CBT36 Speaker Build

by | Dec 9, 2018 | Steampunk

CBT36 Speaker Build

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.

CBT36 Speaker Build

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.