The 745NEOBe Compression Driver from Radian Audio

March 12 2018, 06:00
I featured two of Radian Audio’s aluminum alloy diaphragm 2” compression drivers, the 760NeoPB and the 950PB, in the November 2014 issue of Voice Coil. It terms of corporate history, Radian Audio Engineering, Inc., was founded in 1988 by its president, Dr. Richard Kontrimas, however, Kontrimas has since retired and the company is under new ownership. Radian Audio’s initial offerings were replacement compression driver diaphragms. The diaphragms did so well that it wasn’t long before the company started making compression drivers. Several major loudspeaker manufacturers quickly identified Radian Audio as an important source for their compression driver needs and became OEM customers. Coaxial loudspeakers were introduced shortly thereafter, followed by woofers and finally, complete loudspeaker systems.
Photo 1: Radian Audio’s 745NEOBe available with either a structural aluminum or a beryllium diaphragm.
Photo 2: Since Radian does not manufacture horns, I used a B&C ME90 constant directivity cast aluminum horn.
Figure 1: Radian 745NEOBe free-air impedance plot (solid black curve = driver with horn, blue dashed curve = compression driver only).
Figure 2: Comparison of both beryllium (solid black curve) and aluminum (dashed blue curve) diaphragm free-air impedance curves (no horn).

Today, Radian Audio, based in Orange, CA, is a major player in the OEM loudspeaker component business, the sound contractor/fixed installation market and the portable/tour sound industry. With more than two decades of success under its belt, Radian Audio is now entering its third decade as a pro sound manufacturer.

For month’s Test Bench review, Radian sent me one of their latest beryllium diaphragm 1.4” compression drivers, the 745NEOBe. Beryllium is an insanely expensive material, but also extremely detailed and musical sounding. (The aluminum diaphragm for the 745NEO costs about $101, while the beryllium is six times more at $601). I have developed a high end two-channel product using Scan-Speak beryllium tweeters, and the beryllium diaphragm material really does subjectively sound very musical and detailed.

The Radian Audio aluminum alloy (a proprietary mix of aluminum, titanium, and copper) diaphragms also sound absolutely amazing, which is why they have such a great reputation among recording studios and PA speaker manufacturers. Because both materials, Radian’s proprietary aluminum alloy and beryllium, are known for their musicality, Radian also sent a pair of aluminum diaphragms so that I could do an objective comparison! This you will find rather interesting.

In terms of features, the 745NEOBe has a 5 to 20 Hz frequency range, a 76.3 mm (3”) voice coil diameter wound with edge-wound copper clad aluminum wire on a high temperature polymer former, available with both structural aluminum or beryllium diaphragms (see Photo 1), a neodymium ring magnet motor structure, a heat stabilized polymer suspension that greatly reduces second- and third –order harmonic distortion, a self-aligning diaphragm assembly, 220 W continuous program power handing, 111 dB sensitivity, and gold-plated color-coded push terminals. Since Radian Audio does not manufacture horns, I used a B&C ME90 80° × 60° constant directivity cast aluminum horn (see Photo 2).
Figure 3: Radian 745NEOBe on-axis frequency response.
Figure 4: Comparison of both beryllium (solid black curve) and aluminum (dashed blue curve) diaphragm on-axis frequency response.
Figure 5: Radian 745NEOBe horizontal on- and off-axis frequency response (0° = solid; 15° = dot; 30° = dash; 45° = dash/dot; 60° = dash).
Figure 6: Radian 745NEOBe normalized horizontal on- and off-axis frequency response (0° = solid; 15° = dot; 30° = dash; 45° = dash/dot; 60° = dash).

I began the driver characterization process by using the LinearX LMS analyzer to produce the 300-point sine wave impedance plot shown in Figure 1. The solid black curve represents the beryllium diaphragm 745NEOBe mounted on the ME90 horn and the dashed blue curve represents the beryllium compression driver without the horn. Figure 2 shows the impedance for both the aluminum and beryllium diaphragms without the horn (the beryllium impedance curve is solid black and the aluminum diaphragm is the dashed blue curve). With a 5.45 Ω DCR, the minimum impedance above the resonance frequency of the beryllium 745NEOBe mounted on the 80° × 60° horn was 7.1 Ω at 1.99 kHz. 

For the next group of frequency response tests, I surface mounted the Radian Audio 745NEOBe and ME90 horn in free-air and measured the horizontal on- and off-axis from 0° to 60° at 2.83 V/1 m using a 100-point gated sine wave sweep. Since Radian Audio did not manufacture the horn, I didn’t bother with the vertical axis measurements. Figure 3 shows the on-axis response of the beryllium compression driver/horn combination, which is smooth ±1.75 dB with no major anomalies from 1 kHz out to 6 kHz and a declining response as frequency increases using the constant directivity horn. Figure 4 compares the on-axis response of the beryllium diaphragm to the aluminum diaphragm. 
Figure 7: Radian 745NEOBe horizontal axis CLIO 180° polar plot (in 10° increments).
Figure 8: Radian 745NEOBe two-sample SPL comparison.
Figure 9: Radian 745NEOBe beryllium diaphragm SoundCheck distortion plots.
Figure 10: Radian 745NEO aluminum diaphragm SoundCheck distortion plots.

Radian Audio’s recommended minimum crossover frequency for the 745NEO is 800 Hz with a fourth-order slope. Figure 5 gives the on- and off-axis response in the horizontal plane, with the normalized version of the horizontal plane response shown in Figure 6. Figure 7 shows the CLIO polar plot. Last, Figure 8 details the two-sample SPL comparison showing the two beryllium diaphragm 745NEOBe compression driver samples to be very closely matched.

Next, I fired 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 Radian Audio 745NEO and horn combination in free air on my measurement stand at the same as the frequency response measurements and set the SPL to 104 dB at 1 m (1.86 V for the beryllium diaphragm and 1.52 V for the aluminum diaphragm as determined by using a pink noise stimulus and internal SLM in the SoundCheck 15 software). Then, I measured the distortion with the Listen microphone placed 10 cm from the mouth of the horn. This produced the distortion curves for the beryllium diaphragm (see Figure 9) and for the aluminum diaphragm (see Figure 10), both exhibiting extremely low third-harmonic distortion.
Figure 11: Radian 745NEOBe beryllium diaphragm SoundCheck CSD waterfall plot.
Figure 12: Radian 745NEO aluminum diaphragm SoundCheck CSD waterfall plot.
Figure 13: Radian 745NEOBe beryllium diaphragm SoundCheck Short Time Fourier Transform (STFT) plot.
Figure 14: Radian 745NEO aluminum diaphragm SoundCheck STFT plot.

I set up SoundCheck 15 to generate a 2.83 V/1 m impulse response curve and imported the data into Listen’s SoundMap Time/Frequency software. The resulting cumulative spectral decay (CSD) waterfall plot is given for the beryllium diaphragm (see Figure 11) and for the aluminum diaphragm (see Figure 12). For the Short Time Fourier Transform (STFT) with the color-coded surface plot, Figure 13 shows the results for the beryllium diaphragm and Figure 14 shows the results for the aluminum diaphragm.

The measurement differences between the 745NEO with the beryllium diaphragm and the aluminum diaphragm are interesting. You can see the aluminum break up mode, but its decay is impressively quick in the midband, while the beryllium is rather smooth throughout its entire range. Both materials used in the 745NEO compression driver have a very good reputation among recording engineers and producers, so it’s hard to definitively say one material is superior to the other from objective information. That decision is strictly a subjective one. Certainly the build quality and performance of Radian Audio Engineering 745NEOBe compression driver is impressive for either diaphragm.

For more information, visit the Radian Audio website at

This article was originally published in Voice Coil, October 2017.
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