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A wifi user is in a different room than the router. The computer is having a hard time connecting and receiving the wifi signal.

Can the wifi signal from the router to the computer be improved by opening a door to the room where the computer is?

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    $\begingroup$ If it's the door of a safe room inside FBI headquarters, then yes. $\endgroup$ – Ricky Nov 20 '15 at 0:51
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    $\begingroup$ It's been said that having your modem antenna as high as possible (above the computers, preferably) provides better reception. Try placing your modem higher off the ground. $\endgroup$ – phyrfox Nov 20 '15 at 3:27
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    $\begingroup$ Well, according to internet wifi uses doors, so opening should help. A bit. $\endgroup$ – PTwr Nov 20 '15 at 7:36
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Can the wifi signal from the router to the computer be improved by opening a door to the room where the computer is?

Maybe, but probably not to a noticeable degree.

All structures, including doors, impede the wireless signal from the router by some amount. Generally, the amount of impedance added by the door is a negligible amount and would not be sufficient to noticeably improve the quality of the signal.

That said, differing types of door construction have differing impacts on the signal. A hollow core, wooden door won't impede the signal all that much at 4 dB. A solid core, wooden door will present more impedance at 6 dB. A steel door would provides the most at 11 dB.

Given a computer right at the edge of receiving a reliable signal and being blocked by a steel door, and there is an otherwise direct line of site to the router except for the door, then it might be possible to improve signal reception by opening the door.

More than likely though, there are other structural elements that are having a more significant impact on the quality of the wireless signal. Especially since it's unlikely that there is a direct line of sight between the computer and the wireless router.


Because we like numbers, I dug a bit further to identify some common sources of attenuation. Source data is courtesy of 3COM and the Internet Archive and was also linked from Navas.us and the Internet Archive.

It's worth pointing out that they don't provide any attenuation measurements for differing floor types. That's likely due to the wide variety of framing and construction materials that can reasonably be seen for floor construction.

Building Material                   2.4 GHz Attenuation
Solid Wood Door 1.75"                        6 dB
Hollow Wood Door 1.75"                       4 dB
Interior Office Door w/Window 1.75"/0.5"     4 dB
Steel Fire/Exit Door 1.75"                  13 dB
Steel Fire/Exit Door 2.5"                   19 dB
Steel Rollup Door 1.5"                      11 dB
Brick 3.5"                                   6 dB
Concrete Wall 18"                           18 dB
Cubical Wall (Fabric) 2.25"                 18 dB
Exterior Concrete Wall 27"                  53 dB
Glass Divider 0.5"                          12 dB
Interior Hollow Wall 4"                      5 dB
Interior Hollow Wall 6"                      9 dB
Interior Solid Wall 5"                      14 dB
Marble 2"                                    6 dB
Bullet-Proof Glass 1"                       10 dB
Exterior Double Pane Coated Glass 1"        13 dB
Exterior Single Pane Window 0.5"             7 dB
Interior Office Window 1"                    3 dB
Safety Glass-Wire 0.25"                      3 dB
Safety Glass-Wire 1.0"                      13 dB

n.b. I used Internet archive links as I wasn't able to find current links for either source.

This SuperUser question goes into some detail about understanding the power output from wireless routers. There's quite a bit of variability involved, so I won't attempt to summarize it here.

And this vendor link goes into the calculations involved in trying to more quantitatively identify the effects of signal attenuation. And beyond an obligatory note that decibels (dB) are not directly additive or subtractive in the mathematical sense, this calculation is also a bit involved so I'm not attempting to summarize it here either.

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    $\begingroup$ +1 for most of the answer, but I'm skeptical of saying that a 1.5" thick steel door only attenuates 2.4 GHz by 11 dB. I'd guess the more likely explanation is that no appreciable amount of power is going through the door and you're just getting it through the wall, ceiling, floor, and/or cracks around the door at that point, especially if the door is reasonably grounded. We don't even have 1.5" thick steel on our RF shield room. $\endgroup$ – reirab Nov 20 '15 at 22:11
  • $\begingroup$ @reirab - Those attenuation numbers are from 3COM. I'm willing to give them the benefit of the doubt and assume they know a lot more about how to measure those signals than I do. The Data Logger link that I provide (currently the last link in the answer) really goes into everything that's involved in understanding what will impede the signal on its way from the source to the receiver. $\endgroup$ – user16 Nov 21 '15 at 15:33
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    $\begingroup$ @reirab, these lists are generally chosen to provide typical attenuation through common building materials. When they talk about a 1.5" steel door they are not talking about a 1.5" thick steel slab, which would be a very rare type of door. This is a more common type of door often used as exterior doors or interior doors i some cases. It is a wood or steel frame covered with relatively thin steel, sometimes filled with some sort of insulation. $\endgroup$ – YLearn Nov 22 '15 at 3:52
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This is engineering. Test it. It's not like it takes a lot of money or time to do experimentally.

As far as what the theory says, it will always have a slight effect. The magnitude of this effect depends on the nature of the location, the door, and the wall. More metallic/heavy objects block the signal, so if it's a weak signal and a bad environment, it could make a difference.

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  • $\begingroup$ The premise of this question is a use case. So a test would be redundant. Ergo, this question is obviously one of theory. To which, I thank you for your contribution. $\endgroup$ – Mowzer Nov 20 '15 at 8:11
  • $\begingroup$ @Mowzer, I meant that it should be relatively easy to determine, in your particular use case, whether the signal is, in fact, better with the door open, assuming that this scenario already exists (debugging, not design). $\endgroup$ – Stack Tracer Nov 20 '15 at 14:01
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    $\begingroup$ I'm guessing from that the OP is relying on the usual 3-state measurement : fine / a bit flaky / no dice. There are apps available that allow you to measure the signal strength more scientifically, e.g. Wifi Analyzer for Android - play.google.com/store/apps/…. $\endgroup$ – mikeagg Nov 20 '15 at 16:27
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I live in a big old 1920s built house. The bedroom is one floor above the router, and one room adjacent. The floors in my house are wooden, the walls are stone, the cielings are high and the doors are solid wood. If I try to stream video on Chromecast in my bedroom with the bedroom door closed, it intermittently buffers. Chromecast even grumbled that the wifi signal was weak and recommended using a different connection. (side note, but my phone picks up full wifi signal). If I open the bedroom door, and the kitchen door where the router lives, it NEVER buffers. I have watched whole films and shows without any issue.

Perhaps it is just a coincidence? I thought. But I have repeated this experiment on several different days, at different times of day, and it always yields the same result. Video can be streaming in HD beautifuly, if I go downstairs and close the kitchen door and then the bedroom door, within 5 seconds the video is buffering. I have even tried it with the doors closed over a good 30 minute period. I get small bursts of video followed by minutes of buffering.

So, the numbers shown above, although probably quite accurate and scientifically measured ....

"Generally, the amount of impedance added by the door is a negligible amount and would not be sufficient to noticeably improve the quality of the signal." In my case it is not negligible, and makes the difference between watching video, and watching a spinning icon.

Quite often a real world experiment will give different results to the science backing the accepted answer. This happens all the time, isn't engineering great.

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  • $\begingroup$ Does your older house have solid wooden doors? That probably adds to it. That said, I feel like it's 100% reasonable that opening doors makes a difference, especially when very isolated from the signal. If your house had minimum signal penetration, opening doors would allow a much more open path for the signals. $\endgroup$ – JMac Apr 11 '17 at 10:51

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