What Plywood are you buying?

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AKA - Plywood from Box Stores; this is from yesterdays project :dead:

1st pic - One 7" rip, moved rip to other side so two factory edges are side by side. To my surprise at least a 3/4" gap. This is often the case with oversized sheets e.g. 49" x 97" this measured standard 48 x 96.

Okay, some manufacturing issues with the factory's saw blades; now what about strength? Took some of the small pieces and simply broke them in half with hands, like the glue was watered down and sprayed on between layers.

(While I was there; checked out the plywood edges on the box store racks, there was a lot of de-lamaintion - a bit of a nightmare at $50 per sheet and hours of labor needed for a project)

Posting this here because I cringe when I see some of the guys putting large speakers in box store plywood. Now sure, not all "batches" are the same, some may be fine, but really can't tell until final stages of the project.
 

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I never buy 5 ply (7 if you count the veneer faces) because it isn't strong enough in my opinion. I only buy 10 to 12 ply birch, or Apple plywood. For me it is less expensive to build it right the first time than building it twice. I value my time more than that. If the big box stores don't carry what you're looking for, then look up the local cabinet shop. Many times they are willing to sell ply wood for 10% over their cost.
 
If you can get MEDEX - you'll never use MDF again; less dust, machines nicely and paints beautifully...

Hot DIY tip: Try added a layer of BB ply to back of composite wood boxes, you'll be quite surprised :cool:

Sample MEDEX pic below:
 

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Oh, I wear a mask most of the time, it's just a pain, that damn dust gets into everything, it's nearly impossible to avoid it completely.

My friend works for a big company that build cabinets and speaker enclosures and He has in his house a BIG exhaust fan "attached" to his table saw that gets MOST of the dust out. He used to build MDF speaker cabinets for me long time ago. I think it will help a lot an exhaust fan that can take all the MDF dust out or filtered kind of way.
 
To me the only downside if that is one lol. is MDF is way heavier than plywood and solid wood. But as I said before, MDF is the way to build cabinets for speakers. MDF is the choice of material used in well known and reputable speakers companies. if they trust MDF material for speaker enclosures...so should We.;)
 
Wow, those speakers are very expensive! But it is kind of a contradiction there. Because He is using Metal rods to avoid resonance...and the worse material is ...metal! That is why metal speaker stands are suppose to be filled with sand to cancel the resonance. Metal is good for BELLS! Best material for speaker stands is wood or other material that will not resonate But,not metal...Why? again, because of the poor job to avoid resonances. but maybe I am wrong here hehehehe

PS: You want the best material that will NOT reflect the waves back to the drivers and Metal is extremely solid and will be like a satellite dish reflecting those standing waves back to the drivers. You want "cancelations" not reflections. Even if you put dumping material, it will not be the same.
 
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Wrong.

To me the only downside if that is one lol. is MDF is way heavier than plywood and solid wood. But as I said before, MDF is the way to build cabinets for speakers. MDF is the choice of material used in well known and reputable speakers companies. if they trust MDF material for speaker enclosures...so should We.;)

No high end professional subwoofer box is manufactured with MDF.

It may be used for home/auto boxes where strength to weight is a low priority but the big boys use high quality baltic for big horns and dual 18 boxes that mortals can move without a forklift. It is stronger and holds up better to moisture which along with the dust is why I will not buy another sheet of MDF.

Arco used to be decent but the china ply from the box stores is mostly junk.
 
No high end professional subwoofer box is manufactured with MDF.

It may be used for home/auto boxes where strength to weight is a low priority but the big boys use high quality baltic for big horns and dual 18 boxes that mortals can move without a forklift. It is stronger and holds up better to moisture which along with the dust is why I will not buy another sheet of MDF.

Arco used to be decent but the china ply from the box stores is mostly junk.

Those HUGE speakers are used for DJ's in concerts etc. They do not use MDF because those speakers will weigh so much that you will need a machine to lift them. That is way some speakers are made of Polypropylene material and are very light.
 
Partly that, and partly because if you clobber an edge (and it'll happen in about 10 seconds in a pro-audio environment when the boxes need to be moved) MDF will often suffer fairly terminal damage.

MDF is frequently used
a/ because it's cheap,
b/ because it's dimensionally stable, &
c/ aside from the ends, which are a royal PITA, it takes a very good finish.

If it's a choice of that or some duff quality ply, the MDF, which is usually more consistent than the cheaper plywoods, is unquestionably the better choice since it's not likely to fall apart. However, it is not without its problems, the big one being that it's not really stiff enough for most bass enclosures, if you're going all-out. There's a reason Avalon & some others (whatever you think of their speakers) use massively thick front baffles.

Based on the average MOE values, you need about 1 1/8in - 1 1/4in MDF to ~ equal the stiffness of 3/4in BB plywood. Since you can't eradicate panel resonance, just shunt it to somewhere it's less likely to be excited, that means going down, below the BW of the enclosure, or up, above it. The former is a swine with bass boxes; you need thicknesses with mass approaching a reasonable layer of concrete. Pushing them up, above the BW of the box, is usually somewhat easier. High stiffness (relatively) low mass, & fairly easy to damp out. There's no reason metal rods for additional panel-stiffening should cause any audible problems so long as some common sense is used in their placement & a little damping material added if required. Typically their resonant frequency will be well above the main box operating BW, where there is little energy available to excite them. This is fairly basic stuff; ask any mechanical engineer.
 
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