Rossman Art

CBT36 Speaker Build

by Rossman Art | Dec 9, 2018 | Steampunk

1. About the CBT36

The CBT36 gets its name from its acoustic design—Constant Beamwidth Transducer—and the 36 degree arc of the cabinet design. Coincidentally, between the left and right channels, there is also an array of 36 full-range mid bass drivers. Designer Don B. Keele’s video series explains the engineering behind the cabinets in great detail in the CBT Chronicles and is what first sparked my interest in the technology and the design.

After reading about and listening to various line-array designs, I became convinced that the CBT approach offered advantages over more conventional speakers, which radiate low, mid, and high frequencies from separate sources and can produce a less consistent listening experience as you move around the room.

The CBT36 addresses many of these issues through a shaded array, with the speaker’s distinctive curvature playing an essential role in controlling its acoustic output—not simply serving as a visual flourish.

Here are a few photos of the completed right channel. The following sections document my build and finishing process.

Inventory and testing

The CBT36 kit arrives in three boxes: two with the MDF cabinets and one with the drivers, electronics, hardware, and an 80+ page illustrated manual. It starts with an inventory of the hundreds of components needed for the build.

Some components require testing before the build, especially since replacement parts take time to ship. I found issues with two full-range drivers and a tweeter array that needed replacing. I also returned the cabinets—there’s a reason the manual says to keep the shipping boxes! See if you can spot why I rejected them.

Veneering the front panels

There are too many build steps for one post, so I’m focusing on customizing the front panels. Rather than use the glossy automotive finish chosen by some builders, I wanted a vintage furniture look. I veneered the inner driver bevels using card templates and thin adhesive mahogany veneer. No additional panel prep was needed.

Here is a shot of a few of the cutouts and how I positioned them with the wood grain following the midpoint of each curve. I did this in anticipation of how the veneer would get trimmed in relation to the grain running down the face of the panels. I wanted a contrasting pattern that spread the light out differently on the beveled veneer.

Here are trimmed veneer pieces applied to the panel bevels. I used a soldering iron to heat and burnish them firmly in place, then trimmed the excess with a single-edge razor blade. A finished bevel is visible in the upper right.

Before veneering the driver bevels, I airbrushed cutout markings onto longer sheets of mahogany veneer. I used an X-Acto knife for larger holes, a leather punch for smaller ones, and an Optivisor for precision. Each cutout was left slightly oversized or respectively undersized for final trimming after application.

With all rough cutting completed the front veneer is carefully positioned so that all the edges overlap each hole with additional veneer ready for precision trimming. I used a domestic iron to heat cure the veneer to the MDF, folding the edge of the veneer around the the camphor edges of the panel. Then I used an Exacto blade to do the final precision trimming.

Here I am using a rotary grinding bit to speed up the trimming process on the tweeter holes. There are 72 of these holes on each panel, so the grinder was essential for keeping the time spent on each hole down to about 5 minutes. Careful attention was taken not to enlarge the holes any more than the original MDF, which is about as thick as the vener in these areas.

The final stage in the veneering process was lots hand sanding! I used sanding blocks for the flat sections starting with 320 grit paper, working up to 600 grit. The beveled holes and tweeter holes required the same attention with small hand held sanding strips.

I repeated the trimming, application, and sanding on the second panel, then used Minwax Pre-Stain and Old Maple to enhance the mahogany grain and red tones. After drying, I polished both panels with 1200-grit sandpaper and sealed them with carnauba wax. Total time: nearly 150 hours.

Assembly

Here are the front panels flipped over on a felt lined workstation to protect the finish while mounting the drivers. I have just begun the wiring process at this stage. Most of the electronics assembly is covered in the manual, so I will just focus on some of the areas I deviated from the instructions to customize the look of the speakers, and enhance the build.

The manual had suggested mounting all the resistors with a hot glue gun, but I opted for a technique I read in the forums using zip ties. I also applied acoustic foam between each resistor and the mount to eliminate the possibility of any component causing vibration inside the cabinet.

I used the same technique to fasten bundles of wires down the length of the array for both the full range drivers and the tweeters.

The same wire-fastening method is used here. Each circuit board holds four tweeters and is connected with jumpers and wiring as specified in the manual. Before installation, I tested and ranked each driver’s impedance, placing slightly lower-impedance drivers toward the top of the panel.

Here is the right panel fully wired for testing. I did testing twice since there is no margin for error once the wires and circuits are soldered into place. The first test confirmed all the drivers worked, and that the shading was correct. The second test confirmed the same results with the soldering complete.

The left panel underwent the same testing before sealing the cabinets with 20 wide-flange brass bolts, which I preferred to the kit’s black hardware. Compressible rubber washers seal the cabinet and protect the front panel. Only some bolts are installed here because I opened the cabinets several times during testing.

Additional links still working as of August, 2026:

D.B. Keele — Constant Beamwidth Transducers — Keele’s primary technical resource, including CBT history, theory, papers, CBT36 description, measurements, and related designs. D.B. Keele CBT page
D.B. Keele — Official Website — Main site, with links into his CBT research and material on the CBT36 prototype. D.B. Keele official site
Keele-Omholt Technologies — CBT Papers & Presentations — Includes B&W 801 vs. CBT36 measurements, CBT demonstrations, theory, and technical presentations. Keele-Omholt CBT papers
Keele — B&W 801 vs. CBT36 Technical Paper — Particularly useful technical comparison of the CBT36's ground-plane behavior against a conventional high-end loudspeaker. B&W 801 vs. CBT36 paper
Dayton Audio — CBT36K Assembly Manual — Probably the single most detailed document on the actual production CBT36: construction, driver wiring, Legendre shading, DSP, crossover, impedance, sensitivity, measurements, theory, and setup. CBT36K complete assembly manual
Parts Express Project Gallery — CBT 36 Circular Arc Line Array — Construction overview, driver arrangement, enclosure, DSP, performance, and design explanation. Parts Express CBT36 project page
Audio Artistry — CBT36 Product/Technical Page — Original manufacturer's material on the CBT36, including design rationale, system configuration, CBT theory, and technical links. Audio Artistry CBT36 page
Audio Artistry — 2011 CBT36 Introduction — Don Keele's own description of the production CBT36, drivers, DSP requirements and system implementation. Audio Artistry CBT36 2011 page
Audio Artistry — Original U.S. Navy CBT Papers — Background research from which Keele developed the loudspeaker implementation. Original Navy CBT research
Stereophile — Don Keele & the CBT36 at RMAF 2011 — John Atkinson's first-hand listening impressions and explanation of the 36° curved ground-plane array. The page title incorrectly says “CRT36,” but the article is about the CBT36. Stereophile RMAF CBT36 report
Stereophile — Audio Artistry CBT36 at T.H.E. Show 2012 — Listening report emphasizing how little the tonal balance changes with listening position. Stereophile CBT36 2012 report
Stereophile — Don Keele's Circular-Arc Speakers, AXPONA 2013 — Another first-hand CBT36 demonstration and discussion of its sound-field behavior. Stereophile CBT36 AXPONA report
diyAudio — “Constant Beam Width Transducers line arrays” — One of the most important independent technical discussions. Don Keele himself enters the thread at post #79 and gives a lengthy explanation of the CBT36. diyAudio master CBT discussion
diyAudio — CBT36 Sensitivity — Detailed discussion of sensitivity, power requirements, tweeter performance, crossover frequency, distortion and owner modifications. diyAudio CBT36 sensitivity thread
diyAudio — CBT36 vs. Linkwitz LX521 — Excellent owner-level comparison, including comments from people who actually built and operated CBT36s and discussion of revised MiniDSP crossover settings. diyAudio CBT36 vs. LX521
AMB Laboratories — Epique by Dayton Audio CBT36 — Massive 13-page owner/build thread documenting construction, DSP setup, modifications and listening impressions. One of the best surviving CBT36 resources. AMB CBT36 build thread
AMB Laboratories — New CBT36 Build — A second CBT36 owner construction thread with cabinet and assembly observations. AMB New CBT36 thread
AMB Laboratories — κDCX / CBT36 History — Detailed explanation of why one CBT36 owner modified the Behringer DCX2496 used as the CBT36's active crossover/DSP. AMB CBT36 and DCX2496 discussion
Parts Express TechTalk — CBT36 Array Tests — Early testing and development discussion surrounding the CBT36 production design. CBT36 Array Tests
Parts Express TechTalk — CBT36 Tests with MiniDSP — Particularly worthwhile because Rick Craig, who worked with Keele on CBT36 setup and measurements, discusses alternative crossover/DSP configurations and subjective performance. CBT36 MiniDSP tests
Parts Express TechTalk — What Do the Dayton CBT36K Sound Like? — Owner/listener impressions and links to other historical CBT36 discussions. CBT36K listening discussion
Parts Express TechTalk — CBT36 Flying Hardware Assistance — Discussion of using CBT-type arrays in larger spaces; also contains useful subjective comments on neutrality, crossover behavior and voice reproduction. CBT36 installation discussion
AudioCircle — “Has anyone heard the Audio Artistry CBT speakers?” — Important owner discussion; includes CBT36 owners and technical comments on dispersion, room interaction and subwoofer integration. AudioCircle CBT36 owner thread
AudioCircle — Sykora Sound Technologies / CBT discussion — Later discussion of CBT36, CBT24, Rick Craig's involvement with Keele, driver-quality limitations and subsequent CBT development. AudioCircle later CBT discussion
AudioCircle — “The Next Step…” — Historical discussion from people close to the project while the production CBT36 was still being finalized. AudioCircle CBT36 development discussion
Audioholics — Audio Artistry CBT36 — Six-page home-theater-oriented discussion covering amplification, DSP, subs, room size and expected performance. Audioholics CBT36 thread
Audiokarma — CBT36 Line Array Speaker System — Early discussion of the original Parts Express/Audio Artistry kit and its technical requirements. Audiokarma CBT36 thread
StereoNET — Audio Artistry CBT36 — Discussion of the design, active crossover, horizontal dispersion and listening experiences at audio shows. StereoNET CBT36 discussion
What Hi-Fi Forum — “Speakers immune from room effects?” — Long discussion prompted specifically by the CBT36 and its unusually uniform room response. Includes discussion of Keele's measurements and people considering/building the kit. What Hi-Fi CBT36 discussion
Aktives-Hoeren — Audio Artistry CBT36 — German-language discussion of the two-way architecture, 90 drivers per cabinet, active operation and CBT theory. Aktives-Hoeren CBT36 thread
AudioNervosa — Constant Bandwidth/Beamwidth Transducer — Historical discussion following Keele's development and the introduction of the Parts Express kit. AudioNervosa CBT discussion
SourceForge / Equalizer APO — Linkwitz-Riley Filters and CBT36K — Discussion of implementing the CBT36's required DSP crossover and EQ in software rather than the original Behringer/DEQX hardware. Equalizer APO CBT36 crossover discussion
Manualzz — Audio Artistry CBT36K Manual mirror — Live HTML-accessible mirror of the original manual, useful if the Dayton PDF ever disappears. Manualzz CBT36K manual
Facebook — recent 2026 DIY “Dubbel” CBT36 clone project — A currently active project explicitly based on/reworking the CBT36, including measurements and enclosure/damping changes. May require Facebook login. 2026 CBT36 clone discussion

There are several especially important resources here if your goal is to understand or reproduce the design: Keele's own CBT page, the 108-page CBT36 assembly manual, the 15-page diyAudio thread, the 13-page AMB build thread, Rick Craig's MiniDSP testing thread, and the B&W 801 vs. CBT36 measurement paper. Those six collectively contain most of the useful technical information that survives online.

Steampunk Wacom, Part 1 (The Stylus)

by Rossman Art | Nov 9, 2014 | Blog, Featured, Hands On, Steampunk

The inspiration for this Steampunk Wacom stylus (and soon to be completed tablet, Part 2) was born out of two events that coincided a few years ago. One was the fact that every so often I need to upgrade my equipment to support new software and features. The other was a chance find of an antique lap desk at the local swap shop (technically, the dump) around the time my Intuos 2 became a dust gatherer. I hate getting rid of graphics stuff like this so "What to do with it?" was top of mind.

A lap desk is a throwback to a Victorian era travel necessity for any well connected globe trotter that needs to keep up with correspondence. Perhaps a lap desk could be considered the laptop of the 1800's. It certainly makes sense based on name and function. The surface layout of a Wacom tablet (especially an Intuos 2) is remarkably similar to the divide between the richly veneered wood and felt on the business surface of a lap desk. There are also cool compartments that come along with a lap desk design that can serve as storage space for a stylus and those tiny tips that I keep losing. Although in disrepair, I didn't want to cannibalize the lap desk for parts since it was nearly intact and a little on the small side. Instead I began a slow and methodical process of selectively collecting objects and materials I could use and re-manufacture into like components, all from recycled parts of course!

Original Intuos 2 Stylus

I worked first on the stylus (unmodified original shown on the left) knowing that this would be the most intricate work. Must-have materials in any good Steampunk creation are always brass, wood, and leather. This led me to work out a design for the stylus based off of airbrush, fountain pen, and clock parts which I had lying around. The stylus has three controls other than the tip. The rocking button in the middle of the stylus looks like a single slim button, but once one gets into the guts of the stylus it is clear that the button design triggers two independent toggles on the internal circuit board. The third control is the digital eraser on the back end of the stylus.

Trigger assembly close-up

A rocking motion is an ideal movement for dual trigger mechanisms found on most airbrushes which is why I chose to modifiy the rocking button assembly by mounting a trigger from an old Passche airbrush on top of it. See my Custom AB post for comparison with the image above. This actually works better for me since the trigger puts my finger in a more relaxed position above the stylus, and I don't have to move my finger to opposite ends of a button bar to toggle the two controls. Instead I just use the trigger's rocking motion the same way I would control paint flow on an airbrush. Coincidentally I also happen to own an airbrush version of the Wacom stylus which is even more awkward to use than a traditional button stylus. I was always baffled by Wacom's choice of a hybrid mouse wheel over a traditional airbrush trigger on that device. Wacom built pressure sensitivity into the stylus tip. Why not do the same for virtual paint flow on a trigger?

Tip assembly close

I chose 1/2 inch brass tubing for the stylus body and discovered early on that any type of metal at the front of the stylus interferes with the signal reception at the tip. I changed my design as a result of this, and decided to modify and cover the existing stylus body with non metallic materials. In this case, I used a strip of leather from an old wallet interior applied with a strong cyanoacrylate adhesive, and behind that, permanent black ink from an overhead projection marker to mask the original color of the light gray body. I was able to get away with a gilding process at the tip using 24 carat gold leaf probably because its such a thin metal. The important thing is that it works! The assembly required precise cutting of the stylus body, leather, and brass tubing, plus the manufacture of a small brass strip to cover the rocking button.

Finial assembly close

At the opposite end of the stylus I sacrificed the eraser functionality for a bit of decorative metallic flair. I never got used to flipping my stylus around like a pencil when I could instantly toggle the eraser by moving the function to the back toggle on the trigger. The finial at the end of the stylus is a decorative gold plated band from an old 1930's fountain pen and a finial from a Schatz German table clock. Those parts were merged together with a few threaded brass parts I had laying around (not sure where they came from) and some foil tape typically used for masking photo slides. The foil tape was used to help non-threaded parts like the pen ring fit snugly over the other brass parts. This one detail makes the design LOOK Victorian.

Stay tuned for Part 2 of this post, where I will discuss the process I went through in finding and assembling recycled parts for the tablet's body.

Produce invisible watermarking in photoshop without a plug-in

by Rossman Art | Oct 2, 2014 | Blog, Hands On

Where is the watermark?

Digital watermarking is often seen as a light but visible mark within an image, and can include a logo or URL to show copyright ownership. It is there for everyone to see (and remove). Invisible watermarks take this concept a step further and make the watermark less obvious and harder to remove. Digimarc is an invisible watermarking filter for Photoshop and is automatically included as a default. It is supported by a third party, Digimarc, and requires a subscription to take full advantage of it's features. Its purpose is to embed an invisible watermark into an image to protect against copyright infringement and track the use of the image on the web. Digimarc works on two fronts. It embeds an invisible (strong) watermark into an image by encoding information (Author name and creation date) into a noise tolerant image’s least significant bits. That information is also stored in a database and can be cross-referenced against other copies of the same image all over the web. If an unauthorized use is discovered, the original author can prove who they are beyond any reasonable doubt and call out the infringing party.

I had a problem with copyright infringement of my own and thought Digimarc might be a perfect solution, but discovered that Digimarc’s service would not access the virtual world server where my texture images were stored. This roadblock inspired me to come up with my own type of invisible watermark using Photoshop to regain control over both the stored data, storage method, and file format. It is also important to note that the Digimarc filter can still be used to embed a second watermark into the same image if needed for distribution on the web.

Here are the steps I use for invisible digital watermarking in Photoshop:

Give the original image a New Channel for encoding information. This converts it to a carrier file.
Generate a second black and white image of the same dimensions and place multiple copies of a QR code in it. This is the information file which can carry contact information, a URL, or any message.
Run a Gaussian Blur on the QR code to soften the edges so it will blend well with the carrier file image. Test this with a code scanner, then Copy and Paste it into the New Channel in the carrier file.
Select part of the carrier image using the newly created Alpha Channel, Copy, then Paste it as a New Layer. This produces a second layer with only the coded portion of the image. It should be completely invisible at this point.
To embed the code as imperceptibly as possible, run a Hue Saturation adjustment (altering the image hue by no more than five steps) and add 3% noise into the image with a noise filter. More alterations can be added if needed, but the general idea is to cover the coded layer with noise that uniformly alters the pixels slightly through all colors and shades.
If the effect is too harsh the Opacity of the layer can be reduced to make the effects more subtle.
Copy Merged, Paste the coded image into a New File, Flatten it and Save it to any popular file format (JPEG, PNG, Targa)
Calculate the Difference between the original master file and the encoded file, Copy Merged, Paste into a New Layer. Run an Equalize adjustment on that layer to reveal the code again.
To make the code readable under higher compressions, copy and compress the master file, then repeat steps 7-8.

This steganographic method may not be as sophisticated as Digimarc’s, but works for my application needs and gives a stealthy tracking mechanism for policing my work on a virtual world server hosting lossless JPEG 2000 file formats. It also survives moderate resizing, cropping, and compression. Best of all, it can be done entirely within Photoshop’s tool set without need of a third party add-on or a subscription.

Cat image

Coded cat image

Raw extracted code

Enhanced code

rossmanart.com Receives an Upgrade

by Rossman Art | Sep 18, 2014 | Blog

The old rossmanart.com has a new face on the web. The URL is the same, but new content is better integrated with the major social tools we all use, as evidenced by this post (published @ rossmanart.com and distributed to various social platforms through WordPress). This upgrade will allow Rossman Art to easily reach out to and build upon an existing audience without the added burden of maintaining and propagating isolated content. Credit for the back-end development goes to Elegant Themes for their Divi theme using the WordPress content management system. The major portion of the site still remains a portfolio showcase, but new sections have been added for a Blog and custom curated Newsletter (through paper.li). I visit this newsletter daily to keep up on the latest trends in science, technology, and art. The site is open to subscribers, so anyone can can join to receive updates whenever new content is posted. Those interested in contributing content can contact Rossman Art and ask to have their subscriber status upgraded to Contributor, or Author.

I hope everyone enjoys the new and responsive look of the site!

Best,

Jeff Rossman

Customized Paasche AB Turbo

by Rossman Art | Sep 12, 2013 | Blog, Hands On

An Overview of the Customized Parts on My Paasche AB:

This is an old how-to I resurrected from two previous generations of rossmanart.com. It's been informative to people in the past, and also explains a bit how I use this device.

For those unfamiliar with turbine driven airbrushes, it all started over a century ago in 1879 with an invention by Abner Peeler called the Paint Distributor. This was a system that delivered paint into an airstream on the end of a reciprocating needle. Others developed Peeler's original design into the lighter and smaller instrument seen here. Thanks to Jens Paasche, the modern AB made its debut in 1904, and little has changed with the version still produced today. Most airbrush designs opt for a simple linear mixing of paint and air, but a modern AB remains true to the original design of Peeler's, and has few rivals when it comes to finely controlled paint dispersal. This is a testament to the genius of the AB's design.

Costomized Turbo_top_In_Hand

A normal AB has better control over paint flow than most other airbrushes, so why mess with it?*

The AB's only flaw is its temperamental behavior due to the complexity of its moving parts. This is the reason I chose to modify my own AB. The three main controls , trigger, speed regulator, and stipple adjuster all need regular fine tuning to maintain top performance. Simply put, I wanted finer tuning and better performance, and was going to do whatever it took to get it. I started by making small changes to some of these control variables to fit the AB to my illustrative technique. The first thing that I changed was the long red stock AB handle. I replaced it with a much shorter rubber insert (an eye dropper bulb) seen at #4. Holding the AB this way felt more natural to me. Other modifications followed. Hopefully this tacit knowledge will inspire other AB users with a wish to tinker.

Customization Overview*

Here is a general overview of the five areas of my AB that I have customized for comfort and better performance . (1) A Sharpened needle tip to take advantage of the trigger's precision control. (2) A Low profile grease cup screw (not shown) for comfort. (3) Custom blast jet to narrow the air blast for better performance with a sharper needle. (4) Shortened handle for comfort and easier handling. (5) Dual trigger assemblies: The short one, shown here for comparison. The longer one allows for finer needle control.

The Trigger Assembly*

I use this extended trigger assembly for better control when moving the needle in front of the blast jet. With a longer lever the thumb/finger must travel a greater distance to move the needle. This simple change is a borrowed trigger assembly from another Paasche V airbrush. It is very easy to switch between this and the original short trigger by tightening each assembly by hand. This allows for easy loosening and doesn't strip the delicate brass threads. I rarely use the short trigger any more, so this one stays put.

Needle & Customized Blast Jet*

The combination of a smaller blast hole and sharpened needle is key to my AB's performance enhancement. These two changes alone will significantly enhance a factory model AB. They are examples of what I term "the Maker mindset" - a DIY way of using existing tools to make better tools. My custom blast jet produces a stream of air about half the diameter of the factory supplied blast jet. I made it from a .125" solid brass rod using a jewelers motor, sharpening stone, and micro drill bits. A tighter spray diameter coupled with a sharper needle produces a very thin line. The airbrush needle needs perfect alignment with the front of the blast hole for this to work. Also, I run the air pressure slightly higher than the recommended 25-35 PSI, but no more than 50 PSI to compensate for the narrower blast.

Front view of the customized blast jet*

This angle shows the sharpened needle extended in front of the custom blast jet. There is a narrow window of tolerance where the needle performs best in front of the blast jet. This is all fine tuned by adjusting the needle bend & sharpness, needle bearing, and angle of the paint cup. As long as there is little impact to the airbrush or damage to the needle or walking arm, these adjustments only need setting once until the needle needs replacement.

Sharpening a needle*

The taper on an original needle lengthens by sharpening its tip. This allows for greater control of the spray diameter over a greater distance of needle travel. This graphic shows the difference in a hairline spray diameter between a standard needle and a sharpened one. The red arrows indicate the area of increased performance. The dotted black arrows indicate the effective spray area along the needle. I use a sharpening stone with a jewelers motor to sharpen my needles. However, 1500-2000 grit sand paper also works well. I use this kind of sand paper often to polish and remove dried paint from my needles. This sharpening technique is also documented in "The Complete Manual of Airbrushing" by Peter Owen & Jane Rollason (now out of print, but available through Amazon). I highly recommend getting it if you own an AB.

Disclaimer:

*DO NOT modify your Paasche AB airbrush as described above if you don't have experience maintaining it! Always consult the official AB instruction manual and parts list before attempting any adjustment or alteration to your AB!

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