If you need to put a server in an office where people are working, you may want to know how much noise it makes. It is surprisingly difficult to find out.
Most larger offices will have a computer room with air conditioning and special power supplies. But in some offices you may need to put the computers in a side room, and sometimes just in a corner. You may be renting a prestige office in the city, or have a temporary office in a new country. There are all sorts of reasons you may need to put the server somewhere out of the way but in the same room where people are working. We often have servers in the offices for development and testing.
The noise ratings for servers are tucked away in the technical specifications. Occasionally you will see a reference in the marketing material to "new quiet operation" but not much more.
Noise ratings in the computer industry are usually declared in line with ISO 9296. The standard noise raing is at Idle Minimum, in BELS (10 decibels) for the declared A-weighted sound power level (L WAd). This is given in the specs as L WAd (BELS). The BELS measurement is logarithmic, like the Richter scale for earthquakes and Beaufort scale for windspeed. An increase of about 1 BEL will be perceived as roughly twice as noisy. Noice perception is very subjective, but a human whisper is around 3.4. A quiet PC is around 4.0. Human conversation is around 6.9, a very quiet vacuum around 7.2.
Here are the noise ratings for different models of HP servers:
DL 380 G5 6.4
ML 370 G5 5.9
ML 350 G5 5.0
ML 350 G4 6.0
ML 310 G3 5.7
ML 110 G3 5.5
These are all around 5 or 6, but with the logarithmic measurement the very quietest server is twice as noisy as a quiet PC, and the noisiest is getting towards the level of people conversing, although at a different pitch. You might think that the smaller servers would be designed more to go in offices. There is a slight reduction, but not much. The ML 110, which looks hardly more than a tower PC, is half as noisy again. The bigger servers are too noisy to be in a quiet room. If you have a large open plan office with a lot of people talking, and an out of the way corner somewhere, you might not notice it. But in a quiet office or ante-room you certainly would.
The most impressive thing is the noise reduction of the new ML 350 G5. It is half as noisy as its predecessor, with no similar reduction in other G5 models. And yet the marketing description barely mentions it. You would need to be really looking, and know where to look, to notice it.
If a server is too noisy, perhaps you could consider a workstation. Something like the XW 6400 provides similar performance to a server at a similar price, although without the server durability features. But the XW specifications have no mention of noise. The XW 6200 does not refer to noise. The new XW 6400 has a noise rating marked "TBD".
I rang HP to see how much noise the workstations made compared to the servers. HP Technical Support referred me to Customer Service. Customer Service referred me to Support. I was told there was no-one who knew, no showroom or demonstation centre anywhere at all, ask a reseller. I asked the reseller. No-one could say, they don't have them around, ask HP. There is no noise rating for a workstation, although it is likely to be the noisiest model you would put at a desk.
So if you want a server to put in a quiet office, there is one model that will probably do, the HP ML 350 G5. But you won't be able to check it out first. Going through these specifications, I am very impressed by the effort going in to noise measurement and reduction by manufacturers like HP, Dell, IBM and Toshiba. It is just so hard to find out.