(Click on picture to zoom)
This short blog post describes the difference between the discontinued SB Acoustics SB17NRXC35-4 loudspeaker driver and its replacement SB17NRX2C35-4. In the two pictures above you can see the old NRX driver to left and the new NRX2 driver to the right. The only visible difference is that the new NRX2 driver has a larger dust cap and the label on the backside of the magnet is different.
The questions are — Do they measure the same and is the new NRX2 driver a drop-in replacement for the old NRX driver? I will try to answer this by providing some measurements and a simple cross-over simulation below.
T/S Parameters:
(Click on picture to zoom)
Left: SB17NRXC35-4 T/S parameters measured using “added” mass method in horizontal position.
Right: SB17NRX2C35-4 T/S parameters measured using “added” mass method in horizontal position.
According to the official specification sheets, the old NRX diver should have about 2dB higher sensitivity, but in real life they have just about the same sensitivity as the new NRX2 drivers.
Impedance:
(click on picture to zoom)
Left: Free-air impedance. NRX vs. NRX2.
Right: Close-up of free-air impedance. NRX vs. NRX2.
The impedance plot is similar between the two versions, but there are some variation between 08-2kHz and for the NRX2 version the impedance plot shows a small wrinkle around 6.1 kHz, where the cone break-up is.
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. NRX vs. NRX2.
Right: Frequency response 15deg off-axis. NRX vs. NRX2.
The new NRX2 version has a smoother frequency response between 0.8-4kHz, but on the other hand more pronounced break-up modes between 4-8kHz compared to the old NRX version.
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.
(click on picture to zoom)
Left: = SB17NRXC35-4 — 95dB @ 1m
Right: = SB17NRX2C35-4 — 95dB @ 1m
Both the new NRX2 and the old NRX are low distorting loudspeaker drivers, but there are some differences due to different cone edge resonances and cone break-up modes.
Cross-over simulation:
(click on picture to zoom)
The cross-over simulation shows a simple electrical third-order cross-over with an acoustical fourth-order Linkwitz-Riley cross-over topology. As can be seen by the frequency plot the NRX2 has a smoother response, but the cone break-up modes are less suppressed compared to the old NRX version using the same cross-over.
Conclusion:
The two NRX versions are similar in many aspects, but are they interchangeable of each other in the same cross-over design?
Maybe, but some fine tuning might be necessary depending on the cross-over design. Also, another factor to consider is that if combining the two NRX versions with the same tweeter, the drivers relative acosutical off-set is about 3-4mm larger using the new NRX2 driver compared to the old NRX driver.
For further measurement details of the two NRX versions, see: SBAcoustics SB17NRXC35-4 and SBAcoustics SB17NRX2C35-4.