Speaker impedance and wiring calculator
Wiring speakers in parallel halves the impedance and doubles the current the amplifier must supply. Below the amplifier minimum, it will protect itself or fail.
ohm
W
ohm
Impedance wired in parallel
4.000ohm
- Impedance wired in series
- 16.000 ohm
- Parallel wiring is within the amplifier limit
- 1
- Most speakers you can parallel safely
- 2
- Amplifier output into that load
- 200.0 W
- Power per speaker
- 100.0 W
- SPL gain from the extra speakers
- 3.01 dB
Show the working
- Impedance of each speaker = 8
- Number of speakers = 2
- Amplifier power at 8 ohms = 100
- Amplifier minimum load = 4
- Impedance wired in parallel = 8 / 2 = 4
- Impedance wired in series = 8 * 2 = 16
- series_parallel = 2 >= 4 ? 8 : 4 = 4
- Amplifier output into that load = 4 > 0 ? 100 * 8 / 4 : 0 = 200
- Power per speaker = 2 > 0 ? 200 / 2 : 0 = 100
- Parallel wiring is within the amplifier limit = 4 >= 4 ? 1 : 0 = 1
- Most speakers you can parallel safely = 4 > 0 ? floor(8 / 4) : 0 = 2
- SPL gain from the extra speakers = 10 * log10(2) = 3.0103
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
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The formula
- parallel: 1/Z = sum of 1/Zn, so identical speakers give Z/n
- series: Z = sum of Zn
- amplifier power roughly doubles as impedance halves, until it runs out of current
Nominal impedance is a label. Real speaker impedance swings by a factor of three or more across the frequency range.
Series wiring degrades damping and can audibly loosen the bass; parallel is generally preferred where the amplifier can take it.