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MultiWay Conventional loudspeakers with crossovers 

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17th October 2004, 02:33 AM  #1 
diyAudio Member
Join Date: Sep 2004
Location: New Mexico

calculations
Can some one check my calculations to make sure they are right.
here are the specs. Driver Properties Name: 551875 Type: Standard oneway driver Company: MCM Electronics No. of Drivers = 1 Fs = 31 Hz Qms = 2.193 Vas = 404.9 liters Cms = 0.171 mm/N Mms = 154.2 g Rms = 13.7 kg/s Xmax = 4.4 mm Xmech = 6.6 mm PDia = 405.5 mm Sd = 1292 sq.cm PVd = 0.568 liters Qes = 0.46 Re = 6.8 ohms Z = 8 ohms BL = 21.07 Tm Pe = 400 watts Qts = 0.38 no = 2.528 % 1W SPL = 96.18 dB 2.83V SPL = 98 dB vb:13.34 cubed ft f3: 31.23hz Fb:31.1 hz vbin: 23064.8140131 in cubed Pvd is the volume of the driver i think, so i have to add this to the vbin: 0.568 liters(is also 34.6614866 inches cubed) + 23064.8140131 inches cubed = 23099.4754997 inches cubed my total volume of my box has to be 23099.4754997 inches cubed for length of port it is 1.5 inches radius of port is 2.995 inches and if i want to use the golden ratio to get the dimension of the box what would i have to do? 
17th October 2004, 03:31 PM  #2 
diyAudio Member
Join Date: Jun 2002
Location: USA, MN

Firstly, your port is way too small. A 3" port with an 18" woofer is not enough  even though this woofer doesn't have a long throw. While your alignment will work, it is a fairly large box.
I wouldn't worry about making a golden ratio box. That is more important for midrange, it is more important IMO that your box is well braced and has some absorptive lining on the walls. To figure out golden ratio dimensions you first take the cube root of the volume  the cube root of 23064.8 is 28.465 inches, so that means your box if it were a cube would have internal dimensions of 28.5 inches on a side. Math: 23064.8^(1/3)=28.465 inches 28.465*28.465*28.465=23064 cubic inches To get a golden ratio box, you multiply and divide the cube root by 1.618034. Your box would then be 1.618034*28.465 x 28.465 x 28.465/1.618034 or: 46.0 x 28.5 x 17.5 inches (rounding to the nearest half inch). Multiply that out and get the volume 22942.5. If that size doesn't daunt you, I would go for two 6" ports, each 5.5 inches long. Using a small port will cause lots of air rushing noise. There are other dimension ratios that you can use  if you get dimensions by multiplying and dividing the cube root by the same number, you will always get the correct volume. Try factors of 1.2 or 1.25 (two other recommended ratios) to see how the dimensions come out.
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17th October 2004, 09:11 PM  #3 
diyAudio Member
Join Date: Sep 2004
Location: New Mexico

what do you think about a 4th Order Bandpass Systems. What would i have to do.

18th October 2004, 12:25 AM  #4  
diyAudio Member
Join Date: Jun 2002
Location: USA, MN

Quote:
You can make a smaller vented box if you want to, you could make a 200liter box tuned to 35Hz with 2  6"dia x 11.5" long ports. This woudn't go quite as deep, F3 would be 40Hz, but it would be exceedingly loud with very little power. You could make a bandpass  one that might work is ported volume 84 liters tuned to 68Hz and sealed volume 106 liters. This would have a lower F3 of 40Hz and upper f3 of 117Hz. The rolloff on the low end is only 12dB/octave, where the ported is 24dB/octave, so this would have a bit more bass than the equivalent sized ported box.
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Our species needs, and deserves, a citizenry with minds wide awake and a basic understanding of how the world works. Carl Sagan Armaments, universal debt, and planned obsolescencethose are the three pillars of Western prosperity. —Aldous Huxley 

18th October 2004, 01:38 PM  #5 
Banned
Join Date: May 2004
Location: New Hampshire

All things considered I hope you haven't already purchased this driver. You don't say but it appears you want to use it in the home as a woofer, and there are far better ways to go. A smaller driver with a longer throw will allow you to accomplish the same task from a far smaller box with much better results. This driver is intended for professional use and it really isn't well suited to anything else. For subwoofer use it can be easily outdone in both bandwidth and SPL by a small (3.6 cu ft) folded horn loaded with an eight (MCM 552421).
www.bilfitzmaurice.com 
19th October 2004, 01:58 AM  #6 
diyAudio Member
Join Date: Sep 2004
Location: New Mexico

i know the box is going to be pretty big. I am going to throw some wheels on it so i can roll it around if i need to. I can really care less about the size of the box that dont matter to me i just wanted to get the max out of these woofers. I wanted to go with the 4th order bandpass system and was wondering what i would have to do to calculate the size and demensions of the box.

19th October 2004, 05:27 PM  #7  
diyAudio Member
Join Date: Jun 2002
Location: USA, MN

Quote:
__________________
Our species needs, and deserves, a citizenry with minds wide awake and a basic understanding of how the world works. Carl Sagan Armaments, universal debt, and planned obsolescencethose are the three pillars of Western prosperity. —Aldous Huxley 

19th October 2004, 05:36 PM  #8  
diyAudio Member
Join Date: Jun 2002
Location: USA, MN

Quote:
www.billfitzmaurice.com My keyboard has been droping lettrs lately, too! And I have this real problem with typing teh word teh (or the).... Any new SB articles lately?
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Our species needs, and deserves, a citizenry with minds wide awake and a basic understanding of how the world works. Carl Sagan Armaments, universal debt, and planned obsolescencethose are the three pillars of Western prosperity. —Aldous Huxley 

19th October 2004, 05:53 PM  #9 
diyAudio Member
Join Date: Sep 2004
Location: New Mexico

i was going to go with a Mackie 1400i amp since it has a built in crossover. Right now i have 2 jrx125's powered by a cerwin vega amp a200. i cant figure out how to use the formulas for calculating a 4th order bandpass,

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