How noisy/quiet is new iMac with Retina 5K display?

I just wanted to acknowledge your post. Thank you for listing the different things. I appreciate what you say about your refrigerator. My 'external hard disk aka time machine' is really 'noisy' compared to my new (late 2015 iMac). I am just used to silent Apple computers, so coming to terms with this!😉

I've been buying Macs for 30 years and I've never owned a "silent" Apple computer. Except my MacBook 12" Retina which has no fan as I mentioned. 😎

I have just checked and my late 2015 iMac generates on average 42 DB SPL at idle. So that is more than double what you suggest. And yes, no computer is silent, but 15 DB SPL is 'silent' in my world view. 😉

there is something seriously inaccurate with your decibel meter, or you measured from an unrealistic distance, or you have seriously bad luck with iMacs. 😁

btw, A 20 dB difference in SPL represents a ratio of ten-to-one in sound pressure. so it is far more than double. Decibels are measured on a logarithmic scale.

I have the 27" 5k, 3TB fusion drive and 32GB RAM.

When I run Final Cut Pro or other graphic intense program, the fan sometimes revs up. I have also received alerts that my hard drive temp is too hot at 145°F. Otherwise it is quiet.

I totally agree. I have not noticed any fan noise even fan speed was low on older iMacs (2011,2013) I used before.

Now I just upgraded to iMac 5K with 1TB SSD. And even at 1200rpm, I can hear the fan sound. It almost sound like it has slight grind to it. I am definitely sure it is not the smoothest fan out there.

It is starting to annoy me and thinking of returning it.

Man, I hope Apple use quality fan next time.

I hear it! Very annoying