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Skol303

DIY Acoustic Panels

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A thread for anyone wanting to DIY-build their own acoustic panels.

This method uses mineral wool (glass fibre) to convert low frequency sound energy to heat, thereby reducing the energy of sound waves and their reflection off the hard surfaces of your room. When sound waves encounter reflections it causes peaks ('boominess') and nulls (big dips) at certain frequencies, which can give a misleading interpretation of what you're hearing. This can make accurate mixing very difficult, which is why acoustic panels are recommended: because they help to give a more even and accurate frequency response, so that what you hear in the room is as close as possible to what's happening inside your software or mixing desk.

Before you read on, note that:

  1. In order of importance, acoustic treatment applies to mix rooms, recording rooms and practice rooms. In a practice room you can get away with the sound not being so accurate - it doesn't stop you from practising. In a mix room, if the sound is inaccurate then your mixes will be too (or you'll need to spend a lot of time referencing your mixes). A well-treated room also results in good quality recordings, but you might want to treat a recording room slightly differently to a mix room, ensuring the sound retains some reverberation and 'liveliness'. It's a big topic and too much to go into here! But suffice to say, think about what you want to achieve and read up on the subject a little before you dive in.
  2. Acoustic treatment is not the same as soundproofing. If you want to create a soundproof room, then you'll need to take a different approach.

Right, let's get started...

Tools and materials needed:

  • Stripwood for the panel frame (I like to use 20x20mm or thereabouts)
  • If you’re making a free-standing panel, you’ll also need planed timber for the panel base and ‘feet’
  • A vice, saw and tape measure for cutting the wood
  • Angle brackets (aka corner braces) for constructing the frame (a combination these and these work great).
  • Box of wood screws (I use 4 x 16mm)
  • An electric drill for drilling pilot holes for screws (to avoid wood from splitting)
  • Screwdriver
  • Panels pins and wood glue (neither are essential essential, but both useful for strengthening the frames). You’ll need a hammer for banging in the panel pins - or an exceptionally hard stare! ;)
  • Fabric dust sheet for panel inner fabric (not essential but useful)
  • Cheap ‘breathable’ fabric for rear of panel (I use cheap craft felt)
  • ‘Breathable’ acoustic fabric for main panel wrap (Camira Cara and Lucia fabrics are what’s used on most commercial panels, available here).
  • Mineral wool - use Knauf Earthwool Dritherm Cavity Slab (density ~15kg/m3) when building panels 8"/200mm or deeper; and use Knauf Earthwoold Building Slab (density ~48kg/m3) if building panels around 4"/100mm deep.
  • Gloves and mask (for use when cutting/handling mineral wool)
  • Staple gun and staples
  • Large pair of scissors
  • Jack chain and pliers
  • Pair of screw eyes per panel
  • Heavy duty picture hangers (if you want to mount your panel on the wall).

IMPORTANT note on fabrics: whatever fabric you use, it must be as 'acoustically-transparent' as possible. A simple way to test this is to hold a piece of the fabric tight over your mouth and attempt to breathe! If you can breathe easily, the fabric is good to use. If you find yourself suffocating, it's not.

Finally, some notes on panel thickness:
In small rooms (and by that I mean nearly every UK household), you want to focus on treating the low frequencies and that means applying as much depth as possible. Aim for a minimum of 4” / 10cm thick panels, but ideally 8” or more: 25” or around 64cm is generally considered to be ideal, albeit a bit impractical in most homes. But the general rule is, don’t scrimp!

If your panels are too thin, they’ll become what are known as ‘broadband absorbers’ (affecting just the mid- and high-frequencies) rather than ‘bass traps’ (affecting below 100Hz or so). You’ll almost certainly need some broadband absorbers (e.g. left/right and above your mixing position), but bass traps are what you want to focus on first.

Here’s a very approximate guide to how thick your panels need to be in order to treat certain frequencies:

  • 25” effective down to ~30Hz
  • 16” effective down to ~40Hz
  • 8” effective down to ~65Hz
  • 4” effective down to ~100Hz

*By effective I mean it will have some affect on the sound, not that it will absorb all of the sound at that frequency. As always, "more is more" when it comes to acoustic treatment!

Edited by Skol303

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STEP 1: Construct the frames, fitting the lengths of stripwood together using angle brackets. I find it helps to secure the joints using wood glue and panel pins (being careful not to split the wood when hammering in the pins). Add a length of wood as a support along the rear and bottom of the frame: this will help to hold the mineral wool in place and prevent sagging.

Larger panels may also need additional support struts on the sides and front - for example, the upright panel frame in the photo (right-hand side), which also has a wooden base for attaching 'feet' later on (you don't need a wooden base on panels that are being hung form the wall or ceiling).

Don't add a plywood or other solid backing to your acoustic panel. You want the back to be 'open' so that the sound can pass through it.

1.JPG

Edited by Skol303

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STEP 2 (optional): Cover the panels in dust sheet fabric using a staple gun. You don't have to do this, but I find it helpful for two reasons 1) It keeps the mineral wool in place; and 2) It provides an extra barrier to prevent mineral wool fibres from leaking into your room. Leave a flap on the front of the panel for inserting the mineral wool.

 

2.JPG

3.JPG

Edited by Skol303

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STEP 3: Fill the frame with mineral wool. Cut the mineral wool slabs to size using a large pair of scissors (wear gloves and a mask whilst doing this as the fibres can cause irritation). I like to cut the slabs to the exact same size as the frames so they're a sung fit. Be careful not to squash the mineral wool when installing it, as that will impede how well it functions as a sound absorber.

Be sure to choose the right density of fibre depending on the depth/thickness of the panel you are building. As a general rule:

4.jpg

Edited by Skol303

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STEP 4: Wrap the panel in a final layer of fabric. I like to use cheap craft felt for the rear of the panel and a better quality fabric for the front a sides (but you can just as easily wrap the whole panel in one fabric). Be sure to pull the fabric taut and hold it in place with a generous amount of staples; this will help to prevent the panel from sagging over the long-term.

 

5.JPG

 

6.JPG

7.JPG

Edited by Skol303

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STEP 5: Finishing by adding fittings. You can install your panels however you like; my own preference is to use a length of jack chain on the back of the panel, held in place with screw eyes, and then mount the panel on the wall using a heavy duty picture hook. Very quick and easy. A pair of rubber studs/ aka bumpers can also be screwed on to the bottom rear edge of the panel, to help it hang vertical.

If it's a free-standing panel then two strips of wood, screwed to the bottom, make for a simple pair of feet. You might also want to fix a couple of handles to the sides to make it easy to move around.

Et voila! Job done. Put the kettle on and break out that Kit Kat :) 

Any questions, just ask in the thread below and I'll happily answer if I can.

Edited by Skol303

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PS: this is just one method of making acoustic panels. More complex approaches, such as Helmholtz or resonator traps, can lead to even better results - including membrane panels that are 'tuned' to focus on specific frequencies.

These are more tricky to DIY at home, but here's a link for anyone interested:

Helmholtz bass traps

Edited by Skol303

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And finally, some notes on where to put acoustic panels:

Generally speaking, you want to put thick bass traps in the front and rear corners of your room and thinner broadband absorbers to the left/right and above your mixing position.

Go crazy on the rear wall of your room - this is where you’re likely to need the most/thickest panels to help prevent rear-wall reflections (often the chief cause of nasty ‘nulls’/ dips in low frequencies).

If you run out of space on the rear wall, consider building a freestanding panel (or several!) to be placed behind your listening position. Nothing is overkill when treating a small room...!

Here’s a diagram I borrowed from elsewhere, showing the typical locations for acoustic panels - image courtesy of GIK Acoustics.

874F0051-08C6-49B6-862B-C2D9995273B3.jpeg

Edited by Skol303

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^ You’re very welcome!

Hope it proves useful. It’s all secondhand advice I’ve gleaned from other forums and by reading up on the subject. Thought it might save others time if I dump what I’ve learned here :) 

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@Skol303, just a quick and dirty question!

I'm going to be building some panels for my living room, just as much as I can get away with under the circumstances. It will consist of a couple of panels to treat basic flutter and get as low as I can- probably a couple of inches of broadband rockwool covering the 'front' wall from the perspective of my desk and monitors, and 2-4" on the back wall. However, I can also squeeze a bass trap in the tri-corner above a book shelf to my right.

Now, I've done the research and it seems fine, but can I pick your brain on this- I have a perfect sized cardboard box in which to house the insulation. A bass trap itself doesn't need to be porous to work, does it? My main target is a bump around 150hz, which won't be stopped by the walls of the box, so the body of fibre behind should still be effective as a trap, shouldn't it? The box itself will be wrapped in a thick padded bath towel for aesthetics and some HF absorption, so reflection shouldn't be a problem.

For a Heath Robinson, do it in 5 mins trap, laying some loft insulation in the box up in the corner should still flatten the room response a little shouldn't it? It seems to have helped even with the empty box up there, but that could be placebo!

 

Thanks, Andy

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That's a good question, just how rough 'n' ready can you get with bass traps and still have them work?

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Posted (edited)
20 hours ago, Jus Lukin said:

It will consist of a couple of panels to treat basic flutter and get as low as I can- probably a couple of inches of broadband rockwool covering the 'front' wall from the perspective of my desk and monitors, and 2-4" on the back wall. However, I can also squeeze a bass trap in the tri-corner above a book shelf to my right.

2" won't help at all with the low end, but if that's all you're able to install then go for it - every little helps :) 

4" thick panels are generally considered to be the minimum in terms of having any measurable effect on the low end. They work even better if you can mount them a further 4" or so off the wall (i.e. with an air gap behind the panel). Free acoustic treatment right there!

20 hours ago, Jus Lukin said:

I have a perfect sized cardboard box in which to house the insulation. A bass trap itself doesn't need to be porous to work, does it? My main target is a bump around 150hz, which won't be stopped by the walls of the box, so the body of fibre behind should still be effective as a trap, shouldn't it?

You're absolutely right; the walls the cardboard box won't inhibit the low frequencies at all, so you can happily build bass traps using cardboard boxes. I've seen a photo of a home studio in New York that did just that - literally stacks of packing boxes stuffed with mineral wool.

In fact, some bass trap designs include a hard 'membrane' - usually a thin sheet of plywood, 1-2mm - which vibrates at very low frequencies, helping the bass trap to be effective down to 30Hz or so. But they're more tricky to DIY.

However... bear in mind that hard surfaces (even cardboard) will reflect higher frequencies and this can cause all sorts of problematic phasing issues if you're unlucky - e.g. you might improve the low end a little, but end up with new dips in the mid-high frequencies. But in home studios, that's normally a trade-off work taking as it's the low end that always needs the most work.

So in short: yes, go for it! The cardboard box approach is certainly viable.

In terms of results, in my own room I've recently noticed an 'improvement' of around 3-5db from installing some additional bass traps on my back wall (20cm thick): that is, the null in my low end respond is now 3-5db less deep. That's not a big difference, but it's noticeable by ear. And that's pretty much the amount of benefit you can expect to achieve from 20cm thick traps.

Far more dramatic has been changes to my room layout. By adjusting my listening position, pushing my monitors up against the front wall, tilting my desk forwards, etc, I've gained an improvement of around 10-12db. Much more impactful and it cost me nothing; just some time to move things around, test/listen and adjust.

So make sure you get the basics right first: listening position, speaker placement, etc. Then use acoustic treatment to gain those extra db that can make all the difference.

Edit to say that it might help if you leave the side of the cardboard box facing the room open - i.e. just covered in fabric, no cardboard. This will help the bass trap to absorb frequencies across the full spectrum more evenly, so you're less likely to cause weird phasing issues in the mid-high end. Just an idea.

Edited by Skol303

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3 hours ago, Skol303 said:

This guy wins the prize for the laziest bass traps ever! :D

 

unnamed-1.jpg

Don't laugh, I seriously considered doing that myself!

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Joking aside, you could use unopened bales of mineral wool as bass traps.

They might not be as effective as when opened, as the wool would be more compressed and so the fibres might not be as efficient at converting sound energy to heat. But they would certainly do something.

...although you might have some explaining to do whenever people come to visit :) 

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It probably wouldn't be the weirdest thing I'd have to explain about my place to visitors!

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Thanks Skol, good to know the basic theory works!

The new panels will be fairly limited in their range, but it will cetainly be an improvement over the patches of acoustic foam I have dotted about now!

Once I have the acoustically transparent fabric I'll probably build a proper broadband trap, but for the time being I'll start experimenting with the box solution. I won't have the facility to check whether the box will be acting as a resonant absorber, but it will be interesting to pop it in and out of place and check the effects by ear.

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^ Good stuff! Let us know how you get on.

PS: if you're planning on kitting your room out with acoustic treatment over time, then it might be worth investing in an omnidirectional mic and a copy of Fuzzmeasure (or REW... which is free but not quite so easy to use). Very useful for identifying exactly which frequencies need tackling, reflection points, etc.

That said, I went along way myself without taking any acoustic measurements. So it's not essential, but something to consider.

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Very useful online tool I found recently, which can be used to quickly calculate the likely frequency response from different acoustic materials (at different thicknesses):

http://www.acousticmodelling.com/porous.php

The only snag is you need to know the ‘Gas Flow Resistivity’ of the material, but you can often dig out these numbers by searching the manufacturer’s product specifications.

I’m trying to find the figure for the Knauf Earthwool Dritherm slab mentioned above in this thread… can’t find the exact number but have found it quoted as being around 10,000 Pa.s/m2.

So anyone interested can use that figure in the calculator, type in the thickness of the acoustic panel you want to make and get an approximate graph of the absorption coefficient at different frequencies (the closer the absorption coefficient is to 1, the more sound is being absorbed).

Useful if you want to check, for example, whether your panels are really going to function as bass traps or broadband absorbers.

Honestly, I'm much more fun at dinner parties than you might imagine...! :D 

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Great post @Skol303 

I'll  be hopefully getting a music room, but these traps will make the room smaller.

As you pointed out to Jus lukin, 2" thickness wouldn't help with the low end but it's  better than nothing. 

What else would you recommend. Would  egg boxes be of any use as a starring point? Thanks.

The room will have laminate floor and Persian style carpet in the middle. Two walls joining  together one window each.

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Posted (edited)
5 hours ago, SH73 said:

What else would you recommend. Would  egg boxes be of any use as a starring point? Thanks.

The room will have laminate floor and Persian style carpet in the middle. Two walls joining  together one window each.

Forget egg boxes and also forget about 'acoustic foam' (in case you were considering using it). Both are next to useless at dealing with bass frequencies, which is where 99% of your problems will be. Too many egg crates and/or foam will in fact make your room sound very 'boxy' (dull mids/highs), so definitely avoid.

Persian carpet on the floor is good. Windows behave a bit like bass traps... they're 'acoustically floppy' (!) and will let most of the low end pass right through (whilst reflecting some of the highs back into the room), so they can in fact be advantageous.

If the room is small and anywhere near square-shape then you're in for acoustic problems, there's no escaping that unfortunately. In terms of solutions, it pretty much always boils down to one or a combination the following:

  1. Panels stuffed with mineral wool (aka velocity or absorber panels) and the bigger/thicker the better when trying to flatten the low end. This will mean sacrificing some of the space in your room: you need to be aiming for at least 20% coverage of the room surface area to get real benefit (my own room has 37% coverage, not including the floor, and it resembles a padded cell).
  2. Helmholtz (aka tuned membrane) panels that are designed to vibrate at specific frequency ranges and are great at targeting low end problems. They can be much smaller than mineral wool panels but are difficult to DIY and relatively expensive to purchase. Examples here.
  3. Multiple subwoofers! yes, that might sound counter-intuitive when trying to fix bass problems, but 2+ subs can be set up to create an exceptionally flat frequency response in the low end - and it's a trick that works in pretty much any room. Brief explanation here from SoundOnSound. This approach requires some technical understanding and/or trial and error - not to mention cost - but it's proven to work well.

...and that's pretty much it in terms of options.

Most people (myself included) plump for option 1: mineral wool panels, because it's the most cost-effective, easy to DIY and can be installed to a large extent based guesswork, rather than needing to take acoustic measurements (although measurements are always recommended). DIY is the cheapest option. If you want to buy new, a budget of around £1000 for a domestic room will cover all of the basic essentials. I've done both - bought some brand new, studied their construction and then DIY'd my own equivalents. And I'm quite crap at DIY.

Hope that helps!

PS: there is in fact a fourth option...

Use good pair of headphones. Some rooms simply can't be acoustically treated to any practical level - e.g. if the room is a small square box, or if the acoustic treatment would get in the way of other uses the room might have... like functioning as a toilet! :D In which case, forget acoustic treatment and invest in a good pair of mixing headphones - e.g. Sennheiser HD 600 or 650 - and just do whatever treatment you can to make your monitor speakers more usable. I mixed for several years on headphones alone; it worked for me.

Edited by Skol303

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18 minutes ago, Skol303 said:

Forget egg boxes and also forget about 'acoustic foam' (in case you were considering using it). Both are next to useless at dealing with bass frequencies, which is where 99% of your problems will be. Too many egg crates and/or foam will in fact make your room sound very 'boxy' (dull mids/highs), so definitely avoid.

Persian carpet on the floor is good. Windows behave a bit like bass traps... they're 'acoustically floppy' (!) and will let most of the low end pass right through (whilst reflecting some of the highs back into the room), so they can in fact be advantageous.

If the room is small and anywhere near square-shape then you're in for acoustic problems, there's no escaping that unfortunately. In terms of solutions, it pretty much always boils down to one or a combination the following:

  1. Panels stuffed with mineral wool (aka velocity or absorber panels) and the bigger/thicker the better when trying to flatten the low end. This will mean sacrificing some of the space in your room: you need to be aiming for at least 20% coverage of the room surface area to get real benefit (my own room has 37% coverage, not including the floor, and it resembles a padded cell).
  2. Helmholtz (aka tuned membrane) panels that are designed to vibrate at specific frequency ranges and are great at targeting low end problems. They can be much smaller than mineral wool panels but are difficult to DIY and relatively expensive to purchase. Examples here.
  3. Multiple subwoofers! yes, that might sound counter-intuitive when trying to fix bass problems, but 2+ subs can be set up to create an exceptionally flat frequency response in the low end - and it's a trick that works in pretty much any room. Brief explanation here from SoundOnSound. This approach requires some technical understanding and/or trial and error - not to mention cost - but it's proven to work well.

...and that's pretty much it in terms of options.

Most people (myself included) plump for option 1: mineral wool panels, because it's the most cost-effective, easy to DIY and can be installed to a large extent based guesswork, rather than needing to take acoustic measurements (although measurements are always recommended). DIY is the cheapest option. If you want to buy new, a budget of around £1000 for a domestic room will cover all of the basic essentials. I've done both - bought some brand new, studied their construction and then DIY'd my own equivalents. And I'm quite crap at DIY.

Hope that helps!

PS: there is in fact a fourth option...

Use good pair of headphones. Some rooms simply can't be acoustically treated to any practical level - e.g. if the room is a small square box, or if the acoustic treatment would get in the way of other uses the room might have... like functioning as a toilet! :D In which case, forget acoustic treatment and invest in a good pair of mixing headphones - e.g. Sennheiser HD 600 or 650 - and just do whatever treatment you can to make your monitor speakers more usable. I mixed for several years on headphones alone; it worked for me.

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.

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