Sand filling of 828 horn cavities

[jnorv]

I have 828 cabinets, modified with 2245’s in the bottom, 515B’s in the horn. At about 100 dB, the horn flares have a noticeable vibration component. I plan on fixing this by drilling a 2 inch or so hole in the top and filling the cavity with sand. Am I going to have leakage problems with this fix?

[habichuela77]

Jim:

I have the 825's so it may be different, but this is how I did it:

Lay the cabinets on their front.

Remove the woofer access cover on the back.

To the sides of the woofer mounting board you will see the horn flare cavities.

I sealed mine, which were tight and in very good condition, with a heavy latex paint used to seal basement walls. I did three coats. Yours may require some caulk, before the latex paint.

I then "cooked" the playsand -- literally -- filling big pots and putting them on top of the stove for about 45 mins. to an hour. You will see clearly when all of the sand is dry. Sand particles will not stick to each other. Drying the sand this way will clearly draw quizzical looks from your wife and children, who will confirm their suspicions that you have gone over the bend with this hobby, but it is important to prevent the future development of mold and rot in your precious cabinets from the moisture contained in the sand.

Pour the sand until the cavities are compltely filled. I suggest you let it lie there for a couple of days for the sand to settle in. Gently tapping the horn walls helps the sand settle. You may have to add some more sand. You want the horn cavities to be completely filled with sand. On the other hand, don't not pack it in.

Measure the openinigs to the cavities and cut pine boards to fit. Use wood screws and 25 year caulk to fully and firmly seal the openings. You should not have any leakeage problems.

Some people report good results using other materials, such as kitty litter to fill the cavities. I can only report on my experience, which is that sand works very well in damping the extraordinary resonances created by these very powerful Altec woofers. The 515's simply sparkle. I think this is a very worthwhile project.

Jim, I hope this is helpful.

On the other hand,I also have JBL 2245's and have been pondering the issue of installing them at the bottom of the 825 cabinets.

I am currrently leaning towards a different but similar approach.

I am leaning to cutting the front horn section, sealing and reiforcing it, and to build separate boxes for the JBL's.

The JBL boxes would have a little more than 12 cubic feet, to allow for extensive bracing and for the displacement of the driver. JBL reccommends this size for the proper loading of the 2245 in vented cabs.

I think this approach would yield better, deeper bass and more wieldy "components" (the sand-filled horns alone, with the drivers are more than 160 pounds each!)

I am currently using sand filled boxes to isolate the 1505 horns from the bass cabinets.

With this approach, I intend to buid sand-filled boxes to islolate the JBL boxes from the front horns.

One concern I have is about the interacion with room boundaries of the JBL subs when placed at the very same location of the A-5's (Front horns and 1505's). Theoretically at least, the best location for subs isnear corners and othe room boundaries.

(I am currently using a Rane AC-23 crossed at 500hz --515b's to 288 16 k's -- and 4000hz -- 288 16k's to Fane ST 5022 supertweeters. For the JBL's I will use an additional Rane AC 22 to be crossed at 100 - 120 hz)

I am open to comments or suggestions.

[habichuela77]

Jim:

Certainly, the inability to easily access the cavities is a problem. Your solution should work tough, assuming no splinters or loose screws or nails rupture the bag. Even if this happens, I suspect that the pressure of the weight of the sang against the plastic/enclosure wall should prevent any leakage.

I would suggest to not try to force much of the bag into the cavities beforehand. Allow the weight of the sand and the force of gravity to pull the sand to press against the crevices. The plastic bag should suffice as a "sealer" and vapor barrier of sorts. Again, allow for at least several hours for the sand to settle in, and add sand as needed. BTW, "cooked sand" flows a lot easier.

I have not heard a tactrix, but I am extremely satisfied with the music produced by the 288/1505's. I am aware of the very extensive (and intensive) debate regarding imaging and horns. I find that the 1505's do image well if placed properly within a room. At least, to my taste.

But you know, in audio, perfection lasts but a few months... For now, at least, I am happy.

Do you have pics of your 828/2245's?

Can you post them or email them at [email protected]?

Good luck with your project. I guarantee that you will find the effort very much worth your while.

[jnorv]

In the 828 cab’s, the woofer mounting board is the full width of the cabinet, sealing off the horn cavities. This makes it more difficult to sand fill them without worrying about leakage. I will probably insert some 1 mill garbage bags thru large holes and then sand fill. I netted out 7.5 ft^3 and with generous stuffing if appears as about 8.5 ft^3. Not up to the JBL specs but good enough for me. I was not looking for flat to 25 Hz..

Your proposed solution will probably get you lower response. However for the extra effort I would be tempted to go with maybe the Edgar horn sub and a different mid horn. See some of the data from eso an audio asylum (http://www.AudioAsylum.com/forums/HU...ges/28222.html). ESO seems to be a prot?g? of Bruce Edgar and has developed his own variation of horns. Have not met up with him but intend to make one of Edgar’s SoCal horn meetings one of these days.

Jim N

[Russellc]

I too have 828 with sealed backs. rather than sand, I have heard of people using the expandable foam, then leakage is not an issue, nor drying sand, and it doesn't add as much weight as sand. I do not know if it dampens as well, and I guess you'd be stuck with the results.

Russellc

[stpower]

If you use the expandable foam, take your time and add just a little at a time. Wait a day between injections. I ruined a nice 828 once by rushing the job. One day after injecting the foam all at once, I heard a sickening cruching and splitting sound coming from the 828. All I could do was stand and watch while the horn flares changed to who knows what kind of expansion rate!
Since then, I use kitty litter.

stpower

[bfish]

I just finished reinforcing the horn flairs in my 825s with a little different method; with the cabs face-down and sans drivers, I applied a 1" layer of reinforced concrete on the flair's backside, then sealed both compartments flush with baffle, and filled the remaining voids w/spray-in foam. First, I cleaned out the dust, and squeezed a bead of Gorilla Glue into every joint that allowed it. For the concrete, I cut a piece of 1/2" hardware cloth to just fit in the flairs front-to-back, and 1" wider than the distance between the curved braces. By folding 1/2" of that excess on both edges at a right angle, the piece will just lay in the largest flair cavity, and will leave the turned-up edges to be stapled to the curved braces. Staple in place so that mesh is 1/2" away from the flair. The smaller flair cavity won't need any mesh. Turns out that one 60 lb. bag of concrete will yeild an inch in both flairs of 2 cabs (15 lb./flair). I used fiber-reinforced mud, BTW. Rock and block both cabs so each has a flair cupped near level and do those 2 first. Moisten all wood in area with water with a drop or two of dish soap to aid adhesion, then scoop in the (mixed) mud. Use a gloved hand to spread it, thouroughly forcing it through the mesh and into corners, then take a putty knife and really work it in all corners. By now the suface will be wet enough to finish to taste. I even used an orbital sander as a vibrator on the face of the flair to eliminate any voids. When these two flairs are set enough (2-3 hrs) rock them over and do the other two. When all is dry, vacuum out any loose material, and install (or reinstall for 828s) the panel(s) to close off the flairs, and stand cabs upright. Drill 2 quarter-inch holes into each compartment void, one from below and near the front, and one from the rear, near the top. READ THE LABEL on whatever foam you use. EXPANSION RATES VARY IMMENSLY. Rather than calculate the volume for high-expansion foam, I used the very-common "red-can" from Lowe's, which has minimal expansion (approx. 35%). Empty a can into each flair from below, wait 1 day, then empty another can each into flair from behind (8 cans total). The foam will 'collapse' if disturbed while wet or applied too deep,hence the delay. If done right, you'll get a little foam expansion back out of the top hole, (unless you plugged the hole right after foaming, then see previous post for results!) After a few days, check your results by tapping/listening on the entire flair face, mine came out literally "like a rock". If you do find a dead spot, even a small void in the plywood of the flair, you could drill and inject epoxy from the front. The job takes 3-4 days counting cure periods, but it's only 4-5 hours real work, only adds 30 lbs/cab, and is, as us hillbillies would say, "**** for stout" Now I'm considering something similar for my 511s 'ringing', but with synthetic granite or marble for the WF (not that I have to worry about that!)
"Till the Wheels fall off and Burn!"

[MikeInNH]

All I could do was stand and watch while the horn flares changed to who knows what kind of expansion rate!

<font size="2" face="Verdana, Helvetica, sans-serif">You never know....It might have sounded better. But repeating the process might be a b*tch.

[jnorv]

I finally took the time to sand fill the horn flares. My local hardware store had 3 mil large trash bags which I put in through 3 inch holes drilled in the top and then inflated with my vacuum cleaner. Took about 55 pounds per cavity. Sure makes them dead. The mid range is much clearer now. absolutely no vibration in the horn flares. Hate to think about ever moving them. Now, for the next exercise, how do I go about sand damping my 1005’s? I have just started thinking about this so any suggestions would be welcome. I regret not picking up Brennan’s tar filled 1005’s.

Jim N