Test Bench: Radian Audio 835PB 1.4” Ferrite Compression Driver

April 29 2020, 09:10
Radian Audio Engineering, Inc. was incorporated in 1988 by its founding president, Dr. Richard Kontrimas, with the mission of manufacturing great sounding, high-quality loudspeakers at affordable prices. Radian’s initial offerings were replacement compression driver diaphragms. The diaphragms took off so well that it wasn’t long before the company was making complete compression drivers. Several major loudspeaker manufacturers quickly identified Radian 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 (which the company discontinued a few years later, to focus exclusively on selling drivers for the OEM/ODM market).
Photo 1: Radian’s 835P, a ferrite 1.4” aluminum diaphragm compression driver.
Figure 1: Radian 835BP free-air impedance plot.
Figure 2: Radian 835BP on-axis frequency response.

Today, Radian, based in Pomona, CA, is a serious 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 is well into its third decade as a pro sound manufacturer and introducing new pro sound transducers such as the LT6, the LT3, and the LT2 pro sound ribbon transducers.

Voice Coil has featured several of Radian’s neodymium series of compression drivers, including the 960PB and the 950PB 2” exit aluminum diaphragm compression drivers in the November 2014 issue, the 745NEO with both the aluminum and beryllium diaphragms in the October 2017 issue, the 951PB Neo compression driver in the July 2018 issue, and the 745PB ferrite 1.4” aluminum diaphragm compression driver in the December 2018. This month, I received one of Radian’s ferrite 1.4” aluminum diaphragm compression drivers, the 835PB (see Photo 1).

If you are familiar with Radian’s compression drivers, or have read some of the past explications about Radian’s neodymium compression drivers, the 835PB has the expected rich feature set of other Radian compression drivers. This includes a 1.4” throat diameter, a 190 mm × 190 mm ferrite magnet motor, high temperature 76.2 mm (3”) diameter polyimide voice coil former with a copper clad aluminum edge wound ribbon wire voice coil, 200 W continuous power handing (100 W AES2 Rev. 2003), a self-aligning field replaceable diaphragm assembly, and the most important feature, a proprietary processed and hardened aerospace grade aluminum alloy diaphragm over a three-slit phase plug. The driver has color-coded gold-plated push terminals and a net weight of 14.6 lbs. I should also note that the 835BP is also available with a beryllium diaphragm.

Since Radian does not produce horns for its compression drivers, I perused my inventory of horns and decided to use a FaitalPro 1.4” LTH142 elliptical tractrix horn that has a 60° × 50° coverage pattern. This horn has a recommended crossover frequency of 800 Hz, the same as the recommended crossover for the Radian 835BP. I almost never have any subjective experience with the transducers that I characterize in Voice Coil’s Test Bench, however thanks to Radian’s generosity, the 2" 950PB samples from the November 2014 issue ended up in a farfield monitor that I designed for my home recording studio.

These have the same aluminum alloy diaphragm as the 835PB. The cabinets were built by my friend and Triad chief engineer David Nelson, and utilized a B&C 15BG100 15" neodymium motor woofer with a NBR surround, an Eighteen Sound XR2064C 60° × 40° 2” throat cast-aluminum horn, and a high-performance passive network that included Goertz foil inductors, Jantzen capacitors, and Mundorf M-Resist resistors. Subjectively, this speaker is incredibly musical, detailed, and extremely easy to listen to, certainly a goal for all studio monitors.
Figure 3: Radian 835BP Horizontal on- and off-axis frequency response (0° = black; 15° = blue; 30° = green; 45° = purple; 60° = blue).
Figure 4: Radian 835BP Horizontal normalized on- and off-axis frequency response (0° = black; 15° = blue; 30° = green; 45° = purple; 60° = blue).
Figure 5: Radian 835BP 0° to 180° horizontal plane polar plot
(in 10° increments).

To begin testing the Radian 835PB/LTH142 combination, I used the LinearX LMS analyzer to produce the 300-point stepped sine wave impedance plot shown in Figure 1. The solid black curve was taken with the ferrite motor Radian 835PB mounted on the FaitalPro LTH142 horn and the dashed blue curve represents the compression driver without the horn. With a 5.54 Ω DCR (Re), the minimum impedance of the 835PB/LTH142 was 7.72 Ω and at 2.71 kHz.

For the next set of SPL measurements, I free-air mounted the Radian 835PB/LTH142 combination without an enclosure and measured both the horizontal on- and off-axis at 2.0 V/0.5 m normalized to 2.83 V/1 m, with the LoudSoft FINE R+D Fast Fourier Transform (FFT) analyzer to produce the horizontal SPL data from 0° on-axis to 60° off-axis. Since I have used the LTH142 has been used for compression driver measurements for previous Voice Coil explications, I excluded the vertical axis response; however, FaitalPro publishes that data on its website (www.faitalpro.com).

Figure 2 illustrates the 835PB/LTH142 combination’s on-axis frequency response, which is smooth ±3.5 dB from 800 Hz to 10 kHz with no major anomalies extending to 20 kHz. Figure 3 depicts the on- and off-axis (0° to 60°) response in the horizontal plane. Figure 4 shows the normalized horizontal plane response. Figure 5 shows the 180° horizontal polar plot (in 10° increments with1/3 octave smoothing applied), generated using the CLIO Pocket analyzer. Last, Figure 6 illustrates the two-sample SPL comparison showing the two Radian 835PB compression drivers less than 1.0 dB throughout the operating range of the transducer to 12 kHz.
Figure 6: Radian 835BP two-sample SPL comparison.
Figure 7: Radian 835BP SoundCheck distortion plots.
Figure 8: Radian 835BP SoundCheck CSD waterfall plot.
Figure 9: Radian 835BP SoundCheck Short Time Fourier Transform (STFT) plot.

For the remaining series of tests, I set up the Listen, Inc. AudioConnect analyzer, SoundCheck 17 software, and the Listen 1/4” SCM microphone (courtesy of Listen, Inc.) to measure distortion and generate time-frequency plots. For the distortion measurement, the 835PB/LTH142 combination was again mounted in free-air in the same manner as was used for the frequency response measurements, and the SPL set to 104 dB at 1 m (1.65 V determined by using a pink noise stimulus generator and internal SLM in the SoundCheck 17 software). I then 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 7 (red curve = second harmonic, blue curve = third harmonic).

Following this test sequence, I set up SoundCheck 17 to generate a 2.83 V/1 m impulse response and imported the data into Listen’s SoundMap Time/Frequency software. Figure 8 shows the resulting cumulative spectral decay (CSD) waterfall plot. Figure 9 shows the Short Time Fourier Transform (STFT) plot.

From the test measurements, the 835PB 1.4” ferrite compression driver displays excellent performance in a fairly high power handling package (200 W continuous [3 dB higher than the AES power rating]), and a ferrite motor compression driver build quality that is on par with the best players in this industry. For more information about this driver and other pro sound products from Radian Audio Engineering, contact Radian Audio, calling 714-288-8900, or e-mail.
www.radianaudio.com VC

This article was originally published in Voice Coil, February 2020.
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