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Old 24th October 2012, 07:21 PM   #1
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Default great plains 212 8a cabs

hi
i have just bought some gpa 212 8a drivers and am after some suggestions on a box to put them in

i am thinking either a bass reflex tuned to 43hz or maybe an ml-tl

my goals for the project are the usual ,good tunefull bass and mids with an old school look

any suggestions would be welcome and size is not an issue

cheers sheafer

here is a link to the drivers http://www.greatplainsaudio.com/downloads/212_8A.pdf
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Old 25th October 2012, 01:25 AM   #2
GM is offline GM  United States
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Greets!

Hmm, GPA recommends 4.5 ft^3/43.25 Hz Fb, but the vent diameter seems a bit small to me and BL is a typo, should be ~11.8.

Since I prefer MLTL to reflex loading and assuming a ~36” minimum driver floor height………

L =54.15”
CSA = 242.56”^2 [recommend 19.81” W x 12.25” D]
Zdriver = 18.9”
Zport = 43.6”
Rport = 3”
Lport = 0.75”

All dims i.d. and approximate.

GM
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File Type: gif GPA 212-8A MLTL.gif (6.8 KB, 491 views)
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Old 25th October 2012, 05:18 AM   #3
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hi GM

thanks your a legend!!!

now for a silly question do you have a link or such to the program you used for these sims so i can desipher them
i,m guessing L= cab hieght
the w and d are width and depth
but i am lost on the rest
Zdriver?
Zport
Rport radius of port
Lport length of port
i presume they are refering to the port and driver location and size in the cabs

cheers Sheafer

Last edited by slr 5000; 25th October 2012 at 05:21 AM.
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Old 25th October 2012, 05:49 AM   #4
GM is offline GM  United States
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Greets!

You're welcome!

What?! Not familiar with MJK's MathCad software? : Quarter Wavelength Loudspeaker Design

Yes, you guessed right: http://www.quarter-wave.com/Back_Door/Box_App_Notes.pdf

Add some bracing and damp to 'taste'. A good plan is to make your port adjustable and depending on your room and in retrospect, starting with a 4" rport x 0.75" that raises tuning up to ~GPA's 43.25 Hz might be required.

If you build them, hope you document it with pics, final tuning choice, etc. since AFAIK yours would be the first for this driver. Cross posting it on the Altec User's Forum would be nice too: Altec User's Board

GM
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File Type: gif GPA 212-8A MLTL - GPA tuning.gif (6.8 KB, 472 views)
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Last edited by GM; 25th October 2012 at 05:54 AM.
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Old 25th October 2012, 06:12 AM   #5
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thanks GM

that link explains it perfectly
i will start a build thread as soon as the drivers arrive and will go over to the altec forum for a peep around

thanks again

Sheafer
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Old 26th October 2012, 08:38 AM   #6
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hi GM

is there a way i can get the height lower
marine ply sheets are 1200 x 2400 so i would get the least waste using 1200 as my height (L)

the current modeling is (L) 137.5mm

i would like to still maintain the same driver height off the ground as simed

regards Sheafer
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Old 26th October 2012, 01:27 PM   #7
GM is offline GM  United States
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Greets!

It can be resized to whatever one wants, it just changes the response to a greater or lesser extent. This one has enough net Vb to probably be an inaudible difference.

MLTL – short [slr5000]:

L = 47.25”
CSA = 277.98”^2 [recommend 21.21” W x 13.11” D]
Zdriver = 12”
Zport = 37.8”
Rport = 3”
Lport = 0.75”

All dims i.d. and approximate.

GM
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Old 26th October 2012, 07:11 PM   #8
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thanks GM

that size is perfect

regards Sheafer
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Old 26th October 2012, 07:29 PM   #9
IG81 is offline IG81  Canada
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+1 on documenting the build. I have been wondering about this driver and could not find much more than "would like to try it", including from me, thanks for having the guts to dive-in, especially considering what shipping must cost you.

Good luck!

IG
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Old 27th October 2012, 03:05 AM   #10
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hi IG

ive never heard coax style speakers so i dont quite know what to expect
fingers crossed if i keep it simple they should sound great
i may add some beta 15 subs into the mix later if required and i also have some visiton tl16 super tweeters to play with as well

i,ll start a build thread over the next week or so when i get some wood to play with

cheers
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