SBA Mini
Type: Two-way small sized loudspeaker
Enclosure type: Bass-reflex
Woofer driver unit: 12cm NRX paper cone. SBA 12MNRX2
Tweeter driver unit: 29mm Fabric dome SB29RDC-C000-4
Cross-over frequency: 3,7kHz
Frequency response: 45-25000Hz +/- 1,5dB; 98Hz -3dB; 56,79Hz -6dB; 47,71Hz -9dB
Sensitivity: 89db 1m/2.83v
Impedance: 4 Ohm
Enclosure dimensions: (height x width x depth): 265x140x235mm
Concept:
The idea is coming from my friend Grzegorz who was impressed by the capabilities of the small and cheap speaker SBA 12MNRX. Its cone is very flat (good phase), light. There is a strong magnet system and high efficiency based on 4Ohms impedance. By specification it is a midrange speaker but it will do well in bass reflex design delivering a satisfying bass response.
On top of that, my wife needed speakers for the recording studio in her piano/singing school. Good motivation! They need to be small, pretty, white and reasonable in cost.
Loudspeaker driver units selection
MidBass: SB Acoustics 12MNRX2 (https://sbacoustics.com/product/4-sb12mnrx2-25-4-norex/) due to arguments given above.
Tweeter: SB Acoustics SB29RDC-C000-4 (https://sbacoustics.com/product/sb29rdc-c000-4-fabric/) in my opinion this is a cheaper brother of TW29. I was sure this speaker would do well. Some technical reasoning: voice coil is shorter than a gap, high sensitivity, very linear. Promising set of parameters.
Cabinet
Driven by dimensions and WAF aspect I decided on a small box with a tunel bass reflex.
This is the view on box front side:
Net inner volume = 4,21 liters
Bass reflex tuning 54,3Hz
Bass reflex dimensions = 10,8 x 1,2 x 28,2 cm
Bass performance
Because the slope declines slowly e.g. 98Hz -3dB; 56,79Hz -6dB; 47,71Hz -9dB we can feel good and fast bass. Listening tests confirm that.
In making
Before SB29 was delivered I did my first tests with the XT25 Vifa speaker. It went well. Bass made a huge impression on me. It was a full GO TO project.
Measurements with final box and final speakers
Clio measurements
SB12MNRX2 measurement from 0 deg to 60 deg
We see great directivity here, playing quite flat up to 4kHz! This gave guidance for the xovr frequency.
Nearfield for bass (red) and bass reflex(black)
SB29RDC measurement from 0 deg to 60 deg
So directivity is good up to 30 deg. Bigger angle gives only reflected sound.
Crossover design
After many simulations and tests the first version was low order xovr 1st for tweeter and 2nd for bass. But the phase was not aligned well in a wide range giving poor listening results.
Then later after 6 months I decided to come back to the crossover and re-do it.
This is the effect.
Simulation:
Real measurements with final xovr
3dB peak above 10kHz is due to the microphone from CLIO; it was not corrected in the calibration file properly. Please compare simulation and real measurement for SPL and impulse response. They exactly match.
Linearity +/- 1dB!!!! Great!
In phase / out of phase(red)
Directivity with xovr
horizontal 0; 10; 30; 40; 60 deg
vertical 0 deg; 20 deg; 40 deg
Summary:
First impressions are amazing. Small speakers giving a lot of listening pleasure. Quick and somehow pleasant bass, great mid and high frequencies. A lot of details. I am in love with those speakers.
Directivity is more than acceptable even with narrow and small design.
Final view:
They go very well with my subwoofer FAT BOY both visually and acoustically.
In final environment of recording studio:
