When wiring multiple speakers, impedance readings can be confusing—especially when your calculation says one thing but your multimeter shows another. A common situation is wiring four 4-ohm speakers in series but measuring only 8 ohms on a multimeter. If this happened to you, don’t worry. This guide explains why it occurs, how to diagnose it, and how to fix it for safe amplifier performance.
🔎 Expected Impedance vs Measured Resistance
First, it’s important to understand a key concept:
Multimeters measure DC resistance (R), not true speaker impedance (Z).
- Speaker rating (4Ω) = nominal impedance
- Multimeter reading = voice coil resistance
A typical 4-ohm speaker actually measures:
3.0–3.6 ohms on a meter.
📊 Correct Calculation for 4 Speakers in Series
Series wiring adds resistance:
4Ω + 4Ω + 4Ω + 4Ω = 16Ω nominal
Real meter reading should be approximately:
3.2 + 3.2 + 3.2 + 3.2 ≈ 12–13Ω
👉 So if your meter shows 8Ω, something is wired differently than you think.
⚠️ Why You’re Reading 8 Ohms Instead of 16
1. You Actually Wired Series-Parallel (Most Common)
Often people accidentally wire:
- Two speakers in series
- Two speakers in series
- Then those two sets in parallel
This gives:
Series pair = 8Ω
Two pairs parallel = 4Ω total nominal
Meter reading ≈ 6–8Ω
This matches your reading.
2. Two Speakers Are Bypassed
If one pair isn’t connected properly, only two speakers may be in circuit:
4Ω + 4Ω = 8Ω
3. Loose or Incorrect Wiring
A disconnected terminal or reversed connection can remove speakers from the circuit path.
4. Faulty Speaker Voice Coil
A damaged speaker can read:
- Open circuit → infinite ohms
- Shorted coil → very low ohms
Either condition alters total reading.
🛠 How to Check Your Wiring (Step-by-Step)
Step 1 — Disconnect from amplifier
Never test resistance while connected.
Step 2 — Test each speaker individually
Each should read around 3–4Ω.
Step 3 — Trace wire path physically
Follow signal path:
Amp + → Speaker1 → Speaker2 → Speaker3 → Speaker4 → Amp –
There must be only one continuous path.
Step 4 — Test after each connection
Measure after adding each speaker to confirm increase.
🧠 Quick Wiring Reference Table
| Wiring Type | Expected Nominal | Meter Reading |
|---|---|---|
| Series (4 speakers) | 16Ω | 12–13Ω |
| Parallel (4 speakers) | 1Ω | ~1Ω |
| Series-Parallel | 4Ω | 6–8Ω |
| Two speakers only | 8Ω | ~6Ω |
🎯 Best Wiring for Amplifier Safety
Most amplifiers are stable at:
- 4Ω minimum (common)
- 2Ω minimum (high-power amps)
- 8Ω recommended (home amps)
Running too low impedance can:
- Overheat amp
- Cause distortion
- Trigger protection mode
- Damage components
🧾 Pro Tip from Audio Technicians
If your measured resistance is lower than expected, assume:
“You wired parallel somewhere.”
If higher than expected:
“You wired series somewhere.”
🏁 Final Verdict
If four 4-ohm speakers wired “in series” measure 8 ohms, then they are not actually in series. The most likely cause is accidental series-parallel wiring or a disconnected speaker. A true four-speaker series chain should read roughly 12–13 ohms on a multimeter.