The blog is being migrated and merged with multiple Imphenzia blogs so the format and content will be inconsistent for a while.

Sound Recording Room - Sound Absorption

It's been nearly a year since I built my sound recording room / foley room in the garage. Now that I've launched the new web site, the USFX 1.3 update, and 4 sound design packs, I finally found time to edit some video footage I shot during the room build process to compare the effectiveness of different steps in treating the room to absorb sounds and make it as close to a dead room as I could.

There is a short version of the video which just contains the hand clap comparison for each step.

If you want more detail of what, how, and why - check out the full video below. I hope you find it useful if you are considering building a sound recording or foley room. If you are just here for curiosity of what goes into recording dry sounds I hope you find it interesting. Give me a shout if you have any questions =)

Want to find out more? I also posted "making of" blog posts for the build of the room:
Making of the Sound Recording Room Part 1
Making of the Sound Recording Room Part 2
Making of the Sound Recording Room Part 3

Video: Pitch Shifting and Microphone Specs

The other day I broke a laptop monitor in half and I recorded it using four very different microphones with different specifications. I recorded the sounds with a sampling rate of 192 kHz and loaded the sounds into Izotope RX5 to show the spectrogram and pitch down the sounds two octaves. This video demonstrates how different the sounds are when pitched down since some of the microphones capture audio well beyond what the human ear can hear - yet when you pitch the sound down those inaudible frequencies are brought into our range of hearing:

Microphones Used:
Sanken CO-100K (20 - 100'000 Hz)
Sennheiser MKH 8040 (30 - 50'000 Hz)
Rode NTG3 (40 - 20'000 Hz)
Schoeps CCM41 (40 - 20'000 Hz)

Sound Devices 788T

Software Used:
Izotope RX5

Making of the Sound Recording Room Part #3

It took me another month to complete the room, but I am pleased to say that now it's finally ready!

Sound Room

I'll break down the steps that followed from my last "making of" post. Basically, the room was structurally ready with all the walls, ceiling, and door so it was sound proofing and final touches that remained. I also spent went to the US for a 10-day trip with some friends which ate away some of my time... and funds...

Pre-insulationAt this stage, the sound is like an echo chamber. A rectangular room with flat plaster board surfaces and a hard floor. I also bought 10W LED-lights (750 lumen each) that I put up into the corners and I put some simple electrical wiring up. I ended up opting for normal extension leads because I want to be able to take the lights down and relocate them in the room if necessary. The reason I went for LED-lights are primarily because they are silent (no humming) and they don't generate much heat which benefits both the room temperature and also it won't heat up the metal of the light which in traditional lights have a tendency to start producing clicking sounds as the metal contracts/expands.

FoamA big 2 pallet shipping arrived from http://thomann.de. I ended up buying 40 of their 1x1m 80mm thick sound absorbing SA-P80 foam along with 16 large foam CBT-37 bass traps CBT-37 bass traps. For additional sound proofing I also got 10 Stairville Acoustic Curtains to line the interior walls with.

IMG_0026I used about 10 tubes of "Akrylfog" to seal any and all little corners where the plaster boards met the wood frame - not too sure that it was worth the time it took, but at least I know it's done and if it prevents even the slightest sound from entering / exiting the room I guess I'm happy with that =)

IMG_0032I moved on to put up the insulation in the room. Since I had spaced all the wood beams 60cm apart it fit perfectly with the standard size of the insulation slabs. I didn't go with rockwool because I didn't know where to get it or how much it would be, so I bought standard glass-based 120mm thick insulation called Space Slab (it said it had good acoustic and sound absorbing properties.) I really hate putting up insulation, especially in the ceiling. I had a mask to cover my mouth, a hoodie over my head, and goggles when working on the ceiling. Still, the fibers go everywhere and I couldn't wait to get finished. Finally I was:


I recorded some hand claps during all stages of the insulating process and this insulation really eat up the echo totally. I was very pleased with the sound and just speaking or being inside the room had a really strange feel to it - the sound was extremely dead with no echo. Maybe not the most pretty walls, but there was still many layers to go.

Sound Blankets 1Next step was to put up the Stairville Acoustic Curtains. I didn't want to put any plaster boards up to internally to cover the insulation because the hole idea was for the sound to get eaten up by and absorbed into the insulation. The solution was to staple up the sound blankets using a staple gun. Doing this on my own was a real challenge and a pain in the XXX. Especially tricky was the blanket in the ceiling because A) it had to be put up perfectly in line, B) few stables would not hold the weight of the blanket up, C) even the slightest offset would result in the opposite corner not having enough blanket to cover, D) the blankets are heavy so resting them on my shoulder as I try to staple it upwards in a straight line in darkness (since I was under the blanket) was far from easy - but I got through it.

It took 2500-3000 staples to put up the double layers. I stapled them directly into the stud beams and the first layer was the worst since I was working directly onto the insulation (dusty and itchy fibers!) and the second layer was also worst come to think of it because it was more difficult to feel the wood beams and staples didn't necessarily reach that well through multiple layers of sound blankets, especially in the corners where it was overlapping. Thomann had missed to ship one of the blankets in the order as well so I ended up taking cutoffs to cover the second layer of one of the short walls. They sent me the missing blanket without any hassle but I wanted to proceed with the build - always good to have a spare blanket that I can use in the field.

Sound Blankets 2

Interestingly and surprising (well, maybe no that surprising) there was an echo in the room again with the blankets up. The sound will bounce off the blankets compared to how well the insulation was absorbing the sound waves. Far from what it sounded with the plaster boards, but enough to notice that there was an echo again. Still, I think that it's the better option because the little sound that bounced means that it'll keep external sound from coming into the room as well. The first layer of blankets I put up quite stretched which was a mistake because it'll act like the membrane of a drum. I deliberately didn't stretch the second layer which I hope helped a bit.

Sound Foam 1It was finally time to put up the sound absorbing foam. Since the blankets were stapled directly onto the wood beams I had limited options to install the foam panels. They weren't as stiff as I first anticipated so the ceiling panels were more difficult to install. I ended up going for 4" (10cm) long nails that I hammered through the foam into the wood framework. I had to feel my way to know where I could put the nails and generally I used only 4 nails per panel. Some of the panels were only covering one single wood beam and in the ceiling this was especially a problem since the entire panel would drop down on either end. To solve this I put 6 nylon lines across the length of the room that I secured on either end and on all ceiling beams (every 60cm) - that kept the panels up. There is a bit of a wave-pattern in the ceiling due to gravity but I think that is actually beneficial if anything - sound bounces more off straight areas.

Sound Foam 2

The panels were up and again the echo was gone. Not sure how it exactly compared to just having the insulation exposed but I will be able to compare that when I process the audio recordings and footage that I took between each step. Now it started to look like the sound recording room I had envisioned.

CarpetFinal touch to the room was to add the carpet on the floor. It'll take the final slap echo that the flat epoxy floor produces. I made sure to also cut along the length of the room on both sides and across one of the shorter sides because now I can roll the carpet up to expose a large portion of the solid floor when I need it to smash stuff on, like glass, melons, computers, plates, TVs... you get the point =)

I should also mention that the trickiest thing of the entire room build was to figure out how to get the door to seal properly. I have put rubber strips on the door frame onto which the door shuts, but it needs to be pulled close with a decent amount of force (otherwise it'll glide open.) I'll put a separate post on that someday how I solved it. The main thing was that the door shouldn't only be sealed from the inside, in case of an emergency, so whatever mechanism I went for had to be openable from the outside too. With the door being thicker than standard doors normal handles was no option.

Finally, here are some pictures of the final room and an updated equipment picture. Let the recording begin!!

Floor 2

Sound Equipment


Recording Room

Making of the Sound Recording Room Part #2

Over a month has passed since I started to build the sound recording room so it's time for another update. I have been able to spend about 6-7 full working days since the last update and the room is coming along nicely.

Back in late Feburary I put up the first few plaster boards on the two walls that would be closest to the outer walls of the garage. I had to start by only putting those plaster boards up since I needed exterior access and I if I were to put all boards up it would be difficult to move the already heavy construction close to the exterior walls. There are two layers of plaster boards, the first ones were mounted vertically and the second layer horizontally to minimize sound leaking through the cracks.

Lot's of screws were used and it took longer to put boards up than I first anticipated. Putting up the horizontal boards took some trickery being on my own, lifting up the upper board dropping it onto a 1cm ledge hoping it wouldn't slip off and slam down on my toes :)

After the two exterior walls were finished it was time to move the entire room to its final resting place. I did this by screwing horizontal 6"x2" (120mm x 45mm) studs along the long side and then laying two 6x2 studs across a pallet lift. It was really easy to lift the entire room up and push it into place. The temporary horizontal studs were then removed and I could continue with the ceiling and other exterior walls.

Meanwhile the garage was looking a right mess. For weeks I got increasingly annoyed at stuff being scattered everywhere... The neighbors may have gotten a bit annoyed at me parking on the street for a couple of weeks too =)

I often used sliding-arm bar clamp to position studs tightly in the right place before screwing things together. Most of the time I had long enough screws with long enough non-treaded sections so it would self-contract, but some the clamping method was still very useful, especially when I was screwing from the sides as the screws themselves would not bull the ceiling stud down to the beam it was resting on.

More Boards
More boards were coming up and I found the ceiling to be particularly painful. I had to crawl on top of the cross-beams and lift the boards up myself so I think I spent two full nights doing the ceiling alone. To further reduce the chance of sound leaking I used "Akrylfog" which is an elastic filler in all the seams between all plaster boards. I have probably gone through 15 tubes of that stuff by now!

I have an old web camera in the garage which is hooked up to a NAS and it records upon movement. I just had a look at the footage and decided to put together a little time-laps from some parts of the build. The camera often aims in odd angles as it resets the motors. Not the best of cameras and the resolution is awful, still - it shows some parts of what went into the build.

As you can see in the video, a lot of coffee went into this. Maybe I should have made a proper effort to put the GoPro up to make a proper time-lapse, but never mind, main thing is to just get it finished so I can start recording the audio.

Boarded UpBy 9th March the boards were coming along but not yet all up. I had to balance building the room with my day-job, spending time with my family, riding motocross, and all other things life has to offer. "Not having anything to do" is a feeling I haven't had since my summer time off school in 1990.

Door Frame 1
I spent a lot more time on the door frame and the door compared to what I thought it would take. The "Akrylfog" went between all pieces of wood before screwing them into place.

About time for a #selfie as the door frame was nearing completion. We're now up to the 16th March 2015.

Door 1I built the door out of 6"x2" studs too. I plan to sound proof it the same way I will do with the walls: 120mm insulation + 2 layers of sound blankets + 80mm sound absorbation foam. On the outside of the door I put double layers of plaster board, just like the walls. First a lot of Akrylfog though!

Door Mounted
Now we've caught up with today. I mounted the door on 4 hinges (mounted where the studs are in the door) and it seals the room perfectly. I will add some sealing material for the inner door frame. I put 2"x2" wood on the outer edge of the door and 3"x2" wood inside the frame. As you close the door from the inside it is pitch black and absolutely no gaps to the real world... If I wasn't recording audio in this room my neighbors would seriously wonder what such a sound proof capsule would be used for inside a garage =)

I should also mention that I was WAY too optimistic as I built the door. I thought I made it 5-10mm smaller to fit the hole and I did expect to plane some corners off to allow it shutting... but here is a small part of what I ended up shaving off to allow it to close. It was probably four times the amount of wood I had to take off before it shut properly. Thankfully I had a router and an electric planer that came in very handy.

Stage 1

Finally - room is sealed externally and the door is mounted. Now it's time to continue with the internal space and I've got the insulation ready to go. I will first record some sound in the room as it sits today to measure how effective first the insulation is followed by the sound blankets and the sound absorb foam. Will be interesting to hear the results. Right now it's more of an echo chamber!


Making of the Sound Recording Room Part #1

Finally, after months and months of clearing out the garage (it is incredible how much junk accumulates over 10 years), I have started to build the sound absorbing recording room. The sound room will finally enable me to record source material with as little reverb as possible and I've been putting off a lot of recording until I could finish this room.

[caption id="attachment_349" align="alignleft" width="200"]Sound Curtain Sound Curtain[/caption]

I'm making the room as a capsule in my garage with 120x45mm studs and joists. I will put double layer of plaster boards on the outsides and then fill the gaps with 120mm sound-absorbing insulation.

[caption id="attachment_350" align="alignright" width="200"]Sound Foam Sound Foam[/caption]

I won't put any plasterboard on the inside walls because I want the sound to absorb right into the insulation but I will also be coating the inside with sound absorbing curtains and 80mm sound foam. That should keep the reverb to a minimum and my neighbors happy =)

[caption id="attachment_355" align="alignright" width="300"]Wood Yard Wood Yard[/caption]

This morning I drove up to the local wood yard and bought wood for the frame. I ended up getting 22x4.5m 120x95mm and 10x3.0m 120x95mm beams. Managed to negotiate a 23% discount which I was happy about. They also served free coffee!

[caption id="attachment_356" align="alignleft" width="300"]Child Labor Child Labor[/caption]

Two of my kids came out to help me screwing down some foam on the wood beams that would be facing down - this is to prevent any moisture from creeping up into the framework and also to give a good seal to the floor if there are any uneven areas. The title of the picture is wrong, I don't think it can be classed as child labor because I didn't pay them anything =)

[caption id="attachment_361" align="alignleft" width="300"]Base Corners Base Corners[/caption]My kids quickly abandoned me to watch Pippi Longstocking instead and I moved ahead by screwing together the base frame. I use L-plates on the insides and two long 180mm screws for additional strength. This will be laying on the floor anyway so it's not all that important.

[caption id="attachment_363" align="alignright" width="300"]Base Done Base Done[/caption]Base was done fairly rapidly, so far so good. Now my wife and kids wanted to go for a "fika" (coffee/drink and cake) so we drove off for a couple of hours. I had coffee and a danish, well worth a 1.5 hour return trip drive on icy roads? Well, the company was great and the kids had pancakes.

Darkness fell (sun goes down early here during the winter) and I moved ahead and built another identical frame (without the foam) to go on top. I also cut the vertical studs to length. While doing this I listened to Skeptics Guide to the Universe which is a great science and critical thinking podcast that's been running for 10 years now (500 episodes) - I can highly recommend the podcast.

[caption id="attachment_368" align="alignright" width="300"]Spectator Spectator[/caption]Another spectator, my 7-month old daughter, showed up for a while too. She refused to help me even the slightest little bit but she gave off some sounds that I was unable to determine if it was in favor of my construction work or not. When the room is finished she'll be put in it so I can record a lot of baby sounds anyway so she'll come to some use after all!

[caption id="attachment_369" align="alignleft" width="300"]Today's Progress Today's Progress[/caption]This is where I'm up to after today. The framework is coming along nicely and I'll be putting plasterboards up where I've put up the studs because I then need to push the whole contraption into the corner hoping it's not too heavy by then. I'll get there somehow and I can't wait to finally finish off the recording room so I can get cracking with the backlog of sounds I've been writing down for the past months.

IMG_9142The rest of the garage is still a mess but when the room is finished I should be able to get that in decent order too. Tomorrow I have to go to my normal day-job but hopefully I'll have some energy to keep on building in the evenings now that I'm finally off to a good start.