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

When i finally move out into my own place, i will be getting the M80s as my large floorstanders.

I'm currently using 2x Rotel RB-960BXs (60wpc, total of 120 W per speaker) for bi-amp on my Monitor Audio Bronze B4s. Wondering if the same amps will have enough juice for the M80? Rotels make pretty decent amps with good amp power supplies (this has a dual mono with 2 transformers in each chassis) and nice headroom and all, but the bass is not the most well controlled with the Bronze's 6 ohm load.

So i'm wondering if they will be able to exercise the full potential of the M80s with the 4 0hm load?

Comments appreciated!!

I don't think that biamping the two amps provides double the power...

I agree with David, but the amps should provide sufficient power, as long as you're not pushing to high levels in a large space (eg, past 100dB.)

i have 2 stereo amps, each is 60wpc, total 4 channels of 60w each. I'm using 1 amp for each speaker, 1 channel for mid+high, 1 channel for woofer. That makes 120W per speaker right?

I used to run them bridged, but that was worse as each channel was then driving a 3 ohm load, half of the speaker impedance....

No, that is just 60W for the mids and highs and 60W for the lows, the watts do not get added. You have simply allowed for a full 60 watss to drive the woofers with, instead of a portion of 60 Watts if you hadn't biamped.

Not that you're likely to have been using a full 60W at any time during playing anything, unless it was clipping a fair amount.

Email Rotel and ask what your RB-960 is pushing into 4 ohms, the 200 watt RB-1080 is in the neighborhood of 320 watts or something like that with the 4 ohm M80s.

That amp will drive the 80s just fine.

No slack, not right; as some of the other replies pointed out, you can't add the power from each channel together. They're separate, and each section of the speaker would get(nominally)60 watts maximum. Nevertheless, unless you drive the M80s at extremely high levels dangerous to your hearing, the 960s should be fine.

John,

Do you have a link to the article that explains how bridging an amp does not change the impedance of the speakers load, instead it is the amps characteristics that changes?

I seem to have lost it.

Oh, I finally get it. It's not doubling the power because the speakers aren't drawing double the power. Finally. I knew it was the case, but I didn't get why it was the case until just now.

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.

No this is not correct. As said before the two sections cannot be added to together as neither section is receiving the perceived 120 watts.



This is also not true. As the 60 watts cannot be combined the same goes for dividing the 60 watts. The binding strap are an electrical conduit just as speaker wires are. They will transfer the power to both sections the same as when you are bi amping or bi wiring.



There are no benefits to passive bi amping. To achieve the ability to play twice as loud you need to have TEN times the power......600 watts.

'Yo Wid ... have my man Slack check out this article, it should help him understand the theory behind bi-amping a little easier.

Bi-Amping

Go ahead, you can use the link Ricky.

Good linky Ricky .

We aim to please, big fella.

I think I'm beginning to get it, sorry for the frustration to you guys..*sheepish grin*. Thanks!

If i have the option now to buy a used Parasound HCA-806 to replace the two rotels, i guess it is not considered much of an upgrade in terms of power.

How about the sound quality, build quality and tonal characteristic of the Parasound compare with the Rotel amp?

Amps are about power slack, not sound quality and tonal characteristics, they amplify. Build quality is another topic, which I can't comment as I don't own either brands.

Yeah, but i'm sure every one has experienced power amps that sound different, for one reason or another..: ))

Those reasons mostly being slight differences in volume setting.

Slack, if an amplifier has a "tonal characteristic" when its controls are set flat, there's something wrong with it. It's either a damaged sample, incompetently designed, or intentionally designed not to be sonically accurate and impress those who might equate different with better. An amplifier isn't a musical instrument and its only function should be to amplify transparently, with audibly flat frequency response and inaudibly low noise and distortion within its designed power limits. Nothing more is possible. One of the great features of today's audio scene is that even modestly priced receivers can accomplish this.

Certainly a contrary view exists, but when put to the(controlled blind listening)test it collapses because of the lack of solid evidence to support it. Both of the units that you mention meet the standard for transparent amplification.