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 tweeter).

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 frequency.

Enclosure

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...

Conclusion

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 to 40Hz
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.)