Chopin learned to play on a Bucholtz piano, made in Poland out of pine-wood in his early years.
when he played a concert on his Bucholtz, which was a piano fasioned after the English design (a la Broadwood etc.) his music teacher mentioned that the bass notes could not be heard in the crowd and the next concert a Viennese piano was borrowed which allowed the bass notes to be heard in the room.
Chopin mentions in his letter that he would have preferred to play his own piano.. this gives an indication of his tastes.
It appears, that the English-styled, Polish-built piano which Chopin used before moving to Paris was quite a soft-sounding instrument..
this coincides with a letter written to Erard by his nephew, who was setting-up a factory in London (Erard London) .. he mentions that the English pianos of the time had softer darker hammers than the French model.. he says that the "English pianos have a beautiful yet CONFUSED sonority"...
the round shape of the english hammer and it's construction gave the hammer a deeper, darker sound, as opposed to the pear-shaped hammers which began to come-out in the 1840's, which had a brighter, more focused sound..
The Pleyel hammer was covered with an extremely soft felt made of rabbit fur, alpaca, cachemire and other soft fibres
I have a Pleyel with original hammers and have found two other Pleyels with this exact same felt, one of which was Rossini's Pleyel and the other being built in 1845
I can safely say that there is NO WAY that the piano would sound brilliant or nasal unless the keys were struck very hard..
I had the opportunity to play Mc Nulty's Pleyel, and it is a great instrument, well built etc... great attention to detail.. the sound of the hammers is too hard though, because he is using a felt which typically is used in restorations but is historically inaccurate.
the great problem is achieving BOTH a mellow ppp and a relatively bright FF
A good-quality felt made today of the same density (about 250 grams weight)will give a mellow ppp but the fortissimo is dull..
the fibres of the original Pleyel felt are extremely fine and curly and when the hammer hits the string SOFTLY, the soft felt sets the string in motion without coupling to the firmer layers of leather underneath..
...when the hammer is played harder, the Pleyel felt has the ability to squash and 'bottom-out' almost completely, therefore coupling the harder leather layers to the string and producing a brighter sound..
this is perhaps why the way that the felts were manufactured was VERY different from today's felt
You can read the original PATENTS OF THE FELT MAKING PROCESS IN THE FOLLOWING ARTICLE... Pleyel Hammer Article