Eliminating Empire 598 motor air noise

[master_fo]

Hi, we all know Papst motors are great, but do produce audible hiss. I was lucky to buy a NOS 698 motor which has no vibration - still its rotor moving air can be audible from 2-3 meters away in a quiet room.
Standard resonant Empire wood plinth enclosure, open from below, actually amplifies that sound.
I did put Sorbothane/cork felt inside long time ago, but was reluctant to alter the classic outside look - but after my recent vibration experiments (in another thread) I have installed ebony spikes that definitely improved both vibration resistance and its own sound. So the can of warms was open, and those spikes were a little tall visually, so I tried adding a bottom for the enclosure, using a handy 16"x12" high-density acoustic absorption tile.
Result exceeded expectations! I would estimate about 12dB drop - most importantly, making it absolutely not audible from listening position. Here are the pics. Sure it can be done cleaner and even more efficient - but this already works great.

 

[Nashou66]

Line the inside of the cabinet with a sound absorbing material like this from QuitePC.com

https://www.quietpcusa.com/AcoustiPack-EXTRA-Sheet-PC-Soundproofing-Insulation

I did this tot he inside of my CRT projector in my theater and it helped a lot with the fan noise .

Athanasios

 

[WaynerN]

I don't hear my motor at all........

 

[master_fo]

I don't hear my motor at all........

There are no quiet PAPST motors. Mine is new, as I wrote, never been used.
Depending on the turntable position in the room and room acoustic, your mileage may vary though.
My TT sits on very reflective MDF shelf in ~3m from listening position, the window behind it and the gap under the table (where most of the noise escapes from) is exactly on the ear level.

 

[WaynerN]

Just because I can't hear my motor doesn't mean it doesn't generate some rotation noise and that was never said. However, the bottom plinth area can become a "loudspeaker" enclosure if its positioned wrong or at a bad elevation I also keep the cover on my motor, also rubber suspension grommets are still soft and pliable. I suspect if the grommets get hard, they will transmit noise to the rest of the table. This may also affect speed and/or adjustments.

My AR-XA motor (Haydon) also makes "noise" if I put my ear next to it, but the plinth has a bottom cover that helps abate some of the little there is noise. My VPI table is pretty much dead quiet. My modded ARmod and ARcom tables are extremely quiet as well.

 

[gadget73]

If its air noise, I'd expect just having a sealed plinth would mostly shut that up.

The down side is being closed you only have the air within the box to cool it down. If you can sneak a temperature probe in there to monitor how hot the motor gets with a closed bottom it might be worth doing to confirm it isn't overheating.

 

[billyz]

I never heard my 598 motor unless it was adjusted incorrectly. My plinth did not have the Bottom cover yours does. I know taking the bottom off the Linn LP12 sounds better too. Might try removing the bottom and leaving it open.

 

[foppy]

Cool that you found that fix.

I lived with vibration noise from my 598 for years, well beyond just air noise. Tried new grommets of course, then wrapped mortite around the inside, various new feet, etc.—still would not go away. The only thing that dampened the vibration was holding my forearms against the sides of the plinth, and I don't like to listen to records that way!

I likely would have tried your suggestion of sealing the bottom with acoustic tile, with the feet you like. But I found another solution.

My 598 motor finally just died. (There's a thread about it around here someplace.) And I was the beneficiary of creative destruction. I sourced a replacement motor from an AK member, and now it's very quiet. I can hear a little whoosh very close, but not from 2-3 meters away. (Our ears' sensitivity plays into this too, no doubt.)

I'm listening to records right now. The arm just lifted, and even with the room windows closed, I can hear many things: a utility truck idling a block away, an airplane in the far distance, the hiss of steam escaping my coffee carafe, the refrigerator running in the kitchen, and occasionally my dog's toenails clicking on wood floors on the other side of the house.

But I cannot hear my Pabst motor.

 

[master_fo]

Cool that you found that fix.

I lived with vibration noise from my 598 for years, well beyond just air noise. Tried new grommets of course, then wrapped mortite around the inside, various new feet, etc.—still would not go away. The only thing that dampened the vibration was holding my forearms against the sides of the plinth, and I don't like to listen to records that way!

I likely would have tried your suggestion of sealing the bottom with acoustic tile, with the feet you like. But I found another solution.

My 598 motor finally just died. (There's a thread about it around here someplace.) And I was the beneficiary of creative destruction. I sourced a replacement motor from an AK member, and now it's very quiet. I can hear a little whoosh very close, but not from 2-3 meters away. (Our ears' sensitivity plays into this too, no doubt.)

I'm listening to records right now. The arm just lifted, and even with the room windows closed, I can hear many things: a utility truck idling a block away, an airplane in the far distance, the hiss of steam escaping my coffee carafe, the refrigerator running in the kitchen, and occasionally my dog's toenails clicking on wood floors on the other side of the house.

But I cannot hear my Pabst motor.

My motor is new - I mean factory new - I bought a NOS replacement 698 motor assembly this year that was wired incorrectly (rotated in reverse direction) - so that was quite an assurance it was never used. I also opened the cover to find out for sure what was the deal with lubrication - and sure enough there was plenty of grey molybdenum or lithium grease on the thrust plate, untouched. The motor does not have any vibration, and I have new grommets. All the sound it makes is airborne - that self-cooling huge rotor makes quite a fan.
The new place I live in Gig Harbor, is very quiet - I actually measured noice floor and it was about 12dB lower than at my previous place in Bay Area - when the arm lifts, I hear nothing. That definitely adds to the effect .

 

[master_fo]

If its air noise, I'd expect just having a sealed plinth would mostly shut that up.

The down side is being closed you only have the air within the box to cool it down. If you can sneak a temperature probe in there to monitor how hot the motor gets with a closed bottom it might be worth doing to confirm it isn't overheating.

Absolutely. That's why I did not try to close the bottom completely. Especially that I made a big round hole in my TT shelf to route lightweight balanced tonearm cables I made myself, directly down to the SUT on lower shelf so that the cables do not touch anything else and don't interfere with tonearm suspension. No uptake in temperature registered.

 

[master_fo]

Update: this weekend I made an interesting observation about Empire 698 motor - its airborne noise gets a lot quieter when its bottom is very close (1-2 mm) to the shelf underneath it. So this is part of the reason the bottom cover helps.