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I have never owned or held a Rondo instrument so I neither endorse nor condemn them. From pictures the higher priced ones appear to be comparable to similarly priced instruments. There are plenty of owner comments here on TB, for and against. If you are new to Rondo do a search on them, read them, and form your own opinion.
As to non tension carrying mass affecting the frequency of a bass string, there is a simple experiment you can do yourself to demonstrate that this is true. I used solder wrapped around a C string, you could tape or clip whatever weights you have handy to a string to do the experiment on your own. Shown below is my C string with solder wrapped around it on the left and solder free on the right. I did not touch the tuner, I only wrapped and unwrapped the solder on the string. Adding mass to a string does indeed lower its frequency even though the mass is not carrying the tension.
I have never owned or held a Rondo instrument so I neither endorse nor condemn them. From pictures the higher priced ones appear to be comparable to similarly priced instruments. There are plenty of owner comments here on TB, for and against. If you are new to Rondo do a search on them, read them, and form your own opinion.
As to non tension carrying mass affecting the frequency of a bass string, there is a simple experiment you can do yourself to demonstrate that this is true. I used solder wrapped around a C string, you could tape or clip whatever weights you have handy to a string to do the experiment on your own. Shown below is my C string with solder wrapped around it on the left and solder free on the right. I did not touch the tuner, I only wrapped and unwrapped the solder on the string. Adding mass to a string does indeed lower its frequency even though the mass is not carrying the tension.