*Treatment stage* Fen Cabin Studio - Build Diary. UK

[Waka]

Hi all. Started the cladding today now we have good weather.

It's really coming together nicely .

partial cladding.jpg

Dan

[Soundman2020]

Oh YEAH! Now we are talking! That place is starting to look like a proper building now.

Nice work, by they way. It's looking pretty good!


- Stuart -

[John Steel]

Congratulations Dan - your studio looks tremendous, top to bottom! Obviously the result of a lot of hard work and careful thought.

[Waka]

Hi guys,

Bit of an update for you!
Been doing some external work for the studio, scraping and laying hard standing for the house drive way and paths all around to the studio in the garden. Still got to pour the paths. Cladding is finished, just need to do the fascias and soffits. I've been held back by rain on my days off, this last month or so.
I've finished painting the doors and fitted the seals.

I tested the isolation today with the help of my mother-in-law. I made the mistake of testing during the day, when we have distant low frequency traffic from a busy road, so the baseline level outside was too high for accurate measurements (69-71dBC)

Subjectively, the isolation levels are phenomenal. I played at up to 103dBC inside the studio and you could just strain to barely hear the bass on the patio near the house (about 6m away), and absolutely nothing inside the house.

The measurements were taken using C weighting Slow response both inside and outside the studio. I played through a 2000W active PA (Alto TS312), placed in the lower rear corner on the floor to excite all of the room modes. Inside I measured with bass heavy rock music playing at 100-103dBC, outside the door it was measured around the same as ambient 69-72dBC.
I'm going to retake the measurements in the evening to see what I'm actually isolating in those troublesome low frequencies.

Here's me with 100.2dBC playing silently in the neighbourhood

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Anyone interested in the day time test can see the 45 second video from my onedrive:
https://1drv.ms/v/s!AlQDzTq2dTgSzwBav56 ... u?e=IdzII9

Dan

[Gregwor]

Looks awesome so far! I'd really like to see some SPL measurements where the ambient noise is lower and the volume inside your room is higher. Right now we are seeing ~30dB of isolation. Try to get up around 110dBC in your room. Either way, it has clearly turned out great and your hard work has paid off!

Greg

[Waka]

Hi Greg thanks for the encouragement!

I checked again at 10pm. Ambient had reduced to 57-57.5dBC.
This time I pushed it till it was fluctuating between 110-115dBC, (ridiculously loud for such a small space lol. Glad I had the hearing protection! The room felt like it was shaking.)

About a foot away from the door outside measured between 70-73dBC. Which is about 40dB isolation down to 45Hz (definately a lot of bass (open E) in that song, and the speaker is rated down to 45Hz). Which is pretty good through the door. Still not heard at all in the house.

I'm not entirely happy with my door seals yet though, I use double balloon seals on the sides/top and they seem to pinch at the hinge side, and prevent a really good seal.

I think magnetic seals would be the best improvement here. I think the drop seals could do with some adjusting.

Any ideas how to test whether it's the seals, and not just the resonance within the door cavity or mass preventing better isolation?

I also think gluing some insulation to the back of the inner door would be great for damping resonance. I'll run the door details through the MSM calc again to see if the theory considers 40dB at 45Hz about right for an empty cavity with this mass.

Dan

I've uploaded this video too for anyone interested, though due to reflections on the door windows it's difficult to see what's on the display. You can just about see at one point 72-73dBC displayed. I saw it was pretty stable at that level with they music playing:

https://1drv.ms/v/s!AlQDzTq2dTgSzwFbuVu ... B?e=wB5nWg

[Waka]

Running the door design through the MSM calculator shows that I'm probably close to what I would expect. There is a theoretical maximum isolation of 54dB at 45Hz, but this is very unlikely to be attainable, due to the undamped cavity putting the resonant frequency at 41.35Hz!! (almost slap bang on a bass guitar low E). I would expect good isolation starting 1.4 times above the resonant frequency. An insulated cavity has a resonant frequency of 29.63Hz, which would put me at good isolation above 40Hz (maybe near to that 54dB).

For my next test (hopefully tomorrow), I will lightly fill the cavity with low density loft insulation that I have left over. This in theory should greatly improve the isolation. If so I will work on some frames to hold insulation batts, and then glue them to the inside face of each door. Any suggestions of practical ways of building these would be useful.

I want to also see if I can test the door seals. I might try and cover the door edges with wood all around, to see if any improvement is made.

Although C weighting is most useful for testing low frequency isolation, it's not actually that much of an indicator of the perception of the isolation effectiveness. I might do a comparison on A weighting, as that resembles the perception of loudness more accurately. Looking at the ISO 226:2003 equal loudness curve, shows that the 72dBC immediately outside the room would be equal in loudness to between 40dB and 50dB at higher frequencies.

I imagine a 20dB or so higher transmission loss using A weighting (so 60dB is my guess). I'm taking bets!

Dan

[Waka]

Ok guys, so I performed some more tests this evening.

I preformed the test using A-weighting instead, for perceived isolation. 100-102dBA was the furthest I could push it (switching to dBC showed this at 113-115dBC ). Outside the room I measured, 50-52dBA. Giving me a reduction of 50dBA.

I then added fluffy insulation to most of the cavity (except the window) and retried the test.

The measurements were exactly the same, surprisingly. Leading me to believe that damping the resonance isn't what is needed to improve this STL further, first of all.

I physically pushed against the seals, but wasn't able to try and improve the seals in any way.

I took the measurements on dBC again with the insulation and they too were exactly the same as yesterday's undamped cavity (Inside 113-115dBC, outside 73-75dBC), at 40dBC STL.

A way to estimate the equivalent STC of the wall/doors, is to deduct dBA outside from dBC inside, this will be within 3dB or so of full STC testing. The estimated STC of my wall/doors is therefore around STC63, but with 40dB STL at low frequencies.

If I needed higher isolation, I might have attempted to improve it by replacing one bubble seal with magnetic seals, but as it stands, the reduction is amazing as it is. I can't imagine ever playing anything nearly as loud as I did in my tests. Even a drum kit puts out most of its loudness at the low mid frequencies. Bass drums etc max out around 105dB, it's those snare shots that hit the crazy dB and they are all in the mid ranges.

I think I'm going to focus now on measurements so I can start my acoustic treatments!

I've emptied most of the room, just a few things I need to store in there. So I'll move them out before I take measurements, then put them back in after.

Dan

[Gregwor]

Great news! I'm so stoked for your treatment stage!

Greg

[Waka]

Hi guys,

I'm just waiting for my measurement mic to arrive from Germany, as I got a good deal on Thomann for a Sonarworks XREF 20. I originally purchased a Behringer EC8000 and returned it as they don't come with individual calibration files and there is a lot of variation between mics. Sonarworks provides an individual calibration file for each mic that can be downloaded by entering the unique serial number on their website.

Should be arriving middle of next week I imagine.

I've been busy designing my side wall treatments and working on a minimal desk design in sketchup. I'll be updating the design thread when I have some more to show.

The side wall treatments are likely going to be combinations of low frequency membrane absorbers and mid frequency slat absorbers. I'll be making them as modules that will be screwed into position and tested for effectiveness, and moved/altered as per REW data.
They will have angled fronts to prevent flutter echo but retain high frequency response in the room.

My plan of action once the equipment has arrived:

Rest my speakers (Fluid FX8) on concrete blocks in the place where they will be when the speaker baffles ("soffits") are built.

Accurately measure and mark out the mix position and the measurement microphone position in 3 dimensions.

I'm thinking of hanging a plumb line from the ceiling at the exact height of the tip of the microphone to measure the vertical position.

Then I'll setup up/calibrate REW ready for my empty room measurements.

I'll keep you guys in the loop.

Dan

[Waka]

Hi all,

I come bearing gifts in the form of pure, unadulterated empty room REW data!
https://1drv.ms/u/s!AlQDzTq2dTgSzxrg1my ... 3?e=7hNJfM

I emptied the room.
Set up my PC.
Put my speakers on temporary "speaker stands" (aka stacked bricks) in the correct positions and orientations.
Accurately measured and setup my measurement microphone and marked the position with a plumb line.
And calibrated REW.

This took a huge amount of time! Don't underestimate this people. A lot more hours than I care to admit setting this up .

And I took my initial empty room measurements! I like to refer to the room in it's untreated state as "The Echo Chamber" .

I didn't build inside out walls and my inside out ceiling is currently unfilled with insulation, as I wanted truly blank canvas measurements to begin with , so it's got a crazy long decay rate. Although quite smooth across the spectrum which is a good sign.

I'll post the waterfalls, T30 and SPL charts a little later after my dinner.

Woop woop!

Dan

[Waka]

Here's the initial setup:
I intend to build a custom mixing desk on wheels that I can push in between my speaker baffles, when not mixing. That will be useful when teaching guitar and recording, then I can just wheel it out (with some markers for the correct locations) for critical listening.

So at the moment I have no desk in.

empty room.jpg

Here's those charts I promised:

Frequency Response:

SPL Low End LR.png

Looking at the low end to begin with:

***** Edit *****
On checking the calculations again, the null at 72-74Hz is not likely to do with side wall reflections as the distance is too short.
Expected first reflections nulls:
Side walls: 165Hz
Floor: 145Hz
Ceiling: 125Hz

Looking at the theoretical modal response in the room, puts a strong ceiling - floor axial mode at 67.25Hz. Although a little off, this can be explained by my inside out ceiling. The lowest points of my ceiling (The ceiling joists) would have it's axial mode around 73Hz.

The peak at 65Hz seems to be caused by the 2nd length mode.

If these modes are not sufficiently treated by the broadband absorption in the room, I will consider membrane and Helmholtz traps tuned to these frequencies.
**************

Lots of the usual comb filtering. But nothing too major I can see at the moment. Although with so many reflections there is too much noise to analyse much at this point.

Waterfall:

Waterfall LR.png

Because the decay rate is so long, I've extended the waterfall time range to 2 seconds.

I see strong modes at 65-67Hz (two axials close together) and 95-97Hz (a few tangential and axials bunched together), causing major ringing. Again we see the huge null in the mid 70Hz region.
You can see that due to the lack of a sub, there's not much happening at all below the 60Hz region, which lines up with the speaker specs. I plan to add a sub (or two) eventually.

Spectogram:

Spectogram LR.jpg

Does anyone think this looks a lot like a comb??

Decay Rate:

Decay Rate.jpg

Large dip at 125Hzish.
Two theories:
1)
Ceiling bounce.

2)
Plasterboard absorption. Plasterboard on wooden studs has a very high absorption coefficient at 125Hz (approaching 0.3!). So because 5 surfaces in my room are plasterboard on wooden studs, this has a massive effect at this frequency, with each reflection absorbing some energy.

Of course I need to bring the decay rate of the whole spectrum right down, for my multipurpose room. So expect lots of fibreglass and added variable acoustic devices.

Here you can see the frequency response of the two speakers separately:

SPL LR Separate.jpg

There's not too much variation there, so I'm pretty happy.

Initial treatment plan:

• Flush (soffit) mount the speakers.
• Add "soffit wings" at first reflection points. - Take new REW measurements.
• Fill ceiling with 1 layer of 100mm fibreglass and 1 layer of 50mm fibreglass. - Take new REW measurements.
• Add 500mm depth of treatments to rear wall. Mainly consisting of acoustic hangers. - Take new REW measurements.

[Gregwor]

Man, I'm so excited for what's to come!

Greg

[Waka]

Hi guys,

I started on my speaker baffles. I decided to utilise the space below the speaker shelf as a corner deep slot/slat resonator. I'm using a design similar to John's newer rear corner design.
I don't expect to have problems with desk reflections as I'm building a custom minimal design that has an open back and sides.

Here's what I've done so far:

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[Waka]

I have some progress for you. I went to a local fabric shop and they had a good deal on thick breathable black fabric. The roll was 1.8m and each metre was £5; good deal! So I bought 3m worth so I have some spare. I might use it underneath my finish fabric on the ceiling to black it out some more if necessary.

I've almost finished building both corner slot resonators now. I've just got to seal around all the edges. I'm leaving a panel in the soffit wings unsealed at first until I've run some more REW tests, when the speakers are mounted and baffle fitted. That way if the Q is too high, I can unscrew the panel and chuck some more light insulation into the cavity.

I stapled the fabric to the back of the resonator frame and placed a layer of low density loft roll insulation (5000 rayl estimated) and used some of the insulation netting I had left over to hold it against the back of the slots, where it should be the most effective. I placed no other insulation in the cavity; but as I said, the side panel can be removed and extra insualtion added after measurements are taken.

After sealing and fitting the side panels, I'm starting on the framing for the speaker shelf/box.

As you can see there's no ventilation directly below the speaker shelf, due to the slot resonator being sealed. So I am going to use some of my 150mm diameter flexible ducting, which I will attach to the bottom of the speaker shelf and lay over the slot resonator lid and down into the soffit wing, where it will be attach near the floor behind some fabric. A second length of duct will extend form the top of the speaker box to near the ceiling and be covered by fabric too.

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Dan