Does slipmat thickness matter?
The mat sets the height of the record, which makes thickness a geometry decision.
Yes, but less than density does. Thickness matters because the mat sets the height of the record, and record height sets the angle at which the stylus sits in the groove. Swapping between mats within about a millimetre of each other changes that angle by a fraction of a degree and needs no adjustment. A jump of several millimetres is worth a tonearm height check. Around 3 mm is the working figure: enough to damp, little enough to leave your geometry where you set it.
Thickness is the figure most often quoted about a mat and the least often explained. It matters, but not for the reason people usually give, and the size of the effect is calculable rather than mysterious.
Does slipmat thickness matter?
Yes, for one reason above all others: the mat decides how high the record sits.
Everything else about a mat happens at the surface. Thickness is the only property that moves the record itself, and moving the record moves it relative to the tonearm that was set up to read it. That is the whole of the argument.
What does a thicker mat change?
It lifts the record, which tilts the arm nose-up. That changes two things at once.
The first is the angle at which the stylus meets the groove wall. A cutting lathe cut that groove with the cutter at a particular angle, and a playback stylus reproduces it most accurately when it sits at a matching one. Tilt the arm and the contact geometry shifts.
The second is more mass further from the platter surface, which is a very small change to how the record and mat behave together as a system. In practice the first effect is the one anyone notices.
What does a thinner mat change?
The opposite tilt, and less material between the platter and the record.
A very thin mat does almost nothing about platter resonance, because there is not enough of it to absorb anything. It also binds rather than slips: there is no depth of fibre for the record to sit on, so the record is effectively resting on the platter through a film. Thin mats are the ones that fail at the job the word slipmat describes.
How much does thickness actually change your tracking?
Here is the arithmetic, which is more reassuring than the forums suggest.
A typical tonearm has an effective length around 230 mm. Raise the record by 1.5 mm at the stylus and the arm tilts by the angle whose tangent is 1.5 divided by 230. That is 0.37°.
For context, vertical tracking angle is usually discussed in whole degrees, and the adjustment range on an arm that offers one is a few degrees. So a mat swap of a millimetre and a half, which is a large difference between felt mats, moves you about a third of a degree. Detectable on a revealing system, inaudible on most, and not a reason to avoid changing mats.
Change by five millimetres, which is the kind of jump you get going from thin felt to a thick rubber mat, and you are at 1.2°. That is worth attending to.
Do you need to reset the tonearm?
Only if the change is large, and only if your arm lets you.
Many arms have no height adjustment at all, in which case the answer is academic and the mat is part of the setup you have. Where an arm does adjust, the rule of thumb is simple: if the new mat is within a millimetre of the old one, leave it. If it is several millimetres different, set the arm so it is parallel to the record with the stylus down, then listen.
Tracking force is a separate setting and does not change with mat thickness. If you are chasing a skip rather than a tone, that lives in why records skip.
Why 3.18 mm?
Because it is the thickness at which 21oz felt behaves like felt.
Felt is sold by areal density: weight per unit area, which for ours is 21 ounces per square yard, or 712 g/m² in grammage. Spread 712 g/m² over 3.18 mm and the result is about 0.22 g/cm³, which is an ordinary needled-felt density: semi-rigid, lying flat, enough depth of fibre to slip properly.
Press the same weight of felt into 1.6 mm and you get 0.45 g/cm³, which is hard industrial felt. It is thinner, it damps less, and it slips differently, because the fibres have nowhere to move. The thickness is not a style choice; it follows from the weight.
Does thickness or density matter more?
Density, and it is not close.
Two mats of identical thickness can behave entirely differently depending on how hard the felt was compressed. A low-density 3 mm mat pills, sheds onto your records, holds static and binds under the hand. A high-compression 3 mm mat does none of those things. Thickness tells you about your tonearm; density tells you whether the mat is any good.
Which is why the figure to ask about first is ounces per square yard. Most turntables ship with 16oz. Ours is 21oz, and the difference is obvious before you put it on the platter.
How do you measure yours?
A pair of calipers on a flat mat, away from any printed area, taken at three points and averaged. Felt compresses, so take the reading with the jaws just closed rather than tightened.
If you have no calipers, stack ten records on a table, measure the stack, divide by ten, and you have a working sense of what a millimetre and a half looks like at this scale. It is less than the thickness of one LP.
Every figure for ours is published on the spec page: 298.5 mm across, 3.18 mm thick, 21oz felt. If the diameter is what you are checking, that is what size slipmat do you need.
Questions
- Does slipmat thickness matter?
- Yes, because the mat sets the height of the record and record height sets the angle the stylus meets the groove at. Swapping between mats within about a millimetre needs no adjustment; a jump of several millimetres is worth a tonearm height check.
- How thick should a slipmat be?
- Around 3 mm. Ours is 3.18 mm. That is enough depth of fibre to damp and to slip, and little enough to leave your tonearm geometry roughly where you set it.
- How much does a 1.5 mm mat change tilt the tonearm?
- About 0.37 degrees on a typical 230 mm effective length arm. Detectable on a revealing system, inaudible on most.
- Do I need to adjust VTA when I change slipmat?
- Only for a large change, and only if your arm has height adjustment. Within a millimetre, leave it. Several millimetres, set the arm parallel to the record with the stylus down and listen.
- Does mat thickness change tracking force?
- No. Tracking force is set at the counterweight and does not move when the mat does.
- Is a thinner slipmat better?
- No. A very thin mat has too little fibre to damp anything and binds rather than slips, which defeats the point. Thin mats are the ones that fail at being slipmats.
- Is a thicker mat better for sound?
- More material damps more, but it also raises the record further and adds mass to the platter. Past about 3 mm you are trading geometry for damping.
- What matters more, thickness or density?
- Density, clearly. Two mats of the same thickness behave completely differently depending on how hard the felt was compressed. Density decides pilling, static and slip; thickness only decides geometry.
- What density is 21oz felt?
- 21 ounces per square yard is 712 g/m². Over 3.18 mm that works out at roughly 0.22 g/cm³, an ordinary needled-felt density.
- Why not make a thinner 21oz mat?
- Pressing the same weight into 1.6 mm gives 0.45 g/cm³, which is hard industrial felt. It damps less and slips differently because the fibres have nowhere to move.
- How do I measure my mat?
- Calipers at three points away from any print, jaws just closed rather than tightened, then average. Felt compresses, so a tight reading reads thin.
- What thickness do most turntables ship with?
- Thin 16oz felt, usually under 2 mm. It is the component most often replaced first.