The Phone Encyclopedia

01 / Sound · Part

How a phone
makes sound.

A tiny moving system, hiding in plain sight.

01Speaker
illustrated field guide

A speaker, opened up
Warm pencil and watercolor rendering of an exploded rectangular speaker: aqua diaphragm, copper coil, brushed iron magnetic system, and silver rear frame. 2Coil ↗

An illustrated concept. Select a number; the outlined coil path opens its article.

01

Diaphragm + surround

A thin membrane moves the air. Its flexible edge lets the center travel while holding it to the frame.

2Copper voice coil↗

The idea in motion

What moves?
What stays still?

Current changes direction. The coil feels a force inside the fixed magnetic gap. The membrane travels with it, pushing and pulling the air.

Green and gold cutaway of a conceptual speaker: a pale green film attached to the copper coil in the gaps, distinct fixed iron and permanent magnet beneath.
Conceptual cutaway · the copper coil moves in the iron gaps.
PartCoil ↗PartMagnet ↗PartIron flux parts ↗

From parts to a working speaker

Put the system together.

Four steps. One continuous story.
Follow a Part or Tool link to its making article.

1Build the magnetic systemA fixed field, with a gap for the coil. 2Join coil and membraneTwo parts become one moving assembly. 3Center and sealLeave room to move. Close the edges. 4Connect and testCheck the circuit, motion and sound.
1

Build the fixed magnetic system.

Result → a stable magnetic gap
Cross-section · fixed parts only The fixed magnetic circuitA permanent magnet sits inside a soft-iron return path. A pole plate leaves two narrow gaps beside the return path. The animated line shows a conceptual magnetic flux loop, not flowing material. MAGNET iron return pathiron return path pole plate two clearances → the magnetic gap Everything in this view remains fixed during sound production.

Dashed arrows trace a field path; the field itself is static.

Place the Partpermanent magnet ↗ and Partiron pole + return parts ↗ in the Partframe ↗. The magnet supplies the field; the iron guides its flux toward the coil’s intended air gap.

The Toolalignment fixture ↗ supports the fixed parts against a reference while selected joints are formed with Partadhesive ↗. The fixture is an external tool; it is removed from the speaker.

Check that the fixed assembly leaves a clear, even route for the moving coil. This comes before adding the film, because the gap must remain accessible for alignment.

Fixed magnetic parts + support → a stable gap, ready for the moving coil.
What does the tool control?

The fixture controls position during assembly; it does not supply magnetic flux. Dimensional requirements come from the intended speaker design. The magnet and iron have separate making chains.

2

Join the coil and membrane.

Result → one moving assembly
Assembly transition · underside view The voice coil is bonded to the diaphragmPress Join the parts to bring an orange coil down to the underside of an aqua membrane. A bond ring joins them; the coil and membrane then move as one assembly. insulated wirecompliant surroundbond line

Separate parts → a coil, a membrane and a controlled bond.

Guide Partinsulated wire ↗ around the Toolwinding fixture ↗ to form the Partcopper voice coil ↗. The mandrel provides a repeatable reference shape; its guides support the wire as turns are formed. Insulation keeps neighboring turns electrically separate.

Release the formed coil from the reference, then support it while bonding it to the underside of the Partdiaphragm + surround ↗ with Partadhesive ↗. Keep the compliant edge free to flex.

The fixture’s job ends when the part can hold its intended shape. It does not stay inside the moving assembly.

The coil and film now form one moving assembly.
Why keep the moving assembly light?

The coil, film and their bonds contribute to the moving assembly. Its mass and suspension influence the response, so bonding must support the joint without unnecessarily restricting motion.

3

Center and seal the moving assembly.

Result → supported, free motion
Alignment demonstration · exaggerated clearance Coil centering in the magnetic gapAdjust the centering slider to demonstrate how an offset coil approaches the fixed iron. At the center, both sides have clearance. The surround anchors the membrane’s outer edge to the frame. rest position · centeredsealseal The alignment tool is removed; it is not contained in the speaker.

Centered: the coil has clearance on both sides.

Use the Toolalignment fixture ↗ and removable guides to hold the moving assembly at its intended rest position. Lower the Partvoice coil ↗ into the magnetic air gap between the Partfixed iron surfaces ↗; the Partmagnet ↗ remains fixed.

Bond the Partsurround ↗ to the Partframe ↗ with Partadhesive ↗. The frame anchors the outer edge while the membrane center remains able to travel.

Remove the guides after the joints can support the intended position. Check that the coil stays clear of the fixed iron and that the intended chamber edges are sealed.

The assembly is centered and supported, with room to move.
Tool use and tool making are different pages

This step uses the alignment fixture to hold a position. Its linked article instead makes the fixture from a base, guide parts and locators, using fabrication and measurement tools.

4

Connect the circuit. Test the sound.

Result → checked electrical + acoustic behavior
Test setup · three different questions Five individual tools in the speaker test setupA power source supplies equipment. An audio signal source defines the test signal, an amplifier drives the speaker, a meter checks the coil circuit, and a measurement microphone observes sound. Each external device opens its own making article. Make the Power sourcePower source Make the Audio signal sourceSignal source Make the Audio amplifierAmplifier Speaker Make the Measurement microphoneMicrophone Make the MeterDC ΩMeter DC Ωmeter
Meter ↗Audio signal source ↗Audio amplifier ↗Measurement microphone ↗Power source ↗

A meter checks continuity and DC resistance. No resistance target is specified in this conceptual model.

Join the coil to Partterminals + flexible leads ↗. Use a ToolMeter ↗ across the electrical path to check continuity and DC resistance. The leads must carry current while allowing the moving assembly to travel.

For the motion check, the ToolAudio signal source ↗ defines a test signal. The ToolAudio amplifier ↗ drives the coil using energy supplied by a ToolPower source ↗.

A ToolMeasurement microphone ↗ observes the sound for the acoustic check. Check free movement and rub-buzz, then the intended acoustic response. Each device has a distinct job and its own making article.

Continuity, motion and acoustic response answer three different questions.
What are these demonstrations measuring?

The controls explain which tools participate in each check. The drawings and traces are conceptual, not recorded test data or pass certificates. Actual drive limits, target resistance and acoustic targets depend on the chosen speaker design.

Keep following the making path

Parts, and the tools that make them.

Every child uses the same article layout and returns to its caller.

PartCopper voice coil ↗ToolWinding fixture ↗← Return to Phone

Look a little closer

Pan by scrolling. Tap a numbered label to inspect its part.