Jim Holtz

Notice pricing has increased for all the designs in this section of the forum. People should use the BOM's and check with suppliers for current prices

Edit by moderator to add....here's a link to Chris' website where the details about this design are uploaded.

I thought I'd give a little feedback on Chris's RS150 MTM. My son decided he needed a center to match the pair of Modula M/T's I built for him last winter. I'd heard Chris's design at Chicago last fall and it sounded very good so I decided that would be an excellent match with the Modula's. I did use the 1.8K crossover version.

Jumping to the chase, it sounds smooth and detailed with excellent bass, just as I remembered. It's an excellent match with the Modula's or Natalie P's as a center or of course you could just build three MTM's for LCR also. Anyway, a darn nice speaker that is inexpensive to build.

Good job Chris!

Jim

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FlashJim

Great finish. It just about matches my entertainment center.

I did a search on CJD's MTM. Is it buried in that huge thread or does it have it's own thread? That's a ported design, isn't it?

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Jim

opt-e

Very nice, Jim!



You can find Chris' design here. He has plans for both ported and sealed alignments.

FlashJim

Perfect! Thanks, opt-e!

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Jim

kepler

Jim, Looks very nice. How did it sound off axis? (sitting to the left or right)

Did CJD measure off axis with the 1800hz crossover?

thanks

cjd

Nope. I've not even published any of the more recent measurements, even though the ones up there have some oddities that resulted from a short in my cable (At least I did figure out what caused the spritz at 12kHz or whatever)

You may note Jim took advantage of the lower crossover point and left a bit more space between drivers.

Also didn't use the round-over, which will add some diffraction but nothing too dramatic.

Very nice looking Jim! Glad everyone is happy with 'em.

C

Jim Holtz

I was quite surprised at how well it does off axis. I've had a W-M/T-W center in my system for several years so I'm a bit spoiled when it comes to off axis response. Chris's MTM does extremely well in that regard.

As Chris noted, I don't have a round over on the edges. Looks are the driving factor in this regard. I finished the grill for it yesterday which will probably not come off. My son is more interested in clarity than audiophile quality sound at this point in his life. The MTM will certainly provide that, plus match the Modula M/T's extremely well and give him room to appreciate better quality sound as his system grows.

Jim

MarkR

I hope to have one of these finished in a couple of weeks. I originally thought you had shortened up the cabinet but then I noticed the wider driver spacing as well. Can I assume this is allowable due to the lower (1800Hz) crossover being used?

The speaker look's very nice Jim , is it sealed or ported, would you care to share cabinet dimensions?

cjd

It will change the diffraction results some to move the drivers farther apart, but not dramatically. Less so than not doing the round-over.

It will hurt horizontal off-axis a little too, now that I think about it, because it still increases the center-to-center spacing between the mids, and that's what dictates over what range comb filtering is an issue.

For 95% of horizontal installations, I doubt very much that it's an issue. Where it is, you probably need a vertical TM arrangement in your center anyhow.

C

Jim Holtz

Actually, I wanted a cabinet size that would allow good bass ported or if I chose, the port could be stuffed for a sealed arrangement. I sized the cabinet at 18.3 liters which is 18.5" W x 8.5" H x 11.5" D (with a 1.25" thick front baffle) and used a 2.5" x 4.72" port which provided a F3 of 50 Hz. per Unibox.

The cabinet size fits my sons entertainment center and the bass is strong in the ported configuration so he can run it full range.

The driver spacing is 1/4" between the tweeter and the RS150's so it's not a big change from the spacing Chris used and well with in one wave length at crossover. I have much better luck with veneer when I don't go below 1/4". YMMV...

Jim

dlneubec

What do you all think of using a 2.5way configuration for a center MTM, to reduce comb filtering?

kepler

How close are you all able to use the 27TDFC to a tv? Mine would have to sit pretty much right above the tv without much separation. Just wanted to get your thoughts/experience.

thanks

Dougie085

Depends on what kind of tv it is? if its a rear projection/dlp/lcd/plasma/LCD flatpanel it wont mess with your tv at all. Only tv's that have issues with magnets are the big tube tv's.

Jim Holtz

The 27TDFC/TV version is shielded and won't be an issue.

Jim

cjd

I think it might help some with comb filtering, but it introduces other things that I'm not so fond of, personally. Given the realities of most installations, comb filtering isn't going to jump out and cause you much grief since you can still go 20 degrees off-axis either way with minimal impact.

I have built with the TDFC/TV and it's a drop-in for all intents and purposes here... I wasn't as rigerous with testing, but the goal being one-shot simplicity (or as close as I could get...) - plus I was time crunced when I worked on that one.

C

dlneubec

CJD,

I'm a novice and simply trying to learn more. What are the other things you are not so fond of that a 2.5way introduces to a CC MTM?

I'm using a CC I built from RS125's and 22TAF/G in a 2.5way that was designed by Roman B. It does seem to have good off axis performance, but I'm curious what the trade off's are with this type of design.

Thanks.

kepler

Okay, I've checked my existing center channel baffle size in bds and I think it will be close enough to your (cjd's) sealed mtm front baffle dim. My only question is wether or not using the 1.3mH 18ga perfect layer air core inductor would be any improvement over the jantzen or the sidewinder 16ga 1.25mH? Same question regarding the .2mH "Lm2"?

thanks

HMenke

Super job, Jim. Great craftsmanship.

Henry

cjd

kepler: While .05 isn't a lot in the grand scheme, it may make things slightly more forward since it will slightly boostmidrange output from the RS150's. It won't be a lot though.

The larger gauge (I believe lower impedance) will bring up the lower end very slightly - not a problem in most cases since these are designed with a bit of droop on the bottom to allow for more "average" placements.

C

Jim Holtz

Thanks Henry! I appreciate your kind remarks.

Jim

cobbpa

I'm pulling this thread up Lazarus style, but Jim pointed me here, so a couple of questions for him or CJD...

--Moving the tweeter higher, woofers lower & closer may be a slight improvement, correct?

--Is 1.8kHz definitely the best xover, or would there be an advantage in the alternate 2.1kHz CJD also diagrams?

cjd

Rearranging the baffle as you suggest may help off-axis a little, but it will also introduce different diffraction and baffle step - the net result may not be worth it without redoing BDS work, integrating, and such. All quite do-able, but I wanted a one-crossover simple shape that could be used for center or mains, not too costly, and something that someone could take a Triune box, re-baffle, and have themselves a nice upgrade.

1.8kHz will have improved off-axis horizontally and it will do ever so slightly better with respect to any nasties you might pick up in the RS150. There may be a very small improvement in power handling with 2.1kHz but the Seas and RS tweeters I used are so far above the point where they really have problems (I mean, they're being used at 1.2kHz) that I don't think I would build that version again myself.

C

cobbpa

What about placing this on top of my TV? How does that change BSC in the xover?

cjd

How big is the TV?

It may be enough to simply bump down the gauge (bump up the impedance) of the inductors in the woofer circuit.

Well, I snuck a few minutes to toss some numbers together... swap values as you move across the posted circuit for the following:

Woofer:

.8mH 20ga inductor
40uF cap
.1mH inductor

6ohm/12uF zobel

Tweeter:

10uF cap
.33mH inductor
20uF cap

.05mH inductor/1.5ohm resistor

C

jonathanb3478

I have been looking around for a smaller form factor center channel to use with my RS TMWW (sealed/seas tweeter) when it is completed. May or may not have room to use the big WMTW center when the time comes.

This design looks promising. Just a couple questions, however.

Seas indicates that the /TV version of the tweeter (H1210) has a 250Hz higher FS than the non-/TV (H1189), and has a usable range of 2K+. The H1189 is good for 1.5K+, according to Seas. Also, I see no reference to a shielded version of the tweeter at the design website.

So, CJD, did you intend us to use the /TV (H1210), or not? Maybe they are just interchangable.

Thanks in advance for the clarification!

__________________
Experience is a hard teacher because she gives the test first, the lesson afterwards.
-Vernon Sanders Law

cobbpa

My TV is a 27" CRT. Also, the speaker baffle will be ~4 feet from the front wall.

Thanks for the help!

Brian Walter

Jonathan, did you find that tweeter available anywhere? The last time I checked, Madisound didn't list it on their website. You may actually find that with the 1212 on top and the CC on top of the TV, it might be far enought away thta there may not be any noticable interference to the TV. You might want to check this out.

Brian

BobEllis

Zalytron carries the H1210. www.zalytron.com I've bought lots of drivers and parts from Elliot, a reliable guy.

With my 27" RCA TV, as long as you keep it more than 6" away the H1189 has no impact on the picture. The stray magnetic field seem focused front to back - a foot in front of the tube and it shows, but keep it below or above and it is fine.

Jim Holtz

Hi Brian,

I used the H1210 in the center I did for my son and also used the 1.8K crossover. Here is the link to Madisound.

http://www.madisound.com/cgi-bin/in....10816&pid=1003

It starts to strain a little bit in the upper mids if you really crank it up but under normal usage, it sounds great. I also noticed it in the MTM pair Chris had at Chicago last fall so I don't think it's related to the H1210. The question is, just how much above 90 - 95 DB (I'm guessing) do you play your center channel? Normal volumes sound great.

If you really want to crank your system up to ultra high volumes, I think the W-M/T-W center would probably be a better fit.

My son is happy as can be with the Modula M/T's and MTM center I built for him. They're a real step up from the mid-fi store crap he did have, IMHO.

Jim

Brian Walter

My mistake, I was thinking of the shielded version of the 1212. The Seas website shows it, but Madisound doesn't carry it. I don't remember what the model number was.

jonathanb3478

So you are saying that the MTM pair Chris brought there did not use the H1210, but the H1189?




No arguements on this from me.




No arguements on this from me.

(is there an echo in here?)

__________________
Experience is a hard teacher because she gives the test first, the lesson afterwards.
-Vernon Sanders Law

Jim Holtz

Yes, I believe he did have the 1189 in that pair and it did use the 2.1K crossover if I remember correctly.

The H1189 (27TDFC) and the H1210 (27TDFC/TV) are the same tweeter except for shielding. The FS is a bit higher on the 1210 because it doesn't have a rear cup I believe.

Jim

Jim Holtz

Hi Brian,

The model number is 27TBFC/GTV. I emailed Madisound some time ago about it and they indicated they sold so few sheilded tweeters that they wouldn't be carrying it. I think Solen or Meniscus carry it however. I forget which.

HTH

Jim

Mudjock

Solen has the 27TBC/GTV (H1148 ), which is the non-ferrofluid version. I still have a pair of the 27TBFC/GTV (H1213) from when Madisound closed them out, but haven't seen those anywhere for some time.