General > General Technical Chat
Sound cancelling speakers in bedroom for traffic
Masa:
Actually active noise cancellation does work even in bigger size than the headphones. It's just that you cant of course achieve it everywhere in the space simultaneously, you will have certain spots in the space where you have the destructive interference and there it works, but if you move elsewhere in the space where the waves add together, there it actually increases the sound.
But when you are sleeping, your head usually is in one well known location. So it might actually work somewhat well for sleeping.
It is for example nowadays used in turboprop aircraft for reducing the noise in the cabin with speakers.
The bigger the space, the lower the highest frequency at which it works somewhat well. So with headphones you can practically cancel much higher frequencies what you can in open space.
https://www.diva-portal.org/smash/get/diva2:838339/FULLTEXT01.pdf
Of course, this aircraft case is easier than cancelling out passing traffic nosie, because the sound source is well known and even information about the engine can be used for tuning the cancellation.
Howardlong:
--- Quote from: Masa on May 08, 2020, 05:13:49 pm ---
It is for example nowadays used in turboprop aircraft for reducing the noise in the cabin with speakers.
The bigger the space, the lower the highest frequency at which it works somewhat well. So with headphones you can practically cancel much higher frequencies what you can in open space.
https://www.diva-portal.org/smash/get/diva2:838339/FULLTEXT01.pdf
Of course, this aircraft case is easier than cancelling out passing traffic nosie, because the sound source is well known and even information about the engine can be used for tuning the cancellation.
--- End quote ---
82Hz, ~4m wavelength. The harmonics would be harder, but the fundamental can be dealt with assuming enough density of loudspeakers.
As others have said, passive techniques are far, far more practical in the OP’s case.
I live on a main road, and the difference that secondary (as opposed to double) glazing makes is astonishing.
raptor1956:
ANC is limited both spacialy and by frequency. Moving even a little would require the cancelling sound to change as well so getting this to work in a whole room isn't really practical. It's a sure bet that you could lower, slightly, for most of the room, but there's likely be areas where the sound is amplified. Also, ANC works best with lower frequencies and hardly at all with higher frequency transient sounds.
This is a problem that I am currently dealing with -- I live in an apartment and work a night shift which means trying to sleep during the day with the sound of lawn mowers and leaf blowers and the neighbors yelling at each other. I have a particular problem with my next door neighbor as there young daughter has no inside voice. It may be that she has Tourette syndrome or something similar, but she simply does not speak at normal conversational levels AND punctuates nearly everything she says with a vocal manor involving screeching. So, we have a loud neighbor uttering transient high frequency sounds throughout the day and since we're still on lockdown and school is out for the year she's home ALL DAY. My bedroom shares a common wall with the very room she spends much of her time so sleeping there is ... impossible. I've been forced to setup a temporary bed in my office which is at the other end, furthest away, from the common wall.
Sleep deprivation is not fun!
Brian
ConKbot:
--- Quote from: Howardlong on May 06, 2020, 07:33:39 am ---
--- Quote from: ConKbot on May 06, 2020, 06:13:05 am ---
--- Quote from: CatalinaWOW on August 12, 2018, 10:07:35 pm ---While I understand and agree with the objections to large area noise reduction, there must be some possibilities in this area. Several modern cars use active noise cancellation to reduce cabin noise and by all reports it is at least somewhat successful. I don't know how they do it, but do know that in one example I sat in there were multiple sound pickups and emitters involved. The systems are highly engineered for the vehicle so not the kind of thing you would buy and install in a room.
--- End quote ---
Cars have the occupants heads in a relatively consistent spot, so for lower frequencies, it's is doable. Add a bevy of microphones, do simulation and measurements of sound in the interior, bake that down into something more simple to let the sound DSP run, and you can make 2 quiet zones near the headrests.
--- End quote ---
Won't work. Ears are too far apart, 180 degrees apart at about 800Hz. one ear will have constructive interference, the other destructive interference. Noise cancelling only works practically in the very near field.
--- End quote ---
I would assume in the cars Catalina mentioned, the active noise cancellation is for lower frequency rumble, road and engine noise. The higher frequency stuff can be handled with traditional damping, but trying to block sub 1-200 Hz with physical materials would be heavy. The higher end vehicles with the camera that watched the driver to see if they are dozing (not sure if that is a thing still? ) could get more accurate information on at least the drivers head location.
EDIT: Or if its VW / BMW, they could just turn off ('Cancel') the box that makes vroom vroom noises ("active sound") in the passenger compartment.
Marco:
I wonder if you could make a whole wall an active sound canceller for an arbitrary incoming sound field. Or rather, I wonder if you could do so cheaply. The wavelength of sound is so short for the medium frequencies that the density of sensors/actuators seems to be the rock on which the idea breaks.
The attraction is that you could make it light and relatively thin compared to passive insulation ... but doesn't seem worth the very high cost.
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version