O.T. FYI: An Improved Loudspeaker Frequency Response.......

[GM]

.......by Using a Structure of Rigid Absorptive Panel in a Vented Cabinet

Just saw this on another forum and between Altec being an early adopter of using fiberglass ductboard acoustic insulation [aka OC 703 nowadays] and my limited experiments way back when to confirm it was superior overall, but never been able to prove it to folks on-line, so figured it was worth a look-see and maybe some discussion once enough folks have read/'digested' it: An Improved Loudspeaker Frequency Response by Using a Structure of Rigid Absorptive Panel in a Vented Cabinet

GM

[Petro]

That's cool, I used 703 in the past to make diy acoustic panels covered in fabric for my walls, and they worked great. but I never thought about using them inside the cabs. Guess I need to find a few pieces to experiment with. Thx

[Phil-G]

been a fan since I found a couple sheets that blew off an AC repair truck.

[GM]

Yep, just google image various Altec speakers. Model 820 from the late '40s - mid '50s: https://www.google.com/search?q=altec+valencia&rlz=1C1AVNG_enUS675US675&e spv=2&biw=1030&bih=512&source=lnms&tbm=isch&sa=X&v ed=0ahUKEwiS68_Soe3QAhWIKiYKHet_BakQ_AUIBigB&dpr=1 .1#tbm=isch&q=altec+820

GM

[Petro]

I was looking at the link you put up and saw some very interesting examples but once I saw these, it stopped me dead. Holy crap I love these!!!! But what's going on with the back? Followed the pic to a website which said it's going for a dipole design. Which is a good idea. The reason I didn't go for the smaller scale a7 cabinets for my diy cabs was because the woofer would have been set way too far back in the cab. I need to make those horns!!

[bowtie427ss]

Yep, just google image various Altec speakers. Model 820 from the late '40s - mid '50s: https://www.google.com/search?q=altec+valencia&rlz=1C1AVNG_enUS675US675&e spv=2&biw=1030&bih=512&source=lnms&tbm=isch&sa=X&v ed=0ahUKEwiS68_Soe3QAhWIKiYKHet_BakQ_AUIBigB&dpr=1 .1#tbm=isch&q=altec+820

GM

210's use a panel of it separating the driver chamber and the large open reflex volume of the cabinet.

[juniper]

GM thanks for posting, that's one of the coolest things I have seen on a looooooong time!

[GM]

210's use a panel of it separating the driver chamber and the large open reflex volume of the cabinet.

Hmm, don't know that I'd call it as just 'separating' since it does triple duty as also a semi-rigid acoustic fiberglass insulation [OC 703 nowadays] damping panel to reduce the cab's strong eigenmodes [~13560"/2/~82.5" = ~82 Hz] down to below the horn's ~75 Hz BW as well as somewhat 'critically' damping the vents, yet one more example of why there's been precious few actual speaker design 'inventions' since WWII beyond those due to advances in materials, manufacturing technology.

GM

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GM thanks for posting, that's one of the coolest things I have seen on a looooooong time!

You're welcome! Yeah, 'what was once old is yet new again' or 'if you don't learn from history you're doomed to repeat it'.

GM