SB Acoustics SB17NRX2C35-4

Overview:

 

The SB Acoustics SB17NRX2C35-4 is a 4Ω  6″ mid-woofer from SB Acoustics.

The mid-woofer has a 35.5mm voice-coil with a healthy 11mm (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.

 

Key features:

  • Vented cast aluminum chassis for optimum strength and low compression
  • Proprietary cone material with natural fibers made in-house
  • Soft low damping rubber surround for improved transient response
  • Non-conducting fiber glass voice coil former for minimum damping
  • Extended copper sleeve on pole piece for low inductance and low distortion
  • Vented coil former
  • CCAW voice coil for reduced moving mass
  • Long life silver lead wires
  • Vented pole piece for reduced compression

 

 

Note! This loudspeaker driver replaces the discountinued SB Acoustics SB17NRXC35-4

SB Acoustics Spec sheet: 6in SB17NRX2C35-4

T/S Parameters:

 

(Click on picture to zoom)

Left: T/S parameters measured using “added” mass method in horizontal position.

Right: T/S parameters measured using “known” mass method in vertical position.

The drivers where burnt-in for 3 hours at 6 Volts using a 35Hz tone and then cooled off before measuring.

Impedance:

 

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Left: Free-air impedance driver sample #1 vs. sample #2.
Right: Close-up of free-air impedance driver sample #1 vs. sample #2.

Some wrinkles in the impedance plot are visible at 1.7kHz and 6.1kHz. The wrinkle at 6.1 is the cone break-up frequency.

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.

(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).

(click on picture to zoom)

Very smooth frequency response up to 4kHz. 2.5-3kHz is about the highest suitable cross-over frequency for this mid-woofer. The cone break-up at 6.1kHz might need some attention, depending on the choosen cross-over topology.

2.5kHz is about the highest suitable cross-over frequency for this mid-woofer.

Distortion:

 

Measurement setup:

  • Mid-woofer near-field measurement at 18cm
  • Frequency Range Mid-woofer: 200-10000Hz
  • Baffle size WxH: 20×40cm

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 to high listening levels.

(click on picture to zoom)

Left: = 90dB @ 1m

Right: = 95dB @ 1m

Overall this is a very low distorting mid-woofer. We have some relatively harmless elevated second-order harmonics around 2KHz. The 6.1kHz cone break-up show up as a small elevated 3-order distortion around 2kHz. The rise in distortion at 2kHz and 95dB @ 1m is only 0.24% and is negligible.