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PostPosted: Fri Apr 10, 2020 7:52 am 
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Waka wrote:
Hi guys, sorry for not being around of late!

I've got some more pictures to share. I've done more work since these pictures were taken, but I've not taken more recent photos yet. The photo shows the 25mm first layer on the baffles. I've already added a 12mm hardwood ply layer on top of this. I'm still considering my finish options for this, so any ideas would be great.

Attachment:
20200113_145152.jpg


Attachment:
20200302_112339.jpg


Attachment:
20200302_114354.jpg


Seeing Ron's aaawesome birch veneer finished slot resonator makes me cry when I look at mine now :lol: But it's not something I can add to my resonators now as they're already fitted. I'm thinking of either sanding and oiling them, or hiding them behind a cloth finish (after testing the acoustic effects). My speaker baffles themselves could be veneered, but I haven't done it before (so I'm scared!), or the other option is to paint them satin/matte black, which will look cool with the speakers in them (and a lot cheaper).

So here's the most recent pics I've got. I'll add some more when my baffle wings are ready. It's hard getting building materials in the lock-down though sadly.

Dan


Looking good Dan, I think you should veneer the ply, it's actually really quite easy and very satisfying. It's difficult to get wrong in my opinion because it's basically like applying sticky back plastic...but with an iron! If you do mess it up then it's easy to just reheat and slide it into the right position, or simply remove it and try again. It's also easy to cut the edges completely flush after it's been applied, and you can always sand the edges slightly to help it blend. Try it! I think you'll like it.

If not then I would cover the entire soffit including the resonators with a fabric frame.

Paul

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PostPosted: Fri Apr 10, 2020 8:08 am 
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Paulus87 wrote:
Looking good Dan, I think you should veneer the ply, it's actually really quite easy and very satisfying. It's difficult to get wrong in my opinion because it's basically like applying sticky back plastic...but with an iron! If you do mess it up then it's easy to just reheat and slide it into the right position, or simply remove it and try again.


I am very interested in veneering. It looks great when it's done well. I'm leaving the finishing for now though. It's slightly infuriating having so much time in lockdown and no materials!

Dan

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PostPosted: Sat Apr 11, 2020 2:52 am 
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Was finishing off some fascia cladding around the studio today and I nipped in and took a more recent picture of the speaker baffles.

I actually like the grain on the ply wood, so maybe just light sanding and oiling might finish it nicely.

Attachment:
20200410_162907_copy_1200x675.jpg


Dan


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PostPosted: Sun Apr 12, 2020 10:44 am 
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Wow! That's looking great!

Greg

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PostPosted: Mon Apr 13, 2020 3:18 pm 
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Great stuff man I love to see progress pics!


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PostPosted: Tue May 05, 2020 4:42 am 
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Hi guys, I can get back to studio progress next week. I've got a delivery with some more materials booked for Monday. Deliveries are still difficult to come by, but the Plywood I need to finish my baffles and wings are in stock now, I also got enough 100mm insulation batts off ebay to fill the rest of the wings and the first layer in the ceiling.

So I'll hopefully have some more pictures for you incoming next week,

Dan

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PostPosted: Wed May 06, 2020 12:57 am 
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Can't wait to see your progress!

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PostPosted: Thu Jul 23, 2020 8:31 am 
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Hi all I've made some progress amazingly! :lol:

What has changed:
I've finished the flush mounted speakers and baffle wings (I haven't applied any finishes etc).

I've filled most of the ceiling, added my ceiling reflectors (instead of a cloud). I've leaving a section in the rear third center of the ceiling without any treatment for now, as I will decide whether to use targeted membrane treatments etc here or BAD panels/absorption as I take more measurements.

I decided to move the mix position forward roughly 60mm ish (2.5 inches), as this gave a better ray trace. I'm about 530mm forward from the intersection point of the speakers, which is quite far, but I think the ray tracing improvements justifies the relocation.

I haven't done any rear wall or side wall treatments at all yet, as I want to see how every stage of treatment affects the result.

I've taken some new REW measurements. Look can look back at my initial measurements without any treatments for comparison: viewtopic.php?p=151987#p151987

I tried to capture charts matching the scale as those I did before for reference, but sometimes it wasn't possible!

Here's the NEW mdat file: https://1drv.ms/u/s!AlQDzTq2dTgS5jK5E-P ... j?e=Rn62em
And the OLD one for reference: https://1drv.ms/u/s!AlQDzTq2dTgSzxrg1my ... 3?e=JplF0g

New charts! 8)

Low-end Frequency Response:
Attachment:
26Hz - 340Hz SPL.png


This is lovely, the smoothness compared to the original is awesome. The huge peaks and troughs from 60Hz to 100Hz in the original measurements have been smoothed out beautifully. The 73Hz null has been reduced by 20dB! The 45dB variation has been reduced to a 23dB variation.

Waterfall: (In the original scale for comparison only)
Attachment:
24Hz - 2050Hz Waterfall 2000ms.png


The waterfall shows clearly how bad the original reverb was. I had to set the scale to 2 seconds, i nicknamed it the echo chamber, at the time!
We can see a drastic reduction on decay rate here! Now with only a few modal resonances still ringing out.

Let's look closer at a more suitable chart scale now:
Attachment:
10Hz - 2050Hz Waterfall 500ms new.png


Th first thing I noticed is how much smoother the decay is sub 100Hz, those nulls are far less pronounced!
The second thing I notice is the extremely strange 13Hz resonance. Its outside of hearing range, but still confusing :shock: :?: (If anyone has any ideas on this, please let me know! :roll:)

Spectogram: (In the original scale for comparison only)
Attachment:
LR 43Hz - 571Hz Spectogram -200ms to 900ms.png


It's clear that those giant spikes have disappeared!

Let's see it centralized and we might as well do up to 5kHz:
Attachment:
LR 20Hz - 5000Hz Spectogram -500ms to 500ms new.png


This shows a null is still around 136Hz, but the "hot" spots are reducing, and everything seems to be smoothing out nicely.

Decay rate: I couldn't give you a comparative chart here, because the decay rate has dropped so much that it was off the bottom of the chart!
Attachment:
LR 50Hz - 10kHz Decay Rate T30 0ms to 900ms.png


I'm happy to see the decay rate significantly reduced and really happy to see the low end! It seems those two really deep slat resonators in the lower front corners under the speakers have done their job well! More than I ever expected actually :shock: The 63Hz peak looks like modal resonance as I have two axial modes around this frequency. Theory puts them at 65.8Hz (2, 0, 0) and 68.3Hz (0, 0, 1). A tuned device in the ceiling further back (as you suggested Paul! :wink:) seems to be in order, to target the ceiling>floor mode! I'll revisit it after the I've added the rear wall treatments.

The higher decay rate at 250Hz and above is exactly what I want to see. It means my ceiling treatments haven't sucked too much mid and high frequency energy out of the room. Which leaves me a good amount of leeway with my rear and side wall treatments! 8)

After all that good news I'm sad to see my last chart though :cry:

Seaparated L and R frequency response:
Attachment:
L-R Compare 46Hz - 611Hz SPL.png


Some how in my construction of my flush mounting speakers I have managed to throw off the L to R bass response! My L speaker bass levels are 10dB higher than my R speaker :?
I'm wondering whether this is something I can resolve by pushing the speaker forward or back within the module, so it protrudes less/more and balance the issue.
It's very strange, because I calibrated REW with my handheld SPL metre just before running the tests.

I'll have to experiment.

If you guys have any suggestions please let me know!

I'll add some construction pictures for you in the next post!

Dan


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Last edited by Waka on Thu Jul 23, 2020 9:56 am, edited 3 times in total.

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PostPosted: Thu Jul 23, 2020 9:13 am 
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Front wall, slat resonators and speaker baffles:
Attachment:
20200722_175507_copy_1200x675.jpg


Ceiling absorption:
Attachment:
20200711_141408_copy_1200x675.jpg


Ceiling reflectors (instead of a cloud)
Attachment:
20200722_155615_copy_1200x675.jpg


Ceiling reflector up close. 13 degree angle. 25mm mdf for the first row and 18mm mdf for the second row in to the room.
Attachment:
20200722_154530_copy_1200x675.jpg


REW Measurement setup:
Attachment:
20200722_233833_copy_1200x675.jpg


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PostPosted: Thu Jul 23, 2020 7:48 pm 
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Wow, it's looking really good Dan, really coming on well.

The difference between the speakers is puzzling, I hope you can get to the bottom of it.

Thanks for sharing!

Paul

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PostPosted: Sat Jul 25, 2020 5:39 am 
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This evening I got to work trying to balance the speakers.

Firstly I re-calibrated REW and my speaker levels etc. I found that I had misread an instruction and had my microphone input level too high. This meant charts were displaying about 7dB higher than the correct values.

I verified that the microphone position (that hadn't been moved since I took the previous measurements) was indeed central in the room and at the location and height etc. I measured from the tip of the mic to each speaker, and they were the same to within a few mm.

I then retook my speaker measurements with the new calibration.

Which showed similar results to before:
Attachment:
Recalib. L-R Compare 46Hz - 611Hz SPL.png


So now I decided to reseat the speakers, The left one was overhanging the face of the baffle slightly, so I pushed it in flush with the face, retook some measurements, and inset it slightly more. I reseated the right speaker too and found have a lot more balanced speakers now:
Attachment:
After speaker reseating L-R Compare 46Hz - 611Hz SPL.png



There is still some variation around the 125Hz - 130Hz mark but I'm not as worried about this as a 10dB difference in the whole low end!
I think this is where tolerances in construction comes in to play I think. And whether I managed to get the room to be as square and true as it could have been.

Now it's on to the rear wall treatments!

I'll upload my most up to date treatment plans from Sketchup when I get a chance.

To whet your appetite: For variable acoustics, I plan to have sliding "doors".
There will be 2 Leanfuser modules on each "door". In "control mode", the doors will slide together to meet against a central Leanfuser module, making a 5 module, height modulated Leanfuser in the center of the rear wall. The left and right sides of the diffuser will expose the 500mm of absorption/hangers behind.

To increase MF and HF decay rate the "doors" will slide out towards the side walls covering the exposed absorption; behind the diffusers will be angled 1D BAD panels. This will provide an almost entirely diffusing/scattering rear wall for high frequencies and some mid frequencies, in "Live mode", and hopefully drastically increase the decay rate at these frequencies, without creating a boomy experience. It should be open and airy sounding, great for acoustic guitars etc!

Watch this space for an updated design!


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PostPosted: Thu Aug 06, 2020 5:23 am 
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Hi all. Updates for you!

I've finished the first stage of the rear wall treatments!

Attachment:
Rear wall hangers.jpg


(You may notice that one hanger has netting over it, this is because whilst gluing the insulation I accidentally knelt on a board and snapped it in half! The netting + glued insulation is holding it together fine.)

Details!

Rear corners have super-chunks: 600mm x 455mm: 100mm Knauf Dritherm 37 Cavity Slab. It's one of the lowest density insulation batts I could find that doesn't collapse under it's own weight. It's very good value for mineral wool at £22 a bag from Wickes. It's the same stuff that I used in my ceiling. I added some supports every 6-8 slabs or so made from off cuts of batten etc.
It's all getting hidden behind a finish fabric/diffuser so I didn't make it pretty.

Attachment:
Super chunk in progress.jpg

Attachment:
Super chunk complete.jpg


8 x floor to ceiling acoustic hangers 2.2m x 455mm: I just cut the sheets into 3, to avoid waste. So the cores are 405mm wide. The insualtion comes 455mm wide, so I used the full width of insulation and overhung it a little on each edge.

Attachment:
Acoustic hanger detail.jpg


- Core: 12mm (Ivory) Insulation Board (Aka. Softboard). this is a low-density fibre-board. It's hard to find but much cheaper than Sundeala board/homasote in the UK. My local independent sawmill (Andrews Timber in Spalding, ask for David.) got hold of it from their supplier 2.44m x 1.22m is £15ish. I needed 3 sheets for my hangers.

Attachment:
Hanger core 12mm Insulation Board.jpg


- Insulation: Also 100mm Knauf Dritherm 37 Cavity Slab.

- Fixing: I used spray contact adhesive to fix the insulation to the core. This worked very well, but you have to spray both the core and the insulation and to get a good fix, so uses quite a lot of the stuff! One 500ml can does roughly 2 hangers. But after it's fixed it easily holds the insulation in place. In fact you can't move it once pressed into position without tearing up the insulation!

Attachment:
Contact adhesive spray acoustic hanger.jpg


- Hanging the hangers: I added timbers to the framing angled to the correct amount, this way I didn't need to bother checking the hanger angles. I just drilled though the wood and the hanger core and used cable ties to hang them.

Attachment:
Hanger supports.jpg


I'm planning on taking some new REW measurements over the weekend hopefully, so stay tuned!

Dan


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PostPosted: Thu Aug 06, 2020 8:39 pm 
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Waka wrote:
Hi all. Updates for you!

I've finished the first stage of the rear wall treatments!

Attachment:
Rear wall hangers.jpg


(You may notice that one hanger has netting over it, this is because whilst gluing the insulation I accidentally knelt on a board and snapped it in half! The netting + glued insulation is holding it together fine.)

Details!

Rear corners have super-chunks: 600mm x 455mm: 100mm Knauf Dritherm 37 Cavity Slab. It's one of the lowest density insulation batts I could find that doesn't collapse under it's own weight. It's very good value for mineral wool at £22 a bag from Wickes. It's the same stuff that I used in my ceiling. I added some supports every 6-8 slabs or so made from off cuts of batten etc.
It's all getting hidden behind a finish fabric/diffuser so I didn't make it pretty.

Attachment:
Super chunk in progress.jpg

Attachment:
Super chunk complete.jpg


8 x floor to ceiling acoustic hangers 2.2m x 455mm: I just cut the sheets into 3, to avoid waste. So the cores are 405mm wide. The insualtion comes 455mm wide, so I used the full width of insulation and overhung it a little on each edge.

Attachment:
Acoustic hanger detail.jpg


- Core: 12mm (Ivory) Insulation Board (Aka. Softboard). this is a low-density fibre-board. It's hard to find but much cheaper than Sundeala board/homasote in the UK. My local independent sawmill (Andrews Timber in Spalding, ask for David.) got hold of it from their supplier 2.44m x 1.22m is £15ish. I needed 3 sheets for my hangers.

Attachment:
Hanger core 12mm Insulation Board.jpg


- Insulation: Also 100mm Knauf Dritherm 37 Cavity Slab.

- Fixing: I used spray contact adhesive to fix the insulation to the core. This worked very well, but you have to spray both the core and the insulation and to get a good fix, so uses quite a lot of the stuff! One 500ml can does roughly 2 hangers. But after it's fixed it easily holds the insulation in place. In fact you can't move it once pressed into position without tearing up the insulation!

Attachment:
Contact adhesive spray acoustic hanger.jpg


- Hanging the hangers: I added timbers to the framing angled to the correct amount, this way I didn't need to bother checking the hanger angles. I just drilled though the wood and the hanger core and used cable ties to hang them.

Attachment:
Hanger supports.jpg


I'm planning on taking some new REW measurements over the weekend hopefully, so stay tuned!

Dan


Hey Dan,

It's looking great, well done. I also used a similar core for my ceiling hangers, and can relate to them breaking - my first attempt was to try and hang a 8' x 2' hanger by myself up a ladder - the board snapped under its own weight! I don't know if Homasote is stronger, I don't think it would be since it's made of the same stuff as far as I know. I ended up cutting them all in half and hanging them like that - no breaking but I did find that they bow very quickly without bracing. I don't think you'll have that problem since yours are hanging vertically, straight down whereas mine are at various angles horizontally, but even if yours do bow I don't think it will matter.

Speaking of bowing - is it just me or is the top member bowing down in the middle? Surely the hangers are not heavy enough to cause it to bow?

Paul

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PostPosted: Thu Aug 06, 2020 8:49 pm 
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Paulus87 wrote:
It's looking great, well done. I also used a similar core for my ceiling hangers, and can relate to them breaking - my first attempt was to try and hang a 8' x 2' hanger by myself up a ladder - the board snapped under its own weight! I don't know if Homasote is stronger, I don't think it would be since it's made of the same stuff as far as I know. I ended up cutting them all in half and hanging them like that - no breaking but I did find that they bow very quickly without bracing. I don't think you'll have that problem since yours are hanging vertically, straight down whereas mine are at various angles horizontally, but even if yours do bow I don't think it will matter.


It's definitely delicate stuff! Yes, I would brace them too if hanging horizontally.

Paulus87 wrote:
Speaking of bowing - is it just me or is the top member bowing down in the middle? Surely the hangers are not heavy enough to cause it to bow?


I had the exact same thought, I had to measure it to make sure. The ceiling joist is slightly bowed, it's 2 mm lower in the middle and raises 3mm on the right hand side as you look at the rear wall.
The photo makes it appear much worse, In person it's not noticeable at all. The top member has two additional support braces attached that are screwed to the ceiling noggins near to the center, so it's not carrying the weight of the hangers alone, most is transferred to the ceiling joists.

The weight of the hangers is definitely not an issue. I could probably hold the weight of the 8 hangers myself! If you look closely at the shadow where the rounded edge of the 4 x 2 meets the ceiling plasterboard, you'll see the shadow is the same depth along the whole beam. It's not bowing away from it at all.

Dan

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PostPosted: Mon Aug 10, 2020 9:31 am 
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Hi all, updates are here!

REW measurements after rear wall hangers/superchunks:

Low-end Frequency Response:

Attachment:
After hangers 26Hz - 340Hz SPL.png


I'm extremely happy with frequency response below 150Hz. It's currently +/- 3.2dB with no smoothing! (Until the speaker response starts to roll off below about 33Hz), this reduces to 2dB with 1/3 smoothing.

Waterfall: (Over 500ms to compare with the last measurements)

Attachment:
After Hangers 10Hz - 2050Hz Waterfall 500ms.png


Now again but reduced to 300ms to see more clearly specific issues still existing:

Attachment:
After Hangers 10Hz - 2050Hz Waterfall 300ms.png


I good to see the peaks and troughs smoothing out.

Low frequency resonant issues have now been reduced almost entirely to the axial length mode at 30-33Hz (theoretically 32.85Hz) in the room, and less so it's first harmonic at 62-63Hz (theoretically 65.71Hz).

I can now turn my attention to the mid frequencies and observe the resonant issues here.
The resonant issues around 190-200Hz appear to be a combination of the 3 close together axial modes: 4th width, 6th length and 3rd height harmonics.

My theory as regards to why the first natural modes for width and height don't appear on the waterfall is the deep slat helmholtz resonators.

I designed them using John's newer method, with construction timber varying from 150mm deep to 200mm deep and with an air gap ranging from 50mm to 400mm and an air gap of 5mm. This was to gain absorption targeted at 40Hz to 150Hz.

The decay rate for the first width and height modes was significantly reduced even before the rear wall treatments were added. Then the rear wall treatments cleaned it up even more.

Well that's the theory I'm working with at the moment! :D

The lower level resonances at around 137-150Hz line up with the height mode's second harmonic (136.65Hz) and width mode's third harmonic (144.12Hz) and the resonance at 165Hz matches up with the 5th length mode (164.27Hz).

If we look up the spectrum we see the repeating pattern, as multiples of these figures:
284Hz is double our 140Hz cluster.
380Hz is double our 190Hz cluster.
The 475Hz one is double the 7th axial length mode.
567Hz is double the 284Hz one.

and so on...

Plan of action:

- For testing treating width and height modes I intend to place a stack of insulation slabs, in the center of the long walls on the floor. This should reduce the energy of the higher order modes significantly.

- This should highlight the strongest modes causing issues.

You may notice the huge null at around 650Hz. This is highlighted even more drastically in the frequency response graph:

Attachment:
After hangers 26Hz - 1000Hz SPL.png


This is almost certainly caused by SBIR. Annoyingly (as you will see later) it is not caused by a ceiling or floor bounce!
Which leads me to believe the front wall can be the only culprit. I was hoping my baffles, not extending completely to the front wall would give sufficient baffle extension to avoid the null, but apparently it is a fearsome beast!

A 650Hz null would be cause by the speaker being 135mm or so form the front wall, which is a similar distance that my baffles stop from the front wall.

I will test this by placing a slab of insulation across the front wall and seeing if the null is reduced.

If it is (as I theorise), then I will have to decide between keeping the slab there, or adding a reflective surface between the two baffles.

Spectogram:

Attachment:
After hangers LR 20Hz - 5000Hz Spectogram -500ms to 500ms new.png


The spectogram confirms the 650Hz null, as well as (I believe) modal reinforcement to the problem modes we saw in the waterfall.

Decay rate:

Attachment:
After hangers LR 50Hz - 10kHz Decay Rate T30 0ms to 900ms.png


The decay rate shows the mid and high frequencies coming down to meet the low-frequencies which is great. 250Hz has gone too low though. My rear wall diffusers etc, should increase the decay rate by reflecting some of this energy back into the room though.

I'm not going to focus on 250Hz, but revisit it after the rear wall diffuser.

Now I've completed the initial RFZ treatments Let's look at the ETC:

Attachment:
After Hangers ETC.png


We can see some reflections here above -20dBFS before 20ms. I have confirmed 2 and identified 1 more.

Confirmed:

3.78ms: Floor reflection
  • Confirmed by laying insualtion batts on the floor between mic and speakers

2.73ms: Ceiling reflection
  • This was surprising, as I had assumed the ceiling reflectors would be enough to prevent this. I isolated the problem area to the joist between bay 2 and 3 from the front wall, just before the first reflector row. Direct reflected sound on the face of the joist (only 70mm!) and probably some diffracted sound wrapping around the joist seems to be to blame.
  • I confirmed this by a series of measurements hanging insulation batts below this location.

Unconfirmed:

0.98ms: I strongly believe this to be the cuplrit with my 650Hz front wall SBIR problem.

The other few reflections near to 6ms are quite low level, and possibly some residual energy from my angled baffle extension "wings" being a bit too shallow an angle. I identified 40-50 degree off-axis waves could be directed towards the mix position by the baffle.

Depending on the outcome of the measurements I was going to decide whether to add a "fill-in" angle over where the "wing" meets the speaker baffle extension. I'll decide on this later on.

As you can see from the graph there are no high-level returning reflections after they reach the rear-wall hangers. This is great for removing destructive reflections, but I believe I can achieve an improved listening experience by adding a definite ITDG termination at around 20ms, where additional diffuse energy is allowed to return to the mix position to be fused into the direct signal. My plan for a rear wall diffuser, should help to address this.

Now that was a marathon to type, so I'll add additional photos another day. I have a few showing the various locations of the ceiling treatments I tried in isolating the ceiling reflection, and REW measurements to back up each picture.

Dan


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