Test Bench: B&C Speakers DE680TN 1.4" Exit Pro Sound Compression Driver

September 5 2018, 09:00
The transducer I examined in this Test Bench came from Italian OEM manufacturer B&C Speakers. The DE680TN-8 compression driver is the latest addition to B&C Speakers’ extensive 17 model ferrite and neodymium motor 1.4” exit compression drivers. In terms of features, the DE680TN-8 is designed for use with 1.4” throat horns, which means it has a 36 mm (1.4”) throat diameter and a field replaceable titanium diaphragm driven by a 65 mm (2.5”) diameter voice coil wound with copper-clad aluminum wire (CCAW) on a high Qm non-conducting former. The titanium diaphragm has been redesigned and incorporates a new bent-edge former along with a new dome and surrounds geometry (see Photo 1).
 
Photo 1: The B&C Speakers DE680TN-8 titanium diaphragm.
Photo 2: B&C Speakers supplied the ME90 horn for use with the DE680TN-8.

Other features include a neodymium ring magnet motor, a nominal 80 W-rated power handling (160 W continuous), a 1.2 kHz recommended crossover frequency (second-order or higher high-pass filter), and 2.83 V/1 m 108 dB sensitivity. 

B&C Speakers supplied the ME90 horn for use with the DE680TN-8 (see Photo 2). This constant directivity horn has a 1.4” exit bolt on type made from cast aluminum, and provides an 80° × 60° coverage pattern and a 900 Hz cut-off frequency, making it a good match for the DE680TN-8 compression driver.
 
Figure 1: B&C Speakers DE680TN-8 free-air impedance plot (blue) and (solid black curve) representing the DE680TN-8 mounted on the ME90 horn.
Figure 2: B&C Speakers DE680TN-8 on-axis frequency response.
Figure 3: B&C Speakers DE680TN-8 horizontal on- and off-axis frequency response (0° = solid; 15° = dot; 30° = dash; 45° = dash/dot; 60° = dash).
Figure 4: B&C Speakers DE680TN-8 normalized horizontal on- and off-axis frequency response (0° = solid; 15° = dot; 30° = dash; 45° = dash/dot; 60° = dash).

I began testing using the LinearX LMS analyzer to produce the 300-point stepped sine wave impedance plot shown in Figure 1, with the solid black curve representing the DE680TN-8 mounted on the ME90 horn and the dashed blue curve representing the compression driver without the horn. With a 5.62 Ω DCR (Re), the minimum impedance of the DE680TN-8/ME90 was 7.26 Ω and at 4.58 kHz.

For the next set of SPL measurements, I free-air mounted the DE680TN-8/ME90 combination without an enclosure and measured both the horizontal and the vertical on- and off-axis at 2.83 V/1 m, again using the LMS gated sine wave sweeps to produce both the horizontal and the vertical plane SPL data from 0° on-axis to 60° off-axis.

Figure 2 illustrates the on-axis frequency response of the compression driver/horn combination, which is smooth with no major anomalies with a declining response as frequency increases above 2 kHz, and extending to somewhat beyond 20 kHz, requiring the usual constant directivity horn equalization.

Figure 3 depicts the on- and off-axis response in the horizontal plane. Figure 4 shows the normalized horizontal plane response. Figure 5 shows the CLIO Pocket analyzer-generated 180° horizontal polar plot (in 10° increments with1/3 octave smoothing applied). Figure 6 gives the on- and off-axis to 60° response in the vertical plane. Figure 7 depicts the normalized vertical plane response. Figure 8 shows the CLIO Pocket-generated vertical plane polar plot (in 10° increments with 1/3 octave smoothing applied). Figure 9 illustrates the two-sample SPL comparison showing the two B&C Speakers DE680TN-8 compression driver samples to be very closely matched within less than 0.5 dB throughout the operating range of the transducer.
 
Figure 5: B&C Speakers DE680TN-8 0°-180° horizontal plane polar plot (in 10° increments).
Figure 6: B&C Speakers DE680TN-8 vertical on- and off-axis frequency response (0° = solid; 15° = dot; 30° = dash; 45° = dash/dot; 60° = dash).
Figure 7: B&C Speakers DE680TN-8 normalized vertical on- and off-axis frequency response (0° = solid; 15° = dot; 30° = dash; 45° = dash/dot; 60° = dash).
Figure 8: B&C Speakers DE680TN-8 0°-180° vertical plane polar plot (in 10° increments).

I again set up the Listen AudioConnect analyze, SoundCheck 16 software, and the Listen 1/4" SCM microphone to measure distortion and generate time-frequency plots. For the distortion measurement, I mounted the DE680TN-8/ME90 combination in free-air in the same manner as was used for the frequency response measurements. Then, I set the SPL set to 104 dB at 1 m (1.85 V) and measured the distortion with the Listen 1/4" measurement microphone located 10 cm from the mouth of the horn. This produced the distortion curves shown in Figure 10 (red curve = second harmonic, blue curve = third harmonic). 

I then set up SoundCheck 16 to generate a 2.83 V/1 m impulse response for this driver/horn combination and imported the data into Listen’s SoundMap Time/Frequency software. The resulting CSD waterfall plot is given in Figure 11 and the STFT plot is shown in Figure 12.

The DE680TN-8 displays excellent performance for a fairly high power handling package, and is a nice addition to B&C Speakers' extensive lineup of ferrite and neodymium motor compression drivers. For more information about this or any other B&C Speakers product, contact B&C Speakers N.A., National U.S. Sales Office, at 220 W. Parkway, Unit 11, Pompton Plains, NJ 07444, e-mail Bennett Prescott, call (973) 248-0955, Fax (973) 248-0956, or visit www.bcspeakers.com. VC
 
Figure 9: B&C Speakers DE680TN-8 two-sample SPL comparison.
Figure 10: B&C Speakers DE680TN-8 SoundCheck distortion plots.
Figure 11: B&C Speakers DE680TN-8 SoundCheck CSD waterfall plot.
Figure 12: B&C Speakers DE680TN-8 SoundCheck STFT plot.

This article was originally published in Voice Coil, June 2018.
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