Test Bench: The T34A-4 Tweeter from BlieSMA

August 21 2018, 10:00
BlieSMa, located in Blieskastel, Germany, was founded January 16, 2018, by Stas Malikov. Over the last 20 years, Malikov has worked at Ultrasound Technologies, at Morel as a QC manager and transducer engineer, and for the last eight years at Accuton as a production engineer. The first product being released by BlieSMa is a 34 mm tweeter, the T34A-4. Available from May 2018, the T34A-4 is a 30 mm metal aluminum/magnesium alloy dome tweeter. 
Photo 1: BlieSMA T34A-4 is a 30 mm dome tweeter.
Figure 1: BlieSMA T34A-4 impedance plot.
Figure 2: BlieSMA T34A-4 on-axis response.
Figure 3: BlieSMA T34A-4 horizontal on- and off-axis frequency response (0° = solid; 15° = dot; 30° = dash; 45° = dash/dot).
Figure 4: BlieSMA T34A-4 normalized on- and off-axis frequency response (0° = solid; 15° = dot; 30° = dash; 45° = dash/dot).

This device has a substantial feature set that includes a 34 mm aluminum-magnesium ally dome with variable thickness for a 27 kHz first breakup mode, extremely low moving mass (Mms = 0.28 grams) for better transient response and higher output, and a fully saturated neodymium motor with copper sleeve shorting ring for low non-linear and modulation distortion. The driver also features a 3 mm linear excursion and large pole vent for undistorted low-frequency operation, using a flush mounted narrow surround for less “soft dome” coloration, with the magnet
system rear mounted for flat frequency response and wide off-axis response. 

As BlieSMa highlights, there's no ferrofluid for improved dynamics, and the design uses a underhung voice coil wound with CCAW wire on a titanium former, with flexible and lightweight tinsel leads from Denmark, cast-aluminum powder-coated faceplate and gold-plated terminals. Particularly impressive is the T34A-4's extremely wide frequency range, going from 1.3 kHz to 35 kHz.

I began testing using the LinearX LMS analyzer to produce the 300-point impedance sweep illustrated in Figure 1. The T34A-4 impedance resonance occurs at a moderately low 795 Hz (factory spec is 790 Hz). With a 3.35  DCR (Re) (factory spec is 3.3 ), with the minimum impedance for this tweeter measuring 3.63  at 6.39 kHz.

After completing the impedance testing, I recess mounted the T34A-4 tweeter in an enclosure that had a baffle area of 17” × 8” and measured the on- and off-axis frequency response with a 100-point gated sine wave sweep at 2.83 V/1 m using LMS. Note that I am temporarily using LMS for high-frequency drivers whose low-pass roll-off is about 20 kHz until the new LOUDSOFT FINE Hardware 3 192-kHz analyzer is available.
Figure 5: BlieSMA T34A-4 180° horizontal plane CLIO polar plot (in 10° increments).
Figure 6: BlieSMA T34A-4 two-sample SPL comparison.

Figure 2 shows the T34A-4 on-axis response to be a flat ±2.35 dB from 1 kHz to 20 kHz (±2 dB from 1.05 kHz to 13.5 kHz), with the diaphragm breakup mode centered on 30 kHz. Figure 3 gives the on-and off-axis response of the T34A-4 high-frequency device. Figure 4 shows the off-axis curves normalized to the on-axis response. Figure 5 shows the CLIO 180° polar plot (measured in 10° increments). The two-sample SPL comparison is illustrated in Figure 6, indicating the two samples were closely matched to within 0.25 dB throughout most of its operating range, with some minor 1.5 dB variation at 4 kHz.

Next, I initiated the Listen, Inc. AudioConnect analyzer and the Listen, Inc. SCM ¼” microphone (provided courtesy of Listen, Inc.) using SoundCheck 16 to measure the impulse response with the tweeter recess mounted on the test baffle. Importing the impulse response into the Listen SoundMap software resulted in the cumulative spectral decay (CSD) waterfall plot shown in Figure 7. The same data was used to produce the short-time Fourier transform (STFT) displayed as a surface plot in Figure 8.
Figure 7: BlieSMA T34A-4 SoundCheck CSD waterfall plot.
Figure 8: BlieSMA T34A-4 SoundCheck Short Time Fourier Transform (STFT) surface intensity plot.
Figure 9: BlieSMA T34A-4 SoundCheck distortion plots.

For the last objective test, I used a pink noise stimulus (SoundCheck has a built-in generator and SLM utilities) to set the 1 m SPL to 94 dB (2.44 V) and measured the second (red curve) and third (blue curve) harmonic distortion at 10 cm (see Figure 9). 

As his first product to be released to the OEM driver market, it certainly appears that Malikov is a skilled practitioner. The fit, finish, and overall build quality look first-rate, befitting of a product intended for the high-end speaker market, not to mention that I am definitely a fan of large diameter tweeters that play well to 20 kHz, such as the T34A-4 and the Wavecor TW030WA13.  For more information, visit the BlieSMA website at www.bliesma.de VC

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