I do not have the Loudspeaker Design Cookbook.
There are two ways of calculating it. One way is to measure just the cone.
Famed audio author David Weems recommends including the surround on just one side.
One thing you can do is to go to a site that offers woofers in cm², like www.peerless.dk click "Enter a world...."
Another is to take these estimations I find that are pretty close, based on Weems' formula:
15"=132 sq in=825 sq cm.
12"=84 sq in=525 sq cm
10"=56 sq in=350 sq cm
8"=32 sq in=200 sq cm
6.5"=24 sq in=148 sq cm
To get from sq in to sq cm, just multiply by 2.5².
These are close enough for most purposes. Another way is to take the diameter of the basket-not the cone, the entire basked-subtract 1.5" from the diameter, and use that as the cone diameter.
Thus, a 10" basket will have a cone of 8.5" (8.5/2)² x 3.14=56.7 x 2.5²=354 sq in.
Below 8" subtract 1" instead of 1.5" from the basket diameter.
Works well enough for most purposes.
There are two ways of calculating it. One way is to measure just the cone.
Famed audio author David Weems recommends including the surround on just one side.
One thing you can do is to go to a site that offers woofers in cm², like www.peerless.dk click "Enter a world...."
Another is to take these estimations I find that are pretty close, based on Weems' formula:
15"=132 sq in=825 sq cm.
12"=84 sq in=525 sq cm
10"=56 sq in=350 sq cm
8"=32 sq in=200 sq cm
6.5"=24 sq in=148 sq cm
To get from sq in to sq cm, just multiply by 2.5².
These are close enough for most purposes. Another way is to take the diameter of the basket-not the cone, the entire basked-subtract 1.5" from the diameter, and use that as the cone diameter.
Thus, a 10" basket will have a cone of 8.5" (8.5/2)² x 3.14=56.7 x 2.5²=354 sq in.
Below 8" subtract 1" instead of 1.5" from the basket diameter.
Works well enough for most purposes.
Thanks. Actually 1 sq in = 6.451599999999999 sq cm = 0.00064516 sq m
which would make both the cookbook and weems calculating formulas wrong.Most definitely cookbooks.
http://www.loudspeakers101.com/PortForm.htm
which would make both the cookbook and weems calculating formulas wrong.Most definitely cookbooks.
http://www.loudspeakers101.com/PortForm.htm
Thank you but not necessary.
The program I'm writing is basically nothing fancy or complicated. It's meant to replace a calculator for people who still have to do their own old fashion way measurements Like myself ;-)
It calculates normalized box dimensions. Port length. Internal volume. T/S parameters. 4 different compensation filters. Complex impedance. And couple of extra things. No graph or anything because I find graphs useless. The entire code is based on my entire speaker builder collection from 80's and bullock and cookbook.
The program I'm writing is basically nothing fancy or complicated. It's meant to replace a calculator for people who still have to do their own old fashion way measurements Like myself ;-)
It calculates normalized box dimensions. Port length. Internal volume. T/S parameters. 4 different compensation filters. Complex impedance. And couple of extra things. No graph or anything because I find graphs useless. The entire code is based on my entire speaker builder collection from 80's and bullock and cookbook.
That's true. What are you trying to calculate Sd from? The diameter of the stiff part of the cone? Vas? Qts?
What formulas are the Loudspeaker Design Cookbook giving and how do you know they are wrong?
Most programs let the user enter Sd and calculate the other parameters from that, like Bullock and White's BoxModel.
What formulas are the Loudspeaker Design Cookbook giving and how do you know they are wrong?
Most programs let the user enter Sd and calculate the other parameters from that, like Bullock and White's BoxModel.
Sreten:
I think using half of the surrounds area is as good as any
You are correct. Using half or 1/3 or surround dooesn't make much difference in calculation VAS.
Svante:
If you are writing a program then it should be possible to enter the Sd value, and that's it. ?
It does both.
Kelticwizard:
What formulas are the Loudspeaker Design Cookbook giving and how do you know they are wrong?
The link I posted earlier uses the chart from cookbook. And the given values of Sd for different size drivers are way off no matter what formula you use.
As to why I bother with Sd in my program. Well. It is strictly because of before purchase decision and programming fun.
Years a go I was trying to decide on a pair of 5" midwoofers for a design. And based on published specs, I calculated the actual cones to be close to 4" but, when I got the drivers they were much smaller.
Again, I just wrote this program to speed up calculations when I do measurements.
If you want to see some screen shoots. Shoot me an email.
Thanks for all the feedback's and help.
I think using half of the surrounds area is as good as any
You are correct. Using half or 1/3 or surround dooesn't make much difference in calculation VAS.
Svante:
If you are writing a program then it should be possible to enter the Sd value, and that's it. ?
It does both.
Kelticwizard:
What formulas are the Loudspeaker Design Cookbook giving and how do you know they are wrong?
The link I posted earlier uses the chart from cookbook. And the given values of Sd for different size drivers are way off no matter what formula you use.
As to why I bother with Sd in my program. Well. It is strictly because of before purchase decision and programming fun.
Years a go I was trying to decide on a pair of 5" midwoofers for a design. And based on published specs, I calculated the actual cones to be close to 4" but, when I got the drivers they were much smaller.
Again, I just wrote this program to speed up calculations when I do measurements.
If you want to see some screen shoots. Shoot me an email.
Thanks for all the feedback's and help.
Eton:
I found the Loudspeaker Cookbook formulas to be within 10% of my own calculations and the Peerless specs.
I make a mistake on my 15" rating. I thought I had it memorized at 132 sq inch, which translates into 825 sq cm. But it is 143 sq in and 894 sq cm.
Which compares with the Peerless PA SDS 15 inch, which Peerless rates at 890 sq cm.
Loudspeaker Cookbook rates a 5" speaker at 89 sq cm, Peerless rates theirs at 91 sq cm.
At any rate, good luck with your program!
I found the Loudspeaker Cookbook formulas to be within 10% of my own calculations and the Peerless specs.
I make a mistake on my 15" rating. I thought I had it memorized at 132 sq inch, which translates into 825 sq cm. But it is 143 sq in and 894 sq cm.
Which compares with the Peerless PA SDS 15 inch, which Peerless rates at 890 sq cm.
Loudspeaker Cookbook rates a 5" speaker at 89 sq cm, Peerless rates theirs at 91 sq cm.
At any rate, good luck with your program!
Just incase anybody’s curious, here’s why the variations in cookbook calculated Sd results.
I updated the chart to show the actual value (used) for a specific driver. So 5.25” driver is actually calculated using 4.19097” of cone area.
Driver Diameter Used Sd (M2)
18" 16.0174 0.1300
15" 13.2530 0.0890
12" 10.2272 0.0530
10" 8.07007 0.0330
8" 6.58918 0.0220
6.5" 5.70640 0.0165
6" 4.96678 0.0125
5.25" 4.19097 0.0089
I updated the chart to show the actual value (used) for a specific driver. So 5.25” driver is actually calculated using 4.19097” of cone area.
Driver Diameter Used Sd (M2)
18" 16.0174 0.1300
15" 13.2530 0.0890
12" 10.2272 0.0530
10" 8.07007 0.0330
8" 6.58918 0.0220
6.5" 5.70640 0.0165
6" 4.96678 0.0125
5.25" 4.19097 0.0089
Eton said:
I am not sure I am following your reasoning.
My "formula" said to take the basket diameter and subtract 1.5" from it and use the resulting number as your cone diameter. For speakers under 8", subtract only 1" from the basket diameter.
I selected a Peerless 134mm speaker as an example. I called it a 5" speaker, actually it is a 5.25" speaker. The official Peerless spec is 91 sq cm.
If you call the speaker 5", then my formula is:
5" -1"=4". That is the actual cone diameter. The cone area will be (4/2)² x 3.14 = 12.56 sq in = 78.5 sq cm.
If you call the speaker 5.25", then my formula is"
5.25" - 1" = 4.25". That is the actual cone diameter. The cone area will be (4.25/2)² x 3.14 = 14.18 sq in = 88.6 sq cm.
I do not understand how you figured my formula, when applied to a 5" or 5.25" speaker, yields an Sd of 126.64 sq cm. There must be some mistake.
Eton:
Actually, the subtraction of the 1.5" for speakers 8" or above or 1" for speakers below 8" not only deducts half the surround, but also a the outside part of the frame as well.
Obviously, if you don't subtract that, your number will be way off, unless you have a very large diameter speaker like an 18" or 24". In which case the rim and surround will be negligible compared to the diameter of the cone itself.
PS: I am unfamiliar with this formula:
SD cm^2 = [pi*(D"/0.3937)^2]/4
I thought the way to calculate cone area from the diameter is:
Cone area = (diameter/2)² x 3.14
Actually, the subtraction of the 1.5" for speakers 8" or above or 1" for speakers below 8" not only deducts half the surround, but also a the outside part of the frame as well.
Obviously, if you don't subtract that, your number will be way off, unless you have a very large diameter speaker like an 18" or 24". In which case the rim and surround will be negligible compared to the diameter of the cone itself.
PS: I am unfamiliar with this formula:
SD cm^2 = [pi*(D"/0.3937)^2]/4
I thought the way to calculate cone area from the diameter is:
Cone area = (diameter/2)² x 3.14
You are absolutely correct.
It wasn't my intention to quibble about the minute differences in number.
I was just trying too determine the best formula to use in my program and to find out how in the world Cookbook had derived the Sd number. Obviously when I look at the driver, I can tell the actual size of the cone and if I add 1/2 or 1/3 or surround the VAS value will not change by much.
It wasn't my intention to quibble about the minute differences in number.
I was just trying too determine the best formula to use in my program and to find out how in the world Cookbook had derived the Sd number. Obviously when I look at the driver, I can tell the actual size of the cone and if I add 1/2 or 1/3 or surround the VAS value will not change by much.
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