Load resistance - tone loss.

[peskywinnets]

Ok, so most that have dabbled know that too much load (low resistance) following on from a pickup results in a loss of tone, but what's going on here to explain the loss of tone?

What frequencies are being lost (just the highs..or is the bass end diminished too?) with too much load ......& why etc?

[Mike Sulzer]

Ok, so most that have dabbled know that too much load (low resistance) following on from a pickup results in a loss of tone, but what's going on here to explain the loss of tone?

What frequencies are being lost (just the highs..or is the bass end diminished too?) with too much load ......& why etc?

There is a resonant peak. The load lowers the height of the peak.

[pdf64]

See
BuildYourGuitar.com :: The Secrets of Electric Guitar Pickups
Pete

[frankfalbo]

Even our Customer Service guys a lot of the times just say "It shaves some of the brightness off" because if you think about it, no matter what the pickup the peak is likely in what we consider the treble region, whether it's 4kHz or 9kHz or higher. So when someone thinks a pickup is too bright, taming the peak is usually a "win" but I still think every time about how its not really taking away treble like a shelving filter, just knocking that peak down.

[Mike Sulzer]

Even our Customer Service guys a lot of the times just say "It shaves some of the brightness off" because if you think about it, no matter what the pickup the peak is likely in what we consider the treble region, whether it's 4kHz or 9kHz or higher. So when someone thinks a pickup is too bright, taming the peak is usually a "win" but I still think every time about how its not really taking away treble like a shelving filter, just knocking that peak down.

By the way Frank, when I last looked on the SD web site some time ago, it listed the resonant frequencies of the various pickups, something I find to be a very useful spec. But I could not find any statement of how much external capacitance there is in the measuring setup. How is the measurement made?

[FunkyKikuchiyo]

really stupid question... what load are you talking about? External load, as in guitar harness?

[peskywinnets]

By the way Frank, when I last looked on the SD web site some time ago, it listed the resonant frequencies of the various pickups, something I find to be a very useful spec. But I could not find any statement of how much external capacitance there is in the measuring setup. How is the measurement made?

Actually, when you said earlier that reducing the load lowered the resonant peak (btw: my interpretation of 'load' here is any load the pickup drives ....mainly the vol & tone knob, but also the input impedance of the guitar amp), I went & googled & the 1st thing I hit was Seymour Duncan's site, giving a high level overview of how they measure the resonant peak....

How do you measure the resonant peak of a pickup? - Seymour Duncan Everything Else

[Mike Sulzer]

Actually, when you said earlier that reducing the load lowered the resonant peak (btw: my interpretation of 'load' here is any load the pickup drives ....mainly the vol & tone knob, but also the input impedance of the guitar amp), I went & googled & the 1st thing I hit was Seymour Duncan's site, giving a high level overview of how they measure the resonant peak....

How do you measure the resonant peak of a pickup? - Seymour Duncan Everything Else

Thanks, but that explanation does not tell me the external capacitance in the system. For example, if they have as little as possible in the system, then the actual locations of the peak when using a real cable will be quite a bit lower.

[frankfalbo]

I get your question but I can't disclose any more than what's on the site. But you can infer from the site language that we are listing specs of our pickups, not making an assumption about the end user's cable capacitance. Maybe the guy has an on board buffer, or a wireless. Maybe he has an all-true-bypass pedalboard with a coily cord!

[Mike Sulzer]

I get your question but I can't disclose any more than what's on the site. But you can infer from the site language that we are listing specs of our pickups, not making an assumption about the end user's cable capacitance. Maybe the guy has an on board buffer, or a wireless. Maybe he has an all-true-bypass pedalboard with a coily cord!

Thanks Frank. That is a useful answer.

[peskywinnets]

So, re making a 'resonant peak plotter' ......is it really just a case of winding a transmitter coil, and then attaching the transmitter to circuit with a constant current output (thereby assuring that the frequency response of the transmitter coil is flat?) & having something control/log the test frequency sweep? (eg a PIC)

[Steve Conner]

Yes, except you don't even need to fiddle with PICs. You can get free software that plots the frequency response of an audio system using your computer's soundcard as an IO device. Essentially by feeding the system with white noise and doing FFTs of the output, or similar.

For instance, Rightmark Audio Analyzer or Spectrum Lab.

There are also decidedly non-free programs like Electroacoustics Toolbox.

Re the transmitter coil, you have to be quite sure what "flat frequency response" actually means. Maybe Helmuth Lemme will drop by and explain it all. I've used a coil of a few turns (low resistance and inductance over the whole audio band) with a large resistor in series to swamp it, driven off an audio power amp. But it's by no means clear to me that constant current is equivalent to constant "string-vibratiness".

Also, this approach only tests the last stage in the pickup's sound-modifying chain, the electrical filter. There's stuff before that, the conversion from string motion to flux changes, that also affects the tone but is considerably harder to quantify.

[David King]

Significant loading will actually effect the string's movement via back EMF. Some of the loss of highs could even be audible acoustically. Try shorting your pickup leads while plucking and listening to the guitar in a quiet room, the sustain should be noticeably shortened. It helps if the pickup are mounted very close to the strings obviously.

[bbsailor]

Significant loading will actually effect the string's movement via back EMF. Some of the loss of highs could even be audible acoustically. Try shorting your pickup leads while plucking and listening to the guitar in a quiet room, the sustain should be noticeably shortened. It helps if the pickup are mounted very close to the strings obviously.

David,

Normally ribbon microphone engines are concerned about the loading on the ribbon as the transformer loading affects the frequency response of the ribbon microphone. Ribbons are closly connected to the magnetic field that helps produce the ribbon microphone output. What you said implies that a pickup is more highly coupled to the string circuit than I have previously thought. You did indicate that this is more relevant when the strings are very close to the magnets in the pickups.

I have always thought that the string was very loosely coupled to the magnetic circuit. I would be interested in hearing how one would verify how closely or loosely coupled the string is to the magnetic field damping that you described in your post.

Energy from the string plunk of the hand quickly diminishes through time as the air friction helps to diminish the string amplitude. The magnetic force on the strings is another force that acts as a force to diminish the string sustain. This reminds me of the classic current versus voltage effects of pickups and loads with another twist for string magnetic loading.

We need a clear way to evaluate all the forces that impact the sound of a guitar pickup.

Any ideas?

Joseph Rogowski

[David King]

Joseph,
We could eliminate the forces one by one until the sustain lasts forever. Mount the string on a solid steel beam inside a tube with a vacuum pulled to eliminate the air resistance. If the beam was the least bit magnetized it could interfere with the string. That does that leave? The string won't be perfect so some losses there for sure.