I have had my new Marvin on for a week now so I thought I'd add some impressions to this thread.
I should state that I am primarily concerned with the unamplified arco characteristics; effects on pizz sound are very subtle when compared with arco.
(I think this arco / pizz distinction is the cause of a lot of confusion / dogma, regarding physical upgrades to a bass. Many of the issues inherent with arco playing i.e wolf tones, response time / uniformity across and up the strings are either greatly diminished or not present for the pizz notes. As such the fixes for these issues produce diminished or non existent changes in the pizz note, leading some players to label the fixes as "hokem", and creates the suspicion that laws of physics are bass specific.)
Also very important to note is the tailpiece and tail gut the Marvin is replacing.
Replacing a heavy ebony tailpiece with steel tailgut will produce the most drastic effects, because the floating weight (tailpiece) attached to the strings acts like a damper, removing this weight will allow the top to vibrate more.
The elastic properties of the Marvin will stretch when pressing a string, where as the static properties of the steel will not, making fingering (stretching) the string down to the finger board easier.
In my case I replaced a Wittner ultra light tailpiece with a nylon tailgut. so the weight and elastic effect were not so significant.
The issue is was trying to address was wolf notes on A, the tonal difference (choking sound) playing up the string. and bow response on E and A.
The Marvin did not totally resolve the wolf, but it did improve it, the change moved the wolf slightly and because the strings are no longer coupled together, the A on the D string is not as drastic as it was. I think this was win.
the tonal response up each string was greatly improved. I noticed that bow response is greatly effected by the after length, (mode matching) but straight tailpieces are a one size fits all solution and so getting the G and D in ideal spot puts the E and A in less than ideal. this tailpiece seems to eliminate this issue. Notes up the string now respond better than they ever have.
At first I thought the bow response on the E got worse but realized it was due to my technique, I was used to using so much bow weight, now that weight is not necessary.
Holy crap I wrote a lot... sorry
in short I think if you have a well carved instrument and are not looking for solutions then you are not reading this. My bass is a student level fully solid and this tailpiece has helped playability immensely.
final note on the damper, that I don't think was mentioned, without the damper for certain notes the after lengths will sound even after you mute the upper portion of the strings, almost like a very long reverb effect. could be a cool effect to utilize on purpose, but not ideal in a orchestra, so I use the damper.
