Speaker Impedance & Load Calculator

Calculate the combined nominal impedance of one to four speakers, then see what primary impedance an output transformer reflects with that load. Choose series, parallel or common four-speaker wiring arrangements.

Number of speakers 1 speaker 2 speakers 3 speakers 4 speakers Wiring arrangement Nominal transformer primary (kOhms) Plate-to-plate for push-pull output stages. Transformer secondary tap 4 ohms 8 ohms 16 ohms Custom

Speaker 1 (ohms) Speaker 2 (ohms)

Enter nominal speaker impedance, not the DC resistance measured by a multimeter.

Calculated results

Combined speaker impedance

8 ohms

Reflected primary impedance

8 kOhms

Difference from target primary

0%

Calculated transformer turns ratio

31.62:1

Closest standard secondary tap (if fitted)

8 ohms

Nominal primary target

8 kOhms

Speaker wiring

Other common secondary taps

Hypothetical reflected primary impedances if the transformer has 4, 8 or 16-ohm taps. Not every output transformer has all three taps.

Secondary tap	Reflected primary	Difference

Important: These calculations use nominal speaker impedance, which varies with frequency in a real loudspeaker. Transformer matching is an electrical estimate, not a guarantee that a particular mismatch is safe for an amplifier. Check the amplifier and output transformer requirements, and use an appropriate load when operating a valve amplifier.

How the calculation works

Series: impedances add together.

Parallel: reciprocal impedances add together.

Reflected primary: actual primary impedance equals nominal primary impedance multiplied by actual speaker impedance, divided by the nominal impedance of the selected secondary tap.

Turns ratio: square root of nominal primary impedance divided by nominal secondary impedance.

Example: two 16-ohm speakers in parallel make an 8-ohm nominal load. On an 8-ohm secondary of an 8-kOhm transformer, the reflected primary is 8 kOhms. In series they make 32 ohms, reflecting 32 kOhms through that same tap.

The green, amber and red comparison indicates how far the reflected value differs from the chosen nominal target. It is not a safety certification.