Testing 34 mm AlMg dome T34A-4 from BliSMa/Germany

Copyright 2018 © Troels Gravesen

Stanislav Malikov has a history at Accuton and Morell companies and has started his own production of this unusual large aluminum/magnesium dome and offered me a pair for testing. Click here to go to website and download data sheet here.

I've had a long term affair with large domes from my 8008-HMQ constructions. Here some more stuff on large domes.
What got me interested in this dome is the claimed aluminum/magnesium alloy dome of variable thickness. Secondly its narrow suspension. Current hard-dome manufacturing favours wide fabric suspensions, adding significantly to the radiating area, thus a mixture of soft-dome and hard-dome, although I cannot tell the percentage of sound pressure generated from each. And I rush to say I very much like the performance of current Be domes from ScanSpeak and SBAcoustics, but you never know what a Be dome would sound like if it had a very narrow suspension. Alu domes started life badly back in the late Seventies and one company (JBL) even withdraw their first alu dome due to poor reviews. And bad it was. Later we had better alu domes from e.g. B&W and not least Celestion with their SL6S, which I owned for quite some time. Titanium domes came along and generally got a better reputation, although I never liked them much, maybe due to poor implementation.
280 mg moving mass is quite low for such a large dome compared to most modern soft domes of 25-28 mm diameter, often having 300-500 mg moving mass. The SEAS T35 has 470 mg moving mass.

Click image to view large

So, from what you can see below, we here have is a very well performing large dome tweeter, high sensitivity, flat frequency response up to 25 kHz, low distortion, exceptional dispersion (better than many 3/4" domes!), exceptional clean waterfall plot, very nice finish, etc. I can't point to anything this dome doesn't do well - and even better than many other domes - and price will be similar to the SEAS T35C002 according to Stanislav Malikov, which I think is very reasonable.
I tried setting up the dome with the ATiRi midbass, made a quick crossover and went through some familiar recordings and nothing stood out for not being a worthy candidate for future construction. The tricky part is finding the right partner for this dome, a midbass in need for a fairly low point of crossover - or - you may just use it as any other dome and take advantage of the large radiating area and get the benefit of low distortion, because size matters.
Based on modeling from preliminary data, the T34A-4 seems a worthy candidate for an alternative tweeter for the 8008-CORNER speaker delivering on the very same simple series crossover (different values that is). No immediate plans for such experiments, so please do not ask.
So, find the right partner and here you have what appears to be a very versatile dome tweeter.



High sensitivity and linear response is what appears from flush mounted unit on a 60 x 100 cm baffle.
The break-up peak at 29 kHz is for dogs and bats and should not disturb our peace.
What cannot be ignored is that this dome does flat to 25 kHz despite is large size! Quite impressive.


What came as a real surprise was the dome's dispersion characteristics.
Above dispersion at 0, 10, 20, 30, 40 and 50 deg. off-axis. Very good indeed. This calls for a very even power response.


Above distortion measured at 0.25 m distance normalised for 84, 90 and 96 dB @ 1 meter distance.
Data suggest a dome suitable for very low points of crossover, probably even 2nd order @ 1.5 kHz.


Cumulative spectral decay display a very clean performance, even below 1 kHz.

Above an impedance plot. Fs = 800 Hz.
The T34A-4 displays a fairly wide impedance peak that may need attention in applications with a low point of crossover.

Should we want to flatten the impedance, 5R6+82 uF+0.47 mH does the job, although it's not always desirable.



Click images to view large