Acoustic treatment for the new G1Fourways Auditorium

In the early part of 2017 after many years of searching, GodFirst Church Fourways finally found a new, permanent venue to have church. As part of the staff team I have been involved in the planning process, right from conception to architects plans, demolition of the previous internal structures and the construction of the new auditorium and kids venues.

Get things right the first time… or the 2nd time at least

I wanted to make sure that right from the drawing phase we were thinking about the acoustics of the building and I brought in two acoustic consultants to give us advice. Unfortunately the reality of tight budgets set in and we realised that even though it would cost us down the line, we just didn’t have R100K to spend on consultants, never-mind the cost of implementing their design so we had to take a wait and see approach.

Of-course without any surprise, on completion of the venue, setting up the band and PA and pushing up the master fader, it sounded… terrible!

The auditorium had a lot of large flat reflective surfaces that created distinct echos, as well as virtually no absorptive material meaning that any sound injected into the room, even just by someone talking would bounce around for several seconds before dying out. For the geeks out there, the RT60 time was ~5s.

What should a live music venue sound like

At this point I just want to quickly look at what the ideal room for a band to play to an audience through a PA system should sound like. When a band plays and a PA is in use, the sound of a room needs to be different from that of a theatre or concert performance hall. Those halls are designed to naturally amplify sound on the stage so that a PA is not necessary. In our case, we actually want the sound on the stage to be contained and controlled by the PA.

    1. Quiet
      In a perfect world, the room would be soundproof, i.e. sound from outside wouldn’t get in and sound from inside wouldn’t get out. Absolutely soundproofing a room 100% is not easy, infact near impossible, especially for a larger venue, and besides if the internal acoustics aren’t good, then the PA gets louder and louder and the chance of sound getting out increases, so It makes sense to tackle the sound inside as well as keeping outside noise down.
    2. Intimate
      I can’t think of another way to describe a room that has very little ‘echo’ in it. A room with a lot of echo will make it difficult to even have a conversation in a crowd without the din of everyone else talking overpowering your voice. In technical terms this means that we want any sound created in the room to die out within 1.5s at least. (in other words we needed to reduce our RT60 time by at least 3.5s)
    3. Balanced
      Reducing the amount of ‘echo’ or reverb in a room is quite easy at higher frequencies (over 1KHz) as they do not contain a lot of energy and are easily absorbed. Carpets, curtains etc will easily absorb these frequencies.
      Breaking up surfaces creates diffusion which helps to prevent distinct echos by reflecting sound in various directions, but again it is less effective at lower frequencies which tend to be more omni-directional (they reflect back even of uneven surfaces). Many people who don’t fully understand how sound works will think that using curtains or egg boxes etc can resolve acoustic problems, but these methods will only create a room with very little echo in the critical range of speech (around 3-4KHz) and leave the low frequencies to continue to bounce around.
      A room should ideally have very little echo at any frequency, not just in the upper range.
      Alongside a room needing to have ‘flat frequency response’ the sound coming out of the PA should be as uniform as possible. Although much of this part of a balanced room comes from spec’ing the right PA system, tuning it and positioning it correctly, a room with bad acoustics will have areas where the PA sounds very different, and can even have places where the sound appears to come from a wall rather than from the stage.

To the solution!

So the venue is not sounding right, but how to solve it… and ofcourse, given our very tight budget, how to do that for as little as possible.

I have decided to approach the problem in phases, this way we can spend a bit and make a small improvement, then spend some more until we have got the room good enough.

These are the steps to treating the stage (Phase 1) as I see it right now:

  1. Treat the surfaces around the stage to reduce the reflection of the acoustic instruments, amps and monitors on the stage.
    At the moment, even with the PA system off altogether, the band is too loud.
    Switching to an in-ear monitoring system can help this problem, but it won’t fix the problem in the whole room, so we will kill 2 birds with one stone by introducing some absorption on the stage walls, floor and ceiling.
    This will consist of firstly making 4 acoustic panels to cover the walls indicated below:
    Panel_PositionsHere are the plans for the acoustic panels:
    https://3dwarehouse.sketchup.com/embed.html?mid=cb137ecd-375b-48ad-8ce7-a45867203cd8&etp=im&width=580&height=326
  2. Then we will consider introducing a padded carpet (rug with underlay) to the stage floor.
    The floor is already carpeted, but with thin, hard carpet tiles that don’t provide much absorption. (A loose carpet will also provide a place to hide cables!!!)
  3. Lastly a few suspended panels will be hung above the stage.
    These will be almost the same design for the treatment of the corners (Phase 2) and the back wall (Phase 3)

Acoustic Panels

All the acoustic panels will be made using a semi-rigid fibreglass board encased in a wooden frame and covered in fabric.

For the nerds, the fibreglass boards are 50mm thick and 47.5Kg/m3 similar to what is most commonly talked about on other online articles, Owens Corning 703.
The brand available here in South Africa is Isover and the board is called Energylite. Here are the absorption stats:

(http://www.autospec.co.za/productmedia/owenscorning/glasswool/energylite.htm)

Thickness Density 125Hz 250Hz 500Hz 1000Hz 2000Hz NRC Value
50mm 47.5Kg/m3 0.30 0.59 1.01 1.06 1.06 0.95

Which is very similar to the data on these panels from Genesis Acoustics: http://genesisacoustics.co.za/productdetails.php?id=100005
Actually it seems that Genesis are using the 24Kg/m3 boards.

Just out of interest I contacted Genesis to get a cost on their panels. The S5 panel measuring 1.2m by 1.2m costs R2775

My plans are still evolving as i’m sourcing material, but here is the break down of the parts and total cost to make a similar panel:

Wood
I’m looking at wet off saw planks 100mm by 19mm they cost about R17 for a 2.4m plank
My design requires 7 of these to make a 1.238m by 1.238m panel

Cost R 120

 

Fibreglass
The cheapest place i’ve found is http://egoliinsulation.co.za/ they charge R1388.50 exVAT for a pack of 15 boards… my design requires 2 boards.

Cost R 212

 

Fabric
I’m not sure I’ve found the best fabric yet, but Chamdoor in Deco Park makes some sheeting that i’m gonna try and see what its like. its 1.8m wide and about R30p/m
My design requires a 1.476m by 1.476m

Cost R  45

So my total cost is about R450 including glue, screws staples etc.

We will be building the larger panels and taller panels, and the total cost should be around R5000 although I’m still to confirm if the wet off saw planks will work. They will probably need to be dried first which could take 3 weeks, but hey its about to be Christmas and we’ll only be constructing these in Jan 2018 so we might be fine!
The alternative wood is either SA Pine, kiln dried and planed, or MDF (Supawood) cut into the pieces we need… both of these options would push the price of the wood up to around R900 making the total cost almost 3 times higher so I really hope we can make this wood work!

 

I’ll post some more updates as the build takes place so stay tuned..!

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