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RE: 1.7 frame damping

Posted by zulugone (A) on December 26, 2016 at 18:54:05

In Reply to: RE: 1.7 frame damping posted by Satie on December 24, 2016 at 13:21:59:

Thanks for the feedback.

I vaguely recall reading something recently that mentioned "air damping" and "float" though I wasn't sure if those were terms of art or science :). My acoustic reading was mostly on vibration isolation and damping materials from 3M, Sorbothane and other companies.

One local vendor does acoustic damping for the marine trade...like damping room size diesel engines that sound below 20 HZ for the mechanics in the engine room and the passengers outside... thinking about bass trapping.

I have to admit that it does not seem obvious to me that the MDF bends or sways from the Mylar moving. I can barely feel the MDF vibrate and then only at highest db. I didn't do any exhaustive feel testing but one at a time notes on an electric bass didn't seem to cause as much vibration as more "congested" music with bass. I actually saw the Mylar vibrate yesterday (sock off) from rumble listening to some Christmas tunes recorded in the '40s. Apparently the CD engineer wasn't listening with a subwoofer. I have noticed that when I use the Oppo crossover at 40 or 50 HZ REW shows very little change in the curve above about 37 HZ but does drop the 20 to 30 HZ range and REW distortion goes down.

For giggles I taped a 4' piece of toilet paper (Charmin 2-ply) top front. As soon as the music starts the bottom of the TP moves to the Mylar and stays there most of the time. Static electricity beats air movement?

I will likely try razoring the magnet board with some 3M CLD tape. I could remove the driver and reinstall it over Sorbothane strips or on gel standoffs but I think there must be easier ways to reduce MDF vibration. (Assuming the manufacturer's numbers hold in this application vibration would be reduced between 54% and 95%.)

I found a local source for lead I could use to fill in the 4' x 3 ½" X ½" indentations on the back. I'm pretty sure the moving Mylar will not induce any resonance in lead :). For purely aesthetic reasons I like having everything under the sock.

One thing I noticed about the comes-with stands is that they do not hold be speakers perfectly plumb side to side or front to back and how they position is not consistent from foot to foot or speaker to speaker. So even if I set them on a leveled piece of MDF I still have to shim the ends of the feet to plumb the speakers.

The error rate is something like 3/8" side to side and ¾" front to back. My goal was to be able to easily adjust tilt in to a precise angle on an out of level concrete floor and eliminate comb filtering which according to the experts is either the root-of-all-acoustic-evil or inaudible.

Just addressing sway I do not see why a dowel from the top center of a 1.7 to the wall behind would not work almost as well as any stand.

Edits: 12/26/16

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