OBL-15, built by Eric
Copyright 2020 © Troels Gravesen

Hello Mr. Gravesen,
I have built here in Indonesia your OB-15 design using Ciare NDH 15-4 S driver. All components purchased from Jantzen Audio. I choose the top of the range level 1 for the crossover. You mentioned in the website that the bass are very good but in my system it is poor. I tried with my Line Magnetic 2x 24 W class A single ended amplifier and with Opera tube 2 x 70 W amplifier and got the same poor bass. I even tried bi-amping thinking that the bass driver need more power but same. I think I did something wrong in making the bass crossover (I used the attached drawing). But looking on the schematic diagram I don’t find anything wrong.  Do you have any advice where to look for the problem? It seems that not only bass frequencies are going to the bass driver.
I know it is not easy to answer but maybe you have a hint… for medium and high the sound is stunning J
Thanks in advance and best regards,

After this I had images of Eric's crossovers and could see the wiring for the bass was wrong, so -

Hi Troels,
Thanks for your advice, it was correct the + of the bass driver was not connected properly!!
Now it works perfectly. Those open bafles are incredibly good. Now with plenty of low frequency even with my tube amplifier and 24 watts. The sound is really open and appears to me in 3D... All instruments are clearly separated making a large sound stage...
Another question, on my amplifier I have 3 loudspeaker taps 4,. 8 and 16 ohms. At the moment I use 8. What do you think? Would be better on 4? 
So once again thank you so much for the design and the trouble shooting !  
Warm regards,

When it comes to picking the best tap for speakers it just simply must be tried. I have often found the 8 Ohms taps best for 4 Ohm speakers and I recently read the same thing from John Atkinson's reviews on numerous amps and speakers in Stereophile.