Home » Sponsored » Pi Speakers » BETA 12LTA in a PiAlign enclosure
BETA 12LTA in a PiAlign enclosure [message #44056] Thu, 26 February 2004 17:32 Go to next message
HigherFi is currently offline  HigherFi
Messages: 7
Registered: May 2009
Esquire
Has anyone had experience with the Eminence BETA 12LTA in a PiAlign enclosure?
The folks at DIY audio's Speaker forum thought they might be a good match.

Re: BETA 12LTA in a PiAlign enclosure [message #44061 is a reply to message #44056] Thu, 26 February 2004 22:11 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18670
Registered: January 2001
Illuminati (33rd Degree)
The Beta 12LT will work well in cabinets from about 2ft3 to 10ft3 tuned to 35Hz. PiAlign recommends a 2.5ft3 cabinet tuned to 35Hz using a 2.5" diameter port that's 2.75" long. Response is nice and flat with f3 of 60Hz and f10 at 40Hz.

Re: BETA 12LTA in a PiAlign enclosure [message #44063 is a reply to message #44061] Fri, 27 February 2004 03:28 Go to previous messageGo to next message
HigherFi is currently offline  HigherFi
Messages: 7
Registered: May 2009
Esquire
Wayne this looks promising on WinISD however the recomended post has a mach of 0.44 which is way too high. Is there room for fussing around with the port diameter to lower the vent mach?

Re: BETA 12LTA in a PiAlign enclosure [message #44064 is a reply to message #44063] Fri, 27 February 2004 04:14 Go to previous messageGo to next message
HigherFi is currently offline  HigherFi
Messages: 7
Registered: May 2009
Esquire
If I use 3 1.5" vents 3.5 " long I still get the correct frequency for the ports and a vent mach of 0.14 which should give much less wind noise from the vent. The enclosure would be 18" wide by 28" tall and 11.5" deep using 3/4" plwood.

Re: BETA 12LTA in a PiAlign enclosure [message #44067 is a reply to message #44064] Fri, 27 February 2004 07:31 Go to previous messageGo to next message
Adrian Mack is currently offline  Adrian Mack
Messages: 568
Registered: May 2009
Illuminati (1st Degree)
If the air speed velocity is too high in the ports, simply use a larger port that achieves the same tuning frequency as PiAlign reccomends, if that's what your using.

0.14 mach is 48ms, which is still going to cause some pretty major compression and distortion at high power levels.

Re: BETA 12LTA in a PiAlign enclosure [message #44070 is a reply to message #44063] Fri, 27 February 2004 12:19 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18670
Registered: January 2001
Illuminati (33rd Degree)
The Beta LT has peak displacement volume of 42cc, which is only 2.5 cubic inches. That's not very much to push through a 2.5" diameter port, so airspeed won't get anywhere near 40% mach, which is 300mph. By the way, maximum airspeed is at fb, and falls off above that.

Re: BETA 12LTA in a PiAlign enclosure [message #44075 is a reply to message #44070] Fri, 27 February 2004 19:45 Go to previous messageGo to next message
Adrian Mack is currently offline  Adrian Mack
Messages: 568
Registered: May 2009
Illuminati (1st Degree)
I think he is probably modelling with over 100watts of power which by that time the driver would have well exceeded its max excursion. It only has 0.8mm of voice coil overhang, almost nothing. JBL drivers with zero overhang have xmax rated at 0.060" with the idea to keep distortion below about 10%.

Usable xmax estimate on these drivers is about 15% of VC length added to one-way overhang. VC length on the 12LT is 9.54mm. 15% of this is 1.43mm added to 0.8mm overhang, is 2.23mm. Using the port and enclosure PiAlign suggests vent mach is below 0.05 or 17ms until 26Hz when driven to max excursion of 2.23mm (requires 13w RMS). Below 26Hz it rises to 0.06 mach or 22ms. By this time the port and woofer are unloading anyway as its below Fb. 2.23mm on this driver limits max SPL to ~107db as direct radiator.

Considering other ways to determine xmax will come up with different numbers of course. If you want to use Dumax specification it's when drive force drops by 30%.

djk once gave a different way to determine xmax of overhung drivers which is to take voice coil overhang and add the mean of 15% of the total coil length and 25% of the gap height. A more conservative 10% distortion limit for total xmax is estimated using this method. For the 12LT:

15% of coil length is 1.431mm
25% of gap height is 1.985mm
Square root of the product of those two numbers is 1.685mm
Add 0.8mm of one way overhang to that results in 2.49mm one way xmax at 10% THD.

Assuming 2.49mm usable one way xmax then, vent mach is still very low compared to the other 2.23mm estimate because they are very close.

Re: BETA 12LTA in a PiAlign enclosure [message #44076 is a reply to message #44067] Fri, 27 February 2004 19:46 Go to previous messageGo to next message
HigherFi is currently offline  HigherFi
Messages: 7
Registered: May 2009
Esquire

Here is my best shot at discribing what I feel would fit the PiAlign model.The 5 ports are 1.25" diameter 4.38" long on a 12" radius from the center of the Beta 12LTA. The tweeter is a Fostex FT17H.I have a The WinISD WID file and crude drawing below


Re: BETA 12LTA in a PiAlign enclosure [message #44077 is a reply to message #44076] Fri, 27 February 2004 19:49 Go to previous messageGo to next message
Adrian Mack is currently offline  Adrian Mack
Messages: 568
Registered: May 2009
Illuminati (1st Degree)
The link for the picture and WinISD download file seem to be not working.

I just posted about the 12LT here http://www.audioroundtable.com/PiSpeakers/messages/14110.html about air speeds.

Re: BETA 12LTA in a PiAlign enclosure [message #44078 is a reply to message #44077] Fri, 27 February 2004 20:06 Go to previous messageGo to previous message
HigherFi is currently offline  HigherFi
Messages: 7
Registered: May 2009
Esquire

Finally got drawing in a spot it can be accessed, my ISP didn't like the previous location

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