, 07:12 PM**

Thanks thewire for taking the time to post what you have experienced and pointing them out , I see your using A helmholtz rasonator at the front of your room

....

I was thinking of only using one larger helmholtz resonator in the left front riser to the above diamiter, but I can use both my left and right front risers if I need to to keep things balanced....

Cheers....

**cinema mad** · **05-08-09, 09:35 AM**

I have been playing with the RT60 app in Acoustisofts RplusD & ran A few sweeps in the main listning position "subs only", but I know that you need to run the RT60 with main speakers & subs together when taking readings....

I need A decent calibrated mic instead of my standard ECM8000 mic but good enough for now untill I am ready to do the final tuning of the theatre...

I did notice that the real time analysis reconfirmed the big room modes from 47hz down like the room Mode calc predicted, But I am hoping to rectify the lower frequency room modes with one large or two
smaller HelmHoltz Resonator(s)..
1x large tuning: Volume 624lt,, Q.79, bandwidth of 85.64Hz , F,low 20-25Hz , F High 110Hz
hopfully this will work but either way I will get there with much persistence...

Also Has any one read Floyd Toole's book: Sound Reproduction: The Acoustics & Psychoucoustics of Loudspeakers & Rooms ?? I just ordered it.. Kevin Haskins said it is A must read as well as S Linkwitz...

Here is A croped RT60 graph of the subs running only, Subs crossed over at 80Hz...

Cheers

...

**cinema mad** · **05-25-09, 12:31 PM**

Just picked up Floyd E. Tooles new book today: Sound Reproduction, Loudspeakers & Rooms, Looks like A good bit of usefull easy to understand info in it but its $80au ...

Also I was chatting to one of Australia's room acoustic experts and he seemed to favour the idea of the use of Helmholtz Resonator for treating the lower model region in certin applications hopefully my situation

, also pointed out A few ideas for bass traps that reach A little lower than the 3.0pcf (48Kg/m3 fiberglass 6" broadband bass traps I built that are only realy good down to around 100Hz when corner mounted...

So I am going to modify my rear Broadband bass traps and see how it sound & performs after running R+D...
It cost's another $150au for the extra membrane but there is none in my state so its A 2 week wait... If it works well I will be sure to post the build....

Cheers...

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