simonm wrote: ↑
Sat Feb 02, 2019 11:06 am
What I am concerned about is noise. Tech spec sheet gives two values: 55 dB(A) according to EN12102 and a noise pressure number of 38.8 dB(A) at two meters.
Not a personal experience; just going by the numbers you provided.
EN12102 number of 55 dBA is a sound power
level measurement (not sound pressure level). It just means that the unit produces sound power in Watts (Joules per second) which is at the 55 dB level (i.e. 5.5 orders of magnitude greater than the reference sound power of 10^(12) W - so it's about 0.3 microW). That's the sound energy it emits per second in every direction; not the sound pressure you would perceive at a certain point in space and a certain distance. The number for sound power is independent of distance from the unit. It's like saying this light bulb emits 1000 photons per second in all directions.
What we hear as a result of some device emitting sound energy depends on how far from it we are and the geometry and transmission/absorption of the environment around it and between it and us.
The other number: 38.8 dBA at 2m - gives you the sound/noise pressure level when you are 2 metres away from the unit. That's how loud you will perceive the unit at that distance. That number is dBA relative to a reference sound pressure - 20 micro Pascals. So 39dBA is a bit less than 2 orders of magnitude greater than the reference pressure, about 2 milliPascals).
Unless you plan to be right next to it, it seems the noise level is acceptable. Your ear would have to be at a distance of only a foot from the unit for you to perceive a noise at about 55dB sound pressure
level (there is a relationship between sound power and sound pressure if you assume various things and for a given distance). BTW, if you are 1 meter from it, that formula gives about 45 dBA sound pressure level.
Just make sure that 39dBA is when it is working at full load.
These sound engineers make everything needlessly confusing
55 dBA sound power level is not 16 dBA larger than 39 dBA sound pressure level - they are completely different beasts since the references are different numbers in different physical units - Watts vs. Pascals).