Weekend A7 mods plan .... Suggestions?

[drummerwill]

Well I've got my supplies for the weekend, 3 cans of Spray foam and 3 tubes of Liquid Nail.
Here's the plan for my A7 cabinets. First I plan to cut a new bottom panel made of MDF that would have a vent that 2"3/4 high 28" width for about a 75sq.in vent.
Then I plan to turn them face down , take off the back panel where I have access to the back of the bass horn, Then I'll fill as much of that void as possible with foam.
Lastly if I have the time I'll glue some 3/4" 2" x 2 wood strips to the sidewalls, bottom of the horn and the bottom floor.
How does that sound, are there any other mods for the A7's I should consider?


Also, what are you guys using for footings on A7's for best sound?

Thanks
Willie

[GM]

Greets!

Diagonally brace any area > ~144"^2, either add a layer of MDF to the top or make a MDF horn 'sled' screwed into place with enough screws to adequately brace the top of the horn once properly aligned, use good quality neoprene gasket to ensure a good seal on removable covers, mod as required to get the vent down at the bottom and run a bead of glue or construction caulk along all seams to seal them. Note that braces shouldn't butt up against/attached to any other bracing or corner since it creates a resonant 'hot spot'. Last, but not least, install a brace that mass loads the driver to the baffle/cab and critically damp the vent using the 'click' test or similar impulse signal for smoothest response.

GM

[bfish]

And.....

Be aware of the unexpected power of aerosol expanding foam. Just a little too much, and come Monday AM you could have a 4" driver opening instead of 8".

Tip; Have 4 heavy rachet straps handy just in case...

[Altec19]

Be aware of the unexpected power of aerosol expanding foam - Part 2.

If you're going to fill in the area behind the bass flares do it in layers. Don't try to fill it "almost full" right away. Let one layer finish expanding before applying another. Otherwise, you may find yourself trying to fabricate a new set of flares.

[endeeinn]

I can only tell you what I did with mine. The vent and panel above the vent are framed with 2x4's on edge. The same for the back panel & new access. Also there is a 2x4 that runs from the front panel to the rear panel. The small glue blocks at the walls (top,bottom,front & rear) were replaced with a full length 2x2 glued and screwed in place.All panels have 2x4's on edge running diagonally from corner to corner. 1/8" thick heavy rubber sheet was glued to all walls and the flares foamed in. Prior to foaming the flares, extra 2x4 radius braces were screwed and glued in place. Rear panel screws (6" apart) were replaced with T-nuts for solid fit. Rear panel is gasketed with closed cell foam rubber strips. In many cases I had to screw from the outside of the box, there were filled in with bondo, sanded and painted. Box now weighs a ton but is solid as a rock.

[pomonabill]

Hey Drummerwill;;;
Why did you decide on a 2 3/4 x 28 vent? What does this size port tune the cabinet to?
I believe the original Altec port tuned the cabinet to 60 Hz, correct?
I spoke (years ago) to an Altec tech and he suggested to make the port 1 x 13 3/4 for a cabinet tuning of 20hz... I kinda doubt this though.
Where there other options for tuning, and if so, what dimensions were they?
I would like to know how to tune the A7's, or if the calculations are the same for a ported enclosure below the horns cutoff?
Bill M

[pomonabill]

Forgot to say Thank You in advance.... I know... QUESTIONS.. QUESTIONS!!!
Bill McK

[drummerwill]

Well here's the progress so far

Link: http://www.audiocircle.com/gallery/d...bum=1470&pos=0

I've got the foam done and vents in.
So listen immediately I'm very impressed the dynamics went up a notch and everything is clearer. Oh yeah I added some new wiring to the woofers too.
I may not get to bracing this weekend , not enough time to make the X braces as GM suggested but so far it a WOW!
Have fun
Willie

[drummerwill]

Well its been a while since I did the Foam thing, and from the listen test its been a real improvement.
When I first got the A-7's I like the sound better with a bit of EQ from my full function preamp. I even cut the hi end attenuation on the N-801A Xover's to get a bigger bass sound.
Step forward to after the foam stuff. For my sound I prefer my 26 preamp ( No EQ ) and I'm starting to bring in the Hi's again on the Xover.
The low end seem to get lower but it may be the mid-bass is filled in a lot more. Everything seems more punchy and better definition. As you might tell I'm loving it!


Note: I did notice on my A-7 3rd cabinet (an older A-7-800 ) the woofer cover has braces and the others don't. I think thats gonna change next!
Have fun
Willie