In this blog post I will be looking at the RCF ND-850 1.4 compression driver mounted to the ES-600 Biradial Horn.
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RCF ND-850 mounted to the ES-600 Biradial (original prototype) |
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ES-600 Biradial (original prototype) |
RCF ND-850 1.4 Specifications
- 3" Diaphragm
- 1.4" Throat
- 500HZ - 20kHz
Measurement
Below is the raw frequency response of the on-axis at 1 meter mic distance.
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Raw on-axis Frequency Response for RCF ND-850 on ES-600 Biradial |
Below is the % Distortion Sweep showing D2, D3, and D4. As you can see distortion is at 0.10% across it's bandwidth.
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% Distortion for RCF ND-850 + ES-600 Biradial |
Burst Decay
The burst decay shows very clean output especially near cutoff. However there is breakup which occurs starting at 10kHz.
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Burst Decay for RCF ND-850 + ES-600 Biradial |
Off-Axis Coloured Polar Map
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Off-Axis Coloured Polar Map for RCF ND-850 + ES-600 Biradial |
Subjective listening Impressions
Because of the breakup occurring at 10kHz this driver exhibited some harshness in the upper treble. However when used as a midrange only driver in a 3-way setup the driver really comes into it's own. The midrange is palpably realistic and has genuine audiophile sound quality. There is plenty of lower midrange authority. The ES-600 Biradial horn exhibits very well behave off-axis even up to 16kHz which makes this horn suitable for a 2-way type system. However because of the breakup which starts at 10kHz this driver in stock form is really only a dedicated midrange driver.
Potential for modifications
This driver is a candidate for modification like I've done with other compression drivers. I decided to install a small amount of 30ppi open cell foam into the rear chamber so that it gently presses on the center of the diaphragm.
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30ppi open cell foam placed under rear cover |
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RCF ND-850 with rear cover removed exposing 3" Titanium diaphragm |
Below shows the resulting measurement comparison with and without the foam.
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RCF ND-850 without rear chamber foam |
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RCF ND-850 with foam in rear chamber |
As you can see below there is no difference in the measured frequency response.
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Frequency response overlay with (green) and without (red) the foam |
Distortion
Since my microphone only extends up to 20kHz I was not able to get a distortion sweep comparison for the frequency range of interest (10kHz-20kHz).