It isn’t so much the size of the turbine but the power it produces. There is also the consideration that some turbines have tonal qualities which can make them more annoying.
Even a single turbine will need a planning application which should include a noise assessment. The assessment should be done in accordance with ETSU-R-97 and any noise impact modelling in accordance with ISO 9613. It might be worth looking on the Council’s website to see if you can find the assessment.
Generally there are two options for a noise assessment, the simplified method where there noise impact from the turbine operating at a wind speed of 10 m/s is calculated and if the impact is below 35 dB(A) it is deemed to be acceptable. Depending on the background noise level at your property this limit may result in the turbine being audible.
The full assessment compares noise impact against wind speed, generally at low wind speed the turbine isn’t doing much so there is no noise impact and at high wind speed the wind noise provides masking, the middle ground at around 7 m/s is generally where most problems arise.
I have looked at noise assessment where there are multiple turbines in closer proximity to residential properties than 1/2 mile and the noise impact is acceptable but it certainly depends on the type of turbine installed and the existing background noise level.