Jeff B RS 180 Used as Center Channel?

[coniacvsop]

Before everybody lays into me, I know that MTM design is not ideal for a CC. That being said, I intend on building Jeff B's Dayton Ref. design in a tower configuration. I also plan on building a CC, but all the RS designs are crazy large and the crossovers are super complex. I like Jeff's design because of the simplicity of the XO design. The CC will be near wall, so I wasn't sure if there will be BSC issues or porting issues. The furthest listening position is about 30 degrees offset from the CC Position. Any advice would be appreciated. I just don't want to jump into anything and then be disappointing with the results. Thanks

[cwad8505]

I'm about to do the same thing. Interested in seeing other's feedback on the topic. I can't see where you'd be dissapointed, period. There was talk about the RS28F not being a direct replacement, so there might possibly be some changes to the xo if that is your planned route. I'm gonna build it with the stock XO and adjust from there. I don't believe I'm nearly as critical as many of the members (translation: My ear isn't as trained as some/most). At any rate.. interested in replies here..
Chris

[mdocod]

At 30 degrees off axis, a typical MTM around that size and driver spacing will suffer it's first major destructive coupling centred right around 2500hz between the midbass units. At the 1700hz crossover frequency in this design, the mid-bass units will be -5dB compared to on-axis from destructive (partial out of phase) coupling. I'd expect this to result in potentially as much as a ~3-4dB "dip" in response somewhere in the 1200-2400hz range (simulation could give a better picture, but that would be very time consuming). The 1700hz crossover in this design makes use as a center acceptable depending on the pickyness of the listener. ... Not perfect, but not terrible either I suppose. I couldn't begin to guess how much BSC, if any, has been implemented in the design, appears minimal based on components chosen, in fact, I'd venture to guess that those slopes would not look so symmetrical if the full effect of the baffle were included in the response curves there.

[fbov]

If you need a CC with the form factor of an RS180 MTM, there's really only 1 really good choice - Jon Marsh's Modula MTM CC.
http://htguide.com/forum/showthread.php4?t=11475

The price you pay is the cost of the little tweeter-that-can, as well as Jon's propensity for electronic complexity. I replaced a NatP with one of these, and the difference was very significant - it's voiced for dialog as any good CC will be - even seated on-axis, where lobing issues are not involved. There are advantages to the 9" C-C spacing and 1.1KHz XO point you get using that little ScanSpeak tweeter, that can't be overcome without it. And Jon's another designer with a good ear.

BTW, my NatP CC had a similar XO frequency and C-C spacing as Jeff's... not a criticism of Jeff's design, just a limitation of technology.

Have fun,
Frank

[coniacvsop]

Thanks for the replies. Unfortunately, it doesn't look like the Scanspeak tweet is available anymore. I may resort to the Khancenter. It's just pretty big, but I guess that's what you have accept with the three way design. My wife is going to flip once she sees the size of that thing.

[fbov]

True, but a non-issue... use the D3004/602010. Drop in replacement, per Jon, and my ears agree.
http://www.madisoundspeakerstore.com...-deep-chamber/

Again, there is no question that a WMTW 3-way like the Khancenter is a better option, if it fits. If not, this is the next best IMO. Hard to beat in a 9" height!

Have fun,
Frank

[lostboy77]

Have you considered using Zaph's ZDT3.5 Center. This is what I'm planing on using once I finish building Jeff's RS180 MTMs for my HT. That with my already done RS Microbes as surrounds should make for a VERY nice Home Theater built from three very well respected designs.

[Jeff B.]

The 1700hz crossover in this design makes use as a center acceptable depending on the pickyness of the listener. ... Not perfect, but not terrible either I suppose. I couldn't begin to guess how much BSC, if any, has been implemented in the design, appears minimal based on components chosen, in fact, I'd venture to guess that those slopes would not look so symmetrical if the full effect of the baffle were included in the response curves there.

How does the number of components translate into the amount of baffle step compensation? I show the actual transfer functions, so it's easy to see that a full 6dB of compensation is employed. Full (read: actual) baffle effects were included in those response curves. They are measured responses spliced at around 250 - 300 Hz with the near-field response. All of my stand-mounted designs employ full baffle step compensation. It just sounds better to me that way.

[mdocod]

Hi Jeff,

I believe you misinterpreted what I said (I did not say the number of components, I said "the components chosen."). On further review, realising it's a 4 ohm configuration, I am likely mistaken anyways. (1.2mH just felt too low in my head to kill off a baffle peak as aggressive as I would expect from these driver locations on a baffle).

The important thing, is that we now know that your design employs full BSC, which would probably make them less suitable for use as a center channel. I did not see mention of how step loss was dealt with in the first post of the build write-up ( http://techtalk.parts-express.com/sh...180-MTM-Design ), please forgive me.

Regards,
Eric

[rickcraig]

Before everybody lays into me, I know that MTM design is not ideal for a CC. That being said, I intend on building Jeff B's Dayton Ref. design in a tower configuration. I also plan on building a CC, but all the RS designs are crazy large and the crossovers are super complex. I like Jeff's design because of the simplicity of the XO design. The CC will be near wall, so I wasn't sure if there will be BSC issues or porting issues. The furthest listening position is about 30 degrees offset from the CC Position. Any advice would be appreciated. I just don't want to jump into anything and then be disappointing with the results. Thanks

I have a dual 7" 3-way design with the RS180, Morel MDM55, and Seas 22TAFG. This allows a fairly low profile (9" high) and better coverage than a horizontal MTM.

[coniacvsop]

You and I are on the same page LostBoy. My plan was to build the Microbes as surrounds as well. After looking at Zaph's CC on your suggestion, it appears this is exactly what I've been looking for! Building the Modula CC is tempting, but the Scanspeak tweet is twice as expensive as the Dayton mid and tweet together. No doubt the tolerances on that design are extremely tight...Thanks for the suggestion. I'm interested in how your project comes along.

[Jeff B.]

Hi Jeff,

I believe you misinterpreted what I said (I did not say the number of components, I said "the components chosen."). On further review, realising it's a 4 ohm configuration, I am likely mistaken anyways. (1.2mH just felt too low in my head to kill off a baffle peak as aggressive as I would expect from these driver locations on a baffle).

The important thing, is that we now know that your design employs full BSC, which would probably make them less suitable for use as a center channel. I did not see mention of how step loss was dealt with in the first post of the build write-up ( http://techtalk.parts-express.com/sh...180-MTM-Design ), please forgive me.

Regards,
Eric

You're cool. You are correct though, a speaker with full baffle step compensation like this, designed for stand mounting away from the walls, can sound a bit thick and heavy as a center channel if it is placed too close to anything giving it much boundary reinforcement.

I also agree, that although not ideal, it will work reasonably well as a horizontal MTM due to the low crossover point, so it could probably be used that way without much of a problem.

Jeff

[coniacvsop]

Thanks for the input on your design. The simplicity of you XO is much appreciated. I can't wait to build them.

[lostboy77]

You and I are on the same page LostBoy. My plan was to build the Microbes as surrounds as well. After looking at Zaph's CC on your suggestion, it appears this is exactly what I've been looking for! Building the Modula CC is tempting, but the Scanspeak tweet is twice as expensive as the Dayton mid and tweet together. No doubt the tolerances on that design are extremely tight...Thanks for the suggestion. I'm interested in how your project comes along.

If you do build the Microbes, make sure to use the RS variant (uses an RS28A(S) as the tweeter). There is a link for it at the end of the first paragraph of the original Microbe write-up on RJB's site. That way, you use the same tweeters as your mains and keep all of the drivers (save the tweeter on Zaph's center) within the same family. (aesthetics are important you know . . . just ask my wife)

FYI: my project won't be "coming along" until after Christmas. I'm currently in the research stage. You will likely beat me to this one.

[fbov]

+1 on Microbe SE. If you have to use smaller speakers, this at least gives the top end a good chance of a better timbral match, although a lot of that happens below the crossover...

Have fun,
Frank

[lostboy77]

+1 on Microbe SE. If you have to use smaller speakers, this at least gives the top end a good chance of a better timbral match, although a lot of that happens below the crossover...

Have fun,
Frank

Just to be clear, the RS Microbe and the Microbe SE are two different designs.

[fbov]

You're right, my bad.