Potential increses in the ALS bandwidth make acoustic coupling in the hundreds of Hz region interesting. The figure shows the vertex microphone signal during HIFO-Y and compares it to the signal during S6 science mode. We may well do better than S6 because there will be fewer fans in the LVEA during aLIGO. I include a spectrum from the vertex mic at LLO, also during S6 science mode, because LLO differed from LHO during S6 in that most electronics racks  were outside the LVEA. Thus, in the hundreds of Hz region, the LLO curve may be closer to what we will achieve during advanced LIGO science mode at LHO. At low frequencies LLO is worse than LHO during S6 because we did not reduce the sound from the HVAC as much at LLO as we did at LHO.

The acoustic features above 100 Hz in the HIFO-Y spectrum are driven by sound, so we can expect these features to be at least an order of magnitude smaller.