Woofer Disttortion

[davet753]

I ran across something new this afternoon, and was wondering if anyone else has had this happen.

A few months ago I restored a 50 watt (25 per channel) Magnavox Astro-Sonic console stereo. I ended up replacing every single #%*@ electrolytic capacitor in the stereo, and even the non-polarized cap in the crossover. The stereo sounded great, except for a very slight distortion in the woofers on certain passages. It was very dependent on the type of music being played. For instance, a string bass seemed to make the distortion more noticeable, or even some voices. A male announcer on a local station I listen to has a pretty deep voice, and I seemed to notice a little muddy "buzz" when he spoke. I hooked up a pair of vintage University Diffusicone 12 speakers to the external speaker jacks, and there was no distortion at all.

I read an article somewhere online last night about distortion in old woofers. The guy who wrote the article said that on some of the late 50's-early 60's AlNiCo woofers, the cone will start to "sag" a little bit and cause the voice coil to rub slightly. He claimed this was more common in the larger size speakers (mine are 15"). The article claimed this causes a muddy, distorted sound.

Just for the hell of it, I took mine out, flipped them upside down, and re-installed them.....low and behold, PROBLEM SOLVED! Not only did the distortion disappear, but the speaker sounds a little brighter (to my ears).

I have never heard of such, until now. It does make sense, though. A big, heavy cone sitting there for 50 years with gravity pulling it down could eventually cause some settling. I suppose the spider could also start to loose it's form a little and contribute to the problem. At any rate, I guess turning mine over has pulled it back to center just enough to stop the distortion.

You learn something every day