V15LT 350mH !?
Interesting!
Last time someone measured one of these and posted it, it was around 500mH same as the V15IV.
The body you've measured at 350mH would make it the same as a V15V !
With regards to inductance and the LC resonance - I am not convinced it is as big a deal as people think!
If you measure the L/C/R values, and calculate out the theoretical frequency response of the electrical system...
Then you measure the cartridges frequency response, plug the values into a spreadsheet and DEDUCT the calculated L/C/R response, you will then get an interesting "delta" plot.
This shows two things:
1) electro magnetic "imperfections" (eg eddy current and hysteresis effects, also biasing effect of the signal itself)
2) The raw response of the cantilever including:
- resonances (these are the really obvious thing that shows up!)
- slight drops reflecting the loss of signal at frequencies where THD rises (the energy has to come from somewhere) - this only shows up when using spot or sweep tests, pink noise won't show this.
A couple of interesting things I found out by doing just this (and then started noticing it mentioned in various technical literature about cartridges!) - all cantilevers have a slight dip (depending on the design anywhere from 0.5db to 3db) somwhere in the sibiliance area (3k to 10k Hz)
This appears to be cantilever related, as once I deduct the LCR from the F/R plot it appears that those cantilevers that are boron or beryllium have smaller dip than those that are aluminium.
Secondly the LCR resonance (positioned somewhere between 6k and 16k) of some of the higher inductance designs starts to make sense, as it fills out the dip to provide a flatter effective frequency response, and sometimes also compensates for the subsequent drop in high frequency caused by the high inductance and capacitance.
Where things get interesting is when you look at things like the AT25 family of cartridges... 88mH - seriously low inductance (for a high output MM that is)
With inductance of 88mH and capacitance of 150pf the resonance is well and truly far outside the audio zone - so the audible response quality is exclusively down to the quality and efficiency of the cantilever and magnetic system...
These (like many other AT cartridges) also used laminated core poles, but additionally had toroidal coils - so they were well designed to minimise non linear magnetic effects....
Then you look at the styli that were fitted to them -
Beryllium rod.... the best that AT had. (replaced with Boron in their current TOTL)
The 3k-10k dip is much more controlled than most, and the cantilever resonance is somewhere above 20kHz ( at some point I need to measure that - last time I measured this cartridge I did not have the necessary test record to identify high frequency resonance)
Will this give you better "midrange smoothness" than a higher inductance design that uses the resonances to balance things out? - I'm not convinced one way or the other. The V15IV is a remarkably smooth and neutral cartridge... and uses the LCR resonance as part of its solution
The V15V is better and also uses the LCR resonance albeit more lightly
The AT25 / TK9E does not achieve the flatness of the frequency response plots on the Shures - the LCR resonance is too far out of the way to help! - so the dip is "exposed", and so is the subsequent rise to a resonance somewhere above 20kHz..... pretty much the same as you will see on many very high quality MC's
In fact the TK9E response curve looks almost identical to that from an Empire/Benz MC1 (Boron cantilever eliptical late 80's 2nd from the top model, the top model was the Benz Micro MC VdH - same body and cantilever fitted with the VdH/Fritz Geiger tip)
Does it sound good - yes it does - is it as good a neutral reproducer of the original recording as something like the V15V.... I'm not sure it is.
bye for now
David
