There is a moment in every renovation when the plasterer has gone, the walls are smooth, the paint is chosen, and somebody says the words “where is the television going?” If that is the first time the question has been asked, the answer is going to involve trunking, a cable along the skirting and a subwoofer with a wire across the carpet. If it was asked three months earlier, before the first fix, the answer is invisible.

Home cinema and surround sound are easy to do well and almost impossible to do well late. The planning that makes the difference happens when the room is still a shell.

Decide the layout, then everything else

A surround system is designed around a listening position. Where the sofa sits determines where the screen goes, which determines where the speakers go, which determines where the cables need to come out of the wall. The common mistake is to design the room for daytime, with the sofa facing the garden, and then try to fit a cinema into it. Decide which way the room faces when the lights are off and work back from there.

The standard arrangement is still 5.1: left, centre and right speakers at the screen, two surrounds beside or behind the seating, and a subwoofer. Modern systems add height channels, two or four ceiling speakers that give the sound a vertical dimension, and that is the one that cannot be retrofitted gracefully. A ceiling speaker needs a cable in the ceiling void before the ceiling is boarded.

In-wall, in-ceiling or freestanding

Freestanding speakers sound best for the money and are the right answer in a dedicated cinema room where nobody minds seeing them. In a living room that has to look like a living room, in-wall and in-ceiling speakers disappear behind a paintable grille and give up remarkably little. The front three in the wall at ear height, the surrounds in the side walls, the height channels in the ceiling, and the only visible object is the screen.

In-wall speakers need a back box or a sealed cavity to sound right, and that is another first-fix decision. A speaker dropped into an open stud bay shares its air with the whole wall and sounds thin.

The cables that go in before the plaster

Every speaker position needs a cable back to where the amplifier will live. The subwoofer needs a signal cable, and ideally two positions wired so it can be moved if the first one booms. The screen position needs power, a fibre or high-speed HDMI route to the amplifier, and data. The amplifier location needs power, data and ventilation, which is why it is usually a cupboard with a vent rather than a sealed unit.

Run more than seems necessary. A spare cable to the ceiling for a projector that is not in the budget yet costs a few pounds in the first fix and several hundred after the ceiling is down.

Rooms have opinions

A room with a hard floor, big windows and bare walls will make any system sound harsh. A room with curtains, a rug and bookshelves will make the same system sound expensive. Acoustic treatment does not mean foam panels; it means thinking about where the hard surfaces are and breaking them up with the things the room needs anyway. The first reflection points, where sound bounces off the side walls between the speakers and the sofa, are the places a curtain or a tall plant does the most good.

Bass is the other room problem. Subwoofers excite the room’s natural resonances, and a sub in a corner will produce a boom at one frequency that no amount of equipment can fix. This is why a professional will measure the room with a microphone before deciding where the sub goes, and why the second cable position matters.

Calibration is the finishing coat

Every modern AV receiver has an automatic room correction system. Running it properly, with the microphone at several seating positions, is the difference between a system that sounds like a cinema and one that sounds like a loud television. The professional version uses a calibrated microphone and measurement software and takes an afternoon. Homeowners in the county who are planning surround sound installation in Essex should expect this to be part of the handover, not an optional extra, because an uncalibrated system is a half-finished one.

The conversation to have with the builder

Tell the builder, at the design stage, that there will be an AV first fix and who is doing it. The installer needs a day on site after the studwork is up and before the plasterboard goes on, and another after decoration to fit the speakers and commission the system. Builders are used to electricians and plumbers working to that rhythm; they are less used to AV installers, and the one who is told late is the one whose cables end up in the skirting.

Done in the right order, the whole thing vanishes. Done in the wrong order, it is there every time you look at the wall.