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Polymax Absorb XHD 100mm batts


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On 10/03/2019 at 9:10 PM, zydeco said:

air gap but, if I've got the figures right, then 80Hz would mean 1m which is impractical in our room?

You've got it right

that's why absorption gets too big to work effectively below 125-150Hz. They're big at 150Hz and truly massive at 100Hz.

I would never try to significantly impact an 80Hz issue with absorption - other more effective options are available like moving speakers/subs/LP, adding another sub, EQ etc

 

On 10/03/2019 at 9:10 PM, zydeco said:

How would Earthwool from Bunnings work as a "fluffy"? 

Earthwool is fluffy insulation, so will work fine if you're happy with fiberglass - but forget it for issues < 125-150Hz, and you'll need big traps for it to be effective 125-150Hz.

 

IME big/deep absorption traps clean up room sound very well 150Hz and above - but too much absorption can kill the treble in the room.

Corner placement of absorption assists in not killing treble (treble gets to bounce around a few times before running into a corner), but to absorb bass, the corner traps need to be large, and have material positioned where velocity is high (ie gapped).

 

IMHO anyone trying to treat a room should target the bass end first, and read Paul Spencer's Bass Integration Guide, part 1 here

https://www.hifizine.com/2011/06/bass-integration-guide-part-1/

 

In my leaky room with lots of absorption (12 sheets of 2400x1200x75mm Acoustisorb3), the bass is "reasonably" controlled with a few bands of EQ cut <125Hz. The Acoustisorb isn't doing much under 125Hz even with 3 sheets thick and gapped.

 

With my horns for the top end (PSE144), I don't find my room too dead, and the bass in my room is very good.

 

Mike

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12 hours ago, almikel said:

that's why absorption gets too big to work effectively below 125-150Hz. They're big at 150Hz and truly massive at 100Hz.

 

Sorta Mike, at least in theory.  In practice things are sometimes different.  Recently playing with two (2) unopened bags of Greenstuf R2.5 in my room I had good impact sub 100Hz, especially with cancellations rather than reinforcements.  Enough of an impact for me to consider building proper Superchunk traps to see how they do.

 

Blue = zero room treatment

Gold = 2 unopened bags of Greenstuf R2.5 in one front corner floor to ceiling

 

1507351294_SPLGreenstuf2bags.thumb.jpg.db877f9c8e7cca91b0d681b37b33ea57.jpg

 

15dB improvement @ 64Hz which makes the whole 60Hz-100Hz  fit within +/-2.5db of the first order low pass set at 60Hz.  Some effects as low as 40Hz, and some hope of taming the room modes circa 42Hz, 55Hz, 117Hz with more stuff in the right places.

 

Cheers,

 

Anthony

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1 hour ago, acg said:

15dB improvement @ 64Hz

Just as an aside.....  Remember that the frequency resolution of this data is quite limited.

 

What you are actually looking at, rather than "15db improvement".....  is really turning a total cancellation (actually a combination of multiple total cancellations), into "not-cancelled".     You just can't see these "total cancellations" very clearly as there aren't enough data points on the X axis.    The fact that REW has drawn a continuous line through the data points - hides the reality.

 

It might seem like semantics, but it can be important for understanding.

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2 hours ago, Peter the Greek said:

Be good to see a waterfall 

 

Before (zero treatment):

 

1820394933_ControlRoomWaterfall.thumb.jpg.a55d2c2ed68f0e28cc4bc30a942feea6.jpg

 

2 unopened bags Greenstuf R2.5 stacked floor to ceiling in corner behind speaker:

 

381778442_Waterfall2bagsGreenstufbehindactiveCannon.thumb.jpg.b22c30b18b6b7f6e42cbe984648886fe.jpg

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10 hours ago, acg said:

Recently playing with two (2) unopened bags of Greenstuf R2.5 in my room I had good impact sub 100Hz

 

7 hours ago, Peter the Greek said:

Its still a pretty darn good outcome isn't it? considering the simplicity of what was done.

Agreed - and it's reduced the nulls above 100Hz also...as expected.

...trying to compare the waterfalls, people much smarter than I can do the overlay thing and even animate it - I only managed to scroll up and down many times to compare - looks like a great result, and remarkable for 2 bags of insulation in a corner.

I'm not saying it's wrong, but IME I've never seen such a big change in a room by adding 2 bags of insulation in a corner...

...and I suspect after @acg did the measurements he was thinking, "can 2 bags of insulation really make that much difference?"...and ..."geez, maybe I don't need to bother with VPRs anymore?"...

 

I'm sure @acg will do loads more tests/measurements to come up with a room treatment plan, which I'm hoping includes some VPR traps.

 

My room treatment journey started with unopened bags of insulation stacked around the room. 

The "Midnight Foil" debacle coincided with us moving into a house with "Midnight Foil" installed and subsequently removed under the safety program, and the market for insulation plummeting.

I joined SNA around the same time and learned the concept of "room treatment" and "bass trapping".

We needed new insulation after the "Midnight Foil" was removed and I had an epiphany after finding cheap bags of fluffy fibreglass for $10 a bag on Ebay - get extra to treat the stereo room!

I bought 50 bags - 10 for the ceiling and 40 for the room...

post-112425-0-38328600-1443646859.jpg.d6a8db412c7183b2b80cd43c9119e82a.jpg

...OMFG what a difference those stacked up bags made to the room sound!

The bass was so tight, I was completely addicted to room treatment!

 

Fast forward several years and the outside yellow plastic binding on the bags was letting go - the bags still had a plastic inner bag containing the fiberglass batts, but the bags would explode out of the tubular wrapping which degraded under UV.

I'd come into the stereo room and find more bags had "exploded"...

...I'd also made some room measurements by then, and all those bags of insulation didn't do much under 120Hz.

 

Around that time I was doing a speaker upgrade, and decided to swap out the fibreglass for Poly sheets.

I managed to sell the exploding bags of fibreglass to fund 4 bags of Acoustisorb 3, which I figured I could get home without realising how big they were...

1813744069_acoustisorb3oncar.jpg.7bba840b24ef63b2500294bff433e7b9.jpg

I had a cop pass me in the tunnel home - but he just cruised by...

 

The best part of this story is that the room was naked of treatment after I'd sold the fibreglass, and the poly was stacked in the garage waiting for me to make "proper" traps...

...the wife cranked up the stereo in the "naked" room and said, "this won't do", so we dragged the bags of poly into the room - instant change to good "in room" bass.

 

The room remains pretty similar to this

IMG_3443.JPG.8a9b148c7790a3ff50f7402793f1f6da.thumb.JPG.5f707d6f55ffa1ddf5f10f9bf968781b.JPG

The blue box on the left is the tapped horn sub that never got mounted outside the room.

 

Based on my measurements, the poly treatment is not doing much under 100Hz, but with a few bands of EQ cut <100Hz plus a leaky room, the bass is amazing - the Acoustic Elegance TD18s are simply fantastic - so much mid-bass slam you can't help dialing up the bass on the remote...and with the PSE144's the room isn't "too dead" with so much absorption (IMHO)

 

Mike

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It's a bit easier to see with a gif. Anthony's waterfalls:

 

ACG-TRAPS.thumb.gif.8fc904e5ee61eac9c269c5e12276b477.gif

 

Thanks for sharing the waterfalls. What kind of subjective difference did you notice?

 

When using lower density bass traps with a low GFR, you can improve results by making them thicker. However, when you are using products like Polymax, greater thickness is not always more beneficial. There are trade offs involved between bass and low midrange absorption.

 

The theory doesn't contradict practice. The theory is built into the models which predict that practical resistive bass traps can be made, using dimensions that are much smaller than ideal, with measurable and audible improvements below 100 Hz.

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@Red Spade AudioPaul, thanks for the gif...what a great idea!  Please share how you did that although I could probably google it.

 

Subjectively, I did not listen to anything but sweeps and I shifted the Greenstuff out of the room immediately because it is for something else.  Because Autex have shut up shop here and gone back to NZ I have since purchased some Higgins R2.5 poly insulation to roughly make a corner trap or two for more formal testing.  Just gotta find some free time to cut it up and stack it in place.

 

One thing that I have wondered since taking these measurements is whether the  physical shape of my sub has something to do with the success of the trap.  It's not a normal sub...see below...

 

2066743018_DSETFirstListening.jpg.603bf2b1eee791ae2a166efe95262675.jpg

 

8 x 10" drivers pretty much floor to ceiling.  The two bags of Greenstuf were placed behind that very speaker (horns not yet complete - but close) with the trapdoor down of course (it is up in the photo).  The Cannon stack is made of steel and weighs about 400kg and I think would be a very good reflector of sound even in lower frequencies.  Two things that I have been thinking about regarding the effectiveness of the improvised corner trap are:

 

  • The Cannons almost make a false wall in the room and even though they do not sit in the corner they might be effective at reflecting sound pressure back into the corner trap for 'another bite'.
  • The low excursion, floor to ceiling nature of the sound source may more evenly distribute energy into the corner trap, as opposed to all the energy coming from one spot close to the floor.  Of course I am only thinking about the sound that wraps around the speaker and makes its way to that corner rather than sound that is reflected from all other parts of the room.

 

Of course these ideas might be moot, but I am trying to think of reasons why those two bags of poly were so effective.

 

 

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Guest Peter the Greek
On 14/03/2019 at 7:23 PM, davewantsmoore said:

Sure, I wasn't saying there was anything bad about the result.    Just good to keep sight of "what is happening".

Sorry I didn't mean it like that, more a question as opposed to a statement.

 

In the past I've implemented treatments before speakers are installed, so I've not got much experience with before and after. That will change "soon" (LOL, who am I kidding...hopefully this year) with our new place, so this is all very interesting to me

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22 hours ago, acg said:

One thing that I have wondered since taking these measurements is whether the  physical shape of my sub has something to do with the success of the trap.  It's not a normal sub...see below...

Not as much as you might think.... we discussed this a lot earlier in the thread, where I was repeating that your sub is "not a line source" ... and that the "shape" of your subwoofer wasn't a concern for LF.

 

50Hz is a ~7m wave , and 25Hz is ~14m ...  So, your subwoofer is 1/7th of a wavelength long.   It's still a "point source"   (ie. it's too small to constrain the dispersion of soundwave) .... in fact it's much more like a point source, than mids and tweeters in a typical box speaker.

 

22 hours ago, acg said:

 

2066743018_DSETFirstListening.jpg.603bf2b1eee791ae2a166efe95262675.jpg

 

Cannons  :D :D 

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3 hours ago, Peter the Greek said:

Sorry I didn't mean it like that, more a question as opposed to a statement.

Yeah, I got it.... answer the the question is yes (sure!) still a good result.... which is not unexpected, as like Paul said, simple models of the bass traps, and of a purely pressure/velocity action ..... might say "they won't work" ... the reality is more complex than the model.

 

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33 minutes ago, davewantsmoore said:

Not as much as you might think.... we discussed this a lot earlier in the thread, where I was repeating that your sub is "not a line source" ... and that the "shape" of your subwoofer wasn't a concern for LF.

 

50Hz is a ~7m wave , and 25Hz is ~14m ...  So, your subwoofer is 1/7th of a wavelength long.   It's still a "point source"   (ie. it's too small to constrain the dispersion of soundwave) .... in fact it's much more like a point source, than mids and tweeters in a typical box speaker.

 

Cannons  :D :D 

 

Nothing to do with line source behaviour Dave...I was referring to more to physical reflections due to the size and heftiness of the subs...2.4m tall x 1m deep and 400 kg...a wall of sorts...perhaps with a behaviour of reflecting more of the low frequency energy back into the wall or corner rather than letting it bounce around other parts of the room.  Sound wraps around the speaker, bounces off the side wall (bricks) then the Cannons, then the side wall, Cannon et cetera, getting a little less each time as the wall and the Cannon lets a bit through, but ultimately more energy stays in the corner to be absorbed by the Greenstuf.  It may only be a few or maybe 10% more energy reflected back into the trap by the mass of the Cannons.

 

One thing that I can say is that the bass in the room improved a little just by building the Cannons in situ even without turning them on and still using the ML1's...I reckon there is something in my theory....somewhere...perhaps.

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3 hours ago, acg said:

I was referring to more to physical reflections due to the size and heftiness of the subs...2.4m tall x 1m deep and 400 kg

Ahhh, I see.

 

The object will be beginning to reflect the sound once it's bigger than 1/4 WL .... so not really.    It could explain some of the small effects you see here and there in the results (which aren't covered by some other theory)

 

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  • 10 months later...
1 hour ago, Steffen said:

Did you drive there to pick them up, or did they ship to Sydney?

 

I wish someone in Sydney would stock this stuff... ?

I called the owner and he organised the shipping to Sydney. On a website it does not allow you to put the order through, so give a call to the shop and the owner can organise it.

In fact, Owner himself came to drop off three sheets of polymax for me as he was coming to Sydney anyway. 

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1 hour ago, Steffen said:

Did you drive there to pick them up, or did they ship to Sydney?

 

I wish someone in Sydney would stock this stuff... ?

Forgot to mention, if you want same stuff but by different manufacturer, you can get Autex Acoustic blankets (Same as CSR Martini Absorb HD), you can get this https://pricewiseinsulation.com.au/product/32kg-autex-acoustic-panel/ in single pack of 5 sheets (25mm or 50mm and only in black colour). I had called them about a week ago and they had stock of this and is available for purchase, the other variants are made to order and has minimum order of quantity.

 

If you want CSR Martini Absorb HD 50mm (Polymax HD) in black, CSR did have some stock, which when I called them, I was told to contact a distributor as they will not do direct business, I had reached out to Direct Plasterboard Outlet (DPO) in Campbelltown and was informed they do have a stock of Absorb HD 50mm in black colour (6 Sheets per pack).

 

I wanted these in white and only 3 sheets, therefore I went with actfoam.com.au for white polymax hd in 50mm.

Edited by bluehalk
Updated incorrect number of sheets per pack
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  • 6 months later...

Hi all,

 

Just thought i'd re-hatch and contribute to this post as it was very helpful as a starting point for me in being able to finally find what i needed. Mitre 10 in Matraville here in Sydney can order for you the following Martini Absorb products:

 

130542 – Martini Absorb HD50 2400x1200mm - 6 pack - $237.12

 

130543 – Martini Absorb HD75 2400x1200mm - 4 pack - $236.80

 

130544 – Martini Absorb HD100 2400x1200mm - 3 pack - $236.88

 

130546 – Martini Absorb XHD50 2400x1200mm - 6 pack - $355.45

 

130548 – Martini Absorb XHD100 2400x1200mm - 3 pack - $355.57

 

These are quotes i got for the white panels as this is what i requested, but i'm sure they would be able to source you black panels also.

 

Also of significance, unlike the 8 or 9 other places i called, there are no minimum order amounts so you can just purchase a single pack!

 

These are a special order item though so you have to pay in advance etc.

I'm unsure about shipping as i'm going to pick them up myself in store, but i'm assuming this could also be arranged for you if needed.

 

Get in contact with Sam at samantha.oneil@mitre10.com.au, she was extremely helpful with my enquiries.

 

Stay safe out there folks..

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