SB Acoustics SB17NAC35-4



The SB17NAC35-4 is a 4Ω  6″ mid-woofer from SB Acoustics.

The mid-woofer has a 35.5mm voice-coil with a 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
  • Geometrically reinforced aluminum cone for optimum piston operation and reduced break-up.
  • 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: 6in SB17NAC35-4 REV-3

T/S Parameters:


TS - SB17NAC35-4 WT2TS - SB17NAC35-4 WT3

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Left: T/S parameters measured with Smith & Larson Audio WT2 woofer tester.

Right: T/S parameters measured with Dayton Audio WT3 woofer tester.

Minor differences between the four driver unit samples. High mechanical Q-factor (Qms) and low mechanical loss (Rms).

The SB17NAC35-4 mid-woofer should work fine in 18-22 liter enclosures.



Imp - SB17NAC35-4 3L vs 4R

Note the very low inductance.




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 22cm from the top of the baffle.
Mic position: 1m distance, on mid-woofer-axis.
Smoothing: 1/24 octave smoothing applied.

Freq - SB17NAC35-4 0deg 1L vs 4RFreq - SB17NAC35-4 15deg 1L vs 4R

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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.

Freq - SB17NAC35-4 0-15-22deg

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

Freq - SB17NAC35-4 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 extended response up to about 20kHz.

It has a sloping frequency response from 1.5kHz, but it´s very smooth up to 4kHz.

The typical hard cone driver cone break-up occurs slightly above 10kHz, which is very high up in frequency for a driver in this size. The cone break-up is also very well suppresed and the geometrically reinforced aluminum cone seems to be very effective in reducing the cone break-ups.

2-2.5kHz is about the highest suitable cross-over frequency for this mid-woofer.



Measurement setup:

  • Mid-woofer near-field measurement at 18cm
  • 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.

SB17NAC35-4-#3 -- 18cm 90dbSB17NAC35-4-#4 -- 18cm 90db

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90dB @ 1m

Left = Sample #1

Right = Sample #2

SB17NAC35-4-#3 -- 18cm 95dbSB17NAC35-4-#4 -- 18cm 95db

(click on picture to zoom)

95dB @ 1m

Left = Sample #1

Right = Sample #2

The SB17NAC35-4  mid-woofer has an amazingly low distortion profile. Within its usable frequency range, the third-order distortion is below 0.2%. Above 2kHz, the relatively harmless second-order harmonics rises, but the third-order is still very low without any signs of the typical odd-order distortion peak caused by the cone break-up.

Very good performance for a low priced mid-woofer