RS125-based MTM??

[RPiatt]

Long time listener, first time caller...

I have been searching and reading for several weeks on here and over at avsforum.com (as user "QuabbDude") and after much soul searching I have decided I think I am ready to begin planning my first speaker build. I live in a townhouse, so my only option currently is in my den, which is roughly 11' x 11', with one wall being a half wall leading into the kitchen.

I originally was looking at the Microbe SE (Roman Bednarek - rjbaudio.com), but decided what I really wanted was an MTM design. I looked at the Audax, and then the Modula MTM, and then the NatalieP. The last two I think would be slightly too big for my space, and the audax stuff doesn't appear to be in production anymore (so current stock was my only option).

I did however, read a lot of good comments on here about the RS125 and thought I would investigate that. I think an MTM with that (and maybe the RS28A) woudl make a great speaker (certainly a step up from my Venturi-BIC Americas stuff now).

Other thoughts:
- I am in no hurry here, as I am in gradschool for my MBA and the first half of the year is slammed with three consecutive really hard classes, so other than buying parts, I couldn't start in earnest until the middle of June. In otherwords, I have plenty of time to do this right.
- I honestly don't know much about speakers (but am reading diligently), but am a fair woodworker, so I feel confident in my ability to do something of good quality here.
- Since the room is small, the speakers will have to be fairly close to a wall boundry in all cases (maybe pointing to a sealed design?).
- I want to build 5 of them for a full surround set, with a subwoofer to come later (after I show the boss what quality can be had for DIY prices!)

I have searched here, avsforum.com, and on google to find an existing MTM design with the RS125. I am finding nada. So unless my searching skills suck, then I need some help.

Thoughts?

-Randy

[Outfitter]

I came across this MTM recently....never built but looks interesting.

http://rjbaudio.com/misc/Microbe%20SE25%20MTM.JPG

[RPiatt]

How did I not see that? ops: i was all over that site and must have walked right past it. I have some more reading to do it would seem.

On a side note, the wife just gave me the green light to look into table saws and get myself something for my birthday (mid-june). sweet.

Now back to roman's site...

Any other thoughts/suggestions/etc. would be most appreciated.

[RPiatt]

There doesn't seem to be anything other than that image readily available. I will email him and find out more.

The crossovers also seem significantly more simple that some of the others I have seen on here... This may need further investigation.

[Dennis H]

http://www.eldamar.net/audio/rs150mtm/

[dlneubec]

If you contact Roman, I believe he has an unpublished 2.5way MTM version of the MicrobeSE. I built it, so I know he had it at one time.

Whoops, I see someone has already posted a link to it!

[RPiatt]

If you contact Roman, I believe he has an unpublished 2.5way MTM version of the MicrobeSE. I built it, so I know he had it at one time.

Whoops, I see someone has already posted a link to it!

I still have to email him. What did you think of the speaker when finished?

I am going to try and source all of the parts from PE, so I will be looking at Dennis's posted link as well, but I'll also ask Roman about an all Dayton RS version.

Lots of homework to do...

[---k---]

http://www.eldamar.net/audio/rs150mtm/

Agreed. Great speaker, reasonable price.

Shoot CJD a pm and setup a listening session at his place up in Gurney.

[Jim Holtz]

How about the new 4 ohm version?

I'd like to see a MMT 2.5 way design with the new 4 ohm version using the RS125. I have four of these and wouldn't mind making a small speaker suitable for a bedroom, computer etc.

Has any one seen any designs with the 4 ohm version yet?

Jim

[nerd of nerds]

Jim Holtz:

Funny you should mention that...

I'm about to start on my modula MTs (rs180 and dayton reference tweeter) and I'm looking into what i'll do next...

I really think the RS125-4 could make a dynamite tmm if paired with the vifa D26NC55(John K loved this tweeter because of its amazingly low distortion), sadly this tweeter is going to be unobtanium soon...

The small flange neo version of the XT-25 would be a great contender for a nice mini TMM or MTM (i like the tmm look better personally...) as would the neo versions of the seas 27TDFC and 27TBFC (they have different names and are marketed toward car audio, but John K tested the aluminum version and found it to be a decent neo tweeter)

I think for a 2.5 way with the RS drivers a neo tweeter would be in order with a 2-2.5khz xo point...

Any takers? Once i've got measurement stuff i'd love to do this as a learning project...

[augerpro]

Jim Holtz:
the vifa D26NC55(John K loved this tweeter because of its amazingly low distortion), sadly this tweeter is going to be unobtanium soon...

watchoo talkin' 'bout Willis?

[Mark K]

watchoo talkin' 'bout Willis?

That particular vifa tweeter has gone out of production, last we all heard. There may be supplies left in the pipeline here and there, but when they're gone, they're gone...

Unless tymphany brings them back or develops a new model.

[augerpro]

Well I better buy a few then...

[nerd of nerds]

That particular vifa tweeter has gone out of production, last we all heard. There may be supplies left in the pipeline here and there, but when they're gone, they're gone...

Unless tymphany brings them back or develops a new model.

I really really hope they do...

This is an amazing tweeter based on the distortion graph on zaph's site (zaphaudio.com)

It would be a damned shame if they didn't bring it back! Although, a round flange version would be a great improvement over this weird ass flange they have now...

[stinems]

Jim: About your RS125-4 2.5 way idea, particularly as computer speakers....

I too have a pair of these drivers from DIY Iowa this year, screaming to be made into something . Problem is, I don't see FRD files available to design with. I have full intentions of measuring my drivers as soon as PE comes out with their new woofer tester sometime early this year.

It'd be cool to see a resultant 8 ohm load, so I was thinking the 2 woofers in series with a series low pass on the .5 woofer (freq/order would depend on your setup). Parallel the woofer set with a tweet (Vifa D26 neo? XT25SC50? BGNEO3?) @ 2.5khz ish...

Remember the 4 ohm version will make up some of the sensitivity lost to the series hookup...

Throwin' out ideas....

~Sam S.

[nerd of nerds]

You could see if John (zaphaudio.com) would be willing to test them.

He was doing tests of sub 5" drivers a while back and the RS125S was one of them. He said great things about it and I think we can expect a project from him using this driver (probably a 2 way though) in the coming months to replace on of his D27 designs.

Anyway, i'm sure he'd be willing to test it if you shipped it to him (but don't quote me on that...I'm probably already on his bad side for the 2 emails I sent him asking for measurements that had disappeared from his site :-P )

[Dennis H]

Jim: About your RS125-4 2.5 way idea, particularly as computer speakers....

I too have a pair of these drivers from DIY Iowa this year, screaming to be made into something . Problem is, I don't see FRD files available to design with. I have full intentions of measuring my drivers as soon as PE comes out with their new woofer tester sometime early this year.

It'd be cool to see a resultant 8 ohm load, so I was thinking the 2 woofers in series with a series low pass on the .5 woofer (freq/order would depend on your setup). Parallel the woofer set with a tweet (Vifa D26 neo? XT25SC50? BGNEO3?) @ 2.5khz ish...

Remember the 4 ohm version will make up some of the sensitivity lost to the series hookup...

Throwin' out ideas....

~Sam S.

I think you'd need to model that to see if it works. A series inductor will roll off both series woofers no matter where it's placed in the chain. A shunt cap could roll off one driver but you risk having the impedance dip too low. I think the 8-ohm drivers in parallel are a better candidate for a 2.5 way.

[Jim Holtz]

Jim: About your RS125-4 2.5 way idea, particularly as computer speakers....

I too have a pair of these drivers from DIY Iowa this year, screaming to be made into something . Problem is, I don't see FRD files available to design with. I have full intentions of measuring my drivers as soon as PE comes out with their new woofer tester sometime early this year.

It'd be cool to see a resultant 8 ohm load, so I was thinking the 2 woofers in series with a series low pass on the .5 woofer (freq/order would depend on your setup). Parallel the woofer set with a tweet (Vifa D26 neo? XT25SC50? BGNEO3?) @ 2.5khz ish...

Remember the 4 ohm version will make up some of the sensitivity lost to the series hookup...

Throwin' out ideas....

~Sam S.

Sam,

Great minds think alike. I also had it in my head that connecting the drivers in series would make it an 8 ohm speaker. Dennis has brought up a point that putting an inductor in series (Jeff Bagby topology) for the .5 driver will not allow it to be 8 ohms if I understood his post correctly.

I prefer a MMT but a MTM would be fine too. A very small cabinet like this will require just seems to work a bit better, IMHO, as a MMT. I'm really thinking of these for computer speakers powered by the little Radio Shack 25 watt amp that Neil Davis posted about on PE a month or so ago. It looked like a really easy and inexpensive solution to have high quality desktop speakers.

Jim

[Jim Holtz]

I think you'd need to model that to see if it works. A series inductor will roll off both series woofers no matter where it's placed in the chain. A shunt cap could roll off one driver but you risk having the impedance dip too low. I think the 8-ohm drivers in parallel are a better candidate for a 2.5 way.

Hi Dennis,

I've attached an example of a .5 topology that Jeff Bagby posted about a few years ago that seems to be commonly used to fill baffle step without rolling off the main woofer. Does it also affect the impedance? This example is in parallel but I thought it would also work in series but maybe not.

I'm crossover illiterate so be gentle.

Jim

[Dennis H]

Yeah, Jeff's pic is the 'normal' way to do it. Drivers in parallel and a coil (L1041) in series with only one of the drivers. The current has to flow through L1041 to get to the second driver but not the first driver. But, if you put the drivers in series, L1041 will affect both the drivers so it's a 2-way, not a 2.5-way.

Dumb ascii art:
(+)--Driver--Coil--Driver--(-)

No matter where you put the coil, the current has to flow through it to get from (+) to either driver to (-).

[Jim Holtz]

Yeah, Jeff's pic is the 'normal' way to do it. Drivers in parallel and a coil (L1041) in series with only one of the drivers. The current has to flow through L1041 to get to the second driver but not the first driver. But, if you put the drivers in series, L1041 will affect both the drivers so it's a 2-way, not a 2.5-way.

Dumb ascii art:
(+)--Driver--Coil--Driver--(-)

No matter where you put the coil, the current has to flow through it to get from (+) to either driver to (-).

Well bummer! :cry: Thanks for the excellent explanation. It looks like it will have to be a MTM in series to make it work with these drivers.

Jim

[Dennis H]

More dumb ascii art:

(+)---D---D---(-)
        |
        C
        |
       (-)

Using a shunt capacitor would work for a 2.5-way but you'd end up with a 4-ohm load because the current flows through the first 4-ohm driver and through the capacitor to ground and the cap has a near-zero impedance at high frequencies.

[Jcake5]

Gents,

I have modeled two dayton 5.25 4-ohm woofers in series using the shunt capacitor with series resistor of 2.5-ohms using Speaker Workshop and ended up with a 6.25 impedence. This is something I want to try to build

Regards,
Eric

[omarmipi]

Gents,

I have modeled two dayton 5.25 4-ohm woofers in series using the shunt capacitor with series resistor of 2.5-ohms using Speaker Workshop and ended up with a 6.25 impedence. This is something I want to try to build

Regards,
Eric

Please do, that would be sweet.

[Turn2]

Timely thread for me

I have just begun to acquire materials for the Microbe SE MTM. I would also be interested in any variants that are known. I haven't seen this mentioned yet, although I don't know why you would NOT use the SEAS tweeter if you could:

AZ-2525 RS125-TMF025 MTM

Anyway, this would be my first full-fledged project (x-over, boxes, finish, etc., but not the design) so I'm not in a rush. C'mon modelers, let's see what you've got to add and let's keep this thread up top!

[RPiatt]

I have emailed Roman to see if there is any more detailed information on the Microbe SE 2.5, as well as a couple of questions:

1) Can it be modified to use the Dayton RS28AS?
2) Can it be modified to a sealed configuration?

I haven't heard back yet, but it is the holidays, so maybe he just isn't checking his emails right now...

As soon as I hear something, I'll let you guys know.

[Turn2]

2) Can it be modified to a sealed configuration?

Seems to me that with the regular Microbe RB just plugs the ports. He recommends this when using them with a sub, I believe. Should also apply to the MTM version I would think.

[RPiatt]

Seems to me that with the regular Microbe RB just plugs the ports. He recommends this when using them with a sub, I believe. Should also apply to the MTM version I would think.

That's a thought. I am hoping, though, that like CJD's version, the cabinet gets smaller with a sealed version (in that case, less deep). I have some space restrictions (WAF-related, since we live in a townhouse), so I am trying to get the most speaker in the least amount of space. Roman's ported design is on the upper end of my space limitations, and I'd love to find a design that had a slightly shorter baffle (15" - 16"). But I know not to mess with a baffle size in a given design... most of the time. Additionally, all of the speakers in my configuration will be 12" or less from the wall...

I'll discuss that with Roman as well, when I hear from him...

[augerpro]

Hi Dennis,

I've attached an example of a .5 topology that Jeff Bagby posted about a few years ago that seems to be commonly used to fill baffle step without rolling off the main woofer. Does it also affect the impedance? This example is in parallel but I thought it would also work in series but maybe not.

I'm crossover illiterate so be gentle.

Jim

How would this effect the phase of the second woofer? Would it be 90 degrees off from the first woofer?

[Turn2]

RPiatt-

That AZ-2525 is only 5" x 13" x 8.5" in the INSIDE dimensions with a 6.5" x 14.5" baffle. That's pretty compact for an MTM with nice drivers. You should take a serious look at that if WAF is a high priority.

[RPiatt]

I was looking at that last night. That is pretty small for a front baffle. I don't know enough about this stuff to understand what the smaller baffle will result in for SQ purposes. I have a lot fo reading to do.

(The wife said I could spend X (which is gracious seeing as we have a 7 week old son now as well), and I thought I could get a lot more for X fi I built something rather than buying something. I was looking at the Infinity TSS-1100, which comes with a subwoofer. but for the $700 those cost ($850 if I buy the individual rear center speaker, I thought I could build something much better. Is my logic flawed here?

Anyway, that AZ looks nice. Can anyone help me understand what the smaller baffles will mean for sound, going from CJD's 21" baffle, to Roman's 18" baffle to the AZ's 14.5" baffle?

Like I said, I am a decent woodworker, but have lots to learn about speaker design and building.

EDIT:
Here is the link for the Infinity TSS-1100 I was looking at and want to do better than...

http://www.crutchfield.com/S-mBSkx5VT61P/cgi-bin/ProdView.asp?search=tss%2D1100&i=108TSS11HC

Yes, I have heard these and thought they sounded very good (to what is probably a less than discerning ear compared to some of the more qualified members here)

[RPiatt]

I heard from Roman today. We'll be touching base in a few weeks to come up with a 2.5way MTM with the RS125 and the RS28AS. Once I have the details and can actually start building it, I'll add more to this thread...

Happy new year everyone (24.5 hours early)...

[Turn2]

I guess that would be the shielded version of the Dayton Tweeter? I think I am going to proceed with the Seas TAFG version.

As another alternative, if you really wanted small you could mate 5 of these:

dB313 .1 cu. ft. MTM

with one of these:

Cerberus


and it would only set you back about $450.

[RPiatt]

Yep. The shielded version. I have to set one of them directly on top of the TV.

As far as a sub goes, I think I will also do a small design, and maybe the cerberus is a good idea. But I was thinking more of a 10" or 12" driver. With my woodworking skills, I think I can make it match a couple of "mission style" end tables I have in the room. WAF, don't ya know.

I'll post a new thread once I have time to talk with Roman in a few weeks and get a design nailed down... He mentioned in his email that he thought a RS125-based MTM could be very popular... we'll see. Fits my needs... but maybe not everyone else?