Help with Vb and Lv

[schizted]

So ive read and tried to figure all this math out and here's what ive got

Woofer Specs:
Vas - 0.28 cu ft
Qts - 0.80
Qes - 1.10
Qms - 2.97
Fs - 74Hz

*Formula for (Vb):

Vb=(15)(Vas)(Qts^2.87)
Vb=2.205

*Formula for (F3):

F3=0.26(Fs)\(Qts^1.4)
F3=26.32

*Formula for (Fb):

Fb=0.42(Fs)\(Qts^0.9)
Fb=37.99

I Double checked these 3 through
www,carstereo,com/help/Articles.cfm?id=17 (change the comma to . )

*Formula for (Lv):

Lv={(1.463)(10^7)(R^2)\(Fb^2)(Vbin)} - 1.463(R)

This is where is all goes wrong if i enter a 1in radius and use the Fb=37.99 my Lv comes out negative, so ive tried use Fb=74hz for the resonate of my speaker but it still does not come out correct.

Can some one check my math or help figure out where im going wrong? seems like a awfully big Cubic Feet for such a small speaker..

 

[Adam]

Welcome to the forum!

Lv={(1.463)(10^7)(R^2)\(Fb^2)(Vbin)} - 1.463(R)

In your equation for Lv, what is "Vbin"? Is that the same as "Vb"?

If so, then I don't get a negative number. Make sure that you have everything in the correct units (i.e. inches, feet, meters). When I used Vb in ft^3 and R in either feet or inches, I get a positive number.

 

[schizted]

Vbin is Vb in Cubic inches (2.205 x 1728)

and R=1 inch

What number did you come out with if you dont mind

does 2.2 cubic feet sound right for a 5.25" speaker, i have a 6" woofer now with a 11x9x13 box.
for this 2.205 im coming up with something around 24x20x15 or around that which seems to be a massive box for a small speaker...

 

[Adam]

Okay, with Vb in in^3, I get a positive number for Lv.

Lv = [(1.463 * 10^7 * R^2) / (Fb^2 * Vb)] - 1.463 * R

Lv = [(1.463 * 10^7 * 1^2) / (37.99^2 * 2.205 * 1728)] - 1.463 * 1

Lv = [(1.463 * 10^7) / (5.5 * 10^6)] - 1.463

Lv = 2.66 - 1.463

Lv = 1.2 in

 

[schizted]

kool so now i just need to design a box with a internal volume of 2.205 with a port diameter of 2" and a length of 1.2"


So why such a big enclosure for small speaker?

 

[Adam]

Be sure to double check my math, but that's what I got.

I actually know nothing about speaker design, so hopefully those on here that do (and there definitely are some here) will chime in. I just like math. Best of luck!

 

[lsiberian]

We need the Sd to get the ported box. I have a calculator that will do all the lifting once i have that. I can do sealed if you want to see that.

 

[schizted]

Ya if you dont mind show me the specs for sealed box

How do i find the Sd of my speaker?

this is what i found searching google not sure if its correct, but im useing a 5.25 peerless india woofer...

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.

 

[lsiberian]

Vb 76.62 liters

Port 3" 3.25" length

Box is 18.26 in cube.

That is a very strange size for a small driver. It may want an IB like enclosure.

Can you link the driver so we can verify? Something seems a miss.

The sealed returns a -1 Vb. This means something is off or it's an Infinite baffle design.

 

[schizted]

at least i know im not completely crazy now.

This is the speaker i have.

www*parts-express*com/pe/showdetl.cfm?partnumber=299-065&utm_source=Bazaarvoiceps


*had to change the . to *

 

[schizted]

anybody know whats up with this speaker?

 

[highfigh]

anybody know whats up with this speaker?

Look on the Tymphany site and see if they have an application sheet for this one.

 

[schizted]

Ah Ha! thanks highfigh, they had the speaker on there with way diffrent specs to the other sites.

When i put the data into WinISD everything looks more clear now.
i get a solid drop off line

Box volume of 4.0L
Tunning Freq. of 57.30Hz

but the port length dosnt make sense now

167 EBP - ported
Vent Dia 0.082m
Vent Length 1.124m



????

 

[schizted]

ok did some calculators and this is what they say...
Car Audio - Ported Subwoofer Box Design Formulas & Calculator

Qts - 0.36
Vas - 0.204
FS - 51Hz

Gives me

Vb - 0.163
F3 - 55.43
Fb - 53.72

Speaker Enclosure Volume Calculator

8" High
9" Wide
8" Depth
8" Depth2

.75 Wood Thickness
0.009 Speaker Displacment
53 Port Frequency
1 Port
1" Port Diamater
3.6" Port Length
0.17 Net Box Volume

This looks like a normal sized box for this speaker, can anyone confirm?

 

[lsiberian]

This is ideal for sealed application 1.0 according to the p-e Q/A

Let me know desired your box size and I can work you up a cut list.

 

[schizted]

So its best for a seal box with 1.0 cubic feet? whats the 1.0?

box size dosnt matter to me to much a nice square size, just want it to be best setup for the speaker

 

[TLS Guy]

So its best for a seal box with 1.0 cubic feet? whats the 1.0?

box size dosnt matter to me to much a nice square size, just want it to be best setup for the speaker

That driver is a high Qt driver, Qts 0.8. It is therefore only suitable for a sealed box. The suspension is very loose in high q drivers and you will damage them in a ported box.

I did model it ported, but the frequency response is terrible with a 9 db peak at 100 Hz and rapid fall in output below that.

This driver has an F3 of 83 Hz, so you won't get deep bass from it.

There is no point in making the box larger than 0.5 cu.ft.

Here are your numbers.

me: Peerless India W5-KA538A-SH 5.
Type: Standard one-way driver
No. of Drivers = 1
Fs = 74 Hz
Qms = 2.97
Vas = 7.93 liters
Cms = 0.483 mm/N
Mms = 9.576 g
Rms = 1.499 kg/s
Xmax = 3.5 mm
Xmech = 5.25 mm
P-Dia = 117 mm
Sd = 107.5 sq.cm
P-Vd = 0.0376 liters
Qes = 1.1
Re = 3.2 ohms
Le = 0.53 mH
Z = 4 ohms
BL = 3.599 Tm
Pe = 30 watts
Qts = 0.8
no = 0.282 %
1-W SPL = 86 dB
2.83-V SPL = 90.62 dB
-----------------------------------------
Box Properties
Name:
Type: Closed Box
Shape: Prism, square (optimum)
Vb = 0.415 cu.ft
Qtc = 0.8
QL = 20
F3 = 83.47 Hz
Fill = heavy

 

[schizted]

AWSOME! well i will be building a Sealed Box with a 0.43 cubic feet.

Thanks for everybody's help!


And one last thing, is it worth building small legs for the sub and down fire towards the floor?

 

[TLS Guy]

AWSOME! well i will be building a Sealed Box with a 0.43 cubic feet.

Thanks for everybody's help!

And one last thing, is it worth building small legs for the sub and down fire towards the floor?

I think you have a misunderstanding. That is not a sub driver. It is a mid/woofer, designed for small two ways, in a sealed box. Because of its spec it actually does quite well for that application, as it reproduces down to within 10 Hz of it Fs. The lowest reach of any speaker is generally a little above F3. In most sealed applications usually far above F3.

So your speaker is not going to output sound in sub range. It is dropping out at exactly the frequency a sub takes over.

So that driver is useless for a sub.

However, it would be ideal for the fronts, center and surrounds in a THX system, as the speakers would roll off to the sub at 80 Hz second order, which is what the THX specs require.

If you use that driver as a sub you will have no useful output and likely damage it.

That driver does not have output in the range were you can point it at the floor.

 

[schizted]

Oh ok, Geuss thats why it was so hard tryin to figure out the right box and specs on it...

looks like i need to order about 4 more of these then