Bowers & Wilkins N804; adjustment knob on back?


Anyone have any idea what the adjustment knob on the back of many B&W speakers is for?  I have read about guys adjusting this thing, but I have been unable to find any information on it.  

Seem like it is designed to be adjusted, but also may be some factory adjustment you don't want to mess with.  Ideas?
sd02720
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I had a pair of N804s for 16 years before I traded them in. There is an adjustment screw on the back which holds the midrange driver in place. B&W does not recommend messing with it as the tension is set at the factory. However, if you must adjust it for whatever reason, then hand tighten it until you start to feel some resistance. Then give it one more 1/4 of a turn and your done. That advice came from B&W technical support directly.
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