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Old 17th November 2003, 11:22 PM   #1
Synapse is offline Synapse  Canada
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Post T-Line subwoofer?possible?

Hi,

I have some free time, couple sheet of MDF and a driver I want to use. There is still no enclosure type I would prefer although this design inspired me quite a lot. Is a transmission line achievable with my driver?

12inch, Unknown brand

Vas 125.61L
Qms 1.74
Qes 0.36
Qts 0.30
FS 36.5

…what type enclosure should I choose?
I will be please to ear your opinions
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Old 18th November 2003, 04:47 AM   #2
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What's Re, BL, Sd?

GM
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Old 18th November 2003, 06:54 AM   #3
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With the lowish Q an ML-TL should work well.

dave
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Old 18th November 2003, 12:46 PM   #4
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GM,

Re is 5,2
BL has not been tested
any easy way I could calculate it?


planet10,

how big such an mass loaded transmission line would have to be? How flat, and low, do you think the response will be?


thank you both
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Old 18th November 2003, 06:45 PM   #5
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First off, with a 36.5Hz Fs/lowish Q it's not going to be a subwoofer. You need Sd to calculate BL so I fudged it at 506.709cm^2 for simming purposes, but it should be close enough for reasonable accuracy if it's not a really high excursion driver with a smaller than average diaphragm.

You can calculate it:

Cms = Vas/(Sd^2*rho*c^2)

where:

Vas is in m^3 (liters*0.001)

Sd is in cm^2

c is in meters/sec*0.0001 to get Cms in mm/N

then:

Mms = 1/[(2*pi*Fs)^2*Cms]

BL = [(2*Pi*Fs*Re*Mms)/Qes]^0.5

Anyway, I forgot to ask if the amp is SS or tube, if tube I'll need its output resistance (damping factor) and have to redo the ML-TL sims. Qts is too low for a reverse taper TL IMO, though if tube driven, Qts will go up, enough to tune it somewhat lower and possibly high enough to consider a TL.

I don't have any way to show you the sims, but if you have Mathcad or download the demo viewer from http://www.quarter-wave.com/ I can send you the worksheets to view/change, though you can't save any changes with the viewer.

All dims inside
'XO' = centerline of driver down from top
'rp' = radius of port
'Lp' = length of port
width/depth are golden ratio suggestions, you can make your own based on 'S0/SL (in^2)'
dims can be rounded off somewhat, I just printed out part of a spreadsheet

----------------

T/S max flat:

rp = 2"
Lp = 4.5"
density = 0.25lbs/ft^3

L (in)
20.919

S0/SL (in^2)
156.121

S0/SL (width)
15.894

S0/SL (depth)
9.823

X0 (in)
10.184

Sd (in^2)
78.54

Qts
0.2983

Vas or Vb(ft^3)
1.89

Fs or Fb (Hz)
48

-----------------

Tuned to Fs:

rp = 2"
Lp = 6"
density = 0.25lbs/ft^3

L (in)
27.510

S0/SL (in^2)
152.637

S0/SL (width)
15.716

S0/SL (depth)
9.712

S0/SL (dia)
13.941

X0 (in)
12.471

Sd (in^2)
78.54

Qts
0.2983

Vas or Vb(ft^3)
2.43

Fs or Fb (Hz)
36.5

GM
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