More A7 questions

[VolvoHeretic]

Greetings all, I have but a few hundred questions. I have a set of Altec A7 Voice of the Theater speakers I bought in the mid ‘70’s for $400 ea. As far as I can tell after locating the Great Plains Audio site, they are 828 boxes with 416-8a(?) woofers, whatever horns with 50 watt poly diaphragms and 500Hz crossovers. The boxes have an upper removable rear panel for access to the woofer and a large cloth covered front port panel. I am in the process of sending one of the woofers to Great Plains for reconing. I love these speakers and want to marry them, but my wife says no. I do notice that the mid low and mid high are a lot and the super highs and lows are lacking, although at very high volume and at least 100 feet distance, they sound great. I use them behind a Stax SRA-12s preamp, a heavy dose of Radio Shack 15 band equalizer, and Crown DC300A amp and 8-3” piezo super tweeters per side to fill in the top.
So, is that giant reflex hole in front actually optimized for that woofer? I have tried an online box designer for the 416b that calls for a box size of 15 cu. ft. and a port size of 13.89 cu. in (still nothing below 35hz). I also notice that the horn and box have quite the ring when thumped, so I want to add spray pickup bed liner to the horn bell and encase the box with mdf on the exterior and forming plywood to the outside of the box bell (all plys are in the same direction and are easily bent in one dimension), and then paint them gloss black lacquer to match my grand piano.
Is there an optimum port size for these things? I would like to run these Altecs with a cheap 100 watts/ ch. Technics 5.1 as the front speakers, a pair of Peavey T300 towers as the rear, and build a subwoofer to slave off of the .1 channel, through the Crown amp with either two 4 ohm subs, or one dual voice coil 4 ohm sub. I have looked at a 15” Dayton Titan III and a TC LMS-R 15" DVC, but not at two JBL 2245s. Any suggestions?

This site will not let me post my woofer box calcualtions for 3 more post, so they will have to wait. Sorry

[Altec Best]

Greetings all, I have but a few hundred questions. I have a set of Altec A7 Voice of the Theater speakers I bought in the mid ?70?s for $400 ea. As far as I can tell after locating the Great Plains Audio site, they are 828 boxes with 416-8a(?) woofers, whatever horns with 50 watt poly diaphragms and 500Hz crossovers.
This site will not let me post my woofer box calcualtions for 3 more post, so they will have to wait. Sorry

Two things right off the bat. Replace the poly (Symbiotik) diaphragm with an all aluminium diaphragm. Mid "70"'s I suspect your Crossovers need to be rebuilt.That is one of the first things you notice is the high/low end.You have to reduce the port size as well.Just a few things you can do to make an immediate improvement.

Also you should post High Resolution pictures of decent size and then upload to photobucket,Flickr,any photo site.And then post them here so others can help you better.Just write the word one,two,three, in consecutive posts to get around the posting rule for newbies.3 in a row then you can post pictures ! :2thumbsup:

Read some of this thread Pano made some nice improvements with a pair of A5's same box pretty much 825/828 though http://www.hostboard.com/forums/alte...hlight=journey



BTW: :welcome: To the board.

[VolvoHeretic]

Post reply 2

[VolvoHeretic]

Post reply 3

[VolvoHeretic]

Thanks for the suggestions and topic link Altec Best. I only read it once and will have to try again and maybe comprehend some of it I remember that I have an aluminum diaphragm in one horn and a symbiotic diaphragm in the other. I will have to get another aluminum one. As far as I can figure out, I have the 825 cabinets? Mine has a small rear removable cover just behind the woofer, or are they essentially the same box as the 828? I do have the horn mounted on top of the cabinet in an mdf box someone once gave me and I do have 500hz crossovers.

I am now going to try the 50cu in x 6.5” port and try my hand at bracing the enclosure panels, what kind of glue do you guys recommend, Elmer’s wood glue, brown hide glue, PL400 or 500 construction adhesive, epoxy?

If I just add a layer of 3/4” mdf board to the inside, (or maybe the outside), would it help if I sandwiched a layer of foam such a carpet padding and secured everything with carriage bolt with wing nuts? I will be adding rubber wheels and handles and a lot of weight will make them harder to steal.

How about drilling a bunch of 4” lightening holes in the board to make them lighter?

I was playing around with an online ported box designer to see what these Altec woofers were like compared to a modern sub-woofer and came up with this result. I don't know what it all means but anyway...

[bfish]

... what kind of glue do you guys recommend,...

Gorilla Glue's amazing. read the 'structions.

Ex-nay on the oles-hay...:khan:

If you're gonna skin it, do it on the outside (just not in the horn). You can go midevil on the original with bracing, then cover it up. The horn must brace from the inside.

Your simulator (as are most) is for direct radiators, on a baffle like any speaker box. The horn changes all that, so the simmed response is invalid.

[GM]

Greets!

While mass loading via double wall construction yields increased rigidity, bracing with plywood, board or large dowel scraps gains it cheaper and lighter with the latter a big deal if you ever want to sell or move them up/down stairs. There's tons of threads here and on other forums on bracing as well as various ways to deal with the horn flares, so Google, etc..

The vent is optimized for prosound apps, so normally needs to be tuned a lot lower for HIFI apps, but since you want to use a sub system, best to seal them up tight as a drum and use an 80 Hz /4th order XO level matched via bi-amping.

PL400 has worked well for me since it came out, but many DIYers swear by Gorilla, just follow the instructions as Brad noted or you can wind up with a serious mess.

If you really want to make them heavier, just toss some 50# bags of sterilized sand in the bottoms, it won't affect box tuning enough to matter in this case.

GM

[Altec Best]

Thanks for the suggestions and topic link Altec Best.I am now going to try the 50cu in x 6.5” port and try my hand at bracing the enclosure panels, what kind of glue do you guys recommend, Elmer’s wood glue, brown hide glue, PL400 or 500 construction adhesive, epoxy?

Your Welcome !


A rule of Thumb I have always used with excellent results is for clamped joints,miters,rabbit joints,wood to wood, etc.. Use "Titebond I,II,III, Wood Glue" ! But if there is an area where you need a mechanical fastener (Screws-Nails) use the Loctite PL400 polyurethane adhesive that is the strongest adhesive I have ever come across.This is for an area that is never to be removed.Don't allow it to dry on your hands.You will be picking it and skin off for weeks! If it is an area that has to be accessed (Access Panels) DO NOT use this adhesive there.

One thing I don't like about Gorilla is it develops air bubbles (Foams).I have used lots of different glues they all have a purpose but usually they work great for individual apps.And aren't great for everything.A good wood glue yellow or white will work great for tight joints.I dug up this thread from the "Tech Talk Forum" from Parts Express on adhesives.The vast majority say Titebond, it is also my preference as well ! I have never had a joint fail that used Titebond.As long as it is square(Joint).A joint with Titebond and Biscuit's is one of the strongest you can build. :2thumbsup: You also want a glue that won't leave any voids.Most important WRT speaker cabinets.Titebond is $ cheaper $ too.


What is the strongest wood glue (that WON'T foam up like Gorilla glue™)? - Techtalk Speaker Building, Audio, Video, and Electronics Customer Discussion Forum From Parts-Express.com

[VolvoHeretic]

Greets!
The vent is optimized for prosound apps, so normally needs to be tuned a lot lower for HIFI apps, but since you want to use a sub system, best to seal them up tight as a drum and use an 80 Hz /4th order XO level matched via bi-amping.
GM

If I can get the bass tuned down lower, I shouldn't need any subs right?

[GM]

Depends on room loading and how tonally balanced [~flat] you want its response without resorting to mass quantities of contouring EQ: http://www.lansingheritage.org/image...515g/page3.jpg

Notice the LF horn is completely unloaded by ~110 Hz........ Tuning the vent lower will keep the driver from unloading down to that point and will typically blend better to the room, but ideally a sub system capable of blending to the LF horn's gain BW is the goal.

GM