Mr Peabody
Well-known member
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I try to explain to folks with or looking to buy JBL speakers they aren't exactly tube friendly just because they may be 94dB rated give or take. Same with speakers like Legacy. Especially lower power tube amps. This may vary some with the legacy models of JBL like 43nn models. More modern models have more complex crossovers with low impedance woofers. A tube amp may give you sound but it won't drive the speaker to its potential.
How easy a speaker is to drive depends on sensitivity, phase angle, impedance curve, driver control requirements and how much current the crossover demands.
We know that impedance of a speaker is reactive, so if a speaker is rated at nominal impedance of 4, 6 or 8 ohms that's not what your amp will see constantly. The impedance will swing up or down from that nominal impedance. As the impedance dips the speaker demands more current from your amp. Some tube amps aren't designed to deliver that current. From what I understand output transformers help to some extent but still not optimum as impedance swings the transformer is constantly changing which could effect linearity, and control. There are exceptions like VAC, Mac or ARC who build high quality transformers that deal with the issues which make them better able to drive some speakers.
Legacy, passive, have multiple drivers and often in the mid 90's sensitivity. It takes current to control those drivers, better dynamics, tighter bass, and cleaner transients.
Brands like certain Klipsch, Volti, Zu in contrast are easier to drive and tube friendly due to simple crossovers and benign impedance swings.
Generally a power amp keeps voltage relatively stable so as impedance dropts the speaker is demanding more current from your amplifier. Problems occur when your amp can't deliver. AS an example, at 20v at 8 ohms is 2.5a if the impedance drops to 4 ohms the current is now 5a, 2 ohms 10a.
Other end of things we have brands like Harbeth that are in the mid 80's db yet work well with tube amps. Why, they have smooth impedance curves and gentle phase angles.
So in discussions which comes first we must realize the amp AND speakers have to work optimally together for best results and the health of the gear.
How easy a speaker is to drive depends on sensitivity, phase angle, impedance curve, driver control requirements and how much current the crossover demands.
We know that impedance of a speaker is reactive, so if a speaker is rated at nominal impedance of 4, 6 or 8 ohms that's not what your amp will see constantly. The impedance will swing up or down from that nominal impedance. As the impedance dips the speaker demands more current from your amp. Some tube amps aren't designed to deliver that current. From what I understand output transformers help to some extent but still not optimum as impedance swings the transformer is constantly changing which could effect linearity, and control. There are exceptions like VAC, Mac or ARC who build high quality transformers that deal with the issues which make them better able to drive some speakers.
Legacy, passive, have multiple drivers and often in the mid 90's sensitivity. It takes current to control those drivers, better dynamics, tighter bass, and cleaner transients.
Brands like certain Klipsch, Volti, Zu in contrast are easier to drive and tube friendly due to simple crossovers and benign impedance swings.
Generally a power amp keeps voltage relatively stable so as impedance dropts the speaker is demanding more current from your amplifier. Problems occur when your amp can't deliver. AS an example, at 20v at 8 ohms is 2.5a if the impedance drops to 4 ohms the current is now 5a, 2 ohms 10a.
Other end of things we have brands like Harbeth that are in the mid 80's db yet work well with tube amps. Why, they have smooth impedance curves and gentle phase angles.
So in discussions which comes first we must realize the amp AND speakers have to work optimally together for best results and the health of the gear.