SDA surrounds...

TampaTwo wrote: »

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

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

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.


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)

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 :-)