DIY Acoustic Panels

[Dave Vader]

Are my rolls of carpet underlay in the corners just taking up space then?

Or do they make an appreciable difference in your opinion?

I'm deaf as a post and hardly ever record anymore but would like the space back for bits of tat if they do nothing.

[Skol303]

2 hours ago, SH73 said:

Thanks for your in depth reply. This sounds quite complex.  I've been mixing and recording with headphones and my hearing now suffers. I'll  give acoustic panels a go and see how I get on.Thanks  again.

Acoustics can be a very complicated topic... as I've discovered for myself  ...but the basics are easy enough, especially if you stick to the simpler mineral wool panels: in which case, more is always better!

[Skol303]

2 hours ago, Dave Vader said:

Are my rolls of carpet underlay in the corners just taking up space then?

Hi Dave, sorry to say that rolls of carpet underlay won't do much for room acoustics.

Traditional 'bass traps' work by being filled with mineral wool - the tiny fibres of which vibrate when sound waves hit them and in doing so convert some of the sound energy into heat. The fibres in carpet underlay will be far too heavy and/or dense to function in this way (in any practical sense). They'll dampen some of the mid-to-high frequencies, which are affected by most fabrics, even curtains. But the bass frequencies will just pass right through unhindered - and without any significant amount of sound energy being converted into heat along the way.

So yeah. You're probably losing out on frequencies you want to hear, and doing feck all to hinder those you have too much of. Ergo, ditch the underlay 

PS: you could just stack some plastic-wrapped bails of mineral wool in the corners instead. That's about as basic as it gets, but it would be a helluva lot more effective.

Edited March 12, 2018 by Skol303

[Dave Vader]

No Skol, this is good news. They are in the way, and chucking a blanket over the stack of guitar cases at the back of the room made more difference then they did.

Skip time...

[Skol303]

^ Glad to be of service 

[DaveGillespie]

This is great stuff, most tutorials I've seen have been using materials only available in America.  A few of questions:

1.  Did you use the Dritherm 75 or Dritherm 100 (these are both what I've seen available in B&Q)?

2.  How many traps did you get out of a pack of slabs?

3. For the smaller trap there, did you cut the slabs into very small pieces or big flat panels the size of the largest face of the panel?

4.  What sort of difference did you notice in the room without making measurements?

5.  I'd mainly be treating a room for tracking.  I take it this sort of treatment would be appropriate, maybe along with some blanketing to tame some high reflection?  

[Skol303]

3 hours ago, DaveGillespie said:

1.  Did you use the Dritherm 75 or Dritherm 100 (these are both what I've seen available in B&Q)?

I used Dritherm panels at 100mm thickness for convenience: the reason being that the two panels shown in the example above are both 200mm thick.

Note that you want to use low density fibre for panels at this thickness (200mm or deeper) and higher density fibre for thinner panels around 4"/100mm (density of 48kg/m3 is what commercial companies mostly use for 100mm panels). And example product would be Knauf RS60, which is annoyingly difficult to buy in small batches!

3 hours ago, DaveGillespie said:

2.  How many traps did you get out of a pack of slabs?

This obviously depends on the size of traps you are building. In this instance I only needed to build 4 traps in total, so had plenty of fibre to spare. As an example you could get 4 panels measuring 1200 x 445 x 200mm from a standard pack of Dritherm 37 (which contains 8 slabs at 100mm thickness).

3 hours ago, DaveGillespie said:

3. For the smaller trap there, did you cut the slabs into very small pieces or big flat panels the size of the largest face of the panel?

I tend to cut the slabs to the same dimensions as the panel itself.

For larger/deeper traps (e.g. front/rear wall soffit style bass traps), I'd recommend cutting the fibre into smaller sections and stacking it layer upon layer horizontally, rather than having the fibre sheets standing vertically. This will help to prevent the lower density fibre from sagging.

3 hours ago, DaveGillespie said:

4.  What sort of difference did you notice in the room without making measurements? 

Less echo and a slight 'tightening' in the bass response from my speakers. More level/volume of bass notes that I was previously struggling to hear due to room modes (phase cancellations caused by boundary reflections). Perhaps also better stereo field - I know that's certainly true from measuring, but I think it is also perceptible by ear. Hard to say as it's obviously not possible to switch the acoustic panels "on/off" and hear an immediate comparison. Hence measurements, if possible, are always recommended if you want to really test the outcome.

Two simple methods you can try are:

1. The clap test. Clap your hands and listen to the echo. Does it 'ring out', or does the sound tail off more quickly? Does it sound as though the clap is coming from several places at once, or does it sound more localised at your hands? You'd expect to hear the latter in both cases when acoustic treatment is applied.
2. Sing a low note. The lowest you can manage; your best Barry White impression. Same principle as above... but specifically, listen to how quickly the note tails off once you stop singing it. If you can still hear it ringing for what seems like a few seconds, you probably need more bass traps.

The gist of this is that what really matters are the decay times, rather than the frequency response of your room per se. People get hung up on wanting a flat frequency response, but what's more important for acoustic clarity are even decay times across the frequency range, from highs to lows.

3 hours ago, DaveGillespie said:

5.  I'd mainly be treating a room for tracking.  I take it this sort of treatment would be appropriate, maybe along with some blanketing to tame some high reflection?  

Yes, perfectly suitable for tracking rooms.

Things to bear in mind:

• Fibre-filled panels are broadband absorbers, meaning they reduce sound energy across the frequency range. And the deeper/thicker the panels, the more low frequency energy they will absorb. This also means that if you install too many thin panels (and by that I mean 2-4" thick), you'll end up disproportionately affecting the mid and high frequencies: they'll be reduced, but the lower frequencies will remain largely unaffected. This can result in the opposite of what you're aiming to achieve - i.e. a room with too much low frequency energy in comparison to mid and high frequencies, resulting in 'boominess'. So when building bass traps, go large and go deep  Like, 24" deep if space allows.
• Don't 'over-do it' in a tracking room: you want to keep at least some echo, otherwise your recordings may sound a little dead. But this is all dependent on the size of your room... any space less that 1500 sq ft in volume is going to have problems, and that applies to pretty much every domestic room, unless you happen to be The Windsors. Start with some panels and build up incrementally, listening (and ideally testing/measuring) after each batch is installed.
• Blankets are fine for helping to reduce high frequencies, but again, don't over-do it. The classic 'home studio' with carpets on the walls (and perhaps even egg boxes!) results in a space that will sound boxy and boomy. But sure, some heavy curtains and/or rugs covering bare walls prone to echo is generally a good idea.

Edited April 13, 2018 by Skol303

[Bassalarky]

Thought I'd add this in case anyone is interested in some of the technical side....

If you want to know at which frequency your room resonates:

f - 2l/c

where 'f' is the frequency

'2l' is twice the length (distance between parallel walls)

'c' is the speed of sound (say 320 metres per second - depending on altitude)

If use use this simple equation for each dimension - length, width and height - of your room, you can get a quick and simple guide to the troublesome resonant frequencies - a big issue in turning a domestic house-sized, cuboid room into a studio.  This can help you choose acoustic materials that will be most effective.

I feel that I should mention that egg-boxes have no BS fire-retardant rating and are therefore considered by insurance companies to be a fire hazard!

Sorry if it sounds a bit science-lecture - it can be fun experimenting.

 

[Dad3353]

26 minutes ago, Skol303 said:

• ...any space less that 1500 sq ft in volume ...

[Pedantry] This should be 1500 cu ft, Shirley..? [/Pedantry]

And yes, a 'dead' room for recording is rarely the optimum, in my experience. Having a tailored environment for listening (the control cabin, or mixing room...) is fine, but for recording, most 'ordinary' rooms will have spots for mic placing as good as anywhere. The placing , direction and beam pattern of the mic are the key factors, more than the room's treatment, I'd say. A decent engi will listen in order to find and use these 'sweet spots'. There are obvious extremes to avoid, of course, but an overly neutral recording room is not the most pleasant one to work in. Different instruments (and voices...) need different ambiances from the room.
Just my tuppence-worth.

[51m0n]

Generally speaking the best bang for the buck and bang for the volume required of bass trapping is achieved with a corner design absorber known as a 'superchunk'.

A good example for how to build Superchunks is here:-

http://forum.studiotips.com/viewtopic.php?t=535

Whenever dealing with bass absorption the place to put your absorption material for maximum efficacy is where walls meet ( you can check this out by playing some good bassy music in your room and walking up to the corner where two walls meet, you get a significant boost in bass, soaking this up here gives you more bang for the buck). This is even more apparent where three walls meet. However this also applies where floors meet walls and walls meet ceilings, effectively it is possible to super chunk every internal edge inside the room, giving a maximum of 12 places to put bass traps for absolutely maximum efficiency!

For more general absorption the  most important place to put it is where the sound from your speakers is bouncing off the wall and then coming back to your ears in your central listening position. You can find this with the help of a mirror and a friend. You sit in the listening position, they move the mirror along the wall, when you see you speaker in the mirror, thats where the absorption panel goes, same for the neares and furthest speakers, in many cases an absorber can cover both speakers at once on a wall.

After that A good idea is the wall behind the speakers for a couple of panels, again you can use a mirror to locate the best places for this absorption.

Points to note, too much absorption is not great, the room will go 'dead', at this point you need to consider adding diffusion or a sheet of foil or plastic over the front face of the absorber behind the fabric and in front of the rockwool (or equivalent), or to use plywood with strips cut out of it to cause diffraction/reflection over 500Hz.  Obviously the precise nature of the pattern cut into the board has a massive affect, plenty of examples on gearslutz in their acoustics forum.

You often see diffusers placed on the wall behind the listeing area (the 'backwall' of the room). There are extremely specific designs required for diffusers, they generally only work for higher frequencies, and take up a lot of space if you want to get deeper frequencies affected (up to 6ft deep is possible for a diffuser wall, the diffuser room at Nashville's Blackbird Studios being the best example of this I know of:- https://www.blackbirdstudio.com/studio-c  Note George Massenburg, who designed this room, is a genius, he invented parameteric eqs!)

This will breath life into the room, massively improving it as a space for mixing and tracking and mastering.

Panel absorption across a corner is way better than nothing, but it isnt as good as a well built superchunk. Panel positions within the room are very important to get the best of them.

 

 

[Skol303]

^ Great input in the posts above, thanks guys!

Edited April 13, 2018 by Skol303

[51m0n]

50 minutes ago, Bassalarky said:

Thought I'd add this in case anyone is interested in some of the technical side....

If you want to know at which frequency your room resonates:

f - 2l/c

where 'f' is the frequency

'2l' is twice the length (distance between parallel walls)

'c' is the speed of sound (say 320 metres per second - depending on altitude)

If use use this simple equation for each dimension - length, width and height - of your room, you can get a quick and simple guide to the troublesome resonant frequencies - a big issue in turning a domestic house-sized, cuboid room into a studio.  This can help you choose acoustic materials that will be most effective.

I feel that I should mention that egg-boxes have no BS fire-retardant rating and are therefore considered by insurance companies to be a fire hazard!

Sorry if it sounds a bit science-lecture - it can be fun experimenting.

 

Particular issues lie wherever you have two dimensions or more as multiples of each other, ohhhhh boy inherent unsolvable badness incoming!

I've built non parallel internal rooms to get out of this whole before now for serious studio builds, yes its massive ballache, but you can't beat it in the end.....

[Skol303]

While we're on the subject, here are to links to online acoustic calculators that I fine very useful. I posted one of these earlier in the thread, but here they all are for convenience:

Room Mode Calculator #1: this is by far my favourite; a really well-presented room mode calculator that clearly shows the likely problems based on room dimensions. Includes some well-written notes about room modes here.

Room Mode cCalculator #2: this one is hosted by Bob Golds, who's something of a legend in the world of acoustics. Again, shows the likely problems in a room based on its dimensions

Both of these calculators also include some useful (though somewhat technical) numbers such as:

• Absorption needed to achieve RT60 (the time taken for the sound to decay by 60 dB when the source is removed), based on industry standard recommendations for professional control rooms. Gives an approximation the volume and surface area of acoustic treatment needed to achieve this - prepare to have your jaw drop and your room shrink considerably!
• Shroeder frequency: in simple terms, the frequency below which you should focus on absorbing bass energy, and above which you should focus on tackling mid-high frequency reflections.

Porous absorption calculator: for approximating how effective your DIY panels might be. Flow resistivity numbers can be hard to come by, but there's a handy thread on Gearslutz that has lists of some common materials to help you get started.

As a very rough guide (take with a pinch of salt as I could be wrong!) you can try using the following Flow Resistivity figures for the Knauf fibre I've mentioned in this thread:

• Knauf Dritherm 37 (low density 15kg/m3): 5000 Pa.s/m2
• Knauf RS60 Slab (density 48kg/m3): 12000 Pa.s/m2

Edited April 13, 2018 by Skol303

[Skol303]

1 hour ago, 51m0n said:

A good idea is the wall behind the speakers for a couple of panels, again you can use a mirror to locate the best places for this absorption.

Better still, push your speakers right up against the front wall - literally within a few millimetres if possible - and forego any panels behind the speakers altogether (they'll need to be very thick here anyway to have any useful effect).

This will help to avoid the classic SBIR dip of -20/30db (or more) between 60-150Hz. The trade off is that you'll get a big boost in the low end due to wall proximity - which might not actually be a bad thing if your speakers are small - but this can at least be dealt with by room correction software (EQ), whereas the SBIR dip caused by having your speakers further away from the wall can't.

This thinking runs counter-intuitive to what many speaker manufacturers recommend in terms of optimum distance from nearby walls, but some companies like Genelec are starting to lead the way on this - some great advice from them on page 2 of this PDF file.

EDIT to say that the minimum rear distance they recommend of 5cm is for rear-ported speaker cabinets. Even so, you can still push closer than that. I reduced the SBIR null in my own room by nearly +12db using this method alone!

Edited April 13, 2018 by Skol303

[Bassalarky]

1 hour ago, Skol303 said:

While we're on the subject, here are to links to online acoustic calculators that I fine very useful. I posted one of these earlier in the thread, but here they all are for convenience:

Room Mode Calculator #1: this is by far my favourite; a really well-presented room mode calculator that clearly shows the likely problems based on room dimensions. Includes some well-written notes about room modes here.

Room Mode cCalculator #2: this one is hosted by Bob Golds, who's something of a legend in the world of acoustics. Again, shows the likely problems in a room based on its dimensions

Both of these calculators also include some useful (though somewhat technical) numbers such as:

• Absorption needed to achieve RT60 (the time taken for the sound to decay by 60 dB when the source is removed), based on industry standard recommendations for professional control rooms. Gives an approximation the volume and surface area of acoustic treatment needed to achieve this - prepare to have your jaw drop and your room shrink considerably!
• Shroeder frequency: in simple terms, the frequency below which you should focus on absorbing bass energy, and above which you should focus on tackling mid-high frequency reflections.

Porous absorption calculator: for approximating how effective your DIY panels might be. Flow resistivity numbers can be hard to come by, but there's a handy thread on Gearslutz that has lists of some common materials to help you get started.

As a very rough guide (take with a pinch of salt as I could be wrong!) you can try using the following Flow Resistivity figures for the Knauf fibre I've mentioned in this thread:

• Knauf Dritherm 37 (low density 15kg/m3): 5000 Pa.s/m2
• Knauf RS60 Slab (density 48kg/m3): 12000 Pa.s/m2

Very convenient, thanks!

[51m0n]

6 hours ago, Skol303 said:

Better still, push your speakers right up against the front wall - literally within a few millimetres if possible - and forego any panels behind the speakers altogether (they'll need to be very thick here anyway to have any useful effect).

This will help to avoid the classic SBIR dip of -20/30db (or more) between 60-150Hz. The trade off is that you'll get a big boost in the low end due to wall proximity - which might not actually be a bad thing if your speakers are small - but this can at least be dealt with by room correction software (EQ), whereas the SBIR dip caused by having your speakers further away from the wall can't.

This thinking runs counter-intuitive to what many speaker manufacturers recommend in terms of optimum distance from nearby walls, but some companies like Genelec are starting to lead the way on this - some great advice from them on page 2 of this PDF file.

EDIT to say that the minimum rear distance they recommend of 5cm is for rear-ported speaker cabinets. Even so, you can still push closer than that. I reduced the SBIR null in my own room by nearly +12db using this method alone!

Now that is fascinating...

My main speakers are over 14" deep.

They are therefore placed about as close to the wall as I can get them, about 3" away.

Never really noticed a big dip in the bass, this probably has helped 😆

Worse than that dip in many situations was the problem of putting your mains on the back edge of your mixing desk. 

The reflections off the desk would comb filter with the direct sound to your ear blowing not just frequency response but stereo image as well!

[Skol303]

21 hours ago, 51m0n said:

My main speakers are over 14" deep.

Mein Gott! What speakers are you using, they sound immense!?

21 hours ago, 51m0n said:

The reflections off the desk would comb filter with the direct sound to your ear blowing not just frequency response but stereo image as well!

Definitely. I've experienced this in my own room. I use a large wooden desk (I like to have lots of stuff within arms reach) and found that it was causing some nasty comb filtering. So I made some wooden wedges to sit under the desk and angle it forwards by about 5 degrees (apparently 6 degrees is ideal). Made a big difference.

A smaller desk would of course be ideal, but then you risk suffering a low end dip due the floor reflection.

Everything with acoustics always seems to involve a compromise

Edited April 14, 2018 by Skol303

[51m0n]

2 hours ago, Skol303 said:

Mein Gott! What speakers are you using, they sound immense!?

Heh! My mains are floorstanding transmission lines, they are indeed immense  and also very very old, but I know them ridiculously well, and as a reference for deep bass, and I mean close to 20Hz if you need it, as well as for reverb and other spacial fx levels they are fantastic for me. One day I will upgrade them, I love transmission lines though and I have always wanted a set of PMCs but the 40k+ price is a bit of an issue

I tend to use a variety of tools when mixing and mastering, headphones are superb for setting up transients and compression, anything where real detailed listeing is required, the big mains are superb for balancing bass/mids and the aforementioned spacial fx, I like to use TV/ mobile phone/laptop speakers for checking and mid/top attack settings and that mixes/masters collapse to worst case scenario playback, and the car is great to make sure I've not over done the booooom

Its slow and time consuming to reference on this many systems, but its how I've worked for years, and the result tends to be mixes that translate across pretty much everything.

[lurksalot]

Ok , so having digested most of this thread  , I'm thinking I'm close to having a great sounding room , but do you think that the plaster on the walls need a treatment with a subtle warm buttermilk with a hint of magnolia calico or a harder apple white eggshell 

 

 

 

Taxi ......

[Skol303]

22 hours ago, lurksalot said:

...do you think that the plaster on the walls need a treatment with a subtle warm buttermilk with a hint of magnolia calico or a harder apple white eggshell 

Honestly mate, in the world of acoustics, no permutation is left unturned

...and so on another forum we have this thread:

Does the colour of the room effect the sound (reflextions)?

PS: the answer is no! FFS, no!

[Skol303]

On 4/14/2018 at 20:58, 51m0n said:

My mains are floorstanding transmission lines, they are indeed immense  and also very very old, but I know them ridiculously well, and as a reference for deep bass, and I mean close to 20Hz if you need it...

They sound awesome! No need for a sub when you have monitors like that

[Mornats]

9 minutes ago, Skol303 said:

Honestly mate, in the world of acoustics, no permutation is left unturned

...and so on another forum we have this thread:

Does the colour of the room effect the sound (reflextions)?

PS: the answer is no! FFS, no!

I liked the goose cotton talk in that thread. 

[51m0n]

2 hours ago, Skol303 said:

They sound awesome! No need for a sub when you have monitors like that

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?".

Give ne some mahoosive monitors every time 😆

[lurksalot]

2 hours ago, Skol303 said:

Honestly mate, in the world of acoustics, no permutation is left unturned

...and so on another forum we have this thread:

Does the colour of the room effect the sound (reflextions)?

PS: the answer is no! FFS, no!

quality link my sound guru 

 

its got got me thinking though , if I were to invest a touch into the wife's hobby , and invest in some Miele acoustic vacuum bags , would the room sound 'cleaner' 

[Skol303]

10 hours ago, lurksalot said:

its got got me thinking though , if I were to invest a touch into the wife's hobby , and invest in some Miele acoustic vacuum bags , would the room sound 'cleaner' 

In which case your wife may enjoy  reading this:

Numerical study of the movement of fine particle in sound wave field

And after you suggest that she reads it, you're welcome to sleep on my couch until things calm down, no problem

10 hours ago, 51m0n said:

I hate subs.

They are nightmarish to get right.

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!