Dec 302015
 

As I promised in my Part 1 blog post, using the A5 VOTT loudspeaker system that Gary Fischer restored for me as an example (below), I’ll describe the details of Gary’s restoration process.

Jeff's A5 VOTTs as restored by Gary Fischer.

Jeff’s A5 VOTTs as restored by Gary Fischer.

One thing that I really appreciated was that Gary sent me photos and kept me informed about what he was doing as the restoration proceeded, which really gave me a greater understanding of the A5 Voice of the Theatre loudspeaker system, and what was involved in restoring it.

Gary’s first step in the restoration process is the cleaning, stripping, refinishing, and repainting of the bass horn cabinets.

Gary told me that there were over 250 subcontractors that provided Altec-Lansing with bass horn cabinets for the Voice of the Theatre loudspeaker systems over the years, and those cabinets varied considerably in the materials used and their quality, as well as the quality of construction of the cabinets, and how well the cabinets met Altec’s specifications.

Altec 825 bass horn cabinet drawing from Altec’s loudspeakers enclosure guide.

There is a fair amount of debate among Voice of the Theatre enthusiasts as to which is the most desirable of the vintage Altec A7/A5 bass horn cabinets. The earlier 825 bass horn cabinets used a two-piece rear panel, with the top panel being removable, and with the Altec plans specifying 5/8-inch thick plywood for the cabinets. The next generation 828 bass horn cabinets were made of either 5/8 or 3/4-inch particleboard, and were more heavily braced than the 825 cabinets.

Gary thinks the best of the 825/828 bass horn cabinets built were the 7-plie plywood 825B cabinets, and he picks the very best of those for his restorations. While popular with some enthusiasts, Gary considers the 828 bass horn cabinets to be “Junk!” and steers clear of them. Gary picked out nice examples of the 825B bass horn cabinets for restoration for my A5 Voice of the Theatre loudspeaker system.

Gary told me that a lot of Altec cabinets have been sitting in theaters for fifty years with little or no maintenance, so they have collected fifty years worth of dust, grime, spider webs, bugs, and the like, so the first step is a good cleaning of the cabinets.

Gary told me that he sanitizes and power washes the cabinets, sending “Fifty years of historic dirt and grime down the drain!” The clean 825B bass horn cabinets are then air-dried by large fans for a day.

Gary strips and refinishes the cabinets in a process that he says is “… very similar to refinishing a automobile.” First he takes the existing finish off to see what he has to work with.

Gary told me, “I have seen cabinets repaired with automotive body filler, hot glue, and epoxy, none of which truly bond to the wood. I have seen cabinets literally hollowed out by termites, with renders the cabinet to firewood.”

Gary plugs all the holes with cut dowel rod and wood filler, and then applies surfacing material, and block sands them to a flat surface.

Then they go into the paint booth for repainting. First the top, sides, and bottoms are refinished and painted.

Then Gary strips, refinishes, and paints the low frequency horn section.

Gary told me, “This step is always very time consuming to get it right. I remove the rear driver mount plate to simplify the process (and it is always loose in every cabinet), and then I reinstall it with wood glue and drywall screws to eliminate any resonance.”

Gary went on to tell me, “The various cabinet builders Altec contracted (and there were hundreds), apparently had very little quality control when building the cabinets, and no two cabinets came out the same. I have received cabinets completely out of square, leaning to one side or the other by as much as a half-inch top-to-bottom. I guess Altec did not care. The thickness of the plywood used also varied from cabinet to cabinet. It can make restoring something that was never right in the first place a challenge!”

While Gary was in the process of stripping, refinishing, and repainting the cabinets, we discussed some of the modifications mentioned in John Stronczer’s (Bel Canto Design) article in Sound Practices Issue 11 about adapting the Altec A5 Voice of the Theatre to home use.

In particular, John Stronczer said that in the older cabinets like the 825, he thought they needed to have the area behind the short horns closed off, as well as having the port area closed off by up to 50% to perform at their best. John said a port area of 25.5-inches by 8.25-inches turned out to be nearly ideal for his A5s.

Gary told me, “I stuff the bass driver horn cavities with high-density fiberglass to damp the sidewalls of the horn, and I use 3.5-inch fiber glass on the back and the floor of the cabinet to control cabinet resonance. I don’t think there is a need to mechanically block off the horn side cavities, as they are tightly stuffed. As for the port opening, I will cut a new piece of 3/4 plywood with the opening dimensions John suggests and install it in the port opening.”

Gary also told me, “In the fifty-something pairs of 828 and 825 cabinets I have serviced, none of the horn side walls were blocked off, and not even damped by anything, which in my opinion, was a mistake by Altec. But Altec was not looking for pure sound, they just stuffed these Voice of the Theatre loudspeaker systems behind viewing screens around the world, and they remained there for decades at a time. Now we have a new audience listening to these components, using them for something they were never designed for – high-end audio – and we’ve discovered the need for refinement to get the best sound out of them. That takes a good ear and the ability to re-engineer what we have to work with.”

In the photo above you can see the 825B cabinets after they “came out of the finish & rough-sand stage, and ready to go to the scuff & polish stage … you can see we fabricated the 25 1/2 by 8 1/4 port you requested. They are just sitting in the cabinet for pictures, and are not mounted yet.”

In the photo above you can see where Gary stuffed the bass driver horn cavities with high-density fiberglass to damp the sidewalls of the horn

17 finished 825 cabinets 1

In the photo above you can see the 3.5-inch fiberglass that Gary installs on the back and the floor of the 825B cabinet to control cabinet resonance.

At this point the classic 825B bass horn cabinets are finished.

In my next post on Gary’s restoration of the A5 VOTTs I’ll cover the 515B low-frequency drivers, the 288C high-frequency compression drivers, and the 1005B high-frequency horns.

Thanks for stopping by – more soon!

 Posted by at 5:39 pm

  10 Responses to “Gary Fischer’s A5 ‘Voice of the Theatre’ Restoration Part 2: The Bass Horn Cabinets”

  1. Hi Jeff,

    You are doing a knock-out job describing the Voice of the Theatre possibilities, and Gary’s beautiful and thorough restoration. As a person interested in these possibilities I am so very appreciative. You are doing a service to all of us with VOT interest. My interest was stimulated by hearing the Stokowski VOT units in your small parlor room. I was gobsmacked by the vivacity of the Stokowski units. This experience has created an itch that must be scratched. I’m sure there will be a pair of VOT speakers in my “Garden of Earthly Delights” listening room before too long. Thank you for the inspiration and the very useful information. I look forward to hearing the A5 pair before long.

    Peace,
    Pete

    • Dear Pete,

      Thank you so much for your gracious message. 🙂

      I suspect the New Year will bring us many exciting adventures with these Voice of The Theatre loudspeaker systems from a bygone era.

      I can hardly wait!

      Kind regards,

      Jeff

  2. I am hooked on these ! what a wondefull job and project for me ! I have been a carpenter by trade for years and always have had a love for music and how it works 30 years ago i puchased a pair of Klipsch speckers horns and have been in love with horns all this time have purchased a set of 511b horns and 808-8A drivers and am now out of controll LOL my goal is to find a set of 825B cabenits ! where would i look ? Paul B .

    • Hi Paul,

      With your skills as a carpenter, I would imagine you could build a beautiful set of the 825B cabinets quite easily. Here’s a link to the plans for the 825 cabinets.

      Be sure to let me know how your project works out!

      Kind regards,

      Jeff

  3. Thanks what a grate job and artice !!!! Thanks

  4. Paul,

    Pete Riggle here. I want to encourage you on the Altec A5 project. Just this year I heard Jeff’s A7 speakers and managed to acquire a nice pair of A7-500-8 speakers myself. These have the 511B horns, 802-8D compression drivers, and 8 ohm 416 woofers with ceramic magnets. I was surprised at how good they sounded in my listening room (The Garden of Earthly Delights) with the stock crossovers. Very spacious and nicely voiced with rich mid-bass, but a little bit raw sounding. After I built and connected a set of Hiraga circuit 8 ohm crossovers, with really good caps, the speakers took on a new level of refinement. You can find a schematic for the Hiraga networks, in both 8 and 16 ohms, in John Stronczer’s Sound Practices article on the A5s. I recommend Ronken P61 series capacitors, which you can find new or used on eBay. I listen with the speakers in a large room with the speakers about 8 feet away from the sweet spot. Very spacious, with good front to rear distribution of the apparent sound field. The Hiraga 8 ohm network has a notch filter with a 12 ohm resistor. For the 811B horn I found the notch to be just a trace too deep and paralleled the 12 ohm resistor with a 15 ohm resistor, giving 6.66 ohms. This added just the right amount of pizazz to the sound. I also included an 8 ohm L-pad at the tweeter which I use to decrease the tweeter output slightly. Wishing you good luck with finding the right cabinets.

    • Howdy Pete,

      I can’t wait to hear your A7’s with Hiraga-san’s crossovers in place. I thought your A7’s sounded great the way the were, I’ll bet they’re really sounding amazing now!

      I’ve got the 16 Ohm version of Hiraga-san’s crossover circuit posted here on the blog, which you can find by searching on ‘Hiraga’. There’s also a version here with modifications & components choices that have been suggested by Yazaki-san, which I’m looking forward to building soon (just waiting for the inductors to arrive).

      This Altec adventure sure is a lot of fun!

      Cheers,

      Jeff

      Cheers,

      Jeff

  5. Paul,

    Pete here again. I forgot to mention that the A7 bass was just a touch boomy in my room. I addressed this by blocking the center 17-1/2 inches of the big vent with a rectangular piece of 3/4″ plywood friction fit into place. The bass is now as tight as a drum. You will want to augment the deep bass with a good subwoofer I use my 29 foot long horn subwoofer, but you can do it with a direct radiator subwoofer. With my horn subwoofer I allow the woofer to overlap the bass from the A7s; the roll-off point for the horn sub is 160 Hz at 12 dB per octave. This bass overlap also works with other speakers I sometimes use in this room. But, of course, rooms vary; you will want to play around to see what works in your room. Best Regards.

  6. What kind of paint do you use on cabinets

    • Hi Gary,

      I don’t remember which paint Gary Fischer uses for his cabinet restorations. I do know that he takes an original Altec paint sample, then has it matched from a professional paint provider, so that he get’s a finish with authentic color.

      If Gary Fischer sees this message he can answer your question more specifically.

      Kind regards,

      Jeff

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