SDA surrounds...

[Ron Temple]

Unbeknownst to many of you SDA freaks, someone has been working on finding the perfect surround solution to match your particular model of SDAs.

Example: this CPer lent me a pair of CRS+ to play with...a perfect match I thought (and I'm right) same, tweeter, driver 6510, SDA 6511 and vice versa with the 1Cs...great timbre match, when driven in SDA mode, huge rear soundstage.

While I was enjoying this wonderful upgrade, the mad tinker started working on something smaller. I have a mantle which can accomodate books and he thought the CRS's were too low. Next up, he modded some M4s, with a crossover mod, driver swap, but the same tweeter...Excellent, but just couldn't displace the same air as the SDAs or another surprise bonus, RTA 8ts (same driver and tweeter), but they sure could fit on the mantle.

Forward to last night...I told this guy he couldn't bring anymore speakers down and had to take some back...ok...but he had a surprise. My wife's away and she probably won't divorce me...maybe...so ok, you can bring a surprise down, but take away the other 3 pairs :p .

Since I had commented on the 4s not being "quite right" and the CRSs/RTA8s being "special", he took it as a challenge. What he brought were modded M5s, with the same SDA crossover imported from spare CRSs...lo and behold, they are perfect. Total timbre match, nearly the same bass, but mantle friendly (sort of). We listened to some MCH and watched 300...the modded M5s are every bit as good as either the CRSs or RTAs in the surround role...maybe better. The benefit...precise soundstage, timbre match, can handle 98% of most surround bass, smaller. The mantle is about 1' above the couch/ear level, so by flipping the speaker, the tweeter is right on for surrounds. The other speakers throw a huge soundstage, but the tweeter level being below ear level was noticeable once I got the 5s above it.

Payoff: The guy who did all this futzing around is still not finished. Last I heard, he was going to create some sort of di/bipole CRS combo, that would be small enough to fit in an ear bead( I was getting pretty tired).

Steve...Polk65...take a bow

[heiney9]

I don't get it . The M5 has (1) active driver (sans tweeter) how would adding the x-over from a pair of CRS's make the speaker better. I assume you aren't talking SDA effect but where would the extra connections from the x-over be attached to? More info please.

[Ron Temple]

I believe he took half the crossover, did some modding with the board and popped it back in. Steve showed me, but I didn't retain it.

Hopefully, he'll chime in.

[fredv]

CRS+ schematic without the dimension mid and the 6510 mid replaces the 6502???

[Ron Temple]

CRS+ schematic without the dimension mid and the 6510 mid replaces the 6502???

I believe so...yes he did use 6510s...forgot to mention that.

[fredv]

According to the schmatics posted by Rafie's, the '84 CRS and the '87 CRS+ used 6503, maybe I can give the original 6502's a taste of the CRS style xover :-)

[Ron Temple]

CRS+ vintage 88-89, used 6510s and 11s...I'm assuming he's using the same crossover.

[engtaz]

show drawings of coverted crossover pretty please.

[Ron Temple]

Maybe a pic later...depends on Steve.

RT

[TampaTwo]

I was thinking of doing something along these lines, replacing the monitor 10 crossovers with an sda 2b crossover. any reason why this wouldn't work?

[heiney9]

I was thinking of doing something along these lines, replacing the monitor 10 crossovers with an sda 2b crossover. any reason why this wouldn't work?

Yes, cabinet volume for (the x0ver in the 2bs' is optimized for the 2b's cabinet volume). Also the stereo drivers and dimensional drivers have different characteristics. They are aligned perfectlyin the SDA 2b, the gap between the 2 M10 drivers is probably larger thus diminishing the SDA effect.

It would be a FrankenPolk which is sort of a waste. If you want 2b's get a pair of 2b's. Sometimes I think people think the SDA's were just thrown together. They are pretty sophisticated to get right and even Polk didn't have the best results right away. They had about 4 different generations and each got a little better.

H9

[Ron Temple]

Just to be clear...the M5s are not SDAs, they are surrounds, perfectly timbre matched. The RTA8Ts also sport the same driver (6510s) and tweeter, in a different config...maybe a tad brighter, but exceptional both as fronts and surrounds. The CRS+ same thing, different soundstage, not as precise with the SDA engaged. What Steve did was timbre match the M5s in a package that is portable for better placement options. The lack of SDA is not a drawback. I'm not advocating trying to make M10s into SDAs, though it might be workable.

[fredv]

I have no intention to build the ADB from the M5 cabinets either. It is more like, can the M5 sound better with a totally different xover which happens to be in CRS specs. Ron, do you want to compare? I have a pair of original M5B's. The only enhancements that I made was to add 2 PIO bypass caps which are almost broken in now. That added a touch of sweetness to the tone. Well worth the $2 spent, the total cost of the M5 is now $37 :p

[McCelery]

Hey I think those were my M4s!! Ha, glad they got to spend some time in the mix, even if for just a short while :)

He was such a nice guy about it, he actually asked if it was okay that he was going to mod them!! Man, I think I need to see the setups he's putting together, huh?

[Ron Temple]

I have no intention to build the ADB from the M5 cabinets either. It is more like, can the M5 sound better with a totally different xover which happens to be in CRS specs. Ron, do you want to compare? I have a pair of original M5B's. The only enhancements that I made was to add 2 PIO bypass caps which are almost broken in now. That added a touch of sweetness to the tone. Well worth the $2 spent, the total cost of the M5 is now $37 :p

Sure we can compare...I've never heard stock M5s and I'm not claiming these are better, just timbre matched to the 1Cs.

Hey I think those were my M4s!!

Yep, I think they are...you guys should get together, being so close.

[F1nut]

Between Fred and Steve, ya'll have some tweaking mofo's in the area.

How's that integrated amp conversion going, Fred?

[Polk65]

The other night I visited my friendly neighborhood frankenpolk testing ground. Ron warned me on the way over that his wife would kill him if I brought another pair of speakers. I told him to relax and that sometimes surprises come in small packages. We listened to some familiar songs on DVD-A in direct mode and what I heard was a perfect timbre match from front to rear. Pure Polk ear juju. After talking shop we settled down and watched 300. Sound effects originating at the front wrapped seamlessly to the rear. His front speakers are SDA 1C, CS400i center channel, and modified Monitor 5jr+ in the rear.

One project that has been on my list for awhile is to build or modify a small vintage model for surrounds that timbre match well enough to tickle my ears. When Ron recently mentioned that he was not thrilled with his surrounds this project came to life.

A pair of Monitor 4a's was the first experiment. They came to me by way of fellow polkie McCelery who rightfully grew concerned when I asked him before the purchase if they had any sentimental value. He asked if I was going to part them out and I said no but was planning on some modifications for a timbre match with other speakers. I chose his Monitor 4a's because of what I believe to be an early design. His tweeters were the square plastic 4 ohm type but the grille pegs located at the extreme corners of the cabinet were of interest to me. Previous Model 4's had room for a larger tweeter. Later models relocated the grille pegs inward which creates a problem for mounting larger sl2xxx and RD019x tweeters. This first experiment was a mixture of a Monitor 7 and Monitor 10 crossover with a sl2000 tweeter and mw6503 midwoofer. I found them very forward and bright but was going to see Ron anyway that day so I brought them along. He later described these as lacking the Polk Audio "creamy midrange".

Next I began searching through schematics for a useful single tweeter and midwoofer configuration. The SDA CRS with a separate stereo crossover for sl2000 and mw6503 is good but the later SDA CRS+ version was what I was looking for. This has a sl2000 with 6510 and 6511 that timbre match SDA 1C's. I borrowed the stereo components from this crossover and placed it on a modified standard issue Monitor series round crossover. This sounded smooth enough that I listened to several albums for nearly three hours and just smiled. Highs blend nicely with the mids and it's much more laid back. The bass doesn't compete with larger Monitors but with a sub or as surrounds they are delicious. As Ron said, by flipping the Monitor 5's upside down with the tweeters located just above ear level they make great surrounds. I haven't heard from him as to when I have to pick them up or how much ransom will be, which is a good sign. :D


Notes:

Monitor 4 with Peerless tweeter and outer grille peg location:
Tweeter hole cutting is required for sl2xxx and RD019x tweeters.

Monitor 4a with square tweeter and outer grille peg location:
Tweeter hole cutting is required for sl2xxx and RD019x tweeters.

Monitor 4a with square tweeter and inner grille peg location:
Tweeter hole cutting is required for sl2xxx and RD019x tweeters.
The grille pegs are too close for mounting sl2xxx and RD019x tweeters.
Remove old pegs, order new pegs and textured laminate from Parts Express.

Monitor 4 series 2 with sl1500 and inner grille holes:
Probably will require extensive modification like the previous 4a.

Monitor 4.6 with sl2500 tweeter:
No cutting required. sl2xxx and RD019x tweeters will drop in.

Monitor 5's with sl2xxx tweeter:
No cutting required. sl2xxx and RD019x tweeters will drop in.

The Monitor 4x terminals are the spring loaded type with about a 2" diameter rear hole except for the Monitor 4 with Peerless tweeters which has a standard issue Monitor series round terminal cup. Other Model 4's will require cutting a larger hole to mount a regular terminal cup.

mw6510 with sl2000 tweeter has a DCR reading of 8 ohms at the terminals while the mw6511 + sl2000 reads around 5 ohms.

sl3000 tweeters sound very forward. Perhaps they will settle down with a 5.8 uF cap from the 4.1 TL mod.

The capacitor on the bottom is 20 uF. I disconnected the old inductor from the round terminal cup.

The Monitor 5jr+ offers nice bass response but I like the size of the Monitor 4's and will be keeping them.


1) Monitor 4 with outer grille pegs.
2) Monitor 4a with outer grille pegs.
3) Monitor 4a with inner grille pegs.
4) Original schematic.
5) Schematic highlighted with parts used.
6) Rough cut for a sl2xxx or rd019x tweeter. Old 4 ohms tweeter shown.
7) Rough cut for a sl2xxx or rd019x tweeter.
8) Old terminal cup was too small.
9) Old terminal cup.
10) Old terminal cup and Monitor 4a crossover.
11) sl2000 tweeter
12) rd0194 tweeter
13-) Modified crossover (the stereo side of a CRS+ crossover)

[heiney9]

Sure we can compare...I've never heard stock M5s and I'm not claiming these are better, just timbre matched to the 1Cs.

I am very interested in this. I have 1C's with Sonic caps and RD0's and I have a pair of M5's with Solen's and RD0's. I love the more laid back sound the 1C's have and I have been looking for "fix" to get my 5b's to sound similar. Thye are in 2 different rooms and rigs but the 5's just aren't as easy going as the 1C's.

Please tell me more

H9

[Ron Temple]

Thye are in 2 different rooms and rigs but the 5's just aren't as easy going as the 1C's.

Please tell me more

H9

I don't know if Steve documented the mod as he did with the 4s, but he did pretty much walk us through what he did. His M5(jr+ - I don't think he told me that and I didn't pickup on it) mod, now sounds as good as the CRS+/RTA8Ts which also share the same driver/tweeter combo. The M5s actually are a bit more laid back than either...it's seamless. Since my 1Cs are stock, you'd have to upgrade your M5 xover parts and tweets accordingly, but I'd think it would certainly work.

[fredv]

Between Fred and Steve, ya'll have some tweaking mofo's in the area.

How's that integrated amp conversion going, Fred?

LOL, the strip down integrated amp that was inteneded to convert to a power amp is still as naked as any new born baby. Shamed on me, it has been that way as my work bench for the last 10 months. I have a lot of empty talks but don't have too many complete projects that I can show the ass :D

[fredv]

Steve, what did you modify to the M5 Jr?
Ron, my M5 has the 8" passive woofer, so it will be slightly different from the Jr. You will see.
The xovers of the M5 and CRS are vey different. Since I don't have any of thhe parts in hand, the cost to do the experiment might be a little higher than I would like .......... hee hee, I am cheap :-)

[Polk65]

Sorry for the confusion. I have no photos from the first crossover experiment. The schematic and large crossover photos above are from the second experiment inspired by the SDA CRS+ crossover. This pretty much looks like what is inside of the modified Monitor 5jr+'s. After taking the above photos I decided to turn the large inductor on it's side which allows more clearance inside the cabinet. Moving the large inductor also required relocating the midwoofer outputs to some nearby unused solder points. I chose to drill a few holes in the crossover but you can solder directly onto the circuit board. One new hole is for the (+) tweeter and two others for the silver mica bypass.

To be clear, there were no calculations for any of this. It was an idea based on roughly half the cabinet size and half of the drivers from the CRS+ that has turned out sounding good. The components used are the stereo side of a CRS+ crossover, a mw6510 midwoofer and sl2000 tweeter. I would say just follow the CRS+ schematic but curiously, some SDA crossovers deviate slightly. The 2.7Ω resistor is not located after the polyswitch (per the schematic) but is actually after the first capacitor and silver mica bypass. The photos below will help clarify.


Parts list:

If you have spare laminated magnet wire or wish to DIY the inductors: http://colomar.com/Shavano/inductor_info.html

0.4 mH and 2.5 mH inductors can be ordered from MCM Electronics or elsewhere.

$3.09 x2 (0.4 mH inductor)
http://www.mcmconnect.com/education/product/50-3018/

$6.49 x2 (2.5 mH inductor)
http://www.mcmconnect.com/education/product/50-3029/

$2.15 x2 (2.7 Ω Mills MRA-5)
http://www.soniccraft.com/mills_resistors.htm

$19.60 x2 (12 uF Sonicap Gen-I)
http://www.soniccraft.com/sonicaps.htm

$27.25 x2 (20 uF Sonicap Gen-I)
http://www.soniccraft.com/sonicaps.htm


1) modified crossover bottom
2) SDA CRS+ crossover bottom

[Ron Temple]

You do good work Steve...

Been doing a little A/Bing the 5jrs vs the CRS+ (which I'm now using as intermediate stands :D ). The 5jrs have a little more sizzle in the tweets...not a bad thing, it actually is a better match with the 1Cs. I think it's because the CRS+s are about 8-10" too low. When you hook the CRS+s back in you don't lose a thing accept the sizzle, but add soundstage, midrange and bass. So it's a win/win. For surrounds combined with SDAs, the 5jrs are amazing. If you have the room and can get the CRS+s a bit higher, I don't think you would trade them. I can't really chose which I prefer in this setup, everytime I swap them...except there's no replacement for displacement.