Resonant wall fix with aerated concrete

[Fidach Lad]

The wall in back of my loudspeakers is made of flabby Gypsum plaster (sheetrock in the US) and it starts to resonate somewhere around 40-50hz.

I am looking for a suitable replacement and I came upon aerated concrete as a possible solution. It comes in blocks made ??of sand, lime and cement. When aluminum powder is added during the production process, these materials react with water to create a porous structure. It is lightweight and the blocks can be cut with an ordinary hand saw, fitted, joined and covered with any number of finishing materials.

Does anyone know if this would work to eliminate my problem? The room is narrow, long and entirely open under 1/2 of a roof. It was once a loft. I listen on the narrow axis (about 3m wide). This can not be changed as it is lies in the middle, in between a living and dining space. The wall at my back is made of brick. I like everything about the sound because it can be heard throughout the entire space and I don't actually spend much time seated in front of my speakers when music is playing, but when i do, the only thing that vexes me is the flabby wall in back of my high efficiency speakers, which have adjustable baffles (with different opening sizes) in the back and which don't go much below 40Hz, enough to hear the resonance. It is disturbing. It is not a problem with my LS3/5As.

 

[Rodney Gold]

Changing mass and stiffness of that wall will change the resonant freq.. add the panels securely screwed to the flappy wall and It will most likely move the resonance to a point where it is no longer an issue..

 

[Fidach Lad]

Thanks Rodney. The whole wall-really a half wall - needs to be rebuilt, as it was very poorly framed when the building was "modernized" in the 1020s or 1930s - studs are too far apart and not the right dimension, so I was thinking about this material.

For about ten years, I traveled twice a year to the area around Paarl, Stellenbosch and Wellington for work, but the money dried up with the finance crisis, and I haven't been back since 2010. I never actually looked for a hi-fi shop in Cape Town and never saw one, either. A pity that the Rand has lost so much of its value.

 

[DonH50]

You can change material, add another layer of Gypsum (glue and screwed), add bracing and so forth to reduce wall flexure. However, it is most likely a resonance of the room that is causing the wall to vibrate and, while stiffening the wall is a good idea, it will make the magnitude of the resonance in the room higher (worse). You might want to measure, or get someone to measure, the room's response to confirm and if so treat the source of the issue if that is the case.

 

[mep]

You can change material, add another layer of Gypsum (glue and screwed), add bracing and so forth to reduce wall flexure. However, it is most likely a resonance of the room that is causing the wall to vibrate and, while stiffening the wall is a good idea, it will make the magnitude of the resonance in the room higher (worse). You might want to measure, or get someone to measure, the room's response to confirm and if so treat the source of the issue if that is the case.

Sounds like he needs to tear off the sheetrock and stud the wall correctly. From what he said, the wall was never studded correctly. 2 x 4 studs need to be 16" on center and if you really want to make the wall stiffer, you could space them more closely together. Of course, a complete set of graphs and charts generated from measurements need to be taken before he rips the wall out and after he replaces it in case he says the new wall sounds better and he is asked for proof.

 

[Fidach Lad]

You can change material, add another layer of Gypsum (glue and screwed), add bracing and so forth to reduce wall flexure. However, it is most likely a resonance of the room that is causing the wall to vibrate and, while stiffening the wall is a good idea, it will make the magnitude of the resonance in the room higher (worse). You might want to measure, or get someone to measure, the room's response to confirm and if so treat the source of the issue if that is the case.

In this case the room is about 12m long and 3m wide with no walls between the 3 "spaces", each of which occupy about 4m of length and are 3m wide, the width of the old loft room. (The whole room is open, enclosed by 4 walls. My gear sits in the middle space, without any side walls. How would you measure such a room to detect what is causing the resonance?

 

[Bruce B]

The easiest would be like Don said. Add another layer of Sheetrock. This time, install it 90 degrees to the first layer with a layer of Green Glue between.

 

[mep]

The easiest would be like Don said. Add another layer of Sheetrock. This time, install it 90 degrees to the first layer with a layer of Green Glue between.

I would argue that if his walls were built by some boy scouts instead of carpenters and they were trying to save money from their light bulb sale and put the 2 x 4 studs 24" on center, he's better off tearing it down and starting over.

 

[Fidach Lad]

Thank you, all, for your suggestions. I can do the suggested work as a winter project. The job that was done in the 1920s or '30s was definitely not with 48mmx89mm studs and they were spaced far more than 41-42cm apart.

Apparently, none of you are familiar with aerated cement. Does it even exist in the US, I wonder? It is porous after a fashion, but it is cement based and can even be used for exterior weight-bearing walls, like cement blocks. But, because it has a fine surface, finishing is much easier, for example with glass paper or even gypsum boards.

 

[Mosin]

Thank you, all, for your suggestions. I can do the suggested work as a winter project. The job that was done in the 1920s or '30s was definitely not with 48mmx89mm studs and they were spaced far more than 41-42cm apart.

Apparently, none of you are familiar with aerated cement. Does it even exist in the US, I wonder? It is porous after a fashion, but it is cement based and can even be used for exterior weight-bearing walls, like cement blocks. But, because it has a fine surface, finishing is much easier, for example with glass paper or even gypsum boards.

I know about it. It is called foamed cement here, and it is pumped into forms from a big hose. It is pretty cool because it can be formulated with various additives, so that it meets a lot of different specifications. High fly ash versions, for example, are very durable because they lack internal voids, so they aren't porous. The downside is that the availability of all types of foamed cement is limited to certain areas of the country.

Cement in the US is largely controlled by French owners, by the way.

 

[Fidach Lad]

I know about it. It is called foamed cement here, and it is pumped into forms from a big hose. It is pretty cool because it can be formulated with various additives, so that it meets a lot of different specifications. High fly ash versions, for example, are very durable because they lack internal voids, so they aren't porous. The downside is that the availability of all types of foamed cement is limited to certain areas of the country.

Cement in the US is largely controlled by French owners, by the way.

Thank you, Mosin. I think that is a different product. Look at the pictures, here: https://sv.wikipedia.org/wiki/Lättbetong . Use Google Translate; it is in Swedish.

 

[Mosin]

Thank you, Mosin. I think that is a different product. Look at the pictures, here: https://sv.wikipedia.org/wiki/Lättbetong . Use Google Translate; it is in Swedish.

I have never seen that available commercially, but I have seen something similar for industrial use.

 

[Rodney Gold]

this stuff I used on my ceiling will work real well on your wall , it absorbs and diffuses , looks great too
http://www.rockwoodcladding.co.za/
Im sure you can find a similar product where you are, its made of polyurethane and is quite light , just screwds or is glued on.. easy to work with and very nice aesthetically

 

[Fidach Lad]

Yes, I can find something like this. But I would probably still have to stiffen the wall. What do you think?

Thanks.

 

[Rodney Gold]

I reckon just cladding it will do the trick... use screws, quite a few per panel.. like 10 +
If it doesn't work , unscrew it , do the stiffened wall and apply it anyway..