Overview:
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).
Impedance:
Note the very low inductance. A minor wrinkle in the impedance plot at 1.2kHz.
Frequency:
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.
(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.
0deg = Blue
15deg = Red
22.5deg = Green
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.
Distortion:
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.
(click on picture to zoom)
90dB @ 1m
Left = Sample #1
Right = Sample #2
(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