Evil Twin

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

While it seems there are as many new MTM designs with the RS28A-4 (p/n 275-130) as there are costumed fans attending "Revenge of the Sith" (catchy title ), it may be that it will take the power of the dark side to unlock the capabilities of these drivers to their fullest extent in either a compact, stand mounted cabinet, or a taller floor standing slim tower.

For maximum authority in the bottom end, a small tower enclosure is recommended- 50 liters net for the two shielded RS180's, (p/n 295-364) with a 3" port tuned to 28 Hz (28 cm (11") long if not using a flared port kit); this will produce an F6 of about 29 Hz anechoic.

If space and size are a factor, then a slim bookshelf enclosure of ~ 30 liters can be used with a 2" port tuned to 32 Hz, which will result in an F6 of ~ 38 Hz, with some in room extension below that.


The crossover is the crux- how to deal with the dark side of the RS180 (it's high level break up modes) while retaining a transparent midrange and acceptable component cost.

This somewhat unorthodox solution is proposed.




The predicted SPL response as follows:




The net transfer function is shown here:





And the simulated impedance curve.




BUILDERS PLEASE NOTE: Use the shielded versions of the RS180 drivers and the non-shielded version of the RS28A tweeter

Cabinet Design and Construction

I chose to develop these projects for the PE (Parts Express) cabinets, because for the money, it's very hard to beat the quality and finish considering the time involved.



The cabinets are well braced internally, also.



If you want to go deeper on the enclosure and use a larger port for more bottom end extension, then you may want to build something your self similar to the FP layout of the 1 cu ft enclosure.

Shown below is the front panel layout diagram for the stand up MTM. The tweeter is offset slightly becuase this produces a flattter boundary and diffraction behavior in the 1-3 kHz reigon, according to Baffle Diffraction Simulator.




Here is shown the realization of this layout in the PE front baffle; note that I use tweeter backing plates to isolate the tweeter from the midwoofer pressure wave, and to strengthen the front panel in the weakest area, considering the number of holes.




This close up of the rear of the baffle shows the reinforcement plate and the bevel routing used on the back side to open up the rear radiation window a little; the RS180 has a large shielded magnet assembly which somewhat blocks the rear radiation.






LF Alignment

The PE enclosure will be ported, tuned to about 34 Hz, using a Precision 2" flared port, ~ 9" long, with an alignment in this size box which will permit output to 104 dB per cabinet anechoic down to ~ 30 Hz. The roll off is such that the - 6dB point is about 37 Hz, which should be compensated by correct wall to floor/rearwall/sidewall boundary placement- flat in room to 37 Hz is doable, with strong output to 30 Hz.





I used Precision 2" ports from PE; the center tube will need to be cut to 3-1/4" to 3-1/2"; note that we're both trying to get the correct tuning length AND clear the internal brace baffle (which must have a clearance hole- I used a 3" hole saw), including the distance to the flare. BUT, we also don't want to be too close to the tweeter brace panel, or port Q suffers- this will allow about 3" clearance, while providing the desired tuning. In a pinch, you could use standard 2" PVC tube instead of a flared port, but expect the possibility of chuffing and compressing at higher playback levels. Spend the extra money.

Here's a link to the Precision Port website where one can find information about installing their ports
http://www.psp-inc.com/psp-inc.com/...nstructions.htm

I used a PVC welding cement to first attach the color to the main port flare, then to attach the cut piece of tube. The assembled port is shown below, prior to installation in the cabinet. The cutout hole, which is centered top to bottom, was cut 80% through with a router, after masking with 3M 2070 safe release tape (heavy white stuff, not the blue stuff; you may have to check your local hardware store; not all the big box places carry it. Can be ordered over the net, too).




If you're using the PE piano black enclosures, take some care while working around them! I use a neoprene sheet on the table, and vacuum thoroughly after every operation.

I use slow setting hot glue as the sealent at the inside corner of the port tube baffle; you have to work quickly, seat it firmly, then install theh mounting screws (Grabber fine thread #8 for metal work are my favorite, because of the strength and built in washer like philips head). Drill pilot holes first, of course. I supposed RTV would be OK, too, but it doesn't adhere quite as well to PVC, and has that nasty smell if you get the "strong" stuff.




Next step is to cement the inner port flare in place; in my case, with a 3-1/4" long cut center tube, the back of the port flare sits flush with the inner brace. You'd think I planned it all that way....




OK, here I've slipped the baffles in (cleaned them with Goo Gone to get rid of the residual adhesive from the masking tape- left them sitting up too long), and thought I'd take a quick pic before putting these away to get some other things done. Time to work on those crossovers.





Crossover Design


Here's a picture of the crossover wiring complements of Opt-e



Here's a link to a Parts Express BOM for this design

People should read this website regarding the placement of inductors prior to building their crossovers.
http://www.troelsgravesen.dk/coils.htm

This speaker is designed to be built with air-core inductors. In this thread there are BOMs posted with steel laminate inductors spec'ed. If possible the budget permits use use air-core instead of steel lamination inductors

NOTE, if you're building an in-wall or on-wall version of these here's a link to the crossover design.
http://www.htguide.com/forum/showthread.php4?t=22626

Here's a Picture Gallery of completed NatalieP MTM designs. If you've completed your project, email the pictures to me (ttriff at gmail dot com) and I'll put them in the gallery

Although a transmission line alignment is discussed briefly later in this thread, it was all talk. There are NO plans for a transmission line design

__________________
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Brian Bunge

Evil Twin,

Excellent looking design, as usual. One specific question did pop up though. Why was this not included in the Modula MTM thread as a variation on that design? Is the RS 180 network completely different from that of the Modula? I'd check out the Modula thread myself, but being on dial-up would mean it would take forever for all the links to load.

Oh, and another question: We were building some new MTMWW tower for my dad using the Dayton aluminum 7's, 5.25's, and Vifa alum. dome tweeter. I built a pair of these for a customer and my dad loved them. But I'm wondering if this would be a better design (I assume so) His current cabinets have a raw internal volume of 79L. If I add plenty of bracing I think we could get that down to roughly 65L or so plus a little more for XO boards. How do you think this would work? I simed in Unibox for 65L tuned to 28Hz and I get what appears to be sort of an EBS alignment. It tapers off gradually, about 2.5dB down or so at 30Hz, with 80Hz as a reference, then falls off from there. If need be, I could also seal off part of the bottom of the enclosure and sand fill it. Or do you think going with 65L or so would work well, too? I know he loved the other speakers, but I think these would make him happier in the long run. I know the RS drivers are much better quality. I just wonder if PE would allow me to return the others seeing as they've never been opened. We've had them for quite some time though.

Anyway, any input you could give would be great. I've seen ROTS twice now and really admire your work! (I figure even Lord Vader can appreciate flattery)

EDIT: I wanted to add actual cabinet dimensions for reference. They are 47"H x 10"W x 14"D, external.

Evil Twin

The Natalie P is "suggested" as a lower cost (crossover) alternative to the Modula IV. No Force mind control involved. Not using a conventional C-E type crossover, it's an alternative to consider which is more in line with the component costs of the drivers themselves- a high level of performance at unusually low cost.

The crossover is a quasi-series network using 3rd order allpass in the transistion region, not a Butterworth characteristic, with a modified LP which transistions to a modified 4th order with CE to achieve much higher attenuation rates beyond the first octave so that the many breakup modes of the RS180 will be adequately suppressed- like the efforts I have to take at times to suppress the Rebellion. This grew out of a similar concept using the Peerless 850439, which is easier to control in the upper end, and can be built with even fewer crossover components.

I think an EBS alignment like you describe would work very well; I recommend a downward firing port if you can put the cabinet up on a combination of short riser plates and spikes, like the M8ta.

Regarding the returns, it's hard to tell- but the RS's would be an improvement- they really do have remarkable distortion performance, even if they cost 2X or 3X their nominal price.

__________________
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Brian Bunge

Evil Twin,

Thanks! I just saw Jon's Modula version. I can definitely see where the parts count would be cheaper for the Natalie P. Since it's my dad's money I'm playing with, I'd probably be more inclined to go with this design, even with the quasi-series networks (damn, those schematics just aren't very intuitive. Maybe the dark side of the Force will help me through it). I like the idea of the downward firing port. How thick are the risers used on the M8ta? I'll have to see which way my dad wants to go. I think he's about to sell his current speakers and was going to use the money to buy these drivers from me as well as the XO parts. He might as well spend it on the RS drivers and know that he's got a kit that he'll be happy with for quite some time.

OK, now that you've got the Modula revision and have started on the Natalie P, are you or Jon ready to model that MTMWW 3 way of mine? Did I mention that the Jedi had it coming?

Evil Twin

The risers are 1,5" in height; together with the large spikes, it's about 2.5" in clearance to the sides and back. As the spikes are adjustable, easy to move up to 3".

Yes, I sense a current in the Force moving in favor of modeling your MTMWW system... I even sense the location of the data files in the Imperial network.

Regarding the Jedi and their fate, as Andy Grove would say, only the paranoid survive.

__________________
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Brian Bunge

OK, I'll keep that in mind. Short of putting the port on the bottom, would on the back be the alternate choice? Sorry, the Andy Grove reference is lost on me. Maybe this apprentice is too young (Padawan probably would not be a term used for a pupil of the dark side).

Evil Twin

Andy Grove, long time CEO of Intel: "Only the paranoid survive".

Back would be second choice. Consider that a tower style enclosure with a port at one end (bottom) is the basis for Matin King's MLTQWT, a "Mass Loaded Tapered Quarter Wave Tube" TL (uses a conventional port); the M8ta works kind of like one of these.

Maybe we should come up with a "Son of M8ta" with dual RS180 + RS28a in this size alignment?

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AndrewM

Is R7 really supposed to be 180.01 Ohms?

Either way by my math it should come out around $100'ish cheaper than the other model (using Solen parts on both, no fancy-shmancy caps) sourced from one of our forum sponsors.

Evil Twin

No, it just means that I forgot to pull both R7 and C7 out of the circuit, after running up the value to the point where the network has no effect.

__________________
Your lack of confidence in the dark side is disturbing... do not forget that black is back...

Evil Twin

Click "refresh" (or use Force push; your choice) on your browser and the corret schematic will appear if it hasn't already.

__________________
Your lack of confidence in the dark side is disturbing... do not forget that black is back...

Greg Y

I felt a disturbance in the force and decided to check in on the HT Guide Forum DIY board. I like the Natalie P design. I want to build the Dayton version of the Modula MTM. The parts cost for the Modula using perfect lay inductors, Dayton poly caps and Dayton non-inductive resistors was $286. The parts cost for the Natalie P is $112. That is a big difference.

Is the Modula that much better than the Natalie P.?

I also have a question about resistors. I priced out the crossovers using 10W resistors. Is this amount of power handling in the Natalie P resistors sufficient?

May the Schwartz be with you. Oops, wrong movie.

Rudy Jakubin

Just curious. This is a series filter. How would you adjust or what component(s) for baffle step????

Evil Twin

The Modula is a bit more ruthless at supressing the "out of band" areas for both the bottom end of the tweeter and the upper range of the midwoofer. The RS180's start to get into a little energy storage in the 1800 Hz and up area, but don't go seriously goofy until above 4 kHz.



With a 1400 Hz crossover, the midrange/presence region will be a bit "purer" in the Modula, especially at higher playback levels (over 95 dB). The tweeter will be a bit less worked also. Will it be $170 purer? That only you can decide. The suggested components for the Modula crossover include film and foil caps that are expensive, but do sound good. They could be used in the Natalie P, also- your choice.

Everything tends to be incremental in this endeavor- only you can say where to draw the line and say, "Enough is enough". The reason behind this alternative is that it will still work well compared to most more conventional solutions, and be less expensive than most of those. Everyone has a budget- here's a good approach for those that need to be a little more careful with the dollars, but still want the basic performance the Dayton RS drivers can offer.

__________________
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Evil Twin

Baffle step compensation is already built in; primarily a function of L2. However, both inductors influence the actual corner point, so L2 shouldn't be changed by itself. Due to the interaction, if you desire to change some aspect (such as reduce baffle step for flush wall mounting), I'd suggest at least loading the network design into something like Speaker Workshop if it will model this network. It may not- older versions of LspCAD won't, for example- this was done with LspCAD6.

If you have some specific requirement, let me know- I can probably find time in the next week or so to adjust it and post another version.

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Paul H

That's what I love about LspCAD6 - it lets me model stuff I barely understand

Paul

capslock

Actually, I can't see any pictures in this thread (using Firefox 1.04).

Paul H

Jon said something about the server he uses possibly being down this weekend.

Paul

Evil Twin

Yes, this weekend is quarterly server maintenance, so it will be down part of the time.

Firefox is the preferred Imperial Browser, also.. .

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capslock

Pictures are back!

This design does a nice job at surpressing the cone resonance given the parts count - much better than many pricely commercial designs using metal midwoofers.

Remember that the metal cone will amplify harmonics generated by the motor which go up with excursion. This is something a low pass cannot to anything about. If you're going to be listening loudly, a closed box design with high pass and separate sub might be a good place to invest the $100 saved on the sub in.


Greetings,

Eric (who prefers Natalie M who sings much better)

Evil Twin

Yes, well, you wouldn't know Natalie P can act, either, judging from her roles for Lucas- but if it's not written into the character, what can one do?

Quite a different situation in "Leon the Professional" (especially the European version, released later in the US).

Regarding your point about excursion and midrange clarity, very true. Biamp these with a Delialah xover into a pair of RS270's on each side, and the midrange and upper midbass becomes even more focussed and dynamic.

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dayton-maniac

This seems like a great project to get in on, but I have a few questions.

I drew up a preliminary parts list but wanted to run over a few things.

Part Number In Stock Description Qty. Price Ext. Price Remove

004-20 Yes DAYTON 20 OHM 10W NON-INDUCTIVE RESISTO.. $0.98 $3.92
004-6 Yes DAYTON 6 OHM 10W NON-INDUCTIVE RESISTOR.. $0.98 $3.92
004-.51 Yes DAYTON .51 OHM 10W NON-INDUCTIVE RESIST.. $0.98 $3.92

027-542 Yes SOLEN 3.0uF-400VDC POLYPROPYLENE CAPACI.. $2.15 $4.30
027-568 Yes SOLEN 10.0uF-400VDC POLYPROPYLENE CAPAC.. $4.18 $8.36
027-572 Yes SOLEN 12.0uF-400VDC POLYPROPYLENE CAPAC.. $4.84 $9.68
027-586 Yes SOLEN 24.0uF-400VDC POLYPROPYLENE CAPAC.. $8.25 $16.50
027-578 Yes SOLEN 16.0uF-400VDC POLYPROPYLENE CAPAC.. $6.00 $24.00


266-355 Yes 1.2mH 14 GA. PERFECT LAYER INDUCTOR .. $15.10 $30.20
255-400 Yes JANTZEN .20mH 15 GA AIR CORE INDUCTOR .. $3.29 $6.58

Subtotal: $115.30

1) Is the .51 ohm resistor ok instead of the .47?

2) Should I use 2 16 mfd caps to make the 32 mfd C10, or should I just use the 1 33 mfd Solen cap from PE?

3) How do I make/buy the 1.2 mfd capacitor C11?

4) I am having trouble finding the right inductors for the right price:

a) is the 1.2 mH perfect layer with .24 DCR ok for L2, or do I need to use the 1.2 mH foil inductor with .2 DCR at PE? The price difference is notable.

b) for L3 will a .2 mH 15 gauge inductor with 1.3 DCR work? Is this close enough to 1.5 DCR? Will there be negative results?

c) does the resistance of L4 matter or can i use an 18/20 AWG inductor? PE is sold out of both the 20 and 18 .44 mH inductors. If the resistance does not matter will the 16 gauge .45 mH sidewinder from madisound work?


Finally:

Is the price/performance of this design too good to be true or is this just old fashioned good engineering? Everything seems well thought out, but I don't want to just dive in and get burned. What are the trade offs here? Could this design still be the poor man's answer to a nice seas excel MTM?

Thanks for the great work, can't wait to get a reply. Cheers.

ThomasW

It's your choice, remember that all these components have a +/- tolerance from the mfgr

By combining 2 caps that create that value if necessary. Also check the closeout GE caps at Madisound.

Have you checked Speaker City, Zalytron, Meniscus, etc., for product? No need to buy a foil inductor.

That's close enough for government work.

Check other sources, buy the closest fit to the DCR, using bigger diameter wire isn't a problem.

Yes

You have to break eggs to make mayonnaise. Spend more money get better sounding speakers

You get what you pay for....

__________________

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ThomasW: curmudgeon in training, putting the no in innovation

dayton-maniac

Hehe

Thanks for the reply

Sometimes you just need to hear someone say it

for about $110 in crossover parts I think I can be plenty happy with this design.

The dB717TL -- RS-28 version also looks good and has a C-E crossover for a more reasonable price than the Modula MTM.

dB posted a price list in the Parts Express forum earlier today.

Evil Twin

One definition of good engineering is getting $2 worth of parts to do $10 worth of work...

This design is the product of a lot of effort to simplify the crossover design while still getting the Dayton drivers to play well together. The Modula crossover should allow somewhat lower distortion in playback above SPL's in the mid to upper 90s. The crossover performance versus cost is very much in line with the Dayton drivers themselves- deliver 75-80% of the best possible performance, at under 1/3 to 1/4 the cost. In their price range, I can't see anything better than the RS series midwoofers, and the tweeter is excellent. Possibly the new Peerless Nomex Exclusive series will be comparable in performance, but the cost will be 50% higher.

So, Thomas is correct in that you get what you pay for- but as budget systems go, you get a lot more than average with a good system using these drivers.

Since we aren't selling these and don't have any commercial stake involved in DIY, we're just looking for things that work well at reasonable cost, or designs that work very well at somewhat higher cost.

In a larger TL enclosure, for example, this would be surprisingly competitive with the Madisound Thor- not that I'd say you wouldn't get better performance with the Thor, but certainly not three times better- (cost differential) maybe more like 25% better. If you can afford the more expensive designs, go for it- no problem for us.

If you're like most of us here on HT Guide, who like both quality and value, and have a lot of other things in your system to sink money into, then probably this design could make sense for you.


BTW- no iron core coils, please. Try to stay with air core, AWG14 in the series path for woofer, and shunt path for tweeter.

__________________
Your lack of confidence in the dark side is disturbing... do not forget that black is back...

Jim Holtz

Evil Twin,

Very nice! I have the Natalie P. parts ordered for delivery today. This will be a speaker for my daughter and will probably end up at the Chicago DIY event this year. Perhaps Iowa too if someone decides to host it.

My question is, should I use the same box layout plans as the Modula RS180 design or should driver spacing be different because of the higher crossover point?

Thank you for your efforts! I appreciate the excellent designs!

Best regards,

Jim

Evil Twin

The Natalie P was designed around the identical panel layout, and internal configuration as the Modula.

Simplicity is inherent in the true power of the dark side...

There's really no feasible way to get the drivers closer together, but the 1800 Hz crossover is still much lower than most conventional designs, but realized in a way which will not overly tax the capabilities of the tweeter or midwoofers.

We are most appreciative of your kind comments. Constructive feedback is welcomed, also.

__________________
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stidrvr

Sorry to bring this thread back form the dead, but how well will this crossover work for use as a center channel? I really would like to use this design as I already have the cabinets made for the towers and rears using RS180 and the RS28A. If I can use it as a center everything will match....Driver wise. Thanks for the help

cjd

You want to place it horizontally, yes? It will work OK, but it's not optimized for it.

Any reason you would not consider one of the TM versions with the same drivers?

You can see what horizontal off-axis can look like on an MTM (granted, a nigher crossover point) here - RS150/Seas27TDFC MTM I did. Just gives you an idea of what can happen.

C

JonMarsh

It's really too high a crossover frequency and too wide a driver spacing to work very optimally, unless the forward listening angle (seating and distance from the speaker) is relatively narrow. That's why the Modula center channel project. To get the crossover frequency lower and move the drivers together with good results requires the more expensive crossover design, and a small tweeter like the scanspeak. One compromise would be to use a slightly taller baffle, and wedge in one of the standard tweeters (like RS28a) with the midwoofers pulled together.

The center has some demanding requirements placed on it, yet it most systems it is one of the most "cheezed out" speakers in the system. Unfortunate.

~Jon

__________________
the AudioWorx
_______________________________

Modula MT
M8ta
Modula Neo D CC
Ardent
Modula MT XE
Modula Xtreme


still coming in 2010....

Ardent Cxi (updated design, new woofers)
Ardent CCX (Compact Center Xtreme)

westrock

I just wanted to throw this in for the sake of experience. I had a Dayton Quatro 8" in a 0.70 cu.ft (21 liters) enclosure with a 2" port that was tuned to about 35Hz. Any time I had any really low bass, like 30-40Hz, at a moderate (between normal and loud) volume I would get really bad shuffing at the port. This was a flared Powerport too. It seemed like the port was too small to accomidate the amount of air being moved.

For music it was fine, but stuff like newer movies and even some of the ambient sounds on Halo 2, it would cause some really noticable sounds.

It could have been my particular setup though.

JonMarsh

That's a pretty small enclosure for an 8" woofer, and a 2" port would not be recommended for a moderated Xmax 8" woofer. Especially if tuned to lower frequencies. For the larger version of the MTM with lower tuning, we recommend a 3" port- for using a smaller enlcosure like the PE cabinet, the LF response will be rolling off somewhat anyway, and so far I haven't seen issues, but then I haven't tried to push the LF levels particularly hard. With that enclosure size, it's not practical to tune as low as I prefer for a nice tapered roll off with anything larger than the 2" Precision Port.

__________________
the AudioWorx
_______________________________

Modula MT
M8ta
Modula Neo D CC
Ardent
Modula MT XE
Modula Xtreme


still coming in 2010....

Ardent Cxi (updated design, new woofers)
Ardent CCX (Compact Center Xtreme)

cjd

Hmmm... I spy some turbocharged fun in someone's avatar.

I should add, I have my RS150 based MTM's tuned to about 38Hz with a 3" port and no chuffing, ever. Just astounding bass out of such cute little drivers.

C

Brian Bunge

Chris,

I think your tower version of the MTM's are my first choice for new speakers for my girlfriend's dad. Of course, I've been told that his wife would prefer that I clean up and re-wire their system, and move the equipment rack into the corner, before building new speakers for him. I agree that's probably the best idea since the right speaker got pushed near the corner because of the placement of the equipment rack and is partially blocked by a chair. It's so bad that I can't even properly calibrate the front 3 speakers because I can't even get a 75dB reading from that speaker. I had to back down the left and center speaker a few dB to get them close.

capslock

Still catching up on the last couple of years' movies. Saw Cold Mountain yesterday: yes she can!