Hedgebeth Sonority Tonearm | Interview

02.09.2012..

ReMusic World Premiere | Some days ago, my friend and ReMusic’s Co-editor Roberto, told me excited about his new friend on Facebook, Randolph, the brave Dr. Hedgebeth, Architect. We must be antennas for the news, so, detto fatto, here we are interviewing him, a brand new designer of tonearms.

 

Question: Seems that there is not enough room for brand new tonearms nowadays…

Randolph D. Hedgebeth: I decided to design the Sonority Tonearm to follow my quest of getting very low frequencies in the playback of LPs. In fact, in the LPs, there are innumerable subsonic environmental information, which - I discovered – enhance considerably the musical experience, but dirt unavoidably the high frequencies. Applying an anti rumble filter and/or tuning the system to attenuate these frequencies is, without any doubt, a band-aid solution to get an inadequate system. In fact, the tip will keeps on tracking the subsonic frequencies. It is better to design an arm that will track the grooves in a clean and undistorted way. An arm that can track the very low frequencies instead of “ignoring” them.

 

Question: There were no other tonearms capable of rising to the challenge?

Hedgebeth: I designed the Sonority Tonearm driven out of desperation over tonearms that simply would not track recordings with subsonic frequencies. Starting by the assumption that the tracking of the cartridge is very arm dependent, I tried out several famous turntables and tonearms matched with my system, which goes very down, and using recordings that I know very well with their info that go very down as well. They all failed and one quite dramatically. While tracing the 12 Hz groove of the Liverpool Pipe Organ, the sound was slightly distorted in the entire frequency spectrum and with the 10 Hz groove, it was very distorted. The tracking was missing. When the stylus entered the 8 Hz groove, the tonearm was launched outside the record groove. I had to catch it before it fell back down to prevent the damage of the record. It was clear that the traditional turntable, although optimized to the arm systems, was inadequate.

 

Question: You are speaking about very low frequencies.

Hedgebeth: Yes, I am. Another thing that affects this situation are the seismic waves in most areas of the world. In fact, the earth crust moves and vibrates constantly. We are seldom aware of this because our bodies have been adapted to these constant micro vibrations. The most recent audio gear do not have any sensors or control system to cope with this information. We are only aware of the big quivers and quakes, mostly if we are living in active earthquake zones and near volcanoes. The people that read the seismographs do not report daily to the local TV or newspapers, but they are constantly monitoring the micro-quivers. From the study of earthquakes, we can know how the earth crust works in extreme situations as well as in the micro scale.

 

This form of 'distortion' have to be taken into account when we want to setup our turntable. The frequencies we are dealing with are lower and different from the frequencies of the traditional approach of the ‘Effective Mass’. I know this from direct observation, as I have witnessed the behavior of my LP setup in 2000 during an earthquake with magnitude 4.2. The epicenter was near my house. It did not falter thanks to the way I had suspended the entire system. There were also the noises of traffic, footsteps and other various thumping and banging coming from our neighborhoods.

 

Question: We know, it is a never ending story…

Hedgebeth: In fact, the condition of a tonearm is contradictory. When the arm tracks a record, it needs at the same time the infinite mass and the absence of the mass together with an absolute stability. A condition impossible. I have made any possible effort to solve this situation in the simplest way.

 

Question: Notwithstanding all that, maybe you have found an effective solution.

Hedgebeth: Finally, I have chosen an arm with an effective length of 250 mm. The more practical solution before the Moment of Inertia would become impracticable with a cartridge of medium mass.

 

After considerable time spent to solve all the contradictory aspects of the design, I have chosen a unipivot arm.

 

There is a ‘geometric condition’ created by the most part of the tangential arms that I did not like. Instead, the vertical pivot is well above the record surface where the stylus tracks. The slightest deformation of the vinyl causes an increased angular displacement of the VTA and a greater error with the tangential arm. This is due to the intrinsic rigidity of the system.

 

With this situation of the VTA, the complexities climb to an unacceptable level if you opt for a tangential tracking. It is improbable to get to a satisfactory solution. At least I have not find it. Tangential arms are vulnerable to subsonic frequencies, besides being fragile. I have considered many solutions and rejected in principle or for the conflicting details.

 

Question: We have talked about the tracking. What about the rigidity of the tonearm?

Hedgebeth: Another situation that I deem critical concerns the direct coupling between stylus, pivot bearing(s) and turntable spindle. Here we need the maximum rigidity. Air bearings and magnetic levitation are not up to standards here. Those kinds of suspensions and bearings are outside the rigid system and act making levitating outside part of the system without separating the arm from the turntable spindle or the turntable platter from the plinth. Pneumatically floating the entire assembly would be a great solution to separate it from the outer forces.

 

The first objective was to build a lightest and stiffest arm casting so to resist in a subsonic environment without producing any resonances or sonic colorations in the playback. After having tried all the conventional and not so conventional approaches, I chose a design that employs a thin chassis with three legs. The most important thing is however the dramatic reduction of the moment of inertia. I truly believe that this is the most important aspect. Aside from the basic geometry, it concerns the action of the stylus action in the groove and reduces considerably the moment of inertia.

 

The second objective was to get an infinite mass. I achieved it partly by using the symmetrical damping fluid in unique configuration as you can see in the picture. This has another benefit: to provide the necessary anti-skating resistance. A further simplification, though. To adjust the total mass of the arm I have put some adjustable mass blocks close and around the pivot. The moment of inertia is significantly reduced. Also the counterweight is configured in a similar manner. You get more than a pound (45 gr) of mass without a significant increase of the moment of inertia. It is possible to obtain a mass of about 10:1.

 

The geometry of the arm produces the lowest tracking error within a radius of 60 mm. The housing of the spindle and the stylus tip are in a horizontal plane in respect to the record surface. All that to get the maximum stability and the minimum error at every level. Here is where all the tangential arms I have tested have failed. The mass of the arm is below this level and creates a very stable and well damped system. There is no discernible Q resonances. The operation in a subsonic environment is like a walk-in-the-park.

 

Question: Technically speaking, it is a great result. Since the very first sight, the geometry of your tonearm looks innovative.

Hedgebeth: One of the most important geometric features is that the stylus and the arm pivot are on the same plane. Linked to design of my new turntable, this arm is made in a way that the primary suspension of the systems, on all planes, is on the plane of the record surface. To get the maximum stability, the majority of the assembly mass is well below this plane. Thus, arm pivot, stylus and record surface are undisturbed by external vibrations. External vibrations are not translated into other vectors of arm disruption. Also the deformations of the record are treated neutrally with a negligible effect on the VTA. The deformations have a little effect on the playback. The entire assembly is effectively isolated from external vibrations. The record is perfectly clamped to the platter with a single spindle clamp.

 

This condition makes exercises and mathematics rules on the ‘Effective Mass’ irrelevant. Regarding my previous question on: ‘Why have you design an arm which would resonate anyway?’…


Question: Funny, I was about to ask you the same question

Hedgebeth: The effect that this approach has on the rest of the audio bandwidth is not irrelevant. There is a deep reduction and cancellation of resonances and micro-vibrations in the arm casting in order to obtain the maximum performance of any phono cartridge. A further aid comes from the damping fluid. Without mention the enhanced subsonic capabilities.

 

The selection of the materials for the arm has been made first keeping in mind the absence of any resonance and then any structural or functional need. The configuration of the structure and the choice of the reinforced phenolic paper for the headshell has a profound significance for all the desired characteristics. Magnesium is more than twice the mass and VERY resonant. The sonic differences in a side-by-side comparison are clear and unequivocal. This, along with the Redwood chosen for the arm casting completes the most important assembly. Old Tech is instead preferred for the custom-made super adhesives High Tech Epoxy.


Question: How is made the rest of the tonearm?

Hedgebeth: The unipivot concept is very precise and very simple if applied with the aid of a very high tech plastic cup seat and a mini ball pivot point of 10 grains. I have used a dry system to get the maximum coupling between the stylus and the arm, between the turntable spindle and the platter, between the record surface and the cantilever spiral. The design of my new turntable has a similar bearing system. The solid copper mass blocks of the tonearm assembly favour a perfect coupling of the bearings.

 

Even if not a moving part, the bronze cast of the base is what ties the whole thing together. It has a damping mass, allows the lifting of the arm and can contain the optional phono preamplifier. That eliminates the usual long cable and the cartridge signal is more intimate with the processing electronics. A tube version is available for high output MM and MM cartridges, while for MC cartridges is available a solid state amplifier with current elevation. I chose limo connectors for their high performances.

 

The overall stability of the arm is excellent thanks to the simplicity in the adjustments of the lateral forces and of the VTA.

When the complete system will be available, it is possible to operate via remote control to lift the arm.

 

Question:

Could you give us some ‘listening impressions’? Obviously, from the manufacturer’s point of view.

Hedgebeth: I own a London Reference I have not heard yet. I have had a Decca Gold, modified Garrott, which proved to be ‘the’ arm for the Decca.

My Takeda Labs Miyabi is phenomenal with this arm. I have also had a Sonus Blue, an ADC XLM Mk.II and a Denon 103D. All exceptionally performing once ‘tuned’ with the arm.

 

With the Denon and Decca, you could get telluric basses with a ‘grip’ that I have not heard with any other arm. The other cartridges also behaved exceptionally except for the ‘iron grip’ of Denon or Decca. I think the reason is the specs of the cartridges that my arm can reveal.

 

The startling thing was the ADC XLM. It was incredible in the bass range as the Denon and Decca are and, at the same time, it offered an incredible musical experience, and extremely satisfying. Regardless of its price, it really surprised me. I would not say that it could replace the Allaerts or the Miyabi, but there is not so much difference in tracking the groove.

 

With my arm, I can analyze the cartridges in their entirety. The Allaerts goes very down, 10 Hz, as stated in the specs. Not telluric but it shakes the walls with its depth and power. In comparison, the deep slam of the Decca is a unique audio experience.

 

It is very easy with my arm to catch all the nuances of the performances of the cartridge.


Question: Thank you, Randolph, ReMusic is ready to review your first product.

Hedgebeth: I promise, it will be a world premiere.

 

 

Official technical specifications

Arm geometry: 250mm Length, 16mm Overhang, 22 degrees Offset Angle, supplied with set up and alignment template.

Mass: Arm Wand 13.5g with cables, 12 g bare, Complete Arm 534g with 10 g Cartridge, pair of largest Mass Blocks and Counterweights for balance.

Fluid damping: Paddles have a 54mm radius from the Pivot Point. Viscous Silicone Damping Fluid. This also provides the Anti-Skating Force in the most neutral manner possible.

Adjustments: All adjustments are made either with ones’ fingers or with simple hex wrenches and Allen wrenches. Counterbalance is by simple Counterweight(s) and a small Adjustment Nut. Azimuth is by small nut weights on the rods in the damping fluid.

VTA: The Pivot Post is vertically adjustable. A special locking wrench is provided. Damping and Anti-Skating are adjustable by raising or lowering the threaded rods. The Arm Assembly is completely removable without altering any adjustments. Different Cartridges can be mounted and adjusted on its own arm and exchanged.

For further information: email directly Dr. Randolph D. Hedgebeth

Clyde Keller photo<br />www.clydekeller.com
Clyde Keller photo
www.clydekeller.com
Clyde Keller photo<br />www.clydekeller.com
Clyde Keller photo
www.clydekeller.com
The phenolic headshell sporting an Allaerts MC 1 Boron cartridge.
The phenolic headshell sporting an Allaerts MC 1 Boron cartridge.
The magnesium headshell.
The magnesium headshell.
by Giuseppe Castelli
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