Blade pickup turned 90 degrees

[FunkyKikuchiyo]

As an alternate idea I'd look into using a blade core that's similar in shape to an I-beam (or, a railway track, if you will) - that sounds like it would diffuse the magnetic field enough to make string bending work even in the bridge position. Even then, the I-beam (or, rather, the top and bottom "flanges") would only need only be as wide as, say, the distance between the center-poles of a J-bass pickup (that is, the pair that sits underneath a single string).

Of course, this is all just theory. I'm still struggling to get around to winding my first "common" pickup. Soon-ish.

An engineer friend of mine suggested this, I was thinking this might be a good candidate to try it on. His thought was just that it would be

I'm not entirely convinced of the frequency canceling thing. I mean, if you have two small points in tandem, I can see how some frequencies will drop off, but why would a broad range just get the fundamental? An acoustic top is a pretty broad range, does it not get high frequencies because it is too big? It seems like a very long blade could pickup frequencies whose wavelength is smaller than its total length, it would just mean that it is going to repeat more times over the whole length. To cancel, you need to have the signal of a peak and valley occurring at the same time, which makes more sense with two points rather than a plane. I'm probably wrong.

[David Schwab]

As an alternate idea I'd look into using a blade core that's similar in shape to an I-beam (or, a railway track, if you will) - that sounds like it would diffuse the magnetic field enough to make string bending work even in the bridge position. Even then, the I-beam (or, rather, the top and bottom "flanges") would only need only be as wide as, say, the distance between the center-poles of a J-bass pickup (that is, the pair that sits underneath a single string).

The original Bartolini pickups had a flat planar pole tips.

[David Schwab]

By the way, Bruce, is it normal that opening any links from that page of yours (incl.the pickup page) now produces a 404 error? Did you remove the page on purpose or is it a server fault? I remember reading that page and you really had a plethora of useful info there - definitely interesting directions in pick-up design.

There is a "/Gallery" directory that doesn't belong there.

If you remove that and go back to the main site page, all the links work.

[Steve Conner]

I'm not entirely convinced of the frequency canceling thing... It seems like a very long blade could pickup frequencies whose wavelength is smaller than its total length, it would just mean that it is going to repeat more times over the whole length.

The way I see it, whenever a whole number of wavelengths in the string is equal to the length of the blade, then that wavelength will be cancelled. The longer the blade, the longer the wavelengths that start to meet that criterion.

If several wavelengths fit in the aperture, but not a whole number, then I think everything ought to cancel except the bit of wave left over. So the effective sensing length is not the length of the aperture, but the length of the left-over piece of wave. For the fundamental, the whole length of the aperture works, so this suggests that harmonics will be attenuated in general, making the pickup sound bassy relative to a smaller one.

To be fair though, I imagine real pickups don't have an "aperture" as such, a zone where the sensitivity is the same everywhere inside it and zero as soon as you go outside it. The sensitivity to string motion will be a vector field that varies in magnitude and direction in the 3-dimensional space all around the pickup, so I doubt any harmonics would ever cancel completely.

You could try to visualise it, but I start to think of taking dot products with infinitesimal lengths of moving string and then integrating a whole lot of stuff, and it just makes my head hurt.

Bruce Johnson's pickup isn't really any bigger in terms of aperture than, say, a Music Man bass humbucker. The original post gave an impression of some monster pickup with an aperture the size of a slice of bread, and I think that would sound bad.

[David Schwab]

Bruce Johnson's pickup isn't really any bigger in terms of aperture than, say, a Music Man bass humbucker. The original post gave an impression of some monster pickup with an aperture the size of a slice of bread, and I think that would sound bad.

A MM pickups has two coils and reads the string at two points. Bruce's pickup is like a MM pickup that is a big single coil, and reads a larger section of the string.

[Mike Sulzer]

but why would a broad range just get the fundamental?

It does not. The cancellation of higher harmonics is a function of the phase of the oscillation along the portion of the string over the active region of the pickup. For high harmonics, parts of the string are moving towards the pickup, other parts are moving away, so there is a reduction in the total signal.

On the I beam: If one is using alternate magnetic polarity from coil to coil, then there is a region of zero magnetic field in between, even if you use an I beam. Not much you can do about that.

[Stealth]

To be fair though, I imagine real pickups don't have an "aperture" as such, a zone where the sensitivity is the same everywhere inside it and zero as soon as you go outside it. The sensitivity to string motion will be a vector field that varies in magnitude and direction in the 3-dimensional space all around the pickup, so I doubt any harmonics would ever cancel completely.

You could try to visualise it, but I start to think of taking dot products with infinitesimal lengths of moving string and then integrating a whole lot of stuff, and it just makes my head hurt.

From the simulations I've seen (and common, continuous-space sense), the aperture does exist, but it's obviously not a "brickwall" thing that starts and stops - the aperture has a gaussian (bell curve) intensity, so that can be used as a starting point.

[Steve Conner]

Well if you assume the aperture is a Gaussian, its frequency response is a Gaussian too, so it's simply a lowpass filter and doesn't have any nulls or comb filter type behaviour.

Spatial Filters - Gaussian Smoothing

[Mike Sulzer]

A Gausian could be a reasonable approximation for the narrow aperture of a single coil, but surely not for a blade extending along the string. I would expect a fairly rectangular aperture with a corresponding sin(x)/x response in the frequency domain.

This is of course different from the humbucker response which would be a sort of comb multiplied by the sin(x)/x.

Well if you assume the aperture is a Gaussian, its frequency response is a Gaussian too, so it's simply a lowpass filter and doesn't have any nulls or comb filter type behaviour.

Spatial Filters - Gaussian Smoothing

[Stealth]

Well, that or a raised cosine function with a relatively low roll-off (think 0.25 according to the above image). Naturally, the humbucker'd probably be an odd interplay between the two, as you said.

Edit: Actually, the raised cosine covers a basic sinc shape as well at roll-off 0. So there goes the shape.

[Bruce Johnson]

By the way, Bruce, is it normal that opening any links from that page of yours (incl.the pickup page) now produces a 404 error? Did you remove the page on purpose or is it a server fault? I remember reading that page and you really had a plethora of useful info there - definitely interesting directions in pick-up design.

I'm actually right in the middle of a major overhaul of my site. As new sections are completed, I've been putting them on the server, even though all of the links aren't completed or updated. That particular page is one of the new ones.

[bassjase128]

I wish I had'nt asked now

I'm getting a headache

[Mike Sulzer]

I think the humbucker response would be closer to a comb multiplied by a Gaussian rather than what I wrote above. This is because the aperture of each coil is narrow, but has a smooth fall off rather than an abrupt square shape.

(Sorry if this is causing headaches.)

Well if you assume the aperture is a Gaussian, its frequency response is a Gaussian too, so it's simply a lowpass filter and doesn't have any nulls or comb filter type behaviour.

Spatial Filters - Gaussian Smoothing

[David Schwab]

(Sorry if this is causing headaches.)

These kinds of headaches are good for you!

[RedHouse]

They make some very stylish instruments. Most are a variation of these Hagstroms.

I love those old funky instruments from the 60's/early 70's.

That one looks like it's got an embeded juke-box controller right off the counter at Woolworths cafeteria!.