Question About Microphonics

[tonedeciple]

I have always understood microphonics to be caused by a vibrating coil and that the extent of the affect can be controlled, though not completely eliminated, by potting the coil. With that said, if I remove the strings from any electric guitar, regardless of the type of pickup it uses, and tap the body with a pick, I can hear the tap come out of my speaker. I have done this with the same pickup both before and after wax potting, yet I hear the same tap tone. I had assumed that potting would have diminished the tap sound by reducing the vibration, but it didn't. Is something else triggering the signal? If it isn't caused by a vibrating coil (microphonics), then what is it? I suspect it might have something to do with disturbing the magnetic field. If that's the case, would the term microphonics still apply?

[big_teee]

Usually an unpotted picked has a bright metallic sound when you tap on the cover.
A Potted pickup usually has a duller sound not as loud.
T

[Possum]

With humbuckers microphonic squeal is almost always coming from the cover, not the coils. The coils could squeal if you're playing a 100 watt Marshall stack in your bedroom or doing stadium rock. If you stabilize the cover they won't squeal. Modern covers SUCK, and don't have flat tops on them, they are nicely roundish which makes great for microphonic squeal. I use a two way clamp, and put a couple pieces of paper tape over the slugs and it kills most of it.

[David Schwab]

I didn't see him mention anything about covers. But unless the pickups are screwed right to the wood of the guitar with no springs, you will hear sounds when you tap the body, because the pickups are moving. And even then you might hear some sound. When the body vibrates the pickups vibrate too.

Regarding covers, just follow the lead of thousands of guitarists since the early 70s, and take the damn things off! People started taking them off because the pickups sound better without them. They are archaic and was used for shielding, even though they aren't needed. Most of the great humbucker tones over the years were done with no covers.

[tonedeciple]

But unless the pickups are screwed right to the wood of the guitar with no springs, you will hear sounds when you tap the body, because the pickups are moving. And even then you might hear some sound. When the body vibrates the pickups vibrate too.

So when the pickups vibrate after tapping the body wood, is the signal generated because the pickups components are vibrating within the magnetic field? If so, could this effect be described as microphonic vibration?

[Stealth]

Here's an odd case that happened to a guitar player in my band not a week ago. His neck HB was mounted on standard screws, springs and baseplate, but it was riding a bit higher. It seems the screw had come undone from the baseplate, and worse yet, the spring started to ride up the screw until it was literally pinned against the HB ring. Needless to say it howled like a fury until we reassembled the whole thing.

Could this also be counted as microphonics, given just how reactive springs are to any kind of motion?

[tonedeciple]

I've always thought of microphonics as a bad thing, but now I realize that in certain situations, it can be very desirable. If a pickup squeals, then obviously it's a bad thing. However, if a pickup's inherent microphonic tendencies are able to detect the string's vibration as it passes through the guitar body's wood, this would help to shape the guitar's overall tone. I've had customers request their pickups to be direct mounted to the body because they believe doing so will allow the pickups to better sense the wood's vibration. Based on David's comments above, I would think that mounting the pickups with rings and springs would enhance their ability to detect vibration traveling through the guitar body as well as the neck/fretboard.

[soundguruman]

the sound comes out of the speaker and travels through the air, to the pickup.
The sound wave from the speaker is then detected by the pickup and re-amplified a second time, then over and over again.
This forms a loop, and when the loop occurs, you hear the feedback, squealing, ringing.

During this looping, the sound wave also tends to reach the first preamp tube, and a ringing occurs at the frequency of the glass envelope resonance. There are several methods to stop the tube from ringing, and you may be blaming the pickup for a problem with a preamp tube, or a problem with the actual amp circuit design...

However it is not the pickup that is entirely to blame for the squealing, ringing feedback. It is rather that one particular frequency is being amplified more than all other frequencies. This creates a "hot spot" in the frequency response.
Using an equalizer to notch that one frequency out of the system is a very popular method to stop the resonant ringing at a particular frequency. Once the frequency response has been flattened, and there is no longer a hot spot, the problem is diminished.

But actually it's just as much a part of the speaker, preamp tube, amp design and equalization....as it is the pickup. All these parts put in their 2 cents to cause the ringing, not just the pickup.

[tonedeciple]

the sound comes out of the speaker and travels through the air, to the pickup.
The sound wave from the speaker is then detected by the pickup and re-amplified a second time, then over and over again.
This forms a loop, and when the loop occurs, you hear the feedback, squealing, ringing.

Which just goes to show that a pickup senses more than just a steel string's vibration over the pole pieces. The reason I started this thread was because of an article I wrote several years ago on why wood plays such an important role in shaping a guitar's tone. A reader emailed me and informed me that part of what I had written was wrong. He corrected me by stating that a pickup only senses the steel string as it vibrates. I had written that a pickup can act like a microphone by sensing vibrations as they travel through wood (or through the air from a speaker as you have explained). At this point, I can go back and edit the original article to clarify my meaning.

[soundguruman]

The wood is super critical, without question, along with the neck angle, pickup position. All these things affect the sound in a radical manner. The wood I like is mahogany or koa, ironwood, along with ebony for the finger board. The neck should be integrated with the body, not bolted on. To me, it needs to have at least that, besides the pickups, or I don't like playing it, and I don't like the sound of it either.
Granted, Hendrix played a bolt on neck, and he managed to get something out of it, despite the construction.
I think people put way too much emphasis on the pickups, and not enough to the wood, etc...
I spent $$$ on an L6S Gibson, Solid rock Maple, with all kinds of gizmos and pickups, etc...but even after changing the pickups and all kinds of goofing with the controls, it still did not sound worth a crap. It was for sure, the wood that was dead as a doornail.

[David Schwab]

I spent $$$ on an L6S Gibson, Solid rock Maple, with all kinds of gizmos and pickups, etc...but even after changing the pickups and all kinds of goofing with the controls, it still did not sound worth a crap. It was for sure, the wood that was dead as a doornail.

Nothing wrong with maple guitars. Les Paul put a thick maple top on the LP because he figured with a piece that thick it would simulate a maple body.

I like those L6-S's. Bill Lawrence designed those.

[soundguruman]

I view the L6S as the perfect example of how a guitar should not be built, a real doggie.

[ken]

Now there's a challenge for us all... to make a pickup that makes that guitar sound good

ken

[soundguruman]

I favor a matching transformer inside the guitar. That's the problem, not enough isolation, and not the right impedance for the amp, and severe loss of high frequencies and tone due to the archaic design. I think I would start over again, building the channel switching into the guitar, because I hate footswitches. Remember I said it.

[Possum]

Microphonics are highly desirable, if they are gone you get EMG tone ;-) Taking covers off is cool if you want more treble, thats why players took them off in the 70's. The downside of that is its also a great way to kill humbuckers. Virtually every PAF I restored died because of sweat corrosion because covers were off, its super easy for that stuff to get in the coils, it may take some time but it eats thru the wire eventually if it can find some small spot. There are different kinds of microphonics, guys who play stadium rock, solidly pot their pickups but they also have to cram foam in the rout so the pickup can't vibrate in the mounting ring. I had this happen with a pickup a couple years ago, the pickup itself was literally vibrating as a solid unit, this was in an archtop. PRetty funny to watch it do the shimmy but whoooooooooom isn't a sound I like from guitars....