[Sonny]

So, here's a question...even with a mass loaded plinth and armboard, when I tap ( a good hard tap) on my TT Platform, I hear it come through to the speakers (with volume turned UP)  when the needle is on a NON Spinning record...

Does this happen to you? 

Not that this really is real work test unless you are listening to music and tapping the platform, rack and plinth...

T

[BaMorin]

So, here's a question...even with a mass loaded plinth and armboard, when I tap ( a good hard tap) on my TT Platform, I hear it come through to the speakers (with volume turned UP)  when the needle is on a NON Spinning record...

Does this happen to you? 

Not that this really is real work test unless you are listening to music and tapping the platform, rack and plinth...

T

  I get no feedback.  I take the test of this a little further. With my tonearm/cart sitting balanced on my shure scale I blow on the headshell with just enough force to make a candle flicker a little and watch the teeter-totter. I set my vertical bearing friction this way. A "swag" result is 4 teeter-totters comes out to about 20mg. While sitting balanced on the scale, I knock on the plinth with the force of knocking on a door.
The arm/cart doesn't move a bit. If it should, I have something set wrong in the suspension. The platform my table sits on is constrained layers of various scrap materials of different resonate responses. Probably down into the 2-4hz range.

[Sonny]

Thanks for the further investigation BaMorin....
I just know that if I rest the needle on a record, like it was playing, but the platter is not moving, I get the feedback through the speakers.  My platform is made out of 1.5 inch thick MDF and sitting on three brass cones above a 30" Salamander Synergy Rack (I'll post pictures tonight).  Remember that my plinth is 130lbs of steel with a 22lbs VPI Aluminum Platter, and a 30lbs tonearm stainless steel pod.  I am surprised that I hear it, but I do...but again, this is with the volume up higher than my normal listening level!

T

[BaMorin]

Thanks for the further investigation BaMorin....
I just know that if I rest the needle on a record, like it was playing, but the platter is not moving, I get the feedback through the speakers.  My platform is made out of 1.5 inch thick MDF and sitting on three brass cones above a 30" Salamander Synergy Rack (I'll post pictures tonight).  Remember that my plinth is 130lbs of steel with a 22lbs VPI Aluminum Platter, and a 30lbs tonearm stainless steel pod.  I am surprised that I hear it, but I do...but again, this is with the volume up higher than my normal listening level!

T

sounds like you need to de-couple the table from the rack instead of coupling it.  IE, ditch the brass footers.
You need a material(s) between the table base and rack that forces the energy to be turned into heat instead of transfering energy. All of that mass you have should work for you instead of against you. Compliant material should do this. Using the energy you impart into the rack to try to lift the table. It can't, thus the energy is spent as heat. That is what a sprung suspension does. The energy imparted into the table can only get the the subchassis/tonearm/platters via the springs. The springs resonate at 2-2 1/2hz. That resonation tries to lift the subchassis,arm, platters. That weight is far greater than the energy applied.
Energy has to go someplace. In my case it becomes heat.  Several small inner-tubes partially filled with silicone oil?

[Sonny]

sounds like you need to de-couple the table from the rack instead of coupling it.  IE, ditch the brass footers.
You need a material(s) between the table base and rack that forces the energy to be turned into heat instead of transfering energy. All of that mass you have should work for you instead of against you. Compliant material should do this. Using the energy you impart into the rack to try to lift the table. It can't, thus the energy is spent as heat. That is what a sprung suspension does. The energy imparted into the table can only get the the subchassis/tonearm/platters via the springs. The springs resonate at 2-2 1/2hz. That resonation tries to lift the subchassis,arm, platters. That weight is far greater than the energy applied.
Energy has to go someplace. In my case it becomes heat.  Several small inner-tubes partially filled with silicone oil?

I can't find springs to level off a total weight of near 200lbs...I can try the oil/silcone...are you talking in the TT Shelf itself?  Drill into the 1.5" MDF and add oil or silicone?  I had used some dampening materials, like the stuff that reduces vibration underneath the TT before, but didn't do this test...so, Don't know if that helped or not....maybe I can use a "rubber" mat like materials on the MDF, underneath the plinth, etc?

[BaMorin]

I can't find springs to level off a total weight of near 200lbs...I can try the oil/silcone...are you talking in the TT Shelf itself?  Drill into the 1.5" MDF and add oil or silicone?  I had used some dampening materials, like the stuff that reduces vibration underneath the TT before, but didn't do this test...so, Don't know if that helped or not....maybe I can use a "rubber" mat like materials on the MDF, underneath the plinth, etc?

Yeah, the materials they sell to put under washer and dryers. Or sand bags with soft leather outers. The idea here is to use something that has a low frequency resonate peak, and has a low velocity sound speed.
Brass carries sound at 3800m/s, air is 330m/s

[Sonny]

Thanks, I'll try going back to the washer vibration pads...but it's a pain to move that table!
T

[neobop]

There's another approach you could try when you're feeling strong. Instead of using the cones to mass couple the MDF to the rack, try using the cones points up. This would require shelf saver feet under the MDF to keep the points from digging in. This is the classic way to use cones or spikes to decouple rather than couple. I don't know about your tap test, but it's the only way I can use a TT on an end table, with wood floors.

[Sonny]

There's another approach you could try when you're feeling strong. Instead of using the cones to mass couple the MDF to the rack, try using the cones points up. This would require shelf saver feet under the MDF to keep the points from digging in. This is the classic way to use cones or spikes to decouple rather than couple. I don't know about your tap test, but it's the only way I can use a TT on an end table, with wood floors.

that is true...hm...good advice...I used to have a VPI TNT that was suspended...didn't have this problem...but the music was less focus, I think...then I changed to non-suspended TNT...then to this...
T

[Wayner]

Might I also suggest a big hunk of granite? We used these massive stones at HTI, for our vision measurement systems and they had to be totally vibration free in our manufacturing environment. Mass will stop all vibration migration.

Perhaps that with neobop's suggestion of inverted cones will be the answer. It's not going to be cheap, but I'd inquire with a local monument or counter maker.

My 2 cents.

BTW, if it's not a problem during playback, why do you think it's a problem?

Wayner

[Sonny]

Wayner, you always ask the "right" questions...
I don't know why this bothers me... I mean the plinth, as you can see from my Moniker picture, is 130lbs of steel, the tonearm pod, 35lbs...so, yes...what does it matter???  I don't know.
I will try playing a record, knocking on the platform to see if the cartridge skips.
T

[Wayner]

Phono cartridges, and especially LOMC's are little tiny, very sensitive "microphones". Well, the knock on the surface is far from an induced feedback from a nearby speaker. Your massive rig is probably the only TT in the world that I would think would not have any problems with this!!!!!!

Sonny, you are the man!

 

[neobop]

Thanks for the further investigation BaMorin....
I just know that if I rest the needle on a record, like it was playing, but the platter is not moving, I get the feedback through the speakers.  My platform is made out of 1.5 inch thick MDF and sitting on three brass cones above a 30" Salamander Synergy Rack (I'll post pictures tonight).  Remember that my plinth is 130lbs of steel with a 22lbs VPI Aluminum Platter, and a 30lbs tonearm stainless steel pod.  I am surprised that I hear it, but I do...but again, this is with the volume up higher than my normal listening level!
T

It's the plinth that's 130 lbs, not the piece of MDF you're knocking on. My suggestion helps decouple the platform from the rack, not the plinth. Under real world listening conditions do you ever get feedback? Looking at the big picture, not just this "higher than my normal listening level" test, it's placing your rig on the rack that's suspect. How stable is this (top-heavy?)  rack and table? Is it coupled to the floor? Do footfalls ever effect playback?

Wayner has a good suggestion using mass on the platform to kill vibrations. However this will only be effective if the structure underneath is stable. Another way to kill vibrations is use a layer of lead between wood layers. I have the feeling that you really don't have a problem and just want to talk about your table. How's it working out? Speed stability, PRAT? What cart and phono stage are you using? Do you find that the heavy platter sounds a little thick, ponderous? I forget, is that a rim drive or belt? Got a mat on that steel platter? Where are those pics? LOL
neo

[Delta Wave]

Wayner, aren't those big hunks o' granite called a graplate? Just curious, I've considered getting one, they're not too terribly expensive through McMaster Carr. Just for the "oooh, look at that big hunk o' granite" factor. It's the little things in life.

On another note, those cheapie .25" thick sheets of cork at your local office supply store do wonders in the right places for vibration control.

[Sonny]

On another note, those cheapie .25" thick sheets of cork at your local office supply store do wonders in the right places for vibration control.

I thought about putting cork down on the platform before putting the plinth, armpod and motor on it.  Let me post some pictures tonight so all can see what I am working with!
T

[Delta Wave]

Sonny, did you build that plinth? That is baada***! 

[Sonny]

Sonny, did you build that plinth? That is baada***! 

no I did not...this plinth, courtesy of William Berndt....

[Delta Wave]

Did he make the rim drive too or is that VPI?

[Sonny]

Did he make the rim drive too or is that VPI?

Rim drive is VPI as well as the platter and tonearm (JMW 10.5i)

[Sonny]

To answer some of Neobop's questions:
Are there footfalls that my cause issue?  No, the Salamander rack is on concrete floors
I can jump, drop a 100lbs on the floor and nothing would happen.
Is it top heavy?  Yes, about 200lbs on top of that Salamander Rack.
Is there a problem or do I just want to talk about it.  Well, just want to talk about it.  I haven't notice any issues as of yet.
How is PRAT?  Everything sounds very very good!  Like going from my suspended TNT to no suspended TNT and to this.  Everything is tighter, faster, blacker black, no noise...etc..

See pictures below:


TT on Salamander Synergy 30" rack


TT platform (1.5"MDF) surrounded by walnut butcher block and the brass cones underneath


Plinth/tonearm on MDF shelf....