Kodawari Chronicles: Altec 604 Enclosure

Cabinet Details

It was a given. My complete lack of impulse control had once again won the day. A more methodical individual might have chosen a different route. But I happily did not.

A pair of vintage Altec 604E’s had arrived and I had to listen. I had no enclosure, no stands, no plan. After evicerating the (woefully inadequate) packaging the hulking drivers were plunked them on the floor, resting on the edge of their frames, and lashed to some untested crossovers and from there to still warming F2A’s.

Let’s just see if they work was the thinking. Nothing good can really happen without a cabinet, but they should at least make sounds….

Please make sounds.

Expectations were, understandably, low.

Test Fire

I selected Nat King Cole’s “When I Fall In Love” and pressed play. Three minutes and eleven seconds later I sat in stunned silence. The experience was by no means the technical best I’ve ever heard. The highs were biting in places, the lows were mostly MIA. There was, however, a ray of sunshine. Actually more like a blinding, searing, road to Damascus beam of light. And it was emanating directly from the midrange.

I had never heard such a palpable, visceral vocal presence in my room before. Not from disappearing mini-monitors, nor the standard bearing Watt Puppies. Not from virtually unobtainable and venerated TAD studio gear I thought would be my final speaker purchase. They all did many things better than what I had heard on that day but none felt so dynamic, so immediate as the 604. And I’m a sucker for immediacy.

It was time to find suitable housing for my refugees from the early 1960s.

First stop — the open baffle. These had the benefit of being simple to construct and people seemed to like the combination. I used the JELabs approach(thanks Joseph for all that you’ve shared with us!). Nice enough but in my room it lacked the bass chops I knew a 15” cone was capable of producing. Then there was the additional negative that, as a dipole, a not insignificant portion of the lower registers ended up in the living room of a neighboring flat. I had to move on.

Next station — Altec 612 cabinets. I dug the form factor. Here were (borderline) humanly sized boxes that, with a little TLC, could be made to look presentable. The standard enclosure when 604s were the studio monitor of choice, the 612 had a rich and storied pedigree. Abby Road, Muscle Shoals, Sunset Sound. The 604s were for a period of time the final word in monitoring at these legendary locations.

How did this attempt fare? Better, but not what I knew they could be.

It could have been the materials, the construction, overdamping or a host of other factors but these were still not producing the magic I wanted.

I allowed myself one final attempt. This version was a modified Altec 620, a design I knew others had successfully used. While volume remained similar to the published Altec plan I altered the cabinet dimensions to better fit my space contraints and moved the port to the bottom of the cabinet for a cleaner aesthetic.

As with previous efforts these would have to be placed against a wall with no room to maneuver. I’m (apparently) one of a rare audiophile breed where design and livability need to work hand in hand with sound. If I can’t listen with friends and family in a multi-use space I’m less inclined to enjoy the result. These were to be hulking boxes, no doubt, but practically they took up no more useable space than standmounts.

Constraints firmly in place I designed an 18″ deep, 24″ wide, 43″ tall box milled from 3/4″ ply to which a rip sawn oak veneer would be applied, coated in a danish soap finish.

Bracing would be minimal in keeping with the original specifications, damping via Corning 703 fiberglass panels. Final tweaks were made to the model and files given to a friend for milling.

After weeks of stolen hours devoted to gluing, clamping, veneering, sanding, and soaping the finished product was ready for trial. Would it be worth the effort? (Spoiler: yes)

At first listen the new boxes had solved many of my complaints with prior builds. Bass was now fleshed out, venturing down into the 30’s. A little wooly and a bit muddy but promising to be sure. Midrange was still glorious and crossover tweaking tamed most of the infamous 604 shout around the crossover point.

Dynamics though were a different story. Some of the liveliness, the immediacy, was muted. I began to experiment. Out came one sheet of damping. Then a second. Then all of them. This was definitely counter intuitive. The cabinets were becoming more resonant and the distortion likely higher. Perhaps a case of what’s pleasing to the (my) ear isn’t pleasing to the scope?

Continuing down this road I took things a step further in the direction of “what shouldn’t work”. Out came the solid 3/4” rear doors and in went some 1/2” lightweight ply versions. Finally the jump I needed had returned.

Overall I was pleased. Bass still lacked a bit of punch, highs weren’t as airy as I would like but, all things considered, here was a speaker that simply made music despite its faults. My self-imposed placement limits imaging and soundstage depth but I’m more than happy at the moment to give up some of the illusion in return for the joy of sharing music in a livable space.

The experiments will continue.

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