2.4 GHz vs 5 GHz for Alexa: what your router is doing

The box your internet company supplied does two separate jobs that are easy to confuse. The first is bringing the internet into the building over whatever line runs to the street. The second is distributing it around the house without wires.

Those are genuinely different functions, which is why an internet fault and a Wi-Fi fault may be indistinguishable from where you are sitting while being entirely unrelated.

To do the wireless half, the router broadcasts on two frequencies at once — 2.4 gigahertz and 5 gigahertz. Each connected item under the roof that uses Wi-Fi is on one of the two at any moment, whether or not anyone chose.

The numbers refer to the frequency of the radio waves, and the consequences follow directly from physics. Lower-frequency waves are longer, bend around obstacles more readily, and lose less energy passing through brick and plaster. Waves higher up the scale run shorter, shift more data each second, and give that energy up far more quickly when something solid is in the way.

So it is a trade, not a hierarchy. Distance and penetration on one side, speed on the other. No amount of configuration escapes it, since it belongs to the physics of the waves and not to the hardware.

Here is the part that surprises almost everybody, and it explains a great deal of otherwise baffling behaviour.

Although the router is sending out two distinct signals, it usually publishes them both under a single network name. When you look at the Wi-Fi list on your phone you see one entry, not two, and there is no indication anywhere of which of the two frequencies you are actually using.

The router decides for you. It weighs how strong each signal is where you happen to be standing, how busy each one is, and what your device says it is capable of, then places you on whichever it judges better. It may move you later without saying so. Manufacturers call this band steering, and it exists for a good reason: most people would rather not think about any of this, and the router's judgement is usually sound.

Some routers offer the alternative of publishing the two bands under separate names, often by appending something like -2.4 or -5G to one of them. Where that is done, the choice becomes visible and deliberate: you can see which is which in the list and join the one you want.

Whole-home systems — the kind sold as two or three matching units placed around the house — take the opposite approach deliberately. A single name across the whole house is precisely what the design sets out to achieve, since the system's job is to hand devices between units invisibly as people move around.

Why any of this reaches a speaker on a shelf

A reasonable question is why somebody setting up an Echo should care which frequency their phone is using. The answer is that the companion app passes on the details of whichever network your phone is connected to at that moment. It reads your phone's current connection and hands the name and password across. It does not present a list of every network and frequency in the building, and it does not check that the speaker can reach the one being described.

Where both bands share a single name, that is normally invisible and harmless. It becomes visible in the awkward cases: a phone sitting beside the router while the speaker is destined for an upstairs bedroom, or a household where the two bands were deliberately given separate names.

Concepts are only useful if they change a decision. Here is where the two bands actually bear on choices a household makes.

The router's position matters more than its price

Routers are frequently installed wherever the line enters the building — a hallway cupboard, behind a sofa, on the floor. Every one of those is a poor position. Radio waves are absorbed by masonry, water and metal, and a router at floor level behind furniture is transmitting into all three. Raising it, moving it clear of obstructions, and placing it nearer the middle of the home does more for coverage than most equipment upgrades, and costs nothing.

Distance is not measured in metres but in materials

Two rooms of plasterboard is a very different proposition from one solid Victorian chimney breast. A speaker fifteen feet away through a stud wall may have a better connection than one eight feet away through brick and a mirror. When judging where something will work, count the obstructions rather than the paces.

The band your phone uses is not the band the speaker will use

This is subtle but it explains a lot. Standing beside the router while setting up, your phone will very likely be placed on 5 GHz, because at that distance it is the better choice. The speaker, once carried upstairs, may be far better served by 2.4 GHz. Both facts can be true at once, and the router will generally sort it out — but it explains why the position you set something up in tells you little about how it will perform where it lives.

Congestion is a neighbourhood property

In a terrace or a block of flats, your 2.4 GHz band is shared with everybody within range, and there are only three non-overlapping channels to go round. This is not something better equipment fixes, because the crowding is outside your walls. It is the one situation where 5 GHz is worth favouring even at some cost in range, simply because there is room in it.

None of this requires changing any settings. It is the kind of understanding that makes a decision about where to put a shelf slightly better informed than it would otherwise have been.

Everything above describes a network that has stayed the same. Replace the box it comes from and several of those properties change at once, which is why a single delivery from a broadband company can silence a whole house on the same afternoon.

The name and the key are the router's, not the devices'

A network name and its key belong to the equipment that broadcasts them. Both are printed on the underside of the box that arrives, and both are ordinarily different from the pair the previous box used. Nothing on your shelves has any way of learning the new pair on its own; each one is holding the old, and each one will keep offering it until told otherwise. The speaker is simply the member of the household that cannot mention the difficulty, having no screen to mention it on.

Ask before the engineer leaves

Name and key are settings rather than fixed properties of the hardware, and the pair from the old box can usually be entered into the new one. Where that is done, nothing in the building notices the change: the printer, the television and the speakers all reconnect to a network whose name and key are exactly what they were. It is a two-minute matter while somebody is standing there with the interface open, and a considerably longer one afterwards.

What else may differ underneath

Two properties beyond the name are worth knowing about. Newer boxes tend to publish both bands under a single name where an older one may have offered two, so a choice that used to be visible becomes the router's to make. And a replacement rarely occupies the exact position of the one it replaces — a different shelf, a different cupboard, a different height — which alters what reaches the far end of the house regardless of what the specification sheet promises.

Renaming, and changing the key

The same holds without any new hardware at all. A network renamed through the router's own settings is, as far as every device is concerned, a network that has ceased to exist; a key changed is a network that now refuses them. Both produce the identical afternoon, and for the identical reason.

None of this indicates a fault in anything. It is one property of one box changing, and a number of devices noticing at the same moment.