Didgeridoo recording for Kosmopterix – part 3

Part 3 –Room & Studio treatments and extra treatments…
Before I had an emphasized intention to record didgeridoo CD, I wanted to make myself a room where I can practice didgeridoo playing as much as I want, and record decently in it.
We encounter two „problems“ here: one is to make room soundproof- meaning no sound in or out. The other one is to make it nice to record in, in acoustical sense. One aspect of this is to make your recording room with as flat frequency response as possible. Due to reflections from floor, ceiling and walls, respective to dimensions of the room, some frequency  are boosted, some are squashed. Didgeridoo playing  it means that for example your drone sounds fine, but your first toot shakes the room and the recording. Second aspect is to lower the reverberation. Even though reverb can often sound better than dry (no reverb) recording, it is an uncontrollable factor which blurs the sound picture. In most cases you want to add it afterwards, and there are many many (many many) ways to do it.
So, being a student in various forms for a long time, first I bought myself a book. It was „Acoustic design for the home studio“ by Mitch Gallagher. Why?  It had good reviews on Amazon. It is simply written and has lots of practical advices/examples. Useful, and even more useful if you can read between the lines. Good to begin with.
What I found out inside of the book, is that  I will need a program which measures room frequency response. Thanks to Rumski forum I found out about a free programme RoomEQ – http://www.hometheatershack.com/roomeq/
Two or three professional programs were mentioned in the book, but at that time I had reasoning to go cheap while I was still learning. I did not know what kind of influence room treatment really has. I’ve listened to treated and untreated rooms, but never experienced both in one room.
You can also measure your room „manually“, but it takes much more time, and doesn’t seem like very very fun thing to do.
The other thing you need, weather you use the program or do it yourself is SPL meter. One recommended in the book  is this one:  http://www.radioshack.com/product/index.jsp?productId=210366
With little e-bay magic, we could even get it to Croatia!
About the insulation I would only mention dense rockwool for floor and walls (I didn’t need to do anything with my ceiling because the room is on the highest floor in the building), double gypsum-cardboard and OSB boards on top of it on the floor. Double door heavy as hell (and by now hell should be rather heavy I suppose). The room is not really big, but has some good properties – no equal dimensions of more than two walls. And floor and ceiling are not parallel.
The first thing about absorption was to put 8 broadband absorbers to the ceiling, made with rockwool, separated 15cm from the wall. It made a big difference in the reeeveeerb, and helped to flatten the room response, but was far from superb.
Then to the room came one of the most expensive diffusers in the world, a stand with around 30 didgeridoos. There is also variation for zero (0) money- you bring some branches from the wood. Diffusers make the sound reflect not only in one direction and therefore weaken those frequencies that would boost by reflection between the walls. There are many  diffusers built for that purpose and they probably work much better than didgeridoos, but it was necessary to put them in the room.
Then we added 4 bass traps to 2 corners. They were made by triangles made of rockwool. Some big speakers ended up in one corner, turned to the corner. Another two big broadband absorbers were put  to the wall. And another bass trap.
When I had no more power and energy, Danka came, brought the happiness, carpets, one mattress we had for guests (1x2m), another mattress we had for ourselves (1.6x2m) and a Fatboy.
And voila! After few days of work we had something that can bear with sounds of didgeridoo. Moderately sized.
Here is the picture of frequency responce before and after.

Before is brown/green, after is blue. Should be observed after 50Hz, because speaker that I used for measuring  goes from 40Hz, and here certainly doesn’t have flat response. The higher part is also not really interesing because it doesn’t cause such a problem, especially at 24kHz where the graph ends. In the book a range from 50 to 250 Hz was observed and it was inside 13dB. From this graph you can see that from 50Hz till 1kHz we are inside 10dB. Not bad for  first time. Of course, it is possible that we made some mistake in the process of measuring, but nevertheless, the difference was very hearable and the relative differences present to back that up.
I think all costs did not surpass 500€. There was quite a lot of work. More than I thought.
In the meantime I bought three more books about this matter. From simple to encyclopaedia. I want to develop my  knowledge abou this further. And probably in the future build something interesting and nice to record in.
This room was used for Kosmopterix for recording of some songs. Some extra bass traps were put into. Also an absorber underneath the didge which was levitated…. But more about that later.
For now I just add two photos, of ceiling and didges on the wall.

In the time I made the room i also made two recordings. One is in treated room, and since I was not thoughtful enough to do also one in untreated room, I did one in the hallway which is most similar to this room.
Microphone was Rode K2, 20cm far from the didge, didge is in C, meaning  65Hz, first toot around 130Hz, preamp is Impact II on Studiokonnekt 48 soundcard.
Feel free to comment or contact me if you need anything.
Didge sound test – untreated room
Didge sound test – treated room

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