Some thoughts on dust covers

As a record rotates, the air closest to the surface gets accelerated towards the periphery, drawing a steady stream of air down around the spindle. So reduction of air-born dust suggests closing the dust cover during play.

A dust cover also acts a bit like closing a window, and it will attenuate external airborne vibrations from reaching the cartridge.  My Garrard 301 table is in the same room as my speakers, which are either dipole Quad electrostatics or KEF Reference 1 with rear ports.  The dustcover is an acrylic affair made by SME and is voluminous with plenty of space.  I am very surprised that the sonic effect of closing my dustcover seems to be subtle to non-existent, at least to my ears.

Obviously, there is acoustic output from the needle / cantilever which is partly airborne and partly transmitted through the vinyl record, I am using a 5-mm Achromat to absorb record reflections and transmission to the platter, which leaves those airborne sounds we can just hear if we are close enough. They will reflect internally from a lowered dustcover but I would have thought the sound level would be far less than the speakers generate with the lid open!

So I put the lid down unless i forget!

@lewm 

Household-wide, I normally subscribe to the equilibrium theory of dust - eventually enough leaves to balance the amount arriving!  But if you do use a dust cover while playing, the air volume inside the cover is pretty much a closed system so once the dust settles, no more arrives.  Most seems to end up on my stylus which I can now see with my new Zeiss loupe.

@noromance

I am not surprised you can hear a sheet of paper inserted under a record. A lot of sound energy is generated by the stylus and some of this energy hits the bottom of the record.  If the record is well-coupled to the platter, the energy will pass into the platter and be dissipated.  With paper, it is more likely to bounce back and affect the stylus.

At least, that's the theory behind the Achromat which is basically a vinyl mat infused with tiny air bubbles to absorb vibration.  Vinyl couples well with vinyl!

I am surprised at the lack of acoustic feedback I am encountering. But whether you consider a dustcover to be a massive undamped structure or not, it provides more attenuation than thin air!  It cannot create more sound energy than hits it, and some is absorbed and some reflected.

Of course, if the record surface and the cartridge body are both displaced equally by impinging vibrations, there is no relative movement to contribute to the signal output by the cartridge.

It is pretty obvious most turntable manufacturers would rather not have to deal with dustcovers!

Thought I'd try to measure the attenuation from my cover, so I dug out my Denon Audio Technical CD and played some test tracks.  At the same time, I ran a Sound Meter application on my Android phone and put the phone on my platter mat near the pickup.  I could watch the phone while raising and lowering the dustcover.

On 1000-Hz test tones, the attenuation was about -13-dB with the cover down, while it was only about -3-dB down on white noise   On pink noise there was barely any difference!

I must point out that my plinth and table lean towards the massive side.  The more the mass, the less the amplitude generated by a specific acoustic energy level.  I find it interesting that Pro-ject don't want airborne vibrations to enter their plinth from a dustcover, but are presumably happy for them to enter the platter directly.

Acoustic feedback might make for nicer sounds, and could even explain why so many like records.  But it does not make for accurate playback if that is your thing.

@lewm

I thought you made your position clear in your first post, no need to say any more!

You are right - electrostatic forces are orders of magnitude more powerful than gravity. Another way to create static charges is to rub vinyl with a diamond stylus. Those charges immediately attract dust. Interestingly about 30% of dust extracted from records is diamond!

In my opinion the OP raised a good question - should the dustcover be raised or not when playing a record. Clearly this presupposes there is a dustcover and that it is hinged. If your turntable does not have a dustcover, or the dustcover must be removed when playing, this topic is not going to change anything for you.

I read up about the Wilson Benesh GMT One System turntable, which weighs almost half a ton and uses lots of materials science, university types and research grant money to minimise unwanted resonances. This behemoth does not have a cover, although it costs house-money! Obviouly they don’t worry about airborne feedback, or dust!

For the record (sic) my dust cover is hinged to an outer plinth which only connects to an inner plinth via the sandstone blocks they stand on. Otherwise there is an air gap, a bit like a double-glazed window.

@lewn

Thanks for that Shure thing! I guess it is in a chapter from 1978 in high-fidelity-phonograph-cartridge-technical-seminar-faq.pdf entitled CHARGES ON THE RECORD--A STUDY OF STATIC ELECTRTCITY ON PHONOGRAPH RECORDS.

The only mention of stylus rubbing causing electrostatic charges seems to be "Incidentally, measurements with these instruments will also show that electrification from the direct friction between the diamond and vinyl is, oddly enough, negligible’.

The author created static charges initially by rubbing the record surface with cat fur (labelled CAR FUR in the table!) resulting in 30,000 Volts when the record was lifted from the table. Considering he switched cat fur for a more repeatable 10,000 volt probe, I am not surprised the stylus is regarded as a negligible (but not zero) contributor!

The seminar reinforced that the most effective way to temporarily remove static is to use a carbon-fibre brush. One was attached to the V15 Type IV cartridge but this approach seems to have gone the way of the dodo.

Saved me spending on a Zerostat!

Another surprise for me was learning just how much static electrical forces can change the tracking force!

All good stuff ...

@lewm 

It seems the 30,000 Volts recorded by Shure corresponds to the breakdown voltage of air in a Californian winter - with a very low relative humidity of 10%.

Shure's measured voltage dropped dramatically when the record was placed on the grounded platter (much of the field migrated to the platter side) and returned as soon as the record was lifted.

Prima facie it seems that when you played your record, it doubled the charge so I am keeping an open mind on whether the rubbing stylus can create charges. Charges attract dust like crazy, and dust down to smoke-size particles and even down to a few microns may be significant.

If I remember, I now run my carbon-fibre brush both before and after playing to try to remove fresh dust before the records goes back into its anti-static sleeve.  I am still waiting for an ultrasonic cleaner to arrive from China!

In modern physics theory, electromagnetic and gravitational forces have hugely different magnitudes.  About 1,000,000,000,000,000,000,000,000,000,000,000,000 times different!  Which explains how plastic combs can pick up paper on a dry day, and charged records can significantly affect stylus tracking forces.

That Shure seminar was not too keen on Zerostat-like devices: "Another form of active ionizer is in the form of a pistol-shaped, device, which produces positive ions when the trigger is pulled, and negative ions when the trigger is released. This device is effective for large charges, but it is hard to avoid leaving residual charges on the record since there is no way of detecting the zero charge condition" which accords with your measurement.

@lewm

"Dover [actually richardbrand] is correct that Shure do not describe the experiment that led to their saying static charge due to the stylus is negligible. My own frustration with that lack of detail is what led me to buy a static charge meter and do the experiment myself. The meter also shows me the zerostat works."

So you did not really trust the Shure ’white paper’ you quoted to support your erroneous assertion! That’s quite an admission from somebody who claims to want the information on this site to be as accurate as possible. According to your posts, you had a residual voltage of 100-Volts after Zerostat and 200-Volts after playing, but you have not stated what meter you used or its repeatability.

This is what the Shure seminar actually published on methods to reduce static. My highlighting and [comment]

There are four systems available:

1. Sparking

2. Ionization

a. Active - ac powered, hand powered, radioactive

b. Passive

c. Contact

3. Conduction

Sparking is an automatic mechanism which, as we have seen, limits the free air voltage to about 30,000V and the threshold voltage of a pickup to 4,200V. However, the residual voltage is still high enough to cause all the observed problems and the effect is only included in the list for the sake of completeness.

Ionization, or the production of charge-carrying atomic particles, is a particularly effective way of neutralizing charges. A system similar to the arrangement used to charge records is commercially available for destaticizing photographic film. This system uses an array of multiple points covering both sides of the record simultaneously. Its operation floods the record with positive and negative ions alternately and "washes out” any initial charge on the record. This system is the most effective of any available, but it is expensive and the high voltage construction and safety requirements make it difficult for the home constructor to duplicate.

Another form of active ionizer is in the form of a pistol-shaped, device, which produces positive ions when the trigger is pulled, and negative ions when the trigger is released. This device is effective for large charges, but it is hard to avoid leaving residual charges on the record since there is no way of detecting the zero charge condition.

The third form of active destaticizer uses radioactivity to produce positive ions. This type of device is limited by safety restrictions to a rather low level of ionization and, hence, will deal with mild charges but requires a long time to affect strong charges.

The passive types of destaticizer have used bundles of wire and tinsel, passing over the surface of the record. These devices promote ionization because of the voltage gradient which a charge induces in the vicinity of a point. This arrangement is self regulating, since the ionization is proportional to the charge which produces it. However, in its usual form, the effectiveness is limited by the sharpness of the points available.

This limitation can be greatly diminished by using carbon or graphite fibers which have a diameter of .3 mil, and which must have an effective radius at the cut-off end much smaller than that. A destaticizer using these fibers will be considerably effective even if the fibers do not touch the surface. The difference between a contact mode and an ionization mode is hard to distinguish, but we regard actual contact as the distinction. Since charges have no nobility [I think the author meant mobility], it is necessary to touch each and every point on the surface to discharge it. Here again, the carbon or graphite filament is superior to other types. A wipe with a grounded carbon filament brush can reduce the charge on a record to negligible proportions

@lewm 

"Prima facie it seems that when you played your record, it doubled the charge" First, 0.1kV to 0.2kV is a range where the meter is not very accurate and readings are not very repeatable ..., such a low amount of static charge is inconsequential even if real. ... Do you have a background in this field, or are you a physicist or other scientist?"

I must confess that I was educated in physics at Cambridge and I have tried to keep up since!  Physicists now explain almost every known property of the universe in terms of four fundamental forces which act on the very smallest particles, including the electron. Protons and neutrons comprise three smaller quarks!  These are the objects for the comparison of the four forces.

Gravity and electromagnetism both operate over long distances up to infinity and follow the inverse square law.  The word electromagnetism is used because a moving charge creates a magnetic field. The other two forces only operate over tiny distances about the size of an atomic nucleus.

In everyday life, we experience gravity as a dominant force, but that is because every atom in the earth tugs at us. These same atoms have no net electrical charge, so the way-stronger electromagnetic force balances out as equal attraction and repulsion. But rub a few electrons on to an insulating surface and they will lift paper and cartridges against all the gravity of the earth.  They will also attract and hold dust.  This is the principle used in electrostatic air filters, which my electrostatic speakers would try to emulate except for the built-in dust covers (back on topic?).

"I posted to correct RichardBrand’s statement that the stylus rubbing on vinyl causes static charge".

You did not do a very convincing job because your own measurements indicated the opposite.  The "white paper" you mentioned inferred the contribution was negligible (not zero!) compared to 30,000-Volts produced using cat fur!  Mind you, that seminar was spruiking the benefits of the static-reducing in-built brush Shure introduced with the type IV cartridge.  I contend that any static will encourage dust collection and that is bad for record playback.

I am not silly enough to think your measurements were accurate, since you only stated results and not the procedure used to get them.  Hence I wrote prima facie or on the face of it!

The most reliable way of reducing static is to immerse your record in a conductive medium, like water, but then you have to dry it without re-introducing static.

More contentiously, I believe the best way to reduce the dust load on your records is to use a hinged dustcover, but only if you have one.  Operationally it is not too hard - bit like lifting the lid on a toilet.  Unlike a hinged dustcover, leave the lid up when in use ...

@dover 

Thanks - I have asked Wilson Benesch for a copy of the 'white paper' mentioned in TAS's review, but it is not finished yet!

This is what Google’s generative AI says in response to "can record stylus cause static"!

Yes, a record stylus can cause static:

• Friction: The friction between the stylus and the vinyl record creates static electricity.
• Dust attraction: The static attracts dust, which can cause crackling sounds.
• Record damage: The static can turn your record into a dust magnet, which can damage the record grooves.

To reduce static, you can try these steps:

• Clean your records: Use a record brush to clean your records before and after playing.
• Clean your stylus: Use a stylus brush to clean debris from the stylus.
• Use anti-static products: Use anti-static inner record sleeves, an anti-static carbon brush, or a fluid-based anti-static record cleaning solution.
• Use an anti-static gun: A Zerostat anti-static gun can remove the static charge from the surface of the vinyl.
• Use an anti-static slip-mat: An anti-static slip-mat is less likely to create a build-up of static.
• Play with the dust cover down: Keep the dust cover down on the turntable to protect your records from dust.

I agree with all of this, except that getting a final zero-charge out of a Zerostat is hard - as pointed out by Shure. Also no great surprise that Shure, as the then dominant maker of stylii, did not highlight that they cause static.

@lewm 

"Second, like I said, it is much more likely that my touching the LP had more to do with the difference, if it was even real"

The human body is normally a great drain for static. Rubbing paper against a record creates static, handling it is more likely to drain some away especially if you only touch the edges and the label.  My TAS-recommended AudioQuest carbon fibre brush explicitly relies on the user to drain the static to earth, via a metal handle that contacts the fibres.

The human body is also a great source of dust, shedding its outer skin roughly every three weeks.

Maybe your electrostatic loudspeakers are acting as electrostatic dust filters for your basement?

@billstevenson 

Since when are we taking anything Google's generative AI has to offer as an authority?  Frankly lewm's reference to the published work of Shure years ago is an established, credible resource and those who disparage it must be doing so only because they have not taken the time to read it. ...  After we get done talking dust covers to death, if anybody is left standing let's talk about the good old Dust Bug!  :-)

I did take the trouble to find and read thoroughly the Shure seminar articles.  Have you read them?  There is absolutely nothing about styli causing static except that throwaway line that it is negligible.  No experiment, no discussion, no measurement, nothing.

Generative AI uses large language models to make inferences.  Most likely Google's includes everything you have written on the web, and weighs it against what everybody else has written.  I find it both credible and fascinating.

My dust bug has gone missing, but the base is still stuck to my Garrard 301. I recall it quite audibly played what was coming up on the record, but have no idea why they fell out of favour.

@dover

Can’t trust reviews or media - the GMT has a very nice integrated hinged dust cover. Ideal for those who can’t afford hepafiltration systems for their home/living room.

Have a look close to the end of this Wilson Benesch YouTube video on the GMT One System. The founder says they did design a dust cover, but when they added the transformer box above the tonearm pivot point, it no longer fitted! For what it is worth

Most Technology and R&D Ever in a Turntable? Wilson Benesch Riveting Presentation - YouTube

@lewm 

The ES force is determined by Coulomb’s law, which like Newton’s equation for the gravitational force is an inverse square law. Both forces are inversely related to the square of the distance between the two objects under consideration . The difference is that the ES force is directly proportional to the product of the two charge quantities, where gravity is directly proportional to the product of the two masses. So I couldn’t make sense of that flat statement.

And you claim to be a scientist!  Physics has moved on a bit since Newton and Coulomb as it tries to produce a unified model of all the known forces and their interaction with all the known particles.

If you turn 'proportional' into an equation with a constant, the constant for the electromagnetic force is about 10**36 times bigger than the constant for gravity.  Thats why a very few stray electrons (not ions) easily overpower the gravity of the earth, and why they attract charged bits of dust floating in the air.

Why don't you believe that a natural insulator like diamond rubbing on vinyl creates charges in the same way that paper and cat fur can?  Especially when your own measurements quoted here support that!

Hate to let facts get in the way of a good stouch, but if I may refer back to the excellent 192-page paper Precision Aqueous Cleaning of Vinyl Records PACVR-3rd-Edition, it references the ARSC Guide to Audio Preservation, 2015, which was commissioned by the Library of Congress. I quote:

Record dust/dirt when examined under a microscope consists of grease, stylus particles, abrasive material, and solids which resemble wool fibres covered with a soft waxy substance. An analysis of the “dust” removed from a number of stylus tips, which had been used on dirty records, showed that it consisted of approximately: 12% jagged silica particles, 35% diamond dust, 40% miscellaneous particles, including soot, grit and particles worn from the record groove itself. The remaining 13% consisted of fibers and lint