The 3D CAD file for this product can be found HERE.
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In this blog post I test Horn No.1689 which is a circular 800Hz Fc horn using a 1" throat. This horn features the latest ES horn flare curvature which has an even higher rate of expansion and correspondingly larger horn mouth. These changes further improve response flatness near the cutoff as well as improve the directivity characteristics.
Construction
The horn design features a new driver mounting method which requires the use of a large tee-slot cutter mounted in the CNC machine. The fee-slot cutter cuts the undercut requires to install the M6 nuts onto the driver’s threaded studs. 
A pedestal feature is integrated into the rear of the horn which simplifies mounting.
Measurements
I began testing the horn using the RCF ND350 compression driver.
Frequency Response
Off-Axis Coloured Polar Map
Showing same result however as a waterfall 1 is shown below:
Showing same result however as a waterfall 2 is shown below:
Showing same result however as a line map is shown below:
Burst Decay
Cumulative Waterfall Plot
Step Response
Intermodulation Distortion
Passive Crossover
I rigged up a passive crossover to flatten the response.
Overlaying the crossover response with the raw response is shown below.
SB Audience ROSSO 45CDN-PK
I then decided to test another compression driver. The results for the SB Audience 44CDN-PK shown below.
Frequency Response
The 44CDN-PK does not need the contour network to achieve a flat response.
Burst Decay
Cumulative Waterfall Plot
Step Response
Intermodulation Distortion
The SB Audience shows some resonant behaviour both in the 5kHz and 10kHz region which can be observed in the burst decay, waterfall, and IMD plot.
Faital Pro HF108R
I then tried a third compression driver. The HF108R is shown below.
Frequency Response
The HF108R shows the same falling response as the RCF ND350.
Burst Decay
Cumulative Waterfall Plot
Step Response
Intermodulation Distortion
The Faital Pro shows good performance free of any serious issues across its bandwidth until 10kHz where we see some mild stored energy low down in the noise floor, however this doesn’t show up in the IMD plot.
Passive Crossover
I then decided to use the same passive crossover as used with the ND350 and achieved the following result.
Comparing without the crossover is shown below.
Subjective Listening
https://tidal.com/browse/track/2073069
Overall, I preferred the RCF. Following closely in sound quality was the Faital Pro. The RCF had more body to the vocal region and instruments sounded a little more smooth. However both drivers provided audiophile grade sound quality and I would be happy with either.
the SB Audience lost a little clarity and refinement compared to the other two driver brands.
Conclusion
It was very easy to hear every subtle nuance in the soundtrack making for a very enjoyable listen. It was easy to compare the three compression drivers since the horn gave each driver the best chance of sounding their best. The horn definitely controlls the coverage pattern right down to 600Hz which allows this horn to be used with a variety of woofer sizes even up to 12". The added control definitely improves overall clarity as room reflections are kept low. Adding to this clarity, you can see by the off-axis polar map, this horn is completely free and devoid of any colouration or resonances that may harm sound quality.