How to Intonate the Fretless Bass

[FretLessSince68]

****** DISCLAIMER ******
I am not a luthier, there may be errors or missing information in this text. Let me know if you find something.
The work you do on your instrument is your own, I am not responsible for problems that may arise.
Always work safely.
**** End disclaimer ****

This is a lengthy post on how to perform intonation on your own Fretless bass.

The good news is that intonation is a relatively simple adjustment and can be corrected if not done perfectly the first time. So don't be afraid to try this procedure which will bring you closer to being a master of your instrument. I have found that I do a better job than the local guitar techs (who usually don't understand fretless anyway) and the money saved buys new strings and more.

This is not a 15 minute adjustment. The first time you do this it may take over an hour. I can do it in about thirty minutes now, sometimes less. Whereas your typical guitar tech will cut corners and charge you for an hour of bench time.

If your strings are good and "true" it should be pretty easy. If the strings are bad or full of unwanted "wobbly" overtones then it will be harder.

In this discussion we are talking about a typical solid body fretless bass having a metal bridge. The bridge found on an Acoustic Electric Bass (AEB) is usually made of wood similar to an acoustic guitar and not easily adjustable so is a separate topic.

First the basics just in case you need some background on the what and why before we get into actual intonating.

Intonating refers to the act of adjusting your bridge, or more accurately, bridge saddles to be located exactly at the correct scale length and to compensate for string variations as they relate to correct pitch and scale length in order to provide accurate pitch at every position up and down the fingerboard. Put another way... Adjust the bridge so that your instrument sounds in tune and musical.

Not all strings are alike in the way they deliver a pitch when tuned at a specific tension. In addition sometimes strings respond differently when they get old requiring an intonation. Thus an intonation adjusting capability is needed and most bridges provide this adjustment. Some strings may require a slightly longer saddle location, others may need to be shorter. The act of adjusting the saddle location is called intonation, or to intonate. One may say... "I intonated my bridge." or "I performed an intonation on the bridge." Intonation as it refers to playing a note on pitch during a performance is a separate topic although uses the same word.

Performing an intonation on the fretless bass is a bit more difficult than on the fretted bass but not fundamentally different. If you have intonated an upright bass you will see the similarity. The basic idea is to make sure that the relationships between any markings (such as fingerboard side marks) and scale length are consistent. If your fingerboard is totally unmarked then, while less critical, it is still good practice to have your instrument properly intonated for ease of playing in tune and being able to repeat your set-up should the instrument need disassembly for service.

The bridge is a piece of hardware, usually metal on the electric bass, located near the base of the instrument body. The bridge may be simple or complex depending on various factors however they all share the intonating attribute unless very unusual. If holding your right handed instrument in the normal playing position the bridge would be the large metal assembly at the far right end of the instrument that supports the strings. Upon the bridge plate each string passes over, and is supported by, a part of the bridge called a saddle which usually has long adjusting screws running through it that go through the bridge plate. The saddle is adjustable in two and sometimes three dimensions. Today we are concerned only with the adjustment that runs in the same direction as the string travel. This is the intonation adjustment screw and controls accurate positioning of of the scale length. Scale length is the string dimension as measured from the nut to the saddle where the string passes over and contacts it.

Rarely a bridge does not have intonation adjusting screws, these are very unusual and not covered in this post however the basics are the same.

Intonating your bridge (saddles) is part of a good "Set-Up". We will not be going into full Set-Up today.

It is strongly recommended that you have fresh or new strings installed although not necessary.
Changing to new strings of the same brand and type usually does not require intonation if the instrument was well intonated previously. Changing to a new brand, gauge, or type of string will usually require an intonation.

Tools:
Accurate electronic tuner and guitar cord.
The proper screwdriver or Allen wrench (usually a #1 Phillips).
Measuring tape.
Pencil.

I use a Petersen Virtual Strobe Tuner however any good tuner will suffice. In the old days we did this using a tuning fork and ones ears.

Look at the far end of your bridge and locate the intonation screw heads that adjust the saddle position along the direction of string travel. These screws are often a #1 (small) or #2 (standard) size Phillip. However your screws could be any type so make sure you have the correct tool to avoid burring the screw heads.

You will need an accurate measuring tape (metal, not fabric) in good working condition.

A pencil is used to mark the mid point of your scale length on the fingerboard. If you have a lined fingerboard you will not need to use the pencil.

The Intonation:
It will not be necessary to remove the strings or do any disassembly. Leave it tuned.
1. Examine your bridge and nut for any defects. If there are defects these should be corrected before proceeding.
For lined fingerboards skip to step 3.
2. Using the measuring tape and pencil mark the exact mid point of the scale length on your fingerboard with a THIN line as if it were marking a fret slot. If your scale length is 34 inches the mid point is 17 inches. Measure 17 inches from the nut and mark the fingerboard under the G string. Now repeat this mark under each string until all are marked. If concerned that using pencil will damage your instrument put down a layer of Blue masking tape at this location and mark the tape.

These marks serve as a reference where your theoretical 12th fret (or fret line) would be if you had them. This is also the point on the string where the first harmonic and octave occur. This location evenly divides the string length (scale length) by two and is the critical point used to determine correct intonation.

3. To correctly intonate your instrument you need to be able to play harmonics as they exist at the mid point of the string length. If you are not familiar with playing harmonics then you should practice this until it is natural. A harmonic is plucking the string softly while gently touching the string (but not pressing down onto the fingerboard) with a finger at a harmonic node. You should hear a bell like note that represents a fraction of the string length oscillation depending on which node you touch. Once you become familiar with playing harmonics you will get a "feel" for where a harmonic node exists. You will feel less vibration at the node because the string oscillation is quiescent at that point.

4. Turn on your tuner. Connect to instrument if applicable.

5. Start with the G string. Tune your instrument. Tune the G string as closely to pitch as you can get it. Play the 1st harmonic which should be directly over your pencil mark. Make a mental note if the location of the harmonic node is not over the pencil mark. This will give you a rough idea of how good, or poor your existing intonation is. If the node is exactly over the mark than you are in luck and the intonation may be easy. If the node is towards the bridge then the scale length is too long and needs to be shortened at the saddle. If the node is towards the nut then scale length is too short and needs to be lengthened. This observation will also give you an idea of how much adjustment is needed.

6. Now, using your thumb-pad and thumbnail depress the string so that your thumbnail is exactly on the pencil mark on the fingerboard.

6.5 Press the note firmly and read your tuner. If the tuner reads Flat (b) then the scale is too long and needs to be shortened at the bridge. If the tuner reads Sharp (#) then the scale length is too short and need to be lengthened.

Note: Some strings with course windings are difficult to depress exactly at the correct point. If you encounter this try the valleys between windings versus the crowns.

7. Adjust the saddle intonation screw to change the location of the saddle in the needed direction. Note: Sometimes it is necessary to push the saddle with a non-marring tool if making the scale length shorter. Retune the string each time you adjust the saddle intonation screw.

8. Repeat steps 5, 6, 6.5, and 7 until the harmonic and the fingerboard mark agree in pitch using the tuner.

Now you have adjusted the intonation (scale length) for the G string. It is commonly accepted that the G string is correctly intonated exactly to the mid point of the scale length. This is not always the case, sometimes a string requires compensation in order to sound musical.

9. Check your work by playing notes on that string up and down the fingerboard to make sure that the pitch at any position is the correct note and not sharp or flat. Your ability to play on position accurately is important here. If the notes are noticeably sharp or flat then either the string has a problem or your intonation adjustment needs to be repeated. It is fairly common for the E and B bass string pitch accuracy to fall off above the 12th position so depending on your own interpretation of the word "perfection" decide when enough is enough.

This step is where doing intonation on fretless bass is more difficult than fretted. It is important that you be able to accurately play in position so that the note you read on the tuner is the one you want. I use my side markers as an aid in achieving this accuracy. Again, using the thumb nail to press the string down may help you gain accuracy.

10. If notes up and down the string are not in pitch go back to step 5. The advice in step 6.5 also applies to notes played in all other positions.

Once the G string is successfully intonated you have a good reference for migrating this point to each lower string plus whatever compensation is needed.

Next you will be adjusting each lower string in a similar manner except string compensation will usually be necessary. You have probably noticed that on a well intonated bass that the saddles appear to be farther back (longer scale length) on successively lower strings. Where the E and B saddles are moved quite a bit back. The saddles will usually describe roughly a diagonal line across the bridge as increasing compensation is added. This is due to imperfections in the basic design of strings and stringed instruments. Instruments with fanned frets attempt to correct for this but is a subject for another day. Compensation is adding a small additional length (about 2mm each) to each string scale length as you move successively to lower pitched strings. The up side of compensation is that a difficult problem in intonating stringed instruments has an effective method for correction. The down side of adding compensation is that pitch accuracy is not as good at higher positions. This is most evident on the E and B strings at higher positions (above the 12th) occasionally having an intonation problem. Sometime it comes out great, sometimes not. Depends on the strings. If you do encounter such a problem string intonate it to be musical in the lower positions where you play most frequently.

Just accept that you will be compensating each lower string as you progress. This is where the art of intonating comes in. After you have intonated a few instruments you will get a better idea of just how much compensation is needed. For now assume that you will add about 2mm per string except the B which may be more.

11. Now move on to the D string.

12. Do the same procedure on your D string as with the G string steps 5, thru 10.

The pencil marks you made on the fingerboard at the scale length mid point under each string are "for reference only" when doing the D, A, E, and B strings. The necessity to add "compensation" means that the actual mid-point of the scale length will add about 2mm in length per each string as you move to the D, A, E, B.

13. You will notice that when you check the pitch (using tuner) of various positions up and down the fingerboard that they are probably running a bit flat when compensation is needed. Unless you have bad strings installed this is usually corrected by adding length. Adjust the D saddle back (longer) by approximately 2mm (slightly less than 1/16 inch). This will make the scale longer and raise the pitch at each position slightly.

14. Recheck pitches up and down the fingerboard for accuracy. Re-read step 6.5

15. Re-adjust the saddle intonation screw as necessary until the pitches are correct. Sometimes a string will require quite a bit of compensation where others will not. I like D'Addario strings because they are consistent.

15. When the notes up and down the fingerboard are in pitch relative to the positions (position markers) then you are done with the string. Move on to the next.

16. Now do successively the A, E, and B (if present) strings using this procedure in steps 12 thru 15.

It may be necessary to move the B string saddle all the way back yet you still need more compensation length. This has happened. Just leave as far back as you can get it and call it a day.

For 6 , 7, and more string basses execute the same procedure on your C, F, Bb strings. Keep in mind that you may have to compensate in the opposite direction (make scale length shorter).

Some strings due to age, low quality, or string variations within the windings defy good intonation. Such a string may intonate well in the lower positions but not in the higher. In such a case intonate it for the positions you play most frequently (usually lower positions) as a bassist.

This may seem like a lot of information and a complex procedure but once you have done it a couple of times it should be easy and you won't need this guide.

I hope this information is helpful and good luck being the master of your instrument.