The Michael Trei (stereophile) "scratch test"

[Alexander Gödde]

In the current "Spin Doctor" column (aptly named, since it involves a lot of "spin" of facts) Michael Trei describes a "test" he has to show the importance of "audiophile" cables (https://www.stereophile.com/content...cables-and-collaro-triscription-record-weight):

"If you want a simple test that anyone can try to show that there's more to cable performance than simple loop resistance, try my scratch test. Just turn up the volume of your phono input with no record playing, then tap the tonearm cable with a pen, or scratch it with your fingernail. In most setups, you will clearly hear the noise through your speakers or headphones. That experiment shows the importance of designing (and using) a cable that minimizes microphonics."

While I don't doubt that this will, in most setups, produce audible noise, I wonder about the actual mechanism.

AFAIK microphonics on cables, which is an issue with headphones, is just mechanical conduction of vibrations and does not have anything to do with changing the electrical conduction.

So my assumption is that the noise heard when tapping the cable is just vibrations carried to the cartridge, causing this to create some voltage/current.

Any other explanations?

 

[Multicore]

Some cables are microphonic in that in the right kind of circuit a vibration can induce a tiny electrical signal. In hifi systems this is seldom significant since only the phono input will have enough gain for the extraneous noise to be a problem. And only in phono systems with a lot of vibration in the cable. If your system is vibrating that much then you have problems to solve that a high-end cables can't help you with.

It seems to me perhaps Michael Trei is looking for excuses to buy expensive cables.

Btw, the microphonic effect of headphone and IEM cables is not electrical. It is instead the vibration of the cable transmitted to the ear mechanically.

 

[NTK]

Any other explanations?

Triboelectric effect - Wikipedia

en.wikipedia.org

 

[Multicore]

Triboelectric effect - Wikipedia

en.wikipedia.org

Yes, exactly.

And for those too lazy to visit that Wikipedia page:

 

[Speedskater]

Phono cartridge to pre-amp cables, some microphone cables and some musical instrument cables are a very different bread of animal than modern line level interconnect cables. So yes they are sometimes sensitive to vibration.
While line level interconnects are much, much less sensitive and you is moving or touching their interconnect cables while listening to music?

 

[MaxwellsEq]

"If you want a simple test that anyone can try to show that there's more to cable performance than simple loop resistance, try my scratch test. Just turn up the volume of your phono input with no record playing, then tap the tonearm cable with a pen, or scratch it with your fingernail. In most setups, you will clearly hear the noise through your speakers or headphones. That experiment shows the importance of designing (and using) a cable that minimizes microphonics

So what?

There's almost no difference between the mechanical to electrical generator in a microphone and the mechanical to electrical generator in a cartridge. He has demonstrated that a cartridge is designed to collect mechanical vibrations convert them to electricity and feed them into a high impedance, high gain circuit.

Loudspeaker impedances are very low. Amplifier output impedances are almost zero. The speakers are potentially mechanical to electrical generators, but when listened to they are electrical to mechanical motors. You would need a jackhammer hitting the loudspeaker cable to even slightly perturb a real world setup.

 

[Gregm]

The example put forth by M Trei ("If you want a simple test that anyone can try to show that there's more to cable performance than simple loop resistance, try my scratch test...") simply points to the possibility of a low-level signal being picked and /or created by an extraneous stimulus.

Likewise, if you kick a record player, the stylus is likely to jump.

I am not out to discredit said Mr Trei, just to note that such effects were never under question AFAIK. However, he has not substantiated the causality link between scratching effect and a cable's own sonic effect upon the signal being transferred...
I mean if you remover the extraneous sitmulus (i.e. stop scatching and kicking), everything is fine, right?

 

[sergeauckland]

The example put forth by M Trei ("If you want a simple test that anyone can try to show that there's more to cable performance than simple loop resistance, try my scratch test...") simply points to the possibility of a low-level signal being picked and /or created by an extraneous stimulus.

Likewise, if you kick a record player, the stylus is likely to jump.

I am not out to discredit said Mr Trei, just to note that such effects were never under question AFAIK. However, he has not substantiated the causality link between scratching effect and a cable's own sonic effect upon the signal being transferred...
I mean if you remover the extraneous sitmulus (i.e. stop scatching and kicking), everything is fine, right?

Indeed. The triboelectric effect in cables has been known about for a very long time. It is of concern with long cables that get moved a lot, for example on-stage microphone cables, and cables with materials and construction designed to minimise the effect are usually specified for stage use.

However, at home, cables are static, and even the idea that the sound field in the room will move the cables enough to generate interference is fanciful. There's a big difference between Roger Daltrey swinging a 30m mic cable around and what's behind one's rack at home!

Yet another example of a real effect (like skin effect or cable impedance) being totally misapplied to a different situation.

S.

 

[Mart68]

Just cover your speakers with blankets. In most setups, you will clearly hear the sound becomes very muffled. That experiment shows the importance of not covering your speakers with blankets.

 

[Redacted]

I tend to play drums using only a section of cable, as you do.

I have had the odd bargain-basement guitar lead that was slightly microphonic when kicked, but you'd not notice if playing.

As said, with line-level cables, no big issue - I've had many dozens and none were a problem. Its all about the high input sensitivity needed for cartridges, especially some MC types. Maybe there is a argument to have balanced outpost cartridges, and leads? But then if you really want such poor, ancient tech, you have to live with it.