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PostPosted: March 21st, 2019, 10:53 pm 
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Joined: July 25th, 2013, 9:41 am
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Been spending the last couple weeks reading about that, but was curious if anyone here has ever delved into such design. Not quite as simple as a bass reflex :-)


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PostPosted: March 22nd, 2019, 9:42 am 
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Location: Parkville, Maryland
dkalsi wrote:
Been spending the last couple weeks reading about that, but was curious if anyone here has ever delved into such design. Not quite as simple as a bass reflex :-)


I converted my Altec reflex speakers (actually twin vents flanking the horns) into a "half-ass" transmission line and what I got for my effort was a neutral open lower mid-range and solid detailed bass down to 30-Hz. Word of advice -- if you move on to the venture do not use acoustic foam. Foam is much too reactive. Fiberglass or wool gets you there. At one time fabric shops sold raw un-bleached cotton in bulk that worked extremely well -- actually I kind of preffered the cotton.

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PostPosted: March 22nd, 2019, 11:21 am 
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I actually built two many decades ago. A small, about 3' folded line using a 4" driver as a proof of concept. was so happy with it ( before I could do measurements) that the next project was a 12' line using a 12 inch driver. Bought a Richter Scale low pass filter/analyzer/ calibrated mike/1/2 octave equalizer. The speaker was amazing. Roughly flat to 40Hz, had to cut output at 30Hz, the lowest I could measure, where the response hump was as. 16Hz organ music made you smile.

Unfortunately, a basement flood in my first house destroyed the 2 x 0.75" thick particle board cabinets.

They were as heavy as refrigerators!

I say go for it. I knew (still know) nothing. Just used rule of thumb measurements and they came out great.

Stuart


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PostPosted: March 22nd, 2019, 11:54 am 
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Joined: January 14th, 2015, 11:15 pm
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You might try the Martin King Quarter Wave website. Plenty of info there. Sorry I can't include the URL but a Google search should work.

Ray


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PostPosted: March 22nd, 2019, 12:17 pm 
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ratbagp wrote:
You might try the Martin King Quarter Wave website. Plenty of info there. Sorry I can't include the URL but a Google search should work.

Ray



Thanks for responding, All.

Yes - I've been looking through the website over the past couple weeks. Apparently, Martin had MathCAD based spreadsheets that helped with simulation. Unfortunately, those sheets are no longer made available.


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PostPosted: March 22nd, 2019, 12:54 pm 
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dkalsi wrote:
Apparently, Martin had MathCAD based spreadsheets that helped with simulation. Unfortunately, those sheets are no longer made available.


Last I knew, they were no longer posted, but you could get them if you asked. That may not be true anymore. There's a Yahoo group that Martin is quite involved with...

Roscoe


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PostPosted: March 22nd, 2019, 8:42 pm 
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Roscoe Primrose wrote:
dkalsi wrote:
Apparently, Martin had MathCAD based spreadsheets that helped with simulation. Unfortunately, those sheets are no longer made available.


Last I knew, they were no longer posted, but you could get them if you asked. That may not be true anymore. There's a Yahoo group that Martin is quite involved with...

Roscoe


Thanks, Roscoe. I had reached out to Martin and he did respond that he no longer shares to those files. They can't even be purchased.


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