Test Bench: A Redesigned DE990TN-8 1.4” Compression Driver from B&C Speakers

June 28 2017, 10:00
The driver I examined this month was the newly redesigned DE990TN-8 compression driver coupled with B&C Speakers’ ME90 constant directivity horn (see Photo 1). This compression driver is fairly compact with a 115 mm package diameter, achieved by using a specially milled inside ring neodymium magnet. The new DE990TN-8 was updated with a completely redesigned diaphragm that incorporates a bent edge voice coil former, a new dome and surrounds geometry, and an optimized phase plug. These modifications combine to better control diaphragm displacement and deformations, resulting in lower distortion and a smoother higher frequency response above 10 kHz.
 
Photo 1: The new DE990TN-8 compression driver is coupled with B&C Speakers’ ME90 constant directivity horn.
The redesigned DE990TN-8 joins B&C Speakers’ series of 1.4” throat compression drivers, at this time numbering 14 models (seven ferrite motor compression drivers and seven neodymium motor compression drivers). However, the new DE990TN-8 is the second highest power handling (100 W) model in the line. The DE990TN-8 has a 36 mm (1.4”) throat diameter. It is driven by a titanium diaphragm with an 86 mm (3.4”) diameter voice coil wound with copper-clad aluminum wire (CCAW). Other features include a neodymium ring magnet motor structure, nominal 100 W rated power handling (200 W continuous), an injection-molded aluminum black heatsink, and color-coded chrome push terminals. The horn supplied with the DE990TN-8 is B&C Speakers’ 1.4” throat 80°H × 60°V constant directivity cast-aluminum ME90 horn with a 0.9 kHz cutoff frequency. B&C Speakers recommends a minimum 1 kHz crossover frequency (with at least a second-order high-pass active or passive filter) with a published 500-Hz-to-18-kHz frequency range.
 
Figure 1: B&C DE990TN-8 free-air impedance plot.
Figure 2: B&C DE990TN-8 on-axis frequency response.
Figure 3: B&C DE990TN-8 horizontal on- and off-axis frequency response (0° = solid; 15° = dot; 30° = dash; 45° = dash/dot; 60° = dash).
Figure 4: B&C DE990TN-8 normalized horizontal on- and off-axis frequency response (0° = solid; 15° = dot; 30° = dash; 45° = dash/dot; 60° = dash).

I used the LinearX LMS analyzer to produce the 300-point stepped sine wave impedance plot shown in Figure 1. The solid black curve represents the DE990TN-8 mounted on the ME90 horn. The dashed blue curve represents the compression driver without the horn. With a 5.94 Ω DCR, the minimum impedance of the DE990TN-8/ME90 was 7.35 Ω and at 4.2 kHz.

Next, I free-air mounted the DE990TN-8/ME90 on my manual turntable without an enclosure and measured both the horizontal and vertical on and off axis at 2.83 V/1 m using a 100-point gated sine wave sweep from 0° on axis to 60° off axis. Figure 2 shows the on-axis frequency response, which is smooth with no major anomalies. It has a declining response from 1.5 to 10 kHz with the frequency response extending all the way to 23.2 kHz before beginning its low-pass roll-off.
 
Figure 5: B&C DE990TN-8’s 0°to 90° horizontal plane polar plot (in 10° increments).
Figure 6: B&C DE990TN-8 vertical on- and off-axis frequency response (0°=solid; 15°=dot; 30°=dash; 45°=dash/dot; 60°=dash).
Figure 7: B&C DE990TN-8 Normalized vertical on and off-axis frequency response (0°=solid; 15°=dot; 30°=dash; 45°=dash/dot; 60°=dash).
Figure 8: B&C DE990TN-8’s 0°-90° vertical plane polar plot (10° increments).

Figure 3 gives the on- and off-axis response in the horizontal plane. Figure 4 shows the normalized horizontal plane response. Figure 5 shows the CLIO Pocket generated horizontal polar plot (with 1/3 octave smoothing applied). Figure 6 gives the on- and off-axis response in the vertical plane. Figure 7 depicts the normalized vertical plane response. Figure 8 shows the CLIO Pocket generated vertical axis polar plot (also with 1/3 octave smoothing applied). Figure 9 has the two sample SPL comparison showing the two DE990TN-8 compression driver samples to be closely matched within less than 1 dB.

For the remaining tests, I set up the Listen, Inc. AmpConnect ISC analyzer and 0.25” SCM microphone and power supply to measure distortion and generate time-frequency plots. For the distortion measurement, I mounted the DE990TN-8/ME90 combination in free air and set the SPL to 104 dB at 1 m (2.08 V, which I determined using a pink noise stimulus generator and internal SLM in the SoundCheck 14 software). I measured the distortion with the Listen microphone placed 10 cm from the mouth of the horn. This produced the distortion curves shown in Figure 10.

I set up SoundCheck 14 to generate a 2.83 V/1 m impulse response curve. Next, I imported the data into Listen’s SoundMap Time/Frequency software. Figure 11 shows the cumulative spectral decay (CSD) waterfall plot. Figure 12 shows the Short Time Fourier Transform (STFT) plot.
 
Figure 9: B&C DE990TN-8 two-sample SPL comparison.
Figure 10: B&C DE990TN-8 SoundCheck distortion plots.
Figure 11: B&C DE990TN-8 SoundCheck cumulative spectral decay (CSD) waterfall plot.
Figure 12: B&C DE990TN-8 SoundCheck Short Time Fourier Transform (STFT) plot.

Italian pro sound B&C Speakers is a consistent OEM, with great build quality, performance, and engineering, and the new DE990TN-8, like last month’s DE1090TN, falls into that category.
For more information, visit www.bcspeakers.com.

This article was originally published in Voice Coil, September 2016.
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