testing post
thanks richard. its working on mac but not iPad
I’ve messaged you
Hello Peter,
Been reading into this more and it seems the T50 traps would work behind a sofa as they’re pressure based, as are the panel absorbers above.
Monster bass traps are velocity based so can’t be obstructed.
It’s slowly sinking in 
Cheers,
Mark
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Crafty! 
Hi Mark, sorry but they still won’t work quite in that position. Consider them being pressure activated ie more pressure at the front (facing the source ie your speakers) than at the back, hence creating a difference front to back making the rubber diaphragm move very slightly backwards and with the help of the insulation material inside absorbing the internal increase in pressure.
The pressure along particularly I suspect the front and back wall will be zones of constant pressure more and less particularly if you ‘hide’ your absorber behind the sofa. Ie a T50 is as I see it no different to say a Monster Trap in its dependency of velocity of the sound waves causing the pressurisation.
However a T50 will be very frequency specific to have its absorptive peak at 50Hz assuming that, that is your room’s trouble frequency and there after ‘fall off’ very rapidly. The metric difference between a room’s boundaries will cause pressure problems at different frequencies, front/back, sidewall/sidewall and ceiling floor distance.
I have used 2x 120 by 60cm GIK membrane absorbers peaking at a 100Hz directly behind my speakers ( 110 cm away from rear of cabinets) tucked in discreetly behind my curtains and they actually work better than 2x 7 inch thick Monsters in that same position. I tried my Monsters there and you could hear the difference at instrument tones at my problem frequency at 80-90 Hz.
For me in the end it was a revelation to get rid of my chunky listening sofa, replace it with a light and comfy single listening chair ( my wife has no interest in the hifi tbh.) and subsequently putting 2 low placed Monsters up ( well exposed) 50mm from the back wall to mop up lower frequencies from the front ports on my Facts and also to some degree help against ‘slap-back’ from upper bass and lower mids.
It’s a weird and wonderful game 
Best Peter
( I hope you can make sense of a little bit of my rambling)
PS. If you wish to contact me via Richard Dane feel free 
Mark, I should add there is a huge added gain in moving your listening position forward and away from the back wall. My ears are 85 centimetres away from the absorber/diffuser placed on my rear wall window ledge ( see above photo) Best Peter
There is a problem with using 25mm MDF (or even 15mm MDF) at 1m distance of constraint:
With such a relatively large thickness of the panel compared to the width across the suspension, the panel is no longer behaving purely as a thin material. The elastic restoration force of the MDF panel is likely to approach or even exceed the elastic restoration force of the constrained gas spring formed by the cavity. This will seriously mess up the calculation of resonant frequency.
Thanks for your replies and insights Peter, I see what you mean … I think I’m too limited to do much here. The problem frequency is mainly around 47 hz, I don’t have sufficient room to put anything thick behind the speakers (34 cm to the wall).
Moving my listening position just ~10 cm forward did make an appreciable difference on the graph but I’m still very close at 42cm. My room is a very similar size to yours, except I’m listening across the room, so still more limitations!
I’ll continue to read more on this as I do find it very interesting, and I hate giving up!
Thanks again and Merry Christmas!
Mark
Ps sorry about the link Richard
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Yes I must admit that that the concept of using 25mm MDF as a thin material was a bit of a stretch!
It’s an interesting approach though, will be watching more of those videos as they cover more designs that I haven’t heard of and are easy to follow.
Cheers,
Mark
….now that’s the spirit! 
You have a nice Christmas too and all the best Peter
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Hi @PeterR I followed your suggestion!
After a discussion with my wife, we will tear off the built-in bookcase and redo the room.
The windows will be covered and inaccessible.
There will be floor-to-ceiling absorbers on the left and right walls/windows.
The separation will not be a hard wall.
It will be a wall of absorbers, therefore porous, the air will be able to pass through.
The sidewalls and the back wall/divider will use around 16m3 damping material!
I probably won’t use Rockwool or fibreglass. I’ll probably buy Caruso Iso Bond, produced by a German company, a healthier alternative to rockwool or fiberglass.
The challenge will be to build a door made of absorbers and 45 cm thick.
I will complete the absorption setup with Sub Bass Traps to dampen frequencies below 50Hz.
To keep it a little “live”, I will place the diffusers between the speakers (like now).
The goal will be an almost flat frequency response down to 40-45Hz.
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Hi @Thomas, been thinking a lot today about your project whilst spending more than half the cooking Danish meatballs for the family at Christmas….as you do!
I have some thoughts, but am unsure whether you want me to share 
Anyhow, wishing you a merry Christmas and a healthy and happy New Year 
All the best Peter
Hi @PeterR,
I did not know that Frikadeller was a Christmas recipe 
Don’t hesitate to give your opinion. Any ideas, remarks and criticisms are welcome. This is how we learn. A different point of view from ours is always a good thing.
I imagine you are referring to the possibility of over-absorbing the treble.
If so, you are right. This is the main risk when treating a room.
Absorbing the highs and forgetting about the low end is obviously a problem.
But with the 16m3 of absorbing material, I will absorb at least 60% of everything down to 50Hz. I will then fine-tune according to the result of the measurements, with bass traps calibrated for the frequencies with uncool decay time.
I believe that the most challenging part will be to find time to plan all that…
I wish you a lovely Christmas eve as well and a nice start to 2022! 
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You are such a European Thomas 
…and it’s not really a Christmas dish as you say, but hey we are doing our best ‘not really to do Christmas’, and so far we seem to have failed miserably 
.
Will get back re this promise. Best Peter
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Unfortunately that assumes that the acoustic panel is attached to the frame using a mount with infinite compliance (yet still being sealed), and that the frame has infinite rigidity.
For a practical example of the construction of a LF absorber you may like to look at this:
BBC Research Department Report 1988-05.pdf.
Nice paper @Xanthe 
Parts 3 and 4 are very interesting!
→ http://downloads.bbc.co.uk/rd/pubs/reports/1988-05.pdf
Thanks, that is interesting … I guess the video I linked was more on the theoretical than practical side.
Cheers,
Mark
I am not sure that the design in the publication @Xanthe suggested is suitable for home use. The thing is beyond heavy …
There are lighter designs that are adjustable over a specific frequency range.
The idea is to vary the mass of the front plate, the one that will vibrate and therefore dissipate the energy.
These are the designs that you can DIY at home. In theory, it’s not that complicated. But in practice …
This is what Artnovion offers. But their prices are high. They nevertheless have a “pro” range with less posh finishes, which costs less.
Like most things, you get what you pay for, in Artnovian’s case you get quite beautiful design and materials on top of all the R&D that went into them … love Avalon flow for example
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