Dustcover Blues

Dear @mijostyn : I don't know which kind of material you are using in the dust cover.  Years ago when I was using two Denon TTs 80/75 each one was mounted in an Onyx 50kg base and the other marble of more or less same kgs. and I was using with dust covers made it of tigthness glass really thick and I can't remember any trouble down there. Dust cover material is critical.

I don't use any more.

R.

R.

@mijostyn  : At some time we should just seat and enjoy the MUSIC in each one room/audio system.

That " time " is different for all of us and I can see that it's not yet your time. You are still looking for the best way to arrive at the top quality level in your system.

All of us live years and years of room/system up-dates/up-grades/tweaks and the like.

Today my "time " let me enjoy more and more listening MUSIC hours and I think that my " time " is arriving to its end. Can I be sure about? well more or less.

What am I  doing on my system this weekend? something that's a necessity but not really and up-date or tweack job: my Levinson 20.6 Reference monoblocks amplifiers have around 33 years that were made and these running pure class A design over those years work with no single fault but the power supply filter capacitors  I think " needs " to be changed and that's what I'm doing. The cap´s already arrives from Mouser: Vyshay_Sprega and that's it.

Sooner or latter you will done on your room system with out missing the " fun " of those years of up-dates.

R.

I have custom acrylic dustcovers for my 2 turntables(that are on Townshend platforms) to cover when not playing.

While I wouldn't mind, I thought it wasn't a good idea to use them during playing. 

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.