Testing three SBAcoustics tweeters:
SB29RDC-C000-4, SB26ADC-000-4 and Satori TW29RN-B

Copyright 2016 © Troels Gravesen

There were two tweeters in the SBA portfolio I immediately wanted for testing. The 29RDC appearance has kind of become an SBA brand symbol: The doped dome, making it a kind of ring-radiator without the center plug. It is well know that common soft-dome tweeters' diaphragms do not move pistonic all the way up to e.g. 20 kHz. Due to mass and flexibility only the diaphragm close to the voice coil will generate sound up to e.g 20kHz, hence there are break-up issues and some parts of the dome may move in opposite directions depending on frequency. The alu dome below does not have such problem - at least not in the audible range - and apparently nothing severe at all even at frequences above 20 kz.
The 29RDC appears in several iterations: Another low-cost with small face plate (R29RDNC-000-4) and in the Satori range with aluminium face plate and different rear chambers and magnets (Satori TW29R, TW29R-B and TW29RN. The latter with neodym magnet). Basically they appear to be the same.
I've always liked the ScanSpeak 9800 alu dome and despite smaller diaphragm area, the SB26ADC-000-4 appears to be very well engineered and display exceptional low distortion all the way down to 1 kHz. I'm looking forward to using this dome in future constructions.
The Satori TW29RN-B is indeed a refined version of the doped dome. Rock solid rear chamber, smoother frequency response and an impeccable cumulative spectral decay to name a few features. 


Click images to view large

Download specs: 29RDC-C000-4     26ADC-C000-4

Click image to view large

Satori TW29RN-B. Download specs TW29RN-B


"Infinite" baffle measurements

The tweeters are mounted on a MDF panel supported by a huge piece of cardboard, 60 x 100 cm, enough for readings being valid down to below 500 Hz. 

Test 29RDC-C000-4

Left: Frequency response of the two units normalised for 1 meter distance @ 2.8V input. Smooth response with a slightly elevated area around 13-14 kHz. Dark green and light green are minimum phase.
Right: Impedance of the two units. Fs = 600 Hz.
Overall quite a matched pair - and quite sensitive too! This tweeter can match a 93-94 dB system sensitivity.

Left: Dispersion shown at 0, 10, 20, 30 and 40o off-axis.
Right: CSD displaying no severe resonances all the way down to 500 Hz. Quite impressive.

Left: Distortion measured at 2.8V input equivalent to ~93 dB/1 meter. Very low distortion down to 1.5 kHz from where 2nd harmonics starts rising rapidly.
Same measurements done with +6dB input level, equal to some 99 dB/1 meter.
This tweeter should work very well down to below 2 kHz, maybe even 1.5 kHz.

If we remove the faceplate of the SB29RDC-000-4 tweeter, it fits perfectly with my waveguide used in my TQWT/DTQWT constructions.
How a given tweeter performs with a waveguide has to be tried and in this case not so well, but it was worth a try. It does well in all of the basic treble range, but the top octave display quite a bump at ~13 kHz and quite a dip around ~17 kHz. The graphs shows dispersion at 0, 10, 20 and 30 deg. off-axis.


Test 26ADC-C000-4

Left: Frequency response for the two units normalised for 1 meter distance @ 2,8V input.
Sensitivity 90 dB/1m/2.8V. Blue/green is minimum phase.
Right: Impedance of the two units. Fs = 600-650 Hz.
I'm quite impressed by the flat response of these domes.

Left: I'm further impressed by the dispersion of this alu dome. Quite remarkable.
Only at 40o off-axis do we see some significant decline in level, but still potent up to 16-17 kHz.
Right: CSD. Quite a clean performance.

Let's see these two tweeters side by side with regard to dispersion... Quite some difference, the dotted dome being 10 dB down @ 10 kHz, where the alu dome manage only 5 dB decline relative to the on-axis response.
What appear to be a general feature of the SB tweeters is a minor decline in the 2-4 kHz range combined with a robust response around 1 kHz, something that does not make crossover work easier. I wonder why that is. The lift in response for the dotted dome in the 10-15 kHz range may come handy in maintaining some airiness when listening slightly off-axis.

Left: Distortion measured at 2.8V input, equal to around 90 dB/1 meter distance.
Right: Input increased 6 dB equal to some 96 dB sound level @ 1 meter distance.
Now, I've checked my most recent tweeter tests, and I can't find any tweeter displaying such low distortion all the way down to 1 kHz.
I've repeated these distortion measurements several times and find them consistent. This is what I get.




Left: FR of both tweeter on infinite baffle. Overall smooth response with a slight emphasis on the 10-15 kHz range.
Right: Impedance of both tweeters.
Overall more than a matched pair!

Left: FR with a wider range displayed at 2.8V input, 1 meter. These domes are extremely sensitive, 95 dB - at least.
Pay notice my microphone really doesn't go much higher than 20 kHz.
Right: Dispersion shown at 0, 10, 20 and 30 deg. off-axis.

Left and right: Distortion measured at 2.8V input, equivalent to 95 dB/1 meter.

Left and right: The two units cumulative spectral decay measured at 2.8V input.