Ok electronics/physics gurus, Strat sounds?

[Ratae Corieltauvorum]

OK, I get what for the sake of this post I'll call Pos 1 on the 5 way switch - Bridge only

 

I get Pos 3 - Middle pickup only, and of course Pos 5, neck only

 

Now, the famous Strat quack is to be found in Pos 2 & 4, ie B+M and M+N

 

Why?

 

I know it's a phase issue, but what exactly is going on with the direction of the current inside those pickups, what happens when it reaches the pots, and what is it in the nature of the output signal at the jackplug that makes that glorious sound.

 

I'm just doing a Strat for someone, and they were going with trad Strat wiring, but I've convinced him to go with master Vol, master Tone and a no load blend pot, to blend neck and bridge, a scheme I first did for CSM's 60th birthday Strat, and since then, I don't see the point of wiring Strats any other way...besides which, it allows me to not own a Tele.

 

EDIT: Oh.....and I have Googled and read in particular this, but I'm still sytruggling to understand

 

http://www.premierguitar.com/articles/phasing-out-how-to-get-out-of-phase-sounds-from-a-stratocaster-1

[Chordite]

Another complication is the magnetic polarity of your chosen pups, so there is more to it than the wiring.

 

[video=youtube_share;5pi0i0WP4_M]

 

ps It is interesting that Pos 2 Quacks fine on my HSS and I don't think it is tapped so signal level is about equal from B and M

[WRGKMC]

2&4 positions are not out of phase, its simply a lower impedance signal. If you have reverse wound, reverse polarity magnet in the center its still in phase, its just going to cancel noise which doesn't come from the strings. Two pickups in parallel halve the resistance because current has two paths instead of one.

 

Maximum bass response on a string occurs at the center of the strings length. (pick a string at the 12th fret and compare it to the tone you get when picked near the bridge) The closer the pickup is to the string center, the more fundamental string tone is generated. Because the instrument has frets, this center string position can move towards the bridge as well. Fretting the 12th fret puts the center node over the neck pickup and changes the secondary harmonic response of the other two pickups. Fretting notes creates pitch changes.

 

Pitch can easily be confused with Pickup Frequency. Don't change frequency response or pitch. They have a fixed response range and have fixed positions.

 

The tone effect of two pickups is simply the combination of two different sets of vibrations or nodes along the same string being combined. Each pickup detects a different frequency response from the same musical note much like a tuned filter on a three band graphic EQ. If you select a single pickup, its like pushing up one slider on the EQ. If you select two, its like pushing up two sliders up and the frequency response between the two peaks is elevated.

 

If you reverse the phase of one of the two pickups, then you have frequency cancellation. The frequencies that are common to both get cancelled. Because the pickups produce a fair amount of unique responses at their nodes, those frequencies remain and get amplified. Out of phase pickups on a Strat have a great deal of bass roll off because the bass frequencies are common to both pickups and get cancelled.

 

This shouldn't be confused with the additive response of two nodes. It may sound quacky but its simply a mix of two "narrow" nodes. Other guitars with wider pickups have "Broad" string node response. Instead of two sharp peaks combining you have two wide/broad peaks. Wider peaks means more bass response. When combined these broader peaks overlap allot more so the change heard will be less drastic because the individual peaks wider and less focused.

 

The frequency dip between the two peaks is increased when both are selected to create a ghost pickup response between the two. This is because the ramped sides of the two peaks overlap when both are selected. When the upper response of one pickup is combined with the lower response of another a third ghost voice is generated between them.

 

This can easily be heard if you use a stereo setup. If you run one pickup to the left speaker and another to a right. That third voice occurs in the center between the two speakers, even though there is no center speaker. What is unique to each pickup will stay on the left or right. What is common to both will occur in the center between the two peaks. Since the guitar is mono we only hear the sum of the two peaks.

[Chordite]

"If you run one pickup to the left speaker and another to a right. That third voice occurs in the center between the two speakers, even though there is no center speaker. What is unique to each pickup will stay on the left or right. What is common to both will occur in the center between the two peaks."

 

I might try a track like that, sounds interesting, especially through headphones where you get total separation

[Ratae Corieltauvorum]

OK, I think I get it.

 

I know when I used to dabble in hifi with screw terminals on the backs of speakers and plain high quality copper two strand interconnects I remember wiring my first set of speakers and it didn't sound right, and a friend explained that one was blowing and one was sucking.

 

I'll read this agin when I recover from my lunch, which was far too heavily carbed:)

 

Cheers WRGKMC.........quality posting

[Ratae Corieltauvorum]

Interesting this one. Until recently I got myself in trouble determining whether single coils were north up or south up, until I found out that the North pole is actually south polarity, so when the north indicator on a compass points to the top of a pickup, it's south up

[Mikeo]

I have a degree in Physics and Electrical engineering. What I believe is happening is you have what is called and RCL circuit. The pickup being the inductor (L), the tone control being the resistor ® and the capacitor ©.

 

In an RCL Circuit the current will lead the voltage and they are out of phase. You have a single signal when you are running a the switch in the 1, 3, 5 position. However when you run 2 pickups at the same time you notice the slight phase difference between the 2 pick up. I believe the magnetic pole directions are altered in the neck and bridge pick up too, so not only does it cancel the hum a bit, but it also delivers that quacky out of phase parallel wired sound.

 

The magnets are charged after the pick ups wound, and over the years Fender has charged the north up during the early years, then south up after like the early 60’s

 

All in all is a very cool sound. I have actually left the 3 way switch in 3 of the 4 of my strats and still doing the so call balancing act with those guitars.

 

You’re in good company with this tone, old skool Gilmore, Clapton, Knopfler and countless other used this tone.

 

 

I’m not sure if this helps. I might be right and then again maybe some others can chime in on this one.

 

[Phil O'Keefe]

A question for you to consider Ratae... what happens when you "sample" (record or listen to) a speaker from two different locations (using two different microphones) and then sum the signal?

 

 

[Ratae Corieltauvorum]

Phil you over-estimate me, I barely understand what you're question means......"how many holes in a football net" I can cope with, but ^^^^^^

[onelife]

I'm not an electronics/physics guru but I do play Stratocasters and other guitars. I really got heavily into the strat when the first two Dire Straits albums came out. Like everyone else at the time I was playing "Sultans" with my band. The song has an obvious guitar sound that I feel is an important part of the performance. Imagine my surprise when I was playing a Les Paul Custom in a music store and there it was - the famous strat "quack". Sultans of Swing on a Les Paul and it sounded like Knopfler's strat. What this particular Les Paul had in common with a Stratocaster was a middle pickup.

 

 

I saw a guy playing a tele one time with two pickups on rails so he could slide them to different positions between the bridge and the neck - similar to the photo below...

 

 

He let me check out the guitar after the show and I was intrigued by the tonal variations that even slight movements of the pickups would produce.

 

 

My conclusion, after all of this, is that the characteristic strat sound (which incidentally was by accident and not design) is due to some phase cancellation because, as I like to describe it, the pickups are mechanically out of phase.

 

 

Paul Reed Smith figured this out when he built his LP/Strat hybrid the Custom 24. I believe he arrived at the 25" scale length because, when combined with the 24 fret neck and standard sized humbuckers, it allowed him to position the two inside coils of the pickups in the same position (relative to scale length) as the bridge and middle pickups on a strat. He had to fiddle with the orientation of the magnets to make it work but I think he succeeded.

 

 

 

 

[WRGKMC]

^^^^ I don't know if that applies Phil.

 

Pickups will produce sound in a Vacuum with no air. There is no delay involving sound travel through air. Pickups are purely magnetic and they produce an electrical signal at nearly the speed of light. When using mics, Air is involved in delaying sound waves striking the diaphragms creating phase differences. The distance of the pickups from the strings simply changes the field density and even if there was some kind of ultra small delay it would be inaudible to our ears.

 

If anything there may be delays caused by the pickup coil reluctance, but that's why they wind the bridge hotter then the neck to balance out the coil outputs.

 

 

Tone combinations is Its all about the portions of the string being sampled and how they combine.

 

If the bridge captures more 5K and the middle captures more 3K. The two together contribute to a boost at 4K.

 

Here's an interesting diagram of the wave portions a pickup will produce.

 

 

 

 

This one shows you how they differ depending on the fret chosen.

 

 

 

 

This diagram shows the frequency response of the three different pickups.

 

The neck Neck pickup, 6.375 inches from the bridge. First peak is 165 Hz; nulls every 330 Hz.

 

 

The middle, Middle pickup, 3.875 inches from the bridge. First peak is 271 Hz; nulls every 542 Hz.

 

 

The bridge, Bridge pickup, 1.625 inches from the bridge. First peak is 637 Hz, nulls every 1274 Hz.

 

 

If you combine the peak of the middle at 271 and the bridge at 637 you have a combined peak of 454. Of course its a bit more complex because the musical notes have a wider response so you're combining the entire responses of the two.

 

You can see how the neck produces total higher frequency content compared to the others. The lows drop off a good deal too.

When you combine two pickups there's a certain amount of comb filtering that's going to occur as the two frequency responses combine. You may also have a change in dynamics because the string will have more movement across the pickups closer to the neck. I don't think there's any notable phase cancellation involved.

 

In order to get phase cancellation you have to have the string moving in two opposite directions at the same time.

 

The fundamental note is always the strongest and extends end to end on the string. All three pickups will "always" produce an "in phase" fundamental note.

 

 

Much of the secondary harmonic will likely be in phase as well, at least till you move up to the D note on a standard neck. A strat had a neck position about where the second octave fret would be. When you move above the 12th fret, the second order harmonic will have the string moving in an opposite direction and the 2nd order harmonics begin to phase cancel between the neck and middle pickups.

 

The 3rd, 4th, 5th harmonics can be calculated out but it becomes very complex depending on where you fret the strings and have harmonic cancellation. On the flip side, you have just as much in phase summing as you have cancellation. If one pickup is centered under one harmonic and another pickup under another which are both in phase, they combine to increase harmonic content. Harmonics over pickups may be creating a north going wave above one pickup and south going above another and cancel. They may also be both north or south going and be additive.

 

We hear most of this a frequency response differences. These harmonics are small in comparison to the fundamental wave all pickups generate so its not going to produce anything close to what you get when you reverse a coil polarity.

 

When you reverse a coil, the fundamental waves are canceled leaving only the differences in harmonic content. Like I said, the first harmonic will contain the longest bass waves do reversing a coil makes the tone thing because most of the bass is being canceled.

 

Therefore combining two in phase pickups winds up having more additive harmonics then phase cancellation between harmonic nodes. What we hear is a more complex comb filter effect in the upper harmonics and the result is a third unique waveform unlike either of the two separate waves. Which frequencies are boosted and cut are simply a matter of where the peaks and valleys overlap.

 

Even two valleys can combine to create an increase at that frequency so long as there's something there that can be added together. If you have one valley that's -3db at 6K and another that's -6 db at the same frequency, you get a 1.236 db increase (if my math is right)

[onelife]

. . .

When you combine two pickups there's a certain amount of comb filtering that's going to occur as the two frequency responses combine...

 

That's the key right there.

[WRGKMC]

 

That's the key right there.

 

Yes, but the comb filtering involves the strings upper harmonics only, not the fundamental note. The upper harmonics can vibrate in opposite directions over two different pickups causing the delay.

 

Comb filtering is normally done electronically where you add a delay to the entire signal so its effect is much more noticeable. What you hear form the guitar strings is going to be mild involving the upper frequency harmonics that just happen to be out of phase above the pickup. The lower fundamental frequencies are going to mix together additively.

 

Comb Filtering Definition = In signal processing, a comb filter adds a delayed version of a signal to itself, causing constructive and destructive interference. The frequency response of a comb filter consists of a series of regularly spaced spikes, giving the appearance of a comb.

[onelife]

In signal processing, the comb filtering is achieved by adding the delayed signal resulting is phase reinforcement and cancellation at different frequencies.

 

The three pickup guitar achieves a similar effect of frequency (and harmonic) dependant phase reinforcement/cancellation because of the position of the pickups under the strings. Even on a two pickup guitar, the slight drop in level when using both pickups is due, in part, to similar phase cancellation.

[soundcreation]

I know nothing about the why but to add to Chordite's post, my Carvin is HSS and the singles are actually single coil sized humbuckers. It has a five way switch with master volume and tone and in positions 2 and 4 it does strat sounds pretty well.

[Ratae Corieltauvorum]

Wow, quite clearly we are not lacking in the electronics department.

 

Many thanks guys, I understand more than I did when I asked the question, but not sure I understand everything

[WRGKMC]

I think there's a way to visualize how a string can carry more then one wave at a time. If you throw a single stone in the water it will create one set of waves. If you throw a second third or 4th stone you can have multiple waves occurring at the same time. each set will travel across the pond and retain their pattern.

 

If the two waves happen to meet up in the same spot, they add together to make one large wave. is you have one rippling up and another down at the same time they null each other out at that point, but it doesn't stop the wave expansion across the pond. The waves keep their overall pattern, frequency. Amplitude of course does decrease but that's a matter of inertia and tension, not because of harmonic cancellations. main thing is a string carries several waves at the same time which ride on the main fundamental wave, much like carrier waves are used in radio.

[guitarcapo]

Positions 2 and 4 simply create a humbucking pickup....just with a lot of space between the two coils.

 

As that space increases, you get phase cancelations of those frequencies becoming out of phase between the two pickups.

 

These phase disparities have to do with the positions of the pickups being different along the vibrating string's scale length.

 

The result is the"quack" you hear. The dropout of certain frequencies coming from the phase cancelation between the two pickups.

 

 

[WRGKMC]

The pickups are in phase with each other. They are "not" out of phase and the pickups do not cancel frequencies produced by the string just because they are Humbucking. You'd get the same tones if you had three north or south magnets. They only cancel noise like hum that comes from other sources.

 

The center coil on most Strats is reversed, but it also have a reverse magnet. Hum doesn't come from the string or the magnets. so it gets phased canceled by one of the coils being reversed. This Humbucking, again has no impact on frequencies being generated by the strings.

 

The only phase cancellation that occurs is when the string is moving in two different directions at the same. One pickup generates a negative going wave and the other is generates a positive going wave at the same time. This dual direction string movement only occurs between string nodes. The vibration between the nodes are the harmonics. They ride on the fundamental string note.

 

 

The fundamental note always vibrates end to end on a string no matter where its fretted. Harmonics occur at 1/2, 1/3, 1/4th etc of that string length and its why that can be canceled by pickups. .

 

What we hear is the fundamental note and "one or more" of the upper harmonics either cancelling each other out OR adding together to make those harmonics stronger or weaker then they would normally be with a single pickup.

 

None of this has anything to do with the fact the pickups are Humbucking. Its simply the area where the string is being sampled, and the way the two samples of vibrations Mix together additively or subtractivly.

[guitarcapo]

The devil is in the details. I agree that the two pickups are mostly "in phase". RWRP (reverse wound/reverse polarity) does that. But they don't make exactly the same sound because of their location along the string. Thus, they have a different sound print. Since the precise frequency response is slightly different, certain harmonic frequencies are out of phase and others are amplified. This creates the "quack" sound.

 

You're correct....... but not totally correct.

[onelife]

Positions 2 and 4 simply create a humbucking pickup....just with a lot of space between the two coils...

 

 

 

 

 

 

It wasn't always that way. RWRP middle pickups weren't widely used until the 80s but positions 2 and 4 still produced the "quack".

 

 

 

 

[knotty]

 

 

 

It wasn't always that way. RWRP middle pickups weren't widely used until the 80s but positions 2 and 4 still produced the "quack".

 

 

 

 

Good point.

 

Also, arent there many strat style or strat copies that dont quack?

[Ratae Corieltauvorum]

Generally, nearly all 3 pickup guitars have the quack ingredient, even the horrible 57 3 humbucker black Beauty LPC.

 

I've heard 3 P90s quack decently enough, but as onelife points out the best quack is to be achieved with no RWRP Strat sets with just a revered polarity middle pickup.

 

In my experience anyway...

[WRGKMC]

I think that's exactly what I said several times already.

[WRGKMC]

I used to play a number of vintage Strats. Balancing the switch in the 2 and 4 positions was a bit tricky but possible.There just wasn't any fixed notch for it.