A7 replica cabinet material

After reading Panomaniac's thread on tweaking his A7s, I got to wondering if, rather than going to great lengths to stiffen my cabinets, it might be easier to just start fresh.

My company makes both custom cabinetry and carbon fiber race car components, so I have access to a lot of technology, and the A7 cabinets just aren't all that big a deal.

What material would be best? There are lots of options - very thick MDF - I can buy or laminate any thickness I want, the speakers would be VERY heavy. How about 2 layers of 1/2" MDF or plywood laminated to a 1" foam core? Very stiff panel, reasonable weight, and, I guess, pretty acoustically dead. Thick plywood? Again, I can buy or laminate any thickness I want; weight becomes an issue, and I'd guess that it wouldn't be as acoustically dead as the ply-foam-ply laminated panel.

Any thoughts?

Ed

My vote is carbon fiber, bubinga, and Madagascan ebony...... ;^)



-chris

Well you can get all fancy, but my vote would be for bamboo plywood. It's expensive, but very stiff, very dense. Seems to have rather good acoustic properties.

If you can't find it or don't like it, use the densest, best marine ply you can get. And brace it.

There is fancier stuff to build from, but I doubt you'll do better. Sand filled plywood walls would be the ultimate. Kinda hard to do on an A7, but if you are up for a challenge....

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Originally Posted by edharbur

After reading Panomaniac's thread on tweaking his A7s, I got to wondering if, rather than going to great lengths to stiffen my cabinets, it might be easier to just start fresh......

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Maybe, but I'd think no matter what material you'd use, you would want to have bracing.

Skip the MDF. It's cheap, but flexible. If I were going light weight, I'd think some sort of honey comb core would do well, but I really don't know how it would compare to other materials.

Are these cabs for your work enviroment still, if so just use birch plywood, they would be cheap enough.If you want to build for your home could always get Baltic Birch and it comes in differant thicknesses 1" well braced would do very well.

Well, I've thought about carbon/aluminum honeycomb core, but fragile and expensive. Bamboo ply is unstable - I've got left over material from a job 2 years ago that spontaneously splits while sitting in the rack. Baltic birch is easy and cheap, but is it the best I can do? If I'm going to brace, I might as well just modify what I have. If I brace, the braces will effect the air movement inside the cabinet. Does it matter? I don't care about the weight - within reason. If a 3/4" plywood speaker weighs 175 lb (which I've read, but don't believe) then a 2" MDF speaker would be 4-500 lbs. Yikes. These speakers would definitely be for the shop, and I definitely love the industrial look. That being said, my fiance has asked if I can get a pair for her very fancy living room, which is where the original cabinets would go if I opted to build myself a set of killer cabinets. Whoa!!!

I'd build Magnificent's for the living room if it were me...

continued from "ooops... wrong thread... :o

Hi Ed,
Welcome! You're ahead of the curve, having experience and confidence in materials and construction. There are a couple of schools for boxes; brace/make rigid at intervals that ~remove resonance in the passband, or absorb the energy with constrained layers (like your "Oreo"/foam idea). I prefer the former... rather not waste the HE drivers on wiggling a box.

Unless you have a fetish for vintage plywood, tweak whatcha got for a "feel" of it. Bracing/filling the flares yeilds the best return, then the vent. If cosmetics aren't a concern, thru-&-thru 3/4" dowels/all-thread are easy and effective bracing in the reflex area. :)

13 ply 19mm russian white birch and brace accordingly. if i ever move out of the 210 in the living room stage it would be 820's in their stead. loaded with 515b's and supplmented by subs

Bracing?
I hear so much about the need for bracing, and just as many suggestions regarding the method. Vertically on the inside or outside? Horizontally inside? bracing the horn (many methods here).

And how about the volume of air inside the cabinet after bracing. Does the diminished air volume inside the cabinet affect the sound? I have seen pictures of so much cabinet bracing inside the box and thought to myself, surly that must affect the sound. My A7's need bracing, but I am confused as to how much and where.

My A7's are constructed with the flimsy 5/8 inch plywood. And a poor grade of plywood at that. I wonder if I should brace them to the max, or start over with a more ridged 3/4 inch plywood. As I consider more costly drivers I wonder if i'm wasting my time and money with a poor cabinet. Are there any links regarding bracing in A7's?

Your thoughts and advice are appreciated...

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Originally Posted by Mustang Marvin

... Are there any links regarding bracing in A7's?...

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Maybe you missed them the first time...:)

http://www.hostboard.com/forums/alte...ml#post1790418

Thanks BFISH. Maybe these boxes can be saved after all...

You're welcome MM. Those are pretty good summaries, it's been cussed and discussed for a long time now.

In these boxes, it's pretty hard to screw up anything by bracing. Pretty much anything you do in that regard will be an improvement. :khan:

I really had 2 issues.

1, How and where to brace the boxes.
2, Would the addition of material inside the box negatively affect the sound.

In reading the information from the link you gave me (thanks) it was noted that the A7 or A5 cabinet (825/828) is really too large for the driver anyway. SO, the additional material (2X4's) will actually help sonically.

Sorry I missed the thread on this subject earlier. If there are others with A5 or A7's, they should read this information. Now, where did I leave my hammer...

Agreed. There is more than enough volume in there. You won't hurt it with bracing or adding to the walls. You my need to retune the port a little - but since most of 'em are not well tuned anyway.....

Last night I was eating at a big "butcher-bock" table. It was stained and varnished and very pretty. Mostly it was massive and inert. Should make a killer baffle wall. If course the A7 does not have a lot of flat front surface area, the place you'd normally but thick panel like this, but done on the sides, back or top, it should cut cabinet resonances way, way down.

Just a thought.

Quote:

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Originally Posted by Mustang Marvin

.......it was noted that the A7 or A5 cabinet (825/828) is really too large for the driver anyway. SO, the additional material (2X4's) will actually help sonically.

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This is only true if driven with a very low output impedance amp, i.e. SS or some of the later PP tube amps. That said, sufficient bracing won't reduce its net Vb enough to be audible. Get carried away as one person did though and it might, depending on the final in-room tuning.

BTW, 2x4s are overkill. Scraps of 3/4" no-void plywood or knot free 1x4 boards glued vertically on edge make panels plenty rigid. Just offset them in some acoustic ratio. A couple more to create an 'X' member to tie all six side's 'rigde' boards together and you're 'golden'.

GM

Quote:

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Originally Posted by Panomaniac

Last night I was eating at a big "butcher-bock" table.

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Historically, the butcher block panels sold at Lowe's, Home Depot left a lot to be desired from a structural POV, but recently I happened to notice that their quality looked much improved and definitely so from a flex POV, so considering their pricing Vs BB ply, I plan to try some in the (hopefully) near future.

GM

Is the concern here flexibility or acoustic deadness? Think of a cabinet made of 1/2" steel. There would be essentially no flex at all, but would it be a good speaker enclosure? How about some sort of closed wall foam with infinite thickness - again, no flex, but how good a speaker enclosure would it be?

Ed

Pick one of the ~infinite combinations between the two, i.e in theory you want the cab's resonant structure to be a minimum of -25 dB (preferably -35 dB) referenced to the signal's noise floor and since it's easier to raise a bass cab's Fs far enough above its pass-band to achieve this than far enough below its Fb, rigid rules. In short, we want it to 'ring like a tenpenny nail struck with a ball-peen hammer', so either of your solutions are correct, though a bit of overkill unless used for ultra-wide BW single driver apps. From this we see that as Fb rises, at some point it becomes more practical/economical to use a low Fs material.

GM