Axiom Home Page Forums General Discussion Technical Questions Rotel RB-960BX for M80 - enough power?

I'm still trying to absorb this...?$^$^$^$^

Sorry, it's one of those aha! things. I'm not sure if I can explain properly. But each amp will not be providing more than 60 watts maximum to each driver section, right? So it's not additive.

That's right Ken, it is no difference in power if one were to leave the binding post straps in place. Both ways each section is still only going to get 60 watts max .

If I remember right Mojo had a hard time with the Bi-amp theory as well. Now if I remember right, when you bridge the amps you can add their wattage.

Rick, you're probably referring to our discussion of bridging that took place about three years ago here , and especially to secs. 3.5.3 and 3.5.4 of the linked article.

Slack, I wasn't going to bother discussing the point since you seemed to have lost interest in bridging(which in contrast to the form of "biamping" that you're discussing actually does increase the power available to the speaker), but you might read the sections of the article mentioned. The short version is that the impedance of a speaker can't change(e.g., from 6 to 3 ohms)when the amplifier driving it is bridged, but the amplifier is putting double the voltage(theoretically)into the speaker, and because of Ohm's Law(I=E/R), when the voltage is doubled so is the current, with impedance staying the same. So, the amplifier has to put out more current because of the increased voltage, but this has nothing to do with the impedance of the speaker. The amplifier doesn't "see" a lowered speaker impedance because it can't see something that isn't there.

That's it, thanks John.

hmm, ok, there's two things thats confusing me.

FIrst, By biamping, the mid+high will get 60w dedicated. The woofer also gets 60W dedicated. That does not add up to 120W? I'm not quite sure i get it... Unless you're talking about the mid+high and woofer playing in different parts of the freq spectrum, and the mid+high is getting the top half of 60W, the woofer is getting the lower half of 60W, in the end there is stil only 60W into the speaker?

Second, bridging uses one channel for pull, and the other channel for push. As the speaker impedance remains same, with voltage doubled by using the two channels in bridge, the current, hence power should ideally double, and it does with a beefy amp. I have read articles that describe this as each channel now 'seeing' only half of the speaker impedance, hence current doubled. Not too sure how pushing the amp limits with higher current affects how 'controlled' the bass sounds, but i could hear a difference....(EDIT: ok, just read the article linked in above post, describing the amp as seeing half the impedance is just an analogy. I understand that the speaker impedance remains the same, but the higher current strains the amp and drives distortion up)

Still need help with the bi-amping part though : )

When you use passive bi amping, like you are, each section of the speaker is capable of receiving 60 watts max. The lower half and upper half cannot be added together as neither section is receiving 120 watts, the are still only getting they same 60 watts.

Now, if you were to leave the binding strap's in place and use only one of the amps both section are capable of receiving the same 60 watts max. Once again the upper 60 watts and the lower 60 watts are not to be added together as 120 watts.

So assuming the mid+high is drawing the max 60W from one channel, and the woofer is also drawing the max 60W from the other channel, isn't there 120W of total music power coming out of the floorstander? 60W of mid+high energy from its dedicated channel, and another 60W of bass energy from the other dedicated channel.

If the straps were left in place and the floorstander is driven with only one channel of 60W, assuming a 50/50 split then the woofer gets 30w and the mid+high gets 30w.

In any case, what is the benefit of bi-amping? The ability to pla y twice as loud (120w total music power) vs 60W, or playing with less distortion at the same level as each channel is only at half power.

You could buy the Axiom M60s instead, thereby avoiding the M80's amplification conundrum.