Next project MTM RS225 + RS28a

[Mark K]

Talking to myself again

Just a tease. I finished two rounds of testing on a completed unit.

http://206.13.113.199/ncdiyaudio/mark/whats_new.htm

[JonMarsh]

that's a pretty big tease, Mark - where's the beef!?!

Looking forward to seeing your results.

I'm wondering when the RS midrange driver will become available- might be a nice candidate for a three way WMTW center channel... with the RS225 and Seas H1283, which is finally available from Madisound.

~Jon

[Mark K]

Part 1 is up

http://206.13.113.199/ncdiyaudio/mark/index.htm

[Davey]

Mark,

Do you have plots of the electrical-only responses of the crossover? I would be interested in those as well because it really gives a nice visual indication of how the networks are shaping the responses.

Very nice project and very well documented! (All the off-axis plots are especially nice to see.)

Cheers,

Davey.

[JonMarsh]

Very nice write up and documentation, Mark. I'll be interseted to see Part 2.

I'll probably have to model your crossover just out of curiosity, and maybe can answer Davey's question. Thanks for sharing with us.

~Jon

[TacoD]

Nice website, it is a good read. I can learn a lot about measuring.

[Mark K]

Mark,

Do you have plots of the electrical-only responses of the crossover? I would be interested in those as well because it really gives a nice visual indication of how the networks are shaping the responses.

Very nice project and very well documented! (All the off-axis plots are especially nice to see.)

Cheers,

Davey.

Oh, Hi Davey,

I missed your post. I don't have those yet. I meant to but then shoved everything in the boxes. I'll try to generate some for part two. I just managed to get the other completed tonight and ran an impedance curve just to make sure I didn't short anything out... :uhoh:

[Mark K]

Part 2 is up, with the usual minor grammatical errors... Still no electrical transfer functions

RS22528A 2 way

[Ray_D]

Mark

Your web site is great.

What drivers are you going to use in the 3-way?

Ray

[GrahamT]

Mark

Your web site is great.

What drivers are you going to use in the 3-way?

Ray

I was thinking the same thing.

and it will have a midrange driver with significant Sd, more that the typical diy'er might use

[Mark K]

Mark

Your web site is great.

What drivers are you going to use in the 3-way?

Ray

Thanks!

I'm not sure what drivers. What I'm going to try to do is have a 10" woofer or sub in a small sealed box mated to a smallish sealed upper unit. I've got the L26 and RS10" drivers as candidates for the woofer. Both a bit different, but excellent in their own right. I'm not sure about the mids. The logical choice is 2 RS 7"s because they are excellent and inexpensive, along with a Seas TBFC/G. But that's sort of been done, or very similar. So I may try using 4 RS125's in a MMTMM upper unit 2.5 way crossed to standalone woofers.
I mean, the RS125's are dirt cheap, and have very nice linear distortion. Not very good alone in terms of nonlinear distortion. Stack together 4 and you've got more Sd than an 8". I'll probably play around with a couple of head units, and see what works the best. I'm trying to make a high quality 3 way that's small and visually narrow, just for aesthetics, without compromising. A separate upper unit with the RS125's could be only ~6.5-7 wide and ~26 tall. High spouse appeal. The woofer would be in its own box, designed to be on the floor.

Anyway, it's a ways off. I'm not even going to start it until the new year and then, only slowly. Figure summer or fall 2006.

I've also got some vifa XT 7" fiberglass drivers. I know they're not the favorite around here, but I'm curious about their midrange quality and will compare them to the Peerless nomex 7"s.

[Dennis H]

I've also got some vifa XT 7" fiberglass drivers. I know they're not the favorite around here, but I'm curious about their midrange quality and will compare them to the Peerless nomex 7"s.

Yes, please! If those are the XG (XT series but the model number is XG) glass drivers Zaph tested, I'd love to hear a second opinion about their midrange performance. Zaph's distortion measurements make them look like a real winner in the midrange, i.e. they can cross above the normal 1200-1500 of the metal drivers.

[dlr]

Off-axis change for dip correction

It's just a simple shelving circuit. The attenuating resistor is shunted by a cap. It doesn't really fix the dip but it does mitigate it.

Boy, do I wish I could have an outdoor setup for measuring. Can't do that in my situation (too much road noise). Have you tried comparing that to a close-mic technique and/or T/S model results to see what corrections to the latter two would be required to match the measurements?

I don't like the close-mic approach with its inherent errors, so I rely upon T/S box modeling to get midrange and/or mid-woofer highpass with near-field impulse down to 300Hz. What's your experience with this?

Here's a link to the page describing my handling of what you see on the graph below it.

http://www.speakerdesign.net/designs/25w12mow1/design_issues.htm

Dave

[cjd]

But that's sort of been done, or very similar.

8)

And it sounds sooooo good.

C

[Paul H]

8)

And it sounds sooooo good.

C

Now you leave him alone and let him design and test for his own design :twisted:

Paul

[cjd]

Now you leave him alone and let him design and test for his own design :twisted:

Paul

Why do you think I said nothin more, huh? :P I mean, I know I think I know everything there is to know, but I also know I really don't know everything, you know? :P

C

[Brian Bunge]

Somewhat elaborating on Mark's MMTMM idea with the RS125's in a 2.5-way configuration, I wonder how much trouble it would be to take Chris' existing RS125/28A MTM and expand it into either a MMTMM or MTMMM in a 2.5-way configuration. I would think that the MTMMM could make for a really impressive, slim tower design with a good bit of dynamic capability.

[JonMarsh]

Somewhat elaborating on Mark's MMTMM idea with the RS125's in a 2.5-way configuration, I wonder how much trouble it would be to take Chris' existing RS125/28A MTM and expand it into either a MMTMM or MTMMM in a 2.5-way configuration. I would think that the MTMMM could make for a really impressive, slim tower design with a good bit of dynamic capability.

Well, Brian, what are you waiting for? Spare time? Money for drivers? Sounds like something right up your alley....

~Jon

[Brian Bunge]

Actually, I can find the time or money, it's finding a place to build enclosures...now that I'm in Orlando I don't have access to a woodshop. There's all the HTT guys over in Tampa, maybe Rich could help me out. And then there's Chuck down in Palm Bay. Not sure who's closer.

All of these are potential ideas for new speakers for Ashley's dad when the time comes. He desperately needs a new center channel. I just hate the Klipsch center he has and don't like the towers much more. The center really sounds congested listening to the male announcers on the weekly football games and the powered towers really have muddy bass.

[JonMarsh]

Sounds like you've got some real opportunities, there- hope you find someplace you can do some work.

[tokyofist]

i took advatage of PE's sale on the RS225 over the weekend and picked some up for a pair of bookshelves using mark's design. i intend to use them in the bedroom, which means that they're going to be placed against the wall. looking at mark's data and comments, this positioning will result in overcompensation for baffle step.

is it possible to tweak mark's circuit to reduce BSC to ~3dB (or a more appropriate value) without having to remodel the entire crossover network?

thanks,
dave

[JonMarsh]

i took advatage of PE's sale on the RS225 over the weekend and picked some up for a pair of bookshelves using mark's design. i intend to use them in the bedroom, which means that they're going to be placed against the wall. looking at mark's data and comments, this positioning will result in overcompensation for baffle step.

is it possible to tweak mark's circuit to reduce BSC to ~3dB (or a more appropriate value) without having to remodel the entire crossover network?

thanks,
dave

Well, it's possible to do, but it does require "remodeling" the circuit. I think Mark's had some other requests to do that, but I know he's in a mode where spare personal time is at a real premium.

I have data files for the RS225 and RS28a with which I could model a modified version with less baffle step, probably wouldn't be able to get to it for a week or so (APEC2006 conference coming up, leave for that this Sunday). The crossover Mark used is patterned after my M8ta, which in one version uses the RS225; his enclosure is different and smaller, somewhat narrower, though not a lot- may not affect the BSC frequencies too much.

We'll see what I can come up with; Mark might do something, too, but I can't speak for his free time- mine's a problem, too!

[kgveteran]

Mark K,

Wow, I just found my rear/side surrounds and a rear center.It appears to be sealed ? The MTM are just too big and my room is smallish.

Do you think it would be a good match the the RS Center that I use for my mains and center now ? This is the first i've seen this thread.How cool.

KG


I made some wall shelves that now hold a pair of paradigm MiniMK3's (rear/side surround and rear center ) and these would be a perfect fit.Great job on these BTW!

[tokyofist]

Well, it's possible to do, but it does require "remodeling" the circuit. I think Mark's had some other requests to do that, but I know he's in a mode where spare personal time is at a real premium.

I have data files for the RS225 and RS28a with which I could model a modified version with less baffle step, probably wouldn't be able to get to it for a week or so (APEC2006 conference coming up, leave for that this Sunday). The crossover Mark used is patterned after my M8ta, which in one version uses the RS225; his enclosure is different and smaller, somewhat narrower, though not a lot- may not affect the BSC frequencies too much.

We'll see what I can come up with; Mark might do something, too, but I can't speak for his free time- mine's a problem, too!

np, i probably won't have time to get started on them til mid april at the earliest. thanks for your help!

[tokyofist]

figured i might bump this back on to the first page to so it doesn't get forgotten

as long as i have your attention, does anyone else have experience with markk's design? if so, can you describe in-room placement? if you had them against a wall, is it even necessary, IYO, to decrease BSC? any general listening impressions are welcome as well, although i get the sense there aren't a lot of them out there...

[JonMarsh]

Mark's project has neary full BSC (about 6 dB) and should be well out from the wall. If you're close to the wall, reducing BSC to 2-3 dB will be about right. ONLY if you mount flush in the wall can you elminate BSC. The best approach is to measure the speaker in the situation you want to use it in, do some averaged forward measurements, and use that data for setting BSC.

I'll email Mark this weekend and see if he can share his data files in the cabinet for the re-design.

~Jon

[tokyofist]

The best approach is to measure the speaker in the situation you want to use it in, do some averaged forward measurements, and use that data for setting BSC.

I'll email Mark this weekend and see if he can share his data files in the cabinet for the re-design.

~Jon

Jon:

I do have access to MLS software and a measurement mic. I can mount the drivers and take measurements when cabinets are placed against the wall. I've been looking for a reason to learn this stuff anyways 8) . by averaged forward measurements, do you mean on and off axis? have you had any luck getting ahold of Mark?