advice needed on low frequency transfer

STICKLER66

Standard Member
hi,
been creating a loft room, 9"x2" joist installed filled with rock wool and stud walls sat on top filled with 100mm rock wool slab. the floor will be floating, can i lay anything on top of the joists to aid in the low frequency absorption side of things? i've read felt is a good blocker, any thoughts on this welcome.
 

ARNOLD AKIEN

Novice Member
hi,
been creating a loft room, 9"x2" joist installed filled with rock wool and stud walls sat on top filled with 100mm rock wool slab. the floor will be floating, can i lay anything on top of the joists to aid in the low frequency absorption side of things? i've read felt is a good blocker, any thoughts on this welcome.
It depends on how much you want to pay, but, have a look at this site and see if you can find something that wont cost you more than you can afford to pay .... " Under floor acoustic insulation " ...


soundproofing: Floors


In your situation I'd phone them and ask for advice.
 

Ted White

Novice Member
Hi Stickler. When you say you'd consider something laying on the top of the joists, this means there is no subfloor yet? If so, you could affect some decoupling by intruducing U-shaped rubber isolators. Not a lot of money. Also, you may have a lower density panel product there. We call it Soundboard, etc
 

IWC Dopplel

Distinguished Member
hi,
been creating a loft room, 9"x2" joist installed filled with rock wool and stud walls sat on top filled with 100mm rock wool slab. the floor will be floating, can i lay anything on top of the joists to aid in the low frequency absorption side of things? i've read felt is a good blocker, any thoughts on this welcome.
Without total decoupling low frequency absorbtion is about mass and damping

Bitumen, stone and sand are all friends :D It can get very complex with low frequency transfer. Avoid anything that might encourage drumming and vibration.

In cars a heavy bitumen self adhesive Dynomat works well by stopping panels vibrating/resonating. This is not supercheap but something similar could be worth investigating
 

Ted White

Novice Member
I agree with IWC. Interesting about the damping mats and films. They are themselves damped, but don't damp what they are in contact with all that efficiently. I've been involved with accelerometer tests in the past, and the semi-liquid damping compounts damp much more efficiently.

These pads are primarily designed for extensional damping, which is a surface application. Great for steel panels. However we are needing contrrained layer damping, which involves sandwiching the damping material in between 2 layers of material like plasterboard. For constrained layer damping, we need a semi-liquid damping material for two main reasons.

First, as constrained damping layers get thicker, their ability to damp the panels is significantly reduced. Second, because they are solid, the damping pads do not completely conform to every little nook and cranny of the surface like a semi-liquid "glue" does.

The damping data shows this pretty clearly. So again, nothing wrong with damping pads, but they are designed and optimized for surface damping of sheet steel primarily.
 

STICKLER66

Standard Member
thanks very much for the replies guys, will research these options and see what the budget allows. would the semi fluid sandwich filler be "green glue"... would it be applied in linear beads @ given centers? oh i didn't say but i guess you realised the rooms use would be for films and ps3 jollies.
cheers

stick
 
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STICKLER66

Standard Member
o.k. checked out a couple things on this site customaudiodesigns.co.uk. rang and spoke to a chap and he suggested a new product that's not even on the site yet, a single sided adhesive strip 50mmx6mm in 12mtr rolls @ £17.28+vat (ne360rt) that sticks direct to joist tops, same spec as the "c" section joist cappers but overall about £70 less for about 18mtrs more, nice. next was the perimeter flanking strip (ac160) "2x1" L section @5mm thick foam in 1.8mtr lengths @ £1.78+vat so with del all in £140.

done quite well really with the cost of the whole project should just come in @ around £1k, luckily i work for a timber conservatory firm so had 4 2.4mx1.2m x.110mm celotex sheets (for the eaves) for free and discounted timber through the firm, not so lucky on the labour though basically no help what so ever.

don't know if i need to to anything with acoustics though, room size 4.2mtrs long x 3.6mtrs wide x 2m high, the side walls along the length are about 1.2mtrs high before roof pitch starts giving a ceiling width of about 1.8mtrs accross the width. I'm going to cut across the rear corners which hopefully will act as a base trap, but main purpose is to cover some nasties in those corners. overall can i expect any acoustic problems?

thanks for help

cheers stick
 
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Ted White

Novice Member
With construction, there are 4 things that can help you in the low frequencies:

Mass
Absorption
Decoupling
Damping

A tape on the edge of a framing member doesn't have any of these properties.
 

STICKLER66

Standard Member
With construction, there are 4 things that can help you in the low frequencies:

Mass
Absorption
Decoupling
Damping

A tape on the edge of a framing member doesn't have any of these properties.
hi Ted,
not sure why you say a "tape" has none of the above properties? the 6mm joist tape is a rubber compound with the same spec as the ac200 c section joist cappers but cheaper, the 2"x1" L section is foam based which seals the floor/walls while keeping the floor decoupled. the mass could be 2 flooring materials @ 15mm thick with a thin mat between, giving a good overall thickness "mass" but each individually damping/absorption is higher. new to all this but i thought by floating the floor above the joist with an absorbing compound below and a good gap around the floor perimeter the floor should be isolated? have i misunderstood something i must get this right 1st time no second chance well only @ a cost.

cheers

stick
 

Ted White

Novice Member
Stick, I must appologize. I had posted a reply to your post last week. When I came by today I see there's no post from me. Obviously I did something wrong when posting.

The essence of my reply was that a tape isn't massive. When we discuss mass, we're referring to adding another layer of plasterboard or flooring. That sort of mass.

While the tape itself may be damped, it's not going to damp the framing or panels that it is attached to. That's the difference.

Thank you
 

STICKLER66

Standard Member
thanks for your replies Ted, sorry to go on about this but i just want to understand the concept.

1 the rubber strip will stop transfer only?

2 the greater the floor mas the less vibration, 2 layers of flooring with a rubber mat @ it's center?

3 perimeter flanking strip keeping the floor decoupled whilst sealing to wall?

if the above is correct (please correct me if there not) then doing all 3 should do the trick?

cheers

stick
 

STICKLER66

Standard Member
just parted with £220 Ted,neoprene joist strip, floor membrane and flanking strip. still must be done otherwise the room becomes a really nice storage space! would be nice to get this finished to a decent level for use over the Christmas break.

cheers for now

stick
 

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