How to Wire Tweeters to Speakers Correctly
Tweeters need a crossover or a series capacitor or they burn out. Here are the capacitor sizes, wiring order and polarity rules that keep them alive.
A tweeter must never be wired straight across a full range signal. It needs a crossover, or at minimum a capacitor in series, to block the bass that would burn out its voice coil. Wire the tweeter in parallel with the woofer through the crossover’s high pass output, keeping polarity consistent, positive to positive.
This is the one speaker wiring job where getting it wrong destroys something. A tweeter voice coil is a few turns of hair thin wire on a former the size of a fingertip, and it has no way to survive bass energy. The good news is that the fix is one component and about five dollars.
Why a tweeter cannot go straight across the terminals
A woofer handles low frequencies by moving a long way. A tweeter handles high frequencies by moving barely at all, which is why its coil can be tiny and light. Send a 60 Hz bass note into it and the coil tries to travel a distance it physically does not have, while absorbing power it cannot dissipate.
Most of the energy in music sits below 500 Hz. So a tweeter wired directly to an amplifier is receiving the large majority of the power in the signal, continuously, into a component rated for a fraction of it. They usually last minutes.
The crossover exists to stop that. It is a filter that sends highs to the tweeter and lows to the woofer, and it is not optional.
The single capacitor method, and how to size it
The simplest working crossover is one non-polarized capacitor in series with the tweeter’s positive lead. It blocks low frequencies and passes highs, giving a first order filter that rolls off at 6 dB per octave.
The value comes from the tweeter’s impedance and the frequency you want to cut below:
C = 1 divided by (2 x pi x f x R), where C is farads, f is the crossover frequency in hertz and R is the tweeter impedance in ohms.
In practice you can skip the arithmetic and use these:
| Tweeter impedance | Capacitor | Crossover point |
|---|---|---|
| 8 ohm | 3.3 uF | About 6,000 Hz |
| 8 ohm | 4.7 uF | About 4,200 Hz |
| 8 ohm | 6.8 uF | About 2,900 Hz |
| 4 ohm | 6.8 uF | About 5,800 Hz |
| 4 ohm | 10 uF | About 4,000 Hz |
Use a non-polarized film or bipolar electrolytic capacitor rated at 100 V or more. An ordinary polarized electrolytic from a parts drawer will fail, since audio is alternating current and the capacitor will be reverse biased half the time.
If you are unsure, pick a higher crossover point rather than a lower one. Crossing over too high costs you a little response in the upper midrange. Crossing over too low costs you the tweeter.
Wiring with a proper crossover
A two way passive crossover has one input pair and two output pairs, usually marked HF or tweeter and LF or woofer.
- Run speaker cable from the amplifier to the crossover input, positive to positive.
- Run the HF output to the tweeter terminals.
- Run the LF output to the woofer terminals.
- Mount the crossover inside the cabinet, away from the woofer magnet, because a big inductor sitting in a stray magnetic field picks up noise.
The woofer and tweeter end up in parallel as far as the amplifier is concerned, but the filter means they never present their combined impedance at the same frequency. This is why a two way speaker built from two 8 ohm drivers is still a nominally 8 ohm load rather than 4. Our explainer on what ohm means for speakers covers why that number moves around.
Second order crossovers add an inductor and give a steeper 12 dB per octave slope, which protects the tweeter better and is what most commercial speakers use. They also invert the tweeter’s phase, which is why many are wired with the tweeter connected backwards on purpose.
Polarity
Keep positive to positive throughout a first order design. If one driver is wired backwards the two will cancel each other around the crossover frequency, and you get an audible hole in the midrange with no obvious cause.
The test is simple. Play something with strong vocals, sit centered, and flip the tweeter’s two wires. One way sounds fuller through the mids, the other sounds thin and distant. Keep the fuller one, whichever direction that turns out to be.
On a second order crossover, expect the correct answer to be the tweeter reversed. That is normal and not a mistake.
Car audio specifics
Component sets come with their own crossovers, and the tweeter must go through the one in the box. Wiring a component tweeter straight to a head unit output is the most common way people kill them.
If you are adding tweeters to existing coaxial speakers, wire each tweeter in parallel with its nearest coaxial through a capacitor, using 6.8 uF for a 4 ohm tweeter to cross over around 5,800 Hz. Bear in mind this lowers the total impedance the head unit sees, so do not do it on a channel that is already driving a 2 ohm load.
Mount the tweeter high, on the A pillar or the top of the door card, and aim it across the car toward the opposite headrest rather than straight at the nearest ear. It sounds strange as a technique and it produces a far more even image.
Frequently asked questions
Can I connect a tweeter without a crossover?
No, not without destroying it. A tweeter wired directly across the amplifier receives the bass content of the music, which is where most of the power in a signal lives, and its voice coil will overheat within minutes. The minimum acceptable protection is a single non-polarized capacitor in series with the positive lead, which costs a few dollars.
What size capacitor do I need for a tweeter?
For an 8 ohm tweeter, 4.7 uF crosses over around 4,200 Hz and suits most designs. For a 4 ohm tweeter, use 10 uF for a similar crossover point. Use a non-polarized film or bipolar type rated at 100 V or higher. If you are choosing between two values, take the smaller capacitor, since that raises the crossover frequency and gives the tweeter more protection.
Do tweeters wire in series or parallel with the woofer?
In parallel, with the crossover between them and the amplifier. The tweeter takes the high pass output and the woofer takes the low pass output, and both connect back to the same amplifier terminals. Wiring them in series would send the same current through both drivers and defeat the purpose of the filter entirely.
Should tweeter polarity be reversed?
It depends on the crossover. With a first order design using a single capacitor, keep polarity consistent, positive to positive. With a second order crossover, the filter shifts the tweeter’s phase by 180 degrees, so the tweeter is usually wired reversed on purpose to bring it back into alignment. Trust your ears: whichever wiring sounds fuller through the midrange is the right one.