My Center Channel Project

Nightfall

westmassguy wrote: »

Aesthetics

I see, so it obviously doesn't matter then. I have almost the same center channel, two Monitor 5's on their sides shoved together with the tweeters facing each other on the inside. I always wondered if I was causing any issues by having them (tweeters) facing the wrong direction.

westmassguy

The Polk Tweeters, actually almost any soft dome tweeter, have a 120-140 degree radiation pattern. It can be mounted in any position. What affects it dispersion, is the location and spacing of the woofers. The MTM/ D'Appolito arrangement causes lobing, which Face pointed out. At some point I'll be modifying the plastic trim on the 198, and raising it up as high as possible to mitigate the lobing. I sounds awesome now, but I'll take the advice. I originally tried two 5js then two 4.6s end to end. With the tweeters next to each other, I found it too bright on axis. That's why my design is essentially two 5jr+s with a single tweeter in a single enclosure.

westmassguy

I decided to update this thread, since I've made one, hopefully last change. Based on comments made by Face, others who forgot what I know, and my own research into lobing effects in MTM driver alignments. I raised the tweeter up as far as possible within the restraints of my the cabinet, and my original design. The RDO-198-1 Tweeter's plastic trim had to be carefully cut to be able to fit in it's new location. The plastic trim was removed from the Tweeter. I measured and marked the new size, and clamped my belt sander upside down on my bench. I then slowly ground off the plastic to the marks I had made. The corners were rounded, and finish sanded with 320 then 400 grit paper. New mounting holes were drilled and countersunk.
On the cabinet, I removed a section of veneer, filled the old hole with Bondo for wood, sanded it flat, sealed the raw surface with brush-on lacquer, and installed a precut section of veneer. The new hole was drilled out, new mounting holes and hurricane nuts installed, and a new gasket was cut and the tweeter installed.
My initial impression, is more detail in the crossover region. Voice and vocals seem clearer. The overall sound is still superb, but clearer in a very important frequency range. All that remains is a little walnut filler, light sanding, stain, and finish.




As an aside, I had picked up a CS350-LS, just to compare, and see if it really does match the vintage models. I upgraded the rather simple crossover with a Sonicap, and tested it with my system. It's certainly a very fine center, very smooth, with plenty of punch. It did blend well with my 2As, and surrounds to a point, but in the end, it could not compete with my own custom built unit.

pitdogg2

I agree Dave the CS350 is a solid center but it will never dig as deep as the beast you made.
I missed the update to yours fine job Mr. Craftsman fine job.

westmassguy

pitdogg2 wrote: »

I agree Dave the CS350 is a solid center but it will never dig as deep as the beast you made.
I missed the update to yours fine job Mr. Craftsman fine job.

Thank you sir. I added the two 12 " midfi Sony subs I had, to the center out. They flank my 2As. I cross them over at 50Hz, and keep the gain down. You'd be surprised how much bass the center has when you run it full range.

sansuibutch

Very nice job. Ive been looking to build a cc for my sda srs for a while. The monitor 10 should be timber matched to the sda srs correct? I am ready to pull the trigger on this setup with maybe a little difference to the outside of the cabinet just to match my sda. How did you router out baffle for the mw to recess? Did you just use a handheld router with a homemade guide to get the circles perfect?

sansuibutch

Very nice

sansuibutch

I see now you have SDA 2A-TLs as your front speakers and not the monitor 10s. Should this cc be closely timber matched to my original sda srs. Id also plan on a rdo194 for the tweeter to match the tweeters in my sda. I realize these tweeters xovers are different. Im not to up to speed on thr differences. If anyone can clue me in that would be awsome. Thank you all. Very nice work.

westmassguy

If you use vintage Polk woofers, and the new RD-0194 tweeter, it will match. The holes were made using a hole-saw, with the recess done with a hand router.

sansuibutch

westmassguy wrote: »

If you use vintage Polk woofers, and the new RD-0194 tweeter, it will match. The holes were made using a hole-saw, with the recess done with a hand router.

Awsome. Thank you for that input. Much appreciated. Im figuring i can just rebuilt the xover on a 10b setup to match mine and should be good to go correct? Since il be running different mw's than 10b xover was designed around will i have to change some of the components of the xover for the mw section?

sansuibutch

Or maybe I should just use the 6503 in parallel to closer match the dcr/impedence of my sda srs?

westmassguy

sansuibutch wrote: »

westmassguy wrote: »

If you use vintage Polk woofers, and the new RD-0194 tweeter, it will match. The holes were made using a hole-saw, with the recess done with a hand router.

Awsome. Thank you for that input. Much appreciated. Im figuring i can just rebuilt the xover on a 10b setup to match mine and should be good to go correct? Since il be running different mw's than 10b xover was designed around will i have to change some of the components of the xover for the mw section?

All the info you need is here in this thread. The Monitor 10 crossover had to be modified for two 4 ohm MW6502s

sansuibutch

Thank you westmassguy. I do have one more question. I see you chose to use the 6501. Is that because the VAS figures let them dig a little deeper in the small cabinet? I dont need a ton of bass from my center but mostly to be timber matched. I have a set of monitor 10b (6503) now that i planned on using for parts. Im not trying to reinvent the wheel or do half of the research that you have. Actually id love to but i dont have anyhere near enough time. Depending on your thoughts on this matter will help me decide wich way to go. Thank you agian for your advice and never ending dedication to helping me and others on this site.

westmassguy

sansuibutch wrote: »

Thank you westmassguy. I do have one more question. I see you chose to use the 6501. Is that because the VAS figures let them dig a little deeper in the small cabinet? I dont need a ton of bass from my center but mostly to be timber matched. I have a set of monitor 10b (6503) now that i planned on using for parts. Im not trying to reinvent the wheel or do half of the research that you have. Actually id love to but i dont have anyhere near enough time. Depending on your thoughts on this matter will help me decide wich way to go. Thank you agian for your advice and never ending dedication to helping me and others on this site.

I used two 6502s, not 6501s, due to the size of the enclosure, and the T/S parameters of Polk's vintage woofers. The 6502s along with the two passive radiators, was the only combination that worked.

sansuibutch

I apologize, i meant to say 6502. With that said i will move these monitor 10s down the road and start gathering the parts necessary. Thanks agian.

sansuibutch

I am filling my cart at parts express. I take it im replacing the components in the high frequency part of the xover with just new caps and resistors of the same value correct? Im just not sure if your different value inductors and resistors are part of making the high end blend with the low end for this project or part of the tl mod for the rdo198.. my understading is im going to replace the inductor and cap for the low frequency portion of the xover with your recommendations. For the top end il just replace the resistors and caps with the same values with my preferance of brand , and also the replacement of the polyswitch with whatever value resistor suits my taste.. does this sound right since im using the rdo194? I looked for the 10b tl mod and Im finding mixed options. I appreciate the help.

westmassguy

sansuibutch wrote: »

I am filling my cart at parts express. I take it im replacing the components in the high frequency part of the xover with just new caps and resistors of the same value correct? Im just not sure if your different value inductors and resistors are part of making the high end blend with the low end for this project or part of the tl mod for the rdo198.. my understading is im going to replace the inductor and cap for the low frequency portion of the xover with your recommendations. For the top end il just replace the resistors and caps with the same values with my preferance of brand , and also the replacement of the polyswitch with whatever value resistor suits my taste.. does this sound right since im using the rdo194? I looked for the 10b tl mod and Im finding mixed options. I appreciate the help.

You are correct

sansuibutch

I picked up a nice set of 5jr wich have all the appropriate drivers and also a monitor 10b xover and all the components to do the xover, also have had the knock down cabinet delivered. What size holesaw did you use? The holes in the 5jr cabinets are around 5.6" (142mm). I was plan ing to use a 5.5" holesaw but the drivers are a slight bit bigger than 5.5". I think I might install black vinyl on the face of the cabinet and use 3/8" or 3/4"inch oak on top and bottom of cabinet that overhangs so thr grill sits flush to closely resemble the look of my sda. Im pretty excited about this project. When i redid my sda's I used 5/4" solid oak for the top and bottom caps and i think 3/8" oak for the sides. They look great. Thanks again for this post and all the help.

westmassguy

5 5/8" with a 1/2" router bit as I recall for the woofers and PRs. 4" for the crossover. Best to measure for yourself though

sansuibutch

westmassguy wrote: »

5 5/8" with a 1/2" router bit as I recall for the woofers and PRs. 4" for the crossover. Best to measure for yourself though

Cool that does sound about right. I am a huge fan of measuring 10 times and cutting once. I work with a lot of steel and aluminum and very tight tolerances so I tend to overthink anything to do with wood.

sansuibutch

westmassguy wrote: »

I knew from all the experimentation, that a Monitor 10 B crossover would be used, since it's designed for a single tweeter, dual woofer and PR configuration. I have the T/S parameters for most of the vintage woofers, the only item missing, is the SPL rating for the drivers, which will come into play later. The main problem, is the 10 uses 8 ohm nominal drivers. All the 8 ohm drivers have relatively high VAS figures. I could tune a smaller vented enclosure, but my cut-off would be somewhere in the 70 Hz range, which is not what I was looking for. I decided, that the only way to make this work, was to use the MW6502 4 ohm drivers, which have half the VAS of their 8 ohm brothers, and modify the 10 crossover. I also wanted to use two 6.5" PRs from a pair of 5JR+s I'd picked up off eBay. Instead of fabricating my own enclosure, I decided to find a suitable knock-down, CNC cut enclosure. As it happened, Parts Express was having a sale, and I found the perfect candidate. It's billed as a tower/large center, so I ordered it. The internal volume turned out to be almost exactly twice the size of two Monitor 5JR+s. This meant I could theoretically use 2 MW650s, plus the two 6.5 " PRs. When I began assembling the cabinet, I realized the CNC cuts, left a lot to be desired. Some fill, very careful Belt Sanding (Yes I do know how to use a belt sander), and some final block sanding were required to smooth things out. The front baffle was pre-cut before assembly. After assembly, the cabinet was internally sealed, and Hurricane Nuts installed.

Attachment not found.Attachment not found.

My next challenge, was to modify the Monitor 10 Crossover for use with 4 ohm drivers. The 10 uses two 8 ohm drivers in Parallel, for 4 ohm nominal resistance. The two 6502s would be wired in Series, for an 8 ohm nominal resistance. In order to keep the exact crossover frequency and slope, I would have to double the mh value for the inductor, and halve the uf value for the shunt capacitor.
I found some suitable temporary parts in my ever growing parts bin, and installed a 18 gauge 3mh inductor, and made up the 17 uf cap. The hi-pass section had already been upgraded with Sonicaps and Mills resistors, and had the TL mod dove to it. I made the modifications, and put everything together for a dry run.

Attachment not found.Attachment not found.Attachment not found.Attachment not found.Attachment not found.

After firing it up, It sounded quite good, except for a rather hot top end. The 10 crossover was designed for drivers with higher output, and a much larger enclosure. I decided there were two ways to balance the Tweeter and Woofer output. I could change the value of the .5 ohm resistor I installed in place of the Polyswitch. By raising the value, I could reduce the output of the hi-pass without adversely affecting the voicing of the tweeter. The other option is to install a much lower resistance Inductor, to increase the output of the two woofers. I found a 4ohm, 25 watt L-Pad, and temporarily installed it in place of the .5 ohm resistor. I used the common and 4 ohm leg, and preset it to .5 ohms. I fired up the speaker, and slowly increased the resistance until my ears told me it was in balance with the Woofers. The value turned out to be approximately 7.5 ohms. I wanted to test my other theory, and found a 15 gauge, 3.3 MH P-Core Inductor in my parts bin. I re-installed the .5 ohm resistor. I unwound the Inductor, until I reached the correct 3.1 mh rating on my LCR Meter. I disconnected the other inductor, and installed the P-Core. Woofer output increased, and to my ears, everything was balanced. I don't like P-Core Inductors, since they saturate easily, and have other distortion components. I decided to order a new Erse Hi-Q, Laminated Steel Inductor, which I've used in the past with great results. I also ordered a 17 uf Cap from Sonic to complete the permanent modifications to the crossover.

Here you said you reinstalled the .5 ohm resistor and used the erse hi-q inductor and it was well balanced. I took your advice. Same .5ohm resistor and erse hi-q laminated steel inductor (unwound to 3.1mh inductor😁