100mH Audio-Frequency Inductor
A much larger inductance value than an RF choke, sized to present meaningful impedance already in the audio band — the standard role for the low-pass leg of a passive loudspeaker crossover network.
How this component works
An inductor is a passive component that stores electrical energy in a magnetic field when electric current flows through it. Because it takes time for the magnetic field to build and collapse, an inductor inherently opposes any rapid changes in current.
In DC circuits, an inductor initially acts as an open circuit when power is applied, but eventually becomes a near-perfect short circuit once the magnetic field stabilizes. In AC circuits, its resistance to alternating current (called reactance) increases as the frequency of the AC signal increases.
Deep Dive: 100mH Audio Inductor
At 1kHz, a 100mH inductor presents roughly 2π × 1,000 × 0.1 ≈ 628Ω of reactance — enough to meaningfully attenuate an audio signal at that frequency, which is exactly the behavior a passive loudspeaker crossover exploits. Placed in series with a woofer, this inductor lets low-frequency bass content through with little opposition (reactance falls toward zero as frequency drops) while increasingly blocking the higher frequencies a tweeter should be handling instead — a purely passive, frequency-dependent filter with no active components.
Reaching 100mH takes considerably more wire turns (and often an iron or ferrite core to boost inductance per turn) than the 10µH RF choke in this category needs, which has two consequences: higher DC resistance (a real efficiency loss in an audio path, since some signal power is dissipated as heat rather than reaching the speaker) and a much lower self-resonant frequency. That lower SRF is a feature here, not a bug — the inductor only needs to behave ideally up into the audio range (tens of kHz at most), a far lower bar than the RF choke's requirement to stay inductive up into the MHz range, which is why the two parts use such different construction despite both being 'just an inductor.'
Common Use Cases
- Low-pass leg of a passive loudspeaker crossover network, blocking high frequencies from reaching a woofer
- Tone-shaping or filtering stage in an audio circuit where meaningful impedance is needed at kHz-range frequencies
- Series choke in a tube amplifier power-supply filter, smoothing at lower frequencies than an RF application would need
Frequently Asked Questions
Why does a crossover network use an inductor to block high frequencies from a woofer?
An inductor's impedance rises with frequency, so as an audio signal's frequency increases, the inductor increasingly resists passing it through — placed in series with a woofer, this lets low bass frequencies through easily while attenuating the higher frequencies better suited to a tweeter.
Why is 100mH so much bigger than the 10µH RF choke value in this same category?
Audio frequencies (tens of Hz to tens of kHz) are far lower than RF frequencies (MHz+), and reactance scales with both inductance and frequency. To get a meaningfully high impedance at a low audio frequency, you need a much larger inductance value than you'd need to get the same impedance at a much higher RF frequency.
Could this 100mH inductor be used as an RF choke instead?
Not effectively — its higher inductance and construction (more turns, often with an iron core) give it much higher parasitic winding capacitance and a much lower self-resonant frequency, so it would stop behaving like a clean inductor well before reaching typical RF operating frequencies.
Comparison Notes
Compared to the 10µH RF choke in this category, this part trades a much higher inductance for usefulness at much lower frequencies — the two are not interchangeable substitutes for each other despite sharing the same underlying inductor physics.