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speaker driver - lowering the resonant frequency
smart51 - 31/7/09 at 10:38 AM

Is it possible to lower the resonant frequency of a speaker driver by adding weight to the cone? I don't care if it lowers the sensitivity of the driver, I can always turn the power up, nor if limits the high frequency response.

blakep82 - 31/7/09 at 11:01 AM

nope. the resonant frequency will be to do with internal dimentions of the cabinet. any pictures of what/where?

ah, i see some of the other threads now.


[Edited on 31/7/09 by blakep82]

smart51 - 31/7/09 at 11:08 AM

quote:
Originally posted by blakep82
nope. the resonant frequency will be to do with where this speaker is placed, internal dimentions of the cabinet, or even the room its in. any pictures of what/where?


The self resonant frequency of the driver, Fs, is quoted by speaker manufacturers and you use this to design your cabinet. I assume the resonant frequency of the driver is to do with the mass of the cone and winding versus the stiffness of its suspension - a mass on a spring. More mass = lower resonant frequency. I'd also thought that the higher mass would mean less movement for a given electrical power input and more inertia, giving less high frequency response. More power gives you back the movement.

MikeRJ - 31/7/09 at 12:16 PM

The answer is yes you can lower the resonant frequency by adding mass. The downside is speaker efficiency rolls off as the cone gets heavier, so you need more power to drive it.

You would also need to add the mass in such a way that the forces through the cone remain equal, e.g. a blob of blu-tack at one point on the cone will cause the cone to distort in the area due to the higher forces.

[Edited on 31/7/09 by MikeRJ]

smart51 - 31/7/09 at 02:28 PM

so if I poured a bit of something runny that then sets into the centre cone of a dual cone speaker and sit the speaker level until it sets, I'd probably do it. The mass of the cone and coil is only grammes I'd have thought so it wouldn't take much extra weight to lower Fs a little.

MikeRJ - 31/7/09 at 03:04 PM

Make sure you don't block up any dust cap in the middle though, or it will drop compliance through the floor (since you will have added a small volume air spring to the speaker!).

Efficiency varies as the square of the cone mass, i.e. double the cone mass and you need 4 times the power to achieve the same SPL. Small diameter, long throw woofers are usually among the lowest efficiency speakers to start with.