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I had some spare pieces of high quality MDF leftover from project. I left them out on the side of the house in a scrap pile for 2 years. They got wet frozen baked in the sun. I only tossed them in the trash last week but not bloated ot deformed. They were discolored.  Not sure how or what the crap I bought but I can't say MDF is inferior.

 

As for material use just use what is best for the project.

 

 

 

 

 

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1 hour ago, Dave A said:

Regular plywood though right? Think of all the money they wasted by not using consistent but more expensive up front wood such as Baltic Birch. Wonder how much they lost saving money buying the cheap stuff.  While I have not cut tons of BB what I have cut has been void free.

 

 

I agree, but this was 35 years ago...................

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I’ve worked with four 4 x 8 sheets of Baltic birch and NEVER ran across a void.  That’s not to say they can’t exist, but I never saw one.

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6 hours ago, glens said:

Well, I think that for rough-and-tumble qualities there's only the one choice, and for inert density there's only the one choice.  Too bad they're mutually exclusive in this case.

 

Postscript:  dense plywood is hard on cutting tools, and dense particle board is hard on cutting tools.

I do not agree mdf is heavy and as such when it goes into resonance it is harder to stop so more complex brace work is required, this adds greatly to the overall size and weight of a given design in order to provide stability there is no free lunch. The density of mdf is nice to have but the high Q resonance is not.

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2 hours ago, DizRotus said:

I’ve worked with four 4 x 8 sheets of Baltic birch and NEVER ran across a void.  That’s not to say they can’t exist, but I never saw one.

if you purchase BB ply built with selects and better veneer then you will not see voids because each ply of veneer used is of the grade used for a show top and show back side of plywood there are no knot holes or plugs tolerated in these plys and so by construction the finished plywood will have no voids.

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8 hours ago, Randyh said:

...JBL  , on the other hand , owns the  Pro market , they make their Pro speakers out of MDF -

 

Their smaller pro gear medels are made from poplar plywood, their arrays are made fro fiberglas. I didn't dig any more than that.

 

My much older 4311 bookshelf speakers  (now almost 50 years old) are mdf. Solid as can be and I've hauled them all over. Never dropped them or left them in the rain, though. 😉

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9 hours ago, Randyh said:

Klipsch use  BB  for Pro speakers  , since they want to show how tough the cabs are , and they need to compete in a very crowded market  --------JBL  , on the other hand , owns the  Pro market , they make their Pro speakers out of MDF -

I have 9-904 bass bins, 6-415 bass bins and some KPT-450 horns in the shop right now and not one is BB. Now Klipsch might use Birch veneered plywood but I have never had a Klipsch speaker made of true BB. I have heard reports of some out there but in all I have handled not one.  JBL is a mystery to me as the ones I have heard are not good. They must have a great sales team though.

 

  I was picking up a bunch of speakers from Rescue Audio in St Louis a couple of years ago. Tim had mentioned a rare JBL speaker he could not sell and so he had stripped the drivers out and was going to dump the cabinet. In the mean time we start loading my goodies on the trailer while his labor guys are disposing of the JBL cabinet. THUMP is what we hear and then OH WOW! OK we all want to know what OH WOW is so we go and look. The big box they had heaved into the dumpster had neatly dis-assembled itself and lay there in pieces. Maybe the permanent install JBL's are MDF  but I can't imagine touring or non-permanent install people being thrilled with them. Maybe they all are I don't know and not interested enough to go look up JBL as I really don't like what they make.

 

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5 hours ago, moray james said:

I do not agree mdf is heavy and as such when it goes into resonance it is harder to stop so more complex brace work is required, this adds greatly to the overall size and weight of a given design in order to provide stability there is no free lunch. The density of mdf is nice to have but the high Q resonance is not.

That is an interesting topic all on it's own. I had some Chinese and some true Baltic Birch in the shop at the same time. You could take a piece of each and tap it with your knuckle and there was a dramatic difference in the sound you heard. Talking to a speaker guy in Nashville one day and he mentioned a friend who built speakers for pro use preferring 1.25" Poplar plywood for motorboards because he liked the tone they gave. Some of the old Chorus speakers I have had were Poplar motorboards also and I wonder if the choice was price or tone + price. The idea that cabinets have to be braced to dampen resonance also implies that no matter what we do some resonance will be a part of every box built and then you have to determine how to eliminate what you don't want. Wood suitable for the best stringed acoustic instruments is carefully selected so what is heard when played produces sound at or better than certain critical standards. Now I know acoustic stringed instruments are also their own stand alone "amplifier" but just like people go crazy over warm and mellow and musical characteristics of electronic amps I think the same can be true for wood choices.

 

   In the only real test to compare the two mediums namely BB or MDF I have only tried this with La Scalas. I have heard the MDF La Scalas. I have also heard some La Scalas where I have beaten off the 3/4 plywood sides and replaced them with true 25mm BB and the MDF does not win. Now above and beyond all the durability stuff what I also prefer with BB is I like how it sounds.

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The birch laminated plywood I used 19 yrs ago to build the vert cornwalls was bought at lowes.  I don't remember any voids. If it did, they must have been minimal.   

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 I thought (maybe Jim Hunter would know, or even Andy) what the Klipsch pro stuff was made with early on was a marine grade plywood. It would have had better glues and fewer/no voids.

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By saying that I have seen no voids in 4 sheets of 4 x 8 Baltic birch, I’m not just referring to the surfaces.  Many cuts were made without revealing any voids.  That’s not to say that voids don’t, or can’t, exist, just that numerous cuts NEVER revealed any.  Contrast that to ordinary plywood where voids are frequently revealed when cuts are made.

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My splits were built from factory cabinets from 1974, and one of them has an obvious small void on the side.  I could hear it when I was hand sanding, and once I localized it, it has a bit of sponge-like consistency to it.  It is about the size of a half-dollar.  I thought about drilling a small hole to get a path into it and injecting loctite pl, but decided to just leave it alone.

 

 

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appleply? is that a brand name or what?

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Baltic Birch is graded just like any other plywood, if you find voids in the plies or surface patches you purchased the lesser quality product. It is not all the same.

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nevermind, google is your friend.

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55 minutes ago, Randyh said:

 

here is Appleply ---love it ApplePly

 

 

Good stuff.  That's what my Belle clones are made out of.  No one in my town sells it but there was a place in Little Rock that does I believe.

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