Date: Wed, 26 Aug 1998 02:46:55 +0100 (WET DST)
From: Gary Henderson
Subject: resonance of the engineroom-lid


Re the radio: An obstacle to hearing the radio at all is the huge resonance of the engineroom-lid, which occurs right on our 100 km/h speed limit. The point midway between the hinges really moves! Does anyone have a tidy scheme to nobble this?


Date: Wed, 26 Aug 1998 10:20:34 +0100 (WET DST)
From: Mark Norman
Subject: Re: Lowering (or rather engine lids)

Third hinge in the middle?

Date: Wed, 26 Aug 1998 16:26:43 +0100 (WET DST)
From: Gary and Carol Henderson
Subject: RE: Lowering (or rather engine lids)

The thought had crossed my mind. It would have to be a unique design to align the pin with the others.
I've also toyed with the scheme commonly used to support inboard-end of car radios - a tapered nylon pin which engages in a hole. Again, the geometry is a little tricky here.


Date: Thu, 27 Aug 1998 14:29:49 +0100 (WET DST)
From: Simon Trickett
Subject: Engine Lid

Simon Trickett

Date: Thu, 27 Aug 1998 14:47:37 +0100 (WET DST)
From: Dave Edge
Subject: Re: Engine Lid

I have fitted a piece of universal door seal over the rear lip at each end, this has the effect of damping any movement of the bootlid, or at least it would if it were not for the fact that the lid vibrates on the round pegs that the locks grip, I intend to put a rubber grommet on these to buffer any movement here.


Date: Thu, 27 Aug 1998 16:27:05 +0100 (WET DST)
From: Richard Candler
Subject: Re: Engine Lid

> Attach some weights on the underside of the cover NOT in the
> middle, but 1/3 and 2/3 distance across the cover. This will change the
> vibration

This is in fact a really good way to change the vibrational characteristics of something - the natural frequency of your engine lid is equal to a certain rev speed, and this causes the rattle.
It doesn't matter all that much where you put the weights - the 1/2 distance thing is relevent if you have a mode 1 frequence. If you put them a 1/3 and 2/3 distance, then these will be nodes at mode 2 and therefore if your rattle is caused by a mode 2 vibration, it will not be affected (I hope you understand this!).
The best thing, if you want to add weights, is to put them on a little stalk somewhere near the edge - then you can eliminate all the lower modes of vibration, and you'll probably never reach the higher ones. This is how factory machines, cables for bridges, etc. are damped.