RTA 12C's upgraded for forum member, w/ pics

geoff727

filmfreak1138 wrote: »

Thanks again! I'm looking forward to seeing, and HEARING, these speakers at the April meet-up!

I got both the 15th and the 16th off work, so we are on for Friday afternoon/evening for you to come over here and spend some time getting to know them again. I am putting together a playlist of things I would like you to hear on them. And, if you want to bring some CD's or vinyl, please do so. Then you can listen, uninterrupted, for at least a couple hours. Pick them apart, or just relax and enjoy, either way.

geoff727

Joe08867 wrote: »

Secondly, I had an issue with resonance at certain frequencies on my SDA2's and used a strip of dynamat about 2 inches wide in an X pattern along the sides and back and it worked wonders....

Yes, Dynamat is neat for all kinds of things, isn't it? When Roger and I were deciding on what he wanted to do on these, we talked about the various internal linings. Price-wise, it basically came down to either 5 sheets of 3-layer Sonic Barrier, or a lesser quantity of NoRez. Would the adhesive-backed vinyl layer on the NoRez have made a difference, even in a lesser quantity? I don't know. It may have afforded some damping, it may have increased the mass of each panel wall so that any resonance is a few Hz lower. Who knows. Tough to say without doing some tests.

What I can say for sure is, the clarity of vocals is much better. The 'singing into cupped hands' coloration is substantially reduced, which is a welcome improvement.

geoff727

danger boy wrote: »

I am curious as to why with the increased inside material for sound absorbtion that one of the speaker is resonating at certain frequencies? wouldn't the sonic barrier control that?

Basically, the mian goal here with the application of that kind of material is to cut down on internal reflections that bounce around on bare-wood internal enclosure walls. Internal reflections make their way back out of the enclosure via partially-sonically-transparent driver cones (the 2 mid-bass drivers). This colors the midrange and midbass sound of the speakers. The proper amount and type of internal fill is important also. In fact, it would be interesting to experiment with different amounts of natural wool fill in these, a material which naturally has differing lengths of fibers and typically produces some of the smoothest "fill response" inside enclosures. Actually, I have some other fill on hand and i might experiment before Roger gets here and see if I can get some moderation at that frequency, in case I am wrong about that being an enclosure material resonance.

The 3-layer Sonic barrier has a vinyl layer in the middle that's supposed to act as an "isolation" layer, the intent being to isoalte the effect of the push and pull of sound waves on the enclosure walls. Because, obviously, the more the enclosures walls vibrate, the more they become a sound source of their own, and the more they interfere with the purity of the music. So the goal of this stuff is two-fold: reflection reduction and vibration reduction.

Without bracing the enclosure walls, I wanted either direct vibration damping or isolation in there. As i wrote to Joe above, the choice came down to either the 3-layer Sonic Barrier (which has a measure of isolation but no direct enclosure wall damping) or a lesser quantity of NoRez (which has direct enclosure wall damping but no isolation). I think Black Hole 5 has a little bit of both, but it was beyond the budget at 50-some dollars per sheet.

So, we made our choice and went from there. Indeed, the Sonic Barrier is reducing vibration of the enclosure walls. All you have to do is put your hand on the side of the enclosure while they're playing music, and they obviously vibrate less now. But, it's not a perfect material, so the effect is not 100%. It's almost like controlling symptoms, rather than getting to the heart of the medical matter. The heart of the medical matter in this case is the 3/4-inch-thick particle board enclosures. Now, could Polk have built these out of 1 1/2-inch thick baltic plywood for a sonic improvement? Sure....but then we'd be paying 2000 dollars for a pair of 12's or SDA's instead of 1000 dollars, and Matt Polk's potential market would have gone way down. Which means economies-of-scale would have been reduced, further increasing the price and further reducing the market.

If the enclosures are indeed resonating at that frequency (or narrow range, actually, depending on the Q [width/height relationship] of the resonance), I'd speculate that the isolation layer is probably helping things, and I may be perceiving the resonance because of the added clarity of everything else. This is just a guess. Because the Sonic Barrier is not perfect, if that one frequency is still 'let through' then it will set the enclosure wall into resonance.

But, I think I'm going to experiment, in the hopes that I am misinterpreting what I'm hearing, and that I can moderate that "bump" down a little bit.

G~

This is just an aside, but look at this review of the LSi7. In Fig. 2 of the Measurements section, you can see two definite enclosure panel resonance modes. http://www.stereophile.com/content/polk-audio-lsi7-loudspeaker-measurements

Joe08867

geoff727 wrote: »

Yes, Dynamat is neat for all kinds of things, isn't it? When Roger and I were deciding on what he wanted to do on these, we talked about the various internal linings. Price-wise, it basically came down to either 5 sheets of 3-layer Sonic Barrier, or a lesser quantity of NoRez. Would the adhesive-backed vinyl layer on the NoRez have made a difference, even in a lesser quantity? I don't know. It may have afforded some damping, it may have increased the mass of each panel wall so that any resonance is a few Hz lower. Who knows. Tough to say without doing some tests.

What I can say for sure is, the clarity of vocals is much better. The 'singing into cupped hands' coloration is substantially reduced, which is a welcome improvement.

The resonance wasn't everywhere just a particular note range that would really bring it out. Kind of almost a warbled buzzing sound. Not at all loud unless the volume control was really cranked up. It was more of a nuisance as it took me out of a listening state to troubleshooting state.

Like I said I had the same issue in my SDA2's. and the Dynamat was the difference. The sonic Barrier was good but the two together was awesome. I understand that price is always a big issue, for me as well. I don't want to dump 1,000's into a speaker I paid 250 for. Luckily I had the Dynamat from another project (Car) so it was money I had spent already. So it was free for this project sorta.

I hope you find another method to get rid of the vibration. It would be nice to have another trick to use that wont intrude to much on the volume of the speaker like braces would.

FTGV

Nice job and great attention to detail.The nicest vintage Polk reburb I've seen.

drumminman

Just ordered sonicaps and mills from Sonicraft!

Getting ready to bring my RTA 12C's to the next level, or at least back to as new condition. Still gathering materials so I probably won't start for a week or two. I've struggled a bit with the cost of all this stuff vs. the value of the speakers, but in the end I enjoy doing this type of work. Also, if the improvement is similar to that which I heard with similar mods I did to my DT BP30's it'll be worth it.

Where did you buy the Neutrik connectors and what model are they? Did you consider hardwiring everything, or would it have been too difficult to move the speakers?

Have you had a chance to do any more listening, and, if so, what are you hearing?

Thanks,

Fred

geoff727

FTGV wrote: »

The nicest vintage Polk reburb I've seen.

Those are some very kind words.

Thanks again for the compliments that everyone has written.

geoff727

drumminman wrote: »

Just ordered sonicaps and mills from Sonicraft!

Sonicaps for the whole crossover? Wow, that's commitment!!

drumminman wrote: »

Getting ready to bring my RTA 12C's to the next level, or at least back to as new condition. Still gathering materials so I probably won't start for a week or two. I've struggled a bit with the cost of all this stuff vs. the value of the speakers, but in the end I enjoy doing this type of work. Also, if the improvement is similar to that which I heard with similar mods I did to my DT BP30's it'll be worth it.

It's a labor of love, no doubt.

drumminman wrote: »

Where did you buy the Neutrik connectors and what model are they? Did you consider hardwiring everything, or would it have been too difficult to move the speakers?

They're available at PartsExpress or Mouser Electronics. I'm sure a lot of other places too. About hardwiring them, no I didn't consider it. Roger wanted these to retain the original configuration, and needed them to be detachable to fit in the back of his car for the return trip to his house.

drumminman wrote: »

Have you had a chance to do any more listening, and, if so, what are you hearing?

The midrange bloom around that one frequency is still there, but i think i may have moderated it a bit by settling on a polyfill amount of 70%. I still think this is due to the cabinet, and no amount of polyfill experimentation is going to effectively change this. I may move one of the speakers next to my computer, run an impedance plot, and see if the trace has any small bumps which would verify my thought.

Other than that, the bass is very much cleaned up compared to stock. The treble is much, much better. It will continue to improve when Roger can put in high-quality fuses instead of the cheapies that I have in there now.

G~

vstarkwell

WOW!!!!, great job & thanks for sharing on this forum and for sharing.

danger boy

what's the latest verdict on the updated RTA12's Geoff? is burn in time complete?

geoff727

About as complete as it's going to get, I think. I listened for about 2 hours last night. Everything sounds pretty good to me; my initial impressions still stand. I think the speakers have made a large improvement, all around. I am much happier with the clarity, dynamics, and musical communication from top-to-bottom. I think Roger's money was well spent.

I suppose you are anxious to have Roger over and put them side-by-side w/ your SDA's? Ya, I'd like to listen to that. That would be an interesting comparison, between two similarly-sized same-generation speakers.

I got the 15th off (the day before our get-together, assuming it's still going on) to have Roger over, so I can spend some time with him going over some specifics of the speakers, both functionally and sonically. But I know he's thinking about not doing it if the get-together falls through. So PLEASE help me convince him not to skip this important step. He needs to hear them set up and driven properly to have a 'baseline' sound for setting them up in his own system, and I need to show him specifically some things they're doing now that they were not doing before- subtle things I don't want him to miss. Without this, I think he risks some disappointment with the upgrades. He's invested a fair amount of time and money in these, and definitely should not skip this final step. So can you help me with that?

Geoff

factorz

Geoff I know I have already said this, but your work is amazing. I am sure the speakers sound great.

Lumpwithgoodear

:mad:DAGNABIT! DARN IT!!!!!!!!! I see those and wish I had extra green and time so I could upgrade my two pair! I mean SHEESH! With all the wishful lists on the musical heaven YOU have to make a storm ! LMFAO! Great work!! SEXY TOO!!!!!!!!!!!!!!!!!!!:biggrin:

geoff727

Some of you guys kill me.

I am really gratified with all the good responses this thread has gotten. I'm amazed people are still looking at it! In less than two weeks, they go to the Seattle get-together and then home with their owner.

Toolfan66

Geoff,

That is a very beautiful job!!! Love the detail in your work and your post..

danger boy

Geoff, sorry bud, I missed your response on March 22.. but Roger is very interested in hearing the 12's are your place.. and i'm sure you two have spoken since your post.

I too may be making the trip on the 15th to your place if you don't mind me stopping by as well to hear the newly improved speakers.

Things are moving forward for the get together at bikerboys house the following day. I think you said you'd be there, right?

This will be a fun weekend of speaker and gear listening.

tx_polkhead

WOW, you sir are an artist and a craftsman, I raise my glass in your direction.

To paraphrase ‘If these were mine…I would have...strip the vinyl veneer off.’ I am surprised they have vinyl veneer. My RTA12C’s are only 611 off in serial numbers from these and are finished in real wood veneer, odd.

Thanks so much for the detail you went in to, I have downloaded the picture of the crossover with the values written on the parts. When I build up the courage to take the plunge I will refer to this post as guidance.

Thanks!
Abel

drumminman

I'm 3/4 of the way through rebuilding mine with Sonicaps, mills, and teflon OCC 18awg solid core wire.

Geoff wrote a really clear and concise guide that was a tremendous help to me. :biggrin:

factorz

Now that I am in the middle of doing a lot of these upgrades to my RTA's I have a better appreciation for what Geoff put together.

As Drumminman said this really is a great guide! Thanks Geoff!

geoff727

factorz wrote: »

I have a better appreciation for what Geoff put together.

Ya, they're a pain in the neck, aren't they? :rolleyes:

Anyway, I'm glad this thread helped!

WGDB

Saweet Job geoff - my RTA' 12's are calling your name all the way down from here in San Antonio Texas....

vcwatkins

Excellent work! Thanks for taking the time to share. Very helpful.

geoff727

Thank you, folks. I'm amazed this thread is still getting views.

G~

soundfreak1

Absolutly fantastic job!!!!

BottomFeeder

Might be way off here, but if the owner of these speaks is Roger from Spokane, DangerBoy's friend, I think they used to be mine!

If so, I'm thrilled to see them getting so much TLC!

If not, well, ditto!

Gatecrasher

Yeah this is a great thread. Very well-written and thorough and shows all the meticulous work that went into the project.

Thanks for sharing.

brgman

geoff727 wrote: »

Thank you, folks. I'm amazed this thread is still getting views.

G~

This thread will be historic!
And not in a Hurricane Irene way either.:rolleyes:

turbomustang84

I love my RTA12c's even more after seeing there potential .........
if I could just find a second set I would be thrilled....

but it is inspiring to see such fine craftsmanship ,I do have one question ,mine blows the 3/4 amp fuse located on the tweeter whenever I use my EQ ,
of the upgrades you did would replacing the tweeters with the upgraded model you used maybe fix this issue ?

I am using your completed pics as the wallpaper on my phone..........

drumminman

Do you blow the tweeter fuses in any other situation?

I would have to guess that the settings on your equalizer may be causing this. Also, what kind of amp/power are you pushing them with? If you're cranking 'em up and your amp is unable to deliver clean power that would be a cause as well.

I'm pushing mine with a Carver TFM 42 (375 wpc) and they just sing :biggrin: I've never blown a fuse.

turbomustang84

i use either my Mitsubishi DA-A10DC which puts out around 160 watts into a 4ohm load or my Harman kardon citation 19s but either amp does fine as long as the eq is out of the loop ,so when i drive them above half volume i have to shut the eq off .