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6 minutes ago, Primare Knob said:
23 minutes ago, almikel said:
Now those as slats would be way cool

It would be a good reason for buying another tool.

Keep in mind you said earlier you didn't want to lose the head height...

...but if you were prepared to lose the head height, then a combination of limp mass (for bass trapping) and those amazing slats PtG posted for diffusion and broadband trapping would create a spectacular ceiling.

 

7 minutes ago, Primare Knob said:

I thought by reading a BBC document which uses hardboard instead of Vinyl, that filling it up with absorption drops the peak but widens the bandwidth.

Good work - yes that's correct, but limp mass will inherently have a lower Q (less sharp) than hardboard, and IMO anything that broadens the "narrowband-ness" of pressure traps is a good thing - so filling with absorption is good.

 

mike

 

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9 minutes ago, Primare Knob said:

You guys have made a strong case for the ceiling that I truely considering it.

I am thinking about a combination of limp traps and absorber with a diffuse pattern of slabs.

I hope to be able to DIY this, but it will depend on material costs as well.

The cost of those slabs could quickly become rather expensive.

The ceiling is such a good place for treatment - out of the way, and a large area.

 

21 minutes ago, Primare Knob said:
39 minutes ago, almikel said:
Now those as slats would be way cool

It would be a good reason for buying another tool.

 

11 minutes ago, Primare Knob said:

The cost of those slabs could quickly become rather expensive.

Ignoring the cost of the tool :), the material shouldn't be "too" expensive if you can DIY it. With a slat profile like that, you could ignore using a BAD pattern, and just have regular gaps...

...or just go back to plain profile slats for those sections - a 1D pattern will get some diffusion, but just a regular pattern will still get useful scattering (I'd go the 1D pattern, as there's marginal additional work required).

 

Another of Svenr's useful threads - this one for modular 1D BAD diffusers - he's using them on walls, but no different to ceilings.

cheers

Mike

 

 

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If you got he limp mass route, do it in a manner that you can take it out if not happy.

(a) it looks rubbish (IMHO)

(b) they are VERY fickle about a target frequency - so bang it up, do some measurements, then pretty it up as you desire (assuming it worked)

 

 

Edited by Peter the Greek

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1 hour ago, Peter the Greek said:

 

(a) it looks rubbish (IMHO)

(b) they are VERY fickle about a target frequency - so bang it up, do some measurements, then pretty it up as you desire (assuming it worked)

 

 

good points

(a) Looks have never been my strong point for treatment

(b) they are narrow band devices - so they need to work where you have issues

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After reading a bit more on GearSlutz " to use pressure based absorbers and regardless of type used; they need to be placed at a surface related to the modal/SBIR –related problem that your trying to fix. "

 

This suggest that treating the ceiling isn't going to improve my biggest problems, as those a likely to be room width and length modal nodes.

The question that arises is the need and the how, to make a distinction between modal nodes and SBIR

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I have played around with the subwoofer placement and placed them half way the length off the room along the wall (green line) which produces a better response.

Wether if this is a bennifit or not I don’t know yet, as the ¼ along the front placement (blue line) produces a more identical ouptut compared with my front speakers, which I can’t really move a round a lot to improve their LF response. So I can tune acoustics for them and the subs in a similar way

 

I also mocked up some absorption pannels that I placed in the front corners of the room (red line). They do their work between 100Hz – 200Hz, but I get the idea that they are more effectieve on the Tangential room nodes, but perhaps these are inprovements in the SBIR nodes.

Subwoofer_Placement_and_Absorbtion.jpg

Edit:

When placing the subs halfway the room, it will control the modal length nodes around 35Hz and 70Hz. If I do a good job on the ceiling acoustics I can control the modal nodes around 70Hz and 140Hz. Then there will be left the width nodal node which I can't figure out which sub placement can deal with these using the simulator.

 

The dip in the graph from 50Hz - 60Hz has to do with the Axial width node at 50Hz, which doesn't seem to have a large effect, and the tangential Length/Width node around 62Hz, which seems to have a much larger effect. This could potential being fixed by raising the gain of the subs to lift the dip to about 85dB en EQ all the peaks down. The next room width nodal node is around 100Hz which might not be an big issue when perhaps using an aggressive cross over setting.

 

What would your thoughts be on this?

 

I also discovered that my ceiling height might be closer to 245cm reading the graph which puts it almost exactly at 1/2 the room length.

 

The theoretical response curve would look something like this

Theoretical_Response_With_Ceiling_Treatment_Subs_Halfway_LenghtRoom.thumb.jpg.4d00819ecf66568c00cb58760bce4ac3.jpg

Edited by Primare Knob
Addition

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On 1/16/2018 at 10:49 AM, Primare Knob said:

I have played around with the subwoofer placement and placed them half way the length off the room along the wall (green line) which produces a better response.

 

Subwoofer_Placement_and_Absorbtion.jpg

 

 

The dip in the graph from 50Hz - 60Hz has to do with the Axial width node at 50Hz, which doesn't seem to have a large effect, and the tangential Length/Width node around 62Hz, which seems to have a much larger effect. This could potential being fixed by raising the gain of the subs to lift the dip to about 85dB en EQ all the peaks down. The next room width nodal node is around 100Hz which might not be an big issue when perhaps using an aggressive cross over setting.

 

What would your thoughts be on this?

 

 

That green line shows an excellent improvement 20 - 60Hz or so. I'd leave 1 sub where it is and muck with the placement of the other sub to see if you can get an improvement in the dip below 70Hz, and the peak at 70Hz...

It does become tedious, as it's an iterative process...:( especially if the subs are heavy/bulky.

Where do you plan to cross your subs to mains?

The 70Hz peaks "appear" to be modal rather than SBIR (since same  freq) - although the 100Hz peak shifts a little in frequency - was the mike in exactly the same place across all those measurements? Given the subs moved a lot and the 100Hz peak moved such a small amount it's still likely modal rather than SBIR.

On 1/16/2018 at 10:49 AM, Primare Knob said:

 

The dip in the graph from 50Hz - 60Hz has to do with the Axial width node at 50Hz, which doesn't seem to have a large effect, and the tangential Length/Width node around 62Hz, which seems to have a much larger effect. This could potential being fixed by raising the gain of the subs to lift the dip to about 85dB en EQ all the peaks down.

 

At this stage in the process I wouldn't recommend attempting to fill dips with EQ - EQ is position dependent and you can make things worse elsewhere and run out of headroom very quickly.

I've found lopping peaks off with EQ isn't as bad (as EQ boost) at making things worse elsewhere...

 

On 1/16/2018 at 10:49 AM, Primare Knob said:

 

I also discovered that my ceiling height might be closer to 245cm reading the graph which puts it almost exactly at 1/2 the room length.

 

you own a tape measure right?

The "acoustic" measurements can be quite a long way out based on the flexibility of your boundaries - the models aren't perfect and make a lot of assumptions so that they're easier to drive - don't take what they say as Gospel - but they're still very useful.

 

On 1/16/2018 at 10:32 AM, Primare Knob said:

After reading a bit more on GearSlutz " to use pressure based absorbers and regardless of type used; they need to be placed at a surface related to the modal/SBIR –related problem that your trying to fix. "

 

This suggest that treating the ceiling isn't going to improve my biggest problems, as those a likely to be room width and length modal nodes.

The question that arises is the need and the how, to make a distinction between modal nodes and SBIR

and being a lazy DIYer myself, I totally understand that if going to the effort of ceiling treatment, it needs to achieve what you want 1st time, and in your case also look good.

 

I've not tried limp mass traps myself (yet), so I have no personal experience to be able to recommend a limp mass solution, and reviewing Svenr's posts, he deployed limp mass on the ceiling and a front wall bulkhead - so 2 modal directions (front to back and floor to ceiling) covered, rather than just 1 (floor/ceiling).

Also on his ceiling he had access to a 400mm gap, not 200mm (estimated) in your case.

I haven't seen @svenr on this forum for a while - if he pops up he may comment.

 

Heading down a slat + absorption path on the ceiling will provide good absorption down to 150Hz or so but keep higher frequency energy in the room - "in room" measurements would likely see benefits below 150Hz due to the size if you covered the ceiling - the ceiling absorption would be exposed to absorb "grazing" energy from all lateral modes.

 

Looking at the models - I would recommend using "fluffy" instead of anything denser above the slats - it's cheaper and models better.

Below is 100mm wide slats with 100mm spacing, with above 200mm fluffy (5000 thingies) vs 200mm mineral wool (27000 thingies) - fluffy is blue

5a5f398d70500_slats200mmfluffyvs200mmmineralwool.JPG.51ed2d06a88b073b9ad664158a01f352.JPG

That's a good bass trap (blue line)  - you may only need some EQ below 100Hz (which is where EQ works very well).

 

cheers

Mike

Edited by almikel

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After putting the sub at ear height at the listen position and placing the mic at different positions it doesn't look like it is going to be better than placing them halfway.

It produces the flattest response from 20-40Hz and smallest null/dip between 40-70Hz.

 

Theoretically that null should mostly disappear when racing the speakers up, but the measured results are telling a different story.

 

I have become rather interested in this VPR type acoustic trap since it seems to have a broadband behavior and is also very good in taming decay times.

https://www.gearslutz.com/board/studio-building-acoustics/667929-my-experiment-metal-panel-absorber.html?s=5dfd1dfd745d261f103486db4ddcaca5

 

On top of that, it is rather easy to build. Glue a metal sheet onto an acoustic foam. I still have many pages to read through from that forum topic.

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