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However, this calculator may be of some use: Piston Excursion calculator

Hello,

in order to answer that question, you have to define the peak SPL that you want to achieve, and the cone excursion (Xmax) that you wish to tolerate (arguably, the lower the better for the quality of the reproduction).

The equations that govern this are:

Power(acoustic) = 10^[(SPL-110)/20)]

Sd(m2) = Power * 4*Pi / [(2*Pi*Freq)^2 * rho * Xmax)

For instance, if you impose the following rather strict requirements of:

Peak SPL = 110 dB/W(1m)

Xmax = 2 mm (= 0.002 m)

you get:

20 Hz: Sd = 3300 cm2 (i.e. effective diameter = 65cm ! - here's what Fostex's nominal 80cm woofers are for)

30 Hz: Sd = 1470 cm2 (~ the typical 18" woofer)

40 Hz: Sd = 830 cm2 (~ the typical 15" woofer)

and so on (for 100Hz "bass", a nominal 6.5" unit suffices ;-) )

Of course, if you relax the SPL or Xmax requirements, you may get away with using smaller woofers (but at the cost of decreased realism, both because of lower uncompressed SPL and because the larger the excursion, the higher the IM distortion and the less linear the BL and other T-S parameters).

Hope this helps.

Marco

Hello,

in order to answer that question, you have to define the peak SPL that you want to achieve, and the cone excursion (Xmax) that you wish to tolerate (arguably, the lower the better for the quality of the reproduction).

The equations that govern this are:

Power(acoustic) = 10^[(SPL-110)/20)]

Sd(m2) = Power * 4*Pi / [(2*Pi*Freq)^2 * rho * Xmax)

For instance, if you impose the following rather strict requirements of:

Peak SPL = 110 dB/W(1m)

Xmax = 2 mm (= 0.002 m)

you get:

20 Hz: Sd = 3300 cm2 (i.e. effective diameter = 65cm ! - here's what Fostex's nominal 80cm woofers are for)

30 Hz: Sd = 1470 cm2 (~ the typical 18" woofer)

40 Hz: Sd = 830 cm2 (~ the typical 15" woofer)

and so on (for 100Hz "bass", a nominal 6.5" unit suffices ;-) )

Of course, if you relax the SPL or Xmax requirements, you may get away with using smaller woofers (but at the cost of decreased realism, both because of lower uncompressed SPL and because the larger the excursion, the higher the IM distortion and the less linear the BL and other T-S parameters).

Hope this helps.

Marco

thanks a lot Marco, your reply clears my doubt!

selecting 110dB SPL and Xmax of 2mm makes good reference values.

with the formula you have mentioned i should be able to calculate for other different types of driver sizes/xmax etc.

thanks a lot

Take into account room too. Below the first room mode there is a lot of spl gained. You may be able to relax the reference values. The smaller the room the more the spl gain.selecting 110dB SPL and Xmax of 2mm makes good reference values.

intention was to understand the relationship between, conesize, xmax and lowest frequency achievable at a specific SPL. ofcourse room mode will need to be taken into account for further design of actual subTake into account room too. Below the first room mode there is a lot of spl gained. You may be able to relax the reference values. The smaller the room the more the spl gain.

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- cone size vs lowest frequency table!?