Sub harmonics - what's driving them?

[Steve Browning]

5 hours ago, songofthewind said:

Stewart Ward, of Session amps fame, recounts how changing necks on a Telecaster (sorry guys) changed its tone significantly. 

The stiffness of the necks, due to differing thicknesses, seemed to be the deciding factor, not body material.

Did he prefer it through a valve amp (ducks)?

[songofthewind]

I dunno if he preferred it through a valve amp. But I get your joke.

I’ve swapped necks on guitars and basses, and can hear and feel differences, but I wouldn’t call my experiments scientific.

My eighties Japanese Strat has a baseball bat neck, and it sounds good to me.

[Count Bassy]

On 23/04/2019 at 16:54, Bolo said:

The pups do not pick up vibrations through the body.  They only register disturbances in their electro-magnetic field. Such as the strings vibrating or the phone in your pocket connecting to a network.

Surely if the body of the guitar is vibrating then the pickup will be vibrating with it, and this will be added into the movement between the pickup and the string.  Pretty neigible though I'd have thought.

[Bolo]

4 hours ago, Count Bassy said:

Surely if the body of the guitar is vibrating then the pickup will be vibrating with it, and this will be added into the movement between the pickup and the string.  Pretty neigible though I'd have thought.

The bit that we're belly-muting? 

To the pickups that are mounted on sponge/foam to decouple them.

I agree, pretty negligible.

[lowlandtrees]

Interesting thread this. I am gonna try sticking my bassmax piezo double bass pick up poles to the body of my hollow bodied ebass. The pups should pick up vibrations coming through the bridge onto the bass body? Might sound like poo right enough 

[TrevorR]

On 24/04/2019 at 08:30, songofthewind said:

Stewart Ward, of Session amps fame, recounts how changing necks on a Telecaster (sorry guys) changed its tone significantly. 

The stiffness of the necks, due to differing thicknesses, seemed to be the deciding factor, not body material.

Erm... and/or because of the difference in mass between the two necks both of which are factors of the structure and density of the necks. Which since wood is not a homogeneous material means that it probably WAS a factor if the material used. I recall interviewing Paul from Wal Basses where he said that while you can make broad generalisations about the tone derived from different wood species they can only ever by broad generalisations because of the organic nature of wood and the way the weight and density of wood varies... specifically he said in the context of the presumption that American Walnut is the best wood for fretless basses... "Yes, in general, but to counter the theory we’ve had some great sounding hard faced (like wenge) fretless basses through here – more aggressive sounding though. Also, you mustn’t forget that the density and grain structure can vary even from one end of a single board to the other. There can be a lot of variables even on two basses with exactly the same spec."

 

 

[TrevorR]

On 25/04/2019 at 01:27, Count Bassy said:

Surely if the body of the guitar is vibrating then the pickup will be vibrating with it, and this will be added into the movement between the pickup and the string.  Pretty neigible though I'd have thought.

The much bigger effect would be the effect of the body vibrations on the overtones created in the strings affecting the timbre subtleties in the waveforms picked up by the pickups (whether or not you believe that those differences are audible).

As a science geek of decades long-standing this has fascinated me for ages. People tend to underestimate the strength of sympathetic vibrations and resonances. The videos of randomly started pendulums and metronomes synchronising themselves through sympathetic vibration are hypnotic to watch... 

The vibrations from each metronome through the table force the synchronisation.

But my favourite example is the Tacoma narrows bridge video. Wind whistling across the wires and the deck of a suspension bridge was just right to hit a frequency which resonated. That amplified the vibration in the substructure which fed back into the bridge amplifying it even further... and so on... because the bridge designers never thought to build damping  into the bridge this ran out of control until it tore the bridge apart. Just through the wind blowing across it (it was only about 20 or 30mph, not a gale’ blowing across the bridge). I love this video... esp the 1940s histrionic newsreel voiceover

 

 

 

 

[Al Krow]

@TrevorR - that was fascinating, thank you for sharing those clips!

Two quotes from the comments below the YouTube clip, that struck me as being of note:

"There is no magic involved. This is simply a physical phenomenon known as resonance. The solution is in the table top on which the metronomes are mounted. As you can see in the video the tabletop on which the metronomes are mounted is swinging a bit. This swinging increases as more metronomes come into sync. This is caused because there is a slight unbalance in the movement of all the metronomes together which causes the table top to start swinging. Action = reaction. In theory, if all metronomes would be set perfectly randomly, the resulting force operating on the table top should be zero because they all compensate for each other. But in practice this is not the case as the it is almost impossible for the experiment to be perfect. So there is always a resulting force which cause the table top to start moving. This movement will enforce the kadans of the metronome which are in sync, a physics phenomenon which is known as resonance. On the other hand it will temper the ones which are not in sync, thus slowing them down until they reach the resonating frequency of the swinging table top. Then they will start to resonate too. So the metronomes are not synchronizing to each other, but to the swing frequency of the table top. If you would mount the metronomes on a concrete floor, you will see that they won't come into sync because they can't resonate."

"So sad when the only left rebel metronome finally aligns itself"

I guess the questions that come to mind are: what is the size of any wood resonance in comparison to the string resonance? My instinct is that they will be miniscule. And secondly from the examples you have provided, it would seem that resonance acts to reinforce and therefore to amplify rather than add complexity aka richness to tone?

Edited April 28, 2019 by Al Krow

[TrevorR]

@Al Krow that’s the nub, isn’t it. Musical instruments are complex systems so EVERYTHING has some effect the question is how much. You hear such daft opinion spouted as fact in the tonewood debate. Like “negligible vibration gets transferred from the strings through the bridge into the body because of its mass” yet you can tune a bass by resting your ear against the body and you can turn your wardrobe door into a speaker by touching it with your bass’ headstock.

Personally, I err on the side of the body resonance/filter interactions being a noticeable part of the rich complex waveform in the strings. “But it’s too small an influence, how could anyone ever perceive it?” I hear the mob cry... Well, we perceive some pretty small tolerances every day... a few parts per million of a volatile organic compound with our noses. Difference of a few hz to get just the right colour. A bass where the string height is 1/1000 of an inch the wrong way or where the string spacing varies by half a mm  becomes “unplayable”. I can reliably tell you when the pressure of the tyres on my bike falls below 55-60 psi by the way it feels when I’m riding it. The different waveform between an oboe and a cor anglais.  Why not the different waveform between two basses with similar hardware and build and body woods of wildly different densities?

[TrevorR]

PS the videos were offered to suggest that resonance effects should not be dismissed as minuscule and negligible (as they often are), not that those examples operate in the same way as the colouration Of a vibrating string’s frequency mix.

[Al Krow]

20 minutes ago, TrevorR said:

The different waveform between an oboe and a cor anglais.  Why not the different waveform between two basses with similar hardware and build and body woods of wildly different densities?

So continuing with the 'nub' if I may.

I get that where the wood of an instrument is the sound box, what the wood is made of and how it is finished has a massive bearing on tone e.g. violins and why you pay £50 for one and £500,000 (or more) for another.

The wood of the bass is not, however, the sound box. It is instead the housing for the soundbox (the pups), the rigid framework for the strings and a convenient location for the onboard EQ.

But I take your point that wood resonance will feed back via bridge string saddles and the nut to the string vibrations in some potentially non-negligible fashion.

The question then becomes one of degree of impact? On that score, I guess I'm still at where I was at the start of this thread that:

• pups, strings and EQ will be the dominant drivers of bass tone 
• the wood will have some impact but will likely be relatively small compared to the three dominant drivers

[TrevorR]

27 minutes ago, Al Krow said:

• pups, strings and EQ will be the dominant drivers of bass tone 
• the wood will have some impact but will likely be relatively small compared to the three dominant drivers

Absolutely agree. However, personally I would add two additional bullets...

• but those differences in harmonic content will still be noticeable to the human ear meaning that while it still sounds fundamentally like a bass guitar the design, materials, hardware and construction will all contribute to appreciable differences in the nuance of that harmonic content.
• the non uniform nature of wood as a material and the inability to ensure that other factors are identical (esp in terms of construction and assembly) mean that the differences may not be entirely predicable on the basis of a predetermined prejudice (e.g. mahogany is always mellow, maple is always bright,  x wood sounds warmer than y wood), expensive wood sounds good while cheap wood/other materials sound bad.

[Woodinblack]

10 hours ago, TrevorR said:

But my favourite example is the Tacoma narrows bridge video. Wind whistling across the wires and the deck of a suspension bridge was just right to hit a frequency which resonated. That amplified the vibration in the substructure which fed back into the bridge amplifying it even further... and so on... because the bridge designers never thought to build damping  into the bridge this ran out of control until it tore the bridge apart. Just through the wind blowing across it (it was only about 20 or 30mph, not a gale’ blowing across the bridge). I love this video... esp the 1940s histrionic newsreel voiceover

 

A great advance in engineering knowledge everywhere, and has been shown to everyone studying resonance since as the most dramatic effect, how a 40 mile an hour wind can take out a bridge (and kill a dog).

I think the most amazing thing though, is not that it happened, but they were actually filming it at the time. I know they had a problem with the bridge anyway due to the vibration, but considering how few things were being filmed back in 1940 compared to now, the fact the filmed it was so lucky. If they hadn't, noone would know about the bridge today, it would just be another in the list of bridge collapses.

 

[TrevorR]

3 hours ago, Woodinblack said:

A great advance in engineering knowledge everywhere, and has been shown to everyone studying resonance since as the most dramatic effect, how a 40 mile an hour wind can take out a bridge (and kill a dog).

I think the most amazing thing though, is not that it happened, but they were actually filming it at the time. I know they had a problem with the bridge anyway due to the vibration, but considering how few things were being filmed back in 1940 compared to now, the fact the filmed it was so lucky. If they hadn't, noone would know about the bridge today, it would just be another in the list of bridge collapses.

 

The bridge was just outside Washington if I recall ans was notorious for bouncing up and down - it was nicknamed "Galloping Gertie" by the building crews that constructed it. The rotational twisting started at some point in the morning a few hours before the final failure so I guess that the newsreel crews rushed down with their cameras to see what would happen. Or at the least get some newsreel footage of Galloping Gertie being even more wobbly than usual... I've loved that footage since I was a lad and I think it was used by Professor Eric Laithwaite in his fantastic "An Engineer Through The Looking Glass" Royal Institution Christmas Lecture which had a whole lecture focused on waves and vibrations (and in a later episode demonstrated magnetic levitation!!!). 

 

Post Google... 1974, apparently... https://www.rigb.org/christmas-lectures/watch/1974/the-engineer-through-the-looking-glass

[ahpook]

15 hours ago, TrevorR said:

The videos of randomly started pendulums and metronomes synchronising themselves through sympathetic vibration are hypnotic to watch... 

The vibrations from each metronome through the table force the synchronisation.

That's brilliant, thanks !

Reminds me of 'Pendulum Music' by Steve Reich