In this blog post I compare the latest version of 5" woofer from SB Acoustics against the previous. The first version SB15NRXC30-8 has been replaced by the second version SB15NRX2C30-8.
I use this driver in my 1159 stand mount speaker and so the change from SB Acoustics required that I update the 1159 to suit the newer version. Details on the 1159 can be found at my two blog posts:
The original data sheet on the version 1 speaker can be found here.
HiFi Compass also tested the version 1 woofer here.
Since this change requires a full set of measurements to confirm any crossover changes I decided to compare the two version against each other to see if SB Acoustics made any improvements with the latest version.
While making the change I also decided to switch from the 8ohm version to the 4ohm to match the existing tweeter which is also 4ohm.
Measurements
Below is a comparison between the two woofers. The new version 2 woofer had to be lowered 1.5dB to match the 8ohm woofer's sensitivity. The version 2 shares a similar frequency response with the version 2 driver producing a flatter response past 1kHz. Burst decay shows a cleaner result in the 1-2kHz region as well. Beyond 2kHz the version 2 woofer has a falling response where the main resonance peak develops starting at 5kHz similar to the version 1 woofer. Overall the version 2 provides a modest improvement in linearity across it's frequency band.
Intermodulation Distortion
With the test rig placed outdoors I was able to conduct an IMD comparison to see if the new woofer excelled in the distortion department.
A quick note on IMD
Multiband intermodulation distortion is a good stress test to examine a driver's overall clarity. The multitone test signal closely represents that of a musical signal. The multiband test tone generates many side band spurious tones that are very inharmonic in nature. These side band artifacts raise the noise floor and conceal low level detail from the musical content. For my own designs, I target less than 0.50% IMD (-46dB), and if possible this should be achievable at a listening level of 90dB at the listening position.
Test Results
Click the image below to expand the image. The version 1 woofer is on the left column and the version 2 results are on the right column. These measurements conclude that there is virtually no difference between the two versions.
What we can conclude generally regarding both woofers is that they provide acceptably low distortion below 80dB. This restricts their usage to small listening rooms which seems kind of obvious considering these are only 5" woofers. However it's interesting to see this objectively shown through measurement. It's too bad that this is not commonly published by manufacturers to help consumers select an appropriately sized speaker for their listening space and listening level.
Also worth noting is that the harmonic distortion test isn't isn't quite as good as the IMD multitone test at accurately determining the maximum SPL. A sine sweep test signal used for the harmonic distortion measurement does not adequately stress the driver in the same way as a multitone IMD test. To demonstrate this I've shown a harmonic distortion sweep at 90dB. The 2nd order harmonic distortion product at 1kHz is only 0.12%, and yet the an IMD test at the same SPL produces 1% distortion.
Test result summary (spoiler alert: both versions identical)
Version 2 woofer
IMD @ 80dB = -50dB down (0.31%)
IMD @ 85dB = -46dB down (0.50%)
IMD @ 90dB = -40dB down (1.0%)
IMD @ 95dB = -36dB down (1.5%)
Version 2 woofer
IMD @ 80dB = -50dB down (0.31%)
IMD @ 85dB = -46dB down (0.50%)
IMD @ 90dB = -40dB down (1.0%)
IMD @ 95dB = -36dB down (1.5%)
Updated crossover in the 1159 stand mount speaker.
Below is the updated frequency response for the 1159 stand mount speaker using the version 2 woofer.
The updated crossover produces the following frequency response.
Subjective Impressions
The version 2 woofer provides the same tonal characteristic and sound quality as the version 1. Overall this woofer provides a smooth listening character.