Test equipment:

Terrasonde Audio Toolbox ATB-1
http://www.audiotoolbox.us/

Sound source:

ATB-1 pink noise generator into a single KV2 EX12 powered speaker placed inside the studio in the centre of the floor pointed parallel to the wall being tested..
http://www.kv2audio.com/product.asp?ProdID=EX12&ProdSeries=EX

Test locations:

1) In the centre of the main wall area.
2) At the top of the wall in the centre.
3) At top of the wall by the ventilation duct.
4) At the centre of the door.

Method 1:

The ATB-1 was set to Real Time Analyser mode with octave resolution. Averaging set to 3 seconds.  The spectrum was measured inside and outside the studio 6 inches away from the wall surface.  The measurement inside the studio was taken with the microphone pointing into centre of the room, and the measurement outside, with the microphone pointing at the wall surface. As a check a full spectrum 10sec LEq was also taken at each location with the sound level function.

Results:

The transmission loss value is shown at each test location.  The value for each octave was calculated by taking the incident value for that octave from the RTA spectrum, and subtracting the value measured after transmission through the wall, for that octave. The difference in full spectrum LEq value is also shown as a comparison.

TEST 1:
Wall built, slight open cracks at top of wall by the vent ducts, where the topo 4 inches of wall is also skinned on only one side. Voids between double skins along rest of wall not filled. Single side block packing in corner above door not addressed. Any leakage at electrical conduit tubes not addressed.

I took the LEq measurement partly because I was surprised that the wall centre value was so poor and I wanted to check it was genuine. When you stand at the wall centre you can hear the leakage from the vent duct area to the left, but the readings show much less attenuation than at the vent duct position, so presumably the wall is leaking more even though it does not obviously sound as though it is. Clearly the low attenuation value is not mainly from flanking at the top of the wall in the centre because the values there are higher.  I guess the first thing to do is to seal the open cracks at the top of the wall by the vents and take some more readings before analysing this question further

OCTAVE CENTRE 1 WALL CENTRE 2 WALL TOP 3 VENT DUCT 4 DOOR 31 1.1 20 18.2 15.1 63 7.7 18.9 16.5 11.8 125 10.1 24.6 19.6 14.2 250 8.2 19.6 17.5 21.3 500 14.2 21.1 22.4 21.9 1000 14.3 23.8 29.5 33.2 2000 17.3 32.3 31.5 38.2 4000 18.3 38.4 30 39.5 8000 19.1 45.3 34.3 45.5 16000 22.1 49.5 41.4 50.7           Leq 10.5 21.5 19.1 17.8

METHOD 2:
Take LEq measurements octave by octave over the wall area on each side of the wall, check separation from background noise level.  Each measurement was taken by setting the sound level meter to the octave required, and the pink noise generator to the same octave.

The minimum gap from the measurement to the noise level for that octave was 28dB

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