Hi,
I agree that they are inaccurate in the absolute sense but it has worked well for me in measuring relative noise levels to compare different fans and different speeds.
I forgot to put that silence in the room (no computers on, no cars going by outside and me holding my breath) measured 53.5dba. So the noise levels of the fans will be relative to that. (I guess that my ipad 53.5dba would probably be in the 30-35dba region in reality.) It was just an easy objective way to measure relative sounds levels.
The mic of the ipad was placed directly on the grill of the case above the centre of the fan. I have a protector on the ipad so it was probably 1mm to 2mm above the grill. Interestingly, you can sometimes get a different figure for 'airflow' noise, when you place the mic halfway between the centre of the fan and the outside edge of the fan, also with mic directly above the grill. This only showed up when there is some bearing noise but the airflow was quieter. But if the bearing noise get too loud then it dominates the airflow noise.
And ... to investigate why some fans sounded quieter but measured louder at 0cm, I started measuring dba levels at 25cm and 0cm, and found you can have a fan A that is louder than fan B at 0cm but fan A can be quieter than fan B at 25cm. I would guess it is due to the difference between bearing and airflow noise, the frequencies generated, which then determine how quickly the sound levels drop off.
those meters on those apps are terribly inaccurate not to mention all the variables that could be changed by just the angle of the mic / inches of distance. those DB's are more than likely ambient noise, as im sure that is alot higher than those fans do.
I agree that they are inaccurate in the absolute sense but it has worked well for me in measuring relative noise levels to compare different fans and different speeds.
I forgot to put that silence in the room (no computers on, no cars going by outside and me holding my breath) measured 53.5dba. So the noise levels of the fans will be relative to that. (I guess that my ipad 53.5dba would probably be in the 30-35dba region in reality.) It was just an easy objective way to measure relative sounds levels.
The mic of the ipad was placed directly on the grill of the case above the centre of the fan. I have a protector on the ipad so it was probably 1mm to 2mm above the grill. Interestingly, you can sometimes get a different figure for 'airflow' noise, when you place the mic halfway between the centre of the fan and the outside edge of the fan, also with mic directly above the grill. This only showed up when there is some bearing noise but the airflow was quieter. But if the bearing noise get too loud then it dominates the airflow noise.
And ... to investigate why some fans sounded quieter but measured louder at 0cm, I started measuring dba levels at 25cm and 0cm, and found you can have a fan A that is louder than fan B at 0cm but fan A can be quieter than fan B at 25cm. I would guess it is due to the difference between bearing and airflow noise, the frequencies generated, which then determine how quickly the sound levels drop off.