There's plenty to chose from.... cork, glass, acrylic, felt, brass or copper, even wood. And there's always old-fashioned rubber. Great claims are made for these various products. Turntable mats seem almost to be an obsession amongst vinylistas.
All the more surprising then that so few of the products are really suitable!
Below we give our recommendations. Happily, we have in Stereo Lab a software solution to complement the record mat.
But, let's first ask a question.....
All the more surprising then that so few of the products are really suitable!
Below we give our recommendations. Happily, we have in Stereo Lab a software solution to complement the record mat.
But, let's first ask a question.....
The following list of reasons is hopefully uncontentious.
The last item on the list may appear frivolous but, during the time when a turntable is not being used — which is probably for the majority of the time, it is the mat which dominates the look of the unit.
Translating this into physical requirements. We need a turntable mat material which is:
Apart from their striking appearances, it is difficult to make the case for non-resilient materials in this application. We want the record support-mat to protect the soft PVC copolymer material from the metal parts of the turntable (if one is employed) and we want it cushion the record so as to damp any vibration in the record and the turntable. And we want the material to grip the surface of the record so as to transfer the torque of the turntable to the medium. Hard, inflexible materials cannot fulfil these requirements.
Material hardness was codified during the early 1800s by German mineralogist Friedrich Mohs . He devised a scale and test which is still in use today. The essence of Mohs test is,
❝That which scratches is harder than that which has been scratched.❞It doesn't take too much imagination to imagine that brass and copper leave a nice scratch upon a record. (Test it if you like!) Since we know we don't want scratched records, these materials represent an inappropriate choice for a turntable mat. The only advantage of copper and brass is that they conduct electricity and may thus play a rôle in reducing static electricity buildup on the playing surface; especially when a non-metallic platter is employed (see below).
Worst of all, hard mats demand an impossible level of cleanliness because, any house dust (which is mostly silica and much harder then the record) trapped between the mat and the record will damage the record — especially if the record moves relative to the mat.
A case might be made for a rigid material if it betrayed some striking mechanical advantage. We were attracted by the impedance match argument (see panel) in the hope that a better energy absorber might be available. But a few simple experiments (see panel) and Appendix 2 reveal that the matched impedance theory doesn't apply in this application.
The trouble with these matched impedance transmission line type arguments is that, whilst it is true that reflections take place due to impedance mismatches, adding another length of "line" does not make the problem go away; it simply postpones it. Reflected energy is no less of a problem because it is delayed. Doubling the length of an organ pipe doesn't stop it sounding ! The trick is to terminate the line in a dissipating element, not to extend it.
In his paper Record Contamination: Causes and Cure¹, Percy Wilson studied the effect of static electrical charge on the surface of a vinyl record and the rôle it plays in the contamination of record grooves. He said,
❝An interesting experiment [is to] electrify both surfaces of a disc by rubbing with a piece of silk .... I now place a piece of aluminum foil on one surface and the net charge on the other surface is neutralized. I remove the foil and the charge flows back again. Hence the value of a conductive turntable mat ..... ❞ ¹
Wilson's paper offered an explanation for the mechanism of the effect in terms of Volta's Electrophorus.¹
❝The negative charge on the insulator attracts an equal positive charge on the conductor. Then the charges appear as shown.... The positive charge on the conductor and the negative charge on the insulator are close together and produce no net field on the outside of the insulator. ❞
The effect was confirmed in later quantitative experiments by Anderson of Shure Brothers Inc.4 Anderson pointed out that the effect could more easily be explained by recognising that, in bringing the conductor close to the charged surface (the record), the capacitance is increased greatly, 7 and, since the charge is constant, the voltage must decrease in accordance with the equation V = Q/C.
Anderson demonstrated that the external electric field on top face of the record may be reduced by 90% by placing it on a grounded turntable. Not enough to neutralise the problem completely (Anderson offered further solutions for this in the form of a carbon fibre brush which could bleed off the rest of the charge), but an improvement that it is foolish to relinquish.
Unfortunately, this renders cork unsuitable (and acrylic, wood and glass doubly so) although in almost every other way cork would seem to be a suitable material (see Appendix 2 and note. 12).
In fact, the insistence on soft, conductive materials has nearly left us with no finalists at all. Our remaining three materials: felt; leather; and rubber are all insulators too! However, it is possible to modify all of them to be conductive. Rubber has been modified in this way for many years for its use in car and aeroplane tyres. If the tyres were not conductive, dangerous static charges could build up which could cause an explosion during refuelling.
There has been work to make leather conductive for use as clothing, for example leather gloves which allow the wearer to interact with touchscreens. And there has been work to develop electrically conductive felt. However, conductive leather and felt are still relatively rare and it is not clear that all (or, indeed any!) of the commercial products available use electrically conductive materials.
Highly flexible at ambient temperatures and humidities, most types of leather exhibit viscoelastic behaviour which make it appear suitable both a record protector and as a vibration damper.
However, leather is susceptible to supporting fungal growth and this should sound a warning regarding the transfer of mycelial fragments to records. Being an organic material, leather may not always provide a flat, homogeneous surface which counts against it in this application. Leather will also crack and peel over time. Applying a suitable conditioner which is chemically compatible with record materials and cleanliness is not straightforward.
Leather played a significant role as an engineering material in the early industrial revolution where it was widely used for drive belts - a rôle not too dissimilar to the turntable mat. But it has almost everywhere been replaced by by rubber or synthetic polymer materials. Surely there is a lesson to be learnt from history here.
Felt plays an important rôle as a turntable mat for the DJ where it is called a slipmat.³ The techniques of the DJ (now part of the musical form dubbed turntablism), involve the turntable platter being left to rotate at a constant speed and the record manuipulated with the felt mat acting as a torque limiter which may be slipped by the braking force of the DJ's hands.
This is a legitimate use of the a turntable mat, of course, but torque-limiting isn't the function we are looking for in a record mat for straightforward listening or for needle-drops where even the hint of slippage is most unwelcome. We want our turntable mat to transfer the maximum power of the driven turntable to the record and, in this, we have an outstanding winner.
Rubber offers a very large surface area in contact with another object. Made of long carbon polymer chains with hydrogen attached along the length the chain, rubber offers high friction for two, complementary reasons. 1) it can flex enough to have more atoms available for interaction than almost any other material and 2) its constituent hydrogen atoms are “stickier” than the atoms present in most other materials.10
It is these "magic" properties of rubber which have kept it as the material for road tyres from runabouts to racing cars for over 100 years. The rubber must be rendered conductive to be suitable in this rôle, but that is a standard industrial process.
The only drawback with rubber is that it is probably the least attractive of the materials discussed.
All manufacturing standards from the heyday of microgroove records allow for records with different profiles. The first profile, the so called, flush design, is a simple, a pure disc of vinyl with a diameter of 301.6mm ±0.8mm and a thickness of 1.9mm ±0.3mm. (These are the RIAA numbers, but other standards were very similar.)
Alternative profiles (cross-sections) were specified and were known as raised-rim, raised-label (IEC standard), or contour-design (RIAA). The RIAA verion of the raised-rim, raised-label standard is illustrated above (and the Japanese version below).
The origin of the contour idea comes from the development of the 45 RPM 7" record by RCA. This format was conceived so that a stack of discs could sit on an autochanger deck. By means of a mechanical release in the central spindle, records were designed to fall down and play sequentially; each disc sitting on top of its predecessor.
In order that this stacking process didn't trash the recording-surface of the records by having them touch each other, the central, label area of the 45 RPM record is always moulded so that it is much thicker than the plastic annulus on which the grooves are moulded. The recording surfaces are thereby kept apart.
The contoured 12" record was the solution to enable LP records be stacked and automatically played in the same way as 45s. Because the playing surface was so much broader than with the 7" 45 RPM record, the extra rim was added to stop the playing side "drooping" when separated by the proud label section.
Not specified directly in any of the standards, the rim width dimension must be calculated. This is done in the graphic below. It indicates that the flat part of the contoured record only extends to a diameter of about 292mm (11½ inches).
Whether or not autochanger functionality was much used, we discovered in our own collections, a great many LPs which are moulded with the contour profile. Frankly, this was unexpected. The profile is quite subtle and, we had never noticed how many records were manufactured with a contour.
In fact, the standard IEC 68(1964) allowed for, a raised rim or a raised label area or both and we easily found examples of records with all four possible profiles.
Any record-mat with a claim to legitimacy (especially for a collector or archivist) must cater for all four possible record profiles which we annotate:
Designers of turntable mats appear divided between the need to offer a centre recess for records manufactured with the raised-rim, raised-label profile (see panel for examples of each). The simple, flat turntable mat is a throwback to the days of the 78 RPM record which were always manufactured as a plain (flush) disc.14
The limitation of the pure, flat disc mat is that, should the record have the contoured profile, the mat will only contact the record in the label area and around the raised, annular bead at the edge of the disc: the playing surface is essentially unsupported. This is illustrated below (this time using the drawing from the British Standard profile, to illustrate that it was more or less identical to the American and Japanese standards.)
Thinking in terms of the turntable mat as both a friction clutch and also as an acoustic damper, it's clear that we want, in both cases, to maximise the contact area of the mat and record. Indeed we might say this was the primary requirement. (It is this consideration which led us to the choice of rubber as the best material — because it maximised surface contact at a microscopic level.)
In terms of the mat design, the maximum contact surface is obtained when a flush-design (type.1) record sits on a mat which is a plain, flat disc. Providing the mat is made of a yielding, resilient material, the drive will be communicated over its entire π × (151mm)² = 0.072m² surface.
The contoured record, driven by the same flat mat, will only be driven at the hub, or the rim of the record, or both. At best, this reduces the contact area to little more than π × (51mm)² = 0.008m², or just 11% of the contact afforded the flush (type.1) disc.
Measurements and manufacturers' information reveal that many of these central chambers, when the designer has chosen to include them, are 0.5mm deep.
According to all the various manufacturing standards, the record hub stands 0.38mm proud of the playing surface in a contoured record. The intention of a well 0.5mm deep is presumably to clear the central boss. But, if this is the case, a slightly deeper chamber would be wise. (0.005" clearance is needlessly "tight".)9
If a recess has been provided in the design of the turntable mat, the flush record (type.1) will remain unsupported in the label area. But this is a reasonable sacrifice because the label area only represents, as we saw above, about 11% of the total area of the record. If the clearance is sufficient, the same is true for the type.2 record with a raised hub (but no raised rim).
But there's a major flaw in the central recess design when playing raised-rim (type. 3) and raised-rim, raised-label (type.4) records. In either case, the record will only be supported at its outer edge. In this situation, the centre chamber design scores substantially worse than the fully flat design when playing type.4 records.
The answer to this limitation is to sacrifice another small area of contact and reduce the diameter of the mat to about 290mm and let the proud annular edge drop below the level of the mat as illustrated below. The reduction in surface area with 10mm off the diameter is only about 8% compared to the flush record on a flat mat. This design secures the maximum contact area for all four types of record profile.
A table makes this easier to appreciate why the the 290mm diameter mat with a deep central chamber is the best design. It provides good and consistent drive and damping properties for all profiles of record.
Type of mat/type of record
Chamber & 290mm diameter
* Nominal figure, when only rim contacts with mat.
** Figure assumes the mat chamber never contacts the central hub of the record (raised or not).
The bark of the cork oak tree has a unique honeycomb structure composed of 30 to 40 million tiny cells every cubic centimetre - each filled entirely with air. In a low tech' way, cork is very high-tech'.11,12 Cork is a composite material and one of the very few considered here. Because of this, cork is light, elastic and resilient and has a high coëfficient of friction.
Cork is an excellent insulator of heat and sound. The latter is especially relevant because cork will damp any resonances in the metal platter. Cork is a low density material (200kg/m³). When dry, cork is an insulator of electricity. It doesn't rot or decay with time. And cork has good chemical stability and an excellent resistance to fungus growth.12
Felt is a non-woven fabric composed of interlocked fibres. Standard on the earliest gramophones (or disc phonographs), felt has a long history as the choice for a record mat. Felt may be manufactured from synthetic fibres like acrylic and polyester or from natural wool.
Felt holds its edges and will not unravel when cut to shape. It is available in a wide range of attractive colours. The structure of felt traps air which makes it light and an excellent insulator of both heat and sound. Felt is also a good insulator of electricity.
Both these materials are rigid and unyielding and are much harder than PVC. Brass, being an alloy of copper and zinc, is even harder than copper.
The density of both copper and brass is about 8500kg/m³ — a very high figure. Both are good conductors of heat and sound and thereby do nothing to damp the resonance in the machined metal turntable. They are both good conductors of electricity; especially copper.
The term acrylic turntable mat may apply (correctly) to the synthetic polymer of methyl methacrylate known by the trade names Plexiglas and Perspex. Sometimes, the term should really be acetyl since it refers to polyoxymethylene (POM) which is an engineering thermoplastic used in precision parts requiring high stiffness, low friction, and excellent dimensional stability.
Acrylic (Perspex) has a medium density of about 1200kg/m³ (acetyls are a bit higher). These polymer materials are easily machined, coloured and finished and make attractive record support mats.
From the leather-jacketed aviator to sports car interiors, to baseball gloves and high-fashion apparel, the association of leather with all things cool and luxurious is unsurpassed. There are moral and religious sensitivities which will may rule out leather as a suitable material for some people.
Glass is so familiar that it's easy to forget what a strange material it is. Glass and the glass transition remain unsolved mysteries of the solid-state. Commercial turntable mat products are made from crystal glass which means lead oxide is added to the melt to improve the look of the finished product. Crystal glass has been used for 300 years for decorative tableware.
Glass is a good insulator with a electrical resistivity close to that of a pure PVC copolymer record.
Glass is about half the density of copper, about 3000kg/m³. Necessarily massive, because glass is so brittle, most commercial products are very (6mm) thick and heavy (1kg). Interestingly, despite many options, glass is one of the very few ceramic materials considered for turntable mats.
Vulcanised rubbers are elastomers which means that are not perfectly elastic and lose energy during the compression (or tension) and subsequent recovery. Rubber thereby offers both flexibility and excellent damping properties. Hard rubber has a density of about 1200kg/m³.
Natural rubber does not conduct electricity but it may be processed to conduct electricity by distributing graphite or other conductive particles throughout the raw material prior to setting.
Wood surely needs no introduction as a material. But the woods of different trees and woody plants offer us a staggering range of composite materials. Densities range from that of balsa wood (110kg/m³) to ebony with a density similar to that of Perspex (1100kg/m³).
This range would seem to offer lots of possibilities but commercial examples of wooden turntable mats appear to be limited to a medium density wood like spruce (450kg/m³). Apparently this wood is chosen because it is the preferred material for musical instrument makers. The disc is sanded flat and given a lacquer (shellac) finish.
Wood is a natural insulator due to air pockets within its cellular structure,
The materials considered above possess a vast range of densities, from cork with a density of 200kg/m³ to copper with a density of 8500kg/m³. A turntable mat of identical physical design fabricated in copper will weigh 40 times more than an identical design made in cork.
If the turntable to which the mat will be fitted is a Villchur type with a suspended sub chassis², this wide range of possible weights forces consideration of the effect upon the alignment of the suspension.
A Villchur type turntable designed to operate with a thin, felt mat will be forced out of alignment when fitted with a glass mat weighing 1kg. At best, the turntable will need realignment: at worst, it may be impossible adequately to centre the suspension without fitting new springs. (The converse is true too, so that fitting a lighter mat will equally disturb the suspension alignment.)
Replacing a mat with one fabricated from a more dense material than was anticipated by the original designer may overload the centre thrust bearing. This may increase rumble and reduce the lifetime of the bearing.
One of the more intriguing ideas expressed on the subject of turntable mats is that acrylic better absorbs vibrational energy from the record because it offers a better ❝impedance match❞ with a vinyl record.
It is said that, when the material is very different (say felt, cork, rubber etc.), the vibration energy released during playback cannot easily transfer from the record surface to the mat, and therefore, it cannot diffuse and may end up being transduced by the cartridge, resulting in less clarity.
This idea interested us because we developed a way of measuring the internal vibrations in a record when we examined the effects of record weights and clamps and we thought it would be interesting to apply the same techniques to compare the differences between a rubber and acrylic turntable mats.
The experimental setup was as described in the page on record weights. (See note.5 of that page). Essentially, the technique involves fitting an extra tonearm on the record deck; complete with cartridge but with no amplification.
A test record is employed in which a track of high-level tone is adjacent to a silent track. The test involves recording the output of the main tonarm as it scans the silent track whilst the second tonearm scans the adjacent modulation track. The results for echo in four conditions: metal (record on turntable no mat); acrylic mat; cork mat; and rubber mat were as follows:
|Mat-material||Echo level Lateral
relative to excitation
|Echo level Vertical
relative to excitation
The acrylic mat scores worse than all the others - even worse than no mat at all! The level of lateral echo with the acrylic mat compared with the rubber mat is +8dB, two-and-a-half times worse. The matched impedance theory is not confirmed.
The results of these tests are discussed more fully in Appendix 2.
Much is made about the change to Vertical Tracking Angle due to turntable mats of different thicknesses. This is over-done. The range of thicknesses of turntable mats varies from about 2mm to 6mm, a range of 4mm. Simple trigonometry reveals that a 4mm height difference, using a 230mm (9") tonearm only influences the VTA by about 1°.
❝.... Lessons appear to have been lost rather than learned in the period since records were a mass entertainment medium...... finding the perfect mat is harder than you imagine.❞
Our recommendation, based on the evidence here, is for a conductive rubber mat with a diameter of 290mm and a central well 1mm deep. As covered elsewhere, we advise using a mat of this type without a stabiliser, weight or clamp.
It seems such pedestrian advice! We regret we couldn't have been more entertaining and been able to advocate African mpingo wood or Svalbard reindeer leather, as the ideal material for a turntable mat.
Yet, this unremarkable conclusion hides a remarkable truth. It is astonishingly difficult to fulfil!
Apart from a slew of turntable mats made of inappropriate materials, several promising products purchased for this study reveal that they are often dimensionally ill conceived, so that records of the various standard profiles will not be supported correctly. Centre wells are often insufficiently deep and diameters are too great.
One rubber mat we bought and which was described as anti-static13 turned out to be non-conductive, plain moulded rubber.
Lessons appear to have been lost rather than learned in the period since records were a mass entertainment medium. Rubber mats from the 1960s and 1970s were often graphite loaded (right). As explained above, dielectric materials - however attractive and "cool" - are not suitable in this application because they do not neutralise the charge on the upper surface of the record as it plays. Doing all we can to reduce this charge is fundamental to record care and cleaning.
Amazingly, given the vast aftermarket in turntable "tweaks" - turntable mats being first amongst them - finding the perfect mat, is harder than you imagine.
Happily, this isn't our last word on the matter. We have in Stereo Lab a software solution to complement the record mat.
The idea that playing a disc creates tiny vibrations in the vinyl, which, if left untreated, can return to the stylus and cause spurious output from the cartridge appears to be common currency amongst audiophiles and has been for forty years.6 Although we knew of no experimental evidence of the effect until we developed a way to measure the effect when investigating the effects of record weights and clamps.
Our experiments revealed that these stylus induced vibrations really do exist in the structure of the record: they may be transduced by the cartridge, and at a level which is substantially above the surface noise of the record. The effect is a legitimate cause for concern. (See Appendix 2.) We call it Disc Echo.
Happily, having taken considerable pains to isolate and discover Disc Echo we have the means, in digital signal processing, to eliminate it.
The unique Disc Echo Removal signal processing (only available in Stereo Lab) is engaged in the PHONO settings tab.
Don't confuse Disc Echo with pre-echo in which, as the groove is modulated, it displaces the land (the material between the turns of the groove), so that the imprint of the modulation is spread-out across the disc to adjacent spirals of the groove.
In the following audio example you can hear the energy generated by the drone stylus start as it is lowered onto the record. All is silence beforehand demonstrating that no pre-echo is present. The recorded audio has been bosted 30dB to make the DiscEcho easier to hear.
Go here for demonstrations of Disc Echo Removal.
There is one urban myth which ought to be laid to rest concerning the role of the turntable mat in the acoustic feedback path from the loudspeaker to the record surface and thus to the pickup. This information appears to have been first published in a rather unreliable article published in 1979.6 This date falls in the danger zone we have called the Time Warp and this article may account for why this information still circulates amongst audiophiles.
The phenomenon was studied by Moir and Stevens in 1979. Their (simplified) experimental setup was as illustrated. Essentially they used a loudspeaker fed from a sweep generator to excite a cartridge which was resting on a non-rotating record. The loudspeaker was arranged so that the sound pressure level at the turntable was 90dB above the reference level of 2 × 10-5 N/m². The recorded output was simply the induced signal in the cartridge. Typical levels were about 20dB below standard cartridge output level for a velocity of 5cm/s — easily enough to be relevant to reproduction. They say,
❝In recent months there have been many claims to the advantages in terms of sound quality of using various types of special record mat, so as a matter of interest we tested about six different types of record support pad or mat ..... These mats had many different rib patterns and included mats cut from pieces of soft foam and soft felt.❞
But they conclude,
❝the [measured] differences were only of the order of those obtained by repeating the test on any one type of mat. ...If the design, construction or material of a turntable mat does indeed produce significant differences in sound quality then it is unlikely to be due to their effect in reducing the amount of turntable vibration transmitted to the record surface.❞
The turntable mat tests involved fitting an extra tonearm on a standard direct-drive record deck; complete with cartridge but with no amplification. All this tonearm does is to track the record and provide the reaction of the stylus impedance. The original tonearm is used as the echo pickup.
A test record is required in which a track of high-level tone is adjacent to a silent track. The test involves recording the output of the main tonarm as it scans the silent track whist - at the same time - the second tonearm scans the adjacent modulation track. The tests were repeated four times with different mat materials as indicated in the results table.
Measurements were taken of the lateral (L + R)/2 signal level, and the vertical (L - R)/2 signal level. It was felt that the vertical and lateral signals (as opposed to left/right signal levels) give insight into whether the internal vibrations were longitudinal waves in which the particle motion in the medium is parallel to the direction of the wavefront: or shear waves in which the particle motion is perpendicular to wave direction.
Measurements were taken of the level of the the 300Hz remnant signal induced into the live pickup due to the 300Hz excitation of the stylus of the passive tonearm relative to the level when the active tonarm scanned the modulation track. 96kHz, 24-bit needle-drops were recorded and RIAA EQ'd and rumble-filtered in Stereo Lab. The results were analysed using the spectrum analyser in Adobe Audition.
In our experiments, the excitation was purely lateral (mono) and the waves thereby produced were, in all likelihood, originally longitudinal. However, when sound travels in a solid material, longitudinal waves can be transformed into shear waves (and vice versa) in a process called mode conversion which happens when a wave encounters an interface between materials of different acoustic impedances and the incident angle is not normal to the interface - a situation which is bound to happen in a disc of plastic. Results are given in the table in the side panel above.
The numerical results are fine as far as they go. But we found that we needed a way of visualising the longitudinal wave and shear wave echo energy so as to compare the results more meaningfully.
An interesting way to do this is to plot the the orthogonal echo results in polar form to create an echo ellipse, the area of the ellipse being a measure of overall Disc Echo energy (expressed here as a ratio w.r.t. the energy when the rubber mat was tested). This is done left. Note the axes here are linear: the abscissa is vertical modulation; the ordinate, lateral.
This done, we are able to appreciate cork's remarkable ability of damp shear waves — but its poor damping of longitudinal mode waves.
We can also see that, as discussed in the side panel, the acrylic mat scores worse than all the other materials. This was the principal point under investigation in these tests. The matched impedance theory is not confirmed.
In its splendid damping of longitudinal waves, rubber has no peer. No doubt this is due to the "grippy" surface of the rubber.10 On the other hand, the rubber turntable mat seems to have no effect on damping of shear waves in the plastic record. Due to their large Poisson's ratio11 (≈ 0.5), rubbers have a high compressional stiffness. It may be to overcome this that some rubber turntable mats (especially of classic design) included studs, dimples or grooves in the rubber.
1. Record Contamination: Causes and Cure. Wilson P., JAES April 1965. The mechanism of the electrophorus effect was explained by Wilson's son (the distinguished atomic physicist Richard Wilson at Harvard University) in an appendix to the paper.
2. A New Turntable-Arm Design. Villchur, E. Audio Sept & Oct 1962.
3. In fact the term slipmat seems in danger of becoming a synonymous term for turntable mat so that we have seen advertising copy which refers to a 1kg brass slipmat — a frightening thought!
4. Charges on the record — a study of static electricity on phonograph records. Anderson, C. R. from High Fidelity Phonograph Cartridge - Technical Seminar NYC 1978, available from Shure Brothers Inc.
5. Acoustic breakthrough in record players. Moir, J. and Stevens, W. R. Wireless World May 1979
6. Do turntable mats work? You bet! Stockton, R. Audio June 1979. This article quotes extensive references, but some are only obliquely relevant to the points made and it fails to quote the work apparently undertaken by Denon regarding the role of the turntable mat in acoustic feedback.
7. Knowing that the capacitance of a parallel plate capacitor is proportional to the area of the plates and inversely proportional to the distance between them informs us that the closer the record is to the conductive surface, the lower the external field produced on the playing surface.
8. Sharp eyed readers may have realised that the rubber mat "control" configuration has different values here than those recorded in the record weight tests: the measured vertical component is much lower in these more recent tests. We think that this is due to the different track configuration of the test record used in these later tests in which the sounding track used was inside the radius of the silent track (that's to say, nearer the record centre). Clearly, the configuration was identical during each batch of tests.
9. If the centre recess is carefully engineered to support the raised-label record, there is always the risk that a wrinkled label or a sticker could interfere and force the playing surface away from the mat. If that happens, the loss of contact could be considerable. A deeper centre well, and the sacrifice of a small contact area is the better solution.
10. Natural rubber is one of the simplest natural polymers. It consists of long chain-molecules which consist of repeating blocks of isoprene (illustrated right). There may be tens of thousands of such blocks in one molecule of natural rubber.
The molecular chains of rubber form secondary bonds (or Van der Waals bonds) with the record surface mediated by the many hydrogen atoms in the isoprene. Hydrogen's single electron is shared with the other atom to make covalent bonds and thus, the hydrogen end of the bond is essentially a positively charged bare proton unscreened by any electrons. This highly positively charged end of the molecule is capable of a strong attractive force. This accounts for rubber's famed "grippy" quality.
11. Poisson's ratio is a measure of the expansion or contraction of a material in directions perpendicular to the direction of loading. It is a common observation when a rubber band is stretched, it becomes noticeably thinner. The amount it thins in relation to the extension is the Poisson's ratio. A perfectly incompressible isotropic material deformed elastically would have a Poisson's ratio of exactly 0.5. Rubber has a Poisson's ratio of nearly 0.5. Cork's Poisson's ratio is close to 0, showing very little lateral expansion when compressed. That's why the cork makes an excellent stopper in a bottle; because it doesn't get longer as it is squeezed into the neck of the bottle.
12. Handbook of Composites from Renewable Materials, Design and Manufacturing. Thakur, V.K. et al. John Wiley & Sons. Hoboken N.J. 2017
Carbon fixing is part of a positive impact resulting from the exploitation of the cork oak. Cork oak forests are important with respect to retention of carbon dioxide. Hence, it contributes to the reduction of the greenhouse gas emissions. In Portugal, the cork oak forest is responsible for the retention of around 5 million tons of C02 per year.
The high gas content inside the small cells that constitute cork results in an effective sound barrier and its use in shoe soles and tool supports testify to its good damping properties. But it results in an effective dielectric material. So good that a mixture of cork with rubber is used in the electrical industry as a sealant insulating material for transformers. electrical switches, and lightning rods!
13. It seems almost every turntable mat is described as anti-static in their marketing materials: cork, felt, acrylic, glass are all apparently (and bafflingly) ❝anti-static❞. There is also a great deal of chat on-line about the effects of static electricity and its remedies. Beware of much of the information discussed in these forums. Many of the beliefs given by the various contributors, although no doubt genuinely held, are unhelpful and misleading. A few common misconceptions are:
14. From RIAA Bulletin E 3 October 16, 1963
|10" Records||12" Records|
|Diameter||9 7/8" + 1/32"||11 7/8" + 1/32"|
|Thickness - Measured at 4 points, from outer edge, 90 degrees apart.||0.080" + 0.010"||0.090" + 0.010"|
|Diameter of outermost groove of recording pitch.||9 1/2" + 0.02"||11 1/2" + 0.02"|
|Center Hole Diameter||0.286" + 0.001"||0.286" + 0.001"|
|Minimum Inside Diameter of Recording||3 3/4"||3 3/4"|
|Eccentric Stopping Groove|
|(a) Diameter||3 3/8"||3 3/8"|
|(b) Run-out relative Center Hole||0.250" + 0.015"||0.250" + 0.015"|
|(c) Groove Shape|
|(1) Minimum Depth||0.003"||0.003"|
|(2) Contour||approximately same as music grooves.|
|Lead-in spiral||At least one complete turn between outer edge of record and recording pitch.|
|(a)Nominal pitch||1/8" (min.)||1/8" (min.)|
|(b)Contour:||approximately same as music groove.|
|(c)Depth:||may vary to blend from music groove to eccentric stopping groove.|
|Shape of outer edge
(a) Semi-circular, or
For all support issues, go here.
For Pspatial Audio sales, email: firstname.lastname@example.org
Apple Certified Developer. Stereo Lab, Aria 51, Aria 20, Head Space, Groove Sleuth, iLOOP and FRANCINSTIEN T-Sym are trademarks of Pspatial Audio. FRANCINSTIEN and Bride of FRANCINSTIEN (BoF) are trademarks of Phaedrus Audio. Macintosh and the Mac logo are trademarks of Apple Computer, Inc.