Hey guys. I just wanted to tell any of you guys that want to put fiberfill behind your in-door bass units of your Benz not to do it. I had done the fiberfill trick with some of my home subs, and it worked great, however, I think that the subs in the doors of w124 benzs were designed to use the entire door cavity has a resonance chamber. I put fiberfill in behind the subs just to see the effect, and it moved all the bass down to levels below my hearing, and drastically reduced the "thud" from the subs. Generally, fiberfill can give you cleaner, tighter bass, but in the case of the Aktiv Bass systems... its a no go.

The 124 door units are indeed "tuned" to the enclosures they are designed to work in...namely the door cavities, as you pointed out.

Adding fiberfill lowers the Q, or resonant damping frequency of a woofer, in your case, to a frequency that was fairly inaudible.

I would only use the fiberfill for trunk enclosures...and sparingly...until you get the desired result.

As you can imagine, a door cavity makes a pretty crappy enclosure anyway, so the engineers that designed the woofers to get some plausible results really must have done their homework!

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car

Hmmm, the main purpose behind using a product like polyfill (Dacron, long hair wool, speaker stuff etc.) what ever particular brand you choose is to increase the internal volume of the enclosure. By lightly packing a given volume with say 50% long hair wool (the best choice BTW) you in effect increase internal volume by about 1/3rd since the rear radiation from the low frequency driver has to travel through the material to strike the opposing surface and again back through the material to reach its originating point, this takes longer and thus fools the driver into believing its in a larger enclosure than it actually is.

There is really no affect on the driver or its QTS per say, but your passband would be affected either in a positive fashion or a negative one depending upon the current size of the enclosure. The cabinet Q would be the item affected here since its the volume of the enclosure that is being adjusted.

In the case of the door subs, it probably would be a negative effect, since the internal enclosure is already at a optimum volume for the driver, so what you did was increase the optimum volume by 1/3rd and corrupted the passband of the enclosure.

If what you are after is less panel vibration or less mid range coloration, there are materials available that would allow you to dampen the vibrations without affecting the internal volume. The main ingredient in these products is Borasilicate Ceramic and is marketed by several companies (do a search on the internet)

BTW, you really not going to get much low frequency response out of those door subs, you may want to research an alternate solution. I am not even using the door subs in my car, I have a Infinity Basslink that fires up through the first aid kit opening, while not an optimum solution, Infinity coupled that design with a passive radiator and an active servo control which is a impressive solution for under $250 (10" sub, 10" passive radiator, active servo control, internal 200 watt amplifier, low pass crossover, 40hz level control +/- 10db, light ABS enclosure)

Good luck

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1993 500E
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