Modula MT-XE - You didn't ask for it... it's coming anyway

[JonMarsh]

Jon, isn't that block of wood taking up allot of internal box volume?

1" total thickness by about 7" X 7"? Not really- and part of why we start with a 0.78 cu ft enclosure, not a smaller 0.5 cu ft as often used for 6-1/2" two ways.

The box Fs with 7" port is about 32 Hz, exactly as planned.

[JonMarsh]

The blue curve is with the waveguide, the "crimson" curve is without the waveguide.

Over all it looks very good. There is a little "waveguide dip" at ~13 khz; but it is modest and would be less noticeable (for me and my old ears) than usual (my dips were often around 9 khz). Also looking at the off-axis curves above, one can see that the dip goes away quickly.

These curves appear to be either raw without a crossover or just one blocking cap for protection. This that a good assumption?

These are raw- no blocking cap- at 2.83 VRMS drive, (monitored by the Society for Humane In-test Treatment of Loudspeaker Drivers), no excessive stress, though I wouldn't recommend that for ribbons. :W

Yeah, I'm fairly satisfied, too, with the overall measured performance- as you note, you can run into problems in the 9-15 kHz area depending on the interface between the tweeter faceplate, dome, and waveguide- this looks to be acceptable for the application.

[JonMarsh]

Getting close

In spite of my simulation and pre-purchase efforts, I didn't quite have all the components needed for the provisional crossover design, though pretty dang close- so for now only emulation listening, which seems agreeable enough to order the remaining parts ASAP.


This is what you might call a "perfectionist" crossover, as John Krutke likes to call it, in that I've included a zobel network to control the input impedance, which other wise can get quite high in the crossover overlap region.



L3, C4 and R5 are the tweeter Fs zobel. The parallel shunt network formed by L4, C5, and R6 contour the tweeter response in combination with C3 and R4 in series. The crossover ended up working best up around 2 kHz, instead of my intended target. Such is life....



Impedance is VERY benign with the recommended zobel, but for tube or zero feedback solid state amps, the peaking in impedance would interact with the amplitude response in the crossover region. I just feel better with a more consistent input impedance and damping characteristic. If you want to save money, eliminate L5, C6, and R8, but don't be surprised if it doesn't sound as good.



Last is the transfer function plot, showing the effect of the crossover filters to produce the predicted SPL plot above.



These are in room measurements with 50 msec gating windows, so there are effects like the bump at 200 Hz which reflect room acoustics.

The remainder of crossover parts will get ordered this evening or tomorrow.

[LING GOWA]

1" total thickness by about 7" X 7"? Not really- and part of why we start with a 0.78 cu ft enclosure, not a smaller 0.5 cu ft as often used for 6-1/2" two ways.

The box Fs with 7" port is about 32 Hz, exactly as planned.

Hmm, I just happen to have a PE .75 cu/ft box on hand that's been waiting for a project. Do you think the minor difference in size will affect it?

[JonMarsh]

This IS a PE 0.75 cu ft box that this project is designed for- technically they're 0.78, but who's counting? :W

[LING GOWA]

Very cool!

[frascati]

Is there really a concern with chemical release when using good sharp carbide tools on plastic? I thought it was pretty benign.

[JonMarsh]

Depends on the mix of vapor and dust that are produced- vapor being a product of temperature, which shouldn't be high with clean tools and fast work- neither are good for you- at least a particulate mask is advised, but a volatiles mask is even better.

We're talking a pretty small work effort here, but it makes sense to be cautious.

[JonMarsh]

Hooorahh!

Nice box of crossover parts arrived from PE as planned and ordered Monday!!!

Now, if I can get all my "chores" done on Saturday, hopefully I'll make some real progress on these on Sunday!

Also got my other shipments last Tuesday of cabinets- dang, it looks like a PE warehouse in my living room at the moment... gotta get those in storage!

[cjd]

So, what if you used felt to fill the tweeter/waveguide gap, and cut it with pinking shears so it protruded very slightly into the throat (but not to much) ?

[JonMarsh]

Well, I don't know, Chris- that's one thing I also considered doing. The gap is tapered as currently built and flush at the circumference of the waveguide plate.

Sounds like something interesting for someone else to try out! The trick is, how much?

I'm pretty pleased with how this one measures, I've seen a variety of attempts and done several myself, the trick (in my mind) is to try to get clean behavior without "significant" dips out to say, 30 kHz or so.

As Benchtester and others have noted/experienced, it's easy with some tweeters to wind up with some significant artifacts in the 9-12 kHz area.

If all goes well, I may get to route the front panels for the Modula Xtreme upper module this weekend, too (that depends on weather and outdoor temps), and get some data for the midrange and waveguide built up for that (different drivers). That's sort of a long shot for the April DIY, but I do have all the drivers and 3/4 of the cabinet stuff done. Who knows? Problem will be pricey crossovers, with 350 Hz on the bottom end from mid to woofer.

[cjd]

9-12kHz issues are dictated by the throat right by the surround (i.e. the inner terminus), no? Which is what makes me wonder if a little wool felt in a not-quite-perfectly-round setup in that area would help. Or hurt. Or something. Certainly a lot easier to do than your RTV seal

When I get to experimenting with waveguides you can bet that I'll be doing some whacky things, and much of it with felt. I have some crazy thoughts on what can be done with the lowly BG Neo3

[JonMarsh]

Well, I'll be curious to see what you come up with. The RTV treatment is something I came up with in a specific process, because the way I do it, it is quite reliable and easy. With the wax paper trick, we wind up with a self formed "gasket"; let it cure a day, it's firm, though not as firm as after 2-3 days, but easy to trim with a small vegetable paring knife using the inside lip of the tweeter plate as the cutting guide (no need to get out your Colt router.... ). It produces a very clean interface for this tweeter. Other tweeters might need different tricks. You should see what I had to do for an Accuton D25N-6-13 when I decided I "had" to come up with something the first time. Live and learn.

But hey, the more tested techniques we come up with, the more options builders will have.

[Ryan_M]

Hi Jon,

I'm currently building Zaph's WgTMMs and notice this project has a lot of similarities with Zaph's design. I'm just curious if these are intended to be an upgraded version of those or if it's all just coincidence.

[JonMarsh]

Well, Zaph's design IS an influence, but I do like the D2608/9130 tweeter better, as well as the Seas ER18RNX, so you could say it's an upgraded TM version- which is smaller and simpler than the TMM- though I also have a TMM design completed on paper.

The crossovers are a bit different because the SS tweeter needs a little bit more shaping and I'm chosing to use an LF zobel to control the tweeter low frequency power rise- the tweeters have rather different impedance curves and designs, so this requires a bit of work. I don't think you can make an honest comparison about which would be "better" without putting them side by side. Because I've been testing the D2608/9130 and the ER18RNX and using them in other designs, I chose to use them in this design, rather than just build Zaph's. An unnecessary complication? Perhaps- but that's what makes things fun. The ER18RNX has class beating distortion, playing well out of it's price range- I really like it in the Ardents, suspect I will in this system, too. This first pair are going to some specific family members.

Because of another project I'm working on to get ready for the Northern CA DIY, I probably won't build the TMM version for a while, though I have the basic cabinet stuff on hand and drivers.

[augerpro]

Good stuff Jon! Looks like the waveguide offsets the response rise in the top octave of the tweeter, at least from a power response perspective if not directly on axis. Fortuitous.

Do you have a close up of the WG/tweeter interface? What is the throat diameter? Did you have it end just outside the surround, or did you make it so the faceplate's bevel just outside the surround is exposed? I have two MCM's I milled for the DX25 some time ago with two different throat sizes, which just happened to cover both scenarios above on the SS tweeter (then Peerless HDS).

[JonMarsh]

I'll do some close up photo's and stuff when I get back to working/posting on this- I hate to admit this is all trial and error, but that's how it's been to a degree- it's more a Thomas Edison thing than an Albert Einstein thing, if you know what I mean.

The waveguide was milled to a diameter that matches the inside edge of the aluminum faceplate. Then the RTV is built up, using the waxpaper so you can separate it; it firms up in a day, but still isn't super tough; it's easy to cut with a paring knife or Xacto knife at that point; after a few more days it's much firmer. that seems to work pretty well, and I think the relatively narrow surround of the 9130 is a plus in this application also, as all of these factors keep the cavity size around the dome small. That, I believe, is important to minimizing the dips from what are most likely cavity resonances, and keeping a smooth top end. With this combination, it gives a pretty good response out to 30 kHz.

[HokieJoe]

Well, the jig's no big deal- anyone can make that from a little bit of scrap. Just a small MDF plate and two rib spars to lift it off the table.

It's possibly the router table and Woodpecker Quick Lift with dedicated router (mine is with a Bosch that's compatible with a Porter-Cable 7518, don't remember the number) that might be a stumbling block.


Nothing mandatory about the quicklift, but it sure makes changing router bits a LOT faster, and the control over the router bit height for the Woodpecker lifts has to be seen to be appreciated.

The Woodpecker lift is a nice piece of kit. If you don't want to spend that much money, here's another option:

Triton MOF001 Router

Woodcraft - $229.00

Triton 2-1/4 HP Plunge Router
Model MOF001. Triton’s new 2-1/4 HP Router Kit boasts all the revolutionary features you would expect to see on a Triton router and more. A push button mode changer allows you to switch from free to winder plunge with a 2- 5/16" plunge depth, an automatic collet lock system allows single wrench bit changes from below the base (or above the table if in a router table), a full range micro-adjustability, integrated dust control and a failsafe switch lockout system for added safety. Also included is a winding handle so you can adjust bit height from above your router table in 1/128" increments, an extended base plate with edge guide and circle cutter, 1/2" straight bit, 1/2" and 1/4" collets. The powerful 13 Amp motor offers variable speed from 8,000 to 21,000 RPM, soft start and electronic speed control.


This little router has gotten great reviews in publications like Fine Woodworking, etc. BTW, nice design Jon. Can't wait to see the finished product.


EDIT:
Some Reviews:

http://www.onlinetoolreviews.com/reviews/tritonrouter2.htm

Fine Woodworking Best Overall/Best Value

[JonMarsh]

It's getting close, first crossovers + box test

First pair of crossovers finished today, and tested with the driver test mule. The series resistor for the tweeter was setup as four 30 ohm resistors in parallel, for power handling and to facilitate adjustment (by disconnecting resistors to increase the value). This ended up working well, as the way sensitivities worked out, with 7.5 ohms on the tweeter it was a little hot (red), but with 10 it seemed pretty much perfect (blue).




The positioning for this test is similar to what many folks might use in practice, LF effects and all (40 msec gate), on 28" stands 18" from rear wall.

The axis curves look pretty nice - and it sounds very good off axis, even beyond 45 degrees.

Here, I've measured 0 degrees (black), 15 degrees (blue), 30 degrees (green), and 45 degrees (violet).



I'd say you'd be hard pressed to identify the crossover frequency from these curves, which means you don't really hear it. Reverse null is about -15 dB centered at 2 kHz, and pretty symmetrical, as it should be.

Right now I'm listening to it with some Bonnie Raitt through the Mac Mini and measurement system - just one channel; Level 42 now; and some David Garfield.

Will need a bit of tweaking to optimize the LF damping (probably a little overdamped at the moment).

The mids through the presence region sound more like a three way than a two way... I think that's good. :W

I also did a distortion analysis of a 1 watt sweep, which is ~84 dB output - not sure what confidence factor I'd put on this, but I think we can safely say the waveguide is doing what it is supposed to, in helping provide a radiation load for the tweeter and lowering distortion.



As I hoped, it builds on the good characteristics of the D2608-9130- note both HD2 and HD3 are quite low, at similar levels.

A TMM based on this ought to be a bunch of fun...

[JonMarsh]

Some listening notes

These are a lot of fun on rock and roll for a small two way- they're very clean in the presence range due to the waveguide- this shows up in various ways, such as female vocals, but the one I really noted was listening to a classic Sting album (Fields of Gold), all the cymbals and percussion sound good on "Fortress around your heart", but particularly the ride on the cymbal bell during the chorus. It's not an easy tone to get right for a typical two way, as it straddles the crossover region.

The D2608-9130 is one nice tweeter....

(BTW, I'm listening through the Firewire Solo measurement interface, not the big guns gear!)

[WillyD]

Now I have another darn two-way I need to build. This design looks great Jon! And improvement in the Mk1 in every way.

[JonMarsh]

Thanks for the kind words! BTW, our East Coast office, where my boss is, is in Durham. I haven't gotten out there in over a year and a half, though, due to travel restrictions.

Here's what the final crossover boards look like- both pairs are built now- the schematic is only altered slightly from the LspCAD simulations - will draw and post those by next weekend. R4 is 10 ohms now, and L4 200 uH.



Now I'm back to working on the cherry cabinets today.

[Mark K]

If the power response is similar to the DXT's-then I think they do very well around the xover and above. Brass, female vocals are all very nice, more so that the typical two way. There is a bit stronger, and more uniform presence in this region.

Any that waveguide just looks cool!!

[---k---]

Jon,
You mind discussing your thoughts on doubling up your resistors for increased power handling. When do you think it is needed?

CJD talked about possibly needing it on the mid in my In-Khans, but at the end of the day decided it wasn't needed. I really didn't think it was needed on a tweeter.

Also, I'm surprised by your use of the regular Dayton resistors, since you've spent some money on better caps. Is there no difference in your opinion between resistors? Or was there another reason for the Dayton's? I've heard some swear by Mills.

[JonMarsh]

If the power response is similar to the DXT's-then I think they do very well around the xover and above. Brass, female vocals are all very nice, more so that the typical two way. There is a bit stronger, and more uniform presence in this region.

Any that waveguide just looks cool!!

Yeah, I can't wait to get this pair finished and try them with Harry James, "The King James Version" from Sheffield Labs (for the brass). I have a lot of other cuts of interest, of course - choral works by Arvo Part will be the acid test, but I'm also curious how they do with pop female vocals, like Joni Mitchell, Jonatha Brooke, and others. They do have a seamlessness in the critical presence range that's not easy to find in a two way; I think you know fully what I'm talking about.

From the measurements and a bit of listening, I think it will be a close horse race between these and your ER18DXT. The DXT will probably have better far off axis dispersion due to the diffraction steps, I'd guess. Otherwise, more similar than not.

That waveguide is also a bit "big", I've actually got a front panel from the 0.5 cu ft cabinet like you used cut for one of them and an Accuton C173N-T6-90 for testing together (I have a waveguide with an Accuton C25N-6-13 mounted), and it's a VERY tight fit in that space- most would say too tight.

Remember, the VC diameter is only 26mm, but the surround adds a lot to that and the way I originally built it, it cleared the surround and used an RTV built up matching "gasket" and this measured pretty well even in the area around 10-14 kHz where we see problems with the interface of a lot of tweeters to the waveguide. I think it has to do with the dome shape and interface, but I'll readily acknowledge there was some trial and error- a number of candidate tweeters tried out with the MCM waveguide- some you might expect to work well (the Millennium Excel, for example) didn't. Also, inverted hard domes, like Accutons, were particularly problematic in that region.

How much of a hurry are you in? I have a few sets of wavguides, and later this spring I should be able to find the time to build up another test example.

Also, there were some good suggestions for the tweeter to waveguide interface in the Modula Xtreme thread- I'll go back and look for those and review.

[JonMarsh]

Jon,
You mind discussing your thoughts on doubling up your resistors for increased power handling. When do you think it is needed?

CJD talked about possibly needing it on the mid in my In-Khans, but at the end of the day decided it wasn't needed. I really didn't think it was needed on a tweeter.

Also, I'm surprised by your use of the regular Dayton resistors, since you've spent some money on better caps. Is there no difference in your opinion between resistors? Or was there another reason for the Dayton's? I've heard some swear by Mills.

In some applications I think it's particularly needed - for example, the low Q zobel at the input of the woofer crossover (really, it's just at the input terminals, but I built it on the woofer board), this is compensating a large region in the crossover between woofer and tweeter where the impedance rises to a pretty high value otherwise- so for an octave or so, it's handling power like a small filler driver.

Also, one should distinguish between the power needed to overheat a resistor, versus the power just needed to change the value- from thermal effects- which is less. And, unfortunately, the people who sell us these audio resistors don't tell us dip about that kind of stuff, unlike the resistors I power for other applications, like power conversion.

As regards the Dayton resistors, I tried them and the Mills in different builds of the NeoD CC, and I think from personal experience the Dayton's sound fine, especially when used "liberally", i.e., paralleling to up the power handling and lower inductance. Sometimes, too, as I noted, planning a multiple resistor batch in parallel facilitates quick tests of different values just by disconnecting one or two.

Consider the input circuit to the tweeter- half the power in the tweeter circuit may be dissipated in R4. It's unlikely the tweeter is going to see 20 W RMS, unless someone is beating these to pieces- but sensible derating of power handling to avoid excess internal temperature means I'd prefer to see three or four 10 watt resistors handling that, not one. The thing about maximum power or voltage ratings is that they're maximums- a good engineer will de-rate for reliability and sometimes for performance, too.

In a commercial design, I would run these in with a variety of program and pink noise, and use a digital scope to measure voltage and current and power, and make some decisions about the least amount of components I could get away with to keep costs down. In DIY, I'd rather not spend the time on that kind of engineer, when adding a $1.00 resistor easily lends peace of mind and saves time. That's just how I think about it, YMMV, of course. If I were engineering kits for a 3rd party, it might be different. Or not. I don't like some of the parts I see in those kits...

And of course, this is DIY, anyone could take my implementation of the design as a starting point, and cut a lot of component costs, and still wind up with something that would sound pretty good on a lot of systems- will an added 1 to 1-1/2 dB insertion loss in the woofer and a bit less damping be audible to everyone? Would the difference between ESA caps and Bennic Poly be audible on DVD's with an average HT receiver with their typical Crystal semiconductor volume controls? Possibly not. But put that speaker on an Ayre integrated with a good DAC, and it will be.

So, I'm being a bit of an impractical nutball here, because I'm building the kind of small speaker I'd like to have if that's what I had to live with. Certainly not the cheapest, and not the easiest to build.

This first pair is going up to Sacramento, for some "family" (relations to the ex), so you could say, it's my reputation on the line, and every time I visit! :W

[---k---]

Good thoughts. But, always reading your posts makes me want to go rip apart one of my speakers and change something.

[Johnloudb]

Jon,

You think I could retrofit you MT MKII into this? If I open the tweeter hole to fit he MCM waveguide? The baffle would be a bit taller than you box.

Thiel CS1:

Image not available

[JonMarsh]

How wide is the box? The PE cab I'm using is 10". That's important for BSC in the crossover, of course.

The other "trick" or concern is the mounting plate behind the waveguide, and most specifically, the total baffle thickness needed - in this design, that's 1-1/4" if you mill the waveguide exactly to plan. How thick is the front baffle in those cabinets? If 1", all you need is a 1/4" MDF spacer board. The tricky thing I see here, is that I do rebate the baffle, and you've already got a hole- however, if you have a good set of rabetting router bits, that should be solvable, too, if you can cut the new through hole accurately, maybe by making a template, clamping it on, and using a pattern guide. Then use the rabbeting bit to get the rebate.



Otherwise, you might be better off cutting a plug to fit the old tweeter hole, epoxying that in place, then routing the waveguide rebate and cutting the opening hole with a spiral upcut bit. Many paths to Rome.

[Bear]

Jon,

You think I could retrofit you MT MKII into this? If I open the tweeter hole to fit he MCM waveguide? The baffle would be a bit taller than you box.

Thiel CS1

I'm Not Jon, but... The sloped baffle in the Thiel speakers helps align the acoustic centers of the tweeter and woofer, which is being done (in part?) by the waveguide in Jon's design. You'd be looking at either removing the waveguide, which would require redesigning the crossover, or keeping the waveguide and re-working the crossover to get the phase integration correct. In either case, it's a new crossover. Sorry!

[Jed]

Not necessarily Bear, the tweeter axis is much below the listeners height, so the driver integration with the waveguide might actually work in that case, depending on the listening distance, etc. I'd be equally concerned that the overall baffle shape is completely different and would create a different diffraction response than the measured prototype design, thus a new crossover would be required. In the end... it might be close in the Thiel cabinet but not perfect.

[JonMarsh]

Well, you know what they say, close is OK in horseshoes and hand grenades!

Maybe too, in speakers built in re-cycled cabinets! Jed raises good points, but if you have the means to do any measurements in the cabinet, and send me FRD files, I can update the crossover design.

I think Bear has a valid point, the crossover lobe axis will be perpendicular to the front panel plane, but for a short cabinet sitting low, that's probably a good thing.

[Johnloudb]

How wide is the box? The PE cab I'm using is 10". That's important for BSC in the crossover, of course.

The other "trick" or concern is the mounting plate behind the waveguide, and most specifically, the total baffle thickness needed - in this design, that's 1-1/4" if you mill the waveguide exactly to plan. How thick is the front baffle in those cabinets? If 1", all you need is a 1/4" MDF spacer board. The tricky thing I see here, is that I do rebate the baffle, and you've already got a hole- however, if you have a good set of rabetting router bits, that should be solvable, too, if you can cut the new through hole accurately, maybe by making a template, clamping it on, and using a pattern guide. Then use the rabbeting bit to get the rebate.



Otherwise, you might be better off cutting a plug to fit the old tweeter hole, epoxying that in place, then routing the waveguide rebate and cutting the opening hole with a spiral upcut bit. Many paths to Rome.

The baffle width is 10.5 inches and 1" deep, and as Jed pointed out there is no round over on the baffle. But J.Thiel used the grill covers as the actual baffle (with a wide round over) and it includes a shallow wave guide that extended to the same radius as the woofer like the MCM one. If I flush mount the tweeter it would be 1/2 inches deep, still not as deep as the MCM, I'm sure.





The woofer is also mounted on a 1/4" from the box. Knowing J. Thiel's design philosophy, it was surely time aligned with the drivers he used anyway. But, I'm guessing to use the Thiel waveguide would be quite a stretch and need a new crossover?

Well, you know what they say, close is OK in horseshoes and hand grenades!

Maybe too, in speakers built in re-cycled cabinets! Jed raises good points, but if you have the means to do any measurements in the cabinet, and send me FRD files, I can update the crossover design.

I think Bear has a valid point, the crossover lobe axis will be perpendicular to the front panel plane, but for a short cabinet sitting low, that's probably a good thing.

Thanks for the input guys.

Jon, I think I might try this driver combo in the Thiel using it's built-in waveguide, and take some measurements. If you think it looks okay, I'll use the Thiel cabs. Or is this too far fetched? Maybe no hope of that working?

I guess if that didn't work, I would use the PE cabs. I'm really interested in these, though.

[JonMarsh]

What do the Theil waveguides look like? How much offset from the front panel? With the front baffle tilt back, this will affect the acoustic center alignment, in a favorable way. Because this is a low order LR2 with little difference in the acoustic offset in my design, any design that changes that aspect will have to take it into account. But if you can do measured data, then I think things can be sorted out.

I've even done the crossover design for a straight MT with these drivers, but that would mandate putting the tweeter under the midwoofer to develop an upward crossover lobe.

Panel width sounds OK- overall, probably doable.

[Johnloudb]

The Thiel waveguide has a flat slope extending to 6.25 inches in diameter. It's only 3/8" deep the way it is. But I could flush mount the tweeter and extend it more toward the center dome, with a sloped 1/8" thick wood circle cutout.

Another possibility, would be to increase the removable baffle thickness with a 1/4" piece of wood, and sink the tweeter 1/2" into the cabinet. Then I could mount the MTM waveguide in the removable baffle.

Although, I'll probably try it the way it is and work from there.

I have ARTA software for measurements, would that do? Although I do need to get LSP CAD for measurements within a couple months for measuring the dipole speaker I'm working on.

[JonMarsh]

ARTA should do, anything that will generate FRD or txt files, and with some control over window length (and window shape? ...yeah, probably asking too much! )

Does ARTA do distortion, too? I like checking the finished design with crossover, to make sure we're not pushing anything uncomfortably. I suppose I should download the ARTA manual and read it, but I'm so backlogged on projects and time these days, learning another program isn't at the top of my priorities.

[Johnloudb]

That's great ... it does do distortion measurements. It does window length, and I'm sure it will output text files. I still got to learn it better myself. I have done FR and distortion measurements but only on electronics.

[ergo]

ARTA is a very extensive tool, especially for the price asked.

It consist of three separate programs
ARTA - for gated loudspeaker measurements / room acoustics measurements or spectrum analysis.
LIMP - for impedance measurements and TS extraction
STEPS - for measuring thd with stepped sines instead of sweeps.

***
ARTA part does
frequency response + phase
2nd and 3rd thd products from sweep (needs few special setting though)
step response
energy time curve
cumulative spectral decay
energy decay
+ many room parameters from RT30 to STI, RASTI, C50 etc etc.

LIMP allows using periodic noise for quick impedance measurement but also stepped sines - which is more precise in end for TS extraction especially.

STEPS with its stepped sines does either combined thd or allows separating 2nd, 3rd, 4th, 5th and 6th+ harmonics and plotting all on one graph. If one invest in laser distance meter it even does the THD vs excursion.

***

Anyhow - compared to FuzzMeasure - it does all Fuzzmeasure does beside perhaps the two points
1) ARTA does not have a way to export sine sweep and import the both the ref and measured sweep later that FuzzMeasure does (import field measurement it was I think)
2) ARTA allows overlays of frd graphs, but Fuzzmeasure is so much easier and user friendly if one wants to compare or plot many graphs together.

For me the point 1 was the reason to also get Fuzzmeasure. I used it this weekend to make full on and off axis measurements on two speaker projects - and I love the simplicity and user friendliness Fuzzmeasure gives by allowing to store all measurements into one file and easily overlay etc. But still for detailed THD, very full room acoustic analysis or good impedance the ARTA does very very well.

[ergo]

ARTA should do, anything that will generate FRD or txt files, and with some control over window length (and window shape? ...yeah, probably asking too much! )

ARTA has:

Uniform
Hann 12.5%
Hann 25%
Hann 50%
windows available for FRD

and does export suitable frd and zma format with
freq mag phase
that one can use straight away for LspCad

[JonMarsh]

Then John shouldn't have any problems getting any needed measurement data to characterize his build for a modified crossover design. Thanks for taking the time to post this detailed information!

[Johnloudb]

ergo,

Thanks for posting all that information! I guess, I've got to educated on ARTA and quick.

[TW1]

Jon
I am a newmember and have question if these could be built sealed or vented in a smaller cabinet.If sealed will work what QTC/volume would you sugest.I would not change the baffle size.

[JonMarsh]

You could take these down to about half a cu ft and still have decent performance in the low end. Then I'd change the port tuning to about 5.5 - 6" long. Sealed would be OK if you plan on going with a sub, but the Qts of the ER18RNX is on the low side, so in a sealed box the perceived low end roll off would be substantial. I'd have to revisit my Unibox plots to say just what.

You could probably build these in a PE 0.5 cu ft box, but it would be tight- due to the overall front panel dimensions. I'm building up a test box with this waveguide, mated to an Accuton C25N-6-13, and Accuton C173N-T6-90, which is a 6-1/2" driver- but it's REALLY tight to fit that on the front panel for the PE 1/2 cut ft box. But it makes a cute head unit, so I'm trying it out for the "Modula Xtreme". It would be mated to two of the PE 1 cut ft sub cabinets, each one equipped with a 10" woofer. Something that people could put together quickly without a ton of woodworking effort. Or, at least something I can put together without a ton of wood working effort!! :W

I don't think trying to go smaller than that makes much sense- you need room for the crossovers, too, though they're hardly ginormous by my standards. :W

[TW1]

Thanks Jon If you could review your Unibox plots for a sealed enclosure it would appreciated, I have a sub and will be making my own cabinets any volume is fine. I have been using Unibox with Zalphs data trying to learn a few things and would be interested in what QTC value you suggest.

[JonMarsh]

Sealed box I suggest a QTC of 0.5- critically damped- I'll figure out what size that is.

~Jon