DIY Acoustic Panels

[51m0n]

4 hours ago, Skol303 said:

I'm still tempted to get a sub... my monitors are great down to about 40Hz (exceptionally flat), but I don't have much going on below that. However, it's a small room so I'll need to be careful not to add loads of new mode problems.

I'm going to audition one and check; hopefully this week in fact!

that way madness lies, I warn you

 

[Dad3353]

7 hours ago, Skol303 said:

...my monitors are great down to about 40Hz (exceptionally flat), but I don't have much going on below that...

Is there really that much 'going on' below 40Hz that needs such 'flatness'..? 

[Mornats]

I usually start my high pass filter at around 40hz so wondered the same.

[51m0n]

26 minutes ago, Dad3353 said:

Is there really that much 'going on' below 40Hz that needs such 'flatness'..? 

 

25 minutes ago, Mornats said:

I usually start my high pass filter at around 40hz so wondered the same.

Well you want to be able to hear the bad stuff that might be going on down there.

People tend to forget that 20 to 40Hz is an entire octave (like 10KHz to 20KHz is only one octave).

If your monitors can't do that then who knows what rubbish low end energy you might be chucking out!

[Dad3353]

7 minutes ago, 51m0n said:

...If your monitors can't do that then who knows what rubbish low end energy you might be chucking out!

I took it to read as a lack of linearity rather than dead silence under the 40Hz threshold. It's audible (on good systems...), but does it have to be that flat, was my concern. Any dross will be heard, but slightly attenuated. Is there that much going on that it needs to be linear down to 20Hz (or lower...)..? If the stuff down there is that bad it'll be heard, won't it..?

[51m0n]

17 minutes ago, Dad3353 said:

I took it to read as a lack of linearity rather than dead silence under the 40Hz threshold. It's audible (on good systems...), but does it have to be that flat, was my concern. Any dross will be heard, but slightly attenuated. Is there that much going on that it needs to be linear down to 20Hz (or lower...)..? If the stuff down there is that bad it'll be heard, won't it..?

Well probably not.

Your ears dont really do sub 40Hz very well, Fletcher-Munsen curves and all that.

So given we struggle to hear that low anyway, if your mains are attenuating that low by a further 6 to 9dB (not unusual) then you have pretty much no chance of telling if there is anything there at all.

Now in a mix situation this is not such a huge deal.

But when you are mastering it really does. Anywhere you can get rid of garbage you should. Not only is it wasted energy but its wasted bits and that equates to less apparent level. Now I am by no means an advocate for the loudness wars thing but if it taught mastering engineers anything it was stow all that rubbish.

So you say, big deal, hi-pass filter sorted. Yeah but sometimes what is down there is real weight thats good, in the bass maybe, and losing that makes the mix weak, but the kick is just phat tubby lard as well so now you need to set up a multiband compressor limiter situation to deal with this. And that is when you'll be all kinds of happy that your monitors can give you some definition and decent clues that deep....

 

[Dad3353]

5 minutes ago, 51m0n said:

Well probably not...

OK, I'll bow to all that, in such a context. I've no issue with a 'pro' studio set-up; the 'diminishing returns' make it largely impracticable for Humans, though, especially in a domestic environment. I'm much more deaf than any of that, anyway, at my age, so... 

[Mornats]

49 minutes ago, 51m0n said:

 

Well you want to be able to hear the bad stuff that might be going on down there.

People tend to forget that 20 to 40Hz is an entire octave (like 10KHz to 20KHz is only one octave).

If your monitors can't do that then who knows what rubbish low end energy you might be chucking out!

That'll be a job for my M50x cans and Sonarworks then  

[Skol303]

3 hours ago, Dad3353 said:

Is there really that much 'going on' below 40Hz that needs such 'flatness'..? 

Not always... but sometimes certainly yes. And when there is, you REALLY want to know about it.

For context bear in mind that:

1. I produce/remix a lot of electronic dance music and hip hop (aka “bass music”); and so every ounce of low end insight is useful to me, whether the notes are felt or heard. Especially when producing music to be played over large sound systems in nightclubs, some of which are very capable of reproducing bass down to 20-30Hz (sufficient to rattle the optics behind the bar, as I once witnessed during an LFO gig in Sheffield!). Headphones can only go so far in terms of referencing sub 40Hz; to get a true picture you need to move some air.

2. Subwoofers aren’t just about benefiting the lowest of the low frequencies. Using a sub in a 2.1 set up means that your regular monitors don’t need to work so hard; and evidence shows that can add clarity. Depending on where you set the crossover,  a sub also has the potential to help even out the low end up to 100-150hz: filling in some of the nulls (whilst creating peaks that can be corrected by EQ).

3. My room is well treated - pretty much as far as possible for a domestic room. So although the space is small, it’s relatively ‘sub-friendly’.

4. I’m a perfectionist and unabashed Gearslut 

...all that said, subs are notoriously tricky to set up and can cause more problems than they solve (as rightly mentioned by Si above). Hence I’m going to demo one before committing to a purchase - noting point 4 above often requires a willpower of steel!

Edited April 16, 2018 by Skol303

[Skol303]

On 15/04/2018 at 23:09, 51m0n said:

I hate subs.

They are nightmarish to get right.

If they arent right or you get a skewed mix you are always left thinking "Is it the sub set up?".

Forgot to mention... totally agree with this, but if you have a suitable mic and a copy of REW (free) or FuzzMeasure (what I use) then you can use measurements to supplement your ears when setting up a sub, thus removing some of the guesswork and uncertainty.

You probably know this, but for everyone else what I mean is:

1. Take measurements to find the optimum location, by placing the sub at the listening spot and then moving the mic around the room whilst measuring frequency sweeps. Best mic position = best sub position. A kind of high-tech version of the "subwoofer crawl".
2. Take measurements to help set the volume/level of the sub, by tweaking the gain until the low end frequency response and decay time are as flat as possible.

And of course using your ears!

I have a sub arriving sometime this week for demo'ing, so I'll test it out and report back here...

(PS: I might move these posts to a separate thread on subwoofers).

[51m0n]

5 hours ago, Skol303 said:

Forgot to mention... totally agree with this, but if you have a suitable mic and a copy of REW (free) or FuzzMeasure (what I use) then you can use measurements to supplement your ears when setting up a sub, thus removing some of the guesswork and uncertainty.

You probably know this, but for everyone else what I mean is:

1. Take measurements to find the optimum location, by placing the sub at the listening spot and then moving the mic around the room whilst measuring frequency sweeps. Best mic position = best sub position. A kind of high-tech version of the "subwoofer crawl".
2. Take measurements to help set the volume/level of the sub, by tweaking the gain until the low end frequency response and decay time are as flat as possible.

And of course using your ears!

I have a sub arriving sometime this week for demo'ing, so I'll test it out and report back here...

(PS: I might move these posts to a separate thread on subwoofers).

Yep all sounds great, but the problem with subs is time alignment with your mains around the crossover point. The whole idea that a sub can go more or less anywhere and sound great is misleading at best, it must also be the same distance from both mains (or they will skew, you will get comb filtering and other weirdness etc etc), and any wall reflections need to be taken into consideration. Eventually you find there may be nowhere where your sub doesn't do something funny to the sound in the area where you mains produce something (not enough) and the sub top end.

It can be done, but it is very difficult to do (very very very difficult) even with software, and IME you're better off getting full range speakers to do the job and just take all that guess work out of it

[Skol303]

16 hours ago, 51m0n said:

It can be done, but it is very difficult to do (very very very difficult) even with software, and IME you're better off getting full range speakers to do the job and just take all that guess work out of it

You're no doubt right Si, but a combination of rampant GAS and curiosity (but mostly GAS) has got the better of me on this one

As it happens the sub I'm demo-ing arrived yesterday afternoon. Haven't had chance to properly set it up yet, but as an initial test I've placed it between my main monitors (up against the front wall) and just to one side, to avoid the centre room mode. So far I've only set the gain by ear, but I took a quick frequency measurement and to be honest it looks surprisingly promising... observations:

• It's helped to fill in much of the gnarly dip I had around 70Hz (by +5-6 dB, possibly more)
• It’s showing a very useful response down to 30Hz, where it then tails off (but still giving me around +10-15 dB at 20Hz compared to what I had previously... not that I can actually hear it!)
• Above 70Hz the frequency response is pretty much identical to that produced by my main monitors alone (I currently have the crossover set at 60Hz).
• There's a noticeable boost in the low end, as you'd expect, but I could level that out with DSP software.
• No signs of comb filtering that I could spot from the frequency graph; but I need to take some proper measurements and also check decay times, etc.

So hmmm...definitely not helping my GAS! But the initial signs are that a sub may actually be of benefit in my room. Especially because I don't have capacity to install main monitors any larger than those I currently have.

I'm hoping to do some proper tests at the weekend and will report back, in case the info is useful to anyone here who might also suffer from sub GAS at some point.

[51m0n]

5 hours ago, Skol303 said:

You're no doubt right Si, but a combination of rampant GAS and curiosity (but mostly GAS) has got the better of me on this one

That's it mate - you're soooo screwed

[Skol303]

I know...!

Edited April 18, 2018 by Skol303

[Jus Lukin]

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Edited February 26, 2022 by Jus Lukin

[Jus Lukin]

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Edited February 26, 2022 by Jus Lukin

[Skol303]

8 hours ago, Jus Lukin said:

...a superchunk, covering the lower 50% of the wall, but behind this is still going to be effective, isnt it?

Yeah sorry for the dalliance into subwoofers!  (I may yet move that to a thread of its own).

To answer your question, yes, a superchunk covering the lower section of wall will certainly be of some benefit... but it will be a lot more effective if you build it to the full height of the room. That would not only provide a greater surface area/ amount of treatment, but also help to deal with that upper corner, where bass frequencies tend generate the most pressure (low frequency energy).

So a full height superchunk would be my recommendation - after all, it’s otherwise dead space so you might as we do something useful with it.

But if you want to restrict the height for aesthetic reasons, that’s your call to make, of course. Any acoustic treatment is nearly always better than none

PS: i assume you’re planning on adding other treatment elsewhere in the room?

Edited April 20, 2018 by Skol303

[Jus Lukin]

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Edited February 26, 2022 by Jus Lukin

[Skol303]

^ “Every little helps” when it comes to acoustic treatment, for sure. And in a shared/multipurpose space there will always be compromises... which by the sound of things you’re making the most of. Good approach.

A few ideas and pointers:

1) You could try inserting a thin sheet of ply board into your bass traps - ideally 4-6mm thick, fixed loosely in the front face of the panel so that it can vibrate. This ‘membrane’ will help to further dampen the lowest frequencies and will also reflect some of the mids/highs back into the room. Peg board (with holes) has traditionally been used in studios for this purpose.

2) Don’t over-do it with the 2” panels. If you disproportionally over-dampen the mids/highs you will, in effect, ‘boost’ the bass, making the room sound boomy.

3) Use a more dense material for the 2” panels: Knauf RS60 (48kg/m3) as a minimum; possibly even up to 100kg/m3 density to be effective at that thickness. The fluffy Knauf DriTherm 37 is only really suitable for panels with a minimum thickness of 4” and ideally 8” or more.

Let us know how you get on! And rest assured that anyone who lets you install acoustic treatment in your shared living space is a good catch  

Edited April 23, 2018 by Skol303

[Jus Lukin]

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Edited February 26, 2022 by Jus Lukin

[Skol303]

14 hours ago, Jus Lukin said:

Letting me stick my panels in her living room is about the best can expect these days!

I think that's the first acoustic-treatment-related euphemism I've ever heard! 

14 hours ago, Jus Lukin said:

As for the dampening of the lows, would this require any tuning, as in a Helmholtz type thing, or can it be said that the addition panel will fairly broadly assist in controlling that low energy?

Yes, membrane traps certainly can require tuning, because the thickness of the membrane will determine the target frequency (the peak of the 'bell curve', if you think of it like an EQ).

I've never built a membrane trap myself, but have read up on them whilst nerding around on the subject. I've double-checked in replying to your question, and contrary to my advice above (which I'll edit to correct), the membrane should be between 4-6mm thick for what you're aiming to achieve (not <2mm as I'd originally suggested). For example: 6mm plywood will target ~90Hz. The membrane needs to be either:

• Installed fairly loosely on the front of the panel (behind the fabric), so that it can move back and forth like a piston. I'd recommend a minimum number of panels pins, trying to avoid hammering them all the way in.
• Perforated - e.g. peg board - whereby the perforations help the membrane to flex.

That said, the BBC used to use hardboard without holes as a damped membrane on their Modular LF Absorbers, so there appears to be several ways to approach it.

My own choice would be to use a sheet of peg board, fitted to the front of the trap (behind the fabric). I'm fairly sure that peg board comes in either 3.5mm or 6mm thickness, either of which would be suitable.

14 hours ago, Jus Lukin said:

I'm thinking I'll be OK here- I'll essentially be looking to cover 1.2m x 2.4m of wall with the 2" panels, leaving the ceiling and two walls plain, and one wall with two big windows with thin curtains. I may look into putting half the panels on the rear wall; I could potentially make those 4", and aesthetics would mean using a material which isn't so acoustically transparent and therefore more reflective.

Thicker panels on the rear wall is definitely a good idea, if space allows. You otherwise won't suffer any over-damping with the coverage of 2" panels that you mention. The window is essentially a 'free' bass trap.

14 hours ago, Jus Lukin said:

Initially I was looking at Rockwool RW3 (which may have changed it's name now) at 60kg/m3. The easiest to get hold of seems to be the Rockwool Sound Insulation Board which is surprisingly hard to find proper specs for, but I think it may be the same as the RW45 at 45kg. I'll have another check for availability of that RW3...

RW3 would be a good choice for the 2" and 4" panels. RW45 would also be ok, but you don't want to go any less dense than 45kg/m3 at those thicknesses.

Edited April 23, 2018 by Skol303

[Jus Lukin]

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Edited March 1, 2022 by Jus Lukin

[Skol303]

On 23/04/2018 at 13:02, Jus Lukin said:

I've been amazed at how hard it is to find proper details on insulation products, and more so how awkward they are to actually buy.

Yep, I share your pain! I've spent literally hours trawling online trying to find data on the density, flow resistivity, etc, of certain products to no avail.

Best resource I've found is the page on Bob Golds' website here:

https://www.bobgolds.com/AbsorptionCoefficients.htm

With some 'artistic licence' you can find equivalent products and extrapolate approximate data. Worth a look.

[51m0n]

If thete is one organisation you can trust to give you access to decades of their research ibto acoustic designs in studios its the BBC:-

http://www.bbc.co.uk/rd/search?query=Acoustic&submit=

Enjoy!!!

[Jus Lukin]

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Edited March 1, 2022 by Jus Lukin