10-12-13: Flemke
What effect does the damping trough have on the arm?
Tim - I have tried to answer your question the best way I can in parts.
Here is Bruce's testing results with and without the damping trough. THE CARTRIDGE USED WAS OF VERY LOW COMPLIANCE AND THE TONEARM WAS SET UP SO THAT A HIGH AMPLITUDE HIGH Q RESONANCE EXISTED.
The graph and text below taken from the manual.
Damping Trough Results
Surface irregularities on the vinyl of the LP record are the primary cause of rumble or
random low frequency noise, which causes the tonearm/cartridge spring system to start
oscillating. This oscillation occurs continuously during playback. It is a primary cause of wow and flutter and FM distortion in phono playback. Surface irregularities occur not as a part of the record cutting process, but result from the molding process used in making the record.
You can see visually small ripples on the surface of an LP as it is turning. These continuously excite the tonearm resonance.
TONEARM MEASUREMENTS
A LOW FREQUENCY SWEEP WAS PERFORMED TWICE ON A THE TONEARM, ONCE WITHOUT DAMPING AND ONE WITH THE DAMPING TROUGH. THE CARTRIDGE USED WAS OF VERY LOW COMPLIANCE AND THE TONEARM WAS SET UP SO THAT A HIGH AMPLITUDE HIGH Q RESONANCE EXISTED. THE RESULTS OF THE TEST SHOW A REDUCTION IN THE AMPLITUDE OF THE RESONANCE OF ABOUT 8 DB (HORIZONTAL). NOT SHOWN IS THE VERTICAL RESONANCE WHICH WAS 15 HZ WITH THIS CARTRIDGE AND WAS REDUCED ABOUT 2DB.
The ET-2 Damping Trough Owners Manual is available here for download for anyone from Bruce' site.
http://www.eminent-tech.com/Manuals/ET2damping.pdf
My personal experience has been.
The manual is very clear not to install the damping trough until you thoroughly understand how the ET2 works.
I error-ed and installed it very early on.
Then removed it for a number of years and re-installed earlier this year.
When experimenting with magnetic damping earlier I broke the audiophile rule - don't change more than one variable at a time. I tried it again later in isolation - inconclusive - meaning - magnetic damping doesn't do anything for me.
The trough was re-installed and is staying on my ET 2.5.
In three tries Manitunc didn't get one. I think they end up in a drawer somewhere and are forgotten?
So they are rare. If anyone has one guard it for later use. They can get messy and the tip from Bruce was use only 1cc of fluid.
As I am interested in a 2nd one for my ET 2.0 if RugyBoogie can convince Bruce to do a run with a group buy consider me in as well.
As far as sonically what I hear - I prefer Frogman or Slaw to give us impressions as they have been using the trough for a long time continuously. I will say the trough makes this linear tracking tonearm sound more "linear" in response to me. it does smooth out the bumps in the road especially on some of the nasty lps I own - those vinyl surface irregularities can sometimes imo lead to sibilance and harshness. The trough has made these lps very playable for me.
Cheers.