John Sayers' Recording Studio Design Forum Archive

Thanks Mattsal,
Things have slow down a little construction wise, the truth is... the hangers core varies from 210x15 to 210x62 (in centimetres) the on-hanger insulation is 4,5cm but is a bit fluffy and in reality is 5-6cm per side.The on-wall insulation is said to be 9cm but is over 11, respectively. The total depth of the frame is 60cm.

dio

Minor Sunday update: finished the absorptive door with 20cm of Knauf Ultracoustic insulation (≥5000 kPa.s/m²) and now (keeping in mind that the door does not isolate perfectly) the back wall is considered as an acoustic "black hole" . mdat:
https://mega.nz/file/Rk1UXJqT#9vP9Q4Vwy ... mQIZ0utRSY

Screenshots:
As expected there are only minor changes, mostly visible in the reflections diagram (ir). Here is the comparison between the previous situation (hangers only) and the added door insulation. Some strange behaviour in the mids I believe is from the various stuff that is still in the room and should be ignored: Not big differences but certainly listenable. Music is more "focused" and clean now, details have appeared even in very low volumes, and high volumes are now tolerable..

And now two questions:
1) Planning the final layout many different configurations have passed though my sketchup and I ended up that the safest one for my limited space is with absorbent reflection points (30cm insulation) and full absorbent ceiling (30cm insulation), see previous post. I keep reading that insulation alone will not suppress the early reflections enough end the proper way is to redirect them, something that I am unsure if I can accomplish in this room. Will I gain anything noticeable if I embed hard reflective surfaces inside the insulation on the reflection points?

2) Seeking a way to tame the 42hz standing wave I am planning on using slot resonators in the above and below soffit sections. An also ideal place for a low tuned resonator seems to be the outer part of the soffit: will the resonator be effective being so close to the side wall insulation? How big the gap has to be? Are there other options? Thanks,
Dio

it's LF (42hz) so the proximity of the side wall to the resonator shouldn't be a problem.

Thanks Glenn, actually the gap I was wondering about is this: If the insulation being so close to the resonator makes it less effective.
dio

i don't think it will be a problem

Time has passed and things have moved forward a bit. The man with the drill came and made three really beautifull holes on the wall, where the hvac ducts, cabling etc passed through. Then, I made the "on-wall" silencer and connected the fan. Being aware of the Murphy's laws I made the silencer internals visitable. Playing loud music (~95dbC) inside the room corresponds to about 56-57dbC at 1m from the silencer. I wouldn't call it bad performance for a start. After done with that it was time to begin the soffit construction. Being tight in space and incorporating bass traps the soffits have a little strange shape but being bolted on the stonewall are rigid enough .. And finally time to fit the speakers in! It is allready a really tight fit, but I am thinking of additionally screwing them in the frame to turn it into one mass. Testing with loud tones didn't reveal any rattling or resonances from the (still unfinished) construction, which is good, of course. Coming up next: side soffit slot aborbers! Thanks for viewing,
Dio

nice work Dio!

It's Sunday and it's time for another update! The part the fun begins! Having finished the soffit frame and put the speakers in,I removed the office desk and took a measurement: Mdat: https://mega.nz/file/I4tgSDLB#aiWCNF-eg ... wikcX7_efs

It seems that this office desk was a big problem for this small room, good I got rid of it... but what are these peaks? Something resonating? Been in a hurry to continue working I decided to investigate later. So I proceeded with stuffing the soffits and took another measurement. Mdat: https://mega.nz/file/cp0wFbhK#ruX93jDiw ... NVHtJ_nCPE

Now things are slowly becoming nicer, but these 100 and 200hz things still exist... let's move on and build the side slot resonators and we will find out later. Mdat: https://mega.nz/file/okkwyZbI#X9H2R8rOT ... 9Bb-TPlpmE

Now, these resonators are tuned to 80-110hz, so they are doing their job on damping that 97hz resonance but that 200+ thing is still standing there proud... so with the old and tried method of playing the resonating tone and with the help of our friend "the mute button" the culprit revealed: it is the heater radiator! To verify I took another measurement. The results on the following post.

Dio

So, the next two screenshots are with me in the room holding (and damping) that radiator, the images are self-explanatory, the 200hz resonance is gone! After finished with this it's time for the lower soffit slot resonators, the ones I had big expectations with. Mdat: https://mega.nz/file/BgdyUBDI#cCm2pWXh4 ... qTw6bTP8sM

To be honest in the beginning I was expecting a little more from them in the 42hz issue since the calculator gives o 0,7 coefficient in this region. Then I realised that only two out of ten slots have the cavity depth to absorb this frequency so I sat back and admired the rest of the performance.
First and most impressive is the total disappearance of the 200hz radiator resonance!! Unbelievable. Then the rest of the spectrum <300hz has also been tamed very well at around 200ms, not bad. That bump in the 600-900 hz in the RT I don't know where it came from, could be something from the stuff the still exist in the room.
Anyway, now it's time to finish the soffits with a 30mm thick MDF baffle.
Mdat: https://mega.nz/file/0kNCSDDb#NA9u9S4yL ... fsWQDJFafI

We see the lows have gained a few decibels from the baffle, we also see that the 42hz mode has shifted to 43hz since the room is now a little smaller. The rt60 is a little smoother also, but the cancelations in the 100-130hz region have been increased.
Next move is to built the upper soffit slot resonators, and I haven't yet decide if I should make a copy of the lower ones or if I should try to tune them as low in frequency as I can to hunt the lowest mode. What would you do?
The nicer of all is that the listening experience in the room has dramatically changed. Every tiny detail is revealed and the technical aspects in recordings are easily observed.I defenetely feel that I am moving to the right direction,

Thanks, Dio

you can easily EQ the 43hz - it's nulls you cannot EQ

looking good!

Hello people,
A few days have passed and there are things to share with you. As you may remember I was about to build my upper soffit slot resonators, and that's what I did: And this is what I got after a loooot of effort:
No matter how I tried to tune, retune or detune them, the results were not satisfactory at all...
There was a huge hole in the lower midrange reverberation time while in the lows there was a weird rise of about 100ms (!!) with no real improvement anywhere.
The evidence:
https://mega.nz/file/IhVQTZwA#KJtyaK5uW ... D6MWOx0QOU

The only logical conclusion I can reach to is that sound coming from inside the soffit where interfering with the resonator. It seems my soffit construction is not massive enough to support this kind of treatment built into it. That's why almost nobody does these things, failure accepted and lesson learned.
So it is time for plan B, and plan B was to turn the resonators to big insulation chunks: At least that 150hz dirt has disappeared.. but strangely the very lows RT is still high and the rest is bumpy...
I am tempted to convert the side lots to insulation too.
Later, as I was making the frame for the absorptive ceiling I thought it was a good idea to screw some slats (50mm slats/20mm gap) over the upper insulation chunks: And there is was. Evidence: https://mega.nz/file/sxME0bRS#7I2VGIiKM ... _r53mdc-3s

Minor changes, most of the RT is back to normal except this annoying low section...
It also seems that I have reach a point that in such a small space every thing in every place affects the measurements in various ways. Anyway let's move on!

Cheers
Dio

keep in mind, you can eq out the peaks

I do Glenn, but I want to keep eq as my last resort..

Cheers,
Dio

Ceiling Update!
Finding it easier (and perhaps more efficient) to just make a full absorptive ceiling (27cm insulation 5000 Pa.s/m2) than drilling and hanging clouds in a 2,5m high room, I got to work: And some happy results: mdat: https://mega.nz/file/B0U32Ywa#oBu208tE8 ... w-b7X8cj8I

A nice view of all the spectrum <700hz get smoothed, specially these 150-300 spikes in time. The 250hz resonance is the radiator still singing and the big 120hz null is the floor bounce at 4,5ms (verified with the string trick) that made itself apparent when the (absence of ) ceiling cleared things up.

Then, it was time for these side slot resonators to be converted to insulation chunks, I didn't forget them! mdat: https://mega.nz/file/EtchlaLZ#gopaS-DQI ... JoFnUSOnl8

What we are seeing is a further smoothing of the 150-400hz area in the time domain and at last some damping if our old friend the first 42hz mode being visible in all the time related plots. That was nice! The radiator (250hz ringing) is still there, but not for long..
One more good thing I noticed after finished all this is that the ventilation is completely inaudible even at full speed and the playing music (Muse) at 100dbC in the room corresponds to about 57-59 dbC of low frequency rumbling just next to the ventilation baffle box outside, ok with that for now.
My next move shall be the first side wall reflection treatment with 18cm absorption (as seen in post at the top of the page) and with a feeling of adventure the making of a limp mass absorber in the blank space between the soffits in an attempt to tame this 42hz mode.
Also you may have noticed that I haven't make any comment on the frequency response in all these posts. As you can easily see from the plots attached frequency response tells very little about the acoustic quality of a room, it is relative easy to make a good frequency response graph by heavily equing the monitors but what first matters is a correct time-related behaviour of the room, and that's what I am trying to accomplish, equing will come last.

Thanks for viewing,
Dio

Looking good! How does it sound?