JonMarsh

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

NOTE: a version of this design that uses the Parts Express unshielded RS28A-4 tweeter. To see that version of the crossover click HERE

Here's POST where I've put links to the various BOM's (bill of materials) for the 3 different tweeters that can be used in this speaker

Below is a link to the thread where the inwall/onwall version of the Modula MT is discussed
http://www.htguide.com/forum/showthread.php4?t=22625
------------------------------------------------------------------------

Quite a few folks have been badgering me about an MT design using the shielded RS180, (p/n 295-364) something not as expensive in the crossover department as the Modula MTM which uses an Cauer-elliptical network with modified LR-8 properties.

Well, if you take a look at the natural response of the RS180, especially the stuff above 5 kHz, you’ll see why I’ve been a bit reluctant to take on this challenge. The usual crossover approach to a budget sensitive two way system is something like a quasi-series crossover using 2nd order networks, either All pass L-R or some modified Bessel alignment. But the wide overlap and slow roll of the networks makes them really unsuitable for drivers like the RS180, unless you want to spend your time listening to the HF crud from the midwoofer.



What to do?

Well, I pondered that in my not so copious spare time for a few weeks, and have come up with an approach that looks viable on paper, but probably some folks will call just another hat trick by that guy that uses Doc Emmett Brown instead of Albert Einstein as an R&D role model….

So, I did a little hack and slash on my quasi-series network concept, well, OK, I did a LOT of hack and slash on that, and what we’ve got here is something a little bit different.

First off, considering the natural response of the RS180, no way is any kind of 2nd order network going to do. We don’t want a lot of driver overlap, and particularly we’ve GOT to get off the RS180 as quickly as possible because of the cone resonances up higher. So, let’s up the order to 3rd order, but still try to keep elements of the series connection (one crossover part serving two functions), and then figure out some way to squash like a bug the upper range harmonic stuff.

Now, a classical 3rd order Butterworth crossover has some nice properties, good power response, and can sum well on axis, can be wired either in phase or out of phase, but it also has some real quirks. First off, the phase response through the crossover region is in quadrature, that is, the on axis response is 90 degrees out of phase, which is why it can work both in and out of phase (it’s either 90 or 270), but the problem that derives from that is two fold- broad overlap in the response, and a bump in the response that manifests in an off axis lobe, when you go off axis and the phase shift approaches zero.

Well, there’s more than one way to skin a cat, or make a 3rd order crossover- so instead I implemented a 3rd order all pass, with the phase response complementary and the individual filters down 6 dB at the crossover frequency. Crossover frequency is 1800 Hz nominal. Additionally, compared with the original EM, we now have a modified cauer-elliptic used to increase the transition band attenuation above 4 kHz, from the interaction of C11 with L4. You may notice that there’s what looks like two woofer zobel networks- C7/R7 is focused on the upper range, doesn’t impact the system input impedance, but does increase the attenuation of signals in the break up range of the driver. R3 may require some adjustment; this is value is dependent on how accurate my absolute measurement levels for the midwoofer and tweeter are, which could be off a dB or two.

Here’s the network design. There are a few other odd features, but for now I don’t have time to go into them. It’s the results that count, right?




Next is the net SPL magnitude response, also showing the raw driver response and the network + driver response. Note driver overlap occurs at -6dB. This level may get bumped up a bit when I’m voicing the assembled design, ’cause there’s a very slight BBC dip, which may lead to a lower power response in this region than I’d normally desire. Again, the LF measurement was originally made in a smaller, sealed box, so response below 200 Hz isn’t representative of the final design in a ported PE enclosure.



Here’s the simulated power response curves in LSPCAD - this actually looks pretty fair, but included angle is only to 20 degrees off axis. Still, may just leave things the way they are.



Here’s the inverse connection of the tweeter of the network simulation; nice deep null, so this clearly ISN’T a Butterworth crossover.





Last, the impedance curve. Pretty much anything should be able to drive this, except a crystal radio.





For those who haven't seen some of the previous posts, this is a design intended for the largest "non" MTM enclosure from PE, as I used for building a system for my daughter two years ago- this one used the HiVI D6.8 midwoofer and Vifa XT25 tweeter.



Like the earlier system, this will be ported, with a below resonance alignment tuned to about 34 Hz, using a 2" flared Precision Port.

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/...ns/Drawing2.jpg

Keep in mind, I do consider this to be, in some regards, a collection of compromises. I'd probably rather have the network of the Modula MTM, all things being the same- but this IS markedly less expensive, should fit in the smaller enclosure, etc. Hopefully, it's the right set of tradeoffs.

And Hank, I promise, on a HUGE stack of Bibles, that this will be absolutely the LAST 7" two way I design...


this year.





Or, at least, this month.


~Jon

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

Here's a LINK to a post containing BOMs for the 3 different tweeters that can be used in this speaker

=================================================

Box size info added 10/ 26/06

The PE box has a baffle that's 10 inches wide (exterior)

External Dimensions: 17" H x 10" W x 12.5" D
Internal Dimensions: 15.5" H x 8.5" W x 10.75" D
Internal Volume*: .82 cu. ft.

The cabinet volume slightly oversized to allow room
for driver and port tube displacements.

And a 2 inch port 7.4 inches long

Box cutouts are as described....remember to build these in mirror imaged pairs....


================================================== =

I've added pictures of various versions of the crossover and pictures of various stages of the box assembly. These are all posted and discussed further on in the thread..







I do recommend back chamfering for the midwoofer






Bracing one person used for their scratch build box



Picture of the layout for one crossover for the RS28A tweeter



Block diagrams for using 2 separate crossover boards





[IMG][/IMG]



================================================== ===================
If you build these speakers and want your project webpage posted send me a link in a PM

Modula MT builder webpages

Jon Pike's build pictures
Dan B's Blog

As a reference I've uploaded a pdf of the new PE curved side cabinet. This is a bit smaller than the old rectangular one.

Attached Files

0.75 CU FT Cabinet Sketch.pdf (18.9 KB, 396 views)

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still coming in 2010....

Ardent Cxi (updated design, new woofers)
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Paul H

Looks great Jon. I would think there will be some real interest in this design, given the lower parts count in the crossovers and very good value in the drivers.

We will be monitoring the production rate of your future 7" two-way designs very closely


Paul

Brian Bunge

Jon,

As usual, that looks great. But damn, that series crossover schematic just makes my head hurt!

Dennis H

Cool XO, Jon! BTW, I have it on good authority that Evil Twin will be sensing The Force for any disturbances caused by unauthorized 2-ways.

Dan B

What a cool guy!

Evil Twin

Ah, yes, a truly disturbing ripple in the Force...

While I might concede this is an interesting exercise in crossover design, it does not operate on the scale of DIY which uses the full power of the Force of DIY- it is merely a diversion from the greater challenges which lie ahead- challenges which will require true mastery and dedication to succeed...

It is only in the development and completion of such systems as the Saint-Saens and Arvo Part that these princicples will be realized... the rest is just a distraction, a needless distraction which my master would not approve of.

"Evil Twin..."


Yes, my master?


"Be quiet and mind your own projects, or I'll take away the flux capacitor from your light saber..."


Yes, my master.

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JonMarsh

OK, you guys have been badgering me enough!

Here's an updated version using the RS28A-4, (p/n 275-130), with a further refined crossover. Just the thing for surround MT's, bedroom speakers, wherever you need something a little smaller with all the goodness these RS series drivers can provide, in a small enclosure with a "relatively" inexpensive crossover (for me).


Schematic should look familiar, but every component has been examined and refined. (yeah, I'm writing this like a parady of some of those Quasi DIY kit speaker sites- ) Even stripped out a couple we figured out how to get my without- so go out and buy some nice film and foil caps with the money you save!



Here's the predicted bottom line using LspCAD6 - note that there is a bit of upper end EQ on the tweeter, but with a stopper resistor, too.




Here's the impedance curve- if your receiver can't drive this, it hasn't got a pulse...




And in case you're curious about the net transfer function, or think you want to implement it actively (you know who you are, so do we)



If you want to spend a few more bucks on components and tweak it a little, add a low frequency LCR for the tweeter- just borrow the one out of the Modula design for RS28A.


I'll have to see if I can find the time to order some crossover parts for these soon- there's a pair of cabinets and set of drivers waiting for this, that are going to wind up in upstate NY.

~Jon

edit to add pictures of different people's crossovers



The tweeter section:


The woofer section:

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dawaro

Thanks for the updated design, but I do have one question for you. The value of L2 is shown as 2.60mH with a dcr of .20 ohm, how critical is this value? I only ask because I have looked every where and no one has one close to this.
Here is what I could find:
Pefect Lay 14ga - 2.50mH, dcr - .36
Jantzen 15ga - 2.70mH, dcr - .59
Jantzen 18ga - 2.50mH, dcr - .88
2.70mH, dcr - .92
Erse iron core - 2.50mH, dcr - .162
2.70mH, dcr - .163
I know that the series resistance is probably a lot more important in this network so I wanted your opinion on which one to choose.

Mark S.

Hey Jon
Looking foward to building this one
Can you give more details for the vent? 2" X ?
Thank you

JohnL

Hmm... I think it's it mighty close to the DCR of a 12 g foil coil. Maybe Jon has gone over to the dark side of inductors.

More likely he rolled his own from 11 g magnet wire or possibly made a typo.

JonMarsh

John, you've figured out my not so secret admiration and use of NorthCreek AWG12 inductors!

Seriously, on this little guy, with a 8 ohm nominal load (6 ohm minimum), a 0.36 ohm inductor should be OK, and will only slightly increase the crossover insertion loss (about 5%). That's probably less than the tolerance of sensitivity of the production drivers, for example.

Just for reference, I normally use Perfect lay AWG14 coils except in LCR zobels, where AWG 20 or whatever will work fine, considering the external series resistance. I am a "staunch" air core guy - I've designed and built lots of steel laminated cores in the past, once in a while I still use them, but genearally I prefer to avoid any possibility of saturation, and to avoid hysterisis related distortion. Ferrite cores are a no-no.

Re the port, I recommend 2" at 19 cm long. Why not mix up my units- I'm always using liters for volume, anyway. Spend too much time in Europe and Canada, I guess. This will tune the box to ~32, resulting in a slow taper roll off with an F6 of about 33 Hz. With proper stand placement the room gain can nicely complement the slow drop in LF output below 100 Hz. Should be subjectively flat in room to the mid 30's, output per cabinet (before room gain) up to the high 90's max. (hey- it's only a single 7" woofer- if you want more, do the Natalie P in a 45-50 liter enclosure! With a 3" port, of course).

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

jdybnis

apexjr is selling 8uf poly caps called ultra-caps for $2 each http://www.apexjr.com/capacitorA.html

Do you think they would be an improvement over the solen caps. This page http://home.att.net/~chimeraone/ultracapfactsht.html has some info on them.

taz13

We Canadians mix and match our units all the time

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JonMarsh

I've heard of these, but haven't had an opportunity to try them. Based on the page you linked, they might be pretty good- certainly well worth $2 to try out!

I think it's hard to find a single "number" that translates to cap quality- quality of metalization, foil quality, dielectric purity, quality of lead attachment all play a role... but for paralleling in tweeter circuits, these could well be the ticket for a cost effective upgrade- say, use an 8uf Ultracap in parallel with whatever solen or GE values of metalized film are necessary to make up the net value.

Worth a try---

The parts I HAVE tried lately and like are the AudioCAP Theta's and the Dayton Film and Foil. WHile the latter are relatively inexpensive, they're limited to values like 0.47uF max, and are better for padding out cap values than making most of a main value. Also, they're good in electronics for bypass, though not small.

~Jon

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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)

jdybnis

The PE "deal of the day" is free shipping on all orders over $99 through the holiday weekend. I'm going to jump on this. It'll save me a bundle going to California.

I'm going to try those Ultra-caps and get some of the Solens to compare. I'm I right to assume that the difference between caps will be most audible in the path of the tweeter?

One more question. Could this be turned into an isobarik design so the enclosure gets smaller? The RS180's are so inexpensive, doubling up won't add much to the cost and the smaller PE boxes are bit cheaper too.

ThomasW

Isobaric loading is best for subwoofers, not smallish midwoofers running up to 1800Hz.

If the box gets much smaller the crossover won't fit

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IB subwoofer FAQ page

ThomasW: curmudgeon in training, putting the no in innovation

JonMarsh

I think it would be a problem in the midrange, tend to mess it up. Isobarik works pretty well in the below 100 Hz are. Remember, the midwoofer runs up to 2K +. And after all- 22 liter isn't very big anyway... The room you'd need for the second driver and the driver would wipe out the advantage

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still coming in 2010....

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

Dan B

A few questions for ya,

>>I normally use Perfect lay AWG14 coils except in LCR zobels<<

Where is the Zobel in a CE circuit? Guess I’d use a smaller inductor if it was appropriate?

>>> note that there is a bit of upper end EQ on the tweeter, but with a stopper resistor, too. <<<

What is a stopper resistor?
______________________________________________

Finally how does this budget parts list look?

004-5.1 Yes DAYTON 5.1 OHM 10W NON-INDUCT.. $1.25 $2.50
004-2 Yes DAYTON 2 OHM 10W NON-INDUCTIV.. $0.98 $3.92
004-6 Yes DAYTON 6 OHM 10W NON-INDUCTIV.. $1.25 $2.50

027-410 Yes DAYTON 1.0uF-250V POLYPROPYLE.. $1.15 $4.60
027-421 Yes DAYTON 4.0uF-250V POLYPROPYLE.. $1.85 $7.40
027-430 Yes DAYTON 12uF-250V POLYPROPYLEN.. $3.55 $14.20
027-436 Yes DAYTON 20uF-250V POLYPROPYLEN.. $4.95 $9.90

266-313 Yes .27mH 14 GA. PERFECT LAYER IN.. $7.91 $15.82
266-320 Yes .40mH 14 GA. PERFECT LAYER IN.. $9.23 $18.46
266-380 Yes 2.5mH 14 GA. PERFECT LAYER IN.. $20.62 $41.24

295-364 Yes DAYTON RS180S-8 7" REFERENCE .. $32.70 $65.40
275-130 Yes DAYTON RS28A-4 1-1/8" ALUMINU.. $46.65 $93.30
Subtotal: $279.24


Thanks, Dan B
http://speakerbuilder.blogspot.com/

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jdybnis

Jon, can you post the FR you are using for the RS28a. I'm putting this design into Soundeasy. I'd like to use the same measurements so the results are as comparable to yours as possible.

JonMarsh

My hosting service is doing quarterly maintenance this weekend, so this may not always be available until Monday.


RS180 SPL


RS180 Z


RS28A-4 SPL



RS28A-4 Z

You should be able to right click and save to a text file. Or open with browser and copy contents into notepad.


All measurements on 9" wide baffle; tweeter offset ~ 0.75" from center

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still coming in 2010....

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

JonMarsh

Re your questions, zobels are impedance control networks to make it easier to get the expected frequency response when using a passive crossover; they flatten the impedance curve vs frequency. They can also be used to coutour the impedance in order to modify the frequency response. Common applications are RC network for midwoofer inductive impedance, resonance impedance bump compensation for a tweeter, and RC network for tweeter inductive impedance rise. Locations are the same regardless of filter type. It's an engineering judgement call whether to use one or not, and to what degree. I normally start with a tweeter LCR FS zobel that flattens out the tweeter impedance bump at resonance, as this causes problems otherwise with the low frequency tweeter roll off.

In this crossover circuit, due the realtively flat impedance of the RS28A, we've eliminated the Tweeter RC zobel. If you use a tweeter FS LCR zobel, it will be in the range of 1.5 mH + 68 uF + 6 ohm; DON'T change or modify any values in the crossover, it will just improve the roll off below 1 kHz.

A stopper resistor "stops" the lead compensation in a parallel C around R network, so that the gain doesn't continue to rise until capacitor Xc is nearly zero. The ratio of HF gain is the main resistor to the parallel combination of the stopper and main. There's no point in increasing the ultrasonic drive to the tweeter, and many amps might not like the impedance difference.

You may need or want to trim the value of R3 slightly to get the best balance; use 4 ohms for a little more overall highs and presence, 6-8 ohms to reduce high frequencies and presence range.

Your BOM looks in the ball park to me.

Are you going to build your own enclosures modeled after the PE 0.75 cu ft, (can be done quite inexpensively if you just sand and finish with truck bed spray on liner), or go for the "pretty ones"? I have to admit that for what PE charges, I don't build small boxes anymore if I need them to look nice. The "big" projects and measuring and calculating takes up plenty of time, anyway!

Have fun, and show us how things are coming along. I split the crossover into two boards, to make it easier to build into the PE boxs, which has a large brace parallel with the front and back panels. If you build your own boxes, then you'll have more freedom or flexibility, if they dont' have that brace. OTOH, the brace is a good idea, works well.

Here are some pics of the enclosures for the first "Elaine Marie" built for my duaghter two years ago. This new set, which are in Cherry, not beech, are going to a friend back east.









I do recommend back chamfering for the midwoofer






Testing with the first crossover...





~Jon

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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)

jdybnis

Thanks.

Dan B

I'll be building my own boxes, I was very happy with my results when I built these> http://mysite.verizon.net/res6vgmm/...ctures/both.jpg

Since I coulden't design a crossover to save my life, At least I can build a box I'm proud of. Although they are not even close to bieng as nice as what you build.
Thanks again, Dan B

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Dan B

Jon,
At the PE site it says the baffle is 10 inches wide (exterior)
http://www.partsexpress.com/pe/psho...r=302-732&DID=7
Should I build mine to their dimensions of 10 wide or 9 wide?

External Dimensions: 17" H x 10" W x 12.5" D
Internal Dimensions: 15.5" H x 8.5" W x 10.75" D
Internal Volume*: .82 cu. ft.

The cabinet volume slightly oversized to allow room
for driver and port tube displacements.

And a 2 inch port 7.4 inches long.

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JonMarsh

Go with 10" wide. 9" is the baffle width for the MTM- in practice, there's almost little measurable difference in the baffle step response. If we were talking about 12-14", then that would be another matter.

For the 2" port I highly recommend the flared Precsion Port, available from PE; it's used in the Modula MTM project. ESPECIALLY with these smaller port diameters, the use of a flare at both ends is important.











BTW, you boxes look fine!


Have fun, and keep us up to date on your progress!

~Jon

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

Doug Lockwood

Jon.

Nice design. I am looking for an under $300 out the door project for one of my brothers friends. So I am thinking the 27TDFC may be a better fit for my needs. Do you see any problems with that?

There is always a catch. He wants to put them on a bookshelf!
This would imply moving the BCS lower, maybe 2 dB, no?
Where in Sam Hill would I start to do this with this crossover?
I have the crossover inputted into SoundEasy. its just a bit different.

Also, what format were your exports in?
I wasn't successful in importing them into SoundEasy Right now, I'm using the PE data.

Thanks;

Doug

JonMarsh

Those are straight CLIOWIN text files. I've never had any trouble importing them to LspCAD 5 or 6. You might try just clicking on the links, copying the data to notepad, and saving.

If you build the cabinets as deep as these, you're probably better off leaving the original BSC in the circuit. The front panel is far enough in front that you'll still need most of the BSC.

The only way to REALLY know for sure is to measure the driver in the cabinet in the expected listening position.

One other point- a little extra BSC is much more agreeable sounding than not quite enough- the latter will be quite fatiguing over time. The current design is only 4-5 dB of BSC, becuase I figure folks won't be pointing them out on stands well away from the wall (as I would do) in most cases. Otherwise I'd use a full 6 dB.

Just my thoughts...

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still coming in 2010....

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

Dan B

The last flared port I did >>
http://speakerbuilder.blogspot.com/...ilding-box.html

you can bet I'll be blogin this project!

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jdybnis

I had a bit of trouble importing the files into Soundeasy at first. What I was missing was that I had to set the scale on the import dialog box, for example the RS180 needed to be 88db. After I figured that out it worked fine. Here are the steps I followed:

1. on the import/export menu select CLIO
2. in the windows file browser that comes up open the file (RS180FR.txt)
3. in the import dialog box that come up set the scale (88db) and the efficiency to the same value
4. at the bottom of the dialog box tell it to ignore ("erase") the first line of the file
5. click the amplitude button; or impedance button for the RS180Z.txt file
6. after the import is done click the "repair amplitude" button on the tab where you enter the t/s params

jdybnis

Another question from a cheapskate.

Do you have any experience with metal film resistors? Madisound is selling 10W Eagle metal-film resistors (non-inductive) for $1 apiece. Do you think thats going to be noticable soundwise vs. the $3.50 Mills at PE?

Dan B

Check out this thread>

http://www.madisound.com/cgi-bin/di...cgi?read=345233

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Dan B

6 inches on center with the tweeter off set 3/4 ?

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JonMarsh

The tweeter center if 4.5" from the top, offset 1" from the center (for the EM; the Modula is offset 3/4" ).

Woofer is centered laterally; center is up 7" from bottom edge.

The baffle dimesions are 17" tall by 10" wide. PE enlcousre is 12.5" deep.

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

Dan B

Thanks Jon,
It looks like the tweeter will touch the woofer so I'd like to leave enought room so they don't touch......

Heres how it comming along>>

http://speakerbuilder.blogspot.com/

Thank you for your time!

Dan B

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