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
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
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
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
Attachments
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
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:
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
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
Attachments
Last edited:
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
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
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
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
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
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
+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
Good luck!
IG
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
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
Well, most times it’s due to one or two things or a combination of both when HF horn coaxes are involved.
First, and the most common is that any air leak, even a tiny one, pretty much negates any cab loading, especially a MLTL, tuning it up very high.
The other is that the HF horn is much more sensitive than the woofer, so must be attenuated considerably to tonally balance it in room to the woofer.
Anyway, ignoring any room gain, there should be solid bass to the high 30s once dialed in.
GM
First, and the most common is that any air leak, even a tiny one, pretty much negates any cab loading, especially a MLTL, tuning it up very high.
The other is that the HF horn is much more sensitive than the woofer, so must be attenuated considerably to tonally balance it in room to the woofer.
Anyway, ignoring any room gain, there should be solid bass to the high 30s once dialed in.
GM
Great job, they look good! Glad to see other people are making cabs larger than the kids! 🙂
The 212 comes with a crossover from GPA right? I don't know if it's correct for you baffle width.
IG
The 212 comes with a crossover from GPA right? I don't know if it's correct for you baffle width.
IG
Your port is looking small and short.
I want this USA piece to work, by the way. Otherwise, offshore. Some more.
I want this USA piece to work, by the way. Otherwise, offshore. Some more.
Last edited:
Hmm, my monitor is all but dead and can't even see the port, but if it's 3" instead of 6" diameter, then even if airtight, the tuning will be around an octave below Fs, which would equate to no bass also unless corner loaded.
GM
GM
Hi guys
sorry about the late reply my internet has been down
the port is 100mm x 19mm so should be close , i was also wondering how the crossover would work seeing as the baffle is very wide compared to what gpa would have set it up for so maybe i need to adjust the lpad/resistor to suit
playing them on the ground before i mounted them reminded me very much of my lowther dx2 in that they are very detailed but bass shy and may perhaps need to go in a ported cab designed with a deliberate 2 to 3 db hump in the lower bass to balance out the presentation
a quik calk works the internal volume out at 206 litres after driver and braces and i would have a few air leakes as suggested by gm
aside from the bass i was a little shocked at the size once built but i,m getting used to them
Sheafer
sorry about the late reply my internet has been down
the port is 100mm x 19mm so should be close , i was also wondering how the crossover would work seeing as the baffle is very wide compared to what gpa would have set it up for so maybe i need to adjust the lpad/resistor to suit
playing them on the ground before i mounted them reminded me very much of my lowther dx2 in that they are very detailed but bass shy and may perhaps need to go in a ported cab designed with a deliberate 2 to 3 db hump in the lower bass to balance out the presentation
a quik calk works the internal volume out at 206 litres after driver and braces and i would have a few air leakes as suggested by gm
aside from the bass i was a little shocked at the size once built but i,m getting used to them
Sheafer
I think GM's R for port is semi-diameter , so it needs to be D=6"=152,4mm
most probably that's the reason for missing bass
let GM confirm (again)
most probably that's the reason for missing bass
let GM confirm (again)
Thanks zen mod
i would be wrapped if its that simple
aside from the lack of bass they sound promising
cheers
i would be wrapped if its that simple
aside from the lack of bass they sound promising
cheers
Greets!
Bummer, I’m that way a lot with ‘customer no service’ AT&T, but my only other option AFAIK is $#!% Comcast at a much higher cost, so screwed once again by big business.
The XO point is high enough that baffle size should have virtually no impact on baffle step loss since the WLs involved are shorter than the driver’s diameter.
100 mm = ~3.937" diameter, so is about the size one would try if the speaker was positioned hard up against a rigid/massive corner like in basement, which is a bit lower than I would normally recommend tuning this driver, so still very bass shy even if no leaks.
6" = 152.4 mm and if you wanted to add a bass 'hump', then a 9 - 10" [228.6 – 254 mm] diameter is required, increasing tuning up around the GPA reflex tuning, ~defeating the point of using a MLTL loading beyond getting the driver up to ~ear height, though its much larger Vb would give it more bass ‘thump’ than the reflex.
For those folks wanting the vintage Altec mid-bass prominent ‘West Coast Sound’, this is the way to go.
GM
Bummer, I’m that way a lot with ‘customer no service’ AT&T, but my only other option AFAIK is $#!% Comcast at a much higher cost, so screwed once again by big business.
The XO point is high enough that baffle size should have virtually no impact on baffle step loss since the WLs involved are shorter than the driver’s diameter.
100 mm = ~3.937" diameter, so is about the size one would try if the speaker was positioned hard up against a rigid/massive corner like in basement, which is a bit lower than I would normally recommend tuning this driver, so still very bass shy even if no leaks.
6" = 152.4 mm and if you wanted to add a bass 'hump', then a 9 - 10" [228.6 – 254 mm] diameter is required, increasing tuning up around the GPA reflex tuning, ~defeating the point of using a MLTL loading beyond getting the driver up to ~ear height, though its much larger Vb would give it more bass ‘thump’ than the reflex.
For those folks wanting the vintage Altec mid-bass prominent ‘West Coast Sound’, this is the way to go.
GM
Thanks GM
i just finished sealing up any leakes that were present and will cut the port larger tommorow to see the effects
what would be the equivilent slotted port size and is it just a matter of H x W of the slotted port to equal a round port
many thanks again for your help
Sheafer
forgot to ask ,regarding stuffing is the top half of the cab loosley stuffed a good start or would you suggest something else
i just finished sealing up any leakes that were present and will cut the port larger tommorow to see the effects
what would be the equivilent slotted port size and is it just a matter of H x W of the slotted port to equal a round port
many thanks again for your help
Sheafer
forgot to ask ,regarding stuffing is the top half of the cab loosley stuffed a good start or would you suggest something else
Last edited:
- Status
- Not open for further replies.