MPB's Continuum speakers

This page documents the construction of a pair of Jeff Bagby designed Continuum speakers, so named as they are designed to continue the spirit of the BBC LS3/5a speakers, but with improvements made possible by modern driver technology and design techniques. Compared to the original LS3/5a, the Continuums have lower distortion, greater bass output and higher overall SPL.

The original write-up of the Continuum (with frequency response and impedance graphs) is available at the site here.

Meniscus Audio (website link) sells Continuum kits and are highly recommended.

The Continuums were originally designed using the Aurum Cantus AC130F 5.25" poly cone woofer along with the Dayton RS28A-4 tweeter, since discontinued. Because the Continuum is such a popular design, and the Dayton tweeter is no longer available, Jeff has redesigned the speaker into the Continuum II using a Morel CAT-308 tweeter. Since I had a pair of the Dayton tweeters available, I built the original version of the Continuums.

See my build of Jeff Bagby's Kairos 3 way speakers here.

The following photos show the construction process for my Continuums.

Routing the front baffles.  The tweeter hole is at the right in this photo, and the woofer at the left.  The woofer hole is recessed from the back to rear-mount the woofer.  Later, I'll add a roundover on the front of the woofer hole.  The cabinets will be finished in cherry, and the front panel shown here is a laminate of 3/4" solid cherry and 1/2" baltic birch.  All holes and recesses were made with a router using a Jasper Jig.

Rear side of the front panel showing holes drilled (with a forstner bit) to mount hidden magnets to hold grilles.

Back side of face showing the magnet holes filled with silicone to hold the neodymium grille magnets in place.

The basic cabinet parts shown here machined, sides and top already veneered, and ready for assembly.  You can see the rear recess for the woofer on the panel on the right, and the roundover from the front side on the panel on the left.  Since I used thicker front and rear panels than the Meniscus/Bagby plans, I adjusted the depth to keep the cabinet volume constant.  In addition, I wanted a clean look to the face of the speakers, so unlike the Meniscus plans which call for a removable front panel (like the original LS3/5a), I built a fixed front panel and removable rear panel.

Test assembly.  You can see the corners do not yet have the angled solid cherry trim in place.

Cabinets assembled, ready for damping material.  Note the oak battens at the rear for the rear panel to screw into.  The front and rear panels are solid cherry stock laminated to baltic birch ply.  The sides, tops & bottoms are 3/4" baltic birch with cherry veneer.

Cabinets after staining, Waterlox to bring out the grain, and polyurethane (5 coats, sanded between each coat).  The bottom was painted black.

After cabinet damping added.  I used the recipe that George Short, of North Creek Music, detailed in his Cabinet Handbook from some time ago.  Its a mixture of tacky glue and sheetrock compound that very effectively damps the panels.

Crossover assembled on the back panel and wired up to the drivers.  Damping material has been added to the cabinets and they're ready to be sealed up.  Not visible due to the damping material, but the woofer has already been mounted from the rear at this time.  The crossover was built using the stock parts supplied with the Meniscus kit except I used Sonicaps in the tweeter circuit.  The inductors are glued in place with construction adhesive, the caps with silicone glue.

Rear panel screwed in place.  I typically use Superior 5 way gold binging posts.

Assembled speakers, front and rear view.

Test fitting grille frames (done earlier in the process, before the drivers were installed).  Note the holes at the 4 corners to hold neodymium magnets in locations to correspond to the magnets in the front panel of the speaker.

Initial measurements using my Liberty Instruments IMP/M (old but reliable and easy to use).  My first measurements showed an even higher Qt, but I added some additional stuffing to lower the Qt which also slightly raised Fs to the numbers shown above.  Note these and all measurements below are with very little break-in for the woofer. 

Frequency response measurements made with Dayton OmniMic at 30inches. Ignore the very low end. This graph shows the excellent left to right matching.

Measurements showing the effect of the grilles, red is no grille, blue is with the grille in place.

Finally, measurements of the Continuum (red) compared to an early 15 ohm Rogers LS3/5a (blue). Note there was no change in the signal level, indicating the speakers are quite similar in efficiency.

Continuums next to a Rogers LS3/5a.  My Continuums are slightly larger due to the use of 3/4" baltic birch (vs 1/2" baltic birch in the LS3/5a) and the fact that my front and rear panels are double thickness.  The extra lumber also causes my Continuums to weigh 16.4 pounds each vs 11.4 for the Rogers speaker.

Another view do the Continuum next to the Rogers Ls3/5a, without their grilles.

I built these speakers because they're great speakers with a great reputation in the DIY community, but I also built them to warm up my woodworking skills for a more challenging (or at least physically demanding) project, here.

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