Monitor 12: Crossover, and custom box questions.

plastic_avatar · January 2014

Background:

I got a pair of 12's about... oh... 6 years ago.

One didn't have a tweeter, but for $20... I thought it was a good deal

Ebay'd for a replacement tweeter. All was well. I really liked how they sounded. Not as bright as my 5JR's, and so very full and wonderful.

Problem:

I recently hooked the 5JR's up to an old receiver and a turntable I'm working on (I have to replace the capacitors, damn it), but pulled the 12's out of the closet to listen to them last night.

FAILURE!

One barely played, and sounded HORRIBLE. No highs. Not much of anything.

The other played, but was so muffled and terrible, I couldn't believe it.

Took them apart, and the crossovers are wrecked. Some of the capacitors (G/god(s), why do they hate me?!) have gunk coming out of them.

So, I guess I need to replace those capacitors. Whee!

Anyone have any tips on re-doing the 12's crossover?

On custom boxes:

I've seen some really great copies of original boxes on here, but has anyone seen a M12 in a custom box?

That tweeter screams 'Put me in the middle of the others!' to me.

And something taller and thinner wouldn't be bad for my purposes...

Thanks for any help. I appreciate it!

Steve(n)

plastic_avatar · January 2014

I haven't been on here for so long, I forgot I asked about crossovers before, and got an answer (but more info won't be ignored [chuckles]):

ShinAce

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The cost will depend on the quality fo capacitor you go for.

Obviously, tossing the cheapest non-polarized electrolytics in the wrong place won't help. Likewise, putting foil caps everywhere will cost an arm and a leg.

Yours might or might not have the polyswitches. The switch adds a capacitor to the crossover.

The cap for the woofer won't gain anything from a good cap. This one is 16.4 uF and should be replaced since it's electrolytic(most don't age that well). Myself, I'd be on the fence about using another electrolytic since it's a small enough value(16.4uF) and low voltage(50V). If you do go better on this one, realize that the speakers will probably disintegrate before the new cap goes bad. Feels like putting a new engine in a car rusted with holes.

The tweeter has two major caps. One is 12uF and electrolytic as well. You can upgrade this to something better, but don't go overboard. The other cap on the tweeter is 12 uF and already of decent quality. Replace this with what you can afford.

All values stay the same unless there's an adjustement for the replacement tweeter that I missed. Electrolytic caps usually have a different shape. They won't be perfectly smooth cylinders(like the good caps), they have a ring depression at one or both ends. They also sometimes have NP(non-polarized) written on them. The fact that a cap has to say it's the non-polarized kind does not instill confidence

.

p.s. Welcome to Polk.

and good luck!

agfrost · January 2014

As far as a custom box goes, that's a challenging thing--The speakers have been designed to operate in a box of the volume they came with, and the width is (somewhat) governed by the passive radiator's width. You can see in the RTA series (8T, 11T, 15T) how Polk narrowed the cabinets by using multiple, smaller radiators.

Here's a link to the crossover schematic. LINK If you're going to do the job, it's worth doing well and I'd recommend using Sonicaps in all positions. They can (upon request) do custom values such as that non-standard 16.4uF jobber, although a 16uF should do just fine as the 0.4 difference is under 5% of the value. Soniccraft can hook you up with some Mills 12 Watt resistors as well. Someone smarter than I can direct you as to if you should change the value of the 2.0 ohm resistor to a higher value if you should decide to delete the polyswitch. The inductors will not need replacement.

If you've got a bit of skill, a bit of patience, and the project strikes you as fun, you can/should go for it. Lots of people here to help with advice, support, troubleshooting as needed. I haven't seen many (any?) threads detailing M12 crossovers, so you may not have that as a resource like those with more-common speakers do.

plastic_avatar · January 2014

agfrost wrote: »

As far as a custom box goes, that's a challenging thing--The speakers have been designed to operate in a box of the volume they came with, and the width is (somewhat) governed by the passive radiator's width. You can see in the RTA series (8T, 11T, 15T) how Polk narrowed the cabinets by using multiple, smaller radiators.

I thought about as narrow a front baffle as the radiator would allow, stretching the height to compensate, and separating the woofers just enough to put the tweeter between them (and pushing that cluster closer to the top edge).

Attachment not found.

On the crossover:

Yeah. I have to fix the turntable 1st, then veneer the custom speakers I hope I *finally* get put together this weekend (the veneer will wait a month or two), *then* I can try and justify fixing the M12's.

But I want to be ready, and get the parts.

I hoped I could fix the corssovers on the cheap, but I'm afraid =(

And thank you for your help!

Very much!

pitdogg2 · January 2014

forget about that "custom" box most here will not help you Frankinpolk them out. Redo the XO with quality film caps like Sonicaps there are well proven here. You could go with what ever you want but do a search and you will see tried and true results.

just get that custom box thing out of your head.

halo71 · January 2014

I agree, moving the tweeters to the middle and redesigning the cabinets....is a bad idea. Throwing drivers into a random size cabinet just to fit your decor (I am guessing) is a waste of time. And will yield piss poor results imo. Those cabinets were designed with those drivers in mind. If you are looking for thinner speakers, look for a pair of Boston Acoustics A400's. Or perhaps some more modern designed speakers.

westmassguy · January 2014

pitdogg2 wrote: »

forget about that "custom" box most here will not help you Frankinpolk them out. Redo the XO with quality film caps like Sonicaps there are well proven here. You could go with what ever you want but do a search and you will see tried and true results.

just get that custom box thing out of your head.

Agreed. If you want to stay with vintage Polk, RTA-11s or 15s will give you the narrow face, and were designed specifically for that configuration. The Monitor 12s are pretty rare. If the cabinets and drivers are good, do the crossovers with some good quality components. You can go all-out, with Sonicaps or Clarity ESA Caps, Mills or Mundorf Mox Resistors. You can also go conservative, and put your money in the Hi-Pass/Tweeter section, and use Dayton 5% or Solen Fast Caps in the Lo-Pass, and save a few bucks. I would not recommend NP Electrolytics in the Lo-Pass, unless it was a temporary measure. Electrolytics will only fail again eventually. The odd 16.4uf caps can be made using two 8.2uf caps in parallel. 8.2uf is a standard value.
If you have the earlier 12s, the RDO-194-1 Tweeters are drop-in replacements, but there's also a "TL" Mod which will allow you to use the RDO-198-1 Tweeters as well.

plastic_avatar · May 2020

Post resurrection, guys.

In the intervening years I picked up some more speakers... Nothing better than the 12's, imo.

- I have a pair of RTi10, but I really don't like them for stereo listening =( But I got them for $60 4 years ago, and they do fine for home theater, but I just don't think I'll keep them... They have a broken foot on one, and a grill with broken pegs on the other. The speakers are in really good shape, though, but they don't sound great with my Yamahas.

- I sold my 5jr+ to a friend, and picked up a pair of 5jr for free that need the crossovers rebuilt.

- I picked up a pair of Boston T830 I re-foamed, but I don't like them as much as I liked the 12's... so I'm finally thinking I'll rebuild those crossovers.

So, some thoughts/questions:

- Are the 198's so much better than the 194's that I should try and sell something to pay for them?

- Is there another tweeter option now that might be cheaper and give me the same upgrade as the 198's?

- Someone has some 198's for like $140 for a pair... and I'm guessing a modest crossover upgrade will be around $100... Yikes... $240... And it's not like I can re-do the crossover with the 198 in mind and use it with my 194 and expect it to sound right =(

DAGNABIT.

Or... Do ya'll think I should sell all my bits and look for an RTA or SDA pair?

Argh =(

F1nut · May 2020

If your 12's came with the SL2000, then the only replacement tweeter is the RD0194. If they came with the SL2500 the only replacement is the RD0198.

plastic_avatar · May 2020

F1nut wrote: »

If they came with the SL2500 the only replacement is the RD0198.

Hey, F1, thanks for the insight

They came with 2500's.

I replaced them 10'ish years ago after I got the 12's. They were leaking.

The crossover needs a mid for the 198's, right? If so, how janky do you think the sound would be using upgraded crossovers with 2500's until I manage to be able to get 198's? Pandemic Time is a pain =\

F1nut · May 2020

Since they came with the SL2500, the RD0198 is a direct replacement, no mod needed.

plastic_avatar · May 2020

F1nut wrote: »

...the only replacement is the RD0198.

Here's what may be another silly question:

- I took apart my hombrew speakers to store until I have tge time/money to change them from 2 to 3-ways. I have a pair of Eton 25 SD 2 tweeters. I doubt it's possible, since I can't find the full specs anymore (and don't have tools to test), but it would be a happy accident if they were drop in compatible

- I'm going to check the crossovers for the homebrews and some Paradigms to see if I happen to have compatible parts for the crossovers. That would also be a pleasant surprise.

Monitor 12: Crossover, and custom box questions.

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