# Relationship of excursion, surface and low frequency produced?

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#### shank1207

Hello,
I would like to know what is the relationship between Excursion Xmax, Surface area Sd, of the driver and the Frequency it can Produce?
(I am trying to compare passive radiator in terms of this quality)

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#### shank1207

Thanks for the source i would love to see the equations

#### TBTL

There is none between only those parameters. There is a relation if you include the sound pressure level and assume a closed box (and drive the unit to it's xmax).

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#### shank1207

There is none between only those parameters. There is a relation if you include the sound pressure level and assume a closed box (and drive the unit to it's xmax).

Ok can you tell me that relationship?. I asked this coz i had seen a chart of frequency, Xmax and Sd for a case with same acoustic power. (I think it was for closed box case)

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#### Etocynned

Generally Hoffman iron law stands as follows....Pick 2 of three characteristics

1 small enclosure
2 deep bass reproduction
3 high efficiency

This 8s the case in subwoofers in which the electric motor operates close to stall ( low excursion).

#### Etocynned

As to piston size vs frequency output drops at square of inverse hz below resonance.

This is due to the diagram not being able to 'grip' the air and it moving slower to reproduce longer wavelengths.

The solution is a diaphragm which in creases surface area as frequency drops, TRW-17 or propeller on a plane as used for braking.

#### seanny

2XmaxSd = volume displaced. More volume displacement means louder bass. Has nothing to do with what frequency it could produce.

For passive radiator you need to know how heavy is the cone and how much weight you could bolt on to lower...to tune your pr.

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