Using CALSOD for crossover modeling

I own two programs for crossover modeling – CALSOD by Audiosoft and SoundEasy by Bodzio Software. Interestingly, they are both located in Australia. There really is no comparison between these two programs – SoundEasy is several magnitudes more sophisticated than CALSOD. However it is also painfully hard to learn and understand. For now, I’m not trying to achieve any sort of accurate models. Mostly I want to get a feel for how low the impedance might get with various drivers used in parallel or how low the efficiency might get with various drivers used in series. I know, I know… I’ve already picked the drivers, right? This 4 ohm world we live in is driving me nuts. TDL had the advantage of being able to create any driver they needed – hence the 16 ohm drivers they had available to them. All I want to do for now is make sure I have a reasonable chance to end up with a speaker that will stay mostly above say 3 ohms while reaching say 87 dB efficiency.

So I’m going to use CALSOD, so what? The version I have – 1.30N – was written in 1994. So it is a 16-bit DOS program that uses the character graphics of the original IBM PC (think EGA and VGA). So those were the two problems I had to solve – 16-bit DOS and OEM 437 font.

The first I tried to solve the compatibility mode in Windows 7 Ultimate. To make a long story short – no go. It couldn’t draw the graphs. Otherwise it looked pretty good with Windows 95 compatibility mode.

DOSBox to the rescue. A DOS emulator that runs on Windows, Linux and Mac, DOSBox worked, well, right out of the box. Mostly developed for gamers, it ran CALSOD without a hitch. Great job!

As for the font, I was able to find something called MS Line Draw (linedraw.tff) at this site. Using that along with Wordpad and a font size of 9, I was able to get the user’s guide to format properly. Yippee!

After all that, what does it look like? An old DOS program. A cool old DOS program though:


Simple graph ouput from CALSOD

Screen to configure CALSOD plots

Screen to configure CALSOD plots

Cabinet exterior design (rough draft)

This is a rough draft of the exterior design for the cabinet. The details aren’t there and some things may change. What it did tell me though is that this speaker can’t be built with a single 4’x8′ sheet of MDF, so I’m looking at 3 sheets for a pair of speakers. Ouch. Well, at least there will be room for error.

  • A: Sides of speaker (outside) x2
  • B: Sides of speaker (inside) x2
  • C: Diagonal fronts (woofers) x2
  • D: Front x1
  • E: Back x1
  • F, G: Inside baffles, not shown
  • H: Top, bottom (inside) x2
  • I: Top, bottom (outside) x2
Dimensions of sides

A: Sides (facing out); B: Sides (facing in)


Dimensions of front and diagonal sections

C: Diagonal; D: Front


Dimensions of back

E: Back


Dimensions of the top and bottom

H: Top/Bottom (inside); I: Top/Bottom (outside)

Cabinet drawings started

I’ve been playing around with cabinet drawings for a long time, but now I’ve finally started in earnest. I’ve got some work to complete yet on the outside, though most of the hard work is done. There is quite a bit yet to do on the inside. Still, I have a good enough grip on it now that I’m ready to show a few diagrams. You’ll notice immediately that I’m no draftsman. All these need to be is good enough for me though, which they are.

Top view diagram

Top view of TDL DIY. Note: Not 100% faithful to the RSTL M


Front and diagonal views of TDL DIY. Note: Not 100% faithful to RSTL M.

These are just samples. The full design will be forthcoming when I’m done with it.

Keen eyes will notice that the tweeter cutouts don’t at all match the Scanspeak tweeter I’d mentioned I’d be using. Really keen eyes will notice the woofer cutouts are too large for Vifa NE123W-08s. I’ll talk about that next time. 🙂

IMF woofer closeups

Thanks to Audiogon member Dipolemann, I have a few closeups of oval woofer similar to the ones used in the RSTL. These are actually of the IMF 128/20, which are used in some of the later IMF models, but they are visually very similar to the 3021GT 01 and 3021GT 02 used in the RSTL.

IMF 128/20 front view

IMF 300mm x 210mm woofer - front view

IMF 128/20 - rear view

IMF 300mm x 210mm woofer - rear view

Technical data gleaned from the 1989 Stereophile review

In the 1989 Stereophile review of the RSTL, there was some technical data I hadn’t run across before:

Midrange line is fully stuffed

The midrange line is fully stuffed, unlike the woofer lines

  1. The midrange line is not intended to increase output at all, but rather completely absorb the rear wave. Note the midrange line is completely stuffed, whereas the woofer lines are not
  2. The output of the midrange line is claimed to be 40dB down from the main output
  3. The midrange transmission line does lower the resonance frequency of the driver (to 40Hz), moving it away from the crossover point and hence (potentially) simplifying the crossover
  4. The crossover slopes are 3rd order. It is not clear to me if this is stated in the literature or observed in the measurements. It is also not clear if this is electrical, acoustic, or both
  5. The design mounts the two 6″ midrange units on a 5″ wide front baffle 😉

Point #1 is not surprising given the mids are crossed over at 200Hz in the RSTL, so there is no need for any bass augmentation from the mids.

Point #5 shows just how creative John Wright is!

TDL Reference Standard Loudspeaker – Stereophile Review – December, 1989

In the December, 1989 (Vol. 12, No. 12) Stereophile, Robert Harley reviewed the original TDL Reference Standard (not the ‘M’). For the most part it was not favorable. Here are some excerpts:

Indeed, I immediately noticed an unnatural huskiness in her voice that could clearly be heard to resonate in her lower registers. This peak was also audible on piano as a “wooof” [sic] sound in the left hand. Further listening with a variety of music confirmed these impressions.

…In addition, I detected another coloration, a peak in the upper-midrange/lower-treble area that added an edge to sibilants. This peak was lower in frequency than the common 10kHz – 13kHz range where many speakers are bright. The coloration added more of a nasality and stridency rather than the spitty sound produced by other speakers with elevated top ends. Cymbals also took on a forward, splashy character without being overly tizzy in the extreme top end.

…The RSes’ imaging was somewhat better, but not convincing. …it tended to cling to the sides around the speakers. Throughout the listening sessions, I never had the impression that the speakers disappeared into the music. …just didn’t have the three-dimensionality I have come to expect from speakers.

Not exactly the speakers dreams are made of, would you say? 😉 It was not all a total loss though. After all, this is one of the most ambitious transmission line designs of all time, so hopefully Harley had some nice things to say about the bass? You betcha:

Bass reproduction through the TDL RS was easily the deepest, most effortless, and most enjoyable I have heard through any system. They present low frequencies with power and impact only hinted at by other speakers.

…In addition to this remarkable LF extension, the tonal character of the lower octaves was very neutral, without a trace of tubbiness or boom. Bass was fast, detailed and articulate. …I found myself playing recordings that featured my favorite bass players, reveling in the satisfying combination of seemingly bottomless depth and tight, punchy attack.

In Harley’s view then, the RSTL was something of a one-trick pony. This is the harshest evaluation I’ve encountered, but it is also the only one so far from a professional reviewer under controlled conditions. Next I’ll publish excerpts from the Gramophone review of the RSTL “M”. It is considerably more favorable, but also not nearly as in-depth.