Why do false harmonics vary from bass to bass?

wood, set up, strings, pickups, frets, fingers
all come into play.

 

Also scale length. Iv'e noticed my 35" basses have more harmonics than my 34".

 

Same here.

Different body woods are a big factor - e.g. mahogany and alder are close in weight but have a very different grain structure. Mahogony is fine grained with persistent fiberness to the wood that makes it a little tough to split/crack cleanly. Alder is much larger grained and splits cleanly, ditto for maple.

 

Probably the biggest contributing factor is pickup location and aperture. If the pickup has a narrow aperture and is placed directly under a node (a place on the string that isn't vibrating), it will be very weak and nearly inaudible.

This is why the bridge pickup is generally preferred for harmonics. Its location positions it away from nodes of the first few harmonics (four or five).

 

Pick up location.

 

The biggest factor by far. Jaco chose the J-bass for good reason: a vanilla P-bass barely transmits those upper harmonics.

 

If the bass is voiced with a lot of hi mids harmonics (false or not) will be heard better.
I don't think there is anything else to it.

 

Jaco had no trouble getting them from his 34" jazz basses.... so maybe what you say is true (I agree with you) but it's not a strongly limiting factor at 34" with the right bass either.

Anyhow, imho the biggest limiting factor is electronics/pickup design/location/setting/eq.

I get way less artificial harmonic output level on my america musicman basses... the stingray pickup and electronics fail miserably to output strong harmonics compared to the bridge pickup of a jazz bass or to my BTB with bartolini soapbars in the bridge position.

I can even get stronger output of harmonics on a good precision than I can on a stingray. and yet unplugged the stingray shines at them. so it's in the eq, the pickup location, etc etc.

 

A bass overly reliant on it's truss rod for neck curvature is less prone to full harmonic presentation (think of what happens when a vibraslap is gripped tightly). The more rigid the instrument, the more prevalent the harmonics will be. The more mass the instrument has the more prevalent the harmonics as well.

 

^this

It's why basses with graphite, metal or really dense and stiff wood necks sound different in this way.

 

I've been playing for 25 years and I feel like I am only just learning this stuff too. Thank you inter webs!

 

The tone of a bass is also made up of the presence or lack of overtones, which are harmonics within the note. You hear the fundamental primarily, but the overtones are there to a certain extent. Brighter sounds generally have more overtones. So if you think about what makes a bass sound brighter acoustically, the same factors would make the harmonics more present or easier to produce.

 

Get some saddle pickups and you'll have all the pinch harmonics you could want.

 

I have 10 basses yet two of them, a Precision and a Jazz, stand out with amazing 'false harmonics'. VERY loud, strong and focused. On those two I have never adjusted the truss rod...mmm. They are also both resonant and very loud when not plugged in.