Small Build with pictures and Question about placement and tuning of resonators

[Dave Slevin]

Hi there,
It's really great to see a construction and acoustics forum up on here at last.

Good call

I thought I’d post a description and some pic.s of my little studio here, this is a little room with a booth I’ve designed and built with a machine room, little vocal booth and a control room. Any comments suggestions would be welcome. This is my 3rd build, I did my time in an big studio about going freelance about 8 years ago, and Ibuilt a room to work out of with my PT rig, you know the story… I’m pushing 18 years in the studio game so I guess I’m a pro! And my old man used to do insallation wiring and stuff in radio and television studios years ago apart from that I have no proper training in studio design or acoustics…


The story so far is, we moved out of here…


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We had landlord problems and had to move out of out original studio, we needed to get somewhere fast and start working again, even if it’s only for the relatively short term. If the gear’s not turned on then it’s not paying it’s way. We are intending in using the studio here for mixing, some overdubbing and as a classroom for small workshops for some training courses we do at the studio.

However we managed to renew our lease in the old place, so we are going to rent the old place out to a few bands to practice in for a while and keep working in the new studio. Till we get back in business again. Then it would be nice to renovate the old place and move back in to a really nice studio.

To this end I have a 56 channel AMEK Classic standing by to be commissioned.
But that’s another story.

The whole space is 4.5meters by 4,5 meters roughly, with a little machine room and a little vocal booth. The control room space is roughly 3.8 meters at the widest tapering down one side to a width of about 2.5 meters at the back of the room. The ceiling height is about 2.5 meters sloping to 3 meters towards the centre of the room.

It’s above a shop and shares a floor with a painter on the opposide side of the corridor. Noise transmitting through the floor and through to our neighbour was an issue So on the existing floor, we floated another floor in the control foom on a sandwich of roofing felt and rockwool roll on which we placed the joists with RW 3 between them and 21mm flooring grade chipboard. Hopefully this will help stop transmission through the floor and into our little vocal booth.

Cables from the machine room and booth are through ducts under the floor!! I'm worried about interference on my tape returns etc. from the midi cables and vga cables running along the same duct.

The internal walls are two layers of 17mm plasterboard (sheetrock??) on timber joists, stuffed with RW 3 and one layer of 17mm plasterboard on the inside. I may need to add another layer to the inside of the booth. The whole lot is also clad in tounge in grove timber cladding. I didn’t have space for an air gap. I'm hoping to get about above 50dB attenuation through the booths. We'll wait and see.

The roofs on both booths have two layers of plaster board, RW 3 and another two layers of plasterboard.

Doors into the control room are fire doors in recessed frames.

Here’s some rough google Sketch ups of the layout of the place.

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Big Respect for the Models by Merelin on Google sketch up 3d factory.


And here’s some photos of the state of play at the moment.

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[img=http://img299.imageshack.us/img299/7104/leftbackroomvm6.th.jpg]


Placement of the gear also had a lot to to with the size of the room and the ergomomics of having 3 or 4 people in there from time to time.

And I have a large Auralex setup from the last place including their styrafoam diffusers and some self built 8” gobos and some 4’ absorbers and corner traps.

So here’s my first questions, I’m wondering about where to put my acoustic treatments.


I’m going to test the room with a sine wave sweep before I put up the treatment and I’m betting I’m going to get some narrow band cancelations in the low frequency band especially since the monitors are close to the wall etc.

If I try and build a Helmholtz absorbers in the room how do I go about figuring out how much absorbtion the absorber is actually going to give me. I can calculate the resonant frequency using the slot dept and slot width equation in all the books but how can I figure out how much this is going to attenuate this frequency in the room and what sort of a band width it will have?

PS. I believe there maybe a misprint in the same equation quoted on SAE site etc. I'll find the thread if you'd like to read it.

Any comments and observations welcome thanks.

Dave.

[Ethan Winer]

Dave,

Originally Posted by Dave Slevin

I have a large Auralex setup from the last place including their styrafoam diffusers and some self built 8” gobos and some 4’ absorbers and corner traps ... I’m wondering about where to put my acoustic treatments.

Are you planning to use only that treatment, or is it possible you can add more? Regardless, a complete answer requires far more than will fit into a single reply here. So here's the short version. All rooms need:

* Broadband (not tuned) bass traps straddling as many corners as you can manage, including the wall-ceiling corners. More bass traps on the rear wall behind helps even further. You simply cannot have too much bass trapping. Real bass trapping, that is - thin foam and thin fiberglass don't work to a low enough frequency.

* Mid/high frequency absorption at the first reflection points on the side walls and ceiling.

* Some additional amount of mid/high absorption and/or diffusion on any large areas of bare parallel surfaces, such as opposing walls or the ceiling if the floor is reflective. Diffusion on the rear wall behind you is also useful in larger rooms.

For the complete story see my Acoustics FAQ.

There's a lot of additional non-sales technical information on my company's site - articles, videos, test tones and other downloads - linked under my name below.

If I try and build a Helmholtz absorbers in the room

For a room that size I suggest you skip tuned absorption and focus instead on broadband bass trapping as explained in the links above.

--Ethan

[Dave Slevin]

Originally Posted by Ethan Winer

For a room that size I suggest you skip tuned absorption and focus instead on broadband bass trapping as explained in the links above.

--Ethan

Hi Ethan,
Thanks for reading that long post and thanks for the reply, I see your posts on R.A.P. from time to time, always good information. In fact I'm always telling people about your FAQ!

Anyway,
I'm going to put corner traps in the 4 90 deg. corners of the room , framed corner sections with carpet felt and Rock Wool and Auralex corner traps behind them. About 2 foot deep into the corner.
Around the mix position walls and ceiling will be a mixture of stick-on Auralex foam and framed 4" absorbers hung 2" from the wall on split battens.
I also have 2 8" free standing absorbers I'm reckoning one behind the monitors and one behind the sofa at the back of the room.
The back wall is slightly convex so I'm hoping it will act as a diffuser.

Study of Acoustics etc. is a bit of a hobby and I also teach "studio design" in the local college and it's time for me to go a little deeper in to the subject.

So the question about tuned absorbers was theoretical too. Apart from the "Master Handbook" where else could I find a little more detail (not too much!).

Thanks,
Dave

[jwl]

Hi there, yes you are correct there was an incorrect Helmholtz resonator formula published in a book many years ago, and as a result many of formula calculators you find on the web are incorrect. I do know that the correct formula is posted on the John L Sayers forum in a sticky, check there for details. I'm sure the correct formula exists in many other places online, but I know that one is correct.