Frankly, I never thought I'd do a speaker from all aluminium (cone)
drivers. My most recent experience dates back some 10 years and the
midbass was harsh on my ears. Later the manufacturer modified the drivers
(cone curvature) for
better performance, but I never got around to doing them again.
Comparing three SBA 6" driver in my test cabinet seen below created the graphs above. Orange is a paper cone, green is polyprop and yes, red is the alu cone! The alu driver is a 4 Ohm version, hence highest sensitivity. The alu cone has the smoothest midrange and lower treble range of them all followed by the PP cone and paper is worst. Pay notice any response is dependent on baffle size and shape so they will measure differently on another baffle. Dips and peaks in the 1-4 kHz range are a pain when it comes to designing crossovers. The PP has the smoothest roll-off of all from the 2100 Hz LR4 crossover if this is important to you. Based on modelling PP can do even with an LR2 filter.
It only took few changes to the crossover to fit in all drivers in the current setup and although we cannot tune them to exactly the same response, they sound not that different and I'm reluctant adding any sonic claim to a specific cone. It's hard to say one is more analytical than the others, nor that one is more smooth, lush, clean, etc. than the others. Being exceptionally linear throughout the midrange, the alu cone is probably the most neutral of them all with a small edge when it comes to detail. If you are one of the many having built the SEAS W15/OWI and have room for 5-6 more litres, this speaker may an option for a new project to get same level of transparency - and get some more bass. Now, the good thing here is that you can let your prejudice rule and pick the one you like! How about that?
Capacitors: Now, these SBA drivers are highly revealing and going from standard PP caps to all-Super-caps made a significant improvement. The "problem" is that these 4 Ohms drivers swallow a lot of micro-farad, but if you want to hear what these drivers can do, there's no way around it. All STANDARD-Z cap version will be available and you can later upgrade if you stick to the crossover layout for super-caps.
I will later launch version with the PP and paper cones, but here we go for the alu cone. The PP will be different from the two other as it will feature an LR2 crossover. PP drivers are generally easier on crossovers than hard-pressed paper or alu.
Crossover components' values come with Kit Instruction.
Above my measured TS data. Not that different from the SBA data, but my driver may need some more breaking in to reach e.g. Cms.
Above box simulation from a 16 litre vented cabinet with a port tuning of 45 Hz. This boosts the 50-100 Hz range a little but using the SBA TS date the response is pretty flat, so I guess we're safe here.
It took some experimentation of tweeter placement and on bass panel
shape towards the tweeter. Center placement of tweeter and a rounded
shape of bass panel with a radius of 14 cm made the best tweeter
response, which was fairly flat on an infinite baffle but on a very
small baffle lost level around 3-5 kHz and increased level in the
1-2 kHz range.
For a speaker like this and the 3-way classics I use the same procedure and start like seen above. This way I can make the final rear panels and bracings. When all things fit, I unfold the cabinet again and apply glue to all joints with a brush. As can be seen below I use three straps and a lot of clamps (not shown) to add further pressure to placed where needed.
Everything that can be counted does not necessarily count; everything that counts cannot necessarily be counted". Albert Einstein.
A few comments on MEASUREMENTS before you start
interpreting all the readings below.
Above you see the same graph presented with the
same 50 dB scaling, but at
different width and height. Now, we may think the graph to the right looks rather
rugged, but if we stretch out the presentation (left) it suddenly looks
rather smooth. The left presentation is often used by driver manufacturers to make their frequency response graphs look better. If we
apply e.g. 1/6 or 1/3 octave smoothing things look even better. Just
this to display how easily measurements can be manipulated to look nice.
SBA 61AL MEASUREMENTS
Crossover components' values to come with the kit.
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Level 1 components
Taking any new speaker construction to the living room for further crossover fine-tuning is mandatory. And bless my wife she doesn't mind crossovers on the armrest a couple of weeks. For small speaker the exercise also includes the "OK, here we go again, gotta get used to no bass"-thinking. Not so with the 61AL! Decent bass filled the room and despite nowhere near the ATS4, the 61AL did decent bass, plus it had some extra features capturing further attention. Listening to small speakers not delivering substantial bass response tends to focus our attention to the midrange/treble. We can get almost obsessed with midrange detail and treble balance. In that sense it's much harder to make a small speaker than a large 3- or 4-way. Improve the bass and midrange improves is a common statement - and obviously the midrange doesn't get better, but having decent bass changes our perception of the midrange.
OK, make some stands of 60 cm height to bring the speakers into a comfortable listening height when sitting in your sofa and toe in the speakers slightly and you're ready for listening.
Ravel's piano music is a box set I've
played countless times on my ATS4 and these recordings are not bass heavy
at all (I found the records 2nd hand for 2 USD - vinyl in mint
condition...just have to tell). Well, I was positively surprised! These alu
cones driven by the GlowMaster deliver some extraordinary
transparent sound. Metallic? Please!! Forget it! If your source
material is smooth or harsh, it comes out smooth or harsh - if your gear
is up to it.
Digging into my jazz collection I added one of my
subwoofers and set the crossover to around 60 Hz with minor bass
lift. Sure, the upright bass comes out more solid and articulate. I'd
say a single sub here does well. The SBA-61AL does require some power
despite its 4 Ohm impedance. My 50 wpc GlowMaster has no trouble running
them, but I suggest some healthy 50 wpc as minimum. And your solid state
amps doesn't mind being connected to 4 or 8 Ohm speakers (have this
question quite often). A "4 Ohm" speaker will only draw more current from your
amp for the same volume setting - and play louder. For tube amps it's
more tricky and we have to try 4 and 8 Ohms taps to find what is best. 4
Ohms speakers do not necessarily demand the 4 Ohm secondary transformer
tap. Speakers are by no means linear devices.
You may object to my use of super-caps in abundance, although I did
compromise on the bass section. Sorry, friends! If you want to extract all these drivers can
do, there's no way around it. Standard PP caps are crap and smear detail
and make a massed presentation that may - if you're lucky - be fairly
smooth on the ear (ear-friendly) but never reveal the detail and
super-caps can do. Now, level 2 will deliver most of it and to be
fair, I had to search for recordings where I could actually hear
some difference between level 1 and 2 (acapella male vocal, strangely
enough), so level 2 is my recommendation. If you wear belt and
suspenders - or are filthy rich - you need the Full Monty, level 1