Axiom Home Page Forums General Discussion Home Theater SA XR70 > RB1092

i currently have a panasonic SA XR70 running all axiom speakers (twin M80's and a VP150 up front, ep600 sub and M22's out back) the space is (25*25*18ft) without much absorbtion/ damping

heres where it was supposed to get interesting:
i have the m80's running bi-amped ie: cables from the a and b outputs of the amp, and i have the little bar removed from the speaker inputs. (im still unsure whether that should be attached or not?)

this lets the amp use 2 of its outputs when in stereo mode for my main speakers, but only 1 each for multichannel movies.

thats fine but i dont feel im getting the most out of my speakers, the centre and surrounds i believe hold up fine with the XR70, but the m80's dont feel like they have the punch they should be capable of (forgive my less than audiophile terminology)

thats fine the xr70 was kind of an inexpensive long shot... my proposed solution is to run the m80's of the rotel rb-1092, mmmm 500 watts of sweet buttered digital goodness.

i realise the is more power than i need but driving an amp conservatively is such a magnificent feeling compared to punishing an underpowered amp (and your precious speakers in the process)

i did a search and it didnt pop up on the axiom forums, just wondering if there is a reason for this?

_sam

I think there's a little confusion here. If you're using the A&B outputs of the receiver (and I'm assuming this is the standard terminology), then what you're actually doing is splitting the individual amplifier for each speaker in half (sort of). Bi-amping refers to the use of separate amplifiers (generally not in the same case). A&B outs are not separate amplifiers. If you were using two pairs of 8 ohm speakers and selected both A&B, you'd be presenting a 4 ohm load to the receiver.

Now, I'm not sure what kind of load you're giving the receiver (I'd guess 4 ohm, still), but I would highly recommend just wiring one set of speaker cables to the M80s, and leaving the binding straps on.

As for the missing punch, you should probably have a look at your crossover settings, level calibration, and all that stuff, but in the long run, you're probably going to want a more capable amplifier or receiver.

why thank for the quick responce.
no im quite sure i have my terminology straight, ive been over the manual about 1000 times trying to sort it out myself. normally yes a:b use the same amps, but this one appears to automatically adapt and throw an active crossover into the mix? albeit a crossover with very limited customisation.

from the manual:
"You are able to take advantage of two separate amplifiers for the high
frequency and low frequency ranges. This enables more highly defined
sound reproduction of the two ranges thus producing high quality biamp
stereo sound.
You can enjoy bi-amp sound when the sound is delivered as analog
stereo or PCM stereo sound.
Note
• Before selecting [BI-WIRE], connect speakers designed for bi-wiring using the bi-wiring connection (á page 6).
• Do not select [BI-WIRE] if you have connected two sets of speakers to the A and B speaker terminals."


here is the link. (have a peek if your curious)
http://service.us.panasonic.com/OPERMANPDF/SAXR70.PDF

i have my speakers set to large, and they do seem to be generating some very nice low notes, just not with any authority. the min crossover setting for the sub (on the panny amp) is 100hz that seems to be fine for the sub but im open to suggestions.

thanks for your help
_sam

here is another angle, it is only rated to 6ohms
http://www.soundandvisionmag.com/assets/download/PanasonicSA-XR70lab.pdf

but i was of the opinion that running in bi-amp mode each amp would be presented with an 8 ohm load? (is this correct logic)

but that still leaves my movies seriously compromised as they dont benefit from bi-amping. (this is noticable)

to cut a long story short, has anyone had experience with m80's and the RB1092?
_sam

Wow, OK, that's really weird. Nice bit of obfuscation they've got there. What they're talking about is still not bi-amping, it's bi-wiring. It just allows you to bi-wire (a practice with extraordinarily dubious reasoning) without having to twist together wires. In normal bi-wiring, two sets of cables per speaker are used, with the binding straps removed. The ends of the two sets are twisted together to make one set of cables.

This isn't bi-amping, because there's not (as near as I can tell from that manual) two sets of amps for the front speakers. There's only one; it's just that that twisting together of wires is (figuratively) happening inside the amp instead of outsid the amp. Also, never in the manual is bi-amping mentioned. With bi-wiring, you're still presenting the amp with a 4 ohm load.

Also, the bit about biwiring not working with multi-channel on is worriesome. If that's actually the case (there would be an electronic cut off inside the amp), then what is happening is that when you switch to multichannel (of whatever variety), the woofers in the M80s are being deprived of signal (assuming that the lower set of posts are hooked to the B channel). That would certainly explain your lack of presence!

have another look.
its a little bit "engrish" but it does mention bi amping a couple of times in passing.
i believe the mentality is, it utilises one of the amps that would have driven the surround speakers when in stereo mode you will notice on page 6 there is a wiring diagram showing hi frequency output from speakers a: and low frequency from speakers b: and page 22 discusses it further.

so i am confident it is genuinely bi-amping in stereo mode.

so if this is the case?
is each amp presented with an 8 ohm load?
and if the hi and low frequencies are being managed by the amp (ambiguously i might add) should i leave the binding straps detached?

ie, does detaching the binding straps bypass the speakers crossover?

but you are right that does leave the multi channel output seriously compromised.

thanks again
_sam

I'm not certain if it is 8 ohm; perhaps JohnK, our master of manuals, can help out here. In any case, if you remove the binding straps, it is not so much the crossover that is disconnected as all electrical connection between the bass drivers (the 6.5" woofers) and the mid and treble drivers (the 5.25" midwoofers and the tweeters) that is disconnected.

I'm also dubious about whether bi-amping (especially with what may be identical amps) provides any benefit whatsoever.

I would leave the binding straps detached if it is indeed bi-amping, because if it is doing that, you would end up feeding hte signal from one amp into the other, which is a big no-no. However, what seems a much more logical solution to me is to disconnect the B channel stuff and connect the binding straps.

hahah, damn it so rational its almost dull.
yes thats where is started, i did get a marginal improvement with the bi amped method, but its evident i need to move on to a more apt amp.

thanks for your help
_sam

Sam, I was in fact curious(moderately), so I did take a peek at the manual. My impression is that the relevant parts were ambiguous and/or deceptive. The process is termed both "biwiring" and "biamping", which are supposed to be different procedures. Assuming that a second amplifier channel is actually brought into operation, this form of biamping has no significant benefit, regardless of what the manual claims. The same power supply section of the receiver is used, and the only thing that's happening is that the same amount of power is being distributed through two sets of output transistors rather than one; no doubling of power(or any increase at all)occurs, contrary to some misconceptions about this "passive" biamplification(compared to "active" biamplification with separate amplifiers preceded by an external crossover, with the internal speaker crossover bypassed or removed).

Yes, if you want to follow the routine, you remove the connecting straps, but of course this still runs the signals through the internal speaker crossover. No change in the speaker impedance can result; the separate high and low frequency sections are each(nominally)4 ohms and that's still the impedance that the receiver is driving.

I certainly wouldn't suggest bothering with this, but since there's no harm(as well as no benefit)and you're already wired up, there doesn't appear to be a good reason to change back.

Unless it is actually using the surround amps in stereo and not using them in multichannel. If this is the case (I kind of doubt it is, but it's possible), then
a) it's monumentally stupid on the part of the manufacturer
b) the woofers ain't playing when it's in surround--which should be easy to check. Just stick your ear up against them.
c) attaching the binding straps while the bi-amping is configured could be catastrophic.