Tim's Limp Mass Bass Absorbers

[boggy]

Originally Posted by Tim Farrant

I wonder if linoleum/flooring vinyl might be a litte too stiff for the membrane? It has to do something I guess, but with reduced efficiency.

It is not stiffer than 4mm bitumen limp mass membrane, which can do more than "something" here:

Originally Posted by DanDan

Thanks NLP. Nice Speakers.
I am very impressed by your test. If I may help you and Tim to show off a little....


DD

And AFAIK, vinyl flooring material is denser than bitumen (higher surface density with thinner membrane)

[boggy]

Originally Posted by Bilou

We have tarkett here too.

Could I consider that glueing 2 layers of linoleum of 2,5kg/m3 with neoprene spray will be equivalent to a single 5kg/m3 layer ?
I could buy some to include in my tests if you're interested...

From my experience, glueing of two layers will result with stiffer membrane because glue (even if it is based on neoprene).

Try to find flooring material with nearly 4kg/m2 of surface density... which is not too stiff. Some compromise may be considered.

[Bilou]

I already take a look and always find 2 to 2.5kg/m3 flooring material...
So I'll stay with my 5kg/m3 EPDM for the moment.

[Adhoc]

If I had to choose, I would stick to vinyl instead of linoleum which tend to harden a bit with age. Those Tarkett ones Boggy linked to seem fine. On the plus side would be a choice of colours usually, so they need not be hidden from view with a fabric.

Another vinyl flooring candidate would be Forbos type Sarlon Traffic Boreal which is also used for acoustical purposes, has a bit higher damping against impact noises than those Boggy linked to, about 3 kg/m² though,

[boggy]

Originally Posted by Adhoc

.....
Another vinyl flooring candidate would be Forbos type Sarlon Traffic Boreal which is also used for acoustical purposes, has a bit higher damping against impact noises than those Boggy linked to, about 3 kg/m² though,

I omit some thicker Tarkett types with foam layer (higher damping for impact noises)... I have no clue how they works in this application...

[DanDan]

Newell lives in Portugal. He mentions 'deadsheets' quite a lot.
I believe the company Acoustica Integral supply all sorts of deadsheets, including ones with absorbent foam facings.

DD

[boggy]

Originally Posted by DanDan

....
I believe the company Acoustica Integral supply all sorts of deadsheets,...
..

something like this?
ACUSTICA INTEGRAL - Insulating acoustic materials - LA Absorbent Sheet
ACUSTICA INTEGRAL - Acoustic Insulating materials - PKB

[Adhoc]

From another thread: Entire back wall bass trap thickness question

[johnbomb]

I hope this isn't a stupid question: why must the trap be airtight? This design seems similar to me to the VPR, just with a different resonator. G.E.'s VPR is a steel plate in a corner with fiberglass on either side, with no sealed cavity. Tim, have you (or anyone else) tested one of these membranes lined with a damper such as fiberglass in free air?

Thanks,
John

[DanDan]

The theory is that they need to be airtight. However if you trawl through G.E.'s research you will find all sorts of unexplained behaviour. e.g. Empty boxes outperforming sealed designs.
It is worth remembering that we simply don't have trustworthy test evidence.
There have been some singular test/explorations but nothing rigorous or repeatable.
BBC lab tests show essentially full absorption down to 50Hz from relatively small 1 foot deep boxes. Sealing the cavity eliminates absorption at high and medium frequencies. A Low pass filter. It is hoped that a damped resonant effect enhances LF absorption to the extent that a shallower box may be used.
However the BBC didn't make the boxes shallower, they simply use these things to counterbalance HF only absorption.

I am not aware of tests which compare such boxes or other traps with and without fronts of various types. From the small amount of testing I have seen or done, there has been no LF improvement in SSC's by fronting them with Cardboard, plastic, or Space Couplers.

Newell uses large areas of 'deadsheet' in his compound full range traps.
They are often sheets of mass loaded vinyl with a foam HF absorbing layers.

If one were to hang a 1x2.5M sheet of MLF across a corner, I would be very surprised if it did not have an LF absorbing effect. I also expect it wouldn't need any addition damping to perform.

When considering the VPR I always remember that it is the product of an esteemed Research Institute, the Fraunhofer. i.e. The people who brought us MP3........;-)


DD

[boggy]

Originally Posted by johnbomb

I hope this isn't a stupid question: why must the trap be airtight?.......

.... because this is the only way to have spring from (compressed) air. Without air compression, we will have only pendulum motion of membrane itself.... without much air influence...

[TheLastByte]

Hey All,
Great thread,
I had actually started to use this idea 3 years ago..From JohnLSayers forum....at that time I purchased a few rolls of Nuwave Base 4Kg m2. I'm contemplating making a few traps of Tim's design, though I'm not 100% sure the Nuwave Base is correct - there's not much else here in Australia. I'll upload the PDF File and hope some smarter heads then my own can come to some sort of conclusion. The Product is MLV @4KG m2 though it says it's easier to staple & tape then Glue? This is the problem sealing the traps with a Silicone based Glue and or Thermotec Nuwave Tape then glue seems the only option etc.
Does anyone think this is useable?
Cheers
TLB.
http://www.gearslutz.com/board/attac...1&d=1343967109

P.S this is the website in Australia http://www.thermotec.com.au/insulati...ic-insulation/

[Tim Farrant]

Originally Posted by TheLastByte

Hey All,
Great thread,
I had actually started to use this idea 3 years ago..From JohnLSayers forum....at that time I purchased a few rolls of Nuwave Base 4Kg m2. I'm contemplating making a few traps of Tim's design, though I'm not 100% sure the Nuwave Base is correct - there's not much else here in Australia. I'll upload the PDF File and hope some smarter heads then my own can come to some sort of conclusion. The Product is MLV @4KG m2 though it says it's easier to staple & tape then Glue? This is the problem sealing the traps with a Silicone based Glue and or Thermotec Nuwave Tape then glue seems the only option etc.
Does anyone think this is useable?
Cheers
TLB.
http://www.gearslutz.com/board/attac...1&d=1343967109

P.S this is the website in Australia Thermotec - Accoustic Insulation

That material looks fine. It looks like it has a layer of foam? If you face that into the enclosure, you do not need any more dampening inside. Just use plenty of sealant like No More Gaps on the timber cleating, and staple the material on. The sealant should keep it airtight.

[Tim Farrant]

Originally Posted by johnbomb

I hope this isn't a stupid question: why must the trap be airtight? This design seems similar to me to the VPR, just with a different resonator. G.E.'s VPR is a steel plate in a corner with fiberglass on either side, with no sealed cavity. Tim, have you (or anyone else) tested one of these membranes lined with a damper such as fiberglass in free air?

Thanks,
John

It has to function like a drum, in free air there is no resistance, the pressure at the front and rear of the membrane will be the same so it won't move. We want it to wobble with sound vibration and absorb the energy.

[Bilou]

A plank or a desk can vibrate in a room with no sealed cavity behind it. Why not an MLV layer ?

[Sebg]

I haven't looked into it in great detail but I think it is something like this - a sealed cavity means there is a resonant frequency so that there is much better coupling (and hence energy transfer) between the sound field in the room and the resonant system. No resonance (such as a limp heavy curtain flapping in the breeze) means very little energy removed from the room. VPRs are also resonant absorbers as they appear to work due to modal resonances of the plate being excited.

[TheLastByte]

Originally Posted by Tim Farrant

That material looks fine. It looks like it has a layer of foam? If you face that into the enclosure, you do not need any more dampening inside. Just use plenty of sealant like No More Gaps on the timber cleating, and staple the material on. The sealant should keep it airtight.

Thanks Tim,
I have the Nuwave Base that has no Foam inside or foil though I do have some spare 12Kg M3 Specific Wool Insulation that would slot inside the trap, so looking at what everyones conclusions I'm thinking a depth of 100mm and a size of 1200 mm x 1800 mm (Taking into account the Trap is now 8Kg M2 Back to Back) is this sizing correct for low frequency (As my room is already trapped to the max and performing well save for 150Hz down).

Has anyone got some suggested sizes beside 600 x 600mm and 1200mm x 1800mm ? (Or should I answer my own dumb ass question and just trap where suggested frequencies are shown?) As I really want to take out Bass "Flubber" and smooth those frequencies right down. I have Pic's Waterfall graphs though their on a 3 year old 2.5" HDD and that drive is not spinning well in 2012!

I am Leaning towards 600 x 1800 mm sized traps! x 4 (Oh and the nuwave base is very heavy stuff indeed, even @ 4kg m2.)
Cheers Lads!
TLB.

[boggy]

Originally Posted by Tim Farrant

It has to function like a drum, in free air there is no resistance, the pressure at the front and rear of the membrane will be the same so it won't move. ....

[bolded by me]
It will "move" (it is possibly better to tell "vibrate"). You can hang a significant piece of MLV somewhere in the room, and if you make some non-negligible LF SPL there, you will sense vibrations of membrane if you touch it.

[TheLastByte]

Originally Posted by boggy

[bolded by me]
It will "move" (it is possibly better to tell "vibrate"). You can hang a significant piece of MLV somewhere in the room, and if you make some non-negligible LF SPL there, you will sense vibrations of membrane if you touch it.

Thanks Boggy - Much appreciated
TLB

[joseph]

Very interesting thread.

I'm planning to build this for my control room.

But researching for the material in my area/country always bugging me

I need your help, please. Can I use one of this ?

Indonesia Rubber Supplier and Manufacturer - Bagus Jaya | Products

Or I go with this?
Indonesia Rubber Supplier and Manufacturer - Bagus Jaya | EPDM Rubber Sheet

Thanks alot.

[Adhoc]

Most of them should be suitable, except for those with inlay which would stiffen the sheeting, the silicone one is expensive. I would stick with low hardness (45 Shore) which gives more flex to the membrane.

One thing, not mentioned so far, is smell. Except for viton, several rubber materials can smell from quite bad to almost nothing (may depend a lot on manufacturing company and not only on choosen material) => Ask for info or request a sample.

[joseph]

Originally Posted by Adhoc

Most of them should be suitable, except for those with inlay which would stiffen the sheeting, the silicone one is expensive. I would stick with low hardness (45 Shore) which gives more flex to the membrane.

One thing, not mentioned so far, is smell. Except for viton, several rubber materials can smell from quite bad to almost nothing (may depend a lot on manufacturing company and not only on choosen material) => Ask for info or request a sample.

Thanks adhoc,
I can't get the mass data in kg/m3, they put the spec like this :

density: 1.5g/cc (grade A and B ) 1.6g/cc (grade C)

Also they offer thickness varies from 1-50mm, I can't recall Tim has mention minimum or maximum thickness for the membrane.

Also there's tensile strength spec : 5mpa (grade A), 4mpa (grade B), 3mpa (grade C)

Please need advice

Thanks

[boggy]

Originally Posted by joseph

Thanks adhoc,
I can't get the mass data in kg/m3, they put the spec like this :

density: 1.5g/cc (grade A and B ) 1.6g/cc (grade C)

Also they offer thickness varies from 1-50mm, I can't recall Tim has mention minimum or maximum thickness for the membrane.

Also there's tensile strength spec : 5mpa (grade A), 4mpa (grade B), 3mpa (grade C)

Please need advice

Thanks

cc is "cubic centimetre" g is "gram"

you can get info about surface density in kg/m2 if you calculate this:

(surface density in kg/m2)=(density from Bagus Jaya in g/cc, or "as is")x(needed thickness in mm)

Example:

4mm thick membrane from material with density of 1.5g/cc give us 1.5x4=6kg/m2 surface density.

(EDIT: I have a typo,... surface density is expressed by kg/m2, not kg/m3... now it is ok)

[joseph]

Originally Posted by boggy

cc is "cubic centimetre" g is "gram"

you can get info about surface density in kg/m3 if you calculate this:

(surface density in kg/m3)=(density from Bagus Jaya in g/cc, or "as is")*(needed thickness in mm)

Boggy, I LOVE YOU!
It's strange, when you replied my post, I'm browsing your website! Remarkable!

Thanks alot!

[Tim Farrant]

Originally Posted by TheLastByte

Thanks Tim,
I have the Nuwave Base that has no Foam inside or foil though I do have some spare 12Kg M3 Specific Wool Insulation that would slot inside the trap, so looking at what everyones conclusions I'm thinking a depth of 100mm and a size of 1200 mm x 1800 mm (Taking into account the Trap is now 8Kg M2 Back to Back) is this sizing correct for low frequency (As my room is already trapped to the max and performing well save for 150Hz down).

Has anyone got some suggested sizes beside 600 x 600mm and 1200mm x 1800mm ? (Or should I answer my own dumb ass question and just trap where suggested frequencies are shown?) As I really want to take out Bass "Flubber" and smooth those frequencies right down. I have Pic's Waterfall graphs though their on a 3 year old 2.5" HDD and that drive is not spinning well in 2012!

I am Leaning towards 600 x 1800 mm sized traps! x 4 (Oh and the nuwave base is very heavy stuff indeed, even @ 4kg m2.)
Cheers Lads!
TLB.

No, too big, make them small (600x400) and spread them around the room as I have shown in my drawings. One or two big absorbers is not as useful and enclosures that are square (600x600) are not a good idea. Use the formula and calculate for the material you are going to use. Make different depth absorbers like I have shown.

[Tim Farrant]

Originally Posted by Bilou

A plank or a desk can vibrate in a room with no sealed cavity behind it. Why not an MLV layer ?

Think of it this way so you understand. The panel vibrates and sound waves hitting the front surface are re-radiated from the rear surface. In free air it will be partially acoustically transparent at the resonate frequency (known as the coincedence dip). If you take the vibrating panel, and place it over a sound proof (and airtight) enclosure the re-radiation cannot be heard anymore, make sense?

A stiff panel hanging in free air might still have resonance, but I doubt a limp mass panel will have any resonance at all without the enclosure.

[boggy]

Originally Posted by Tim Farrant

.....but I doubt a limp mass panel will have any resonance at all without the enclosure.

Kinetic energy of (moving) air particles will move it as always... with or without box behind. Box behind membrane may only shift resonant frequency (this introduce bigger movement than usual, so there is more influence) in range where it is more usable.
Freely hanged limp mass sheet may have modal resonances as any thin sheet of material (metal, MDF, etc)

[Tim Farrant]

Originally Posted by boggy

Freely hanged limp mass sheet may have modal resonances as any thin sheet of material (metal, MDF, etc)

But MDF and metal have significant surface tension and therefore stiffness, so when you strike them they have an audible "note" or resonance, but a piece of leather or similar limp material has no note. I don't think you can equate the characteristics of a stiff panel to that of a limp one IMO, quite different things.

[boggy]

Originally Posted by Tim Farrant

But MDF and metal have significant surface tension and therefore stiffness, so when you strike them they have an audible "note" or resonance, but a piece of leather or similar limp material has no note. I don't think you can equate the characteristics of a stiff panel to that of a limp one IMO, quite different things.

MDF and limp mass membrane aren't same thing, of course, but even if you cannot hear a clean "note" from leather or limp mass membrane, this doesn't mean that sheet of this material cannot vibrate in free air, because loudspeaker's SPL. Sheet of paper will vibrate in front of loudspeaker... you can try...

[johndykstra]

so this has been bugging me for a while, and since this is a moderator hosted thread, perhaps I can get some insight. There are a few threads I'm subscribed to (this being one of them) that always log me out when I click on it. Everytime I click "view first unread", I'm no longer signed in. Even stranger, it only happens when I'm on a PC.

Any ideas?