1. Why Does the Wi-Fi Signal Drop in the Next Room Even with the Same Router?
Many home routers can send radio waves on two different frequencies: the 2.4GHz band and the 5GHz band. GHz (gigahertz) is a unit that represents how many billion times the radio wave vibrates in one second. [1]
Even with the same router, one frequency may struggle to connect through a wall while the other works better. The cause is not just one thing. In this article, we break down the causes into three parts. The first is the wavelength of the radio wave. The second is the weakening caused by distance, which happens even without walls. The third is the material and thickness of the wall itself. [1]
2. How Diffraction Lets Radio Waves Bend Around Obstacles
The phenomenon where radio waves bend around obstacles is called diffraction. Diffraction is said to happen more easily when the frequency is lower (meaning the wavelength is longer). On the other hand, radio waves with higher frequencies behave more like light and tend to travel in straight lines. [1]
Because of this, higher-frequency radio waves are more likely to create "shadow" areas behind buildings where the signal does not reach. [1]
A familiar example is sound from behind a fence. You can hear voices, but the light from a flashlight does not reach around the fence. However, radio waves, sound, and light are different things, so this is just an example to help you imagine the concept. [1]
Between 2.4GHz and 5GHz, 5GHz is the higher frequency. Therefore, it is thought that 5GHz has a tendency to get blocked more easily by walls and furniture. It is not that it "cannot pass," but that it has a "tendency to have difficulty passing." How much a wave passes through a wall is not determined by frequency alone. [1]
3. How Radio Waves Weaken with Distance Even Without Walls
The weakening of radio waves is measured in decibels (dB). If the signal drops by 3dB, the power is about half. If it drops by 10dB, the power is about one-tenth. If it drops by 6dB, the power is about one-quarter. [2]
Even in open space without walls (free space), radio waves weaken because they spread out. When the frequency doubles, this weakening increases by about 6dB. [2]
In one calculation, the weakening at a distance of 100m (about 328 feet) is about 80dB for 2.4GHz and about 86.4dB for 5GHz. The difference is about 6.4dB, which means the power is about one-quarter. [2]
These numbers are calculations for ideal conditions with no walls at all. In a real house, the weakening caused by walls is added to this. [2]
4. How Wall Material and Thickness Affect Wi-Fi Signal Loss
NIST (National Institute of Standards and Technology) in the United States measured how much building materials weaken radio waves. They investigated materials like brick, concrete, glass, plywood, wood, plasterboard, reinforced concrete, and rebar grids at various thicknesses. [3]
For the 2.4GHz band, one manufacturer provides rough estimates. Clear windows cause about 3dB of loss. Wooden walls cause about 10dB. An inner wall about 15cm (about 6 inches) thick causes 15 to 20dB. A load-bearing wall about 30cm (about 12 inches) thick causes 20 to 25dB. [4]
In terms of power, a window reduces the signal to about half. A wooden wall reduces it to about one-tenth. A thick load-bearing wall reduces it to about one-hundredth to one-three-hundredth. If you simply add the dB values, crossing two inner walls results in 30 to 40dB, which calculates to less than one-thousandth of the original power. In real houses, reflections and other factors change this. [4]
However, these numbers are manufacturer estimates and only apply to the 2.4GHz band. These estimates do not show how much 5GHz changes with the same walls. [4]
5. What Is the Weakness of 2.4GHz Wi-Fi Besides Walls?
Based on the information so far, 2.4GHz might seem better because it is stronger against walls. However, the 2.4GHz band has another weakness. [1]
This band is an ISM band (for Industrial, Scientific, and Medical use) and can be used without a license. Because of this, many devices use the same band, including microwave ovens, cordless phones, and Bluetooth devices. Interference from these devices can cause communication to slow down. [5]
It is important to separate the weakening caused by walls from the slowness caused by congestion. Even if the connection feels "weak," the cause might be different. [5]
6. How to Compare Wi-Fi Signal Strength Around Your House
After asking your family for permission, you can walk around your house while looking at the Wi-Fi bars on your smartphone. Write down the number of bars for each location on a rough sketch of your floor plan. Compare spots like near the router, the next room, the hallway, and in front of the bathroom. [1]
If your router has different names for 2.4GHz and 5GHz, you can switch connections to compare them. However, the bars are just an indication for each device, not a precise measurement. If you know the material and thickness of the walls, add that to your diagram. [1]