The DE640-16 is shown in Photos 1-3 along with the Eighteen Sound XT1464 60°×50° coverage horn. The DE640, along with the new B&C Speakers DCM414 midrange compression driver and the DE360 (discussed in Voice Coil, May 2018 and available here) represent a line of two-point suspension (the normal outside perimeter that interfaces with the voice coil, and at the center of the diaphragm) ring radiator type compression diaphragms. One of the major advantages of the two-point ring radiator suspension is suppression of rocking modes. The Advent hifi speaker used one of the first ring radiator high-frequency devices in audio.
The horn I used in conjunction with the DE640-16 was from B&C Speakers’ sister company Eighteen Sound, the Eighteen Sound XT1464. This elliptical flare horn has a 1.4” exit bolt-on type mounting flange and is made from injection-molded polyurethane. The XT1464 provides a 60°×50° constant directivity coverage pattern and a 800Hz cut-off frequency (constant directivity from 1.5kHz upward), making it a good match for the DE640 compression driver. Figure 1 and Figure 2 give the horizontal and vertical directivity maps for the Eighteen Sound XT1464.
Testing began using the LinearX LMS analyzer to produce the 300-point stepped sine wave impedance plot shown in Figure 3, with the solid black curve representing the B&C Speakers DE640-16 mounted on the Eighteen Sound XT1464 horn and the dashed blue curve representing the compression driver without the horn. With an 8.75Ω DCR (Re), the minimum impedance of the DE640/XT1464 was 11.25Ω and at 6.4kHz.
For the next set of SPL measurements, I free-air mounted the B&C Speakers DE640/XT1464 combination without an enclosure and measured both the horizontal and vertical on- and off-axis at 2.0V/0.5m (normalized to 2.83V/1m) from 0° on-axis to 60° off-axis using the Loudsoft FINE R+D analyzer and the GRAS 46BE microphone (supplied courtesy of Loudsoft and GRAS Sound & Vibration).
Figure 4 displays the on-axis frequency response of the DE640/XT1464 combination, which is ±2.5dB from 800Hz to 17kHz with no major anomalies throughout its operating range from 1kHz recommended crossover frequency to about 18kHz.
Figure 5 shows the horizontal SPL data from 0° on-axis to 60° off-axis, with the normalized version depicted in Figure 6. Note, since Eighteen Sound supplied the horizontal and vertical directivity maps for the XT1464, I chose not to do the vertical SPL measurements, and just provided the horizontal polar plot using the CLIO Pocket analyzer (Figure 7). Last, Figure 8 illustrates the two-sample SPL comparison showing the two B&C Speakers DE640-16 compression driver samples to be very closely matched ≤0.5dB throughout the operating range of the transducer up to 10kHz.
For the remaining series of tests, I set up the Listen AudioConnect analyzer, SoundCheck 21 software, and the Listen ¼” SCM microphone to measure distortion and generate time-frequency plots (courtesy of Listen, Inc.). For the distortion measurement, the DE640/XT1464 combination was again mounted in free air in the same manner as was used for the frequency response measurements, and the SPL set to 104dB at 1m (1.65V determined by using a pink noise stimulus generator and internal SLM in the SC21 SoundCheck software). I then measured the distortion with the Listen ¼” measurement microphone located 10cm from the mouth of the horn. This produced the distortion curves shown in Figure 9 (red curve=second harmonic, blue curve=third harmonic). Note the very low third harmonic, in fact, it’s so low, the second harmonic totally tracks the THD curve.
Next, I set up SoundCheck 21 to generate a 2.83V/1m impulse response for this driver/horn combination and imported the data into Listen’s SoundMap Time/Frequency software. Figure 10 shows the resulting cumulative spectral decay (CSD) waterfall plot, and Figure 11 shows the Short Time Fourier Transform (STFT) plot.
The DE640-16 ring radiator displays excellent performance and is definitely an interesting new addition to B&C Speakers’ extensive line-up of neo motor 1.4” compression drivers. For more information about this new driver and other pro sound products from B&C, contact B&C Speakers. E-mail Bennett Prescott, or visit www.bcspeakers.com. VC
This article was originally published in Voice Coil, September 2024.