SB Acoustics SB15MFC30-4



The  SB15MFC30-4 is a 4Ω  5″ mid-woofer from SB Acoustics.

The mid-woofer has a 30.5mm voice-coil with a healthy 10mm (p-p) linear coil travel. It has a very low voice-coil inductance and is fitted with a copper sleeve on the pole piece to ensure a low distortion performance. The cone is made of mineral filled Polypropylene (PP).

Key features:

  • Vented cast aluminium chassis for optimum strength and low compression
  • Mineral filled PP-cone made in-house
  • Soft low damping rubber surround for improved transient response
  • Non-conducting fibre glass voice coil former for minimum damping
  • Extended copper sleeve on pole piece for low inductance and low distortion
  • CCAW voice coil for reduced moving mass
  • Long life silver lead wires
  • Vented pole piece for reduced compression


Considering its features, build quality and measured performance this mid-woofer has a very high price/performance ratio.

SB Acoustics Spec sheet: 5in SB15MFC30-4

T/S Parameters:



Good consistency between the driver unit samples. Higher Fs and slightly higher sensitivity than official specs.

The mid-woofer has a high mechanical Q-factor (Qms) and low mechanical loss (Rms).



SB15MFC30-4_Imp 1L vs 2R WT3

Note the very low inductance. A minor wrinkle in the impedance plot at 1.2kHz.



Frequency measurement conditions:

The mid-woofer is measured mounted on a baffle in an 14 liter closed enclosure with the following conditions:

Baffle size (WxH): 24×35cm with 18mm round-over on the baffle edges (r=18).
Driver position: Mounted on center-line with driver unit center 21,5cm from the top of the baffle.
Mic position: 1m distance, on mid-woofer-axis.
Smoothing: 1/24 octave smoothing applied.

SB15MFC30-4_Freq 1L vs 2R 0degSB15MFC30-4_Freq 1L vs 2R 15deg

(click on picture to zoom)

Left: Frequency response on-axis (Blue=sample#1 Red=sample#2).
Right: Frequency response 15deg off-axis (Blue=sample#1, Red=sample#2).

The two mid-woofer samples measures virtually the same. Smooth frequency response up to 4kHz.

SB15MFC30-4_Freq 0-15-22deg

0deg = Blue
15deg = Red
22.5deg = Green

SB15MFC30-4_Freq 30-45-60deg

30deg = Blue
45deg = Red
60deg = Green

Due to the mid-woofers very low inductance and flat impedance response, the on-axis frequency response has an extremely linear and extended response up to 10kHz.

The broad hump between 0.5-1.5kHz is partly due to the shape of the baffle and the baffle step.  We have a minor notch centered at 1.5kHz due to the low loss surround causing a cone edge resonance. It has a very smooth frequency response between 1.6kHz and 4kHz

3.5-4kHz is about the highest suitable cross-over frequency for this mid-woofer.



Measurement setup:

  • Mid-woofer near-field measurement at 15cm
  • Frequency Range Mid-woofer: 200-10000Hz
  • Baffle size WxH: 24×35cm


The distortion measurements are done in near-field and the amplifier output level was adjusted for each driver so that the fundamental is 90dB and 95dB at 1m. This setting simulates medium-high and high listening levels.


SB15MFC30-4-1L -- 15cm 90dbSB15MFC30-4-2R -- 15cm 90db

(click on picture to zoom)

90dB @ 1m

Left = Sample #1

Right = Sample #2

SB15MFC30-4-1L -- 15cm 95dbSB15MFC30-4-2R -- 15cm 95db

(click on picture to zoom)

95dB @ 1m

Left = Sample #1

Right = Sample #2

Overall this is a low distorting mid-woofer. We have the expected relatively harmless elevated second-order harmonics due to the cone edge resonance.

Elevated third-order distortion at 6kHz indicating some break-ups at 18kHz, most likely due to the hard plastic dust cap.

Good performance for a low priced mid-woofer