Letsmakeadeal wrote:Marc or BRF - Will you please explain what we are looking at here.
I am by no means an expert in this area, but I can try and help with how to read the graph and give some general impressions.
The graph is merely an amplitude vs. frequency plot. Amplitude is expressed in db which is a logarithmic scale based on orders of magnitude, rather than a standard linear scale. Mike used a 1kz test tone to create a repeatable reference point which is plotted as 0db on the y-axis. All subsequent measurements are referenced to 0db.
An out of phase motor is used to generate vibrations. These vibrations include various frequencies which are plotted on the x-axis of the graph.
Motor vibrations (frequencies) travel from the arm board, through the pivot spike, down the arm tube and then excites the MC stylus which creates an electronic signal which is feed to a broad band frequency analyzer. The output is then displayed in the graphs above.
I found Mike’s use of a cartridge as the transducer to produce an electrical signal to be both unique and interesting. My initial thought was why not use a piezoelectric accelerometer to read the vibrations that feeds the output to the broad band frequency analyzer? Mike did mention that his test and conclusions are subjective and based as much on experience and personal biases, therefore, I can only assume that Mike wanted to recreate a more real world resonance test that would include the mass of a cartridge and the compliance of the suspension, all combined with the tonearm. It should be noted that output results “could” vary based on the cartridge employed as the cartridge is now part of the tonearm.
What does a perfect tonearm resonance spectrum look like? The plot should be flat and consistent with little amplitude as possible. This means that when the tonearm is presented with a parasitic frequency, it dampens (reduces) the oscillations in the tonearm/cartridge system and dissipates/decays that energy after a disturbance as quickly as possible without addition or subtraction.
Based on my experience and understanding, the three graphs presented by VPI illustrates three (3)
well-designed and
well implemented tonearms. IMHO, the resonance peak at 120 hz can “possibly” be attributed to the pivot point bearing interface or a secondary harmonic distortion of the 60hz line frequency of the motor. Since we are talking about the 100-150hz range, the ear would have a difficult time discerning the difference in magnitude. Personally, I am not concerned.
From 225hz and up, all three arms demonstrate an on average of -80db flat response with very little change in amplitude. This means that the tone arm will not impart a sonic signature regardless to the frequency band. Using Mike’s Bell analogy, you do not want to see a resonance peak where a certain frequency is emphasized over the expense of the entire frequency band.
Which tonearm is the best? From the data presented, I cannot draw a definitive answer as I do not possess the technical analytic wherewithal to make an informed opinion, plus there are a lot of “other” variables than just resonance that determines a tonearm’s overall performance. BUT, after seeing the graphs, my perspective has changed. I was expecting the “reference” arms to demonstrate superior test results, but what I wasn’t expecting is how excellent the standard arm measured! IMHO, the reference arms deliver the results as expected, but the standard 12-3D over achieves.
I’ve owned a 12-3DR arm longer than most on this forum, and I can tell you based on my personal experience and listening, the 12-3dR is the real deal!