It's useless to talk about 4ohm speaker and 8ohm speaker, as none are flat at that impedance across the audio band, they are very different. And the best way to treat it is to look at the lowest impedance and - phase angle and base an amp around that.
1: There can be dips in the impedance curve at certain frequencies that can be very low.
2:There are also negative phase angles at certain frequencies that can be very high.
Combine the one and two at certain frequencies and you have almost a short as seen by the amplifier "usually" in the bass.
EG:
Wilson Alexia is spec'ed by Wilson at 90db and 4ohm
Independent test measured:
I in the power region of the bass between 60hz and 110hz approx it has a nominal impedance of just 1.9ohms!, combine this with the negative phase angle of around -45 degrees and you have an EPDR (equivalent peak dissipation resistance) that the amp sees as just .9ohm!!!!!
So much for being designated as a "4ohm speaker"!!!
And the Sofia 3 is even worse than this.
Cheers George
1: There can be dips in the impedance curve at certain frequencies that can be very low.
2:There are also negative phase angles at certain frequencies that can be very high.
Combine the one and two at certain frequencies and you have almost a short as seen by the amplifier "usually" in the bass.
EG:
Wilson Alexia is spec'ed by Wilson at 90db and 4ohm
Independent test measured:
I in the power region of the bass between 60hz and 110hz approx it has a nominal impedance of just 1.9ohms!, combine this with the negative phase angle of around -45 degrees and you have an EPDR (equivalent peak dissipation resistance) that the amp sees as just .9ohm!!!!!
So much for being designated as a "4ohm speaker"!!!
And the Sofia 3 is even worse than this.
Cheers George