1005b Protection for the Road

[House de Kris]

I would like to use my 1005b horn with my little portable PA system. I read, on this site, the Altec catalog pages where they package an 805b horn in a box for road use and call it a 1225A. They say that on its own, "a multicell is delicate and fragile," thus the protective box.

Well, I've got a box around my 1005b horn, but I'm wondering if I need more protection for my delicate and fragile horn. To this end, I was thinking of bringing my boxes to work and filling it with the expanding foam stuff in the shipping department. Our packaging engineer thought the expanding foam might not be too hot, since it hardens to be quite stiff and will transfer impact engergy to the horn. He also said the expansion has quite a bit of force and may bend or otherwise damage these fragile horns. This gives rise to a couple of questions:

1- Is expanding foam a good idea, or pure bonkers?
If so,
1a- Should the foam be allowed between the cells?
1b- Should the cells be isolated from the foam by plastic?
2- Would soft foam cut to size be superior?
3- Anyone got any other good thougths?

Here are a couple pictures of what I'm trying to provide protection to, and what the box looks like.

Oh, and thanks for any comments.

[Tom Loizeaux]

I've thought about using the expanding foam as well, but my horns are large fiberglass horns that have "lips" that extend out in front. The foam, in my case , would be used to firm up the fiberglass to help protect it from impact damage and to eliminate vibration or resonances.
Instead of pouring foam into the rear of the horn cabinets, I built plywood covers, boxes really, that mate and latch to the front of the horn boxes, completely enclosing the front of the horns.

I suspect that any damage from being on the road with your Altec multi-cells would be from the front. Firming them up with foam might not do much to protect the vanes from damage. Unless you put things inside your boxes during transit, I don't see the back of the horns being in danger. Maybe a front cover would be more effective?

Tom

[Steve Schell]

Seems to me that an enclosure to protect a multicellular horn would need to have rounded lips in front that protruded far enough to protect the horn if the assembly were dropped on its face. I once fitted a pair of 805Bs to Karlson enclosures, and mounted them on boards that stuck out enough in front that they would protect the horn if the speaker tipped over forward.

The box should also fully protect the driver in the rear to absorb impacts. Mounting the horn securely in the box would also be important. I eye with suspicion your use of a front mounting bracket to support the horn throat. It looks like it will interfere with the seal between the horn and the throat, will bend easily, and would apply any stress loads to the horn unevenly. It would be better to use the cast mounting flanges on the throats, and build strong brackets if you do not have the original ones. Another option would be to support the driver by its outer diameter with some sort of wooden bracket with a semicircle cutout for the driver to snuggle into, and a padded strap over the top.

I don't see any advantage in putting foam around the horn or between the cells, except that it will damp the horn walls and improve the sound. The old tar filled horns sound better than the later ones, though they would be way too heavy for a portable PA. It would be best to build a strong enough box to withstand impacts without the forces being transmitted to the horn inside.

Good luck with the project. You should end up with an excellent sounding PA system.

[House de Kris]

Thanks Tom and Steve for the advice. I did see that the Altec 1225A does have a removable cover for the front, but didn't realize that it is this front protection that is the most needed. I somehow thought they were making a big deal about the box itself. So this is good news!

That support bracket in there now is indeed on the wrong side of where the throat mounts, it ended up like that from handling and being temporarily loose at the moment. But, a more rigid support at the driver/throat end does seem to be in order. So, as long as I have the mouth and driver anchored/supported, it seems I should be in good shape, true? I'll work on something to attach to the fronts for transportation.

Again, thanks!

[Maron Horonzakz]

On the throat septas I see welded beads along the edges. These need to be filed down. Back reflections into phaze plug/diaphram area can cause distortion.

[House de Kris]

Maron, thanks for the comment. I take it the welds you mention are the ones INSIDE the hole from the view in the attached picture? Is the intent to remove just the excess bead, or should I try to shape the joint to a sharp edge, or bend radius, or flat?

[Steve Schell]

I'm not sure how much difference filing these edges would make, but they did do a much more careful job of this in the early horns. In the earliest Lansing horns the cells begin in a flat (plane) grid, then curve in the throat to establish their individual directions. The leading edges of the cells are filed to knife-like sharpness- I once cut my finger on one. Then the horns were redesigned to use straight cells, but the edges were still carefully filed for a while. As the years went on the soldering and finishing got more sloppy- the posted photos are typical of the later non tar filled horns. Filing the edges on these could certainly do no harm, and would bring the horn closer to the designers' intentions.

[Maron Horonzakz]

I would file them. But afterwords clean throat so filings dont get into driver.