A Few Turntable Measurements using the RPM Android App

As is often the case, measurement is the issue. RPM is a continuous quantity only in the abstract. In all practical applications, it is an average. Maybe over a fraction of a millisecond, but that still is a far cry from continuous.

So the major issue, variations on the 10 - 20 KHz level, may be averaged out and not be addressed at all. Unless the specs indicate the time span over which the average is taken, the results don't mean much. As one of the greats from the glory days of audio once told me, "The best audio analyzer available is hardwired to your brain." (Jonas Miller)

I like the Nottingham sound too, which is why I built my air bearing with a 45Kg platter and a 1.8 watt motor.

@lewm I have not been able to find specs on the Nottingham or the Walker tables. It is quite difficult to make comparisons on table performance without basic speed and vibration specs. I will never buy a table again without seeing these specs.

One's ears are far less sensitive than the equipment used to measure table speed and vibration performance.

This is one of the eternal arguments among vinylphiles. In belt drive world, we have the light platter/high torque motor crowd vs the heavy platter/low torque motor acolytes. Then we have the idler/DD aficionados who jeer (privately) at both. Modern methods of speed control have leveled the playing field somewhat. My dirty little secret is that I finally couldn’t stand the ritual of having to push start my otherwise perfectly good Nottingham TT and so was driven to experiment with idler and direct drive. (On one occasion I nearly knocked the Nottingham off its wall shelf with my overzealous push start.)

What Lew said. Low torque motors transmit minimal vibration and noise to the platter (and all parts of the table) Some belt drives use tooth floss for example to further reduce transmission of motor artifacts while relying on inertial mass to keep the platter spinning accurately. 

I cannot think of a reason why AS decided to do this. I can’t see an engineering reason.

There is a common rationale associated with the combination of a high mass platter with a low torque belt drive. The idea is that speed stability comes from rotational inertia, not motor torque. The Walker Proscenium, all Nottingham tables, and many tables of Germanic origin are examples of this approach.

@ossicle2brain My Acoustic Sounds WOW XXL table is an excellent case. From a cold start, it needs a push on the platter rim to begin spinning.  One never knows when it is up to speed. There is no feedback. The REW app provides some idea. The app has a delay prior to beginning measurement. The WOW barely gets to speed before the measurement starts.

The motor used in the WOW has minimal torque, just the opposite to that of the Technics SL-1200  or the Denon DP-57L or DP-88.. I cannot think of a reason why AS decided to do this. I can't see an engineering reason.

@kevemaher  You said some belt drives need a long time to settle.  Is that because of the "rubber banding effect" of the belt stretching on start up?  

Good.

It’s obvious you don’t care :)

Here’s a simple test of your theory. Center the phone as well as you can using simple measurements and run the test. Then move the phone obviously off center by about 25mm and rerun the test. I did and saw no difference in results for speed or wow/flutter out to 2 decimal places. 

About platter balancing, I consider my Basis platter well made but I see no indication of it being dynamically balanced other than simply being machined accurately. 

Duckman, I am talking about the weight of the phone being unevenly distributed on the platter. That’s not the same as a record weight that fits over the spindle, or as a peripheral ring. In a high quality TT the platter has been dynamically balanced. The phone would destroy that balance. Does it matter? I neither know nor care.

It cost so little to try. Give it a spin. :)

https://drive.google.com/file/d/1f5dal0O-pXY6Gk-0PMd5HyMvyHk5XyyO/view?usp=drivesdk
 

@duckmanst3 Hi, I'm not questioning the accuracy of the hardware, although that would be nice to know. I'm concerned about the logic and math used to make the calculation. That info has not been published and probably won't be because (I bet) the person who created this app was doing it for fun, not for the rigor needed to develop a product for sale.

Yeah, using a phone for this measurement has little to no affect on the performance of the table.

Some belt driven tables take a long time to get to speed and settle, longer if weight is added. If he app starts before the TT has a settled speed, the measurement result will be invalid.

Measured my AudioGrail Garrard 401 with SPH grease bearing, PAC platter, Artisan Fidelity idler using RPM Speed and Wow app. Table was running for at least 4 hours.

Wow 2Sigma = 0.08%

..and then there is flutter.  Which I guess is just faster wow.  Maybe the DD turntables have more of that?  How do you measure that one and maybe it's more important then wow?

Great.  Now with an app we can be even more OCD about listening to music. I mean audiophilia.  Whatever.  

Gosh. My iPhone weighs nothing compared to some record clamps I’ve used. And I’ll bet NASA wished they had accelerometers as accurate when they put men on the moon. :)

Its just a fun app to play with. :)

@ossicle2brain One way to find out how much weight is too much is to add weight to the table, then measure the RPM and WOW with the app. Continue to add weight until the speed changes or the WOW increases. This will probably happen before anything breaks.

But be aware. Too much additional weight may cause long term damage to the motor moving parts due to the increased load. It is very difficult to estimate that without long term measurements or manufacturer's recommendations.

I should point out that the RPM app has not been independently verified for rpm accuracy. As I reported above, the repeatability is good.

The WOW 2 sigma reported by the app has also not been verified. In particular, the method of calculating the WOW has not been described. For example, is it the standard way of measuring? Is it weighted?

I can say that this app is good for comparing turntables and modifications to tables. The absolute accuracy of the reported rpm and wow is unknown. I would find it difficult to compare findings from this app to manufacturer's published measurements.

 Just did another platter comparison.  This time between an acrylic one which weighs about 2.4 and my modded steel 3.4 pound platter.  The sigma for the acrylic was 0.14 and the steel was 0.11.  Science!!  

I think I'll be returning the acrylic one.  Not enough room to add the weights and doesn't seem any quieter.  Looks cool though.  

How much weight can I add to the platter before the motor blows up and belts snap?  

I can’t see how a small off center mass would alter the wow and flutter.... if the platter is level. But like "animal" above I also use a small plastic bowl over the spindle so the phone can be centered.

The app I’m using is called RPM speed and wow. Fun stuff. I used it to gauge how well my fishing weight platter mod worked. I glued four four oz lead fishing weights around the perimeter of the platter. I was careful to balance it by teetering it on a marble. Then I used the app to see the change. Went from 0.18 to 0.14 with the extra pound. Platter went from a massive 2.4 up to an incredibly heavy 3.4  pounds!  🙄  The table is a Music Hall 2.3, so fun to mod, and it needs it.

My concern is that the weight of a cell phone placed eccentrically on the platter will per se skew the reading, especially for wow and flutter. Furthermore, is there independent evidence that the rpm readout is accurate? I thought there was some doubt about that. Repeatable, perhaps, but accurate to for example +/- 0.1 rpm? Or even +/-1.0 rpm? I dunno.

I have to say that the RPM app should be bought before you spend a lot on a strobe. I have the manual Clearaudio Device - its' good but the App is just so consistent and sensitive. I used a spray can lid to place my phone on when i use the app (for decks without a weight with a flat top). Slightly off-topic but i very much doubt that the phone weight will skew the reading once the deck is up to speed what say you guys

Dear @kevemaher  : Good that you shared those measurements that speaks by it self what I knew of the Denon quality.

I still own two Acoustic Signature old top of the line TT's alog Denon, Technics, Luxman and the like. Inside the external PS in my TT's I can fine tunning its speed and you can do it with your table too:

"" The Wow XL is driven by an ultra-precise synchronous motor that employs a 20MHz microprocessor that provides “perfect” speed stability and fine-tuning. Two small recessed buttons on the back of the ’table allow ±0.1% speed adjustments, so you can dial-in the speed during initial setup. I checked the speed after I set up everything, and it was spot on. I checked it three weeks later, and things were still spinning correctly. It’s safe to assume that once you initially set the speed, you can leave it be without worrying—it’s always good to check speed if you move the ’table, though. The motor is extremely quiet, too. Fitting the belt was easy, and once the motor was turned on any twists were straightened out after a few revolutions. Two stainless-steel buttons are located to the left of the platter, an on/off button and a 33/45 button to easily switch speeds. Turn the turntable on, and a red LED blinks above the speed button until the precise speed is reached.  ""

Regards and enjoy the MUSIC NOT DISTORTIONS,

R.

The Wow XXL does have adjustable speed, but it is not well documented.  There are 2 tiny buttons on the back of the table.  Each push of a button will either slightly raise or lower the speed.   I don't recall which button raises or lowers, so you will have to experiment.  This won't change variations, but at least will allow the RMP to get closer 33.33. 

I’ve played around a bit with the IOS app. Interesting new use for the phone.

I found that changing the oil in my spindle bearing and cleaning the belt on my Basis TT improved wow & flutter by 0.04%. :)

Very nice write up. Enjoyed reading how you used the meter. I’ll try one for IOS to see how it, works