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In this blog post I test the RCF ND950 2.0 large format compression driver which features a 4" diameter titanium diaphragm and a copper shorting ring in the gap. The diaphragm also uses a plastic surround although it is not perforated like the smaller ND850. I purchased this driver to test.
The RCF ND950 retails for €445.00 ($495 USD) or $664 CAD. This driver is more cost affective than the Celestion Axi2050 and about the same cost as the B&C DCM50.
I tested the ND950 on the ES290 Biradial horn No.1670.
Published Data
The published response shows a somewhat irregular response with peaks across the midrange and a -5dB shelf starting at 5kHz. So certainly RCF is not attempting to embellish their data. In fact I find that RCF under publishes their data by mounting the compression driver to an under performing horn.
Impedance Sweep
The measured impedance sweep shows the FS centered at around 314Hz. There is a secondary peak right after this as well as a strong peak at 1.8kHz. We see breakup starting at 8kHz.
Frequency Response
The measured response is quite a bit smoother than published with no sign of the -5dB shelf at 5kHz. We do see a small -2.5dB drop at 8kHz. The breakup peaks at 11kHz seem well under control, perhaps the plastic surround is helping damp these out.
Extending the graph to 50kHz...
Time Domain
Burst decays shows a little stronger decay than the recently tested 18Sound ND1460.
The CSD plot shows some stored energy in the 3kHz region which is unexpected. We can see this in the frequency response as well as small disturbances.
Distortion
I tested at 85dB and 95dB. We see excellent distortion figures especially compared to the recently tested ND1460 where distortion remains low even in the 500Hz-1kHz region.
The 95dB signal shows benign H2 dominating while H3 and H4 are pushed into the noise floor of the electronics.
Intermodulation Distortion
My target for IMD is -70dB for the 85dB test signal. Here we see the ND950 actually exceed this target by about 3dB. Distortion obviously takes a rise in the breakup region starting at 9kHz.
Gedlee Metric (Gm)
I tested Gm distortion at 95dB for both 1kHz and 10kHz.
1kHz result:
10kHz result:
Subjective Listening Impressions
I found the RCF ND950 to have the same powerful and dynamic sound character as the B&C DCX464 and BMS 4590. This large diaphragm driver provided excellent clarity across the frequency bandwidth along with world class dynamics, especially on male and female vocals, being able to project into a large listening space with shocking realism and affect.
The upper treble was not as resolved as some of the smaller format drivers, but this is an expected tradeoff for the attributes mentioned above. I would suggest crossing over to a dedicated upper treble horn perhaps at around 7kHz.
Conclusion
Overall the RCF ND950 is a world class product providing excellent overall sound quality.