SB Acoustics Satori SBA-761 2.5-Way Kit by Troels Gravesen

SB Acoustics Satori SBA-761 2.5-Way Kit by Troels Gravesen

Shravanth VangaApr 25, '20

The construction here is the first of two SBA speakers designed for the DIY section of the new SBA website. These two constructions will be "open", displaying the values of crossover components, thus you are free to use whatever components you may favor. Still, a complete kit will be available from Jantzen Audio to replicate what can be seen below.

SBA made this proposition with no further strings attached. I was free to pick whatever drivers I would like and whatever type of speaker I wanted to make, being a floor-stander, stand-mount, or whatever.

A 2½-way with Satori drivers has long been on my to-do list and in particular mating the MW16 and MW19, the latter giving quite a lot extra power in the lower registers. The two drivers are very much alike except for size, thus has the same sonic signature and well suited for a 2½-way despite being slightly different in size.
The MW16+19 combined make some 277 cm^2 membrane area, close to a 10" bass driver and it pays of in bass and not least upper-bass and lower midrange. This is a very important frequency range giving volume to grand piano and the cello and if good, makes us - at least for some time - forget about the missing 15" bass driver. We can't have it all from a skinny floor-stander, but getting this frequency range right we've come a long way.
 
The MW16 is one of the few drivers allowing a 1st order crossover, thus just a single coil to this driver. Overall the crossover topology is much inspired by my two most recent constructions, thus no high-pass filter for the MW16 and having this in an smaller aperiodic cabinet allows quite some power handling.
The tweeter works 1st order down to around 2 kHz from where it gradually declines 2nd to 4th order.

The sound of speakers featuring 1st order crossovers may sound quite different from what we're used to. The naturalness of treble and midrange is unusual, and so is the dynamics. I find the SBA-761 extremely dynamic with a strong midrange presence that never gets aggressive - given you have good amplifications and source material. Having the 7½" MW19 helping at the bottom really helps throwing a decent punch and bottom weight given the overall modest size of the speaker.

Basics:

  • 2½-way, 3-driver floor-stander.
  • Dimensions: 22 x 28 x 103 cm, WxDxH (incl. feet).
  • System sensitivity: 90 dB/2.8V/1 meter.
  • Impedance: 4-8 Ohms.
  • Point of crossover: 2300 Hz.
  • Power requirement: 20+ watts/channel.
  • Power handling: 100 watts.

Drivers:

Tweeter: TW29RN-B-8

Midwoofer: MW16P-8

Woofer: MW19P-8

Crossover:

SB Acoustics Satori SBA-761 2.5-Way Kit by Troels Gravesen

The filter features a 1st order topology and overall simplicity. R4/C2 help suppressing at little too much energy of the MW19 in the 5-10 kHz range. I've tried it with and without this RC circuit and it's clearly audible when running the MW19 alone, not so much when all drivers are connected, yet I find it worthwhile not having the MW19 mingle with the treble range, even a little bit.

Should you choose different brand coils L3 can be 0.2-0.5 Ohm, L2 0.1-0.4 Ohm and L1 0.1-0.3 Ohm.

When it comes to the crossover layout, please also read this page: http://www.troelsgravesen.dk/LCR-RC.htm

Cabinet:

SBA 761 cabinet

Cabinets were made from 20 mm Baltic birch throughout. 19-22 mm MDF can be used. No further drawings or CAD files available. This is as simple as it gets. Around 2.5 sqm of 20 mm Baltic birch/MDF should be enough for two cabinets.
All internal panels except front panels were added 8 mm felt damping. 1.5 sqm in kit.
MW16 cabinet was added 125 grams wool and the Ø50 x 100 mm port stuffed with a roll of 100 x 150 mm acoustilux.
The MW19 cabinet was added two layers of acoustilux on top and behind driver, 18 x 50 cm. See photo.
The cavities next to the port at the bottom were each added 2 pieces of folded acoustilux, 18 x 50 cm. In total 12 pcs of 18 x 50 cm = ~1.08 sqm acoustilux. 1.2 sqm provided in kit.
Height above floor is 30-40 mm. I use 30 mm and the impedance graphs below is recorded with this height.
The crossover can be placed on the rear panel behind MW19 driver. You can also place the crossover at bottom to the rear by making a bigger hatch and even seal off the crossover by placing a top on the cavity like seen below. Increase cabinet depth to compensate for loss of volume.

SBA 761 crossover

For More details, and guide for construction visit : http://www.troelsgravesen.dk/SBA-761.htm

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