Microphonics

[xcortes]

I'm planning on using sorbotane "vibrapods" under my BP. How about tube dampers? I've heard  about herbies and duende criaturas. Other ideas? Experiences

[Paul Birkeland]

The BeePre is a good foundation on which to test the efficacy of tube dampers.

I think you'll find that those which only contact the tube don't really do anything.  (Sorthobane feet seem to be a nice tweak, Doc B. knows the proper durometer)

-PB

[Doc B.]

I am still working on different approaches. The most effectve approach seems to be to keep the vibration from getting into the chassis in the first place. Once the tube's internal structure starts to vibrate, no amount of junk on the glass envelope is going to do much. Our listening room is on the second floor and thus we have a somewhat springy floor to fight with. One of the best setups we found was a piece of folded bubble wrap under each corner. Of course this was also the worst looking setup. Right now I have 20mm diameter 50 durometer sorbothane hemispheres under my prototype. I have a set of 30mm on order that might work a bit better, but they will not be as neat a fit under the corners. The Sorbothane does help, but I think my ultimate goal is a granite-on-inner-tube kind of setup for most of my gear. I've had these Ikea racks for ten years, time for some experimenting...

[xcortes]

OK.

I'm not concerned at all from movement from the floor as my house is pretty solid (brick and mortar this side of the border) and the shelves sit directly on the walls. I was more concerned by it being close to a corner behind the speakers and thus prone to getting vibrations from the air. Of course the turntable is in the same situation and doesn't seem to be a problem but it's in a massive plinth. I wonder if adding mass to the base would help?

(http://www.bottlehead.com/smf/index.php?action=dlattach;topic=1231.0;attach=671;image)

[Doc B.]

My hunch is that you won't have much of a problem. I haven't noticed much vibration induced from the air, and I crank my system up pretty loud at times. It's the vibration from footfalls hitting the springy floor that are the only really noticeable source in our room. And that is pretty minor. I don't want everyone to panic about the microphony, if it was really bad we would not have put this product out. I find it similar to the amount you might expect from an Eros when you tap the chassis. I suspect that eventually we will find that some particular 300B tube is less susceptible than others. In general I would guess that shouldered envelopes will be a little better than globe envelopes.

So I would say try it stock and see how it works. If you want to try to change things, start with the standard kind of isolation that we use for all audio gear. Maybe start with Sorbothane feet and if necessary move to a massive shelf over springy sorbothane or an inner tube. On the remote possibility that airborne vibration is found to be an issue, that is, the sound is actually hitting the glass envelope and setting the insides into vibration, then maybe some from of acoustic absorption between the speaker and the preamp might help.

[corndog71]

Mapleshade sells really nice brass feet.  I haven't tried them yet but I'm very curious about them.  I want to get a set for my Rega P25.  I also want to incorporate their maple boards too. 

[Doc B.]

I find it curious when manufacturers make isolation stuff out of materials known in the musical instrument business to be particularly resonant. Maple is used for guitar necks because the neck is the heart of the guitar's "acoustical transmission" system. The reason that players like old guitars is that the wood in the neck has broken down a little so the neck isn't as bright and thin sounding. Brass - you mean like in a trumpet?

The goal should be to get the piece of gear on something fairly massive, then put that mass on a large quantity of something very squishy and well damped to create a system with a very low resonance frequency. Vibration gets dissipated in squishy stuff. It might be useful to make a shelf out of a box filled with sand (a pretty good energy dissipation material itself), and rest that on an inner tube or sorbothane hemispheres. I will note here that they don't make many guitars or trumpets out of sorbothane or sand.

[xcortes]

Something that should help while being cheap and easy to test would be some sandbags over the chassis. And maybe some dynamat under.

[Doc B.]

I haven't found extra mass on the chassis to be more effective than the silicone rings themselves. But I haven't tried sand bags, just lead and silicone pucks. If you can get something thicker and squishier like Sorbothane hemispheres I suspect you will get even a little more benefit than you will from Dynamat. Try the bubble wrap idea, it looks dumb but works great. I folded strips into three or four layers - the stuff with the bigger bubbles, not the little ones we use to wrap parts in the kits.

[xcortes]

I guess I'd better start building it to have something to test on

[RPMac]

Xavier, lot of nice woodworking in that picture. Your handy work?

Doc, had a gunsmith friend that had a pad of sorbothane to use as a recoil pad for a 50 cal target rifle. Neat stuff!

Mine will be sitting on a heavy marble top table with my amps. Haven't noticed any micro phonics problems.

[corndog71]

I find it curious when manufacturers make isolation stuff out of materials known in the musical instrument business to be particularly resonant. Maple is used for guitar necks because the neck is the heart of the guitar's "acoustical transmission" system. The reason that players like old guitars is that the wood in the neck has broken down a little so the neck isn't as bright and thin sounding. Brass - you mean like in a trumpet?

The goal should be to get the piece of gear on something fairly massive, then put that mass on a large quantity of something very squishy and well damped to create a system with a very low resonance frequency. Vibration gets dissipated in squishy stuff. It might be useful to make a shelf out of a box filled with sand (a pretty good energy dissipation material itself), and rest that on an inner tube or sorbothane hemispheres. I will note here that they don't make many guitars or trumpets out of sorbothane or sand.

I have to admit, I thought something similar when first perusing their catalog.  But the maple boards are pretty thick which I would think would be less resonant.  The bigger brass feet are pretty massive.  Again, I haven't tried them but have read many positive testimonials. 

I currently use thick pieces of shipping foam in my set-up.  You can jump up and down and the record won't skip.

[Demsy]

Anybody has tried using acrylic? I'm thinking of using 8mm or 10mm thick for the base of the Paramounts, as it's size is only 30cmx30cm, or maybe even thicker if needed. Acrylic is known as 'acoustically dead', isn't it?

[Doc B.]

Acrylic is more dead than metal, but it's still pretty hard material. You really want something as soft and squishy as you can get away with.

[Jim R.]

I've had a pretty good amount of experience with a lot of different isolation approaches and products, and I do have to say that overall, in general, the Mapleshade stuff absolutely does what it claims and does it very well.  However, I've never had a piece of gear that was truly susceptible to airborne or external vibrations, and in that case, I do believe Dan is right with the isolation approach.  The mapleshade approach is based on a whole different take on the problem -- that the internal vibrations in a piece of gear need to be drained out of the piece and into something that have naturally pleasing resonances -- even as minute as they may be, which is why the massive feet and boards.  Of course all of this works much better if you have a solid, massive, and extremely rigid rack to begin with.  So, take an amp like the s.e.x. which seems very immune to outside vibrations, but still has a power transformer which will be the source of most of the vibrations this amp will experience.  In this case it is probably advantageous to use the heavy brass feet either directly into a very rigid rack, or into one of heir thick maple boards, which is then in turn isolated from the rack with some sort of compliant substance.

I recently took the set of mapleshade brass micropoint feet I bought for my dac and placed them under a inexpensive but decent CD player in the other system, which is on a mapleshade rack, and the change was not subtle at all.  It took this $700 player and made it sound more like a $3500 player using it's internal dac, but when used as a transport, the improvement was even better.

So, it's hard to say which approach will work best in any given situation, but the one thing I can say with confidence is that the mapleshade system has never made anything sound worse -- maybe sometimes there is little to no improvement, but unlike a zillion other products -- some cheap, some insanely expensive it was a real crapshoot as to whether or not the sound would be made worse, and unfortunataly, it often was.

I don't say this lightly beecause everybody's situation is different and I was totally and completely skeptical about the mapleshade stuff at first but a lot of experience (this is the 3rd rack of theirs I've owned, not to mention a whole lot of their other products) I simply cannot think that they are onto something.

P.S. -- I wish I could use their cables, but my cat is way to attracted to them and with their micro thin dielectrics, a cat can easily runin the cables with one bite.  Don't ask me how I know :-).

So, the stuff isn't cheap, it's expensive to ship, but if you are willing to try it, you may find it pretty good for your overall sonics.  I have and will continue to do so where it makes sense.  And no, I'm not on their payroll and have zero to gain from relating all this, just that maybe someday some of you guys may try this stuff and be as pleasantly surprised as I was.