View Full Version : Altec 825 cabinet bracing, improvements

03-08-2013, 12:33 AM
Hi, new to the site as of today. Audiokarma has been my main hangout recently. I purchased the other day a beater set of 825 cabinets that I am in the process of restoring. Not to long ago I bought at a flea market a set of old Community PA system with 90 degree radial horns and mid bass 15" horn loaded speaker cabinets. Took them home, hooked them up and I was immediately enlightened to the benefits of high efficiency horn loaded speakers equipment driven by my Sargent Rayment el84 tube amp. The empty 825s showed up on the local craigslist for $60, so I could not pass them up. They appear to be home built, but for the most are well done, and match the plans I have seen on. I will utilize the speaker I have for the time being out the the community equipment, plan on updating to the appropriate speakers, drivers and horns in the future, when money allows. My question at this point, and I'm sure its been covered many times in the past, but I'm new here. I understand that the original cabinet design can be very resonate, and I was wondering if the are any write ups on bracing, and dampening of the cabinets, or if anyone has any specifics on how they did it, along with any other ideas on how they can be improved. I have looked at them and have some basic ideas on what would probably work for bracing and dampening, but thought I would go to the source before I got started, for other ideas and opinions on what works best. Appreciate the help in advance. Thanks

03-08-2013, 07:11 AM
There is tons of info on this subject. I just did the same project with a pair of 828's. They are very similar. The biggest difference is the 828 specs 3/4" ply. Where as the 825 specs 5/8's. I laminated 3/4" plywood sheets on the top and sides of my cabinet. I use gorilla glue since it expands quite a bit as it cures. I started a thread about the adventure. It might be a little help.

The big improment for the 828 is filling in the back side of the horn flares. Im betting the same goes for the 825, but im not certian of that.

They are very nice loudspeakers. But the 6db drop below 100hz is a little hard to get use too. The big issue as I said with the 825 is the thinner material used for the sides. I few strategically placed cross braces could help. Also laminating another sheet of plywood on the outsides of the cabinet will help. You can also play around with changing the reflex tunning. Stock they cut off at around 75hz I believe. With a smaller port you can get it down a little lower. But it ont go down real low with stock drivers. Speaking of drivers, what do you have to use?

Feel free to pm me with any questions you might have. Im no expert on the sudject but Ill give you any info I have.

Have fun.


03-17-2013, 09:14 PM
Yes, you should read Nick's thread - it's great, and shows a modern approach to rebuilding 828's.
And yes, there is ton's of info out here about this.
By the way Nick, decided what your next cabinet is going to be? I'm running 816's in the garage and they sound awesome with old 416As with a new custom-built crossover at 900.