Axiom Home Page Forums General Discussion Stereo Tube Driver Pwr

I have a Soundstage One Hybrid Tube Integrated Amp (25 wpc, Chinese knock-off), and would like to know whether It would be capable of driving the Axiom MT 80's or MT 60's. I play at moderate home levels, and obviously don't expect nor do I want to, shake windows or walls. My primary music concerns are are classical and jazz (if that should make a difference).
Thanks

I would have to think the M60s would be a pretty safe bet with your amp. If it has 4 ohm taps then you could consider the M80s.

Now my confusion.
The M80's have an input impedance = 4 ohms, and an spl=95 dB/W/m.
The M60's have an input impedance = 8 ohms, and an spl=93 dB/W/m.
And both require 10W min. to be driven.
This tells me that for a given I/P power, regardless of the input impedance, the MT80's are easier to drive than the MT60's.
Where did I error?
Thanks

Because the M80s are 4 Ohm speakers, they require more current to drive than the 4 Ohm 60s.

For the same amount of power, the M80s will produce almost twice the sound pressure level compared to the M60s. However, the M80 will require more current than the M60. The question is, can your tube amp provide the current required for the SPL levels you are interested in? If it can function as a 25W amp for the M80s' 4 Ohm load, you will achieve 98dB or more at 9 feet. If you normally listen at 75dB, you will have more headroom than you could ever ask for.

If the amp is not rated for a 4 Ohm load, adn you constantly play it "cranked", be prepared to be changing your tubes frequently as you will be drawing excessive plate curent.

ummmm Peter, the 60's are 8 ohm.

I meant 8 Ohm. Too late to edit.

Tam, welcome. You're really not in "error" in your comment. Assuming that the Axiom specs are correct, the M80s require less power than the M60s for a given sound level. The 2dB difference would indicate that the M80s require about 63% as much power. This tends to offset the effect of the lower impedance on the current required, so that at the same sound level the M80s would draw very little more current. For example, at the 25 watt power rating, which should provide for a peak of a little over 100dB with the M80s at a typical listening distance in a typical size of room, the calculated current requirement using Ohm's Law would be square root(25/4)or 2.50 amperes. The M60s using about 40 watts for that same sound level would have a current requirement of square root(40/8)or about 2.24 amperes. So, although for a given amount of power a 4 ohm load requires about 70% more current than an 8 ohm load(not double, as is sometimes said), if the 4 ohm speaker is more sensitive the difference is reduced, eliminated or even reversed at a given sound level.

Whether your amp would be adequate depends on how loud you play the material and how wide its dynamic range is. As was said above, it should be okay for peaks of at least a little over 100dB. You may never need more than this if, as you say you don't expect to listen at extremely high levels.

Correction: the additional current required at the same power level into 4 ohms as compared to 8 ohms is 41.4% more, not "about 70%". Shouldn't try to do everything in my head.

On a tube amp, the output impedance matters greatly as it isn't close to zero like solid state amps. If it's an 8 Ohm rated output, he may need as much as 50% more current for his 4 Ohm M80s.

Looking at pictures of this amp, it's a single-ended design. It probably has an output impedance of 3 Ohms. With an 8 Ohm speaker, the system impedance would be 11 Ohms. With a 4 Ohm speaker, the system impedance would be 7 Ohms. You need 11/7 (about 1.5 times) more current with the 4 Ohm speaker. That's 50% more plate current than what the amp may have been designed for.

Have lots of tubes on hand if it wasn't designed for a 4 Ohm load .