CJD RS150 Center Project

[catacon]

Hey everybody,
I've been looking for a center channel that will match my RS180 Modula MTs and MTMs. Well it seems that Chris' RS150/27TDFC center channel fits the bill. It will be a little while before I build, but I thought I would start early with my questions.

1) In this schematic which end is positive and which is negative or does it matter?



2) Under the Box Design it says there should be a 3/4" roundover on the vertical. Is this necessary or is the design doable without it?

3) Is the 1800Hz crossover favored over the 2100Hz version? Why?

I will probably have more questions later, but that's it for now.

Thanks!

[---k---]

1) the top side is positive. the bottom that everything connects to is the ground. make sense?

2) the long sides should have the roundover. the short top and bottom don't. without the roundover, you could get a little bit of a bump at specific frequencies due to baffle defraction. see the sims in the first post of my Khanspire thread. I've read books that claim this isn't audible, but I don't agree with it. It is one of those last 10% optimization type of thing.

3) 1800hz sounds better.
I think it has to do with clearing the RS150 cone breakup issues.

[catacon]

Great, thanks! That helps out a lot. The roundover may be an aesthetic issue since all the rest of my speakers don't have a roundover, but I will think about that some more.

Are Jantzen 18ga. inductors and Mills resistors decent? I would like to order as much as I can from PE and they have everything if the Jantzen and MiIls are good. Also, is it OK to get a 35uF cap by twisting the leads on a 10uF and a 25uF?

Thanks!

[---k---]

yes and yes.

Just FYI for others, the design is here: http://www.eldamar.net/audio/rs150mtm/

[catacon]

Awesome, thanks!

How much noticeable effect will not using the roundover have? This isn't going to be a top of the line speaker, so a little difference won't be a huge deal, but if the difference is significant I will do the roundover.

[cjd]

Well, it *is* going to be a top of the line speaker, for most people (sound-wise)

That said: IMO it's going to be most noticeable in a tuned environment (hearing a difference with round-over) and a very practiced ear. If you're using this as a center, there are almost surely going to be many other things around introducing much worse diffraction or reflection issues, relative to no round-over.

Jim Holtz, who has a very good ear, built this without round-over, so... I'd not worry obsessively about it.

C

[catacon]

Yeah, I certainly don't have a good, trained ear, and my "theater" is not ideal, so I think many other things will cause distortions, etc. Thanks for clearing that up.

[catacon]

Does it matter how the bracing is done? I was thinking it might be better to do two boards running the length of the speaker horizontally (like the baffle and back). The first brace would be 4" from the front of the baffle and the next brace would be 6.5" behind that (4" from the back). Each would have 5x3.25" holes in them.

Image not available

[Jim Holtz]

Well, it *is* going to be a top of the line speaker, for most people (sound-wise)

That said: IMO it's going to be most noticeable in a tuned environment (hearing a difference with round-over) and a very practiced ear. If you're using this as a center, there are almost surely going to be many other things around introducing much worse diffraction or reflection issues, relative to no round-over.

Jim Holtz, who has a very good ear, built this without round-over, so... I'd not worry obsessively about it.

C

Hi Chris,

Thank you for the kind remark! I appreciate your vote of confidence.

You are exactly correct in my opinion. Any anomolies introduced by not rounding the front baffle edges are dwarfed by the room and surround mixing. I think it's a fine center that provides excellent sound quality.

Jim

[catacon]

Another question...Does the tweeter need a backing plate like with the Modula MTM?

Thanks!

[cjd]

Need? no. It definitely won't hurt performance. So you're absolutely welcome to include one.

[catacon]

I will probably put one in just to be "safe". How does the bracing I linked look?

[---k---]

its fine. you might want to add a small piece to the large back panel.

[---k---]

Actually, looking at it a second time your holes in the brace are probably too small to get your hands through to fish the wires from the terminals and to fit the crossovers though.

Bracing is good, and overkill is always welcomed. But, CJD has built a couple of pairs of these. I would do like he has. He would have included more bracing if he thought it would help.

[catacon]

Ok, so his bracing is two ~10" about 12" apart?