Reed

Design Principles

A tonearm is a mechanical, acoustical and electronic system. The set of parameters of this system determine the characteristics of the tonearm and how the tonearm will ‘sound’ depends on how many parameters were taken into account while designing it. The main parameters of a tonearm are (1) Effective length, (2) Effective mass, (3) Moment of inertia, (4) Acoustic damping of the armwand and (5) Wiring impedance.

(1) Effective length
The effective length of a Reed tonearm can be from 9″ to 12″.

(2) Effective mass
The effective mass of a tonearm is very important when matching a cartridge. Cartridge compatibility with tonearm is determined by the Tonearm Resonant Frequency. It should be 10Hz (-4Hz + 6Hz) however it may vary from 8Hz to 12Hz. The Tonearm Resonant Frequency can be calculated by using following formula:

where:
ƒ_rez – resonant frequency of tonearm
m_ef – effective mass of tonearm
m_c – weight of cartridge
m_s – mass of the screws, nuts, spacers, washers, shims
c – compliance of the cartridge

Since the effective mass of different Reed models can be from 8g to 25g, Reed tonearm can be matched with almost any cartridge.

(3) Moment of inertia
The tonearm moment of inertia consists of two parts:

a) Cartridge moment of inertia I_c
b) Counterweight moment of inertia I_w

Because I_w should be (and usually is) at least 10 times less than I_c , we will use it only for approximate calculation.
The cartridge moment of inertia I_c is calculated using the following formula:

m_c – cartridge weight
m_ef – tonearm effective mass
l_ef – tonearm effective length

Best result is achieved when I_c is less than 20000 g*cm².

If the LP is perfectly flat, then I_c does not have any influence. I_c becomes important when LP is not flat. In such cases the cartridge and tonearm are moving up and down while the record is playing. Even if the swinging amplitude is around +/- 0.5 mm, the tonearm with a high I_c may not be able to catch up with the LP swing. This causes instant VTF, VTA and SRA changes which lead to sound distortions. To reduce LP swinging, clamps are used.

(4) Acoustic damping of armwand
The stylus, while moving in the vinyl’s groove, produces not just the musical signal, but also oscillates the cartridge. This oscillation can be transferred through the armwand, be partially reflected from the counterweight, travel through the tonearm bearings, tonearm support, chassis, platter bearings, platter, mat and the vinyl record and return back to the stylus. The stylus also causes vinyl plate vibrations that travel through the mat, platter, platter bearings, chassis, tonearm support, tonearm bearings, armwand and return to the stylus again.

The interference of these two acoustic vibrations can impact the sound quality. To deal with these vibrations, acoustic oscillation damping can be done in two ways:

a) Vibrations transferring to the floor.
This is the most widespread method. The most common solution is to build a tonearm that should carry away these vibrations as quickly as possible and via a mechanical connection, transfer them to the floor. Designers sometimes increase the weight of a platter so that it can suppress vibrations and at the same incorporate soft suspension systems in order to allow less vibration energy to get back to the stylus. This can be done quite easily in heavy decks but this is not fully effective as measurements show that some vibration finds its way back to stylus eventually. The amplitude is not too big but considering the size of the groove this vibration may still introduce some distortion.

b) Choosing right armwand material
Reed tonearm armwands are made of carefully selected different types of wood, so their sound damping characteristics cover the whole range (exponential). This method was chosen after a lot of testing of different armtube materials and bearing setups.

(5) Wiring impedance
It is very important to harmonise cartridge output impedance, wiring impedance and preamplifier input impedance. The cable used in Reed tonearms is made by Stereo-Lux Musikanlagen, has no soldering points and is harmonised perfectly.

After a lot of tests and listening to customer feedback we found out that tonearm adjustment is important not just for installing the tonearm for the first time but also after changing a cartridge or even a LP. That’s why Reed tonearms feature user-friendly and precise adjustment for azimuth and VTA.

Reed Website