[robmiller]

Acoustics consultant here. Its too bad there's no mention of using a windscreen on the sound level meter, especially at 2 inch distance. It would make sense if the mesh performed best, while airflow was restricted nearly most if air rushing by the microphone element was contributing to the level measured, and not the noise of the fan itself.

[roberthahn]

I would have expected that you'd _want_ to factor in air noise because humans don't only hear fan noise in their computers. Or am I misunderstanding?

[MengerSponge]

You know how someone blowing in your ear makes more sound than when you blow in someone else's ear? The airflow itself can make sound from eddies and whatnot.

Most people don't put their ear next to a case fan to see if it's annoying or not. You experience its sound from several feet away, and the measurement should reflect that.

[ehnto]

I think they mean the excess noise of a volume of air moving past your ear, which is due to the turbulence created while air is passing over your ear and not the soundwaves being transmitted by said volume of air.

Practically speaking no you wouldn't want to factor the turbulence generated at the microphone because the user of the computer wouldn't be hearing that.

[joshuahutt]

What a cool and fascinating job you must have.

[robmiller]

Hey thanks. Yes, esoteric enough to keep it interesting day to day. I mostly work with architects and design engineers to coordinate quiet building systems and good interior acoustics--projects anywhere from K-12 to major performing arts centers to commercial offices, including some of your US offices...

On that point, I feel everyone's collective pain on the situation with open offices. I don't have the power to avoid them, so the best I can do is advocate for getting the signal-to-noise problem solved right.

[nomel]

> signal-to-noise problem solved right.

One evening, I was sitting alone in the eating area of a very high end office, and noticed a whooshing sound coming from the top edge of the room. I thought it was maybe some air vent, but there was no wind outside. I stuck my phone camera up behind the front lip of a shelf and saw a set of speakers. They were playing something close to brown noise!

And, I learned about sound masking [1]. So, apparently there's two ends to be avoided, in the signal-to-noise problem!

1. https://cambridgesound.com/learn/sound-masking-101/

[robmiller]

There are various factors:

1. Partitions around workspaces create a modest barrier effect, not so much realizable for your nearest neighbors but those more distant. No one installs partitions up to 48" or 52" but you have to at least break line of sight to the noisemaker to realize any improvement. This reduces signal.

2. Acoustically absorptive ceilings avoid the overhead reflection that would be the next cue to an occupant. The partition comes first, but this is second. Another signal reducer.

3. Background noise, whether a consistent HVAC system or sound masking system raises the noise floor of the environment. We have a pretty good sense of what level is acceptable to most people, but there will always be those with sensitivities. The noise is usually pink noise with some EQ to sound like HVAC air distribution. Unfortunately there has to be some treble in the noise signal to reduce the consonants of speech, which can be more annoying.

You won't make nearby co-workers inaudible, but the hope is that those 20 ft or so further will be less problematic. For inaudibility you have to get S/N to around -10 dB, that's a noise floor of 10 dB higher than the source, which is only realizable with walls at least to the ceiling.

[robomartin]

A couple of decades back I was very involved with work that required paying attention to acoustics.

I remember building this room with walls lined with 1 foot thick Helmholtz resonators tuned to a range of frequencies. The same with portions of the ceiling. And, of course, there were broken-up and angled surfaces to help diffuse sound, avoid creating standing waves and stimulation of room modes. Back then I even wrote a bunch of software to run acoustics analysis and evaluate room characteristics based on a range of parameters, including construction materials, etc.

Here are a couple of screen shots:

https://i.imgur.com/sXQmc8d.png

https://i.imgur.com/q0kHVbQ.png

Since then I have always been very aware of acoustics in every environment. Restaurants are particularly horrendous. Nearly all of them seem to be reverberation chambers designed to destroy sound. Most would benefit greatly by deploying a few very simple tools to control sound and allow patrons to have conversations in a reasonable environment.

[lelandfe]

I adore how diverse the HN audience is.

[Darkphibre]

Thank you so much for what you do.

[larrik]

They measured the intake side, though, so it was more of a vacuum effect. Would a windscreen still make a difference in that scenario?

[oliveshell]

I can’t think of why not. The velocity might be lower, but moving air is moving air.

[robmiller]

Yes, I agree. Inlet side is quieter than discharge for most fan types (propeller, centrifugal, etc), but noise due to air movement are on both sides.