left/right on rta 12b's

soundfreak1

Can anyone "splain" why the rta 12b's are marked left/right. I understand it on the sda with the interconnect cable but can't for the life of me see the need in the 12b'S ( matbe I'm being dense ) but trying to learn!! Thanks in advance!

heiney9

They are mirror imaged and time aligned, hence the Right and Left designation. LSi's are the same way being that they are mirror imaged, there is an intended R and L based on the dispersion pattern.

With SDA's it's a little more critical to make sure they are properly placed.

H9

soundfreak1

Ah ha!! I was being dence ie the "real time array" thanks H9. Btw I like your taste in preamps. (Love my sl2000a(se)

drumminman

When I hooked mine up after having them in storage for many years, I inadvertantly reversed them - left on right, etc. The stickers had fallen off the outside of the cabinets.

I thought something sounded not quite right. I remembered about the mirror image thing so I swapped sides.

Big difference - the huge, deep 3D soundstage returned!

audiocr381ve

drumminman wrote: »

When I hooked mine up after having them in storage for many years, I inadvertantly reversed them - left on right, etc. The stickers had fallen off the outside of the cabinets.

I thought something sounded not quite right. I remembered about the mirror image thing so I swapped sides.

Big difference - the huge, deep 3D soundstage returned!

I didn't know they HAD to be hooked up left and right. I just thought if you wired them correctly that would be fine. I think I lucked out and put them in the correct position because my soundstage is siiiick.

soundfreak1

Did the same thing and thought I'd blown something. Very different!

Schurkey

I don't see schematics for the 12C, but the 12B--which appears to be a symmetrical speaker--uses a non-symmetrical crossover for the mid-woofers. There is an "inside" and an "outside" mid-woofer in each speaker pair. The speakers are mirror-imaged and not truly symmetrical.

Thus the "left" and "right" speakers.

geoff727

The mirror-image feature is due to the fact that the "inner" mid-bass drivers continue playing into a higher frequency range than the "outer" mid-bass drivers do. There is a valid design reason for this regarding off-axis dispersion of the speakers; if this is why they did this on the 12's, I don't know.

Vette C6.r

I have RTA15's. They do not have any left and right markings. If there was a sticker that designates it no longer exists.

There is a stamped model and serial number at the bottom that doesn't state left or right.

Any other way of telling ???

Joe08867

I think the RTA12's were the only ones marked left or right as they were the only ones with side by side mids not vertical like the rest of the series.

heiney9

Vette C6.r wrote: »

I have RTA15's. They do not have any left and right markings. If there was a sticker that designates it no longer exists.

There is a stamped model and serial number at the bottom that doesn't state left or right.

Any other way of telling ???

The only true Real Time Alignment speaker is the RTA12, all others use that moniker but aren't really, so left and right don't matter.

H9

dorokusai

The RTA12 isn't mirror imaged and the only reason for a left and right sticker was due to customers needing to know how to place them. For some reason, the need for guidance in this respect, created a sticker. The speakers radiate the same frequencies at all times, in that their are no cascaded drivers or fiddling with the xover assembly. I wish I had a more exciting answer to all of this.

As far as the time alignment, that's just inherent by the actual design of the loudspeaker. The tweeter(HF) assembly is set back, behind the mid-bass drivers(LF) to allow all the frequencies to arrive at the listener, at the same time. The older Monitor series did this in a cheaper way by using a stand with a upward tilt to them....the "poor man's time alignment".

If you heard a difference in placement, I don't doubt it and all I can say is that you heard what you heard. I'd suggest placing them in the configuration that sounds best and forget about it.

Vette C6.r

Ok I am getting my models confused.

Thanks

heiney9

Sorry Mark, but if you look at Polk literature the RTA 12 is mirror imaged, hence the reason for Left and Right. Not trying to be a poopie pants like the others that have dogged on you recently but I wanted to get the facts straight.

http://www.polksda.com/pdfs/1985Sales.pdf

H9

dorokusai

I know H9 and have the same document. I'm just going by what Polk engineering and KS have told me historically. I'd put more weight in the literature if the physical loudspeaker had a change, difference or layout that made them mirror imaged like you would do to a pair of DQ10, for example. They just don't and I can't speak for why its talked about in that way but it's just not mirror imaged by definition. No worries at all man, as we're here because we like to talk about speakers....well, some of us at least.

Polk's use of marketing speak isn't exactly accurate when it comes to the actual product. Kinda like the fluid coupled bass radiator....

I'll inquire further about the marketing and literature when I go to HQ again.

geppy1

Outside drive 60-600HZ Inside driver 60-2000HZ You can even hear the difference if you unplug and play the two drivers seperatly. This applies to RTA 12Bs and Cs. The early RTA 12 (the ones on the stands) DO NOT roll off the outside driver and are not mirror imaged. They have only one crossover.

drumminman

When I rebuilt my crossovers, one of the leads passes through the upper crossovers before going to one of the woofers. The other woofer has the postive wire coming straight from the lower crossover.

What does this mean?:eek:

I dunno, other than they're not both receiving the same signal.

Joe08867

I have to agree with H9, geppy and drumminman. Looking at the schematic 12b's and c's are mirror image speakers.

dorokusai

I believe this simply requires another Q&A with engineering to solve the issue. Like I said, that's coming from Polk and I don't see a reason why they would be mirror imaged after looking at the xover. Wouldn't they have two different harnesses, or wiring protocol if they were mirror imaged? Excellent comments guys.

If someone can point that out, just let me know some specifics that I can remind them of.

Can someone pull the drivers on their RTA12 and check the wiring to see if it flips between loudspeakers? That's an easy way to figure this out.

Joe08867

After looking at the three schematics we have on the site. It looks like the outside speaker is the one that goes through the tweeter network for it's positive signal on the 12b. My guess is they had very shallow bass response before this. I have not heard original 12's but I bet I am right. The revision would send more lows to one of the drivers. And looking at the values of the one that goes through the tweeter circuit, it looks like they were really trying to meld the sound of the tweeter to the mid driver on both series. Also taking the one driver out of the tweeter circuit would put it's bass and midrange response further ahead of the tweeter circuit. Bringing the mids forward and the bass out more.

Also looking at the original 12 schematic, it looks like both drivers go through the tweeter circuit so the original is not mirrored like the 12b. But like I said they had to be thinner on the lows.

PS, That crossover has always had me confused. I think I understand it but damn they went through a lot of work to get there.

geppy1

I have taken all models of RTA12s apart many times.

This apples to RTA 12Bs and Cs The inside drivers are fed from the inside crossover (white and black) and cover 60-2000HZ Two more wires (white and black) run from the inside posts all the way to the top Xover. Two wires then come back down into the cabiner (blue and white) and go to the outside driver which covers 60-600hz. You can hear the difference in the drivers buy pullin the top pl;ug and letting just the insde one run and then disconnect that one and listen to the outside one. Definite rolloff

Mark, the boys at POLK are talking about the early RTA12s with the stands.. They are not mirror imaged as they use 6500s that cover the same 60-2000. There is only one xover which is on top. Nothing in the cabinet at all. I was surprised by that myself.

dorokusai

Geppy - I believe that's the problem, as one engineer is talking about what he recalls and another....another. I do see the difference you explained and thanks for pointing it out exactly. I only know what has been relayed to me offline and basically take it for granted. You've clearly done your homework across models.

soundfreak1

Didn't mean to stir things up but I've learned a lot thru this discusion. I honstly never noticed the marking as it is in the serial # ( L-and # and R-and #) but had rotated them to another room and back and must have got them inverted. Really started noticing a change in the mid-bass responce- seemed. Narrower and vague and the sound stage colapsed a bit! A friend just bought a pair and asked me about it(that's the only way I figured it out.) Thought I had some caps failing maybe? Was actually concidering rebuilding the crossovers! Once switched back correctly they came back the way were, which was great! Mine are fully original and I hated messing with them. Their is quite a diff. In sound stage and mid- bass accuratecy!! But the sound stage opened back up substancely. So it" sounds" like a good example of mirroring image too me. Thanks for the info though I learned a lot here!

soundfreak1

Sorry about the double reply, small keys-fat fingers LOL. These were my first polks and I must say I'm quite pleased with them. The more I listen to them the more "I" like them. They have had a vairing list of pre's and amps hooked to them but this combo I have now I wouldn't change, seem to have hit the right combination and they sound wonderful. I have been foaming at the mouth to try a pair of sda's but the right deal hasn't presented itself yet!!! I won't give up the 12b's though. I've had many speakers and they all have their strengths but I find the polks handle a wider variety of music than most speakers. From jazz to techno and everything in between. They just reproduce the recording in such a warm and accurate manor that I can listen to them for hours on end.