Some 60 years ago a copy of Popular Mechanics
came into my hands, in Denmark Populær RADIO Mekanik. These
were mostly translated versions of the American issues, which often meant that all
the wonderful things that could be made couldn't be done due to
unavailability of components. In the US you had postorder catalogues,
something that was still in its infancy here in Denmark.
From the issue I had there were 10 watt EL84 PP tube amplifiers from ready made boards - highly
unavailable. There were large speakers with drivers totally unavailable.
And even if available, the price would be way above a young boy's pocket
money.
Anyway, these publications fueled our imagination and led to
countless projects in the pursuit of better music reproduction. My
older sister would listen to Radio Luxemburg all the time - and I wanted
that too - in my own room.
Eventually my parents got a transistor radio and
I had their old tube radio and dismantled the whole thing and had the
chassis with all its glowing valves standing on the floor and the speaker
driver hanging from my bedpost. Good fortune saved me from being
electrocuted having high-voltage next to my bed.
What was immediately learned was that the sound coming from a free
hanging driver wasn't as good as when it was in its wooden radio cabinet. Hmm..
How could that be?
This was where Popular Mechanics came into the picture, because one
chapter was dedicated to a very simple speaker construction shown in the
images above. Some years later, having bought the book
Loudspeakers by Gilbert A. Briggs, I would understand this was a short
transmission line, supposed to enhance bass performance and not least taking
advantage of room-gain.
So, I went to the local carpenter and had a board made, one board - mono
times - some 25 x 100 cm and drove it home on my bike and made the shown
"cabinet".
This was for sure a game changer and lead to further reading of the
publication on a corner speaker with double Peerless full range drivers - at
least these were available being made in Denmark. Also the famous Karlsons speaker cabinet was shown, albeit way out of reach using a
suggested 12"
coaxial - or even triaxial speaker driver - as though that would be
available anywhere near!
When I finished my Illuminator-71 speaker, I was
really excited about the sound and thought this was the best
two-way I had ever made. Eventually the guy who had bought my SBA-761
and later Discovery-861 sent a mail and told he had a friend that would be
interested in the Ill-71s. Well, a quick sale doesn't hurt and the
speakers were gone. Only bad thing was that after some time I found out
I missed them. I missed their transparent midrange, their - for the size
- astonishing bass and I missed the smooth treble.
Only thing to do was build another pair! I want this speaker to be one
on my few stock speakers as an example of what can be achieved from a
simple 2-way.
Cabinets are exactly the same, 21 mm Baltic birch, bitumen pads all
over, same damping, etc. Only difference is an insanely expensive beer can for treble as can
be seen below, and crossover placed at bottom due to size of the copper
foil capacitor. One of these copper caps costs as much as a pair of 6600 tweeters, but I
had them surplus, so why not? I love the sound of the 6600 tweeter, so
much I'll treat it with the best available.
So, the whole point of this scribbling is that
after having made more than two hundred speaker constructions, would I be as
excited setting up the new Ill-71 as I was some sixty years ago when I
placed a small ~6" driver in a transmission line?
The answer is yes! Call it an obsession, call it crazy, call it whatever.
For sure it's a bug that never goes away, so be warned before engaging
in DIY speaker building.
Looking at the 18W/4741T00 Illuminator driver we
have come a long way since then! Underhung voice coil providing linear
excursion, SD3 symmetric drive ensuring low voice coil inductance,
non-reflective motor system, sophisticated sandwich cone, titanium voice
coil and way better power handling, etc., etc. All ensuring low distortion and subsequent
midrange clarity*.
The tweeter dome was hardly invented back then and today we have an
abundance of excellent tweeters at our disposal. We have much, much better
crossover components and we have measuring equipment to get the basics
right. Only thing left is the choice of crossover topology and adding our personal taste to overall voicing
of the speaker system.
*
For the record, some of these technologies were at its infancy back
then, but never combined and brought to full fruition as seen in the
Illuminator driver.
And look at the 6600 tweeter, linear from
700-20000 Hz. If we just had that back then...
My new Illuminator-71s in my workshop.
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