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12-01-2013 Post does not mapped to Knowledge Tree
N-set
Gdansk, Poland
Posts 454
Joined on 01-07-2006

Post #: 41
Post ID: 20331
Reply to: 20330
Sand context
fiogf49gjkf0d
Paul, I can olny speak within my context and with no audio tests, only knuckling.
I use pure silca sand in 3 granulations (2 of them fine unfortunately), mixed with steel shots.

Of course the sand is there to quench the steel ringing. But while achieving this very nicely
(I hear zero ringing, only deep, bell-like "thunk") it adds something: lowers the construction
resonances and makes them less damped (the effect of the added mass). In my case I clearly feel
gelly-like subsonic vibrations, lasting >1s !!! Now everything depends on the context how the support is used.
For electroncs I'd not care much with <5Hz.
But I have the air springs resting on the columns with ~3-5Hz fres. The frame with its own ULF vibrations in that range instead of
providing a solid support for the springs adds them additional very hard work. You see what I mean? I'd prefer to have frame resonances
somewhere higher, 10-15Hz region where the speings start to work efficiently.

Perlite: yes, it's very light. I have it now in the upper table holding the springs. When knuckled at some points
it does have a faint ringing in the 2-3kHz region, barely audible also through the slate (!),
so the perlite is not so effective but I needed some additional kilos to be saved here.
In the horizontal braces I have a third material: perlite ore. This is unexpanded perlite, denser than the expanded one but
lighter than the sand (1.1g/cm3 vs ~1.6g/cm3). It seems to work nicely where it is: the initial knuckle tone is higher but lasts shorter (feels dumber
vs organic with the sand), there is some LF vibration but not so pronouced and I do not feel much of a subsonic one.
I'm thinking of buying a simple guitar piezo and looking at the resonances instead of shooting in the darkness.






Cheers,
Jarek
12-02-2013 Post does not mapped to Knowledge Tree
N-set
Gdansk, Poland
Posts 454
Joined on 01-07-2006

Post #: 42
Post ID: 20332
Reply to: 20331
Hmm...
fiogf49gjkf0d
I think I've slowly started to understand the behavior of my rack.
A very approximate calculation shows that in my case I should have the profile fundamentals around 20Hz, so
perhaps what I take as subsonic vibrations are actually 20Hz, poorely damped due to the added sand mass.
 I've ordered a dirt-cheap guitar piezo and try checking that. The wooden floor I have seem to have the resonances
+/- in the region of the frame (hope my piezo experiments will shed some light on that too): stepping hard close to the frame excites it.
I've followed the mass principle with my mastodont frame hoping big mass=small displacement with a given excitation,
but mass lowers the frame frequencies and looks like I've come close to the floor resonances?

Paul, you seem to have some experience in construction engineering. Does it all make sense to you?

Another random fucktor are the spikes: they look fantastic and they fantastically couple floor vibrations to the frame.
I will try 7cm round feet instead of the spikes to see what happens.

Cheers,
N-set






Cheers,
Jarek
12-02-2013 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,157
Joined on 10-12-2006

Post #: 43
Post ID: 20333
Reply to: 20332
Floor Resonances
fiogf49gjkf0d
N-set, you may remember that from the beginning I encouraged you to try a wall mount, for all the reasons you have just cited, and this approach seems even more obvious if the walls are concrete/masonry vs. floor joists and sheet subflooring, not to mention open joist bays.  A stethoscope will tell you broadly about noise in the frame, but it will take spectral analysis to narrow it down. A cheap pick-up should work, but you will probably have to figure out and write a curve for it, if it will do <20 Hz in the first place. The idea with spikes is not to couple directly to a wood floor system but to couple directly to an effective interface between the rack and the wooden floor system; that's why I suggested you try felt. Various band pass "breaks" like bladders, etc. should help with 20 Hz, but (of course) they may result in other mostly ULF motion(s). Naturally you are only ultimately concerned with output from the device or devices that sit on the rack. I can tell you that long-span floor joists often have very persistent vibration, both primary and modal, so good luck coupling to a wooden floor system. It is generally better near the walls as far as primary resonance, but all bets are off for cavity and modal resonances.

Best regards,
Paul S
12-02-2013 Post does not mapped to Knowledge Tree
rowuk


Germany
Posts 229
Joined on 07-05-2012

Post #: 44
Post ID: 20334
Reply to: 20332
The best pickup - is a pickup
fiogf49gjkf0d
Hi N,
I just use my turntable, arm and cartridge to measure the effects of vibrations. Don't turn the platter on, drop the cartridge into a groove and your phono corrector output will tell you everything that you need to know - as it would happen during playback. You can even locate the position of least destructive resonance by moving the turntable around until you are happy.

Just plug the phono corrector into a PC and you will have a very effective source for spectral analysis.

I am very suspicious of digital sources that are microphonic. There is simply no need for a DAC to be sensitive to airborne vibrations. I would suspect that cables would have to be hundreds of times more "sensitive" and no one uses lead shot or sand there............... 

Although, I might just try.......


Whenever I feel blue, I start breathing again.
12-02-2013 Post does not mapped to Knowledge Tree
N-set
Gdansk, Poland
Posts 454
Joined on 01-07-2006

Post #: 45
Post ID: 20335
Reply to: 20334
Spike pickup
fiogf49gjkf0d
Paul, I hear you clearly re wall mount. Well...I have chosen the hard way an occasion to have one, +/- universal solution I could "copy&paste"
if I change location.  Go through that hell and have it done once and forever.
I even ask my daughter to put this mastodont on my grave when I die. Not so much as a symbol of my biggest
achievement but rather something that shortened my life Smile

I'm not sure I was clear with the spikes. I see them on 100% of all "high-end" racks  (but never-ever on e.g. optical tables, where nano-vibrations can ruin everything) and I've "smartly" decided to follow the crowd,
semi-backed up by the fact that they are also used as a simple antivibration mounts in industry. What escaped me is that
I've approched the subject from the ass: in the case of vibrating machinery, what is on the mounts is vibrating and we want
to decouple that from the floor. And there the spikes can work as they provide some angular and torsional freedome of motion
Here of course is to the opposite: floor is vibrating and we want to decouple the rack form the floor.
By achievieng super high pressure the spikes are tightly coupled to the floor and I believe happily transmitt everything.
A nonsense "solution" in other words. That's why I'd like to try a wide feet with a big area, low pressure contact to see how they behave,
if there is any difference at all. The felt idea sounds ok, but felt gets compressed and has to be exchanged from time to time
and I dont want to do that with a 300-400kg mastodont.

As for the bladders that break the vibration path, let me repeat: I don't want the support rack to add them additional work by its
own resonances, magnifying the floor modes. I start to believe that a better strategy than mine would have been a lightweight, rigid frame, topped with baldders and a high mass, not a high mass frame. Well, I can always get rid of all the profile filling and will end up probably with a pretty rigid
frame, given the sizes of my profiles.

Rowuk, of course I do what you describe!! This is how I learn e.g. the vibrational spectrum of my neighbour's waching machine. But I wanted
a cheap solution to check every frame member. For 10Eu I don't expect much, but hope it to have some output below 20Hz. I don't need
the exact amplitudes of the modes, only a very rough guide: the lowest present modes must be the fundamental and should be attacked first.

Cheers,
N-set








Cheers,
Jarek
12-02-2013 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,157
Joined on 10-12-2006

Post #: 46
Post ID: 20336
Reply to: 20335
Re: curve
fiogf49gjkf0d

The primary mode may not be the lowest present mode, but it will only be apparent if the pick-up's own curve is known over the desired frequency band.

As for spikes, I see no reason to use them on a suspended wood floor, but in any case the idea is to get the frame itself down to "one mode" if you can, and then deal with that one mode by going back and forth between targeting the dominant mode directly and spreading it out, backed up by listening, of course.  If felt on broader contacting feet works to reduce the transmission of floor-generated/borne noises, then...  Yes, the cartridge-on-an-LP method is very effective at amplifying noise that affects the stylus under those "static" conditions.

Again, you might gain something by fastening the rack to adjacent walls and adjusting the tension and/or damping of those connections. In any case, you'll want to prevent swaying of a TT support, and likely a CD transport, as well, and it might even damp some noises that enter the frame from the floor, just like standing there and poking it with your finger.


Best regards,
Paul S

12-03-2013 Post does not mapped to Knowledge Tree
Jorge
Austin TX
Posts 137
Joined on 10-17-2010

Post #: 47
Post ID: 20337
Reply to: 20336
Sand
fiogf49gjkf0d

For some reason I cannot post pics, they wont upload to the server so I cant select them.

The way Aurios work is with 3 ball bearings rolling inside a round chanel, something like an inverted doughnut...top and bottom.
On the center they have a bolt that allows for some movement but wont let the whole contraption get dismanteled, in case, lets say, of a big hit on the side.  Each ball bearing is held in place by a thin plastic circle that hold the bearings in a triangle shape.

The main thing is they work very nice and slide sideways with a lot of ease.
There is no way they will damage the bottom plate of any piece of equipment, imho.
They couple to the shelf, with a big area and some felt, and to the equipment on top with a ball bearing: I have used a small brass cone here and heard no change.


I dont use the sand inside the posts that make up my rack,  I could, but I see no need just yet.I used pretty thick material.

Each shelf of the rack is supported by something like a sand box, with a lot of area and about one inch deep of sand, 
each shelve has its own sand box: this gets rid of a lot of vibrations.  Let say Each shelf couples to the rack via sand.
The easiest and fastest way for me to do it, was to use Plywood shelves,  I know, not my first choice.
The idea was to use them temporarily untill I ordered some Marble or Granite shelves cut to size.
I havent got around to ordering the heavy shelves...

For my TT I use a 2 inch slab of Maple, I detach it from the shelf with Sorbothane, and form the TT plinth with Brass cones.
It works pretty good and it is still sensitive to added weight on top.   If I jumpt right next to the rack I will hear a thump if the record is playing.
My listening room is made of brick and mortar with concrete floors.

12-03-2013 Post does not mapped to Knowledge Tree
N-set
Gdansk, Poland
Posts 454
Joined on 01-07-2006

Post #: 48
Post ID: 20338
Reply to: 20337
Stoned beaings
fiogf49gjkf0d
 Jorge wrote:

For some reason I cannot post pics, they wont upload to the server so I cant select them.

The way Aurios work is with 3 ball bearings rolling inside a round chanel, something like an inverted doughnut...top and bottom.
On the center they have a bolt that allows for some movement but wont let the whole contraption get dismanteled, in case, lets say, of a big hit on the side.  Each ball bearing is held in place by a thin plastic circle that hold the bearings in a triangle shape.

The main thing is they work very nice and slide sideways with a lot of ease.
There is no way they will damage the bottom plate of any piece of equipment, imho.
They couple to the shelf, with a big area and some felt, and to the equipment on top with a ball bearing: I have used a small brass cone here and heard no change.


Hard to imagine without a picture. What does the ball touch at the top? Directly the equipment or another puck? This felt below the lower puck doesn't sound right to me: one wants here very hardcoupling to the shelf to set the ball in motion with a slightest micromovement.

 Jorge wrote:

I dont use the sand inside the posts that make up my rack,  I could, but I see no need just yet.I used pretty thick material.

If you ever feel need, be carefull!

 Jorge wrote:

...
The idea was to use them temporarily untill I ordered some Marble or Granite shelves cut to size.
I havent got around to ordering the heavy shelves...


I'd avoid granite. It rings.

http://www.newport.com/Granite-Optical-Structures/139776/1033/info.aspx

Marble...maybe but a selected one. If you go through all the stone pains why don't you rescue some

vulcanic slate from n old biliard/snooker table like I did? There is  reason English snooker players moved from once traditional

marble tables to vulcanic slate (Itlian slate) ones. Better damping. And the color!! My pics don't do the justice to the stone,

it's just hypnotically beautifull, with absolutely no graveyard pretensions! Some people even think it's plastic, until they touch it.

 Jorge wrote:

For my TT I use a 2 inch slab of Maple, I detach it from the shelf with Sorbothane, and form the TT plinth with Brass cones.
It works pretty good and it is still sensitive to added weight on top.   If I jumpt right next to the rack I will hear a thump if the record is playing.
My listening room is made of brick and mortar with concrete floors.

How is sorbothane working under compression? Does it leak? Would you please share some technicalities:
which duro sorbothane, which thickness, how big mass it supports and through what area?

Cheers,
N-set




Cheers,
Jarek
12-03-2013 Post does not mapped to Knowledge Tree
N-set
Gdansk, Poland
Posts 454
Joined on 01-07-2006

Post #: 49
Post ID: 20339
Reply to: 20336
Ad hoc fixes
fiogf49gjkf0d
 Paul S wrote:

Again, you might gain something by fastening the rack to adjacent walls and adjusting the tension and/or damping of those connections. In any case, you'll want to prevent swaying of a TT support, and likely a CD transport, as well, and it might even damp some noises that enter the frame from the floor, just like standing there and poking it with your finger.



Paul, instead of ad hoc fixes, I'd prefer to understand what's going on and find a real solution.

What I have now are low lying but long lasting frame vibrations, caused most probably by the added
mass to the profiles, esp. te sand+shot in the vertical columns. Quite counterintuitive, the sand-filled profile vibrations feel
also like higher amplitude than those filled with lighter stuff,
which should not be the case as higher mass should displace less given the same excitation.
What feels right ot me by knuckling is a middle path between light mass (perlite) and high mass (sand+shot),
achieved in the horizontal members by the perlite ore. I'm mentally preparing myself for exchanging
the sand for the perlite ore in the colums to see what happens.

Cheers,
N-set



Cheers,
Jarek
12-04-2013 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,545
Joined on 05-28-2004

Post #: 50
Post ID: 20340
Reply to: 20338
Granite
fiogf49gjkf0d
 N-set wrote:
I'd avoid granite. It rings.
Granite rings?  I am not a huge fan of granite but ringing us not the character that I would attribute to granite. N-set would you care to elaborate on it and tell how did you come to the ringing observations?


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
12-04-2013 Post does not mapped to Knowledge Tree
N-set
Gdansk, Poland
Posts 454
Joined on 01-07-2006

Post #: 51
Post ID: 20341
Reply to: 20340
Ringing
fiogf49gjkf0d
Rings=poorely damped, due to its crystaline structure. Take a granite tile with two fingers, put your ear close to it and knuckle. Observe the sound.
Repeat with other stones to compare. For that reason it's neither used in nanolabs anymore (see e.g. the Newport link)
nor in, say, billiard tables, not ot mention TT plinths. But looks good on graveyards Smile



Cheers,
Jarek
12-04-2013 Post does not mapped to Knowledge Tree
N-set
Gdansk, Poland
Posts 454
Joined on 01-07-2006

Post #: 52
Post ID: 20342
Reply to: 20332
Vibrational jungle
fiogf49gjkf0d
 N-set wrote:

A very approximate calculation shows that in my case I should have the profile fundamentals around 20Hz, so
perhaps what I take as subsonic vibrations are actually 20Hz, poorely damped due to the added sand mass.
 I've ordered a dirt-cheap guitar piezo and try checking that.


It has arived today. What a little, freaky gadget! Bloody sensitive to EVERYTHING, I had to sit a complete silence
and still, attached to the frame with a masking tape it was catching the slightests sounds, like my laptops vent...
So what it catches is a mix between vibrations of the frame and airborne vibrations.

Spending some charming 2hrs positioning the piezo and endlessly hitting the rack and the floor with the base of my palm,
 I got some glance on the vibrational frequencies:

the top of the rack, hitting the bottom: 2-3 (?) , 5-7(?), 15, 30, 50, 75, 150Hz

The most pronouced (with an unknown piezo response curve of course) were 30 and 50 Hz depending on how I hit the rack.
The lowest two I'm quite unsure of (the piezo does have an output below 20Hz, it reacted happily to
some idiot testing his motor outside, showing 10-15Hz broom). Might be the vertical and the horizontal modes of the airsprings.
As to the rest I don't know to what extent they represent the frame frequencies and to what the airborne vibrations (the dull
sound of my palm's base hitting the rack).

here are the floor freqs alone: 12, 25, 30-50, 100-200Hz (the last two are whole regions, shown with 256k FFT!)

If all that is true, than avoiding floor resonances is like avoiding raindrops biking in a heavy rain. Of course
the rack is heavily coupled to the floor via spikes hence the "rack vibrations" come from
the rack-floor-air intercation.

Next I'll try putting the TT and see how it reacts to footfalls.

Chhers,
N-set


Cheers,
Jarek
12-04-2013 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,157
Joined on 10-12-2006

Post #: 53
Post ID: 20343
Reply to: 20342
Harmonics
fiogf49gjkf0d
12(.5), 25, 50, 100, 200...  Now you just need to track down the dominant mode.  25 sounds about right for a floor mode, but a long, loaded joist span might be way down there. And we still don't know how principal modes are "translated" by your rack. A "grouping" around 20/30 might be span + cavity resonances. I wonder how much hitting the rack feeds the floor/cavity(cavities).

Best regards,
Paul S
12-04-2013 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,545
Joined on 05-28-2004

Post #: 54
Post ID: 20344
Reply to: 20341
Observe the sound… with your brain or ears?
fiogf49gjkf0d
 N-set wrote:
Rings=poorely damped, due to its crystaline structure. Take a granite tile with two fingers, put your ear close to it and knuckle. Observe the sound.
Repeat with other stones to compare. For that reason it's neither used in nanolabs anymore (see e.g. the Newport link)
nor in, say, billiard tables, not ot mention TT plinths. But looks good on graveyards

N-set and others…

Even I do not disagree with all that you writhe here generally and on the subject in particularly but I would like to remind you that all your comment about racks, suspension, desolation and everything else do not have direct correlation with sound. It might have but it also might not have.  I certainly do not want to diminish the value and the efforts you spend on your rack and it is very good project but the relation between the auditable benefits and purely intellectual investment you made into your rack is not so simple. Your complain about granite is a good example of it.

I am with you and I do not like granite. I do not think that it rings, come on get real. It in my experience adds some “coldness” to sound but only in some cases, in other cases it does not. I spent a lot of time listening shelves, equipment, chassis’, isolators, platforms, suspenders and anything you only can only imagine with stethoscope and heard how different type of vibrations get propagated, absorbed, dissipated or consume by different surfaces. However, during all my experiments I was not able to observe the obvious correlation between the quietest chassis and better sound. It was always case by case and in some circumstances it were absolutely absurd results. If I tell you that I know one DAC with which I was able to put the cone under and by moving the cone with 1-2 inch I was able to attenuate HF response within 2dB then you will tell me that I am a fool of it. Well, I demonstrated it to one famous industry person and it in fact very true story.

So, what I am saying is that all that we do and discuss about the subject has only intellectual stimulation. What we say/do on the subject is not wrong but it is not sufficient to be right. The rightness comes from the actual Sound we accomplish and it is not always Copley with your best intellectual objective and methods. Sometimes, live, ringy and shaky platform sound the best in this or that applications and all theories need to be set aside. I do not know the answer but I think not to have precompiled answers is the best approach.
 


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
12-04-2013 Post does not mapped to Knowledge Tree
N-set
Gdansk, Poland
Posts 454
Joined on 01-07-2006

Post #: 55
Post ID: 20345
Reply to: 20344
I could not agree more...
fiogf49gjkf0d
...with Romy. So far it has been all abstract, following some known good solutions (like Vibraplane)
...and it will largely stay like that for some time unfortunately.
My actual space is too small to build a reasonable acoustical system, I use headphones, so the rack will not see the
the real acoustical field soon, at this moment it's goal is to deal with the floor.
Anyway, I do what I can given the circumstances. Perhaps foolishly, perhaps wisely...I have no idea.
I hope to have a good base which I would only tune when it starts working embedded in an acoustical field.

Cheers,
N-set




Cheers,
Jarek
12-04-2013 Post does not mapped to Knowledge Tree
N-set
Gdansk, Poland
Posts 454
Joined on 01-07-2006

Post #: 56
Post ID: 20346
Reply to: 20343
Floor feedback
fiogf49gjkf0d
 Paul S wrote:
I wonder how much hitting the rack feeds the floor/cavity(cavities).


Paul, standing barefoot right next to the spikes and hitting the rack  with my palm's base moderately
(like if I wanted to push a bit blocked door), I can feel some faint floor vibrations, so they do communicate
through the spikes.

Cheers, N-set



Cheers,
Jarek
12-04-2013 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,157
Joined on 10-12-2006

Post #: 57
Post ID: 20347
Reply to: 20344
Brain or Ears
fiogf49gjkf0d
Romy, I'll bet everyone has been thinking like you all along (I know I have), but N-set has already dismissed simple "results-oriented" solutions as "ad hoc" and indicated that he is determined to work with his rack as it is and understand each action/reaction as it regards his original design, and then move on from that knowledge base. N-set, at this point I have assumed that this is simply because you want to understand what is going on, in the spirit of scientific inquiry. And I certainly appreciate the desire for repeatable results.

Best regards,
Paul S
12-05-2013 Post does not mapped to Knowledge Tree
N-set
Gdansk, Poland
Posts 454
Joined on 01-07-2006

Post #: 58
Post ID: 20348
Reply to: 20347
Yes and no
fiogf49gjkf0d
Paul, I did not dismiss result-oriented solution. I'm fighting hard to get one actually.
Honestly, I initially hoped that brutal mass loading will be enough to deal with what I have,
and as a bonus I'll have a +/- universal solution I could move when I change the location. Well, the live is not so simple
and having invested quite a lot in this mastodont I'm a bit slow to trash it. That's why I dismissed wall fixing as ad hoc in this context.
As for repeatable results and understanding,
you are right, I wanted to have some base, at least to know what is shaking and how to move on with sound tests.
And this is what I'm about to begin.

Cheers,
N-set





Cheers,
Jarek
12-05-2013 Post does not mapped to Knowledge Tree
decoud
United Kingdom
Posts 241
Joined on 03-01-2008

Post #: 59
Post ID: 20349
Reply to: 20347
The science
fiogf49gjkf0d
It seems reasonable to begin with the science -- as a preliminary to listening -- but I do not follow the logic here. The source of the vibration is principally the floor: the table should therefore not be coupled with spikes but decoupled from the floor. Once decoupled, the high mass would be damping, rather than acting as a reservoir of kinetic energy for the transmitted vibrations, especially if when decoupled the perturbing forces are non-stationary, as I imagine will be the case (random footsteps, something falling nextdoor, etc). The situation seems to me analogous to sound proofing, where what works best is sandwiching a high mass layer between two decoupling layers, no? 
12-05-2013 Post does not mapped to Knowledge Tree
N-set
Gdansk, Poland
Posts 454
Joined on 01-07-2006

Post #: 60
Post ID: 20350
Reply to: 20349
Mass decoupling
fiogf49gjkf0d
Decoud, if you look carefully at what I'm doing you will see how and where the table is decoupled.
The logic behind the high mass I've already explained. I was unaware though how tricky it is to implement-this is my 1st construction.
The logic behind decoupling where I have it is to decouple also from the support structure vibrations--the closer to the
TT the better, I think it's clear. The spikes I've already discussed -- I'll try wide feet instead of pointed spikes.

Cheers,
N-set



Cheers,
Jarek
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