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Some thoughts on dust covers

Over the course of time there have been many discussions concerning the subject of dust covers.  They tend to revolve around the central question:  Should the dust cover be down or up while playing records?  Some of these discussions have been nasty, consequently I have refrained from participation.  It is hoped that I can provide some common sense that was given to me by someone of unquestioned authority many years ago.  During college and after, from 1970 to ~1980 I worked in HiFi retail, selling high end lines of audio equipment.  One of these lines was Thorens.  Sometime around 1977 or 1978, if memory serves, Thorens introduced their new TD126, as a top of the line TT with their own arm and I sold the first one at our store to very good customer.  He came back very unhappy after the first night of frustration with it.  The problem was that with the dust cover closed some of his favorite records were hitting tangentally on the very back were the platter came closest to the dust cover when it was in the closed position.  I called the manufacturer's rep and he set up a three cornered phone call with himself, the Chief Engineer of Thorens at the time, and me.  I don't recall the man's name, but it doesn't matter, it is what he said that matters, then and now.  The Chief Engineer explained that the problem was caused because the hole in the offending records was slightly off center so there was an eccentricity as such a record rotates about the spindle.  The solution was simplicity itself, the dust cover should be removed always when playing records.  That the intent of the cover is to protect the turntable when not in use.  I pointed out that we lived in a semi-arrid environment (San Diego, CA) which is dusty to which he replied that if the environment was too dusty for records it should also be considered unhealthy for people to be breathing the air.  He recommended are filtration, not dust covers to address environmental concerns.  The rep asked about air bourne feedback from speakers and the Thorens guy laughed and said that if that was a problem in a given system, relying of the dust cover was a very flimsy and ineffective solution and that proper measures should be instituted to provide meaningful distance and isolation to ameliorate the problem.   So the often offered extremes:  a) Always play your records with the dust cover down, or b) put the dust cover away in it's box and never use it, should both be recognized for what they are are - not solutions at all.  First principles:  Identify the problem(s), seek solutions and alternatives, prioritize.

billstevenson
ltmandella's avatar
ltmandella
166 posts
 

Regarding ambient sound feedback:  I did an experiment one time in my listening room, with my RT-909 tape recorder and my Music Hall MMF-7 TT (project OEM tonearm).  The cartridge was a higher end GRADO.

I started the record playing, recording into the RT-909.  After the record play was about 1/2 way of the LP, I unplugged the TT BUT KEPT THE 909 TAPING.  So, the needle is sitting motionless in the groove of the motionless LP, with the RT-909 continuing to record the cartridge output.

They I walked around the room, clapping, shouting, humming, singing, and even stomping a couple times, all at various amplitudes.

You guessed it: when I played the tape from the "non playing" sections back, I heard many of the clappings, many of the shouting, some of the higher amplitude singing, and all of the stompings.

My deduction was that ambient sound feedback from the listening room and speakers is significant and audible...

lewm
13,150 posts
 

There is no correct answer. No corporation or engineer can give you the correct answer. Do what makes you feel good, but I’d advise against scolding others who do not see the issue in the same light as you (meaning any of us).

noromance's avatar
noromance
9,856 posts
 

I don’t use covers on my turntables. But I used to run a Linn LP12 decades ago. I did some experimenting with the lid up and the lid down. With a blindfold on and my partner gently raising and lowering the acrylic, I could hear the lid going up as a veil being lifted, literally freeing the music. Lid down, music became closed in. Same drill with covers on small signal tube amps. 

lewm
13,150 posts
 

.."My deduction was that ambient sound feedback from the listening room and speakers is significant and audible.."

But it's fair to say that you don't stomp around and shout out while actually listening to music. Nor do you use a buzz saw, etc. Chances are you are sitting quietly when listening to music, so your experiment only demonstrated what we already know, that a cartridge is a transducer and as such can act weakly as a microphone, converting ambient sound wave energy into an electrical signal just as it converts wiggles of the stylus into an electrical signal. Now consider the opposite case which very much does pertain to the actual use of a cartridge: Have you ever stood near your TT and heard low level music signal emanating direct from the headshell? Most of us have observed that phenomenon.  When you play an LP with the dust cover lowered, it is possible that the low level music signal emitted directly from the cartridge can bounce around the inside of the dust cover  and feed back on the desired work of the cartridge, causing distortion.  Also, ambient sound in the room, minimal though that may be, will cause the dust cover itself to vibrate, since its horizontal top surface is like a drum skin. That too can be picked up by the cartridge.  In any case, whether these issues play into it or not, I hear what Noromance hears, and I concluded long ago that I don't want the dust cover anywhere around the TT when I am listening. (Raising the cover on its hinges also has its issues, since then the cover presents as a sort of reflector.) But I still recommend that you decide for yourself.

dekay's avatar
dekay
5,620 posts
 

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DeKay

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