Dustcover Blues

@vinylzone , This is the very first time I have seen a dust cover contibute to feedback. What it does demonstrate is that a tonearm can pass on airbourne vibration that is outside of it's resonance point. It can not be the record vibrating because it is vacuum clamped. Under most conditions the dustcover attenuates sound getting to the tonearm by as much as 15 dB at some frequencies. This can be demonstrated by putting a measurement microphone under the dustcover. This weekend while I am farting around I will do this and take screen shots of the curves generated inside and outside the dust cover which I will put up on my system page. I will use a short sine wave sweep from 10 Hz to 20 kHz. My arguement is dustcovers can improve the performance of your turntable and help to keep your records clean also diminishing stylus wear. Dustcovers are hearing protection for your cartridge. Mark Dohmann related to me in an email that he is working on a dust cover for his Helix turntables to be used during play. 

When I press down on the dustcover the feedback does stop probably because I am closing the gap at the bottom not because I am damping the dustcover. Closing the gap with felt strips is a more elegant way of solving the problem. 

If the table is subject to vibrations, dust covers could easily exacerbate the problem. Best to avoid vibrations reaching the table always but if not possible and dustcover exacerbates things just take it off when playing. Dust cover vibration is not an issue for me these days personally. My table is rock solid. 💪

@mapman , What are you using? Even if a table is "rock solid" attaching a dustcover directly to the part of the turntable that holds the platter and tonearm would be more prone to causing trouble. Historically, the tunetables that came with dust covers were suspended such as the Thorens TD 125, The Linn LP 12 and the Sota Sapphire. They were isolated from their dust covers. I favor this type of construction. It is not as flashy as some designs but isolating the platter and tonearm from the rest of the environment has significant functional and sonic advantages. Mass loaded turntables can work very well if located on a very sturdy rack on a concrete floor. I do know of people putting turntables like the Kuzma Stabi XL DC on MinusK platforms. 

@mijostyn Linn Axis table with Denon Dl103r cart on low profile solid cherry table at foundation level, concrete foundation with thin dense carpet and pad. See my system photo.

@tvad , Yes, you are quite correct. The very best tables came with dust covers and for a time even the less expensive tables came with them. Then manufacturers learned from Transcriptors (I think) that if you made your turntables cool looking enough you could sell a lot of them even if they are lousy tables. I should know as I fell for that. Soon they became so odd shaped there was no way you could attach a dust cover. But, visual stimuli dramatically improves the hearing of a large population of people. This whole mess ends at the Techdas Zero, without a question the coolest looking turntable on the planet and technically it is very impressive. Personally, I would rather spend that money rescuing geto kids from a toxic environent and getting them someplace where kids can have fun being kids like a summer camp.