(Click on picture to zoom)
This short blog post describes the difference between the SB Acoustics SB17NBAC35-4 and the SB17NAC35-4 mid-woofers. In the picture above you can see the NBAC driver to left and the NAC driver to the right. The only visible difference is the color of the aluminium cone.
The questions are — Do they measure the same and is the only difference the color of the cone? I will try to answer this by providing some measurements below.
T/S Parameters:
(Click on picture to zoom)
Top: SB17NBAC35-4 vs. SB17NAC35-4 T/S parameters measured using “added” mass method in horizontal position.
Bottom: SB17NBAC35-4 vs. SB17NAC35-4 T/S parameters measured using “known” mass method in vertical position.
According to the official specification sheets there are some small difference between the two versions. The measured T/S parameters also show small differences, but in reality it could be the variations between different production batches.
Impedance:
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Left: Free-air impedance. NBAC vs. NAC.
Right: Close-up of free-air impedance. NBAC vs. NAC.
The impedance plot is similar between the two versions. The cone break-up is slightly higher up frequency for the NAC version, 10kHz vs 9.7kHz for the NBAC version.
Frequency:
Frequency measurement conditions:
The mid-woofer is measured mounted on a baffle in an 17.6 liter closed enclosure with the following conditions:
Baffle size (WxH): 20×40cm. No baffle edge round-over.
Driver position: Mounted on center-line with driver unit center 17cm from the bottom of the baffle.
Mic position: 1m distance, on mid-woofer-axis.
Smoothing: No smoothing applied. Measurement valid down to 275Hz.
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Left: Frequency response on-axis. NBAC vs. NAC.
Right: Frequency response 15deg off-axis. NBAC vs. NAC.
Virtually the same frequency response. The slightly different cone break-up mode is visible around 9.7-10kHz.
Distortion:
Measurement setup:
- Mid-woofer near-field measurement at 18cm
- Frequency Range Mid-woofer: 200-10000Hz
- Baffle size WxH: 20×40cm
The distortion measurement shown is done in near-field and the amplifier output level was adjusted so that the fundamental is 95dB at 1m. This setting simulates a high listening level.
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Left: = SB17NBAC35-4 — 95dB @ 1m
Right: = SB17NAC35-4 — 95dB @ 1m
Both versions are very low distorting drivers.
Conclusion:
The NBAC and NAC versions are very similar in measurements and they are they interchangeable of each other in the same cross-over design. The small differences shown above are most likely caused by measuring different production batches. In fact there are a couple of years between the production of the above mid-woofers, so consistency seems to be good between production batches.
The only real difference between the two versions is the color — Pick your favorite color and looks!
For further measurement details of the two versions, see: SBAcoustics SB17NBAC35-4 and SBAcoustics SB17NACC35-4.