Cloud absorbers vs Atmos Ceiling speakers

[cct]

I'm going to add some absorption to my ceiling, which has Atmos in-ceiling speakers. I'm thinking of using panels 4'-6" thick, and hanging them to leave an air gap of about 6". Commercial panels would typically use 1"x6" framing boards around the sides. I'm wondering about reflections from the ceiling speakers from the framing boards, and whether the panel design should have open area on the sides as well as top and bottom. Maybe make the absorber frame out of 1"x1" sticks so most of the sides would also be open.

 

[HiMu]

I'm thinking of using panels 4'-6" thick, and hanging them to leave an air gap of about 6".

What problems do you expect to solve with that configuration?

 

[Bjorn]

Airgap isn't really beneficial. If an airgap going to be used, it's best to use max 4 cm. What's better is to use thicker material instead and which is also cheap when correct material is being used.

 

[bert stoltenborg]

Airgap isn't really beneficial. If an airgap going to be used, it's best to use max 4 cm. What's better is to use thicker material instead and which is also cheap when correct material is being used.

Could you please sustain these bold statements?

 

[Tassin]

According to the technical info sheet, acoustic panels manufactured by Saint-Gobain Ecophon offer more absorption above ±600 Hz when the air gap is 10 cm.

Source: https://www.ecophon.com/en/ecophon/free-hanging-units-and-baffles/solo/solo-circle-xl/# (See "Acoustics").

 

[DVDdoug]

I don't remember where I read this, but there is another benefit to a gap If the absorber doesn't cover the whole surface... Sounds bounce off of the hard surface near the absorber where they are reflected into the back side of the absorber rather than back into the room.

 

[Bjorn]

Could you please sustain these bold statements?

It's based on Ron Sauro's researchers. The energy flows out when the air gap is too big and absorption is lost. Unless of course it's completely sealed.

But it's a pretty much a waste anyway since using thicker material is better and is also cheap

 

[cct]

My first goal in adding cloud absorbers is to reduce early reflections off of the ceiling. That goal can be accomplished by a 2" absorber mounted on the ceiling.
My second goal is to reduce reverb time of the room, especially at low frequencies. I will do some thick absorbers in the corners to act as bass trap, but since
I have 9 ft ceiling I can make use of the space up there to add more thick absorbers. My understanding, from multiple sources, is that an airgap adds significantly to the effectiveness of the absorber, especially at low frequencies. I found a calculator (see below) that indicates the low frequency performance of a 150mm absorber improves by a full octave (moves curve to a lower frequency) with an 200mm airgap. Smaller gaps move the curve down a smaller amount. I've attached a couple of plots from an online calculator, Addition of a 200mm airgap to a 150 mm absorber, then comparing a 150 mm absorber with no airgap to a 75mm absorber with a 200mm airgap.

 

[bert stoltenborg]

It's based on Ron Sauro's researchers. The energy flows out when the air gap is too big and absorption is lost. Unless of course it's completely sealed.

But it's a pretty much a waste anyway since using thicker material is better and is also cheap

 

[Tassin]

Did you not read the 2nd sentence of the document? Or did you get written consent?

ALL included data is copyright protected and can not be distributed, neither complete nor partly, nor direct or indirect, via hard copy or on-line without the written consent of the author.

And what's the point of just dropping a doc without elaborating?

 

[Bjorn]

2" absorbers for reflection control is too bandlimited for a good result. It will only address primarily reflections above 800-1000 Hz.

If a larger area in the ceiling is going to be treated with thick absorbers it's important a part of it isn't absorptive of higher frequencies.

 

[bert stoltenborg]

Did you not read the 2nd sentence of the document? Or did you get written consent?

ALL included data is copyright protected and can not be distributed, neither complete nor partly, nor direct or indirect, via hard copy or on-line without the written consent of the author.

And what's the point of just dropping a doc without elaborating?

Haha, a bureauocrat. That will clear stuff up . And look at the document that is fairly easy to understand. And when you even then have no clue I'm glad to explain

 

[HiMu]

My first goal in adding cloud absorbers is to reduce early reflections off of the ceiling. That goal can be accomplished by a 2" absorber mounted on the ceiling.
My second goal is to reduce reverb time of the room, especially at low frequencies.

Deep frames will cause some reflections and diffraction, but it is impossible to even guesstimate how problematic without more information.

Do you have any REW measurements from the current situation? Can you provide more information about your room, layout etc.

 

[kyuu]

Haha, a bureauocrat. That will clear stuff up

Ironic statement from someone who has done nothing but made opaque and unhelpful comments so far.

And look at the document that is fairly easy to understand. And when you even then have no clue I'm glad to explain

We shouldn't have to look at a document attached to a post to understand why we would be interested in it in the first place. The person posting it might think to explain at least that much.

In any case, after looking at it, the applicability to the topic at hand is questionable. The OP isn't discussing the use of a diagonal absorber between the walls and ceiling.

 

[bert stoltenborg]

Ironic statement from someone who has done nothing but made opaque and unhelpful comments so far.

We shouldn't have to look at a document attached to a post to understand why we would be interested in it in the first place. The person posting it might think to explain at least that much.

In any case, after looking at it, the applicability to the topic at hand is questionable. The OP isn't discussing the use of a diagonal absorber between the walls and ceiling.

What is such an absorber? When you take the question of the op in account?

 

[Torin Krell]

Mesh like frames (or minimal open framework) will reduce or eliminate frame reflections and also increase the exposed surface area of the sound absorbing material - improving its effectiveness.

 

[cct]

Deep frames will cause some reflections and diffraction, but it is impossible to even guesstimate how problematic without more information.

Do you have any REW measurements from the current situation? Can you provide more information about your room, layout etc.

REW mdat file attached. Sweep from center channel, mic at MLP.
Room is 25' wide, 16' deep 9' high. Or 7.6m wide, 4.9m deep, 2.7m high.
Display and L,C,R speakers on are the wide wall, door openings on both the short walls.
Volume is 3600 cu ft,, 100 cu m.
Nine speakers in horizontal plane, 6 overheads, 4 subwoofers (each corner on floor).
I think I need to tame early reflections, and suck up some bass.
I've just found a local supply of Rockwool AFB at attractive pricing.
The bass trapping is the big challenge. There is a lot of room near the high ceiling, but then back to my original question about overhead absorbers interacting with ceiling speakers. I'm now thinking to support the ceiling mounted rockwool in an open wood frame, made of 2cm square sticks, hoping fabric covering will hold the rockwool in place. Thus most sound hitting these from the ceiling speakers would be absorbed and not reflected. Then to arrange the panels so they are out of the way of direct path from ceiling speakers to listeners; easier the closer the panels are to the ceiling, but supposedly they are more effective lower down leaving an airgap.
I will also arrange absorbers near the the corners at ceiling (above the subs) as those locations are touted as best for bass trapping. (per playing with baffles paper that was attached above)

 

[HiMu]

Based on just that one sweep, the level of early reflections is not a major issue. My quarter-butt cheeked guess is that the higher decay time in the 1-6khz region is due to flutter echo, which is easy to treat. But that is only one measurement.

As Björn mentioned, if you want to get the full benefit of porous bass traps with air gap, the sides have to be closed and the back should have a maximum of 1" opening from the wall. If the back is open more than that, pressure will leak out and the benefit of the air gap will be less or insignificant. That is based on information from Ron Sauro, who also states that the porous corner treatments are very low efficiency. But that statement is a can of surströmming I'm not comfortable opening and contradicts the article that Bert Stoltenborg provided.

I hope that John Brandt & Ron Sauro would (finally!) publish the paper about the testing they have done and get the results peer reviewed.