HOW IT WORKS
Coil, magnet, cone
An alternating current in the voice coil makes it attract and repel the permanent magnet, so the coil vibrates and drives the cone that pushes the air.
Inside a speakerHOW SPEAKERS WORK
Two speakers,
one triangle.
Every loudspeaker is a small electric motor pushing air.
A coil of wire sits inside a magnet and drives a cone back and forth, thousands of times a second. Where you put the pair matters as much as what is inside: the European Broadcasting Union describes a simple layout for its listening rooms that works at home too.
Check the layout Read the short answer
01 Coil, magnet, cone02 Ear height, not floor03 Off the wallSimple physics, better sound
THE SHORT ANSWER
A motor for air,
placed with care.
The physics is the same in every speaker.
The room layout is up to you.
THE LAYOUT
Make a triangle
The EBU layout puts the pair 2 to 4 metres apart at a 60 degree angle from the listener, who sits about 0.9 times that gap away.
Check the layout
THE ROOM
Give them space
Free-standing speakers should be at least 1 metre from the walls, with their centres at least 1.2 metres up, about seated ear height.
Set it upA QUICK LAYOUT CHECK
How far, how high,
how wide?
Pick a measurement to see what the European Broadcasting Union's listening-room guidance says. The bar gives a rough sense of the scale involved.
These figures describe reference rooms for judging sound quality. In an ordinary living room, treat them as a starting point rather than a rule.
TWO NUMBERS WORTH KNOWING
A wide angle,
a small return.
One figure on the layout,
one on how little power becomes sound.
STEREO ANGLE · EBU
Optimal angle between the two speakers
60°
Seen from the listening position, the two speakers sit 60 degrees apart, with the listener about 0.9 times the speaker gap away.
EFFICIENCY · MIT COURSE NOTES
Share of electrical power that becomes sound
0.5–2%
Loudspeakers are very inefficient. Most of the energy is lost as heat from the voice coil and the circuits, including the crossover.
That is why speakers need an amplifier: the original signal is too weak to move the cone audibly, so the amplifier produces a copy with the same frequency but a much larger amplitude.
FOUR STEPS FOR A STEREO PAIR
Borrow the
broadcaster's layout.
These steps follow the EBU listening-room layout, scaled for a home. You need a tape measure and a little floor space.
- Space the pair 2 to 4 metres apartPlace the two speakers symmetrically either side of the spot where you will sit.
- Sit on the centre linePut your chair about 0.9 times the speaker gap away, so the speakers sit 60 degrees apart.
- Raise them to ear heightAim for the middle of each speaker at about 1.2 metres, the height of a seated listener's ears.
- Pull them off the wallLeave about 1 metre between free-standing speakers and the walls around them.
INSIDE A SPEAKER
Six parts,
one job.
A typical driver has a magnet structure, a voice coil, a spider that carries the coil's movement, a cone that pushes the air, a basket that holds it all together and a dust cap. Cones range from about 1.5 to 18 inches across.
The signal's frequency sets how fast the cone moves, and so the pitch; its amplitude sets how hard the cone pushes, and so the volume. Our ears are most sensitive between about 1 and 4 kHz and less sensitive at high and low frequencies.
QUESTIONS PEOPLE ASK
Frequently asked
How does a loudspeaker make sound?
An alternating current flows through a coil attached to a cone. The coil is alternately attracted to and repelled by a permanent magnet, so it vibrates, and the cone pushes the air into sound waves.
Why does a speaker need an amplifier?
The signal from a source is too weak to move the cone audibly. An amplifier produces a copy of the signal with the same frequency but much larger amplitude.
How far apart should stereo speakers be?
The EBU listening-room guidance gives a gap of between 2 and 4 metres, with the listener about 0.9 times that distance away so the speakers sit 60 degrees apart.
Why do speakers get warm?
Speakers turn only about 0.5 to 2 percent of the power they use into sound. Most of the rest is lost as heat from the voice coil and the circuits.
Is there a standard for surround sound layouts?
Yes. Multichannel layouts with and without a picture are set out in ITU-R Recommendation BS.775; the version in force, BS.775-4, was approved in December 2022.
SOURCES
Where the facts come from
Each figure on this page comes from the sources below. Check them for the full detail and context.
- EBU Tech 3276: Listening conditions for the assessment of sound programme material, monophonic and two-channel stereophonic
- ITU-R Recommendation BS.775: Multichannel stereophonic sound system with and without accompanying picture
- Florida State University, Molecular Expressions: How a speaker works
- MIT course 2.972: How speakers work
- UNSW Physics, Music Acoustics: Hearing test, equal loudness contours and audiometry