One of my 18BR40 has developed a rattling noise when playing 20-80hz at moderate levels. It seems that the rattling follows the excursion. If i lightly touch the cone while its playing, the rattle goes away. The pitch changes slightly if i adjust the bolts holding the driver in the box. The rattle is barely audible when the driver is in free air. I have two that has been used as subs for the past 8 years or so, only one of them have started making the noise.
Any ideas what this could be?
Any ideas what this could be?
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There could be many causes. One cause can be a loose basket to magnet connection. Most are glued and bolted to the motor, but if the surfaces are not properly flat, or the bolts don't fully clamp the basket to the motor, there may have been a gap from factory.
If you can temporarily reverse mount the driver, play some music through it and apply pressure to the magnet assembly to see if the rattle goes away.
If you can temporarily reverse mount the driver, play some music through it and apply pressure to the magnet assembly to see if the rattle goes away.
Looking at the impedance graph, there appears to be inductance countermeasures such as shorting rings or sleeves in the motor, sometimes if the tolerances are poor, these can come loose, causing a rattle too.
The speaker baffle may be warped, causing the coil to drag slightly due to frame misalignment.
