Turntable speed: how to check your record player is at 33 1/3 or 45 rpm

Why does turntable speed matter?

AnalogMagik, which makes turntable setup software, calls proper speed the starting point for any cartridge setup, because an incorrect speed affects all the other setup parameters. Speed also shows up directly in the music: play a record too fast and the pitch goes up, too slow and it goes down.

There are two separate things to check:

• Average speed: is the platter turning at 33 1/3 or 45 rpm on average?
• Speed wobble: does the speed drift up and down as it turns? This is known as wow and flutter.

How do I check turntable rpm with a strobe disc?

A strobe disc is a printed disc with rings of evenly spaced bars. You place it on the platter over the spindle and light it with a mains powered lamp. Fluance, a turntable maker, describes the method:

1. Print and cut out the disc that matches your lamp. In the UK, use the 50 Hz version.
2. Put it on the spindle and shine the lamp on it.
3. Set the speed you want to test and let the platter spin. You may need to turn off auto stop.
4. Watch the bars. If the speed is correct, they appear to stand still. If it is too fast, they move clockwise. If it is too slow, they appear to move backwards.

Hudson Hi-Fi explains why this works. A mains lamp flashes at twice the mains frequency (once per half cycle), so 100 times a second on 50 Hz mains. The number of marks is the flash rate divided by the rpm, times 60. For 33 1/3 rpm with 100 Hz light that is 180 marks. At 45 rpm the maths does not come out even (133.33 marks), and rounding down to 133 marks gives 45.11 rpm rather than exactly 45. Hudson Hi-Fi also warns that compact fluorescent lamps flash at an unrelated rate and are useless for this.

What is the most accurate way to check the speed?

AnalogMagik says a strobe disc only gives a close approximation, because you are judging it by eye. It also points out that once the stylus is on the record, its small dragging force slows the platter down.

Its preferred method is a test tone: a test record with a tone recorded at exactly 3,150 Hz. Only the correct speed plays it back at exactly 3,150 Hz, so software can measure the speed while the stylus is playing. The same kind of test can measure wow and flutter. AnalogMagik says a good setup should read below 0.2%, a very good one below 0.1%, and that above 0.2% the human ear may be able to detect a very small change in pitch on a constant tone.

Can a phone app measure platter speed?

Yes, with caveats. A phone app placed on the platter can read how fast it is turning from the phone’s motion sensors. It is quick and needs no printing or test record. But Fluance warns that phone apps may not be completely accurate, because the phone puts weight unevenly on the platter, and accuracy can differ from one phone to the next. The stylus is also off the record during the check, so stylus drag is not included.

A phone check is a good first look. For fine setup work, a test tone is the more precise method.

How do I read a result?

Results are often shown as a percentage off the target. For example, a platter turning at 33.0 rpm when it should be at 33 1/3 is running about 1% slow (33.0 divided by 33.33 is about 0.99). If your turntable has a speed adjustment, check its manual for how to use it; Fluance, for example, has speed adjustment videos for some of its models.

Questions people ask

Where Turntable Speed: RPM Meter helps, and where it does not

Turntable Speed: RPM Meter is our Android app for checking platter speed with your phone. Lay the phone flat in the middle of the spinning platter and tap Start. It waits for the platter to settle, times five whole turns, then buzzes and holds the result, so you read it after picking the phone up: the rpm and how far it is from 33 1/3, 45 or 78. Because phone motion sensors vary, each reading is also timed against the phone’s compass, which goes round exactly once per turn, and the app learns how far your phone’s motion sensor is out. If a magnet near the platter blocks the compass, it says so and uses the corrected motion sensor. It reminds you about slipping and scratching before your first measurement. You can share a result card (free cards carry a small mark). It works offline with no account. A one-time Pro purchase adds history for each turntable, a fine-tune mode for adjusting speed, a wobble graph and extra speeds.

What it is good for: a quick, free check of whether your platter is at the right speed. With Pro, you can track a deck over months or set its speed with the fine-tune mode.

What it will not do: it measures with the stylus off the record, so stylus drag is not included, and it does not replace a 3,150 Hz test tone when you want weighted wow and flutter figures. Never leave the phone on a spinning platter unattended.

Questions or bugs: Email us.

Sources

1. How can I measure the speed of my turntable?Fluance Support · support.fluance.com
2. How a turntable strobe worksHudson Hi-Fi · hudsonhifi.com
3. How to set proper turntable speed, and measure wow and flutterAnalogMagik · analogmagik.com