Or how about 1" MDF?
Has anyone here ever built an 825 or 828 enclosure out of ONE inch thick Baltic Birch, or Europly?
What was your direct experiences, build-wise, and most of all, listening wise, to such a creation.??
Thanks in advance.
Jeff Medwin
Or how about 1" MDF?
I have a FEELING, BB or Europly will sound better than MDF.Originally Posted by Elitopus1
Has anyone done this ??
I HAVE the wood, in my place, stashed away.
Am I to be the first to do so, ........like this new Type 46 SE amp I just built for ALTECs???
Jeff
Jeff
You should build some 1" plywood 828 cabs and tell us how they sound
Yes
I'll pop up and listen !
I've built with 1" marine no-void plywood, but only MLTLs. Works great, but basically only reduces the need for bracing in a large cab as it's already heavy enough with 3/4" [19 mm]. IIRC there's been at least one pair of A7s out of 1" ply posted online long ago, but no link/whatever and a quick Googling netted nothing.
WRT comparing thicknesses, rigidity increases at the cube of thickness and going just from memory using Ga-Pacific MOE specs, 3/4" [19 mm] BB, etc., no-void plywood [~1.8 m psi] Vs MDF [~527 k psi], it takes 1.125" thick MDF to ~match the plywood's rigidity, so yes, they will sound different and worse; as the plywood moves the cab's composite [Fs] up with increasing rigidity, making its harmonics decay quicker to the point where the cab's mass self damps it, the MDF's [Fs] is shifting down in frequency with higher amplitude, longer decaying harmonics that adding more rigidity can't overcome except through added mass, 'chasing your tail' till it finally falls well below its intended passband.
For LF reproduction then, shift cab [Fs] higher with high rigidity and for mids-up, go with increasingly lossy materials with increasing frequency. When designing based on mass loading for LF reproduction, Jeff/LowOhms proved that it takes mass quantities of it to shift it below the cab's Fs far enough to damp it down, so considering how much it takes to do a ~62 Hz tuning, it becomes obvious that it will take a lot more to damp 20 Hz and guessing a concrete bunker to dip below 10 Hz.
In short, with MDF or similar low MOE panels one needs to build LF speakers based on seismic design theory using multiple drivers in bipole configuration to cancel out most of their vibration modes and spikes or properly designed Sorbothane or similar isolation pads to damp the rest.
Anyway, if building from scratch, making the horn out of braced MDF and the rest of the cab out of at least 3/4" BB or similar plywood with some bracing is theoretically the best overall balance between mass and rigidity in a compound horn and using 1" will probably negate any need for bracing the back cab except the large removable rear cover, though better to either use a small rear cover or make the MDF top two piece and use a full size horn sled to tie it all together.
GM
Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.
GM,
That was so nicely done ! Thank you, so much !!!
Jeff ....Low Ohms
No Jeff, you will not be the first to do so. We did this in Europe 30 years ago. I bought my pair in 1988 in kit form frpm the Swedish distributor of the French "Maison de L'Audiophile" gear. All the flat panels were 25 mm baltic birch ply, the flared horn parts were made up from thin sheets of ply glued together in a jig and about 35 mm thick. No buzz, rattle, flex or vibration there, I can tell you. I opted for the early style 825 with two vertical vents as this version looked much better to me than the later version with a single horisontal vent. The vents in the kit were narrower than in the original 825. This design also featured a special 10 mm wool felt covering all interior surfaces and a curtain of the same material from the bottom of the woofer board to the bottom of the box. The kit was obviously inspired by the Jean Hiraga A5s that Panomaniac helped rebuild a year or two earlier. You can read what Panomaniac thinks of Jean Hiragas A5s in post #4 of his thread "My A7-500s. A Journey" on this very forum. For my part, I haven't looked at another speaker since.
The thread: My A7-500s. A journey
Last edited by mah; June 26th, 2017 at 09:24 AM.
Opinion is only as valid as its verifiable supporting evidence.
No Jeff, you will not be the first to do so. We did this in Europe 30 years ago. I bought my pair in 1988 in kit form frpm the Swedish distributor of the French "Maison de L'Audiophile" gear. All the flat panels were 25 mm baltic birch ply, the flared horn parts were made up from thin sheets of ply glued together in a jig and about 35 mm thick. No buzz, rattle, flex or vibration there, I can tell you. I opted for the early style 825 with two vertical vents as this version looked much better to me than the later version with a single horisontal vent. The vents in the kit were narrower than in the original 825. This design also featured a special 10 mm wool felt covering all interior surfaces and a curtain of the same material from the bottom of the woofer board to the bottom of the box. The kit was obviously inspired by the Jean Hiraga A5s that Panomaniac helped rebuild a year or two earlier. You can read what Panomaniac thinks of Jean Hiragas A5s in post #4 of his thread "My A7-500s. A Journey" on this very forum. For my part, I haven't looked at another speaker since.
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