The Kingswood Warren LS3/5A Box Test

box testI was contacted by Jim Finnie who used to work at BBC Research Dept at Kingswood Warren (KW) during the LS3/5A days. He gave me the following details about "The Box Test"

"Do you know of the box test? At KW they used to test the integrity of the box as a whole by gently pressing the bass unit inwards (towards the cabinet). It should move slowly and with some difficulty, as the box equalises to the compressed air. On release it should move back outwards to its rest position slowly, almost reluctantly. If it moves out quickly (or instantly) you have a sealing problem. Happy days. I mention this because many KW people thought it to be the critical factor - the boxes that did best on this test tended to sound best (taking for granted that everything else was to spec.)"

It was suggested to me that from time to time the seals should be checked using the Box Test and if necessary the cabinets be undone and resealed. Plasticine was suggested as a good sealant.

I tried this out on a pair of my own Chartwells. I first performed The Box Test Chartwell sealand noted the behaviour of the B110. I then removed the baffles and inserted a fillet of Blutak right round the cabinet so that when the baffles were screwed down again the Blutak would make an airtight seal. In order to ensure that the screw holes remained airtight I arranged a "D" shaped piece of Blutak around each screw hole.

The baffles were then screwed back on, working round and round the screws and tightening each a little at a time. The screws need to be tight but take care not to overtighten and strip the threads.

When I tried the Box Test again the B110 moved outwards much slower than before, taking 2 or perhaps 3 times longer to return to the resting position.

The change in sound was very pronounced. Everything tightened up but the greatest improvement was to the stereo imaging and soundstage.

Warning! You do this at your own risk. It will be hard to get the baffle off again if you use Blutak as a sealant. Perhaps Plasticine would be a better choice. Take care!