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An interesting problem solved..


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I had a problem with driving my British Series speaker in my home built cabinet with my Mackie 808M powered mixer and even to some extent with my practice amp. Volume was practically a whisper with nothing but heavy clipped distortion. It had performed beautifully when I tested it out at home with my practice amp. I then made a steel protective grille (very open like the type used to hold lava rocks in gas grills) to go over the front of the cabinet (not even touching the speaker and no screws anywhere near the speaker). That is when the trouble started.

I went to play through it using my Mackie 808M powered mixer and, well, I described the sound above. The practice amp did better, but still distorted at low to medium levels and was nothing like it was at home.

Taking off the steel grille completely solved the problem... Apparently it had to screw up the magnetic circuit to a point where impedence must've been almost non-existant... Put the grill back, what little sound there is is total crap. Take it off, and it lives in all its glory. Who'd have thunk it?! I am going to have to find some black anodized aluminum for it. Anyone ever hear of this problem before? Boggs

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The grille was not in contact with the speaker in any way. The screws that secured it into place were only in at the edge of the baffle and were nowhere's near the speaker or the connector to it. The practice amp would drive it at medium levels but became distorted from clipping beyond that. The powered mixer was highly distorted as soon as you could hear any sound at all. The effect appeared to be load (or lack thereof) induced. It responded differently to two different amps which have different load sensitivities. I did not move the cabinet or the wires. I was careful in my approach. Removing the grille without touching anything else solved the problem. If I didn't see and hear it with my own eyes, I never would have believed it. I design and conduct system tests at Xerox for a living. The only factor changed was the grille removal. Fascinating!

Here are pictures of the front and the back without the grille. Unfortunately, I do not have pictures of the grille at this time. You can see though how the speaker baffle is recessed in and how the speaker frame extends out from the front of the baffle. The speaker mounts from the front. You have about an inch from the front of the speaker frame (which is a good 1/4 inch forward from the speaker surround) to the very front of the scabinet side overhang and the grille was bent forward to a point where it would be almost flush with the overhang. It was not touching the speaker or interfering with the motion of the cone or surround at all. Here are the pictures...




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