tysontom Posted April 18, 2019 Report Share Posted April 18, 2019 The Collapsed Spider We have discussed this in years past, but good advice is that when storing old Alnico #3700 12-inch or 200003-0 Ferrite 12-inch woofers, do no place it magnet-down (or magnet-up) for prolonged periods of time. This is true also of the AR speaker cabinets themselves using this woofer; i.e., when storing (or mounting) the speaker, do not place or store the speaker cabinet face-up or face-down for long periods of time. This can result in a condition known as "collapsed spider." This sounds quite ominous, but the spider fabric is literally stretched somewhat, and the cone doesn't want to center properly, and the woofer will therefore not operate correctly. This condition applies to other AR woofers, too, but to a lesser degree. The suspension system used on these early AR woofers is extremely compliant—more so than about any other similar woofer. Originally, AR designed the "classic" acoustic-suspension woofer to have approximately 85% acoustic restoring force and 15% mechanical restoring force, just enough to center the voice coil in the gap. The result is the very low harmonic distortion exhibited by these woofers when mounted in the AR-3, AR-3a, AR-11, etc. cabinet. For many years the AR woofer had the lowest distortion of any loudspeaker, and today there are precious-few speakers of comparable size and performance than can equal, let alone surpass this performance. By contrast, most competitive and most contemporary drivers with similar parameters have significantly less compliance, probably on the order of 60/40 or even 50/50 acoustical/mechanical, but with other comparable parameters. These stiffer suspensions work fine and are more robust, but these designs actually have higher distortion, all things remaining equal. Insofar as the voice coil/cone assembly is relatively heavy, more than 80-100 gms or so, the compliant spider and surround (skiver) cannot hold the weight of the moving assembly and will tend to settle. Therefore, if you are preparing to re-foam some AR 12-inch woofers or just storing spares, do not store them magnet-down. —Tom Tyson Quote Link to comment Share on other sites More sharing options...
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.