Discussion in 'Pickups & Electronics [BG]' started by colcifer, Jan 14, 2012.
I don't know if anyone does. You usually only see things like "bass-5, mids-6, treble-5."
It's not easy to get an accurate frequency response, because there are many variables involved. What you use to disturb the magnetic field to induce a current to flow in the coil, and what sort of loading is against the coil will influence the way the circuit behaves.
The only thing that would sound believable to me would be something like a controlled mechanical vibrator driving a mu-metal rod (no jokes, please!) or maybe a series of tuning forks that are also mu-metal (steel for example.)
This is not an easy thing to do and even if you did, trying to interpret the results vs your strings and setup is probably equally difficult.
When it's done, it's done by using a small coil that feeds a signal into the pickup from a frequency generator. Then the output of the pickup is plotted against the signal as it's swept.
You can also probably do it with white noise.
But hardly anyone does this.
Bartolini made a mechanical string picker once! But that was to measure output, and not frequency response.
It's more difficult than it looks to get reliable results.
Using an induction method does not take the response time of the magnetic field into account. A non-ferrous disc with steel "poles" that is spun in the field will give a descent indication of frequency response. The wheel must be well balanced (like a car tire) and safety precautions observed in case the wheel comes apart. The output is basically a sine wave and tells nothing about attack and decay characteristics. A mechanical picker is needed for that and the alignment of the tested pickups and age of the string in the setup is critical to obtain usable info. Ferrous materials cannot be used in the fixtures except for the bits that excite the magnetic field.
Here's the coil method.
BuildYourGuitar.com :: The Secrets of Electric Guitar Pickups
Where does the article address the frequency response of the exciting coil? If its not flat (or a correction made for it) I ain't buyin' this.
The lower its impedance, the flatter it is. Or, if it's immediately preamplified it probably gets to within ~1 dB (or even tighter) to flat.
...funny how noone ever made a Wal-like exciter coil. Or an Alumitone-like one. That'd give a pretty flat characteristic.
Wal? They use multiple coils with lots of turns of wire! I'd rather use a speaker coil.
A year later...
While I was digging around last weekend researching pickups and electronics, I found that Lemme article. Really cool way to help see what you hear in a pickup. Even if it's not perfect, you get a sense of where that resonance is. More useful than a DCR reading at least. I'm surprised I didn't find more related threads on TB. It sounds just like the thing that'd get people's attention here. (At least it would in the Amps forum. )
Here's another interesting link I found. Repurpose an old hard drive's coil to drive your pickup.
Wonder if it's better or worse than using a cheapy guitar pickup off ebay. (I'd suspect better.)
I hope to get a testing setup like this going when I get all my parts together for the next build. Should be fun to play with different circuits and scope 'em to see what's happening. Again, not AES level, just to see how the pickup's RLC interacts with the components.
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