Modified Hifi 12/2 speakers
My main speakers are DIY speakers based on Hifi 12/2
(designed by Hifi-lehti in 1980's). I have modified
the enclosure (narrower shape & tuning) and cross-over
(mainly compensated the narrower front of the speaker).
I had listened many highly ranked speakers (Jamo Concert
8, Dali Coupe, Genelec 1029A, Gradient Intro, Hifi-talo
designed speakers "Chorus"-brand etc.) but I didn't like
them too much. Most biggest problems to me on those high
ranked speakers are tweeter quality and problems on bass.
The tweeter problems are caused by designing speakers
on directivity point of view. Therefore low quality
tweeters are driver with very low cross-over points
and some distortion always occurs. Also some tweeters
seem to lack the accuracy on 5000-10000Hz range, which
is also often called by owners of those speakers "warm
sound" (which is needed if the speakers are driven by
low quality surround amplifiers in order to have decent
The bass problems can be divided to two: quality of bass
and lack of low bass. Quality of bass is caused by two
reasons, using too high Q drivers in improper enclosure
and loss of dynamics due to too small reflex pipes.
The text above is written in the end of 1990's and the
Hifi-talo speakers didn't have transflex enclosures.
Transflex enclosures do create very good quality bass,
the bass extension and quality are both quite good.
But at least in the cheap modes the tweeter is still
very distorted cheap Seas driver with too low cross-over
The main problem on original enclosure of Hifi 12/2 is
too small enclosure and too small bass reflex pipe (40mm...)
which caused the enclosure to act as closed enclosure
on high sound levels. In first revisions I used 75mm
round pipe to tune the enclosure and in the most recent
enclosure tuning is done with "tunnel" which starts the
bottom of the enclosure and exit is in the back of the
enclosure (there is ~50cm empty space below the speaker
because the speaker stand is integrated to the speaker).
The tunnel has same cross section area as 65mm pipe.
I also don't like the "shelf" speaker shape since speakers
never could be put to shelf (sound quality on shelf is very
bad) and speaker stands are always needed. This is why I
have build the enclosures to "floor" speaker shape, even the
whole volume of speaker isn't used.
Pictures to be added...
I like very much my speakers but cannot recommend them
since Dynaudio is no longer selling the drivers for DIY-people
and therefore the original design cannot be built anymore.
There is also design called 12/2-M, in which the Dynaudio D-28
is replaced with Morel MDT-37. The tweeter is very similar
with Dynaudio and I plan to built this 12/2-M for center
speaker to my home theater. (When I do, I will update
this information as well).
Update! I did build 12/2-M for center speaker
use and I highly recommend 12/2-M kit.
Pros: good quality tweeter, good quality bass which goes down
Cons: there are far better bass drivers currently available
than Seas P17/Rex (more excursion, less thermal compression, but
they also usually have bad cone break-up between 3-4kHz and
therefore could not be used with high crossover frequency.)