This webpage documents the construction of a pair of Jeff Bagby designed Kairos speakers and their associated woofers, built fall 2016.
1. Intro to the Kairos
3. Kairos cabinets
4. Woofer cabinets (and bases)
7. Final assembly
Jeff designed the Kairos back in 2012-13 to utilize the then-new Satori tweeter and mid-woofer. He added a woofer design in 2015 to make a full range 3 driver system.
The Kairos is special in that it uses very high quality drivers, which are mated with Jeff's very sophisticated crossover magic* to create a quasi-transient perfect design.
"... it is very close to being a
minimum phase / transient perfect system and will preserve transients and time domain information
better than all but a couple of speakers available on the market today. The speaker is exceptionally
linear in both the frequency domain and the time domain and offers a level of performance not often
found at any price."
The mid and tweeter are from the SB Acoustics high end line called Satori, made in Indonesia. I understand the design engineers are former Scan-Speak designers, and the Satori products compete with the Scan-Speak Revelator and Illuminator product lines.
Above: The Satori SB29R
ring dome tweeter. 2 part faceplate for mechanical decoupling, non-resonant diaphragm, vented pole, low resonance (600hz). Also note the integrated gasket, so no foam gasket need be used on the cabinets. This tweeter is available with the outer ring in silver, as shown above, or black, as in my speakers.
Above: The Satori MW16P mid-woofer. Neodymium magnet, papyrus based cone material, vented pole, copper sleeve on pole. Also with integrated gasket.
Above: the SB Acoustics SB29NRX75-6 10" woofer. Note the large pole vent at the rear.
3. Kairos Cabinets
The cabinet construction started with one 5' by 5' sheet of 3/4" baltic birch and one
4' by 8' sheet of 3/4" Medex MDF, supposedly an upgrade over traditional MDF (among other things, better moisture resistance and formaldehyde free). The FSC (Forest Stewardship Council) certification indicates the wood was harvested sustainably. Along with a few spare pieces of baltic birch from my stock, I was able to build both pair of Kairos speakers and the associated woofers.
Above: The cabinet construction technique I used is based on George Short's Cabinet Handbook (George was the founder and President of North Creek Music, now with Wisdom Audio). It calls for 1.5" front and rear panels laminated with baltic birch and MDF using a soft glue (Aleenes Tacky Glue). The cabinet tops, bottoms and sides are MDF, and all braces are baltic birch (If I recall correctly, because it resists compression and expansion). This photo shows the front and rear panels being laminated together. This was done for both the Kairos cabinets and the woofer cabinets.
Above: I made a couple jigs from scrap wood (one shown on the right here) to route the cutouts in the baltic birch internal braces (on the left).
Above: The Kairos cabinet parts (except fronts), cut and ready for assembly. The sides are routed both for stronger joints and to correctly (and easily) align the parts during assembly. The internal braces are rounded over with a 1/4" roundover bit for smooth air movement in the cabinet - probably not necessary, but it just takes a couple minutes..
Above: Test fitting the Kairos cabinets, slanted front is to the left. I made one change form the stock design: I wanted the crossover external (for accessibility), so I designed a recess in the bottom for the crossover, and made the cabinets deeper to keep the cabinet volume the same. Also, since I was planning to use them with the woofer Jeff designed, the cabinets are sealed, not vented. Note the two braces have not yet had cutouts made (shown earlier).
Above: Kairos cabinets partially assembled. The small wooden block near the front are to cover the threaded inserts that will be used for the spiked feet. The tops were not yet attached to allow the damping material to be installed...
Above: Damping material installed between the braces. I used Sonic Barrier from Parts Express. Note that dacron batting, per Jeff's original design, was also added just before final assembly.
Above: Once the damping material was installed and the tops glued in place, I veneered the cabinets, shown in progress here. I used a single 4' by 8' sheet of of cherry from TapeEase.com for both the Kairos and woofers. I decided to veneer the backs in cherry also, and used some extra veneer from my stock for the backs.
Above: Routing the driver recesses and thru-holes, after veneering. I use a Jasper Jig (shown at the top above attached to my Dewalt router) for this process - makes it quick and easy.
Above: Test fitting the drivers to the front panel, including checking the 45 degree chamfered recess in the back to allow unrestricted airflow - mandatory with extra thick baffles.
Above: Fitting the solid cherry trim for the 1/2" roundover on the sides and top of the cabinets. Once that trim was glued in place, the cabinets were sanded to 320 and stained.
Above: The cabinets mid-finishing. They were first treated with Minwax pre-stain wood conditioner, then stained with Watco Danish Oil Finish - Cherry color. Then a coat of Waterlox Sealer/Finish (to highlight the grain), then several coats of spray polyurethane finish, with light sanding between every coat.
Above: The crossover cavity in the bottom of the cabinet. Note the M6 threaded inserts for the spiked feet at the front and rear of the cabinet.
Above: Once the poly finish had dried, a coat of black paint on the bottom finished the Kairos cabinets.
4. Woofer Cabinets (and bases)
Above: The woofer construction progressed simultaneously with the smaller Kairos cabinets. Shown above is the pile of woofer cabinet parts after cutting to size.
Above: Woofer parts after machining driver cutouts, routing for braces, etc. The braces are on the top. Like the Kairos, the front panels were veneered before routing the cutout for the driver.
Above: The rear woofer panels. You can see the lamination of the mdf and baltic birch. Also shown is the channel I cut to route the cable from the input at the base of the woofer to the rear of the Kairos.
Above: Test fitting the woofer cabinet parts, the cabinet is on its side here.
Above: Test fitting the woofer driver.
Above: Rear (inside) view of the woofer driver, showing the chamfering around the woofer cutout. Cabinet braces have just been started here with only 1 of 12 baltic birch braces in place.
Above: Once the woofer cabinet was assembled and the baltic birch braces added, I applied the side damping material. For the woofers, I used the North Creek "glop" (the white stuff above), consisting of Aleenes's Tacky Glue mixed with drywall compound in a 2:1 ratio. It is applied to one side, then has to dry for a day before rotating the cabinet for the other side.
I decided to build the woofers as sealed boxes instead of vented, as I planned to use them mostly with subs, and in general like the sound of sealed systems. I'm hoping that combined with room gain, these will play low enough that I'll be happy. However, I spaced the braces to allow me to add the 3" vent per Jeff's vented design if I later decide otherwise.
Above: Once the cabinets were assembled and veneered, I added some solid cherry trim ("shoulders") at the top to match the width of the Kairos cabinets. Above shows those parts being glued in place.
Above: Woofer cabinets stained and finished. Next up: building a base...
Above: Solid 3/4" oak used for the base, during assembly. The base has 3 purposes: to raise the speakers to the correct height, add some protection for the cherry veneered cabinets from vacuum cleaners, etc, and as a location to house the woofer crossover.
Above: To mount the spiked feet, I countersunk 1/4" heavy duty T-nuts into a piece of baltic birch (shown upside down above), then glued it to the base. In this configuration, the T-nut is captive and cannot come loose.
Above: Captive T-nut mounting glued in place.
Above: The bases are designed to be about 1/2" wider than the woofer cabinets all around, and are beveled at a 10 degree slant to mate with the woofer cabinet. Here I'm test fitting the binding posts.
Above: Bases were completed with a coat of satin black. They are mounted to the bottom of the woofers with 6 screws each, so if they get scuffed or damaged, they can be removed and repaired and/or repainted.
Above: Woofer mounted to the base. Also attached are the Soundcare Superspike feet, which have an integral base for the spike (to protect wooden floors). I've also attached the female grille mounts.
Above: The cabinets are shown here completed, and are ready for crossover assembly.
5. The Crossovers
Note: The crossover for the woofer section (both high and low pass) has graciously been made available by Jeff Bagby (see link at top of this page), so those component values are visible and/or listed in my description. The Kairos crossover is, however, proprietary, so I've obscured the values of the components. As mentioned above, the Kairos kit (and the woofer kit as well) are available from Meniscus Audio (who are very helpful and highly recommended).
Above: The woofer crossover. For the 3 ohm resistor, I used a 1% 50 watt non-inductive Dale resistor, mounted on an aluminum plate for some heatsinking. The 200uf cap is a Solen polypropylene. The cable to the right goes into the cabinet and to the woofer. All wiring for the system is AudioQuest Type 4, and I used about 16' total for both the Kairos and woofer sections. The twisted pairs of red and black cables attached to the binding posts on the left are simply jumpers going up the channel in the rear panel to connect to the Kairos.
Above: The Kairos crossovers, mounted in the base of the cabinet, binding posts are on the right side but hidden from view. I upgraded the tweeter cap to an M-Cap Supreme, and the resistors to Mills 1% 12 watt units. The 150uf cap (for the high pass section of the woofer crossover) is composed of three 50uf polypropylene caps bypassed with a 0.47uf Sonicap. The 10 Ohm resistor in the woofer crossover is upgraded, like in the low pass section, to a Dale 50 watt 1% non-inductive resistor mounted on a heatsink. Again, the values of the Kairos crossover have been obscured here as they are proprietary.
I did make one slight change from the stock Bagby crossover design. The default design calls for the 150uf high pass caps to the Kairos to be in series with the entire Kairos crossover, including the tweeter circuit. I simply bypassed the 150uf caps for the tweeter circuit, connecting that circuit directly to the inputs and eliminating the large cap from the tweeter circuit (which has its own high pass components, obviously).
Although it is trendy to have speakers with no grilles, we have children and housecleaners around occasionally, so they are mandatory in my case.
Above: Fitting the grilles to the Kairos cabinets. These grilles are made of 3/8" baltic birch, and the woofer grills were made 5/8" thick to accommodate the longer excursion of the woofers.
Above: I added 1/4" thick felt around the inside of the grill near the tweeter to help control diffraction, in a similar fashion to the felt around the tweeter in the LS3/5a speakers (this felt in fact was left over from an LS3/5a repair). With this felt in place, my OmniMic measurements indicated virtually no changes in frequency response with and without the grills.
Above: A Kairos grill being assembled. For grill material, I like to use material that Magnapan uses on their speakers. It is significantly lighter and more transparent than most other grille cloth I've seen.
7. Final Assembly
Above: Cabinets with acoustic stuffing. The woofer cabinets used polyester fiberfill, and the Kairos speakers use dacron batting, per the original Bagby design. You can see the Audioquest Type 4 cable used for the entire system here, ready for driver connections.
Above: Cabinets with the drivers mounted.
Above: Front view with the grilles in place.
Above: Side view, clearly showing the slanted Kairos design.
Summary: The system has been breaking in for the past few days, and I'm very pleased with the results. Very high resolution, not at all fatiguing, deep extended bass (after I spent some time experimenting with room position).