Hi folks,
I have been trying to learn a bit on the compliance of a cartridge and its matching with a particular arm. On the net, I found several excellent (to me) discussions on this. For others' benefits, let me list some of them here:
1) PHONO Cartridge Compliance, Tonearm Mass, System Resonance, Loading of MC and MM Capacitance, RIAA Characteristic
2) Tonearm/Cartridge Capability
3) What does cartridge 'compliance' really mean in practice? - AudioKarma.org Home Audio Stereo Discussion Forums (read post #11 by user "Pauln")
4) Cartridge / Arm Matching
5) Ortofon - Advanced phono cartridge guide
The resonance of the cantilever that connects the cartridge body to the tracking diamond tip cannot apparently be avoided (in layman's terms, it is quite nicely explained in 'Pauln"'s post in the third link above). The idea is to push the resonant frequency below the audible level, but not too low so that any external vibrations can enhance the resonance. The ideal resonant frequency is suggested to be between 8 and 12 Hz.
The resonant frequency = 1000 / [2 pi * sqrt(M * C)]
where, pi = 3.14 (approx), M = total effective mass in gm of the arm plus cartridge, and C = compliance of the cartridge in um/mN (um is micrometer and mN is milliNewton; um/MN is the same unit as micro cm/Dyne). Frequencies are always in Hz (number of vibrations per second).
Take for example the Rega RB251 tone arm. Its effective mass is 11 gm. Couple this with Ortofon Super OM 10/20/30 MM carts with mass of 5 gm. Taking into account also the mass of the screws etc (typically taken to be 0.5 gm) to fix the cart on the arm, the total effective mass of the combo is 16.5 gms.
Now the compliance of these carts are typically 25 in the units stated above.
If we now plug these into the above formula, we get the resonant frequency to be 7.84 Hz. Seems fine to me. But is it too low?
The Ortofon Super OM 10/20/30 carts actually come with a brass weight attached to the cart body. One can remove it to make it lighter and then mass of the cart actually becomes 2.5 gm, leading to a total effective mass of the cart+arm combo to be 14 gms. In this case, the resonant frequency increases to 8.5 Hz which seems a bit safer. So my conclusion would be to remove the brass weight from these carts if one is using them with the Rega RB251 arm.
Is this correct? Or are there any other factors involved here, some other disadvantages by making the cart lighter?
I have read it in many forums that the newer MM carts from Ortofon, the 2M Red/Blue/Bronze/Black are made to suit the Rega arms. Okay, let us examine that statement. These cartridges weigh 7.2 gm and compliance is typically 20 - 22 in the above-mentioned units. This leads to resonant frequency of 8.23 Hz (if compliance is taken to be 20) and 7.85 Hz (if compliance is taken to be 22).
From the above, can one say that the newer 2M range makes a better match with the Rega 251 arm? I suppose not. Are there any other factors in the matching?
Your comments will be appreciated. For many out there, looking to buy a TT like me and wondering about lots of stuff like the above, this kind of discussion may be useful. Really looking forward to receiving some advice from the experts and impressions from novices and not so experienced like me too.
Regards.
Note to the Mods: There is a similar thread started by jls001. If you want, you can perhaps merge these two threads. That thread went in a somewhat different direction, although still very useful. I have no problem if you merge these threads.
I have been trying to learn a bit on the compliance of a cartridge and its matching with a particular arm. On the net, I found several excellent (to me) discussions on this. For others' benefits, let me list some of them here:
1) PHONO Cartridge Compliance, Tonearm Mass, System Resonance, Loading of MC and MM Capacitance, RIAA Characteristic
2) Tonearm/Cartridge Capability
3) What does cartridge 'compliance' really mean in practice? - AudioKarma.org Home Audio Stereo Discussion Forums (read post #11 by user "Pauln")
4) Cartridge / Arm Matching
5) Ortofon - Advanced phono cartridge guide
The resonance of the cantilever that connects the cartridge body to the tracking diamond tip cannot apparently be avoided (in layman's terms, it is quite nicely explained in 'Pauln"'s post in the third link above). The idea is to push the resonant frequency below the audible level, but not too low so that any external vibrations can enhance the resonance. The ideal resonant frequency is suggested to be between 8 and 12 Hz.
The resonant frequency = 1000 / [2 pi * sqrt(M * C)]
where, pi = 3.14 (approx), M = total effective mass in gm of the arm plus cartridge, and C = compliance of the cartridge in um/mN (um is micrometer and mN is milliNewton; um/MN is the same unit as micro cm/Dyne). Frequencies are always in Hz (number of vibrations per second).
Take for example the Rega RB251 tone arm. Its effective mass is 11 gm. Couple this with Ortofon Super OM 10/20/30 MM carts with mass of 5 gm. Taking into account also the mass of the screws etc (typically taken to be 0.5 gm) to fix the cart on the arm, the total effective mass of the combo is 16.5 gms.
Now the compliance of these carts are typically 25 in the units stated above.
If we now plug these into the above formula, we get the resonant frequency to be 7.84 Hz. Seems fine to me. But is it too low?
The Ortofon Super OM 10/20/30 carts actually come with a brass weight attached to the cart body. One can remove it to make it lighter and then mass of the cart actually becomes 2.5 gm, leading to a total effective mass of the cart+arm combo to be 14 gms. In this case, the resonant frequency increases to 8.5 Hz which seems a bit safer. So my conclusion would be to remove the brass weight from these carts if one is using them with the Rega RB251 arm.
Is this correct? Or are there any other factors involved here, some other disadvantages by making the cart lighter?
I have read it in many forums that the newer MM carts from Ortofon, the 2M Red/Blue/Bronze/Black are made to suit the Rega arms. Okay, let us examine that statement. These cartridges weigh 7.2 gm and compliance is typically 20 - 22 in the above-mentioned units. This leads to resonant frequency of 8.23 Hz (if compliance is taken to be 20) and 7.85 Hz (if compliance is taken to be 22).
From the above, can one say that the newer 2M range makes a better match with the Rega 251 arm? I suppose not. Are there any other factors in the matching?
Your comments will be appreciated. For many out there, looking to buy a TT like me and wondering about lots of stuff like the above, this kind of discussion may be useful. Really looking forward to receiving some advice from the experts and impressions from novices and not so experienced like me too.
Regards.
Note to the Mods: There is a similar thread started by jls001. If you want, you can perhaps merge these two threads. That thread went in a somewhat different direction, although still very useful. I have no problem if you merge these threads.
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