So after 4 years of development and thousands of dollars, I have finally reached the end of the road for the bass cabinet. When I bought my speakers, I thought that a change of amp would fix it - but it turned out to be more involved than that.
I then started to wonder what the horn would sound like if I removed its crossover
The overall efficiency of the system is 92dB/W/m. Obviously, the horn is much more efficient than this so it HAD to be padded down to match the efficiency of the woofer. It should be a fairly simple matter to get at the internal crossover network, snip off a few wires, and then connect it directly to the Cary power amp, right?
WRONG!!! We manhandled the incredibly heavy horns off the box and I proceeded to undo the screws. The horn would not come off, so I thought it might be bolted in from the back. I undid the rear screw, only to be greeted by the sight of SAND pouring out the cabinet and onto my pristine living room rug made from genuine New Zealand lamb wool!! I quickly plugged the hole with my finger and replaced the bung (not easy when you have 40kg of horn cabinet on your lap!). Turns out the horn is screwed into the cabinet AND glued on. A sharp twist of the horn got it off, and this is what we saw:
A Dynaudio D-52H midrange driver, customized for Acapella! Finally, a decent driver. The Thiel-Small parameters are
here. Compare the F/R curve supplied by Dynaudio with my own measurement of the midrange horn F/R
here. Obviously it looks different because it has the crossover in place and it is horn loaded.
After we drained all the sand out, we finally managed to get a good look at the horn crossover. It was sitting at the back of the box, covered in sand:
As expected, there are a few resistors to drop the efficiency of the horn to match the woofers. Check out the construction of the box:
As my friend said, it's very German in design. Only a bloody German would build a box out of double ply, then line it with lead. And then think to himself "hmm, maybe it's not dead enough. Let's fill it with sand!!".
Getting the sand back in is a simple procedure of using the fill hole at the back, like this:
Right now, I have almost reached the end of the road. All the major modifications to the system have been completed. Things left to do:
- Subwoofer upgrade. The subs now sound slow compared to the rest of the system. Considering a Wilson-Benesch Torus, but it is a little bit too spendy. Might get a pair of custom built subs instead.
- Refine the crossover settings. Will be running more sweeps and more sims over the next few weeks. With the Marchand XM44 it is a simple matter of ordering plug-in cards. At some point, I will send the unit for upgrades to the op-amps.
- Don't need the 110W Cary's to drive the midrange horns any more, considering these are 98dB/W/m sensitivity. Ridiculously overpowered. Will probably welcome back the 50W Cary SET's into my system, or try the Einstein OTL.
Well, that is my journey. Hope you enjoyed reading.