I had BT4 light, BT4 heavy, BT4S heavy.
I used some pin gauges with the 0.01mm accuracy to Go/No-Go measure the throat diameter.
The throat diamter of my BT4 Light is 7.10~7.11 mm.
The throat diamter of my BT4 Heavy is 7.05~7.06 mm.
The throat diamter of my BT4S Heavy is 7.15~7.16 mm.
Btw, my BT4 Light should be produced in earlier years. I bought these two heavys in Jun 2024.
I used 60 steel balls to try to get a rough idea of the inner contour shape.
The cup sharps of two heavys are same, which are a little bit larger than the old BT4 light.
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Btw, there is one opinion from my friend, fyi.
He feld that the two heavy mouthpieces both have one problem, the tone color is not uniform in high and low ranges. My old BT4 light does not have this problem, it is consistent.
My teacher told me that different mouthpieces should be played in different ways to achieve the best and most suitable effect.
My understanding is that it is like singing the same song in different singing methods and singing styles.
For example, when playing the same one Rochuts,
Greg Black New York 5 Medium weight can play warmer, deeper, and the sound is very solid, more like the aria.
Greg Black New York 5.25 Regular weight, the sound is exquisite and flowing, more like the musical drama.
Greg Black New York 5 Regular weight will be more relaxed, like the lullaby for baby.
Griego Alessi 5C will be more performative and emotional.
Griego Alessi 4C sounds more open, like a big voice.