How can I find effective piston area?

[mstar]

Hi,
I was trying to plug in some numbers in a computer program for box volume and can not find a listing for the Sd (effective piston area) for the Dayton RS150-4 (file 295-372z)
I am new to this so please bear with me. Is it listed in any of these numbers?
D: 102.00
MmS: 6.53 G
Cms 1.13 (mm/N
Bl: 3.79
L1K: .38 (mh
L10K .14
All the other numbers seemed to have a spot to enter into the program

Dimentions A: 5-5/16" B: 4-13/16" C" 2 3/4"

Is there a way to get the Sd?

Thanks for a prompt response.

 

[hitsware]

measure accross the driver from the center of the surround on one side to the center of the surround on the other side (at the widest part) then Sd ~ pi * (measurement/2)^2

 

[kelticwizard]

The Sd< 9diaphrgm area), does not have to be exact. A ballpark figure will do nicely, and not change the frequency response .

Here is a list of Sd's for various size drivers.

15": 132 sq inch, 825 sq cm

12": 84 sq inch, 525 sq cm

10: 55 sq inch, 344 sq cm

8": 32 sq inch, 200 sq cm

6.5": 21 sq in, 131 sq cm

5.25: 12.5 sq in, 78 sq cm

Your speaker is a 6". not 6.5 in, so it would be safe to assume an Sd slightly below 21 sq in-like 18 sq in, or 112 sq cm.

 

[kelticwizard]

6" should be a bit below 21 sq in-like 18 sq in, or 112 sq cm .

 

[mstar]

Hi,
I do not know this math.
I do not have the driver yet. I was trying to figure out if the driver willwork in my volume and needed the Sd for the computer formlas to work.
All I know is that it is 5 15/16" in diameter end to end.
Is this enough info?

 

[mstar]

Thanks. What about a 6"?

The Sd< 9diaphrgm area), does not have to be exact. A ballpark figure will do nicely, and not change the frequency response .

Here is a list of Sd's for various size drivers.

15": 132 sq inch, 825 sq cm

12": 84 sq inch, 525 sq cm

10: 55 sq inch, 344 sq cm

8": 32 sq inch, 200 sq cm

6.5": 21 sq in, 131sq cm

 

[mstar]

Thank you

 

[Norcad]

Hello
In Bassbox Pro 6, the Sd is calculated to 81.16 sq cm.

Norcad

 

[hitsware]

Hello
In Bassbox Pro 6, the Sd is calculated to 81.16 sq cm.

Norcad

Then the 'D' given must be effective diameter.
So the radius = D/2 = 51 (mm)
area = pi * r^2
Sd = area = 3.14*51^2 = 3.14*2601 = 8167sq.mm = 81.67sq.cm

 

[jamikl]

A formula we always used in the motor trade for area of circle which means not having to use the radius, as the dia. is nearly always given is 11/14*D^2
jamikl

 

[kelticwizard]

Hello
In Bassbox Pro 6, the Sd is calculated to 81.16 sq cm.

Norcad

I gave the Sd value of 6.5" speaker as 21 sq in, or 131 sq cm.

A Peerless 6.5" gives a value of 138 sq cm-very close.

Clearly, a 6" speaker's Sd will be very close to a 6.5 incher. So it would make sense to reduce the Sd only slightly-to 115 sq cm, (18.4 sq in) for instance.

81 sq cm is obviously too low for a 6" woofer. Such a calculation means that the 6" woofer has only a 4" diameter cone. That would be a very, very unusual speaker.

 

[johninCR]

My understanding is that Sd is typically computed by the manufacturers as the area of the cone plus 1/3 of the surround, so just measure it yourself and compute the area.

 

[Navy_44]

The measurement of "effective Sd" is a tricky one.

Usually one of the two methods of TS params measurement is employed:

- delta compliance (the driver impedance curve is measured with and without a sealed box of approx. 1/3 predicted Vas).

The parameters - Fs, Qes and Qms can be determined from the impedance curve without the box, and the ratio of Fc/Fs together with the volume of the box gives the Vas according to formula : Vas=Vb*((Fc/Fs)^2-1)

This method however does not fully describe the driver while we do not know anything about Cms and Mms.

- delta mass (the driver impedance curve is measured with and without an added mass of approx. predicted Mms or less).

This way it is possible to determine the Mms of the driver along with Fs, Qes and Qms from the "no added mass" impedance curve. The ratio of Fdm (Fs with added mass) to Fs and the amount of the added mass (dM) give us the value of Mms:

Mms=dM/((Fs/Fdm)^2-1)

Additionaly the suspension compliance can be calculated from the formula:

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

This way we have both parameters needed to determine the "effective acoustic" Sd - Vas from delta compliance method and Cms from delta mass.

The formula is:

Sd=sqrt(Vas/(Cms*ro*c^2))

Where ro is the density of the air and c - velocity of sound. While their values depend on the temperature and pressure - please refer to wikipedia for the values most appropriate in your situation.

The method described here - although correct from theoretical point of view - is quite complicatad and prone to measurement errors coming form various sources, including Vb estimation and suspension nonlinearity (usually the Fs goes down when the drive level increases) so that the estimation of Sd by measuring the diameter of the cone plus 1/3 of the surround may be even more accurate in real life.

The data on the RS-150 includes everything needed to calculate Sd - we have:

Vas=13.98e-3m3
Cms=1.5e-3m/N
ro=1.184kg/m3
c=346.3m/s (25C)

So the effective Sd would be 0.0081m2 which equals 81cm2. This would give the effective diameter of 101.16mm which is quite close to the D=102mm from the datasheet (if we are not sure what the D there means).

 

[kelticwizard]

My apologies.

81 sq cm is the correct number.

I did not look on the response graph, which listed the effective cone diameter, as dimension D, of 102 mm. Which is almost exactly four inches.

In my defense, I would point out that normally a 5.25" speaker has a effective diameter of about four inches, and an Sd of about 80 sq cm. For instance, here is a typical Peerless 5.25 incher with an effective piston area of 80 sq cm.

This Parts Express speaker is not so much a genuine 6 incher as it is a 5.25 incher with a slightly larger than normal rim.

 

[hitsware]

81 sq cm is obviously too low for a 6" woofer. Such a calculation means that the 6" woofer has only a 4" diameter cone. That would be a very, very unusual speaker.

I think not.