In this blog post I test the Kartesian CMP50-VPA-S 1" compression driver. I purchased a pair of these drivers for testing purposes from toutlehautparleur (translates to "all speaker") in France. I wanted to investigate the possibility of using this model in my Autumn Series of DIY plans with the goal of introducing a 10" 2-way onken style using the ES-800 Biradial No.3073.
About Kartesian
| Feature | Details |
|---|---|
| Founded | 2011, near Strasbourg, France |
| Specialization | High-end driver design & manufacturing (woofers, tweeters, etc.) |
| Engineering Approach | Custom driver variants, advanced tools, performance-focused R&D |
| Industry Role | OEM/ODM and components provider for Hi-Fi, pro audio, and high-end brands |
The key features of the CMP50-VPA is the larger 2" diaphragm compared to the more common 1.70" that we would see in this size category (small format). It is my assumption that the larger surface area will provide a more open sound quality by virtue of the lower distortion gained by the larger diaphragm surface area. The larger diaphragm results in 38% more surface area.
Other details include:
- €142.83 each ($228.80 CAD)
- Grade Y40 Ceramic Magnet
- Optimized pole pieces design made of low carbon steel
- Demodulating ring (Aluminum)
- Treated Titanium Diaphragm
- "Accurate sounding with very low THD from 1kHz to 20kHz."
Side Note: VPA (Vapor Phase Aluminide) coating is a process used to enhance the corrosion and oxidation resistance of aluminum.
What caught my attention was the low FS of this driver. For use with the ES-800 Biradial it is critical for the FS to be lower in frequency than the low frequency cutoff point of the horn (800Hz).
The published data shows a usably flat response from FS (630Hz) to 20kHz using an exponential horn 258mm deep. This horn depth would provide a cutoff (Fc) of 325Hz which is quite a large horn for a 1" compression driver.
My own measurements confirm that the FS is at 600Hz. This is much lower than the RCF ND350 which has an already low FS of 1kHz. The response graph below shows the raw frequency response (blue) against the response with a 3.9uF capacitor (Red) along with the raw impedance curve (grey), mounted on the ES-800 Biradial No.3075.
The measured response is flatter than published with breakup free performance out to 17kHz.
I decided to measure harmonic distortion with the 3.9uF capacitor in place since this more closely represents a real life use case for the driver. At the 95dB test signal level we see H2 predominate hovering around the 0.10% distortion mark. H3 and H4 are below the noise floor (0.003%) with the exception of a small rise in centered around the 6kHz region.
In any case, harmonic distortion is well below the audibility threshold for domestic listening.
The CMP50-VPA shows a clean CSD waterfall.
The burst decay is also relatively clean even with the vertical scale increased to 35dB.
Conclusion
The Kartesian CMP50-VPA is a well performing driver from a measurement standpoint. As a result I plan to investigate its use for the Autumn Series 10" 2-way DIY Plan Set by evaluating its subjective sound character in a highly optimized stereo setup.
