# How a Coaxial Speaker Cone Works How a coaxial car speaker splits sound between a large cone for bass and a small centre dome for treble, and how its coil moves the air\. By cosmic\-panda\-235bcc64 Topic: Physics & Chemistry [Open the interactive Jig](https://ask.jig.com/j/NUUnGK0JEZeI) ## Transcript ### 1. A speaker inside a speaker This is a coaxial speaker, the kind found in many car doors\. It is really two speakers sharing one centre line: a big cone for low sounds and a small dome in its middle for high ones\. A quarter has been cut away so you can see inside\. Drag anywhere to turn the stand and see the back\. Coaxial means sharing one axis\. ### 2. The parts that make sound The light, stiff cone is the part that moves the air\. Behind it sit a heavy ring magnet and a small coil of copper wire glued to the cone\. Around the edge, a soft rubber ring holds the cone in place, and a rippled cloth disc hides underneath\. Speakers are named by their mounting size: this "6\.5 inch" speaker has a moving cone only about 13 cm across\. ### 3. Electricity becomes a push The wire coil sits in a narrow gap inside the magnet\. When the music signal flows through the coil, it becomes a magnet too, so it is pushed out or pulled in\. The magnet stays still; the coil and the cone move together\. Send one pulse and watch\. The gap around the coil is very narrow, so the coil must never wobble sideways and rub\. ### 4. Pushing and pulling the air Music makes the signal swing back and forth, so the cone swings too\. Moving out, it squeezes the air in front of it; moving in, it spreads the air apart\. Watch the dots of air bunch up and thin out\. Each dot only wiggles in place, but the squeeze travels on to your ears\. The cone really moves only a few millimetres\. Here the motion is made bigger and much slower so you can see it\. ### 5. Springs at both ends The cone needs to slide straight in and out, like a piston, and then return to the middle\. The rubber ring at its edge, called the surround, and the rippled disc behind it, called the spider, both flex like springs\. Together they keep the coil centred in its gap\. The spider gets its name from its web\-like ripples\. ### 6. The little tweeter High sounds need very fast wiggles, thousands each second, and a big cone is too heavy to keep up\. So a small dome called the tweeter sits on a post in the centre\. It has its own tiny coil and magnet and makes the high notes, like cymbals and whistles\. The tweeter dome here is about 25 mm \(1 inch\) across\. High notes have short waves, so its squeezes sit close together\. ### 7. Sharing out the music A crossover splits the signal: deep notes go to the big cone, high notes go to the tweeter\. In many coaxial speakers it is just a small part called a capacitor, here on the frame by the wires\. Choose what to play and see which part moves\. Sound travels at the same speed for every note, so low and high squeezes move upward together\. ### 8. One point, the whole song Because both speakers share one centre line, low and high sounds start from the same spot and reach you together\. That is why a coaxial speaker fits in a single hole and still sounds clear\. Next time you hear music, picture the cone and dome dancing\. Humans hear from about 20 to 20,000 vibrations per second\.