Why your Wi-Fi is slow in one room

There is a specific kind of frustration in paying for fast internet and still watching a video buffer in the back bedroom. The natural response is to ring the provider and upgrade the plan. It almost never helps, and understanding why takes about two minutes.

Two different numbers are being confused

Your internet plan describes the speed arriving at your house — at the modem, where the line enters. Your Wi-Fi describes the speed between the router and the device in your hand. They are separate links in a chain, and a chain is only as fast as its slowest link.

If the signal in that back bedroom is weak, the connection between your phone and the router is the bottleneck. Doubling what arrives at the modem does nothing at all to that link. You are widening the motorway and leaving the country lane at the end of it untouched.

What actually blocks the signal

Wi-Fi is radio, and radio is absorbed by mass and water. The usual culprits in a home are dull but specific:

• Concrete, brick and stone — particularly a basement wall or a chimney breast in the middle of the house.
• Foil-backed insulation, which is effectively a mirror for radio waves and is common in newer builds and renovations.
• Older lath-and-plaster walls, where the wire mesh behind the plaster acts like a screen.
• Large appliances and anything with a lot of metal, including a fridge or a filing cabinet in the wrong spot.
• Distance itself, which matters more than people expect on the faster 5 GHz band.

Then there is the router's own position. In most houses the internet line enters at whichever corner was convenient during construction, so the router ends up in a basement corner, inside a cabinet, behind a television. Those are all bad, and one of them is usually free to fix.

Why the extender you bought made things worse

A basic range extender listens to your router and rebroadcasts whatever it hears. Two consequences follow. First, if you place it where the signal is already weak — which is exactly where people put them — it faithfully rebroadcasts a weak signal. Second, because it is receiving and transmitting on the same radio, it typically halves the available throughput for anything connected to it.

A mesh system is a different design. The units are built to coordinate with each other and to hand devices between them, and the better ones use a separate radio to talk back to the main unit. That is why a mesh usually works where an extender did not.

The order to try things in

• Move the router. Central, elevated, out of a cupboard, away from metal. This is free and frequently enough on its own.
• Check which band you are on. The 2.4 GHz band is slower but travels much further through walls; the 5 GHz band is faster over short distances. A device clinging to the wrong one behaves badly.
• Look at channel congestion. In a townhouse complex or an apartment block, dozens of networks may be sitting on the same channel.
• Add a mesh unit or an access point, placed where the signal is still strong — not where it has already died.
• Run a cable if the layout allows. One cable to an office or a television removes those devices from the airwaves entirely and improves everything else at the same time.

When it is worth asking someone

If you have already moved the router and bought hardware without improvement, the problem is probably specific to the building, and guessing gets expensive. Measuring signal strength in the rooms that matter takes a short visit and turns the question from "what should I buy" into "here is where the signal fails and here is what fixes it".