1.) All coil driven loudspeakers vary their impdeance depending on frequency. The single number expressed in ohms on the back of the speaker is of only passing interest.
2.) You want to look at a plot showing impedance v. ferquency for your speaker.
When you look at this plot - look for violent changes in the low bass area ( You may also see some strange stuff happening around the crossover points.) To control the cone at lower frquencies you want current. A amp capable of driving the variable impedance of a real world loudspeaker will double in wattage as the load drops in impedance ( 50 into 8 ohms ,100 into 4 ,200 into 2 ohms for example. This takes power supply components that are not cheap - but they will sound more effortless in the bass area in almost all cases. Such a near ideal bass amp may or may not light your fire in terms of mid or high frequency reproduction.
Tube amps have to be able to send power through output transformers and much as I love the sound of good tube amps - I've never heard one that was simply stunning in deep bass reproduction.
Most true class A biased amps will produce the near perfect power to impedance ratio I describe above. After all - you've got to have a gonzo crazed power supply section to be able to do class A opertion to begin with - making it able to drive low impedances well is nearly a gimmie at that point. Class A's are a lot like tube amps in that a true A's watts seem to have a lot more hair on 'em than even well executed A/B amps. Probably at least part of this is because they can recover from clipping much faster than a A/B that 's been hammered to the wall. In other words a 50 watt class A amp will often walk all over a 150 watt A/B.
Disadvantages of True A biased amps - heat -weight-price - electric bills -patience.In my experience - every A amp I ever listened to - sounded much better once it had a chance to heat up ( usually seemed to take 40 min. to an hour). This is probably because in most amps bias and DC offset are interrelated in terms of adjustment. DC offset is always done once the amp has hit it's optimum temp.
Hope this is some help.
2.) You want to look at a plot showing impedance v. ferquency for your speaker.
When you look at this plot - look for violent changes in the low bass area ( You may also see some strange stuff happening around the crossover points.) To control the cone at lower frquencies you want current. A amp capable of driving the variable impedance of a real world loudspeaker will double in wattage as the load drops in impedance ( 50 into 8 ohms ,100 into 4 ,200 into 2 ohms for example. This takes power supply components that are not cheap - but they will sound more effortless in the bass area in almost all cases. Such a near ideal bass amp may or may not light your fire in terms of mid or high frequency reproduction.
Tube amps have to be able to send power through output transformers and much as I love the sound of good tube amps - I've never heard one that was simply stunning in deep bass reproduction.
Most true class A biased amps will produce the near perfect power to impedance ratio I describe above. After all - you've got to have a gonzo crazed power supply section to be able to do class A opertion to begin with - making it able to drive low impedances well is nearly a gimmie at that point. Class A's are a lot like tube amps in that a true A's watts seem to have a lot more hair on 'em than even well executed A/B amps. Probably at least part of this is because they can recover from clipping much faster than a A/B that 's been hammered to the wall. In other words a 50 watt class A amp will often walk all over a 150 watt A/B.
Disadvantages of True A biased amps - heat -weight-price - electric bills -patience.In my experience - every A amp I ever listened to - sounded much better once it had a chance to heat up ( usually seemed to take 40 min. to an hour). This is probably because in most amps bias and DC offset are interrelated in terms of adjustment. DC offset is always done once the amp has hit it's optimum temp.
Hope this is some help.