Reactance is active resistance and changes with frequency, from caps, speakers etc. A speaker impedance rating is only the voice coil resistance, in practice this changes with the frequency.
SVT tube heads run at either 4 or 2 ohms only.
Amp and cabinet question
Moderators: rickenbrother, ajish4
John Drysdale - I agree to a point.
With today's super high watt SS heads or amps, unless you want a wall of cabs, many times you will have a more powerful head than cab rating and MUST keep the levels out of the amp sane or you will fry a speaker, as Rikk experienced. In the heat of the battle that is not always followed, thus the rubbing sound Bob reports, which is the voice coil overheated and warped and no longer fitting smoothly in the gap it is designed to move in.
Bob also states "In my experience as long as you have a good clean sound you don't have to worry" and that is really good advice. It takes discipline to listen for the rattiness that indicates overdriven speakers.
Bob - I would add to your statement "A speaker impedance rating is only the voice coil resistance, in practice this changes with the frequency" that it is AC resistance. DC resistance is the resistance of the wire in the voice coil and is almost exclusively if not always lower then the impedance rating. There is that reactive element (again AC) that is a vector math function (as Ed relates) that will result in the impedance being higher than the DC resistance.
*My opinions* - the reason there are 1500W SS amps is to try and get the punch a 300W tube head will provide easily. I prefer tubes over SS because of the tones capable. I prefer light amps, just haven't found an SS solution I can afford.
With today's super high watt SS heads or amps, unless you want a wall of cabs, many times you will have a more powerful head than cab rating and MUST keep the levels out of the amp sane or you will fry a speaker, as Rikk experienced. In the heat of the battle that is not always followed, thus the rubbing sound Bob reports, which is the voice coil overheated and warped and no longer fitting smoothly in the gap it is designed to move in.
Bob also states "In my experience as long as you have a good clean sound you don't have to worry" and that is really good advice. It takes discipline to listen for the rattiness that indicates overdriven speakers.
Bob - I would add to your statement "A speaker impedance rating is only the voice coil resistance, in practice this changes with the frequency" that it is AC resistance. DC resistance is the resistance of the wire in the voice coil and is almost exclusively if not always lower then the impedance rating. There is that reactive element (again AC) that is a vector math function (as Ed relates) that will result in the impedance being higher than the DC resistance.
*My opinions* - the reason there are 1500W SS amps is to try and get the punch a 300W tube head will provide easily. I prefer tubes over SS because of the tones capable. I prefer light amps, just haven't found an SS solution I can afford.