The feedback problem I had with springs under the turntable is a damping problem. Its a problem because there is a certain range of frequency and amplitude level where we want the spring to be a spring. To let the shelf or component move freely. Damping factor by definition interferes with this. But we do want damping, just a certain very well defined amount.
This is where the story catches up to where we are in the real time here and now. Because the last week or so I’ve been looking into this and now happy to say have found a really good solution: Townshend Pods.
So good in fact I’m done writing for the night, got some listening to do which is a whole lot more fun. |
Regular old granite. Lots of different stuff in there. |
Getting back on track. The springs I've been using lately are just that, springs. Some from eBay, different sizes, are just plain springs. Nobsound are just springs too, only with caps or footers drilled out to hold them in place. Point being they are all bounce, with no damping. Like Max said his engineering indicates an ideal .16 damping.
Didn't seem to matter with speakers. Plain springs under the Moabs worked fine. Under the subs, ditto. Even under the turntable, seemed to work fine- at least at first. Got some more, put them under the power conditioner. Speaker cables, power cords and interconnects are on rubber bands. Virtually the whole system is now suspended, one way or another. Not exactly free to move- a lot of the cables are pretty stiff. They will restrict free movement and at the same time feed vibration into the component. Hard to avoid. But for the most part it is all suspended or if you prefer isolated.
One day I notice this drone or rumble. It happened on a lead-in where there's no signal so I thought it was really bad rumble and my bearing or motor or something was shot. But no. Darn noise would come and go. One time I got up to go check and while walking to the turntable it stopped. Went away. I froze. No rumble. Okay. Went to sit back down, came right back!
Took a very long time to realize this was undamped resonance feeding back into the turntable. At just the right frequency the system would be excited and with no damping it would feed back and amplify until it was just super alarming loud.
Even a small change anywhere in the system would stop it, like me moving my weight around the room. Tried different things, the best so far is to add a 5th leg under the table this one with a very small bit of sorbothane that eliminates the feedback.
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Ordinary 1/4" drill bit, springs fit perfect. Only need to go 1/8" deep, as far as the springs are concerned. If you need to go deeper to have them recessed for looks then drill again oversized so the springs don't rub the sides.
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What? Apatong looks exactly like the tight grain reddish brown exotic hardwood in my shop, extremely dense but it is only about as hard as aluminum and can still be cut with router or table saw, you just have to be careful to feed slower. Had mine forever because I hate working with it- one mistake and it takes forever to sand out, if you even can! If you have wood harder than that.... man that's some hard wood!
Nobsound springs are 1/4" dia and about 1" high. If the speakers are softer on the bottom you could drill 1/4" holes about 1/4" deep and slide the springs in there, however many you need per corner. Only other thing I can think of would be to screw an L-bracket on the side. Wouldn't look quite as good but would only need to stick out 1/4" and you could paint or even cover with a bit of trim.
Would be nice if you could use springs. They sound better than anything else you could use for this. Or stick furniture felt on the feet and call it good?
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Vibration control is a balancing act. They do this with all musical instruments. Some parts are designed to vibrate a lot, others for stiffness to better control vibrations. Think neck and frets on a guitar. Craftsmen fine tune this with layers of lacquer. It all contributes to the sound. Its just for some reason when it comes to our systems we don't think of it this way. But it sure seems to be the case. Things I've been doing lately seem to point in the direction of suspending things freely. Everything's a trade off, finding the right balance. Springs alone can leave things free to resonate, and maybe at times too much. My turntable and other stuff sounded great on springs. Until one day there was a deep drone or rumble. It took a lot of chasing down to figure out it was some kind of resonant feedback. The slightest damping of the springs under the turntable would make it go away. As John posted above, Max Townshend being an engineer figured out:
The ideal is to have the resonant frequency as low as is possible, ideally around 2Hz in both the horizontal and vertical planes and with a damping ratio of about 0.16. This will give an attenuation of about 25dB at 10 Hz increasing at 20dB per decade above.
This will ensure excellent isolation for the deleterious audio system vibrations which are from 5Hz to 500Hz.
This fits with what happened with my turntable. At least to the extent I'm able to see with my eyes, not having anything to measure this with. But it sure seems to fit with everything I am able to see and hear. |
Perfect timing, I was just getting to springs. This was a real hard sell for me. Rixthetrick had some pretty good arguments that made me think. Max had some very compelling videos that made me think even more. But thinking has gotten a lot of guys including me in trouble. Only one way to know for sure. Rick was very generous and found me the right springs on eBay for me to check it out.
Not any springs will do. They do need to be sized for the weight of the component. Its kind of like what John is saying above, there's always going to be a resonant frequency and you want it to be very low ideally according to Townshend around 2Hz.
I still was skeptical. It just seems a speaker on springs, when the cone moves one way the whole loudspeaker is going to move the other way, and there goes your dynamics and transients.
But unlike the few others who never acknowledged these problems both Max Townshend and Rick did admit this does happen. Because, physics. Kind of silly when people try and deny physics. (See: using just one sub.)
What I was missing though, and what engineer Max points out, is that yes you do lose a tiny amount to that but you gain something much more valuable- a huge reduction in ringing.
Ringing is the term for when the whole system is set vibrating and continues to vibrate long after the transient signal that started it all. Ringing is why we want speaker cabinets to be extremely solid and inert. But then we put them on a floor that is anything but. Then we make it worse by using spikes to couple the speakers to the floor.
As we already know the idea of spikes as diodes and vibration being a one-way street is unfounded. Vibrations go both ways. Once the floor starts vibrating it sends those vibrations right back up through the loudspeaker cabinet to the driver.
At least this is the theory. When it comes to stuff like this I'm pretty agnostic. Too many wonderful theories just don't seem to pan out. My grandmother was from Missouri, the "show me" state, so its in my blood. So I tend to say, nice story. Show me.
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Great, what I was hoping. So here's my idea: springs between the speakers and the stands. Don't run! Do it like I'm gonna say and they will look almost exactly the way they do now, BUT they will sound a lot better and no more problems with the stands.
First get one set of Nobsound springs for every TWO speakers you want to do. One set will do 8 corners. You can do other springs but that will mean a lot more work for hardly any money saved.
Cut holes in the stands at the corners where the speakers will go. Hole saw or router. If the stands are as thick as they look you can router them out deep enough and just drop the Nobsound springs in. You will have to experiment to find the right number of springs. Then cut the hole depth just right and the speakers will float on springs with only a barely visible space just above the stands.
You do not need a lot of space since the springs only move microscopically when playing music. It will just take a bit of trial and error to get them level at the right height. The springs will pretty much take the stands out of the equation, especially if you put some furniture felt stick-on thingies under their feet.
With those speakers you will probably only need 3 or 4 springs per corner, meaning one set of Nobsound will do 8 corners. The springs fit snug into a 1/4" hole. Could hardly be sweeter.
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If you just want to fill, mix sand with mineral oil, not much just enough to get good and damp so it packs better. Then mix with lead shot and fill your legs. But those legs are stubby, doubt this will do much.
I have a much better idea but need to know: Are the stands and speakers two separate things or all fastened together?
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Yes indeed. Funny you should ask. I look for truth from simple experiments Exactly. In a way, what this whole thread is about: trying things out. Rick checked in at an opportune moment because this is right about the point where he comes in. Up to this point I was pretty well convinced the key to vibration control was basically to clamp or fix things in place so they can’t move. When done with the right materials this definitely improves a lot of things. But as my system kept getting better and better there was this sense of a sort of hardness creeping in. Not an edge really just certain sounds were harder on the ears than it seemed they should be. I now suspect this was due to ringing. But we’re getting ahead of ourselves here. Rick it turns out is big on vibration control, has been working on this a long time, and is a big proponent of springs. Seemed like a waste but he was pleasant enough, and even better had a good argument: No matter what you do (the old-school cones/spikes way) vibrations are going to get into the floor, rack, shelf, etc. and then the whole speaker/floor/room system is vibrating. Well then if that is the case (which it is) then a lot of that energy is coming right back into the speaker, and its vibrating, only now not the way we want but in sympathy with the floor. Worse, the same thing is feeding up into my precious turntable. Everything else too of course. So Rick is telling me springs under the speakers will be huge. First because the speakers themselves will sound better, and also because less vibration going into the floor means less into the rest of the system. |
Well whoever gave me the idea it seemed crazy at first but sure enough with bass playing the speaker cable vibrates hugely obviously even at a fairly moderate to low volume level. Knowing this will come in real handy and make even more sense as we go along.
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Vibrations produce fascinating patterns that vary with frequency. https://youtu.be/WmwnN_T_wW8?t=31 Happens in all materials, forming different patterns with different shaped materials. Happens everywhere from the cantilever to the speaker diaphragm. Even seemingly inert wires. Mahgister I believe it was you who suggested holding a speaker cable while playing music. The vibrations especially with bass are surprisingly strong. In hindsight this makes total sense. Electric current produces magnetic fields that attract and repel. So of course an alternating current will produce alternating magnetic fields that will cause it to vibrate. |
Glad to hear we agree for once. Except the metaphor for vibration control in a car would be better shocks and springs, which definitely will improve handling making the car faster. Still, nice to hear you admit vibration control does "move the needle" in the direction we want it to go.
Let's see now, where were we.... Oh yeah-
Everything seemed to be saying load it up, clamp it down, constrain layer damp it, spike it, drain it. Even people talking isolation were still using spikes, doing the same thing, just calling it something different by pretending the spike is a diode.
This approach definitely had some good things going for it- or me and a whole bunch of other people wouldn't have been doing it! The stiff, massive and highly damped approach definitely improves bass extension and slam, and dynamics, lowers the noise floor, and makes more details pop out. No wonder it became so popular.
Its also easy to experiment with it. Really soft low mass high damping factor stuff like sorbothane can be used to tame a hot top end. It sucks a bit of the dynamic life out of the music, but used carefully can be a good compromise. Same for things like sand boxes. Not the stiffest material, but massive, good for eliminating low amplitude high frequency noise especially from things like turntables. Mahgister has a lot of great examples of this where he has experimented by listening and matching different layers of different materials until he comes up with the right overall balance.
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millercarbon wrote: That's a big part of what I'm trying to get across with all these stories: no one thing is perfect, but we can hear the effects and use what works. The same is true for all our components. So as our systems change something that once worked well for what we had then might not work so well with what we have now. |
That's a big part of what I'm trying to get across with all these stories: no one thing is perfect, but we can hear the effects and use what works. The same is true for all our components. So as our systems change something that once worked well for what we had then might not work so well with what we have now.
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Around this time another experiment that might seem unrelated was going on: cable elevators. They work. No doubt about it. But, why? One theory was that insulation quality makes a big difference, carpets and flooring aren't quality insulators, and so the improvement was in being further from them. Another idea was elevating them somehow reduces harmful static electricity. I don't recall anyone then - or now, for that matter - thinking it had anything to do with vibration control.
Spoiler alert: I do now!
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The early bird reads the good post. Got to be fast to beat the snowflakes and censors around here. oldhvymec triggered someone with his edifying and entertaining post, now removed, leaving us all the poorer. Such are the times these sad dark days.
Why don’t you just move along if it bothers you so much? Not like anyone is forcing you to read this. Far from it. If you’re not man enough to handle diverse points of view why bully your intolerant narrow mindedness on everyone else? Why not just move along? Please?
The prevailing wisdom back then was vibration flows, and you can "drain" vibrations with sharp spikes that are like diodes, allowing vibrations to flow out but not back in. Huge amount of guys bought into this.
This never made any sense to me. On the one hand we were supposed to believe the spikes had to be sharp to cut through carpet and stuff and go into the floor, the better to rigidly couple or anchor the speakers. But on the other hand these same spikes were supposed to somehow drain energy from other components, or prevent room vibrations from getting into the components. Or something like that. The story changes every telling, no one ever bothering to point out the logical inconsistencies.
To me it seemed most of the vibrations were coming from the components themselves. That would explain why a phone book or other mass placed on top affected the sound. It changed the vibrations of the component itself.
One totally unexpected experience seemed to prove this. Doing a Cone demo one time for a friend, instead of stopping and starting I lifted the CD player to remove the Cones with the music still playing. My friend said he heard the sound change- and become worse- the instant it was lifted off the Cones!
If isolation was so important then surely my hands are more isolation than Cones. It should have sounded better not worse. If sharp spikes was the answer then it should sound better on them instead of being better on the rounded off BDR Cones. Just one of many observations that had me pretty well convinced the key to vibration control was control. As in stopping it. With stiff and highly damped mass.
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Limited time and money. So everyone knows the rack and everything else we're talking about here is a compromise of some kind.
I'm talking about the rack because that's when I really started thinking seriously about vibration control. Which is funny because even before the rack there was the turntable. Turntables are a study in vibration control! The whole thing is doing nothing but vibrating. Something that now seems almost self-evident, but to me back then (as with a lot of guys it seems) it seemed like all the vibration was coming from the floor, or rack, or whatever. There was almost no thought given to the cartridge, arm, the table itself. Oh well. Live and learn.
My first table was a Basis 2001. At first it went right on the floor. Then it went on two sheets of 3/4" MDF glued together. With different things, eventually BDR Cones, under the MDF. With a Graham 2.0 arm and Benz Glider I thought this sounded really good!
For some strange reason I can never quite understand turntables seem to be really mysterious. Maybe because I went with the Basis it never was quite so hard to understand. The Basis arrives disassembled. Its really nothing more than 1" acrylic with some holes drilled, into which you screw four footers, the bearing, and your arm. An awful lot of turntables are to this day nothing more than that: plinth, feet, holes. Okay, motor.
The trick it turns out is in how each of these controls vibration. The Basis used four pods or footers that were little cylinders filled with silicone fluid. Inside that were springs with little paddles that made the whole thing like a sort of shock absorber- spring and damper all in one.
Looking back, why I did not experiment with different viscosities, or none, is beyond me. Oh well. Live and learn.
Because that was my first hands-on experience with springs, only it wasn't much experience, because I wasted the opportunity to try and learn. Been making up for lost time ever since....
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Thank you, oldhvymec, made my day. How right you are. mahgister-
The impactful results of resonance/vibration controls embeddings is very
audible....The problem is the way to reach results is a complex
problem... Yes indeed we are on the same page. As you well know. And as will become even more clear as the story unfolds. We left off with the turntable stand. https://systems.audiogon.com/systems/8367 This was based on everything learned in those two years of testing out what was around at the time. Remember again, have to keep reminding people, this was before the internet. Now you just change your browser from Goolag to one that actually works and find what you want in no time flat. At this time, based on everything tried, I had come up with my own working principles of vibration control based on stiffness, mass, and damping. Stiffness in materials gives a faster sound. Mass improves bass extension and impact. Damping lowers background noise. Each of these also has its downside. The trick is like mahgister said to find the right balance. What I came up with was solid concrete, with a sand bed cast into it, and granite on top. The idea being the sand will damp the stiff and massive concrete and granite. Seemed like a good idea until the granite came and holy crap granite rings like a bell! Important Lesson Number Two: Shape matters! A block of aluminum seems pretty inert, an empty aluminum can doesn't ring either. But what's a tuning fork made out of? Aluminum. And those things ring and ring like forever. So shape is really important too. Thinking fast, what if the three solid concrete shelves are bolted solidly together? Take ABS, fill it with concrete, with bolts cast in so they screw into matching threaded inserts in the shelves. Super strong, stiff, and massive, now also damped by virtue of the bolted together columns. When bolted together its almost like one solid block of concrete. It worked! The whole thing bolted together and with the granite on top weighs in around 700 lbs. Its pretty dead too. The sand bed however turned out totally inadequate to control the granite ringing. You could hit the granite and hear it, "ting". Not "tiiiiinnnngg" like before. So better. But still.... So I got another machinists plate and put it on top of the first one, with a layer of Blue Tack in between. A sort of reversible constrained layer damping. That's why there's granite on top of granite here. This by the way is exactly what mahgister is talking about. No one material by itself has exactly the perfect set of properties we want. By trial and error, and with a lot of serious listening, they can be matched together to get whatever balance of sound we are looking for. Or close as we can, given limited time and money. ;)
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Wow. turnbowm, The propensity for ignoring useful information to hatefully go after me is just staggering. Because how could anyone fail to understand? Its clearly stated this was the 1990's. For you who are so challenged, math I know can be hard, that was like 30 years ago. English too, apparently. Takes at least grade school level reading to understand everything in the OP happened way back in the 90's. Is it not clearly stated this is a journey? Its only just begun. Okay so here's how it works. You take a jab like that, turnbowm, boy do I hope you got your money's worth. Because congratulations, you made the list. This is the one and only response from me you will ever get. I am my own moderator, and you are banned. I see your name, I stop reading. Got it? Good. Yes Easy, this being 30 years ago there's probably all kinds of stuff that's better by now. In fact I KNOW there's at least some stuff that's better now. As will become clear, that is the whole point of the journey. One step at a time. Sorry. Okay. Now where were we? Oh yeah, DJ. DJ had this great saying: The best rack is no rack. This being the 1990's and me being tapped out from remodeling all my meager money went into components with precious little left over for fancy racks. Especially not if the rack was liable to only make things worse. (I did of course buy one anyway. But that's jumping ahead.) In the beginning my McCormack amp (yes the one with the vibration control spike, the spike that started it all) was on a plank. Just a bare plank. 2x12. When you see guys with the cinder block and plank looking for a better rack, that was me. Except I didn't even have the cinder blocks! Because, being sound quality obsessed, in order to add a rack it had to be better than the floor. Or at least not too much worse. Which almost all racks are. (Do NOT take my word for it- try it and see for yourself!) For sure this being the 90's all racks were much worse than the floor. All I could afford anyway. Fortunately one thing I figured out early was you can test materials in small pieces. Learned this from the McCormack spike. Manual said try things like a coin under the spike. Sure enough the coin did change the sound! Different materials had different sounds! Tried a whole bunch of different things. Wood of different species (pine, oak, cocobolo, etc) sounds good, but not neutral. MDF sounds neutral (less colored) but not as good, if that makes any sense. A lot of guys prefer the little added euphonic kick of certain hardwoods. I was leery of something that made certain instruments sound "better". I don't want them to sound any particular way at all. That's the job of the recording, mastering, and pressing people. Mine is to display, not editorialize on, their work. This took a good year at least. Long enough to be sick and tired of laying down on the floor to play a record. But also all that time made me good and familiar with that on the floor sound. My rack had better be at least as good as the floor! (DJ would build me a rack, but for about $7k and remember: 1994. That's about a million in today's dollars.) What finally came out of all this, sure enough, did turn out to be at least as good as the floor. https://theanalogdept.com/images/spp6_pics/C_miller_web/TTstand_1.jpg |
