Home Mix Room Overhaul - DIY Panel Build - w/ REW Charts/3D Sketchup

[shybird]

Has anyone messed with this reflection simulator?! It's pretty neat. Doesn't work in 3D I don't think but could be helpful as a starting place in various situations.

https://amcoustics.com/tools/amray

[SoWhat]

Any idea's how we might go about that?

Haven't the foggiest of how to really do it.

But perhaps, and this would only be viable IF you are not moving the panels frequently (read: multiple times in the same session), some soft flexible material (maybe weatherstripping???) in the channel (NOT attached of course) should dampen any vibrations.

If it works, you can take credit. If it doesn't, you didn't hear about it from me.

All the best,

Paul

[shybird]

Haha fair enough! I will make sure everyone knows it was your idea if it fails! jk

That sounds like a plan though. Cheers and TGIF!

[endorka]

Source of the postmethinks that the "mechanism" needs to be damped somehow to prevent sympathetic vibration (or as we common-folk prefer to call it, rattling) in the channel.

Oh aye, well spotted. One of the blinds here is prone to that, but only when pulled fully closed. Leaving it a tiny bit up is sufficient to stop the vibration. Took ages to find the source of that rattle the first time.

I don't recall the pivots and rails on the doors here rattling, but then I'm not firing 100s of watts of bass at them day in day out. They have a sliding part that fits very snugly into the rail and moves surprisingly easily. No idea how it works, perhaps some sort of low friction nylon bushing? I think a lot of the art of getting these to work well it to fit them very precisely.

Cheers,
Jennifer

[SoWhat]

Greetings,

I will make sure everyone knows it was your idea if it fails!

There's no such thing as bad publicity.

ow friction nylon bushing

Yes. Essentially a wheel on its side. Here in the US, many Washer/Dryer sets are often "hidden" behind track doors. Completely stupid since EVERYONE knows what's there, not to mention the ergonomics are terrible: "Hmmm, let me think. I'm carrying a huge load of laundry. I know, give me two extra doors to open. That's the ticket!"

All the best,

Paul

[endorka]

Source of the postAlso, for that 36Hz mode (which seems to be closer to 40Hz in the actual REW test I did), if I follow the 1/16 wavelength rule then I would need 1.96' (59cm) of insulation to affect that frequency (which is 31.38 feet long!). Fortunately, I'm hitting that exactly with these superchunks. However, I read a post Stuart made that said 1/16 is the minimum when using absorption alone, and 1/8 is much better. That would mean I need 3.92' (119cm) of insulation or more. Like I said, it depends what I can count as depth in regard to these superchunks but I'm definitely not going to hit 4' from middle of face to back cornerr

Bear in mind the effectiveness of these broadband absorbers does not fall off a cliff below a certain frequency. It's a gradual roll off. You can visualize this in the porous absorber calculator. So there will be an effect at these low frequencies. Whether it is sufficient or not is another matter depending on many things, not least of all your requirements and budget.

Also worth noting is the angle of incidence to the panel. Sound hits it at all angles, not just 90 degrees to the face. So at some angles the wave will go through an absorbent path great than the panel depth. The extreme of this is the example you note about the superchunks running lengthwise absorbing sound going lengthwise in the room. A very deep trap indeed. I built my panels with an open frame to gain maximum benefit from this effect. Superchunks by definition have an open frame, right?

Proof of the pudding: Here's an REW graph comparing my main room empty and the treatment it had nearly five years ago. The bass traps are 4x2' with 4" deep Rockwool RW5 insulation. Arguably too dense at 100 kg/m3, although the jury is out on this at 4" depth. In retrospect RW3 would have been a better choice. There were some 2" deep commercial panels on side walls and ceiling too.

So a room of similar size to yours with fewer absorbers of far lesser depth made with the "wrong" insulation. Yet an effect down to 40Hz is obvious. The treated low end frequency is a pretty decent realization of the frequency response of the Genelec 8030 monitors (-3 dB @ 55Hz). The empty one apparently goes deeper, but it's just nasty room resonances giving a false representation of the bass. The bass became massively tighter after this treatment.

Before and after spectrograms demonstrate the effect clearly too;

Stuart suggested acoustic hangers earlier in the thread. Apparently very effective and well worth considering. I've never tried them but would like to, we just can't get the Homasote panels in the UK and it seems to be a crucial part of how these works.

Cheers,
Jennifer

[shybird]

Source of the post I think a lot of the art of getting these to work well it to fit them very precisely.

This is my main fear with going this route! I can only imagine how challenging it might be to get it right...

Source of the post There's no such thing as bad publicity.

Haha that's the spirit!

Source of the post Bear in mind the effectiveness of these broadband absorbers does not fall off a cliff below a certain frequency. It's a gradual roll off.

Yes, totally! I forget to think of it on that level. I've noticed this though and probably should have reworded my question to, like you said "will it be ENOUGH to tame that lowest mode down to a reasonable level."

The extreme of this is the example you note about the superchunks running lengthwise absorbing sound going lengthwise in the room.

Glad to get some reassurance on this!

Proof of the pudding: Here's an REW graph comparing my main room empty and the treatment it had nearly five years ago.

That is a drastic improvement indeed! And with only 4" and 2" panels too. This makes me reconsider the possibility of just using all of my 6" panels and accepting whatever improvements are made by those. However, I'm still pretty revved up about getting this place tuned as good as possible because I've always wanted to work in a space that I can trust and rely on. I spend so much time mixing music that it just makes sense to put in everything I can.

Stuart suggested acoustic hangers earlier in the thread. Apparently very effective and well worth considering.

Yes I'm still in the dark about how these things work and how they are made. I've heard they have to be cut to certain sizes because the Homasote panel acts as a tuned membrane of sorts? I don't quite have enough details to understand how to implement them into a drawing. I also don't know where to put them considering the strange layout of my back wall (door and fireplace). I'll do some more research in the forum to see if I can clear up my questions on hangers.

Thanks again for the help. That post was super insightful and gives me another point of reference in determining how I want to move forward with this room when taking into account budget/time/energy.

Cheers everybody!
Trevor

[endorka]

That is a drastic improvement indeed! And with only 4" and 2" panels too. This makes me reconsider the possibility of just using all of my 6" panels and accepting whatever improvements are made by those. However, I'm still pretty revved up about getting this place tuned as good as possible because I've always wanted to work in a space that I can trust and rely on. I spend so much time mixing music that it just makes sense to put in everything I can.

In your shoes I would stick to the superchunk plan rather than going back to the 6" panels. Reason being that while the treated room above was a big improvement, there was still a lot that could have been done better with hindsight. In fact I will be redoing the room with this benefit of hindsight. If I were you I'd take the opportunity to get it correct in the first place.

One of the biggest oversights I made was going for surface area of absorption rather than depth. Done with the intention of getting the best value for money by spreading thinner insulation over a larger area rather than deep in a smaller area. It worked, but a side effect was too much broadband absorbing surface area taking too much high frequency reflections out of the room. It also took up a lot of space.

As I say I'll be doing it again with superchunks and so on.

Also worth noting that while there was a big improvement, the low end acoustics were pretty decent to start with. I suspect your room is starting from a worse place and thus will require more attention.

Cheers,
Jennifer

[Soundman2020]

Man, this thread is moving real fast! And you are getting some great advice here!

... And I just noticed that I skipped a whole bunch of earlier posts, so I'll don some catching up here....

- - - - - - - > > >>

Someone might have already covered this later in the thread, but I'll add it in anyway:

But after making one test panel with some burlap from Joanns, I was not pleased. The weave is just too loose so you can see the framing behind the fabric. And then there is a space between the fabric and insulation due to the 1x2 framing, which essentially creates a contrasting shadow. First photo below of what I'm talking about.

Black. Use some simple, thin, low-cost, fine-weave black fabric under the final finish fabric. You get that visibility problem with pretty much any type of breathable fabric: at some angles, light will get through and you'll be able to see the ugly stuff behind. The black fabric blocks the visibility. And it can be the cheapest, ugliest black fabric you ever saw! Nobody will ever see it: it is only there to block the light. D

Do that with all of your acoustic treatment, to hide the ugly stuff behind the finish fabric.

- Stuart -

[Soundman2020]

Source of the post Ahhh that is extremely helpful! And MUCH cheaper haha. I will make sure to find one with similar ratings to that then. I had done some readings about airflow resistivity and how it was the main thing that affected the acoustical absorption characteristics. Still a little fuzzy on which rating to get for various applications but I feel confident now for this one which is all that matters for now!

GFR (Gas Flow Resistivity, a.k.a. air flow resistivity) is a measure of acoustic impedance, so it's real indicator of how well the material will perform. As a general rule of thumb, lower GFR implies better absorption at lower frequencies. High GFR implies less low frequency absorption, and good high frequency absorption. This too might help in your quest to get better acquainted with GFR, thickness, and frequencies! : http://www.acousticmodelling.com/ Have fun!

- Stuart -
(PS. that tool just uses a simplified model for the prediction: it is a bit more complicated in reality, but it gives you a reasonably good idea of how things work with porous absorption).

[Soundman2020]

I think the main question I need answered right now (so I can confirm my fabric order) is whether or not the black plastic I linked to (see below) will be ok (acoustically) to use on the facing of the panels beneath the burlap?

Jennifer gave a great reply there, so I'll just add this: Acoustically, plastic acts like a foil. It reflects some frequencies, and allows others to get through. The governing factor is the surface density of the plastic. The equation is:

F = 90 / m

Where:
F = The frequency at which the foil transmits 80% of the sound
m = The surface Mass of the foil in kg/m2

But of course, it is not a sudden sharp cutoff! It's a slow gradual curve that spans an entire 4 octaves! This graph is maybe more useful than the equation, which is a bit cryptic!

So basically, if you use thin plastic, it only reflects the very highest frequencies while the rest get through. If you use very thick plastic, you reflect all of the highs and some of the mids, only letting through the lows-mids and lows.

One caveat for both the equation and the graph: the plastic must be free to move. ie, not stretched tight, and also not clamped flat between the insulation and the fabric. It can touch the insulation, sure: no problem. But it must be able to vibrate freely, in it's own natural way, or the equation is not valid.

- Stuart -

[Soundman2020]

Source of the post My preference would be to address this afterwards with wooden slats or what have you on top of the fabric face of the superchunks. These can be tuned as required.

Yup! Plastic is tricky.


- Stuart -

[Soundman2020]

Source of the postsome applications where I would not leave it acoustically to chance;
1) Anywhere there are potential first or second reflection points from speakers to the mix position. Bear in mind that you may move your speakers around to optimise sound once treatment is in place.

2) If I was building a "vocal booth" from gobos. Don't want these reflections in the mic.

Big agree! Point #1 also includes ceiling clouds. Plastic up there can indeed send reflections right back at the mix position... unless the cloud is angled quite steeply.

- Stuart -

[Soundman2020]

I've also heard breathability isn't always necessary depending on what the fabric is made of? Like as long as it isn't reflective...or is that completely wrong?

If it is not breathable at all, then the GFR is basically infinite... Thus, it reflects. Also, if it not breathable, then it potentially becomes a limp membrane trap, if the device behind happens to be reasonably well sealed, or at the very least it becomes somewhat of a drum head...

Breathability is important for fabric coverings... unless you actually want a reflective membrane trap!


- Stuart -

[Soundman2020]

But Starlight mentioned it has a low GFR and therefore won’t reflect sound. Based on that, it seems the most important part is that whatever material covers the panel should either be “breathable” OR have a low GFR so it does NOT reflect sound. And it seems that a low GFR does not always mean breathability...am I interpreting this correctly?

Its the same thing: What GFR actually measures is the ratio between the applied air pressure differential, and the speed that air moves through it. In simple terms that we normal people can understand: to measure GFR, you put a piece of your test material in some type of frame, you increase the air pressure on one side, then see how fast the air flows through it... which sounds an awful lot like putting a piece over your mouth and blowing!

- Stuart -