Topics: Tonearm Mounting Data

If you’re customizing a turntable, changing tonearms, or making a DIY project table, you’ll need to know the correct distance from the platter’s center spindle at which to mount your tonearm base. Mounting distance varies with the effective length of the tonearm and also the size of record that you’re setting the turntable up for.
If you’re a collector of 45 RPM singles, or 78 RPM disks, or of 16 inch transcription records, then you’ll want a dedicated turntable for playing those records. Setting up a tonearm and cartridge for 12 inch LPs and then using it to play other size records will produce less-than-optimal results.
If your tonearm has interchangeable headshells then you can probably set up extra headshells with their own cartridges and adjust each for a unique alignment setup. Hopefully, your headshells provide enough travel adjustment to allow for the different effective lengths prescribed for each size of record. For example, a tonearm with an effective length of 9 inches will need to be mounted at a distance of 8.2845 inches from the spindle. To keep that mounting distance and set up the tonearm for 7 inch records, then you’d have to move the cartridge back in the headshell by 0.285 inches, to change the effective length to 8.715 inches.  The offset angle will also change from 24.1276 to 18.3284 degrees, meaning you’ll want to twist the cartridge slightly toward the outside of the playing band.
People change tonearms on their turntables for a variety of reasons.  The various considerations that go in to the choice of a tonearm are discussed at length on the Playback Quality topics page.

Tracking errors are more significant with shorter tonearms.
This chart shows what happens when you use shorter or longer tonearms with your 12 inch records. Longer tonearms produce significantly less error.

Aftermarket tonearms can provide higher-quality playback because they have better pivot bearings with less chatter, or better anti-skate mechanisms, or because they’re lighter, longer, or vibrate less. Longer tonearms produce lower angular errors, but they must be mounted further away from the spindle than shorter tonearms.

Here you will find data on mounting tonearm of any length, for every size of record, and according to both the Baerwald and Löfgren-B alignment models.

Tonearm Mounting Data Sheet for 12 Inch Records – Baerwald

Tonearm Mounting Data Sheet for 12 Inch Records – Löfgren-B

Tonearm Mounting Data Sheet for 7 Inch Records – Baerwald

Tonearm Mounting Data Sheet for 7 Inch Records – Löfgren-B

Tonearm Mounting Data Sheet for 10 Inch Records – Baerwald

Tonearm Mounting Data Sheet for 10 Inch Records – Löfgren-B

Tonearm Mounting Data Sheet for 16 Inch Records – Baerwald

Tonearm Mounting Data Sheet for 16 Inch Records – Löfgren-B