Project Rusinos Maximus P23

My good friend Piotr is an extremist. He stops at nothing to build the ultimate highend system. So far he succeeded to get very very close, and after just 15 years of building it - he discovered thanks to me the beauty of vintage equipment and so we must start almost from scratch. At least the speakers.
The monstrous Project4 had to go to the corner, and make room for the ultimate cost no object Project 23 Rusinos Maximus.

The design criteria: The best, cost no object, WAF no object, look no object speakers money can buy.
Sounds scary?
Well, it is not necessarily as expenceive as one might think, nor it must be hard to build.

It so happens that two of the three best drivers in a category is (WAS) made by Altec Lansing - best bass drivers and best midrange (well, I must admit - arguably best, because there are really no compromise exotic midranges from Japan and Germany which are probably better, like Feastrex D5NF Gold from Tokio)
But for the purity of the initial thesis, lets agree that Altec Biflex is a damned nice midrange.

Piotr decided, that since bass and mid will be Altec, it would be particulary elegant and kosher thing to do to go all the way with Altec and use their tweeter as well.
Below there are the beautiful alnico tweeters with original Lansing Trombas (horns).
I admit to have never heard these before, but I accept the challenge of crossing them to the Biflex seamlessly at .. say .. 7kHz or so.

Altec Lansing  806-8A Alnico  tube tweeters

The horns are cast aluminium and the model is 811B

HORN 811

Test drive with the SABA and comparison to RAAL ribbons


Altec Lansing  Biflex 420A (15 inch Alnico  midrange !!!)
On paper its usable range without any XO is 28-14000 Hz !

It has same basket as the bass drivers with 15 inch cast frame and Alnico V magnet, but the paper cone is divided into two, connected by specially selected suspension. It is like a 20 cm midrange glued to the circular remains of a bass driver. At frequencies around 100 Hz the mechanical coupling allows the surrounding bass part to start moving. Above that - the surround is too heavy and behaves like a frame. Very clever, inn'it?  I think someone called this a "mechanical crossover".

The first thing to do when you have this driver is to REMOVE the alu dustcaps. Just pry it with a knife or something. They are added for "fake" HF extension but we do not need this extra dirt on the pure sound.

Also see my own P24 for this driver details.


The no-compromise member of our duo forced me to use two basses per channel to compansate for the extraordinary sensitivity of the two other drivers above.
So we will end up using 2 basses in a semi-open box, and mid/tweeter on open baffle standing separately.
Uff, I am glad Piotr did not request D'Apollito biflex arrangement.   ;-)

2 per channel  bass drivers Altec Lansing Alnico from 5xx series

The XO will be a second order accoustical at 300 and 7000 Hz.
The completion date is probably before Christmas.
Which Christmas - our sources don't mention.

UPDATE in january 08 - the prototypes look really promising. And they already sound great. Beforew any serious fine-tuning, the sound is absolutely better than expected. I am stunned with the midrange quality (best so far in my life) and also the horn tweeters prove to be fantastic. I do not recall better trebles ever before. Blending them though is a tough job.


At the time of writing - 08 feb. 08 (I am flying over Greenland right now) the XO is really simple. It took me 3 nights worth of testing to arrive at these part values, and without my fantastic software TRUE RTA I would have never done it. This tweeter is a nightmare to blend.
Anyway, here it is: C1=1 uF (precisely);  L1=0,39 mH (flatfoil)/ RDC < 0,5 Ohm; L2 = 1 mH RDC <0,5 Ohm;  in addition L2 in mid section should be preceeded by a capacitor in series - 100uF or larger. L2 should be followed by the 10 uf paralell capacitor (can be placed simply in speaker terminals.)    L3 =  2,3  mH (or slightly bigger) and RDC < 1 Ohm;  C2=10 uF MKT or MKP,  all phases are "positive".

First - the midrange - which is really the heart of the system. On open baffle, sans dustcaps and without any filter - they sound just fantastic. Almost well enough  without any other stuff. So the tweeter and the bass must only add one octave from each side of the spectrum of the midrange. The spectral analysis of the biflex mid reveals extremely uneven characteristics, which as usual sounds lively, natural and rich.  The only thing I wanted was to shave off the tiny little bit of the front edge, the top of the driver response peak near 15kHz. The L2 is just for that purpose. So the driver plus the L2 can be considered as a fullrange speaker with a re-touch correction.
This combination sounds smooth and natural. The human voices are from heaven.

Now comes the tricky part. The tweeter was designed to be really a mid-tweeter in a two-way, to blend with the 15 inch bass unit at 1 kHz. So it has WAAAY too much midrange content to begin with, plus the horn makes it bloody loud. It must be 10 dB louder than the biflex.
So first I had to push the output to the righr, to roll it around 8-10kHz instead of its natural reach all the way down to 500 Hz. The C1/L1 does just that (2-nd order electric and accoustic as well). At the same time, the overall treble level comes down to acceptable volume to blend with the biflex.
The magnets of biflex and tweeter horn are geometrically alligned.

The bass (two paralell drivers) are in the sealed box, and they must reach a bit higher frequency than the usuall 300 Hz to support the falling characteristics of the biflex, which is on open baffle. To avoid a dry and lean sound, the bass is first order filtered at circa 800 Hz. Given the ULTRA SMOOTH behavior of the Altec bass in the midrange zone, this is doable, unlike for typical modern bass drivers.

Overall, the measurements and listening show that this XO is a good compromise. Over-filter - and you end up with dull, technical, closed in sound. My XO strikes a balance where it measures kinda flat and sounds like a live band visiting the room. YOUR ROOM. (Actually - Peter's room  really).
At realistic SPL the sensation is awesome. Even a couple of watts literally nailed me to the chair. This is as far as you can get from a BBC minimonitor on stands kind of over-civillised hifi sound.

Second iteration of the system (in the center there is a pair of Altec speakers with Biflex drivers and even more center - the happy owner Piotr) Picture is from a telephone.