Advent 5012 Grilles - Rattle Problem

[Pete B]

Must have been a bad day in the factory when they made

the grilles for the pair of oak finish Jensen 5012s that I just

finished restoring. As I mentioned in another thread one

grille is about 1/16" too wide and is a VERY tight fit to get

in place, the other is about 1/16" too narrow and flops

right into place.

I gave these a listening test and noticed that one side made

a rattling sound in the bass, not quite like a voice coil rub

but similar. Pulled the grille and it went away. I noticed

that the grille frame had no holes drilled for the woofer

screws and reasoned that the wood might be hitting the

screw heads, so I added some felt on the baffle board.

Another listen and it is still there. Finally used a software

function generator on the lap top to stimulate the system

with a sine wave. Between 45 and 55 Hz it seems like

the black grille backing material is slapping against the front

burlap material. This is loud, even with just about 5W

input. The other grille does not do this but it is a very

loose fit, so there is a lot of leakage around the outside

of the frame where the air is not forced through the

woofer cut out.

I am about ready to cut out the rear black material just

from the woofer cutout, but as I tap on the burlap I

notice that it alone seems to be slapping against the

baffle board. The rear black material is somehow glued

to the baffle board so it does not flop around. Thinking

now that cutting out the black material is not going to

help if it is the burlap alone against the baffle board.

Not sure what to do ... I'll continue listening with the grilles

off for now.

I could cut down the baffle board so that it is not such

a tight fit, or try to shrink the burlap - it is fairly tight as

it is now.