Using 2 mw6503's with peerless tweeter...Which crossover?

jakelm

Ah HAH!!...The original 7's had a 2.7ohm and the original 10's had a 2.5ohm. This would make my center brighter.

I feel like Sherlock Holmes

jakelm

Picture of my 7b's w/peerless.
A=4.5ohm---> (is this going to my mids????)
B=2.7ohm
C=12uF
D=12uF?? (not sure, it should be, but cant read it)
E=.23mH

So compared to the 10 xover, how do I get the tweeter to match?

Jake

jakelm

Would I replace the 2.5ohm with this 2.7ohm?

I swoped the resistors like you told me. But if I were to replace the resistors, would these work? http://www.mouser.com/catalog/specsheets/XC-600041.pdf

I shop at mouser.com but I am having problems finding the reisitors with the exact same specs. I think Polk used 5w 10% cement resistors. All I can find is 5w 5%. Would that work?

Jake

Polk65

Jake,

First, I'm not all that experienced with this. Second, with a custom center you are going to have to experiment.

A few things to check aside from the crossover. Verify that your receiver or processor has the same volume levels set for left, center, and right speakers. You may need to adjust the center speaker angle up or down a little bit. Speaker wire and amplifier power could also be possible issues but not likely here.

SHORT ANSWER: Change resistor 1 ( 'A' in your Monitor 7 photo ) from 2.5 ohms to something between 3.0 ohms and 4.0 ohms to your liking. When you increase this value your center's tweeter will become quieter than your Monitor 7's.

LONG ANSWER: Depending on how close of a match you would like your center to be it can take alot of effort. Each part that you change has subtle effects on how the tweeter sounds so getting it just how you like it will take time.

I decided to jump from looking at schematics to a mock setup similar to yours. Testing was done at low to moderate levels at a distance of only 4 feet from my workbench in both stereo and mono. The results will be different for you in a large room and with your speakers.

I took my pair of Monitor 5jr's apart and changed the crossover values to those in the "original Model 7" schematics. They have MW6502 mid-woofers and the sl2000's were replaced with Peerless tweeters which mounted pretty flat with two screws at opposite corners.

resistor 1 = 4.5 ohms
resistor 2 = 2.7 ohms
capacitor 1 = 12uF mylar
capacitor 2 = 34uF electrolytic
capacitor 3 = none
inductor 1 = 0.22mH (0.23 is used but I only have 0.22 available)

One of my Monitor 10's became the third candidate. The crossover values were changed to those similar in other Monitor 10's. Peerless tweeters went in the same way as above.

resistor 1 = 2.5 ohms with (capacitor 3) 12uF electrolytic capacitor in parallel
resistor 2 = 2.7 ohms
capacitor 1 = 12uF mylar
capacitor 2 = 34uF electrolytic
capacitor 3 = 12uF electrolytic
inductor 1 = 0.40mH

resistor 1, capacitor 2, capacitor 3, and inductor 1 were changed to different values many times and I gave each change a listen.

resistor 1 was tested with many values but I found 3.0ohms - 3.5ohms sounded good. Experiment here and see what you prefer.

resistor 2 with the value of 2.7 ohms seems to be a constant in the Monitor 5, 7, 10 and RTA 11's(*). Observing this I decided to leave this alone even though it goes to the tweeter inductor. You may want to try some higher resistors and see how it sounds to you. The Monitor 10 with sl2500 tweeter and RTA 11tl remove resistor 2 and one side of inductor 1 replaces it. If you try this you may need to increase the value of resistor 1.

capacitor 1 like resistor 2 also seems a constant so I didn't bother changing it. Later Monitor 10's and RTA 11's(*) used 16uF which you might want to try.

(*) I looked at RTA 11t's and RTA 11tl's because some of their values are similar to the Monitor 10's.

capacitor 2 is nearly always 34uF in the above series speakers with some exceptions like the Monitor 5A and Monitor 10 (the version with sl2500 tweeter). I tried this with a 27uF mylar (Monitor 5A use mylar and Monitor 10 with sl2500 use electrolytic) but did not notice much of a difference. You might also give this a try.

capacitor 3 runs in parallel with resistor 1. At first I used it then removed it. Try it and see what you like.

inductor 1 was swapped with 0.22mH, 0.3mH, 0.4mH and I noticed subtle differences. Coblio wrote that he liked the air core inductors from Madisound http://www.madisound.com and are a good bang for the buck.

Replace the ceramic resistors with Mills 5% wire wound resistors from Parts Connexion. http://www.partsconnexion.com/catalog/resistors.html

After thinking about other models which used one Peerless tweeter and two MW6503 mid-woofers I thought of the original SDA CRS speaker. It came with Peerless tweeters and was later changed to the sl1000 (silver face with Polk Audio stenciled in black letters). These have a slightly different sound than the sl2000. The sl1000 came out just after the Peerless were being used and are about the same size. So with this in mind I decided to try some of the original SDA CRS stereo crossover values for your project.

(SDA CRS stereo crossover)
resistor 1 = 5.6 ohms with (capacitor 3) 0.5uF mylar capacitor in parallel (*1)
resistor 2 = 2.7 ohms with 27uF electrolytic capacitor in parallel (*2)
capacitor 1 = 12uF mylar (and 750pF silver mica in parallel)
capacitor 2 = 20uF electrolytic (*3)
capacitor 3 = 0.5uF mylar (*1)
inductor 1 = 0.40mH

(*1) I did not have this part and substituted 0.47uF electrolytic
(*2) I tested with a 27uF mylar capacitor and it seemed smoother than 20uF electrolytic
(*3) I did not test this value because I felt it was a lower value due to only one mid-woofer being used

I felt these changes smoothed the response but made it sound quieter and less bright than your Monitor 7's.

In the end, I decided these were too many changes and additional cost so I decided on just changing resistor 1 to 3 ohms and removing capacitor 3. Finding what sounds best to you will take experimentation.

resistor 1 = 'A' in your Monitor 7 photo
resistor 2 = 'B' in your Monitor 7 photo
capacitor 1 = 'C' in your Monitor 7 photo
capacitor 2 = 'D' in your Monitor 7 photo
capacitor 3 = wired in parallel with 'A'
inductor 1 = 'E' in your Monitor 7 photo

SDA CRS stereo crossover from June 1984 (for reference)

jakelm

Thanks for all the info Polk65, I will read it carefully. I'm thinking just changing the value of resistor A to a higher value and leave the mids at 2.5ohm, and see how it sounds. Resistors are cheap. The caps are 12uf in the m10 which will be left alone.

You are fantastic , bringing me all of this great info...This will help me out a bunch.

Thanks
Jake

jakelm

Polk65 wrote:

Jake,



I took my pair of Monitor 5jr's apart and changed the crossover values to those in the "original Model 7" schematics. They have MW6502 mid-woofers and the sl2000's were replaced with Peerless tweeters which mounted pretty flat with two screws at opposite corners.

resistor 1 = 4.5 ohms
resistor 2 = 2.7 ohms
capacitor 1 = 12uF mylar
capacitor 2 = 34uF electrolytic
capacitor 3 = none
inductor 1 = 0.22mH (0.23 is used but I only have 0.22 available)

I could not find this. I could not find the schem with the 4.5ohm resistor 1. As a matter of fact I could not find any schem with the 4.5ohm in it.

Jake

P.S I emailed Ken to see what his thoughts were...But I think your right...leaving everything alone and changing the resistor A to a higher value (between 3.0 and 3.7ohm)

jakelm

Does the 4.5ohm on the 7's xover go to the peerless?...If so..thats a big difference than the 2.7ohm on the 10's.

cap 2 is the only other difference in the 7's and the 10's. In the 10's its 12uF, in the 7's its 34uF. What affects does this have on the mids?

Jake

jakelm

A couple of pics of the final project. Notice I went with the PExpress cabinet, which I must say is a very well built cabinet.

jakelm

Sorry the pics are so bad...not the greatest camera. The box is 22"w x 9"h x 13.5"d. Which is approx 1cuft, so no port and stuffed lightly. Sounds absolutly fantastic, especially with my new HK635. Absolutly seemless transition between the 7's and the center.

Jake

jakelm

Just replaced the crossover (original monitor10) with a 10A crossover, sounds much better. The 10A seems to have the same specs. Only difference is the color of the caps, the original 10 had black smaller caps with a large yellow one, while the 10A has blue caps. I'm starting to think the original 10 crossover was infected or defected, because the new 10A crossover has a much smoother sound.


Jake