Bi-Amping RTA12C

Crashdot

Greetings,

I noticed notations the words "for Bi-Amping only" on the crossovers in my RTA12C's. Has anyone Bi-amped theirs, and/or can anyone describe what changes are needed to accomplish this? I previously had my RT55i's Bi-amped, since my receiver has provisions for this, and would like to do the same with these if possible.

Thanks

intangible

That would require fairly extensive modifications for next to zero benefit if all you are going to do is run them off two channels of the same receiver.

geoff727

If you're running both sets of binding posts off of the same amplifier (or receiver, or whatever), what you're doing is called bi-wiring, not bi-amping. Bi-amping involves the use of two separate amplifiers. For the RTA 12C, this is not something I would recommend. Like intangible said, there will be a lot of modification required just to incorporate a passive bi-amping option. For this, both amplifiers are driven with the full-range audio signal and the onboard crossovers of the speakers are still used. This is the king of option you see on all other Polk's. This will require a second set of binding posts, among other things internally. The sonic benefits of doing this are dubious, especially if your system is not extremely carefully set up.

But, to do true active bi-amping with an electronic crossover network (this is where the benefits really come in), you will really open up a can of worms with the 12's if you don't really know what you're doing w/ active bi-amping. My own system incorporates a full active bi-amp, and the benefits are many. But, it was also a very simple application, i.e., drivers of the same impedances and sensitivies, identical amps (same timbre, rise times, gain, and input sensitivity). To do a successful active bi-amp implementation involves a fair amount of study and knowledge. And, for the 12's, it would require some test equipment as well to nail down the parameters of the drivers. Also, on the 12's, I'm sure you've figured this out already, the inner and out mid-bass drivers have different responses bacause of the crossover. That involves another complication.

Honestly, I would never do this speaker as a first-time bi-amping project. My recommendation is to upgrade the passive crossover networks and do some other things, and just enjoy them as-is. I'm sure you've seen my recent thread on them; I can't say anything bad about the parts and procedures that were used, and I'd recommend doing exactly the same thing.

Good luck!

Geoff

geoff727

P.S.

If you click the audiogon link in my signature, you can scroll down to look at the System Plan and see how a (very simple) active bi-amp set-up is implemented, and the Comments will make it more clear.

Crashdot

intangible wrote: »

That would require fairly extensive modifications for next to zero benefit if all you are going to do is run them off two channels of the same receiver.

Can you explain why the RT55i would experience an immediate and significant benefit from bi-amping/bi-wiring, and the RTA12C would not?

Thanks

Crashdot

geoff727 wrote: »

If you're running both sets of binding posts off of the same amplifier (or receiver, or whatever), what you're doing is called bi-wiring, not bi-amping. Bi-amping involves the use of two separate amplifiers.

I am not sure I understand the difference, since it was my understanding that the Denon AVR-4306 has a discrete 130w power amplifier for every one of its 7 channels. The manual specifies that this is a Bi-amp configuration, so that is what I am operating from.

I'll defer to the use of the term bi-wire for this discussion if this is correct.

From my understanding of how this receiver works, bi-wiring to this amp is not the same as with other amps where the same channel would just be sharing the load of the second set of connections. If I don't Bi-wire, two of the amplifier channels and the associated power available is simply not being used. For this reason, when I Bi-wired the RT55i, they sounded significantly better, presumably due to increased power available to each speaker section by dedicating entire amplifier sections to each. My brother thought it sounded so much better that he wanted to bi-amp his speakers too, but does not have enough outputs on his Pioneer Elite to run bi-amp and rear surround.

geoff727 wrote: »

For the RTA 12C, this is not something I would recommend. Like intangible said, there will be a lot of modification required just to incorporate a passive bi-amping option. For this, both amplifiers are driven with the full-range audio signal and the onboard crossovers of the speakers are still used. This is the king of option you see on all other Polk's. This will require a second set of binding posts, among other things internally. The sonic benefits of doing this are dubious, especially if your system is not extremely carefully set up.

There appear to be holes in the crossover that may accomodate binding posts, and otherwise, adding such a connection would be trivial. What I am curious about is what needs to be remain disconnected vs what stays connected. There are three wires that connect to the 12C crossover, two that are obvious from the speaker input, but one of them goes through one of the midrange drivers first. I am not sure why the passive bi-amping would not yield the same sonic benefits as they did with the RT55i.

But, to do true active bi-amping with an electronic crossover network (this is where the benefits really come in), you will really open up a can of worms with the 12's if you don't really know what you're doing w/ active bi-amping. My own system incorporates a full active bi-amp, and the benefits are many. But, it was also a very simple application, i.e., drivers of the same impedances and sensitivies, identical amps (same timbre, rise times, gain, and input sensitivity). To do a successful active bi-amp implementation involves a fair amount of study and knowledge. And, for the 12's, it would require some test equipment as well to nail down the parameters of the drivers. Also, on the 12's, I'm sure you've figured this out already, the inner and out mid-bass drivers have different responses bacause of the crossover. That involves another complication.

I wouldn't attempt such an active bi-amp approach, since what I am trying to achieve is the same kind of result that came from the other speakers, namely improved clarity and bass response. I assume that this is the result of simply having more power or current.

Honestly, I would never do this speaker as a first-time bi-amping project. My recommendation is to upgrade the passive crossover networks and do some other things, and just enjoy them as-is. I'm sure you've seen my recent thread on them; I can't say anything bad about the parts and procedures that were used, and I'd recommend doing exactly the same thing.

As I mentioned, this is not my first bi-wiring configuration, and there were immediate and obvious benefits from doing that. I would just like to know what I should connect to what in order to get the same benefits with these speakers. I get the feeling that 130w is not sufficient to drive these speakers properly, and was hoping that bi-amping/bi-wiring might bring these speakers to life.

In addition, the crossovers in these 12C's were already fully upgraded with mills resistors, sonicap capacitors, and RD0194 tweeters by the previous owner, so I doubt there is anything I can do to further upgrade them aside from cabinet dampening, rings, and other physical modifications.

Thanks

intangible

Bi-amp is the correct term if you are using two separate amplifiers (here two boards in the same box), as you are. Bi-wiring is what it sounds like - running two sets of wire from a single amplifier to the speaker.

If your goal is to get the most cost-efficient improvement, which is what it sounds like, then buying a better amplifier is the way to go. If you are looking for a project, then by all means go for it. Unfortunately, I can't be much help there.

Crashdot wrote: »

Can you explain why the RT55i would experience an immediate and significant benefit from bi-amping/bi-wiring, and the RTA12C would not?

Thanks

I could what I think, but it would just make you angry, so I won't.

Crashdot

For simplicity, lets say I have two amplifiers and want to bi-amp the 12C's, what do I need to do in order to connect things? Do I just install binding posts in the upper crossover board, disconnect the three pin connector, and attach one of the sets of speaker outputs to these posts?

Thanks

Crashdot

intangible wrote: »

I could what I think, but it would just make you angry, so I won't.

Oh come on, what are Internet forums for, other than telling people things that will piss them off Please tell me what you think by all means. I have to say that it seems there are numerous people that share my positive experience with bi-amping the RT55i. I could perform a double blind A-B test, but to be honest I don't like the way those speakers sound so even when bi-amped, they still don't compare to the 12C's in my opinion.

Cheers

intangible

Look at the crossover schematic. (I am assuming that the RTA12B-rev is the 12C.)
http://www.polkaudio.com/forums/showthread.php?t=38755

You could isolate the tweeter circuitry pretty easily, by highjacking the white and blue lines before they get to the woofers, as you suggest. This leaves you running full range to the midwoofer, however, because it depends on the same crossover circuit as the tweeter. I'm not sure what would happen to the second woofer tuned to bass frequencies. One way to get around this is to use an active solution, as Geoff pointed out, but that has its own complications. The most obvious way to do it I can think of with a passive solution would be to build a second crossover board with a resistor in place of the tweeter, although that would be prohibitively expensive.

There are more technically inclined individuals here than myself. Maybe one of them will come along with a more elegant solution.

Crashdot

I do happen to have a spare set of crossovers...

geoff727

Man, I keep trying to type, and the Internet keeps crashing on me (fingers crossed this time)

Crashdot wrote: »

I am not sure I understand the difference, since it was my understanding that the Denon AVR-4306 has a discrete 130w power amplifier for every one of its 7 channels. The manual specifies that this is a Bi-amp configuration, so that is what I am operating from.

I'm looking at that on P.76 in the manual. What they have drawn there is a passive bi-amp. Using one amp channel to drive the Tweeter input, another channel to drive the woofer input. However, both amp channels are still responsible for reproducing the entire audio spectrum; the crossover inside the speaker is doing the frquency splitting.

I guess my question is this. How 'stiff' are each of these channels? I noticed on P.8 the usual caution about not running too many lower impedance speakers together off the amplifier section, which suggests to me that they may all have one common transformer. Do you know if this is correct? You'll have to forgive me, I admit I don't know that much about H-T receivers.

Crashdot wrote: »

From my understanding of how this receiver works, bi-wiring to this amp is not the same as with other amps where the same channel would just be sharing the load of the second set of connections.

Well, if you were to take Channel 1 only, and run two sets of speaker cables off of it - one set to the tweeter input terminals, and one set to the woofer terminals, that's bi-wiring. One channel, two sets of cables.

Crashdot wrote: »

For this reason, when I Bi-wired the RT55i, they sounded significantly better, presumably due to increased power available to each speaker section by dedicating entire amplifier sections to each.

So again, just to get our terminology straight, that's passive bi-amping. And there-in lies the advantage of this approach. But, it and bi-wiring are a couple of those funny things in audio. Some people seem to experience gains with it, other people call utter BS on it.

When my magnepans still had their passive networks, I tried bi-wiring. I can't honestly say there was any difference one way or the other. But, of course, that's a totally different speaker technology that the 55's. Things are bound to be different.

Crashdot wrote: »

There appear to be holes in the crossover that may accomodate binding posts, and otherwise, adding such a connection would be trivial. What I am curious about is what needs to be remain disconnected vs what stays connected. There are three wires that connect to the 12C crossover, two that are obvious from the speaker input, but one of them goes through one of the midrange drivers first. I am not sure why the passive bi-amping would not yield the same sonic benefits as they did with the RT55i.

It sounds like you pretty much have the connection figured out. Let me try to remember back 2 months ago.....

That black wire goes up from the binding posts through the connector, splits, goes through the 3.2mH, then back down through the conn. again via the blue wire, then to the 6501. So, to make them bi-wirable/passive bi-ampable....

Install another set of binding posts on the binding post cup, which will be the Low-Pass. You could run a wire from those Low-Pass binding posts that are now for the mid-bass drivers only (call it the "red" wire). The red could go up through the connector, which would require a 4-pole connector now, not a 3 (use the same Neutrik that I did, it's a 4-pole). Then right into the 3.2, and back to the 6501 via the blue. The original split of the black wire between the tweeter network and the 3.2 could be permanently cut now, but re-enabled w/ binding post jumpers if you wanted. The .61mH would have to be connected to those Low-Pass binding posts ONLY. So.....the + on the Low-Pass posts would be connected to the red wire and the .61. The black wire would still be the same, except it only goes to the tweeter network now and doesn't split off to the 3.2. Ya, that would work.

Sorry, just thinking out loud here. I better draw this before i confuse myself.

Crashdot wrote: »

I get the feeling that 130w is not sufficient to drive these speakers properly, and was hoping that bi-amping/bi-wiring might bring these speakers to life.

RTA12C's should not need anywhere near that, except, of course, on the most demanding transients.

Crashdot wrote: »

In addition, the crossovers in these 12C's were already fully upgraded with mills resistors, sonicap capacitors, and RD0194 tweeters by the previous owner, so I doubt there is anything I can do to further upgrade them aside from cabinet dampening, rings, and other physical modifications.

Outstanding!

Crashdot

With regard to the Denon, the literature says:

Newly-developed large-current power transistors in 7-channel power amps of
uniform quality for all 7 channels. Large-output power amp section and power supply configuration,
for stable high-power output

A review from http://www.audioholics.com/reviews/receivers/denon-avr-4306/listening-environment-build-quality-and-set-up says:

The AVR-4306 features a very hefty equal power amplifier section, with discrete output devices on all seven channels. It has a large power supply that took up a rather large chunk of the interior of the receiver and is coupled with a rectifier diode and oversized power supply capacitors to stabilize the power at high output levels.

It looks like it uses a single transformer.

It may be that a 5000 series is needed for discrete transformers, such as the AVR-5308 that has five transformers.

What I have done with the RT55i's doesn't seem to be specifically the same as bi-wiring, since I was not using the same output terminals for high and low frequencies, and it does not seem that all of the output terminals are linked. Maybe it isn't bi-amping either if bi-amping requires discrete transformers, but my limited understanding of such things led me to believe that there are amplifier circuits that are not being used unless I bi-amp or run surround back speakers that I have no room for. When I bi-amped the RT55i's they sounded significantly better, for whatever that is worth. I'm fine with passive bi-amping if it is possible, as going active is more than I can chew.

Thanks for all of that information; this will give me something to research and think about. Let me know if you draw that thing up!

Crashdot

I contacted the appropriate person at Polk Audio, who said that the bi-amping feature was never implemented in the RTA12, and that attempting to do so would open a huge can of worms due to the to the interdependent crossovers. In any case, he said that such an endeavor would not be recommended and would not yield better results that the upgrades that these speakers have received already.

Cheers

geppy1

That is funny as under the wiring diagram section there are directions fronm Polk and a picture of how to do it.

geoff727

They've probably gotten so many calls from people like us (modders) over the years that they go, "Oh God, NOT another one!":rolleyes: When I was starting to mod my Magnepans, I found something that really confused me in the panel hookup; the L and R speakers were opposite one another in their hookups and at the time I couldn't figure out why. So I called Mark Winey, son of the company's founder, who answered the call at tech. support. I told him what i was doing, and I could just sense it at the other end..... "Oh God, NOT another one!":rolleyes:

Well, we ended up having a pretty good conversation after a few minutes, with me feeling kind of emberrassed at having troubled him.

We figured out the answer to my question (with success). On a different occasion, I also had a couple great conversations with the (very knowledgable) person who used to write the set-up manuals for Maggie's back in the day, and he had some great suggestions, which also led to a successful implementation.

So see, sometimes it does work!

geoff727

geppy1 wrote: »

That is funny as under the wiring diagram section there are directions fronm Polk and a picture of how to do it.

I can picture the folks at Polk in the '80's in a room somewhere, saying, "Ya know, this thing on the 12's, let's not do that. I mean, the things are kind of complicated, there's gonna be lots of folks who try it and goof it up, and then we're just gonna have to fix 'em. For poeple who know what they're doing it's fine, but there's just so many folks out there who aren't gonna know the difference anyway. So why don't we just scrub that bi-amp thing?"

I know if i was in their shoes, that's probably the conversation I'd be having.

Crashdot

I didn't realize that the document entitled schematic_rta12_pcb2.pdf was titled "Biamplification of the RTA12" and seems to contain exactly the information I was looking for. Has anyone evaluated the instructions in that document or entertained the notion of trying it?

Cheers

geoff727

That requires putting the cables to the tweeter right on the top board instead of having a second set of binding posts on the lower terminal cup, so the top hat cover isn't going to be secure on there anymore and won't fit right. But, I guess if that doesn't bother you......

Crashdot

Maybe this is blasphemy, but I could install binding posts on the rear of the top hat, or simply tip it up slightly to allow the cable to fit beneath. I hadn't been thinking too much about the physical installation as I am mostly wondering if this mod will work safely and if I will hear a difference. I may have to get out the spare crossovers for this.

Does anyone know what the beveled plate that the tweeters attach to on the RTA12 is called?