Tiny All-In-One room

#31

Starlight thanks for the comments. You are right, at the time of the soffit making there was no ceiling treatment because it was much easier to first finish the front wall. There will be a ceiling update following soon.
I am aware about the invalidity of rt60 in small spaces but rew actually measures rt30 but it still names it rt60. Do all these designers mean t30 also?

Dio

#32

I believe they mean all RT measurements, not just RT60.

#33

Have you considered (if not already) measuring those speakers in an open space outside, like a parking lot? Are you sure you're not getting issues because of the crossover design?

#34

Hi dvuckovic,
The truth is that my speakers are not yet “tuned”, and perhaps this is one cause of their bumpy frequency response . Unfortunately it is not practical to move them so the tuning must be done in the room, when the room is treated enough to make this possible. But anyway I don’t think my low frequency time issues have something to do with the crossover, which takes place much higher (about 580hz for the low-to-mid ).

Cheers,
Dio

#35

I was thinking that the general lack of low end is maybe a polarity issue

#36

If you are referring to the 120hz hull it is the unavoidable floor bounce..

Cheers,
Dio

#37

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:

: Absorptive ceiling

: Absorptive ceiling

And some happy results:

: Absorptive ceiling RT60

: Absorptive ceiling Waterfall

: Absorptive ceiling Spectrogram

: Absorptive ceiling FR

: Absorptive ceiling IR

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!

: Side soffit insulation

: Dio Ministudio side soffit chunck RT60

: Dio Ministudio side soffit chunck wtrl

: Dio Ministudio side soffit chunck spectrogram

: Dio Ministudio side soffit chunck FR

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 #16) 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

#38

Seeing the slow but steady incremental improvements from all your hard work is both inspiring and fascinating. Thank you for measuring the progress in such detail. A joy to behold.

Cheers,
Jennifer

#39

Thanks Jennifer! It's a great feeling sharing thoughts and work and know that someone, somewhere out there is inspired by them.. We may work alone each one, but we are not alone !

Dio

#40

RFZ Update.
Two panels 200x60cm of 18cm insulation + 12cm air gap installed in the first reflection points L-R respectively. Results following:

: First reflection insulation

: First reflection insulation RT60

: First reflection insulation Waterfall

: First reflection insulation Spectrogram

: First reflection insulation FR

mdat: https://mega.nz/file/k1sERSoZ#TrpUgjJZq ... TpU5qROJzM

Nice things happened here summarized in a word : smoothing. From frequency response to waterfall to Spectrogram, every plot has been beautifully smoothed and this is also easily audible. One interesting thing to notice is that the temporary placement of the amps on the floor (see photo) has effect in the floor cancelation..
The RT is now very short, with is natural with all this insulation, what is not natural and needs investigation is the strange behaviour of the low frequency decay with its ups and downs in every measurement. Anyway generally things improve and as we can see from the before-after rfz panels comparison the listening position is almost free of first strong reflections.

: RFZ side insulation before-after comarison.jpg

Despite the very low RT the room does not feel dead and been there is not uncomfortable at all, the hard front wall is a good choice.. Listening music in there is apocalyptic I would dare to say, you can observe easily every detail in the recordings and at the same time get involved in the music as a listener, not as a technician, I like that!
One more thing a trained eye can notice in the room photo is the absence of the pc tower, and this is why:

: Pc box model

: Pc box

The box is not sealed yet but the pc working is barely audible only as a low frequency murmur.
Coming next is my last attempt to do something new with my 42hz demon.

DIo

#41

Hi Dio
Just wondering if you’d managed to get anywhere with a 42Hz absorber?

Cheers
Gareth

#42

Hi Gareth,
I ‘m quite busy these days as our “beloved” government rapidly opens everything up. I do have something to share, hold on a bit…
Cheers
Dio

#43

Wow! This place is coming on fast and furious! And looking really nice too! I need to go back and read over the entire thread, to catch up on where you are. Great work, by the looks of things!

- Stuart -

#44

After a long time back here to continue that small project. What I had was a small cavity between the soffits, ideal to build some limp mass absorbers, why not?

And then painted the soffit wall to look like wood and put some fabric and lights.

To verify thet the absorbers are tuned correctly I swept simple tones from 30 to 55hz and by lightly touching I felt the membrane begin vibrating from 36-38 hz and stop at about 45-47 hz, so I guess the constriction is correct.
Measurements:

mdat:
https://mega.nz/file/Q8lGVD7J#iu4kbnZola9-br7w4KOhEVW_Oe5yulZLiqH00LuYmXc

We see that the two mlv absorbers did something in the 40something hz area, but very little, perhaps their 85x165cm surface is not enough? Anyway, they smoothed the upper bass area and that alone is fine.
More to come in a few days..
Dio

#45

I'm seeing some strange things in the images of graphs you posted, but it might just be the settings you chose. I'd like to have a look at your MDAT files directly, but for some reason your upload service in New Zealand won't let me download them.

You can upload your MDAT files directly to the forum: there's no problems with capacity or bandwidth, and the forum will happily accept MDAT files, as well as many other file types. That also means that your files will always be accessible, and not subject to the vagaries of upload services.

So please upload your MDAT files here, and I'll take a look.

I also noticed that your overall decay times are very low: around 100 ms. That's a little too dead for a room that size. I'd suggest that you do something to return some life to the room: diffusive reflective surfaces, in front of the deep absorption, for example.

Also, an answer to an earlier question you had brought up:

I am aware about the invalidity of rt60 in small spaces but rew actually measures rt30 but it still names it rt60. Do all these designers mean t30 also?

This is more of a semantics issue: For small rooms, the measurements should more correctly be called "decay times", rather than "Reverberation Times". Even though small rooms do not have reverberant fields that decay over time, they still do exhibit just plain old "decay". In other words, the sound levels for each frequency band diminish over time, just as they do in a large room. The issue isn't that decay doesn't occur: clearly, it does! The issue is that, technically, it cannot be called "RT" (Reveberation Time), because there is no statistical reverberation time in small rooms. So what is "decaying" in small rooms is not a true reverberant field: just the sound level. In fact, the final outcome is the same: sound levels decay over time, at different rates! So the issue is really about what to call it, from a technical point of view. The only real difference, from a pure acoustics point of view, is that you can't validly use the statistical analysis tools to analyze what is going on... but you can still use the rest of acosutic theory to understand the issues, and to design treatment for them.

Bottom line? For most home studio builders, it doesn't really matter what you call it! RT is technically not correct, but it's a lot easier to write "RT60" than "non-statistical sound level decay times".... so pretty much everyone still refers to it as "RT60", even though it really isn't, from a pure technical point of view.

Also, "RT30" means basically the same thing as well. This is a different issue, but worth mentioning too: Since it is pretty hard to have a loud enough sound field to accurately measure a true decay of 60 dB, "RT30" measures the decay time over a range of just 30 dB, and extrapolates that to 60 dB. That's the issue. In practical terms, it's the same thing just measured a different and slightly less accurate way. The reason is simply this: The noise floor for the low end of the spectrum in a typical home studio might be 35 dBC. To get a good measurement, you'd want your lowest level about 10 dB above that, so call it 45 dB. Therefore, to measure "RT60", you would have to have to start with a level of 105 dB or more. That's LOUD! Your speaker might have trouble dong that, it's harmful for your ears, and even then it STILL isn't loud enough, strictly speaking: To get a true "RT60" measurement, you should start with an extremely loud, extremely short "impulse", such as a gunshot, or a large balloon bursting. Since you probably don't want to be firing guns or popping hundreds of large balloons in your room, that's not the way it is measured. REW uses an entirely different method, which is just as valid, but doesn't need any gunfire.l¿ And it can also do it at lower levels: around 30 dB lower than would be needed for a true 60 dB decay. Thus, it can estimate RT60 rather will by only measuring 30 dB of decaty, then using mathematical methods to extrapolate that to 60 db.

Hopefully, these explanations help to clarify the issues a bit!

- Stuart -

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