ATB
AudioTechnology-BlieSMa
Copyright 2018 © Troels Gravesen

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DRIVERS   CROSSOVER    CABINET    MEASUREMENTS    SPEAKER-KIT     CROSSOVER LAYOUT     SOUND

Last winter I had a pair of unusual domes for testing from Stanislav Malikov/BlieSMa/Germany and was taken by the impeccable finish and performance and started looking for a suitable partner for a potent 2-way stand-mount.
I had a pair of AudioTechnology Flexunits 6I52 midrange drivers on the shelf - made quite some years ago. Had used these for testing various surround materials and coatings and time was ripe for re-coning. So, I went to Per Skaaning and had him re-cone the drivers for mid-bass application - and not least using a titanium voice coil former. As expected this driver had quite a swing around 800 Hz and needed some edge coating. My vinyl cleaner, fitted with a cup made to fit the magnet of the 6I52, made a perfect rotating table for edge coatings. So done, the 6I52 had a flat midrange response facilitating a simple 2nd order crossover. Now, the 6I52 is actually of a true 7" driver having a cone area of 174 cm^2, nicely in between an average 6" and average 8". Not many drivers around in this size. A large tweeter dome allowing a low point of crossover should make an ideal partner for such driver targeting a point of crossover around 1.5 kHz.
Before implementing the T34A-4 dome I met with Stanislav Malikov in Munich at the High-End Show, and had a second pair of domes, this time with a beryllium dome, T34B-4. Both options will be shown here.

Basics:
Two-way stand-mount from 7" midbass and 34 mm Be/AlMg dome tweeter.
Sensitivity: 88 dB/2.8V/1 meter.
Impedances: 4 Ohms, minimum 4.7 Ohm.
Point of crossover: 1600 Hz.
Cabinet dimensions: 250 x 335 x 450 cm (WxDxH).
Power requirement: 20+ watts.
Power handling: 160 watts. Please also read this: http://www.troelsgravesen.dk/power-handling.htm

Useful links:
http://www.troelsgravesen.dk/tips.htm
http://www.troelsgravesen.dk/crossovers.htm
http://www.troelsgravesen.dk/LCR-RC.htm


DRIVERS
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T34A-4 to the left and T34B-4 to the right.
Click links to download data sheets.

Click images to view large


AudioTechnology 6I52-17-06-SDT, Re = 4.2 Ohm. Edge coated.


Above my TS data.

AudioTechnology does not apply the edge coating. I do and I charge you 125 EUR for both drivers. PayPal preferred. When you have paid for the drivers at AudioTechnology incl. shipping, ask AT not to send the drivers and send me a copy of the invoice and I'll pick up the drivers and do the coating. The drivers will then be delivered back to AudioTechnology to be shipped to you.


CROSSOVER
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The crossover features a simple LR2 filter. Point of crossover ~1.6 kHz. Due to the low point of crossover and the T34A(B)-4's somewhat high Fs (~850 Hz) it was necessary to include an impedance correction circuit, thus R7+C3+L3. Extended listening tests at loud levels would reveal a minor hardness on certain recordings until the LCR circuit was introduced. After that, smooth and easy on the ear - also a levels higher than this speaker should be used at. The dynamic headroom of the drivers will inevitably make you play louder that you should be. It's still only a 7" driver doing it all.


CABINET
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Click images to vie large.

The basic cabinet is made from 27 mm Baltic birch. Front panel from 25 and 35 mm HDF, high density fiberboard. Bracings are made from 27 mm Baltic birch. Use 22 mm MDF if BB is not available. If 22 mm MDF is used throughout I strongly suggest adding 4 mm bitumen pads to your order.
You may use 22 or 25 mm for the basic cabinet and you don't have to adjust volume or port tuning.
The inner front panel can be made from 22 mm MDF and the outer front panel must be 35 mm for proper time alignment of the drivers. Use 22+12 laminate. Thickness can be 33-36 mm.
Ports are best placed on rear panel as ports usually leak midrange - and not the good midrange. Ports are Ø50 x 185 mm. Port dimensions, see here.
The rear panel is attached with screws to allow easy access to crossover placed on rear panel. If you use 22 mm panels, you have to add fillets to the rear cabinet to attach the rear panel by screws.
This time I decided to use a vertical brace, supporting both side and top/bottom panels in one. The rear panel is supported by a center placed horizontal brace. With the front panel being 60 mm thick, it doesn't need additional support. Generally a rock solid cabinet.


Workshop images.


Use chisel or planer. Some hints here: http://www.troelsgravesen.dk/tips.htm#Faceting
The lower front panel is made from 25 mm HDF chamfered to 20 mm depth.


Use Fein or elbow grease.


Chamfer driver hole 45 deg. some 18 mm deep. The front sub panel is chamfered too.
All this to allow the 6I52 to breathe freely. Read this.


Front panels ready for final size cuts. Cabinet sheets filing up.


Sheets for bracing and rear panels ready. Ø69 mm for ports.
Yes, you can place the ports on the front. I know I'll have this question whatever I choose.


Rear panel in place and front panel trimmed for cabinet width and height. Time for lacquer and paint.


Cut 4 pieces of 11 x 50 cm felt for rear chamber.
Cut 2 pieces of 11 x 110 cm felt for front chamber.
Fasten with floor & wall tac. See here.


Felt material in place and front panels ready for gluing to cabinets.


Crossover fine-tuning starts.


T34A-4 in place for testing. Crossover mounted on rear panel.


MEASUREMENTS
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A few comments on MEASUREMENTS before you start interpreting all the readings below.
First of all, if we think measurements will tell us how a speaker sounds, we're wrong. The perception of sound is way too subjective to be reflected in any measurements we can perform. A loudspeaker system is meant to give us a satisfying idea of an acoustic event and for some people a pair of 5 USD ear-plugs are enough, others spend 200 kUSD on a truly full-range pair of speakers - and the latter may not be happier than the former.
Measurements may give us an idea of tonal balance of a system, i.e. too much or too little energy in certain areas, although dispersion characteristics play a vital role here. A two-way 7+1 and a three-way 7+4+1 may display similar horizontal dispersion, yet sound very different. Measurements may tell us about bass extension if far-field measurements are merged with near-field measurements. In addition to this, ports may contribute to bass extension. Most of we diy'ers do not have access to an anechoic room for full-range measurements from 20-20000 Hz.  
What cannot be seen is what kind of bass performance we get in a given room. Bass performance is highly dependent on in-room placement of your speaker and the same speaker can be boomy in one place and lean in another. Actual SPL level at 1 meter distance and 2.8V input is useful for en estimate of system sensitivity and combined with the impedance profile may give an idea of how powerful an amplifier is needed to drive the speaker to adequate levels.
What measurements do not tell is the very sound of the speaker unless displaying serious linear distortion. The level of transparency, the ability to resolve micro-details, the "speed" of the bass, etc., cannot be derived from these data. Distortion measurements rarely tell much unless seriously bad, and most modern drivers display low distortion within their specified operating range. 
Many people put way too much into these graphs and my comments here are only meant as warning against over-interpretation. There are more to good sound than what can be extracted from a few graphs. Every graph needs interpretation in terms of what it means sonically and how it impacts our choice of mating drivers, cabinet and crossover design.
What measurements certainly do not tell is the sonic signature of the speaker, because speaker cones made from polypropylene, aluminum, Kevlar, paper, glass fiber, carbon fiber, magnesium, ceramics or even diamonds all have their way of adding spices to the stew. Nor do measurements tell what impact the quality of the crossover components add to the sound, from state of the art components to the cheapest of coils and caps, they all measure the same if values are correct, yet sound very different.


Above the modified 6I52 driver's response mounted on actual baffle. Easy on crossovers I should say.


6I52 impedance profile in free air. Very little disturbance around 800-900 Hz. Fs = 30 Hz.


T34B-4 tweeter on stepped baffle (green) vs. flat baffle (red). As can be seen the impact of the stepped baffle is minimal.


SPL of drivers driven from crossover and summed response (orange).


Impedance with 145 mm ports. Minimum impedance = 4.7 Ohm.


SPEAKER-KIT
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I suggest bitumen pads of you use e.g. 22 mm MDF for cabinets.

6I52-17-06-SDT, Re: 4.2 Ohms, driver to be bought at mail@audiotechnology.dk

AudioTechnology does not apply the edge coating. I do and I charge you 125 EUR for both drivers. When you have paid for the drivers at AudioTechnology incl. shipping, ask AT not to send the drivers and send me a copy of the invoice and I'll pick up the drivers and do the coating. The drivers will then be delivered back to AudioTechnology to be shipped to you.

Domes to be bought at info@bliesma.de



All kit and component prices may be subject to change and are always to be confirmed by Jantzen Audio.

Download Complete Kit Sale Presentations (pdf file):

All technical questions to troels.gravesen@hotmail.com

All questions regarding purchase of kits, please mail Jantzen Audio at contact@jantzen-audio.com


CROSSOVER-LAYOUT
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Bass crossover layout

 

 


Tweeter layout

 

Wiring


Pay notice to tweeter inverted polarity!


SOUND
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Going from The Loudspeaker with its 18" bass driver to a small 2-way stand-mount certainly takes some mental adjustments, but firing up these two drivers immediately tells you we have to do with two drivers with very low distortion. The clarity and dynamic headroom is phenomenal.
Expectations were high - and I wasn't disappointed. Actually once again surprised of how deep and potent bass these 6I52 drivers can deliver. My initial intention was a lower port tuning than seen here, but trying it out I stayed with the 145 mm ports giving a port tuning around 47 Hz.
Clear transparent midrange and a clean treble, utterly transparent - that is if your source material provides. There's nothing forgiving about these domes.
I'm running the speakers from my EAR 868 pre-amp/EAR 861 tube power amp - and it's a magic combination.
If you want a seriously potent smaller 2-way for monitoring or just ordinary living room entertainment, I cannot recommend this speaker enough. It's my decent island 2-way stand-mount.
Be or alu dome? Honestly, it's up to your gut feeling - and budget. Both do remarkably well.