LF is caused by odd-ordered harmonic content in the signal, usually harmonics of the 9th order and beyond. These harmonics are emphasized by the use of negative feedback in amplifiers and by non-linearities in transistors (and to a lesser degree by non-linearities in pentodes).
IOW, LF is usually not caused by speakers alone. To reduce odd-ordered harmonics, one will have to use a tube amplifier with little or no feedback. Such an amplifier will need a linear impedance curve from the speaker, so if low LF is your main priority, then you now know what you have to look for!
IOW, LF is usually not caused by speakers alone. To reduce odd-ordered harmonics, one will have to use a tube amplifier with little or no feedback. Such an amplifier will need a linear impedance curve from the speaker, so if low LF is your main priority, then you now know what you have to look for!