My Altec Valencias - Part II
The project with the Altec Valencia Iconic loudspeakers described at
has been proceeding as planned, so I guess it is time for a short update.
The Onken enclosure
The woodwork for the Onken enclosures was finalized in the beginning of May by two students of the local polytechnic institute. The enclosures are constructed according the plans by Jean Hiraga (http://www.ispra.net/audio/Onken/Audiophile_n2_dec1977/articulo-hiraga01.html) with only few exceptions. The first and the biggest difference is due to the material cost - instead of 25mm birch plywood only MDF is used veneered from all sides. The second difference is that at the moment the main support between the front and back baffle is not in place as well as the panel reinforcements with all of the damping material.
Despite of the house move for our family I have had time to make the initial setup for the speakers and also listen variety types of music during the last two months. Altec 416-16z woofers are attached to the enclosure with original cork damping rings and the horns are laying on top of the enclosures at three solid cork pieces, turned slightly downwards towards the listener. The original Altec N-800F crossover is attached inside of the cabinet and the original cabling is in use.
As described in the part I, with decent analog source and Shindo amplification the speakers are able to fill out the room with very realistic sound having presence and density that many modern speakers lack severily. With the Onken enclosure this is even more valid statement as the bass region has now much more depth and quality than before with improved timing. The dynamics/transients attack with ease and resolution and the same applies also to the mids. I have not performed any measurements to the speakers but have planned to do so after finished installing the support between the front and back baffle, reinforcement panels and damping material inside the enclosures. I might say that with subjective scale the low frequency response is now well extended below 40Hz region.
The most interesting thing for the speaker system is still its ability to focus to the music as a whole and despite of the little longer distance between the woofer and the horn the speaker sounds still very coherent. However the Onken enclosures have also pointed out some disadvantages as the overall balance is now slightly shifted towards the low frequency region. At times the performance of the Altec 806A driver with H-811B horn does not seem to be competent enough to match the Onken design, especially when complex music is listened with louder levels than average. The issue is not the high frequency response in terms of cut off frequency, more like a issue with the resolution and overall quality. The damping of the horn with some Vibroplast M1 improved the situation but more experiments are still needed.
And what next?
During the summer I’m going to perform some tests with different reinforcements and damping materials without any huge changes and hope that this will further improve the sound. The performance of the speakers at their current form has set my mind for a decision that I will most likely stay with passive crossover. The active solution would need more investments and due to the high crossover frequency I really do not feel comfortable to leave wonderful Shindo Montille only to the High/Mid and use some other amplification for low frequencies.
I have been questioned several times for the need of supertweeter and I have to admit that adding suitable high quality supertweeter might have some advantages and also lead to more spacious and airy presentation. However changing the speaker as three-way system would have serious challenges at the crossover design, so most likely if going to add supertweeter will consider solutions that can be added parallel the current horn solution. I have also been offered a change to try little bigger Altec H-511B horn but I still think the multicell solution as a next logical step if going for the upgrade path in horn department. Perhaps in addition to dampening the H-811B cast horns I will also add wooden frame to it or somekind of supportive stand, which also allows easier adjustments for tilting the horn towards the listener.
In real life - I'm likely to finish the system as it is with just few items on my task list, settle for the original N-800F dividing network and study some alternative passive solutions from the Altec messageboards etc. In my opinion also more time is needed to listen variety of kinds of music to only understand the full nature of the system at this point. Perhaps after that I am competent enough to start planning the next steps for this never-ending project..