Fibrous Damping Material in Subs, Why Bother?

[AndrewJ]

Damping in a sub-woofer box is a very inyersting subject.
On the one hand one could argue that it is not needed if the first standing wave is sufficiently above the crossover frequency.
However, that assumes that the drive force to the cone from the motor system is perfectly linear.
It is not. Any distortion generated by the driver is not by definition filtered by the xover, and therefore the harmonics will excite the standing waves.
Depending upon the severity of the standing wave and the amount of driver distortion, the result may be audible.
So, this would suggest that damping should be used, just in case.
BUT.....any damping in the box will reduce system Q, and especially in a reflex enclosure will reduce the peak output from the vent and so reduce the bass response.
Also, loose fibre filling will move around at highlevels, so the amount of damping or added mass will change with level, impacting the accuracy of the bass dynamics.

The answer....experiment, listen, then choose


Andrew

[PHEONIX]

Originally posted by AndrewJ
Damping in a sub-woofer box is a very inyersting subject.
On the one hand one could argue that it is not needed if the first standing wave is sufficiently above the crossover frequency.
However, that assumes that the drive force to the cone from the motor system is perfectly linear.
It is not. Any distortion generated by the driver is not by definition filtered by the xover, and therefore the harmonics will excite the standing waves.
Depending upon the severity of the standing wave and the amount of driver distortion, the result may be audible.
So, this would suggest that damping should be used, just in case.
BUT.....any damping in the box will reduce system Q, and especially in a reflex enclosure will reduce the peak output from the vent and so reduce the bass response.
Also, loose fibre filling will move around at highlevels, so the amount of damping or added mass will change with level, impacting the accuracy of the bass dynamics.

The answer....experiment, listen, then choose


Andrew

Hello Andrew

Do you think that fibre loading of sealed box is needed , you make mention about reducing system Q and its affect on a vented box design and subjective sound performance , its affect is not so pronounced in undesized small sealed box subwoofers.

Regards
Arthur

[noah katz]

I'm stuffing the 12 cf box I'm building more for the effective volume increase.

In Dickason's LDC in a 1 cf box the response at 20 Hz was increased by about 4 dB with a 50% fill of foam.

That's like 2.5X the amp power for free w/o power compression.

But I read somewhere that the effect is less in large boxes, though I don't know why that would be.