Why this comparison?
The 2265G-1 is a service part for the JBL VRX915S Subwoofer and available as a special order. It includes JBL's own Differential Drive motor technology. More information on this unique motor architecture can be found here. The RCF L15-554K happened to be available to me and represents a more traditional motor structure and includes a copper plate to reduce distortion. Comparing these two drivers will highlight any performance advantages with JBL's differential drive technology. Although the JBL is a subwoofer and the RCF is a woofer, there should be some overlap between the two that we can draw some conclusions relating to the differential drive (if any).
The RCF has a more aggressive rising response through the 80Hz region. The RCF has a very low QTS of 0.24. JBL does not publish the QTS on the 2266.
Above 150Hz the drivers share an almost identical response out to 500Hz.
The JBL shows a strong resonance peak at 1.2kHz.
Both drivers show very similar burst decay. The JBL shows again the high Q resonance at 1.2kHz.
The JBL has a little longer group delay at 5.5ms versus 4.5ms on the RCF.
Here we see the RCF show a slightly cleaner step response that decays slightly quicker.
The impedance sweep shows my cabinet reflex tuning of 33.6Hz. The RCF dips down to 9ohms while the JBL dips down the 3.6ohms.
D2 is already at 0.50% at 95dB at 150Hz while the JBL remains low at only 0.10%. Could this be where the JBL starts to take the lead?
Increasing the SPL to 100dB has the JBL remaining still at only 0.10% (D2, 150Hz). D2 on the RCF continues to rise.
The JBL shows lower intermodulation distortion through the bass region, only creeping above the RCF at 600Hz.
Increasing the SPL to 95dB highlights the difference between these two drivers. Distortion remains low on the JBL until you get above 222Hz where the RCF holds it own. However distortion has increased on the RCF to 1.3% below 100Hz.
IM Distortion remains below 0.50% on the JBL between 50Hz - 600Hz at 100dB SPL. The RCF rises well above 0.50% IMD in the bass region.
From this data we can conclude the following:
- Has extremely low IMD in the bass and mid-bass region (<0.30% IMD)
- Is fully capable of providing audiophile sound quality from 40Hz-350Hz at 100dB SPL
- The JBL is capable ultimately lower IMD numbers than the RCF. This may be due to the JBL Differential Drive technology and it's ability to lower distortion.
- Has very low numbers as well in the mid-bass to midrange region.
- Is fully capable of providing audiophile sound quality from 80Hz-600Hz but limited to 95dB SPL if keeping below 0.50% IMD
- Struggles to achieve <0.30% IMD
What mid-bass options are there if wanting to achieve <0.30% IMD and +100dB output capability? You would have to move to a dedicated mid-bass horn. Below is an comparison between the RCF and the 1274 mid-bass front horn using dual 12" mid-bass drivers from B&C. I will be featuring the 1274 bass horn performance data in upcoming blog posts.