Multiple Belts?

Multiple Belts?

Postby fsonicsmith » Sun Sep 18, 2016 11:11 am

I ordered an HRX pulley and extra belt for my Prime yesterday. I have a second belt on hand already so I will soon try two belts and three. But I have to wonder about the physics of the whole endeavor. Besides the simplicity involved, the popularity of belt-drive has to do-I thought-with vibration isolation. Why do some hard-core audiophiles jettison the belt and use thread with a surgeon's knot? To further reduce vibration transmission. So, it seems counter to that design philosophy to use multiple belts. Seems to me that the more belts between motor and platter, the more vibration transmitted. So, why are two or three belts better?
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Re: Multiple Belts?

Postby Pevo » Sun Sep 18, 2016 12:25 pm

My understanding is the multiple belts make up for the very slight give and take that rubber belts, by their nature, provide. In other words a very slight oscillation in speed from varying loads of the cartridge tracking the groove and belt creep while circumnavigating the pulley and platter. The alternative belt materials, e.g., silk thread, do not have the "give" that rubber does. Personally I also wonder how a silk thread can "get a grip" on the pulley, but it obviously works for some folks. I would say all drive options involve compromises, some more agreeable to some folks and others more agreeable to the next group.
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Re: Multiple Belts?

Postby Bill Stevenson » Sun Sep 18, 2016 3:55 pm

The first thing to think about is how a belt works on a turntable. Think of it this way. The torque of the drive motor pulls on the belt and a belt made of an elastic material like rubber stretches as it brings the platter up to speed. Once up to speed, the tension on the belt relaxes a bit and the belt stops stretching so much until the platter starts to slow, at which point the torque of the motor pulls on the belt and stretches it again and so on. So a belt made of an elastic material is constantly stretching and relaxing. More belts reduce this action without appreciably affecting transmission of vibration or noise from the motor. I have 2 belts on my Prime and found that to my ear going from 1 belt to 2 made a slight difference in favor of 2, especially when using the periphery ring. I could detect no appreciable difference going to 3 belts. That is me, my 68 year old ears. YRMV.
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Re: Multiple Belts?

Postby Ayre Conditioned » Sun Sep 18, 2016 5:13 pm

When you said going from 1 belt to 2 made a slight difference in favor of 2 exactly what did you hear?
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Re: Multiple Belts?

Postby Bill Stevenson » Mon Sep 19, 2016 10:08 am

Ayre Conditioned wrote:When you said going from 1 belt to 2 made a slight difference in favor of 2 exactly what did you hear?


Crisper, better transients, especially on percussive sounds, like piano. Better bass, rosen on the bow type stuff.
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Re: Multiple Belts?

Postby Brf » Mon Sep 19, 2016 10:13 am

Another benefit of using multiple belts is less belt maintenance. Using 2 or 3 belts will lengthen the time between belt replacement by a factor greater than the number of belts employed.
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Re: Multiple Belts?

Postby Bill Stevenson » Mon Sep 19, 2016 5:13 pm

Brf wrote:Another benefit of using multiple belts is less belt maintenance. Using 2 or 3 belts will lengthen the time between belt replacement by a factor greater than the number of belts employed.


My HW19 MKIII has been in service using only 1 belt since it was bought new in 1992 or so. I have replaced the belt only once or twice in all those years including once earlier this year. This TT always sounds good to me and in truth replacing the belt has never been done because of a degradation in performance. I can't imagine belts lasting 2-3x longer though. VPI makes good stuff.
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Re: Multiple Belts?

Postby Brf » Mon Sep 19, 2016 6:23 pm

Bill Stevenson wrote:
Brf wrote:Another benefit of using multiple belts is less belt maintenance. Using 2 or 3 belts will lengthen the time between belt replacement by a factor greater than the number of belts employed.


My HW19 MKIII has been in service using only 1 belt since it was bought new in 1992 or so. I have replaced the belt only once or twice in all those years including once earlier this year. This TT always sounds good to me and in truth replacing the belt has never been done because of a degradation in performance. I can't imagine belts lasting 2-3x longer though. VPI makes good stuff.


Don't forget that average VPI platter now weights 20lbs, that puts a lot of stress on a belt. With a lot of talk about the need for 0.001 speed accuracy, belt uniformity along the length is important for consistent linear transfer of power.
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Re: Multiple Belts?

Postby jaragaki » Mon Sep 19, 2016 9:37 pm

I measured the speed of my Prime with the Feickert and it's "faster" but no steadier with two belts instead of one. I attribute this to overcoming drag from the needle.

The noticeable difference is the transmission of hum from the motor to the platter. It's very audible from the listening position with two belts and not audible with one. So I'm sticking with one, despite losing the advantages of having two. I'll likely keep it this way until there's a different solution for the hum.
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Re: Multiple Belts?

Postby rateourmover » Tue Sep 20, 2016 8:55 am

I’m aware this post isn’t one of those preferred staccato contributions and may also seem to be a specific request to solve my specific problem. I trust it in fact covers areas precisely relevant to others interested in this thread.

I use three belts on my SSM Ref – up from the as-supplied two.

I find it provides increased ‘speed’ – meaning transient attack - and generally a move towards some of the other documented benefits of rim drive (which I abandoned after experiencing similar problems to other frustrated abandoneers).

I too have audible hum which I too believe to be transmitted motor noise. However, I pay that price because it’s only audible between tracks. However, I’m convinced by you alI here and elsewhere in this Forum, I’d immediately realise the benefits of no hum during playback.

I’d therefore welcome your views on the whys and wherefores of two improvements this Forum has recommended and which I’d like to try – one cheap and one rather expensive. I doubt they are mutually exclusive.

The cheap one is to replace rubber belts with silk thread.

Questions:
One silk thread ? If more, how do you manage to tie them off at exactly equal lengths ?
Doesn’t the knot cause a micro-blip of some sort ?
Why doesn’t VPI offer non-rubber belts as an alternative – similar to their different centre weights/clamps and footers ?
Best specification of thread if I have to source it myself ?
Any cautionary tales ?

The expensive solution is to buy Stillpoints.

My deck is currently stood on Eden Sound Terracone feet and the motor on its stock rubber feet - with both deck and motor on the same Symposium Ultra platform.

Questions:
I believe Stillpoint Ultra 5s (say) without optional bases are unadjustable for height. Only minimally so with bases (which doesn’t impress Roy Gregory for one). So I’m down to levelling the rack ?
To quote Stillpoints:
“ If you have a device that has direct contact from top to bottom, (12 o’clock to 6 o’clock) like single bearing devices, no matter what the materials used, it is damping -- not isolating.
True isolation does not have a direct path between surfaces. Stillpoints patented technology stacks bearings such that there is no direct contact between the component and the surface upon which it rests. “

I read this as implying my Symposium Ultra platform – which is designed for damping/coupling – would become redundant ??


Any thoughts, experiences and observations gratefully received – and please don’t feel you have to comment on all of this. Selected bits would be welcomed.
SuperScoutMstrRef. Terracone feet onto Symposium Ultra. Mystic Mat, 3belts, Lyra Skala, Dorian mono, MusicMaker III Moving Iron. HRX & Stillpoints LP1 wts. Hovland HP200P & Radia. (HP100 & Sapphire in their boxes. Interested ?)
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