Dustcover Blues

There's one way to use a dustcover when playing that will actually work in terms of both dust and vibration control.

Raul, I think you are right. The material a dust cover is made of is important. It can't be flimsey but it can't weight too much either or hinges won't be able to hold it open. The Sota cover is much heavier than it use to be. It is made of butte joined 1/8" Laxan with all the edges chamfered. It is acutally quite a nice cover. There is a lot more going on here besides the cover. Read on!

 @lewm , Your speakers should be able to go down a few Hz lower than mine because they are 4" wider. You do not listen to the music I do. As I remember you are into old jazz and singers? If you want to know how your system would handle what I listen too sometimes get a copy of Soundgarden's Badmotorfinger and play the 1st cut at 100 dB peaks, 95 dB is probaly enough. Measure it with a meter. I do not think you will like what you hear. You'll be OK at 85 dB. That kind of bass is going to distort the heck out of everything. The voice will actually modulate with the bass. Like you I have had one ESL after another since 1978. I set up one pair of Beverages in a big system in Miami. ESLs will make bass but they will not like doing it. You listen to relatively polite music. Going down to 40 Hz is probably enough but even in jazz the bass drum can go down lower. Even on very old recordings from the early 60s the bass drums can go quite low. With modern recording, drum and synthesizers there is a lot of information below 40 Hz.

I use 4 12" subwoofers each one with an X-max of over 2 cm. They are in a linear array so acoustically they function as one driver with useful output down to 10 Hz. Each driver gets 2000 watts. I cross over to them at 100 Hz and use an 8th orde slope or 48 dB/oct.  Look at those frequency response curves I put up on my system page. That is the frequency response of my system and room at the left lateral side wall with the microphone sitting on the plater. The response at the listening position is much flatter with the bass up 5 dB at 20 Hz and the treble down 3 dB at 20 kHz. The bass and treble curves are intensional. I programmed the system to do that because I like it that way. At the wall it is very bass heavy which certainly does not help but I am now stuck with that position so, I have to work with it.

Now for the juicey part. I put felt strips under the dust cover to seal it when closed and..... the feedback got worse. I hate when that happens:-(   But, lift the cover and it goes right away. I do not know what made me do it but I put two fingers under the turntable where you can feel the underside of the subchassis and it was boucing at 24 Hz! Lift the dust cover and it stops. Put it down and the subchassis starts bouncing at 24 Hz. This is way above the chassis's resonance frequency. Somehow I have created a 24 kHz musical instrument. When I am listening loud it will have to be with the cover up until I figure this one out. There are three spaces. One under the dust cover, one above the subchassis and below the plinth the one below the subchassis and above the granite the table sits on. There is an open port at the tonearm board between chambers 1 and two. Also, I do not have to be playing the turntable. If I play a CD with a heavy bassline the subchassis will start bouncing to the music. There is no feedback path so it stops immediately. Lift the dust cover and it all stops. My brother has a PhD in aquadic acoustics. His response was to tell me to think about sound waves like water waves. "Now you can figure it out for yourself."  Wondeful. 

Dear @mijostyn  : I used the Denon hinges and the really heavy glass dust cover thickness were made it especially for that application as how the hinges were fixed to the onyx/marble plynths.

The glass dust covers where made by 5 sides joined each one with special silicon like.

R.

what did Donna say ? 

Yes Raul, like a fish tank. You could have one made up here easily. Not sure about the hinges. They would have to be very hardy to hold the weight. My old Transcriptors had a glass plinth and cover. I only kept it for a few months. It was awful. I got an Oracle after that and it was almost as bad. After, I went back to the Linn LP 12 until I found the Sota Sapphire. Breath of fresh air.

@tomic601 , Donna really does the business end. Christan is the one to talk to about the technical aspects. I have not brought it up with him yet but, I will as soon as I have it figured out. I am making a"skirt" to go around the bottom of the plinth closing off the cavity under the turntable. Switching cartridges does nothing.