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Rubber mats to enhance a "duvet booth"?

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Rubber mats to enhance a "duvet booth"?

Postby Fishnish » Sun Feb 02, 2020 5:33 pm

I'm lucky in that my home recording space is quite spacious (about 4x6m) with a highish vaulted ceiling. I have some big dense traps in the corners and some homemade foam/rockwool/ airspace panels (as described in the classic SOS feature). As a whole the room sounds well enough for me,

The room has beams running across it about 2.5m above the floor so it's very easy to hang up a duvet or 2 which together with a reflection filter make a DIY vocal booth for when I want things drier.

However I'm finding with the "duvet booth" things seem to get a litle imbalanced as regards low end and have been wondering whether hanging up a couple of strategically placed large heavy duty rubber backed office type doormat jobbys might act as DIY limp membrane absorbers aiming for the low end. Has anyone tried using these in this way?
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Re: Rubber mats to enhance a "duvet booth"?

Postby Hugh Robjohns » Mon Feb 03, 2020 11:41 am

All the practical commercial applications of limp mass membranes I've seen has them hanging reasonably close to the wall boundaries, rather than in the middle of the room.

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Re: Rubber mats to enhance a "duvet booth"?

Postby blinddrew » Mon Feb 03, 2020 11:57 am

Is that because, although the air movement of low frequencies is higher in the middle of the room (nodes aside), the pressure is higher near the boundaries and a heavy limp mass will actually take a fair amount of pressure to move (and therefore absorb)?
Or is it just the practicalities of hanging thick rubber mats across the middle of the room?
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Re: Rubber mats to enhance a "duvet booth"?

Postby Hugh Robjohns » Mon Feb 03, 2020 12:40 pm

I think it's a pressure thing...

It's the air particle velocity that is important for conventional absorbers (foam, mineral wool, etc), which is why they are most effective when placed a 1/4 wavelength from the boundary surface. But a large non-porous barrier matt will respond to pressure changes more than velocity, and as you say, acoustic pressure is maximum close to the boundary surface.
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Re: Rubber mats to enhance a "duvet booth"?

Postby shufflebeat » Mon Feb 03, 2020 1:59 pm

Imagined:

"Honey, can I choose the wallpaper this time?"

"Of course, nice to see.you take an interest."

@Hugh, for the record, what does "reasonably close" mean? (+ poss dumbass q?) I would imagine mirror points are irrelevant at the frequencies discussed, is this correct?
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Re: Rubber mats to enhance a "duvet booth"?

Postby Moroccomoose » Mon Feb 03, 2020 2:21 pm

In the event that I might get a room that was worth treating, I often wondered if, when going DIY absorber route, if hanging one of those heavy rubber backed door mats as a limp mass bass absorber, in the gap between the rock wool and the wall. Would the rockwool negate the bass absorber's usefulness in that arrangement? Would the bass mat negate the gap's usefulness? Has anyone tried this arrangement before?

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Re: Rubber mats to enhance a "duvet booth"?

Postby Hugh Robjohns » Mon Feb 03, 2020 2:24 pm

shufflebeat wrote:...what does "reasonably close" mean? (+ poss dumbass q?) I would imagine mirror points are irrelevant at the frequencies discussed, is this correct?

Mirror points are irrelevant in this context, and by reasonably close I'd say about a foot or less ... but this is just a gut feeling based more on observations and practical messing around, rather than real knowledge. I'm not a trained acoustician...
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Re: Rubber mats to enhance a "duvet booth"?

Postby Hugh Robjohns » Mon Feb 03, 2020 2:27 pm

Moroccomoose wrote:... hanging one of those heavy rubber backed door mats as a limp mass bass absorber, in the gap between the rock wool and the wall.

Most implementations I've seen have some absorber between the membrane and wall boundary. In my own corner bass traps (designed by Max) there are triangular chunks of mineral wool in the corner, with the membrane hanging in front, and then a 150mm thick panel of Owens-Corning 703 in front of that.
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Re: Rubber mats to enhance a "duvet booth"?

Postby Fishnish » Mon Feb 03, 2020 6:28 pm

Thanks everyone. I will have a play around. By happy accident the cross beams make it ridiculously easy to hang things in a variety of configurations all around the room (including near to and parallel to the walls), so it would only take a minute or two to try.
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Re: Rubber mats to enhance a "duvet booth"?

Postby DanDan » Tue Feb 04, 2020 12:01 am

An intersting question. In this case IMO the rubber mats would create a new sort of boundary. Close to the source and a blocking effect, so higher SPL than at the real room boundary. As well as blocking they are bound to vibrate, and thus absorb somewhat. How much damped absorption vs blocking is a matter of thickness, mass, stiffness. And to a smaller extent depending on distance from or contact with the Duvet. I would rather see 100mm fibre batts btw. If you do try this please do record a vocal before and after. Note that devices such as HF MiniTraps have a layer of foil glued on the back. This blocks a bit but also increases LF absorption a bit. Useful bits.
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