Treatment for (slightly) odd shaped mix room

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civvie
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Treatment for (slightly) odd shaped mix room

#31

Postby civvie » Mon, 2020-Sep-07, 20:02

ericwisgikl wrote:Source of the post I put your measurements into Sketchup, traced side walls lines till they meet, measured the angle, which is about 11.5º, and traced a line al 5.75º, the half of them both. Then I took measurements from right side wall to this centre line, and that is your new center.


Amazing, thank you!
endorka wrote:Source of the post Definitely - see the walking mic link test link for a method to do this rigorously.


Lot's of testing today using a slightly simplified walking test method in two different speaker positions.

Test 1 "Symmetrical" test is essentially the same listening position as before but with the left speaker brought forward approx 22cm to bring it in line with the 'symmetrical centre' of the room as described by Eric above. 20cms inside the equilateral triangle is where it sounds best to my ears so this is marked as '0' in the walking test. So '+20' is the tip of the equilateral triangle (I've read Stuarts and John Sayers posts about how equilateral triangles are not necessarily the ultimate, I prefer a wider image personally but my room has some obvious width limitations)

"Symmetrical test" positions:
20200907_232120.jpg

20200907_232305.jpg


Baseline test mdat:
Symetrical Baseline.mdat
(7.54 MiB) Downloaded 876 times
Symetrical Baseline.mdat
(7.54 MiB) Downloaded 876 times


Walking test (where '0' is same position as above):
Symetrical_Walking Test.mdat
(40.21 MiB) Downloaded 993 times
Symetrical_Walking Test.mdat
(40.21 MiB) Downloaded 993 times


The second round of testing was the 'Corner' test. This is with the speakers pushed right up against the back wall and in the corners.
To get them in there I had to remove the 100mm absorber panels you can see in the photo above.
To keep things in line with the symmetrical method the left speak is again brought forward approx 22cms so it's not quite in the corner.
Again the listening position is 20cms inside the tip of the triangle so is marked as '0' on the walking test.
The corner position seemed to raise the DB level by 1-2 db so I had to re-calibrate REW to compensate for this.

This is a sketch of the test positions:
20200907_232149.jpg


'Corners' test baseline:
Corner Baseline.mdat
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Corner Baseline.mdat
(7.55 MiB) Downloaded 841 times

'Corners' walking test (where '0' is the same position as the 'Corners' baseline above):
Corners_Walking test 2.mdat
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Corners_Walking test 2.mdat
(32.78 MiB) Downloaded 1016 times



The bass was definitely different in the Corner tests. In some positions it was smoother for sure. But the big drawback that I immeadiately noticed was the loss of definition in the mids. You can see this on the tests. A big dip in the 2-4k region. This really surprised me and I have no idea why this has happened. I moved the side absorber panels back when I moved the speakers back so I don't think that's it. One thing that I couldn't move is the cloud. In the usual (1st) position the speakers are just under the front end of the cloud, but in the corners they would be approx 40cms in front of it. The cloud is very large and would certainly be blocking first reflections still in this position. No idea how to explain this loss of mids but it really ruins this corner position. I will take smooth mid response over smooth bass any day, but I am determined to try and get both! :)

One final test which is interesting is another full L / R / L+R measurement from the exact mic position from the "Symmetrical Baseline" test, but with the speakers moved to the corner position. I thought this might illuminate which issues are SBIR and which issue are modal.


There's a lot of data here and I'd love it if anyone had the time to take a look at it. At the moment my initial position still sounds the best to me, I'm guessing because of the flatter mid response.

Thanks all, Civvie.



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Wheresthedug
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Treatment for (slightly) odd shaped mix room

#32

Postby Wheresthedug » Tue, 2020-Sep-08, 04:03

I’m not able to view the mdat file at the moment but - is the loss of mids the same for both speakers? I would expect it to be worse in one than the other. My guess is it is a phase cancellation from the front wall reflection (probably from the speaker furthest from the front wall). If the bass is better in this set up that is good news. How high is the problem with the mids? If it is high enough you should be able to treat it fairly easily with some insulation on the wall behind the speaker.



civvie
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Treatment for (slightly) odd shaped mix room

#33

Postby civvie » Tue, 2020-Sep-08, 14:21

Wheresthedug wrote:Source of the post My guess is it is a phase cancellation from the front wall reflection (probably from the speaker furthest from the front wall).


Ahha!! I think you are on to it here.
Below are a bunch of screenshots until you can dip into the mdat

'Sym' is original position and 'Corner' is the corner position with the mid dip.
As you can see the dip is between 2-5k

'Sym' position:
Sym Baseline.jpg


'Corner' position:
Corner Baseline all.jpg


Both positions Left channel
Left.jpg

Both positions Right channel
Right.jpg

Both positions L+R
L + R.jpg


And here are some pics of the phase data, I don't know how to read this but it looks to me like theres a lot going on around the problem region on the Corner L+R graph.

First the phase of the 'Sym' position
Sym phase L.jpg

Sym phase R.jpg

Sym phase L+R.jpg


Now the 'Corner' position
Corner phase L.jpg

Corner phase R.jpg

Corner phase L+R.jpg


I'll try testing again in the Corner position with my 100mm panels behind the speakers.
Any other tests you would recommend?



civvie
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Treatment for (slightly) odd shaped mix room

#34

Postby civvie » Wed, 2020-Sep-09, 16:17

Hi all,

I think the phase cancellation was from my second monitor, which is normally behind the speakers, but with the speakers in the corners it was between the speakers and the mic, to make things worse it was angled off to the side in position that could reflect sound better. I've taken it away now and the phase issue is gone.
However I still prefer the mids and the imaging with the speakers more forward away from the wall, I found a spot today that sounds best to me, so I am now thinking about flush mounting the speakers in this position. This is the mdat from today of this listening position:
Listening pos 2.mdat
(9.03 MiB) Downloaded 852 times
Listening pos 2.mdat
(9.03 MiB) Downloaded 852 times


The method I would like to use is one proposed by Thomas Barefoot on the John Sayers forum back on 2003: https://www.johnlsayers.com/phpBB2/view ... f=12&t=718
With this method I could probably use my existing speaker stands with a few modifications and then build the free standing baffle in front of them. I would leave a gap in the bottom like in John Sayers design and put a lot of bass trapping in the large cavity behind.

Johns design with gap at bottom for bass trapping:
speakers_1.jpg


I've also taken some inspiration from this thread: viewtopic.php?f=14&t=788 Though my baffle can be permanently installed.

By combining these designs I would have one large space approximately two feet deep behind the baffle which would be dedicated to bass trapping. Possibly with a combination of superchunks and hangers and what ever else is suggested!

In addition to this I plan on putting superchunks along the top left and right wall-ceiling corners down the length of the room. And I'll remove one of the carpets to expose the wood parquet floor to stop things getting too dead.

Also I will hard back my large cloud to get more of a RFZ effect in the listening position.

Here's a better pic of my space so you can see what's there and imagine what I mean.
20200909_185248.jpg



Would love to know all your thoughts on this plan?



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ericwisgikl
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Treatment for (slightly) odd shaped mix room

#35

Postby ericwisgikl » Wed, 2020-Sep-09, 22:42

Hi civvie,

Your plan seems to be very good.

Did it end sounding better being symmetric between side walls?

From .mdat files, it looks better, but you being there, listening, have the final word. As speakers at corners, beside midrange dips, seems to be better for low end, but it's good if you prefer the current position, since you had the chance to listen boths.

Also, if you are going to make the baffle in order to flush mount speakers, your current position sure is great.

I'm downloading last measurements and keep in touch.

Best regards,

Eric



civvie
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Treatment for (slightly) odd shaped mix room

#36

Postby civvie » Thu, 2020-Sep-10, 13:39

ericwisgikl wrote:Source of the post Did it end sounding better being symmetric between side walls?


Yes I think so! Hard to tell by ear when there's a 15 minute break to move speakers around between A and B. It's definitely not worse and I think the REW data looks better. Also, there's a psychological comfort in being in the acoustic centre of the space ;)

Here's a sketch of where my flush mount baffle would go in the room if I keep the current position
Studio flush mount1.jpg
Studio flush mount1.jpg (47.64 KiB) Viewed 28234 times
Studio flush mount1.jpg
Studio flush mount1.jpg (47.64 KiB) Viewed 28234 times


I'm going to do a little more testing and experimenting before I lock in the position.

What would you suggest for bass trapping in the cavity? I was thinking floor to ceiling superchunks and then hangers in the open space. Also basic insulation panels on the flat parts of the walls and backside of the baffle so there's no hard surfaces.



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Wheresthedug
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Treatment for (slightly) odd shaped mix room

#37

Postby Wheresthedug » Thu, 2020-Sep-10, 18:17

civvie wrote:Source of the post What would you suggest for bass trapping in the cavity?


More. Just more. Like, “this insulation goes to 11” :lol:

I could be wrong but my understanding is that, in your case you can’t go wrong with adding as much insulation as you can manage/afford. As it will be behind the rigid screens you should get the benefit in the bass end without sucking out high frequencies.



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ericwisgikl
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Treatment for (slightly) odd shaped mix room

#38

Postby ericwisgikl » Thu, 2020-Sep-10, 18:28

Wheresthedug wrote:Source of the post in your case you can’t go wrong with adding as much insulation as you can manage/afford. As it will be behind the rigid screens you should get the benefit in the bass end without sucking out high frequencies.

I agree. Just be sure to let air flow through a path in order to avoid monitors run under overhitting.



civvie
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Treatment for (slightly) odd shaped mix room

#39

Postby civvie » Sun, 2020-Sep-13, 09:31

Wheresthedug wrote:Source of the post More. Just more. Like, “this insulation goes to 11”


:lol: Got it! I plan on superchunks floor to ceilng in front corners with a 90cm width (90x60x60), and hangers, but I still can't find what materials to make the hangers from in the UK. I can't find a supplier of Homasote or anything similar so far, any suggestions?

ericwisgikl wrote:Source of the post Just be sure to let air flow through a path in order to avoid monitors run under overhitting.


Definitely, a major concern with my new Barefoot babies. I'll make sure there is plenty of air flow around them.


I'm doing some more very careful tests to find the perfect monitoring position before I lock it in by building the flush mount wall.
I know that normally you would be looking for a position where the bass is good and then work around that, but because I plan on flush mounting and that will (hopefully!) dramatically improve the bass, I'm making my decision more based on the mids and imaging. Does this logic make sense ?

I found a position that sounds great to my ears, this is what the positioning looks like:
P1.jpg
P1.jpg (27.25 KiB) Viewed 28171 times
P1.jpg
P1.jpg (27.25 KiB) Viewed 28171 times

Please note that the 88 and 77cm lines are in the wrong spot, that is the distance from the wall to the FRONT inner corners, not the back as the image suggests.

And here's the freq response:
P1 9.5k dip.jpg

As you can see, from 750 to 7k the mids are in a 5db range which is probably why it sounds good to me as that range is so crucial for mixing.
But the REW data shows a worrying dip around 9.5k that seems to be a phase null between L + R as it does not appear on the individual L and R sweeps.


Here is an mdat for that position plus -20 and +20cms from the listening position.
P1 walking test.mdat
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P1 walking test.mdat
(27.08 MiB) Downloaded 621 times


How would I best determine what is causing that 9.5k dip?
Is there anything else I should be concerned with with this position?

I am going to build the superchunks and hangers and also hardback my cloud before the flush-mount wall goes in so more testing and experimenting will happen before it's all locked in.



civvie
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Treatment for (slightly) odd shaped mix room

#40

Postby civvie » Sun, 2020-Sep-13, 10:56

Regarding material for hangers, these are the specs:

Homasote Pinnacle
Density: 416-448 kg/m³
Thickness: 13mm
Size: 2440mm x 1220mm
Weight: 14 kg/panel

I found this which is a very close match

Sundeala K board
Density: 500 kg/m³
Thickness: 9 mm
Size: 2400 x 1200 mm
Weight: 13.54 kg/panel
https://sheetmaterialswholesale.co.uk/sundeala-pinboard-9-x-1220-x-2440mm/

Only issue is that it's £55 a panel :(

EDIT:
According to this research paper "the core is nominally a 19 mm chipboard panel, but
somewhat thinner plywood is also sometimes used"
https://www.researchgate.net/publication/229076726_Sound_field_characterisation_and_absorption_measurement_of_wideband_absorbers

Well if that works it's a hell of a lot cheaper!

I'm thinking OSB could be a good affordable option

OSB
Density: 620/640 kg/m³
Thickness: 11mm
Size: 2440 x 1220
Weight: 7.30 kg



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Wheresthedug
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Treatment for (slightly) odd shaped mix room

#41

Postby Wheresthedug » Tue, 2020-Sep-15, 05:11

I can’t remember just now but there are designs for these either on here on on the old John Sayers site. I think fixing some Rockwool to a piece of ply was the method used but I could be wrong.



civvie
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Treatment for (slightly) odd shaped mix room

#42

Postby civvie » Tue, 2020-Sep-15, 13:08

Hi all,

First things first - I've solved the phase 9.5k dip issue! - And it's been a big lesson in using REW and being PRECISE with MIC PLACEMENT!

I'll just illustrate with a few screenshots:

Mic Centred.jpg

1 inch off-centre.jpg

1 inch off centre.jpg


That's a 10+db dip and the only difference between those two measurements is a 1 INCH mic movement.
Get your mic exactly centre guys :!:
I will note that I could not hear this dip, it's more a phenomenon of different phase points hitting a single mic capsule, a reminder that mics are not ears!

OK, so I have been reading more and more about soffits/flush-mount baffles and the theory around it and I'm a bit confused as to what I should do between my baffles. As they are close together they can either meet or I can leave a gap. I'm concerned that if they meet together then the sound might diffract at the centre angle and shoot straight out at the listening position. On the other hand, if I make a gap then I'm breaking the "infinite baffle" and leaving an edge for diffraction. From what I've seen, having a gap with absorption in it is a method many use with more widely spaced speakers, but will it work with closely spaced speakers like this? The Third option is to have a straight hard bit of wall but I don't know what that would do either so perhaps too unpredictable to consider.


Baffles meeting:
Flush1.jpg
Flush1.jpg (43.64 KiB) Viewed 28134 times
Flush1.jpg
Flush1.jpg (43.64 KiB) Viewed 28134 times

Gap with absorption between:
Flush2.jpg
Flush2.jpg (45.6 KiB) Viewed 28134 times
Flush2.jpg
Flush2.jpg (45.6 KiB) Viewed 28134 times

Straight hard panel:
Flush3.jpg
Flush3.jpg (43.25 KiB) Viewed 28134 times
Flush3.jpg
Flush3.jpg (43.25 KiB) Viewed 28134 times


Thoughts and advice on this?

Wheresthedug wrote:Source of the post I think fixing some Rockwool to a piece of ply was the method used but I could be wrong.


I've seen that done in forum posts too. I'm getting the impression that the core must be pretty light and not too dense, I would have thought that something non-resonant (like Homasote) would be key, but as the study shows, ply is often used and works fine. Mysterious things these hangers!



civvie
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Treatment for (slightly) odd shaped mix room

#43

Postby civvie » Mon, 2020-Sep-21, 12:11

Hi all,

Here's a rough placement for the hangers. How's this look?

Hangers.jpg


I've noticed most designs have the hangers perpendicular to the speakers like this. I assume this is for a reason. From what I've read it seems important that they are at an angle to the boundary walls, but I'm not sure if having their edges face the speakers is also important.
If not, here's another design where I can get fewer but much larger hangers.

Hangers 2.jpg


Thoughts on all this?

Also if anyone has an opinion on me leaving an absorbant gap in the middle between the speaker baffles let me know!



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ericwisgikl
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Treatment for (slightly) odd shaped mix room

#44

Postby ericwisgikl » Wed, 2020-Sep-23, 23:52

Hi civvie,

I've been following your last posts, but I don't have the right answer for neither both questions: gap and hangers orientation.

So, I'm looking forward to see if anybody could give a good suggestion.

Best regards,

Eric



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endorka
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Treatment for (slightly) odd shaped mix room

#45

Postby endorka » Sat, 2020-Sep-26, 20:42

civvie wrote:Source of the postif anyone has an opinion on me leaving an absorbant gap in the middle between the speaker baffles let me know!


I honestly have no idea! In your shoes my first thought would would be to try it without & make measurements. Then install a temporary centre section, then make more measurements. Then analyse them to determine: "What is best?"

Cheers!
Jennifer




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