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DIY Air Bearing Linear Arm
DIY Air Bearing Linear Arm
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Old 24th August 2016, 11:27 AM   #111
niffy is offline niffy  Europe
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Join Date: Nov 2013
Location: Dartmoor
Hi Jim,

I'm a bit confused about your implementation of the air suspension. The SME 20 as standard is hung from compliant rubber o-rings. These allow the base of the deck to move both laterally and vertically whilst the suspended chassis remains stationary. If I remember correctly SME tuned their suspension to 2.5hz with the ability to user-tune this by increasing or decreasing the number of o-rings used. It appears from your description and photos that you are now supporting the vertical componant using the air bearings, which I assume are the pad type, and using the o-rings solely to keep the chassis aligned over them. My problem is that this type of air bearings is very stiff vertically whilst being free moving laterally. Even with the high mass of your deck this high level of vertical stiffness will result in a suspension tuned to a very high frequency, effectively shorting it vertically. In other words you will have only lateral suspension and no vertical suspension.
Have I misinterpreted your description? Are you actually supporting the whole deck, suspension and all, and if so how are you controlling lateral movement?
Have you performed any comparison listened tests with and without the air suspension whilst using the same arm, cartridge and system? If so, how did it effect sound quality?
I'm asking these questions as I have great respect for you and all the fine work you have done and I am always looking for new approaches and techniques that I may wish to implement to improve my own system.

Niffy
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Old 25th August 2016, 12:21 PM   #112
super10018 is offline super10018  United States
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Join Date: May 2010
Hi Niffy

Excellent question. In fact, I didn't think the way as you do.

The suspension system on SME is still there, but it doesn’t hold the top chassis by itself. At first, if you go back this thread, you can see I made a suspension system, I called it as mini Brooklyn Bridge . The suspension system of SME combined with my suspension system, mini Brooklyn Bridge, to hold top plinth and both air bearing arms and arm’s bases because SME suspension system alone isn’t strong enough and can’t hold the both tonearms and its base. The combination of my suspension system and SME’s did allow vertical and horizontal movements.

To my understanding, ideal turntable platform should eliminate outside resonance transmitting to cartridge, and to the stylus. For o-ring suspension system, outside resonance will still transmit to the stylus in certain degree. O-ring can’t completely eliminate outside resonance.

According to New Way air bearing, air film has very high damping factor. I don’t know the damping factor for SME’s suspension system. So, outside of resonance will be effectively damped by air bearings.

Now the question is that which method is more effective comparing rubber o-ring and fancy air bearings. I don't know.

On my turntable, it is the combination of SME’s suspension system and air bearings. Of course, air bearings play main role here. There are not much of vertical movements, but some because SME's suspension system is still in use. However, horizontal movements are very loose now. My goal is to eliminate any outside resonance which may transmit through mechanical device.

Speaking of the sound with air bearing feet, I think bass is tighter, and background is quieter now.

All criticisms are welcome. So, you don’t need to worry. I am just a hobbyist and can be wrong.

Jim
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Old 25th August 2016, 04:21 PM   #113
niffy is offline niffy  Europe
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Join Date: Nov 2013
Location: Dartmoor
No criticism intended, just inquisitiveness and intrest.
I know from my development work on the isolation system for my deck just how much difference a well sorted suspension can make. My deck is a cross between a suspended sub-chassis design and a solid plinth deck with a dedicated isolation platform. The deck and isolation platform being fine tuned to each other. I ran the deck as just a solid plinth deck for about a year whilst I was building the isolation system. The addition of the full suspension is probably the single biggest improvement in sound quality I have achieved. Greater than all the improvements that my investigation into bearings have wrought. Possibly even greater than upgrading my cartridge to one costing three times as much. The deck is now almost immune to outside influence. So yes a well sorted suspension is really important.
Of course the most important things with your implementation is that you have improved sound quality over the previous incarnation and that you are happy with the results.

Niffy
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Old 25th August 2016, 08:22 PM   #114
super10018 is offline super10018  United States
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Join Date: May 2010
Niffy,

Actually, my table is sitting on a very heavy diy stand. I think the total weight is over 200 lbs. Please see the drawing for the stand. The hand balls are actually sitting in the sand. I used bicycle tire before. The problem is bicycle tire could not keep the air pressure for long time. I had to pump the tire from time to time. The stand makes huge difference for table like VPI, which has no suspension system. It makes difference for SME, too, but it is not as huge as for others because SME has nice suspension system.

So, back to the SME table, if there is varbration, it comes from mostly the motor which sits on the bottom plinth of SME table.

Jim
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File Type: jpg stand.jpg (38.1 KB, 377 views)

Last edited by super10018; 25th August 2016 at 08:27 PM.
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Old 26th August 2016, 03:01 AM   #115
super10018 is offline super10018  United States
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Niffy,

Would you share your design if you don't mind? Thank you!

Jim
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Old 26th August 2016, 03:47 AM   #116
niffy is offline niffy  Europe
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Join Date: Nov 2013
Location: Dartmoor
Hi Jim,

That's a good solid table design. The open sand tray is a great idea. I used to use motorcycle inner-tubes sandwiched between two paving slabs for my equipment supports. I never had issues with the tubes going down though I did find levelling them could be a bit tricky. I would still be using them now if it wasn't for WAF.
Is it my decks suspension/isolation design you wish me to share? Although it's quite simple the full description would be quite long-winded and way off topic for this thread. It might take a while to type up but I'm happy to share.

Niffy
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Old 8th September 2016, 06:36 PM   #117
super10018 is offline super10018  United States
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I have been listening to the 1” air bushing tonearm for weeks now. I used same cartridge and same records to compare it with 3/4” air bushing arm. After many listening sessions, I think it is safe to say that 1” air bushing has the best sounding comparing to 1/2” and 3/4” air bushings. One inch air bushing’s sound is more musical. Its sound stage is “bigger” than any other sizes of air bushing’s. Its sound has a kind of authority. Bass is improved as well. Here are two videos I made.

https://youtu.be/QfOqodJHeXw

https://youtu.be/iE06iaPpqco
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Old 13th September 2016, 03:00 PM   #118
niffy is offline niffy  Europe
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Join Date: Nov 2013
Location: Dartmoor
Hi Jim,

Your latest creation is not just your best sounding but also your best looking. You might have a hard time convincing people that you built it yourself.
I wonder what the proportion of the sound quality improvement is due to the new air bearing and what is due to the improved carriage construction. Of course this is an impossible question to answer, the overall improvement being due to many factors. Excellent job.

Niffy
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Old 14th September 2016, 01:19 AM   #119
super10018 is offline super10018  United States
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Join Date: May 2010
Hi Niffy,

Thank you!

I can’t say for sure what contribute to what, but I can do some educated guesses based upon my experience.

First, bigger air bushing will improve sound stage. From my experience, I started with 1/2” air bushing, then, 3/4” and finally 1”. The sound stage was improved as the size of air bushing getting bigger. I think bigger air bushing provides large air contact area. Larger air contact area will keep the stylus to follow the groove precisely.

Heavier mass of carriage may improve bass. As you know, bass information are lateral movement. Tracking lateral groove correctly needs cartridge to keep relatively stable. Heavier mass of carriage has stronger down force of gravity to keep carriage stable. In my experience, I started with 90 grams polycarbonate carriage combined with counterweight, etc. Then, 120 grams aluminum, 160 grams aluminum, and finally 200 grams carbon fiber with aluminum bushing. 200 grams has the best bass replay.

But for mechanical linear tonearms, heavy mass of carriage is not desirable because heavy mass will increase friction. For air bearing tonearm, it is not a problem with heavy mass.

The full carbon fiber head shell and carriage may reduce the noise and make the sound more natural and musical. Aluminum head shell and carriage may provide slight punchier bass and higher dynamics. But carbon fiber does make sound more balanced without lacking bass information. Carbon fiber makes sound more organic. You may remember that I was complaining the carbon fiber I bought was not as solid as I expected. But now, I can’t say it is bad or good. Although I sank the head shell in epoxy, I touched the head shell. It was very hard. But its deep inner may still be kind of loose. It may actually provide better anti resonance feature.

I generally prefer full carbon fiber head shell and carriage at this moment. However, the lot of 1” air bushings I bought consists 4 air bushings. I have enough air bushings to do some experiments. I also have some 2024 aerospace aluminum and a piece of magnesium round bar in hand. I may try to make an aluminum mixed with magnesium head shell and carriage. Magnesium is very “dead” material as lead.

Jim
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Old 14th September 2016, 01:08 PM   #120
super10018 is offline super10018  United States
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Btw, I don't mind it is off the topic if you can share the design of your decks suspension/isolation.
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