Speaker Symbol
Definition: The Speaker symbol represents an electro-acoustic transducer drawn as a rectangular voice-coil body connected to a triangular cone (diaphragm) with two radiation-arc lines indicating sound emission, and two terminals (+ and −), denoting a device that converts electrical alternating-current audio signals into acoustic pressure waves (sound), as defined in IEC 60617-09 and ANSI Y32.2/IEEE 315.
Also known as: loudspeaker symbol, audio speaker symbol, sound transducer symbol, woofer symbol schematic, LS symbol circuit.
What the Speaker symbol means
The Speaker symbol identifies an electro-acoustic output transducer in an audio circuit. When an alternating audio signal is applied between the positive and negative terminals, current flows through the voice coil in the speaker's magnetic gap, creating a force that drives the paper or polymer diaphragm back and forth, compressing and rarefying the surrounding air to produce sound waves. The + terminal indicates the polarity that drives the cone outward (forward motion) when a positive voltage is applied, which is critical for correct phase alignment in multi-speaker systems.
In circuit diagrams, the speaker symbol is the final stage load element in an audio amplifier output chain, appearing after power amplifier stages, crossover networks, and sometimes a protection relay. The symbol communicates the impedance load (typically 4 Ω, 8 Ω, or 16 Ω) presented to the amplifier. Multiple speaker symbols may be shown in series, parallel, or series-parallel combinations to achieve the desired total load impedance.
How to identify the Speaker symbol
The Speaker symbol consists of a vertical rectangle on the left (representing the voice-coil former and magnet assembly), connected on its right edge to a triangle pointing rightward (the cone diaphragm expanding in the direction of sound emission). To the right of the triangle, two arcs (one longer, one shorter) indicate radiated sound waves — an open-mouthed curved line near the cone and a larger curve further away. A horizontal line exits the left edge of the rectangle as the input signal terminal. The positive (+) terminal is the main input lead and the negative (−) terminal exits from the far right. The triangle-plus-arcs combination uniquely identifies the speaker symbol versus a microphone (which would have arcs pointing inward) or a buzzer (which uses a circle with radiating lines).
Function in a circuit
A speaker converts electrical audio energy into acoustic energy. The voice coil, wound on a cylindrical former and suspended in a permanent magnetic field, carries the audio-frequency current. The interaction between the current and the magnetic field produces a force proportional to the current (F = BIL), moving the coil and attached cone axially. The cone displaces air, radiating a sound pressure wave matching the electrical waveform's frequency content. Speaker efficiency (sensitivity) is typically 85–100 dB SPL at 1 W / 1 m, and frequency response varies by design from subwoofer (20–200 Hz) to full-range (80 Hz–20 kHz) to tweeter (2–20 kHz).
Standards: IEC vs ANSI
| IEC 60617 | IEC 60617-09 (telecommunications devices) defines the loudspeaker symbol as a rectangle connected to a triangle with optional sound-radiation arcs. The IEC symbol appears in audio and telecommunications circuit diagrams. IEC 60268-5 defines the performance characteristics of loudspeakers (sensitivity, impedance, frequency response). |
|---|---|
| ANSI/IEEE 315 | ANSI Y32.2-1975 (IEEE 315) defines the loudspeaker symbol as a rectangle (voice coil) with a triangular horn or cone and radiation arcs. The ANSI symbol is functionally identical to IEC 60617-09. The standard designator for a speaker/loudspeaker in North American schematics is LS (loudspeaker) or SP. |
| Key difference | The IEC 60617-09 and ANSI Y32.2/IEEE 315 loudspeaker symbols are essentially identical — both use a rectangle connected to a pointing triangle with sound-radiation arcs. No functionally meaningful glyph difference exists between the two standards for this symbol. |
Terminals / pins
| Pin | Name |
|---|---|
| pos | + |
| neg | - |
Typical values
Impedance: 4 Ω, 8 Ω, or 16 Ω (nominal; actual impedance varies with frequency). Power handling: 0.25 W (small piezo) to 1000 W (professional subwoofer). Sensitivity: 85–100 dB SPL at 1 W, 1 m (typical; higher is more efficient). Frequency response: 20–20,000 Hz (full-range), 20–200 Hz (subwoofer), 2,000–20,000 Hz (tweeter). Voice coil DC resistance: approximately 3.2–14 Ω for 4–16 Ω drivers.
Where the Speaker symbol is used
- Audio amplifier output stage diagrams showing speaker impedance load connected to power amplifier output
- Public address and intercom system schematics documenting speaker lines, transformer taps, and zones
- Consumer electronics block diagrams (televisions, radios, soundbars) showing audio signal routing to speakers
- Alarm and notification circuit schematics where a small speaker or piezo element provides audible annunciation
- Automotive audio system wiring diagrams showing speaker locations, impedance, and wiring polarity
- Professional sound reinforcement system diagrams with crossover networks feeding subwoofer, midrange, and tweeter symbols
Example
In a class D audio amplifier output circuit, the speaker symbol (8 Ω load) is connected between the BTL (bridge-tied load) positive output pin of the amplifier IC and the BTL negative output pin. The + terminal connects to the amplifier's OUT+ pin and the − terminal connects to OUT−. A series inductor and parallel capacitor (output LC filter) immediately preceding the speaker symbol filter the PWM switching noise from the amplifier before it reaches the speaker, preventing high-frequency heating of the voice coil.
Key facts
- The Speaker symbol represents an electro-acoustic transducer with two terminals: positive (+, pin id: pos) for the polarity that drives the cone forward, and negative (−, pin id: neg) for the return path, as defined in IEC 60617-09 and ANSI Y32.2/IEEE 315.
- The standard schematic designator for a speaker is LS (loudspeaker) per IEC/ANSI conventions, though SP is also used informally in consumer electronics diagrams.
- A speaker symbol's impedance is the nominal load it presents to the amplifier: 4 Ω, 8 Ω, and 16 Ω are the most common values; the actual impedance varies with frequency and typically has a peak at the resonant frequency (Fs).
- Correct polarity (+/− terminal assignment) is critical in multi-speaker systems — reversing polarity on one speaker causes phase cancellation where it overlaps acoustically with other in-phase speakers, significantly reducing bass output.
- Speaker sensitivity (efficiency) is rated in dB SPL at 1 W input, 1 m distance; a 3 dB increase requires doubling the amplifier power, making sensitivity a key factor in amplifier sizing.
- The IEC 60617-09 speaker symbol uses a rectangle (voice coil block) connected to a rightward-pointing triangle (cone) with radiation arcs, visually indicating the conversion of electrical energy into outward-propagating sound waves.
- A speaker's nominal impedance (e.g., 8 Ω) is not its DC resistance; the actual DC resistance of the voice coil (Re) is typically 75–85% of the nominal impedance (e.g., approximately 6.4 Ω for an 8 Ω driver).
- Speakers in series have additive impedances (two 8 Ω speakers in series = 16 Ω total); speakers in parallel have halved impedance (two 8 Ω speakers in parallel = 4 Ω total), which affects amplifier loading and minimum impedance limits.
Diagrams that use this symbol
- car audio wiring diagram
- car stereo wiring diagram
- car radio connection diagram
- car radio wiring diagram
- subwoofer wiring diagrams
- speaker wiring diagram
- radio wiring diagram
- speaker connection diagram
Frequently asked questions
What does the speaker symbol look like in a circuit diagram?
The Speaker symbol shows a vertical rectangle on the left (the voice-coil/magnet body), connected to a rightward-pointing triangle (the cone diaphragm). Two curved arcs to the right of the triangle represent radiated sound waves. A horizontal line exits the left edge as the + signal input terminal and the − terminal is at the far right. This triangle-plus-arcs combination uniquely identifies loudspeaker symbols.
What does the speaker symbol mean in an audio circuit?
The Speaker symbol represents an electro-acoustic transducer that converts alternating electrical audio signals into sound waves. In a circuit, it is the output load of an audio amplifier, with the + terminal receiving the audio signal that drives the cone outward on positive half-cycles and the − terminal providing the return path.
What is the difference between IEC and ANSI speaker symbols?
The IEC 60617-09 and ANSI Y32.2/IEEE 315 loudspeaker symbols are identical — both use a rectangle connected to a rightward-pointing triangle with sound-radiation arcs. No glyph difference exists between the two standards for this symbol.
What is the designator letter for a speaker on a schematic?
The standard schematic designator for a loudspeaker is LS (loudspeaker) per IEC 61346 and ANSI Y32.2/IEEE 315. In some consumer and automotive electronics diagrams, SP (speaker) is used as an informal alternative. The designator is followed by a number: LS1, LS2, etc.
What impedance values do speakers have?
Speakers have nominal impedances of 4 Ω, 8 Ω, or 16 Ω in most consumer and professional audio applications. The actual impedance varies with frequency — it is higher at the mechanical resonance frequency and lower in the mid-band. The amplifier must be rated to drive the speaker's nominal impedance; connecting a 4 Ω speaker to an amplifier rated for 8 Ω minimum load can overload and damage the amplifier.
Why does speaker polarity matter in a schematic?
Speaker polarity (+ and − terminal assignment) determines whether the cone moves forward (outward) or backward on a positive signal half-cycle. In a single-speaker system, reversed polarity causes no frequency-response change. In a multi-speaker system with overlapping coverage, a polarity-reversed speaker is acoustically out of phase with its neighbors, causing destructive interference and significant bass cancellation in the overlap zone.
What standard defines the speaker symbol?
IEC 60617-09 (graphical symbols for diagrams — telecommunications, telephony, and telegraphy) defines the loudspeaker symbol as a rectangle connected to a triangle with radiation arcs. ANSI Y32.2-1975 (IEEE 315) defines the same symbol. IEC 60268-5 governs the measurement of loudspeaker performance parameters (sensitivity, impedance, frequency response).
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