If you hear something as having a "plastic" or "nasal" quality/timbre, then you need to have an idea of which harmonics to any given fundamental tone are giving rise to that quality.
Please note: That you state across the board that the Grotrian, Steinway B, Blüthner all have this quality -- leads me to suspect your fine-quality Beyerdynamic DT770's are receiving or putting out some common tonal characteristic, despite every one of these Pianoteq models originating from unique soundboard configurations. Hmmmm.
I am not trying come off as a know-it-all by addressing your question in this manner, but what type of plastic are you referring? PVC? Polyethylene? Polybutyldiene? Polypropanol? Next, what thickness and shape of plastic are you referring to? A sheet, a solid (round, square or hexagonal) bar, a cylinder, a sphere? It's not a sarcastic question, as each of these commercially available plastics has its own resonant frequency and harmonic series associated with the grade of plastic and its geometric configuration.
The same types of questions pertain to one's nose when describing something as "nasal". Are you dealing with a resonance in one's nose? In one's nasal passages? A stuffed nose? A runny nose? Are you describing this nasality as coming from between one's own ears, or from hearing someone else sounding nasal? A human sounding nasal? A cocker spaniel sounding nasal? An elephant's trunk sounding nasal?
So we see that describing a tonal characteristic as being "plastic" or "nasal" ... is rather like trying to describe the color "red" to a person who has been blind since birth.
So, unless you specify, say, that the 5th and 7th harmonics of "before A1" (which by the way usually pertain to only one single copper-wound string per note) need to be depressed 0.73 and 1.27db, respectively, for example, we will be left with only descriptive analogy (such as plastic and nasal or woody or throaty) and will remain going around in circles.
Cheers,
Joe
P.S. Ever wonder what the diaphragms of your $179.00 Beyerdynamic DT770s are made of? Yes, ... "plastic". Even the best 000.00 planar-magnetic and electrostatic headphones's diaphragms are made of mylar (i.e., plastic). Case closed.
Last edited by jcfelice88keys (04-01-2018 15:33)