DIY equipment racks - any acoustic / dampening tricks to share?

 

Silver Member
Username: Varney

BirminghamEngland, UK

Post Number: 376
Registered: Sep-04
Hey all,

Looking at the price of equipment racks and hi-fi furniture, I'm driven immediately by their prices and often hideous looks into building my own.

So - here's the techspot for any likely lads to dump a few hints, if you'd be so kind:

I'm looking at making something which will last through future upgrades - so that in years to come, it remains as a solid placement for new and better kit.

My prefered material, if making a cabinet type is wood. I can use real timber or MDF, but reckon that MDF will not only be cheaper, but more acoustically sound.

Then again, I have the idea to make a rack-type pole construction, using sqaure wood I can turn myself or perhaps banister-rail to save time.

Okay, so with the latter, I'm planning on using this as a sturdy subframe, which is hidden by an outer shell which resembles a solid 'antique' style cabinet. I plan to construct each shelf section as a seperate unit, which will be spiked to the next one down (like a multiple bunk bed if you like), in an effort towards isolation/vibration damping (you've seen the ads!). The 'cabinet' will be no more than a cosmetic shell, which doesn't actually touch the inner rack, to isolate it from the real supportive structure, since it will be made from a thinner plywood and either stained or grained to give the appearance of solid oak. I'm also contemplating metal hinges and other ironmongery on it - another good reason to isolate the panels from the superstructure.

Which would be better in the long run to use as the actual shelving material - solid wood, MDF or glass?

Any other acoustic/dampening tricks in a rack system I should be aware of?

Any additional ideas and possible advice welcome.

V



 

J. Vigne
Unregistered guest

http://www.cognitivevent.com/sandbox.html

I've got a DIY stand somewhere, I'll keep looking.


 

Silver Member
Username: Rick_b

New York USA

Post Number: 821
Registered: Dec-03
V,

www.mapleshaderecords.com

Please look at their racks and platforms, and read why maple is the best choice, in their opinion. Also look at the brass isolation cones. I can attest to these. I have used and recommended them for years.
Cheers!
 

J. Vigne
Unregistered guest

I find the best way to go about DIY is to look at the way others have done their commercial product. Unless you want to reinvent the wheel, that is. Most of the hardware for stands and many tweaks come from another product being put into use in a hifi system. These pieces of hardware are available if you want to seek tham out.

http://www.enjoythemusic.com/magazine/equipment/0502/grandprixaudio.htm

http://www.enjoythemusic.com/magazine/equipment/1000/cheaptweaks.htm



 

J. Vigne
Unregistered guest

http://www.enjoythemusic.com/magazine/equipment/1203/isolationshootout.htm

 

Silver Member
Username: Ca_convert

CardiffUK

Post Number: 129
Registered: Jan-05
Varney, this is going to be an interstin project. I am really keen to hear how you get on with this, since I am also in a similar position.
 

J. Vigne
Unregistered guest
There is, at this point, one more layer of disagreement among well heeled audiophiles concering equipment stands. There are basically three and one half schools of thought on how the rack should be built. The concepts are: rigid and heavily damped; rigid with cone type isolation; rigid with a suspension of the shelves and, favored by the Linn crowd, rigid and light. All try to isolate the shelves and mostly vary only in how they manage this task. Naturally, each type has its own "sound" and can be used to tweak your system even further.

Some manufacturers will combine methods to create a suspended unit with damped shelves or some other combination. Steel, glass, acrylic, marble/granite, MDF, solid hardwoods such as maple and beech and exotic items such as carbon fiber skins over an eggcrate interior are used along with dampening materials such as sand, lead shot, kitty litter, silica and air bladders. Isolation comes in the form of cones, feet, pads, slabs, ball bearings and inflated bladders and balls.

It becomes a tiresome job to sort our all the individual ideas behind shelving. On top of the basic design many racks allow the user to tune the stand to their system. It is almost as complicated and prone to exageration as cables. If you have access to "HIFI+", what appears to be a British magazine, they did a survey in the 15th November issue, #34.



 

Silver Member
Username: Ca_convert

CardiffUK

Post Number: 134
Registered: Jan-05
The interesting question is whether to connect your units to "earth" as rigidly as possible, which would perhaps necessitate very rigid supports, or to isolate them. I can see the need to either bolt the units directly to my concrete floor, or to suspend them from the ceiling with long rubber "springs". I'm trying the latter route first for obvious reasons.

Those links you provided Jan are interesting, if perhaps slightly more difficult to follow than my own disjointed postings :-)
 

Silver Member
Username: Varney

BirminghamEngland, UK

Post Number: 380
Registered: Sep-04
Fantastic response guys! Will get back to you soon when I've had chance to read thoroughly and look at all the relevant links posted. Cheers,

V
 

Silver Member
Username: Ca_convert

CardiffUK

Post Number: 136
Registered: Jan-05
The cheap tweaks article is particularly amusing. I have just found in my kids toybox some discarded "goo", which is a jelly like substance which has very little elasticity. The problem is containing it, since it has has liquid properties.

I am also considering using plasticine, which is unlike Blu-tak in that it has no elasticity at all. I used some years ago to line the internal seams of a pair of speakers I owned to good effect, since it has very good damping properties.
 

Silver Member
Username: Varney

BirminghamEngland, UK

Post Number: 382
Registered: Sep-04
I am led to believe, through looking at a British portrait painter's site that Blu-tack is hard to find in America. The reason he uses it, is that it makes about the most efficient and verstile pencil erasor known to man - that, and the fact he's found a niche market in exporting the stuff. Just about everything I own is blu-tacked down to the bench (including the wife - hah! No, I jest - I could never own her outright with my income!). I don't think plasticene is really 'sticky' enough to hold everything down. Doesn't it cool down and become brittle? Well, if you've used it, then that is proof it works I suppose. Dampening properties, however, I can definitely see would be in this material. It gives me an idea, now you come to mention it....

V
 

Silver Member
Username: Ca_convert

CardiffUK

Post Number: 138
Registered: Jan-05
I'm not sure you will use it for its adhesive properties when trying to find a good isolator or damping material.

Blu-tak is exhibits some dilatant material characteristics in that it becomes elastic at high strain rates (i.e. it bounces..just), but yet you can pull it apart at lower rates (a bit like cornflower and water mixture). This is because the polymer strands are long enough to become intertwined to such a degree that they act as a rubber at these high strain rates, such as would be found in vibration. Plasticine on the other hand is the opposite in that it (like clay) is thixotropic whereby high strain rates reduce its elasticity. With enough strain they can behave like a liquid. But, the dilemma is that a liquid is pretty good at transmitting sound pressure waves, which is not what we want. From experience, this shear thinning is not so prevalent as to make plasticene useless. In fact, its modulus is still probably too high to be a really effective isolator, but would work well pasted to the surfaces of your rack!

You are correct that it becomes harder when cooled, but unless you listen in a refridgerated room this will not be of any significance.

I have had more time with the bubblewrap, and I can detect definite improvements in various areas. The one area that has hit me like a hammer is the focus of the soundstaging - this is the first time that I have heard instruments outside the edge of the speakers (U2 - Achtung Baby - the opening guitar riff is about 2 ft left of the left hand speaker). The bass is also much cleaner, with less muddiness (again I can follow Adam Claytons descending bass line easily, and Flea's playing on the peppers By the Way comes across much more authoritavely).

So, next stop will be some form of integration of plasticene and bubble wrap. I'll make a set for anyone, just send me a cheque for £200 all yours ;)
 

Silver Member
Username: Varney

BirminghamEngland, UK

Post Number: 387
Registered: Sep-04
Hehe! Looks like you got yurself a business plan there, CA :-)

I like this - I can see how plasticene would do the job, as you say. Read about Plastozote, if you can though. I haven't actually tried any of these methods yet, but will go the extra few yards when I have built the rack-unit I've been talking about.

V
 

J. Vigne
Unregistered guest

As the back room of my home will become the new music room once the remodel is completed, I'm going to need another rack in that area. (The rack the system sits on now has been taken over by other equipment for the HT system.) I think I'll have the advantage of being able to place the rack in a large closet, so appearance is up to my tatses and not what anyone else might see. Having read a bit on the structure of the new racks and the advantages and disadvantages of each type, I've almost decided to do a hybrid of two suspended stiles and one post fixed to the floor for stability. Since I have a mix of tube and solid state equipment that will go on this rack, I'll try to benefit the tube first. If the tubes are happy, the ss is likely to be happy also. My turntable already has a support system that has worked well for a number of years so it will not change. My plan is to suspend the most important shelves on a filament stretched between the two suspended posts with the third, back support at the fixed post being a spiked support. I hope this will give me the needed isolation in the rack itself with just enough stability that the rack will stay in place as I need to work with the system. I've accumulated enough isolation devices over the years (spikes, cones, footers, isolation platforms,etc,) that getting the desired results out of that rack, isolated itself from the main room, shouldn't be much of a problem. I hope. Let me know what you find in your reading and experiments.

In the US the substitute for plasticene was Mortite. Good dampening properties but it would eventually dry out and become more of a problem that a solution. BluTak is a trade name apparently. Here there is a product named PlastiTak that is the equivalent. Sold in a 2x6" bar for $1.99 at The Container Store. Photo mounting plastic is the same thing from what I see, though its packaging raises the price slightly.

Sorbothane has the unusual property of converting motion to heat very effectively over a wide range of temperatures and for a long period of time. The site I linked to will probably have better information than I can pull out of my memory right now, but a favorite use for Sorbothane is as an adhesive panel that can be mounted inside the chassis of CD players, pre amps and integrated amps. It will withstand the heat from all but the most inefficient amplifiers. It can be placed on individual parts to damp vibration is small pieces, or on a large expanse of circuit board. I've used small pieces in my tube pre amp to lift the circuit board free of the chassis and to isolate the top and bottom panels of the chassis from the body of the unit. (A doubled sandwich bag filled with lead shot sits on the top panel of most of my electronics to damp vibrations in addition to the Sorbothane inside.) Several companies sell a footer that is made from Sorbothane. AudioQuest has the Big Foot that has a recess for a small or large cone to fit under the foot. The combination of the Sorbothane feet with an aluminum cone under each foot and the pieces described above have made the largest improvement in my tube pre amp. I believe Norsorex has superceded Sorbothane as the most efficient dampening material, but is difficult to find. Sorbothane is the material you'll find in some insole inserts and mouse pads.

The Vibrapod seems to have replaced the Sorbothane feet at a much lower cost. $6 each in the US.

http://www.vibrapod.com/

My memory is the bubblewrap has been replaced by two items. Either an inflatable inner tube or an inflatable hemerrhoid ring. Both allow some level of adjustment to the amount of firmness need by an individual piece of equipment. A simple box frame is placed around the inner tube/ring to maintain appearances. Two small inner tubes can be placed under a heavy piece of equipment to keep the power supply transformer from weighing down one side. One can be inflated to a stiffer level while the other provides soft isolation.

An effective platform for CD players and amps is a triple layer of MDF from the harware store. Stop at the car stereo shop and buy a package and can of panel damping material. The material is a good deadening device, though it will not stop vibration as effectively as it prevents vibration from passing through. The panels are self adhesive and can be placed between each layer of MDF. The panels can also be used on the back, bottom or sides of a speaker to deaden the vibrations. (Be careful as some manufacturers have worked inevitable resonances into their design and killing the vibration could change the speaker in a direction you may not like.) The can is a spray material that can go inside a CD player's top panel. Top the MDF with a final sheet of glass, marble or acrylic. Ask at cabinet shops that install kitchen counters if you can buy a scrap of granite or marble that was left over from installing a sink into a countertop. A few small ball bearings placed under this sheet of material will also isolate the top sheet effectively. Weight will usually hold it in place.

One more DIY that comes from the aftermarket is a foot scrubber. The open cell abrasive pads sold to remove a callous from your heel has one or two layers of cork rubber cemented on the top and bottom. These can be doubled for better isolation or hollowed out for a ball bearing to sit underneath. I saw one where the user had partially drilled a hole through the pad and inserted an arrowhead to act as a spike.

The sand box type isloation boxes can be filled with metal scraps to act as an RFI barrier to stray fields around the equipment. BrightStar markets models that do just this function. My understanding is metal shavings from a machinist's shop can be substituted or a box of small screws. The metal is placed above the unit's power supply transformer. The sand box can also be a hybrid with an air bladder, metal and sand combined.

I think that's all I have right now.

When do we tackle the room itself?





 

J. Vigne
Unregistered guest

http://www.polymerambassadors.org/happyandsad.pdf


 

Silver Member
Username: Varney

BirminghamEngland, UK

Post Number: 389
Registered: Sep-04
Well, (Heh!) I for one am not going (Ahem!) into the Chemist to ask for an inflatable (Snigger!) hemaeroid ring!!! (Pwpppfff!)

Blu-Tack is, as you rightly point out, a trade name. However, it is (apparently) not the same as the equivalent. I have tried the pink 'Pritt Buddies' and other (blue) generics and can testify nothing quite is as sticky and long lasting as the original 'Blu-Tack'. But anyway....

" A simple box frame is placed around the inner tube/ring to maintain appearances."

Way to go, man - I like it!

All the rest - noted and kept for reference. Thanks for sharing, J.

V


 

J. Vigne
Unregistered guest

I've used the PlastiTak for years. From everything I've read about BluTak, they would appear to be equivalent other than the color. I have applied the PlastiTak to multiple pieces of equipment with the desired results. It adheres instantly to make a bond that cannot be dislodged vertically. A speaker on a stand has to be twisted horizontally to break the seal. There is no deflection in any direction while the bond is in place. The material remains pliable in the package or on the speaker stand for years. If I change my mind, I can roll it back up into a ball and reuse it later. I finally used the last of the package I purchased over eight years ago and the last piece was as compliant as the first though the package had sat open all that time. I can say I'm quite pleased with the performance of the PlastiTak for anyone who cannot find the original BluTak or who wishes to save a few dollars. (That nasty exchange rate that George has let run up strikes again.) I can't comment on the photo mounting material since I've never tried it but have only seen it mentioned as an alternative.

As to the hemerrhoid ring, the answer is simple. Send the wife.




 

Silver Member
Username: Cheapskate

Post Number: 101
Registered: Mar-04
regarding "blu tack", i've been using a "dollar store" knockoff variety to couple my superzeros to my sand filled stands and it works just fine. in fact, it works TOO good whenever i need to tweak my speaker's positioning. you'd thing that once to position speakers, you'd be done. LOL i guess stands "settle" on carpeted floors.

as to diy stands, just go for mass to damp them. instead of one layer of 3/4" mdf, sandwich two together or even 3 if you want to go into overkill mode.

i bought a sub cabinet that was listed as having 3/4" mdf, but only the front and back did, so i lined the insides and pedistal with pieces of 3/4" mdf which damped the box just fine. it doesn't produce a "note" anymore, just a slight "click" sound when rapped.

if you built a 1 1/2" mdf rack, it would take some serious (as in earthquakes or parties of dancing people) to induce major resonances in your system i'd think unless you have really bouncy floors.

whether you couple equipment to your shelves (1 1/2" too ?) or isolate with some sort of suspension (pucks bladders etc.) a massive diy rack would isolate more than even $1000 racks.

moving it would be a pain though.

less recommended is lining your rack with lead to dampen it for health reasons.

if you have the tools and skills, you can easily make better and cheaper wood products than most products. if i had the tools, i'd trade my 12" sub in for a punchier more neighbor friendly 8" or even 6 1/2" sub.

hope something here helps you. just make sure you build your rack large enough to allow for equipment upgrades down the road and consider adjustable shelves.

if you want a really cheap massive rack... you could always buy bricks and slabs and start stacking. (marble?)
 

Silver Member
Username: Ca_convert

CardiffUK

Post Number: 139
Registered: Jan-05
Jan, such thought provocation is indeed intriguing (as ever):

Now to the room...I am driving 4 25ft piles into the foundations of the music room floor, and have built the house on a 2 ft bed of clay slurry which should both provide a decent energy drain for unwanted equipment and room resonances through the deep piles, but will also filter out the ULF noise from passing cars / trains etc though the thixotropy of the slurry (or maybe its pseudoplasticity...semantics need not worry us unduly).
I have also painted the edges if my carpet slippers green.

The next step will be to provide a seperate power supply for each component (literally) using discrete 3Kw diesel generators sited approx 100 yards from the listening room. These generators are house in individual buildings, each isolated and acoustically damped. The "mains" supply will be fed by underground shielded OFC cables. I am wondering about the benefits of what might be called "direct coupling" of the external power supplies to the input rails of the amp and cdp, thereby ridding unwanted noise from the transformer in the power supply channel. I am sure that microprocessor voltage control to within +/- 0.001V is achievable. Can anyone tell me if a DC supply would be advantageous (thereby exterminating nasty 50Hz hum), but am not sure about DC supplying an AC output stage..

Returning to the real world, plasticene does not dry our over time (I know having picked it out of carpets many years after the original felony was committed). I am going to try to cover the underside of the one shelf with some form of foam pad material, which should also assist in the reduction of the shelf resonance.

I had toyed with the idea of tuning the shelf system to compliment the ~40Hz tuning of the bass port on the speakers, but the additional mass required would probably ruin my carpets. I have also though about changeing the density of the air through some kind of inert gas addition.

I will report on the foam pad effects later, the other ideas I cannot be yet certain of.
 

J. Vigne
Unregistered guest

The matter of mass takes us to the Linn approach. In this case, rigid and light. It is a rejection of the idea that mass alone will act as a dampening agent. It is true that mass will take away more energy that light, but the problem becomes what is happening to the energy while the more massive piece is passing the information. The more massive the stand, the lower its resonant frequency. This will place the resonance at a point that is likely to be in a sensitive area of the frequency bandwidth, either exciting similar frequencies in the equipment or simply acting as a drone added to the whole. A light stand will push the resonance up into the midrange or higher. This would be even more destructive if the resonant frequency fell in an area sensitive to our hearing except for one thing. The light stand will release its energy quickly, while the massive stand will hold the information due to its density. Therefore the Linn approach is to use a fairly light material, damped by light weight material, which allows the signal to enter and exit quickly. The more massive stand will allow the resonance to "hang around" for a while and release the energy into the systen after the note that excited the resonance has passed. You can look at the differnce as quick and dirty vs. slow and dirty. The trend in stands today falls somewhere between the two extremes of massive or light. Mostly the effort is to stop the transmission of the resonance from entering consecutive layers of material. The suspension accomplishes this as do the spikes and cones. A dense material such as the sandbox employs attempts to damp the information before it can be passed to the shelf on top of the sand. The air bladder makes the same attempt using the isolation of air. By itself, the spring of the air bladder might create other problems. Always a trade off.

In the case of the MDF shelving, the more layers you have the better. But adding a dissimilar material between the layers will change the frequency each layer passes and will diminish the resonace with each successive layer. If the material adds dampening properties, as the panel dampening sheets will do, a layer of MDF/sheet/MDF/sheet/MDF will get the most benefit. Constrained layer dampening material will give more benefit, but I know of no inexpensive source. The three layers of MDF alone will all have the same frequency they will pass one to the next. Top the MDF/sheet combination with yet another dissimilar material and you add another layer of filtration. Add a spike or ball bearing to make the smallest area of contact between the top MDF and the top material and you have cut down, and altered the transmission path. The same effect can be had by placing the spike or bearing between the layers of MDF if you add a small bit of material that will maintain the smallest point of contact.







 

Silver Member
Username: Ca_convert

CardiffUK

Post Number: 141
Registered: Jan-05
Jan, your comments about MDF layers are exactly right. This boundary layer damping characteristic is also evident in metallic materials (I once conducted a study of heat treatment effects on chiming properties of tubular bells). The best material for transitting vibration are homogenous elastic materials. The boundary layer is in effect a disruption of the mechanical "spring" that is conducting the mechanical vibrations.

 

J. Vigne
Unregistered guest

Then I'll ask you what your opinion is of the mass vs. light idea. This has been the prevalent approach in audio for years. How well does it stand up?


 

Silver Member
Username: Ca_convert

CardiffUK

Post Number: 142
Registered: Jan-05
I think that firstly there needs to be consideration given to the size of the energy sink. Practically, if you connect to the earths "mass", then the resonant frequency is so low as to be non existent. This is largely impractical, therefore I believe that the art of the damping is therefore in the tuning. I have always personally believed in mass is beautiful: coupling speakers to concret pillars and so on. This is borne out by my preference for suspended turntables vs solid plinth with damped feet (interestingly for Linn, this is manifested to some degree between the Axis/Basik vs Sondek). Arguably, if you have a resonant Frequency between 0-2 Hz, then you can manage the dissipation of this energy as heat far more easily (example being a hydraulic damper as in car suspension). Such a system can be mechanically arranged to provide an equivalnet of high order low pass filter.

The "light" approach is I think harder to manage the dissipation, and relies on the material/shape etc. The danger is colouration of the sound in the audible spectrum.

I suspect that in practice, the light material designed approach is easier to obtain acceptable results compared the mass approach, since the mass required is substantial, and the energy dissipation systems correspondigly also.

I do know that to my ears, a suspended turntable placed on a concrete shelf built into a brick wall sounds better than one placed on a wooden shelf. Unfortunately, this is not practical in my domestic situation, though if I had the ideal listening room, then the units would be placed on integrated rigid massive shelves, and speakers likewise on similar structures integrated into the house foundations. It would certainl be an intersting experiment, though I suspect one that has been conducted already many times.

One thing I think needs to borne in mind is that there are two effects: one is the tuning of thefundamental resonant frequency through mass and elascticity of a support, plus seperately the internal damping characteristics of the support materialto dissipate any vibrational energy being transmitted.
 

J. Vigne
Unregistered guest

It appears the trend in the aftermarket racks is to use a fillable column that can be damped with assorted materials, or the use of rigid and light "T" shaped aluminum legs. After that the isolation of shelves is a matter of choice between mostly the suspended and the spiked. The shelves often will vary in material and construction. Shelves for amplifiers receiving less severe isolation and damping than one for a source component.


 

J. Vigne
Unregistered guest

Here's my turnatble support. Three "L" shaped legs spiked to the floor and cross braced. The columns of the legs are filled with concrete and have upward facing spikes. Three layers of MDF with damping material between the layers sit on those spikes. Another layer of marble is on top of the MDF shelf with small bearings between the shelf and the marble. Three 10 lb. diver's weights of lead with ball bearing feet sit on small bearings on top of the marble. The table, a VPI suspended subchassis, sits on spikes on top of the diver's weights. There is an additional 10 lb. weight which has spikes beneath it; this weight is connected to the decoupled motor assembly by one large adjustable spike to eliminate vibration in the motor. The wooden base of the table has been stiffened with additional cross braces at each corner. The base of the table is open to minimize box resonance and the inside of the base has been lined with several layers of lead shot and spray foam insulation. The springs for the plinth have three small bearings on each of the four springs and the springs are damped internally. The plinth is a 19 gauge stainless steel sheet with reinforcements and a 3/4" acrylic layer bolted to the top of the stainless steel with a damping material between the layers. The arm and platter ride on small bearings to minimze energy transmission. The dustcover has a rim of Sorbothane to minimize vibration entering the table from the large surface of the cover and the hinges are decoupled also. The arm rides in a bath of silicone damping fluid. I'm satisfied with the sound.


 

Silver Member
Username: Cheapskate

Post Number: 107
Registered: Mar-04
i seem to remember reading that greater cabinet thickness raises resonant frequencies, but this probably is a factor of sealed speaker cabinets more than open racks. obviously heavier objects will vibrate slower than light ones.

i do know that my sub cabinet made a deep "thunk thunk" sound when i first got it, but after lining it, it makes more of a low level "tick tick" sound. sand filling my metal speaker stands had a HUGE effect on dampening ringing.

regardless of what effect mass has on resonant frequencies, it surely has to lower their level as it takes more energy to move more mass.

you could also try sandwiching two different materials with different resonant qualities to dampen each other's resonant frequencies eg. mdf and acrylic as in the principal of dynamat which is used to dampen body panel resonances in autosound competition vehicles. perhaps someone makes a high density thick rubber sheeting that you could line a rack with to dissipate vibrations. soft materials are great at energy dissipation. that's why metals have a tendency to ring.

hard materials store more energy. soft ones dissipate it. that's the concept behind air bladders or spring tuned turntable suspensions.

mass rejects energy absorbtion and dampening dissipates it.

"inert" materials that don't resonate like lead and brick are good candidates if you want maximum resonance control, but they're a little impractical.
 

Silver Member
Username: Varney

BirminghamEngland, UK

Post Number: 392
Registered: Sep-04
Whoa! After all that, I'm sure you must be satisfied with the sound, J. I don't see how a turntable could be better and more sturdily placed.

V
 

Silver Member
Username: Ca_convert

CardiffUK

Post Number: 147
Registered: Jan-05
Budget, sorry to be pedantic, but to correct some of your scientific assumptions:

Quote "obviously heavier objects will vibrate slower than light ones."

Only and only true of the same material. The resonant frequency of a body is primarily a function of mass AND elasticity.

Quote "hard materials store more energy. soft ones dissipate it. that's the concept behind air bladders or spring tuned turntable suspensions."
Not true. Hard materials have by definition a higher modulus, which means they will transmit vibration faster aswell as posess a higher resonant frequency (remember its a function of mass AND elasticity). Soft material also have the capability of transmitting equal amounts of energy (EPDM at room temperature is not hard, yet is also quite good at transmitting energy), the issue is at what frequency do they transmit, and what are the internal damping characteristics. Air in a bladder has a very low modulus, hence although it will transmit energy at very low frequencies, it does not at high frequencies. The low frequencies do not have much effect on the sound of your system, and are mostly converted into heat (friction) at the material boundaries.

Mass does not reject anergy absorption, a thick piece of copper alloy makes a great precussion device, pretty damn loud, with a long decay! However, damping does indeed dissipate vibration.

I'm still not sure if I should be grinning at Jan's turntable support!


 

J. Vigne
Unregistered guest
Grinning? Tell me why. It is largely an experiment in the school of do something and listen to the results. The problem with that method is always if you leave it alone after you hear what you consider an improvement, there is the possibility there is still a better solution. The spikes and dissimilar materials are based on my knowledge of isolating and dampening vibration transmission. As you stated with your comment on earth grounding being the most desirable, the idea of spikes and cones is to place a large amount of mass on a very small contact point. This is intended to exagerate the actual mass of the unit in terms of weight per surface area of contact. My knowledge says this is about as good a path toward earth grounding as I can achieve without sinking those 25 ft. columns into the Texas soil. The small contact point of the spike should minimize the amount of information that can be transmitted through from the floorboards to the stand. Though the whole contraption sounds like a Rube Goldberg invention, the amount of mass seems to be doing a good job of selective frequency transfer and vibration control, the stiffness provided by the concrete filling moving the frequency upward from the point of even a sand filled coulmn; the dissimilar materials between layers providing a break in the frequencies that are transmitted; the spikes and bearings minimizing the transmission of information from layer to layer while still providing a mechanically solid foundation from layer to layer; the stiffness of the whole system doesn't seem compromised in any way (I've never heard a suspended table sound good on a lossy system); and, the decoupling is at points that can put informatiion into the system (i.e., the motor and cover) that I can't control any other way to my knowledge. As is, the whole system is meant to minimize vibration transfer upward, shift the frequency transmitted from layer to layer of dissimilar material to eventually take each frequency down in level, mechanically ground each layer to maintain stiffness and decouple where I don't have another choice due to proximity to the motor and arm. That was the thinking behind the construction. If you have a suggestion, I'll be tearing this down when the back room gets set up and would try another approach if there is good logic behind the system. As a further note, at the points where I have three spikes, bearings or cones, the order is reversed front to back at each layer. The legs have one spike in front and two in the rear. The MDF to table connection is made with the single spike in the rear so it doesn't sit diectly above the point where energy transmission is at its highest in the lower layer. Anything to contribute?

In terms of b.m.'s addition of material to his subwoofer and the resultant tick from the earlier thunk, my knowledge would say the benefit of the additional material is not in mass but in stiffness. The stiffer material raises the resonant frequency and can be accomplished several ways. In taking this approach, unless I misread his post, a layer of dissimilar material between the layers of MDF would have gone a step further toward making the cabinet inert. Anyone have comments to add?

Again unless I read his post incorrectly, b.m. added the material to the inside of the cabinet thus reducing the overall internal capacity of the box. Since the cavity on the backside of the woofer is a determining factor in the extension of the bass response, placing the woofer in a smaller cabinet will also affect the resonance and the efficiency of the whole system. Though most of the bass response in a powered sub is done with EQ of the lower frequencies, this could shift the resonant point of the whole system upwards and affect, to some degree, the extension of the system.


 

Silver Member
Username: Ca_convert

CardiffUK

Post Number: 149
Registered: Jan-05
Jan,

sorry for any misunderstanding. I was only wondering if you had seriously gone to such lengths for your support. Clearly you have, and in that I am damn impressed!. My "grinning" comments was one of suspected joke, but I wasnt so sure! It certainly wasn't meant is any derisory sense.

I haven't the time to fully read and absorb your post to be able to respond right away, I will do so later this evening.
 

Silver Member
Username: Ca_convert

CardiffUK

Post Number: 151
Registered: Jan-05
The only comment I coud make is that the spikes that are grounding the support will act as couplers to your floor (this is why spiked speaker stands on suspended wooden floors often sound prro since you are exciting the floor). Therefore, any floor vibration will also be easily transmitted back into the support from the floor via the spikes, they cannot act as drains in one direction, and an isolator in the other. It's perhaps only a consideration, and if your floor is solid concrete floor, then they would be ideal.

The multilayer board approach seems highly logical: you have many mechnical interfaces which will absorb vibrations through a decoupled interface; and also using materials of differing modulus, and therefore different fundamental resonant frequencies should act mechanically in the same way as capacitors and inductors add roll off filter effects.

To my own system, I have obtained some sheets of some expanded rubber foam, I cannot be sure what it is but its tradename is Isolene L10. It feels like an expanded EPDM, nonethless it has what appeasr to be the ideal mechanical properties to isolate the cdp and amplifier from the support. I have re-isntalled the system using these pads, and the difference is astounding, but not where I expected. Its in the upper mid, treble areas that are so much clearer. Cymbals now really crash out with great definition, but no hint of harshness. I could hear some detail not heard before, particularly the drum kit ride cymbals seemed so much more clearer and vibrant. I coulkd hear some backing instruments that I simply havent heard before. I feel that the improvement is much greater than interconnects or bi-wiring.
 

J. Vigne
Unregistered guest

ca - If you came to me with a request for what direction to take to get the desired response from your player, I would suggest a better footer. A device that does tend to couple and decouple at the same time. I know that is an impossible feat in reality, but I was taught to look at the problem you're experiencing as a closed loop with information traveling in both directions. As such, the idea is to decouple in the upward path and couple in the downward path. The large surface of the footer acts as a drain while the small contact area on the shelf performs as a partial decoupling device. Like cones, these type of footers are usually describe in literature as mechanical diodes.

This is the purpose of products like the Vibrapod. Read the information on this product and tell me what you think.

http://www.vibrapod.com/


They run $6 each.




 

J. Vigne
Unregistered guest

http://www.6moons.com/audioreviews/vibrapod/cones.html

"
The effects of my inconsequential efforts are numerous and consequential. First and probably foremost, I get bass. Particularly when placed under tube preamplifiers and CD transports, the effect on the bass region is considerable. More bass. Better defined bass. More musical bass."


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