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Post by antigua on Apr 30, 2020 17:04:44 GMT -5
This experiment revolves around microphonic pickups, and the assertion that if you can talk into a pickup and hear your voice out of the guitar amp, that it must be picking up acoustic sounds of the strings, and that this is somehow mixing into the final tone to some beneficial effect. This is an unpotted Strat pickup, with a very typical, semi-flat semi-round coil, making noise into the Velleman PCU-200:  Around the 100Hz to 500Hz, shouting over the pickup appeared to cause some very small blips:  In order to approximate the "acoustic contribution" of electric guitar strings, without inducing any magnetic flux change, I suspended the pickup over nylon guitar strings and strummed them. There were some very tiny voltage spikes in between those noise cycle spikes, not much louder than background noise. I wish I had a way to negate the noise, but that would be a lot more involved.  This is the voltage output with the pickup suspended over ordinary electric guitar strings, in a capacity the pickup is meant to operate.  Thus, once again, testing shows that the voltage product of acoustic sound with an unpotted pickup is nill as compared the magnetic flux product. But if I hook the pickup up to an overdrive pedal, fed by a nine volt battery, and max out the knobs (volume and gain at 5 o'clock), then the difference is not so vast... The noise is a lot more choppy, there appears to contain various harmonics:  Talking into the highly amplified pickup produces a lot of action around 1.3kHz, surprisingly not so much in the 100Hz range of my voice. This suggests to me that the pickup isn't acting as a microphone so much as the sound, or the air coming out of my mouth, is causing the wires to wiggle and oscillate at that higher frequncy:  Here is the amplified case with the pickup mounted over nylon strings, and there is a surprisingly rich amount of content, but once again, a peak around 1.35kHz that seems to have little to do with the noise source and more to do with a physical resonance/vibration in the coil.  Finally, the electric guitar strings into the amplified pickup, essentially the ceiling:  So, while I think it's safe to say they pickup is not audibly microphonic without gain, on the other hand, with copious gain, sound, or air pressure changes, cause an output that is easily distinguishable from the noise floor. So the question is, if you can hear the output represented by the last two plots by themselves, can you distinctly make out the two different outputs when the two are combined as as single signal? Which is another way of asking, under high gain, are you hearing both acoustic and magnetic components of the guitar string? Guitarists who thing there is value to a microphonic pickup would have you believe the answer is "yes". My guess would be, "no way", but I think I can do this test again with a DAW instead of a USB oscilloscope and create practical demo. |
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Post by blademaster2 on Apr 30, 2020 17:12:02 GMT -5
I agree that the acoustic contribution compared to the magnetic contribution would be minimal - unless the amplifier gain in the room created a much louder acoustic signal that was then picked up microphonically.
Based on this, do you accept that Brian May's guitar as depicted in the movie Bohemian Rhapsody could be used as a microphone for Brian to talk back to the studio control room through it? I still have a hard time imagining that those Burns pickups, even the middle one that was not potted, could be so microphonic (but then why would Brian not have said that it was not accurate when they made the movie?)
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Post by antigua on Apr 30, 2020 20:37:25 GMT -5
I agree that the acoustic contribution compared to the magnetic contribution would be minimal - unless the amplifier gain in the room created a much louder acoustic signal that was then picked up microphonically. Based on this, do you accept that Brian May's guitar as depicted in the movie Bohemian Rhapsody could be used as a microphone for Brian to talk back to the studio control room through it? I still have a hard time imagining that those Burns pickups, even the middle one that was not potted, could be so microphonic (but then why would Brian not have said that it was not accurate when they made the movie?) I never saw that movie, so I'm not sure of all the details, but the TriSonics have metal covers on them, which can be microphonic apart from the coils. The TriSonics I have are modern makes for Strat, but I know the old ones had a strange pre-formed coil that was placed into the pickup housing after being wound. It's unconventional, and I can easily believe that a coil that's loosely fitted into the pickup housing could be rather microphonic. a  |
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Post by wgen on May 1, 2020 3:40:26 GMT -5
Thank you Antigua,very well done. I don't know, I'm seeing the peak of the nylon strings strumming down by only about 7 dB if compared to the sound generated by change of the magnetic field, when the overdrive is used. The latter would have double of the volume perceived, but I think the mix of the two would be significant as an overall result.
I guess the situation is similar to what an Ibanez Tube Screamer gives, because this one mixes the overdriven tone, clipped by the diodes, together with the dry signal. I didn't hear this at first with my TS9,but when I tried by strumming a guitar loaded with a high output humbucker, I could easily hear the dry clean tone, with an underlying fizz underneath.
Very interesting and well conducted, though.
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Post by antigua on May 1, 2020 12:10:35 GMT -5
I guess the situation is similar to what an Ibanez Tube Screamer gives, because this one mixes the overdriven tone, clipped by the diodes, together with the dry signal. I didn't hear this at first with my TS9,but when I tried by strumming a guitar loaded with a high output humbucker, I could easily hear the dry clean tone, with an underlying fizz underneath. Very interesting and well conducted, though. It could be an audible mix. One difference between this and a clean/dirty Tube Screamer mix is that the microphonic pickup is very non-linear, it's more weighted to the trebles than the magnet pickup, as well as some other artifacts, such as a spike at 1.35kHz. So it would be like a Tube Screamer whose clean component was also ran through a high pass filter. This gives a good clue for further testing though, I could make some recordings with audio software, mix them in a way that is similar to this distribution, and see how they sound together. A test like this can't really validate or invalidate some claims about microphonic pickups though, because someone might have a pickup that is exceptionally microphonic, or not microphonic at all, and it's impossible to get any guarantees about some important variables. People will say their particular setup sees the microphonic stars aligning, but to my mind, it's impossible to have a pickup that is microphonic enough to mix in cleans like a Tube Screamer, and yet not have that rig feedback very badly in a live situation. Especially because of that 1.35kHz ringing, that appears to occur due to vibration alone, I think that would cause and oscillation and squealing, with ease. I have a little battery practice amp for simple testing near the computer here, and I did dangle the pickup infront of it while plugged in, and it whistled, like a person whistling with their lips. I don't remember if it was a 1.35kHz whistling, but it was in that ball park. Here are pictures I forgot to post:   |
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Post by wgen on May 1, 2020 17:01:27 GMT -5
Thank you. Fact is, I never had a microphonic pickup as a choice. And yeah I was wondering if such a pickup would be usable overall if used with such an overdriven tone,or if one would throw this pickup in the trash can before appreciating all the "nuances" of this novelty... If the squealing is so annoying I guess there is no use for such a pickup anyway.
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Post by antigua on May 1, 2020 21:52:12 GMT -5
Thank you. Fact is, I never had a microphonic pickup as a choice. And yeah I was wondering if such a pickup would be usable overall if used with such an overdriven tone,or if one would throw this pickup in the trash can before appreciating all the "nuances" of this novelty... If the squealing is so annoying I guess there is no use for such a pickup anyway. I'm going to install some unpotted pickups in a Strat this weekend, I'll report back. I just want to discover how useless they are or are not, see what sort of gain it takes to "talk into them" and so on. |
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Post by pablogilberto on May 16, 2020 2:26:24 GMT -5
I never saw that movie, so I'm not sure of all the details, but the TriSonics have metal covers on them, which can be microphonic apart from the coils. The TriSonics I have are modern makes for Strat, but I know the old ones had a strange pre-formed coil that was placed into the pickup housing after being wound. It's unconventional, and I can easily believe that a coil that's loosely fitted into the pickup housing could be rather microphonic. a What do you mean when you say that metal covers can be microphonic? What's the reason behind this? |
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Post by pablogilberto on May 16, 2020 2:32:29 GMT -5
Thank you. Fact is, I never had a microphonic pickup as a choice. And yeah I was wondering if such a pickup would be usable overall if used with such an overdriven tone,or if one would throw this pickup in the trash can before appreciating all the "nuances" of this novelty... If the squealing is so annoying I guess there is no use for such a pickup anyway. I'm going to install some unpotted pickups in a Strat this weekend, I'll report back. I just want to discover how useless they are or are not, see what sort of gain it takes to "talk into them" and so on. Do you have an update on this? I'd like to understand more about this phenomena. Were you able to confirm that unpotted pickups are more microphonic than the potted ones? How is the signal being generated by vibrations even without changing magnetic fields (string movement)? Is it because the coil is "forced" to move due to the vibration or air/sound waves? |
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Post by antigua on May 16, 2020 16:36:54 GMT -5
I'm going to install some unpotted pickups in a Strat this weekend, I'll report back. I just want to discover how useless they are or are not, see what sort of gain it takes to "talk into them" and so on. Do you have an update on this? I'd like to understand more about this phenomena. Were you able to confirm that unpotted pickups are more microphonic than the potted ones? How is the signal being generated by vibrations even without changing magnetic fields (string movement)? Is it because the coil is "forced" to move due to the vibration or air/sound waves? Regarding the covers being microphonic, it's known that if a PAF or Tele neck pickup are not very tight against the pickup, or damped with wax, such that there is an air gap and the cover is able to vibrate like a membrane, or a metalic drum head, it will oscillate in response to sound waves from the guitar amp speaker and feed back, because even though the cover is not magnetic, it still has a capacitive potential in relation to the coil, so there is a varying voltage across the circuit, and that's how the feedback loop completes. In theory, if the cover is not grounded, it shouldn't feedback, since there would be no capacitance between the cover and coil in that circumstance, but that would defeat the purpose of the cover. I loaded three unpotted Strat pickup into a MIJ to try them out in situ. The unpotted Strat pickups do feedback more easily than the potted pickups, it's a high pitched squealing sound that corresponds to the physical resonance of the coil, which is a high frequency because of the small size of the coil and its wire. If I'm close to the amp and I activate two overdrives at once, it will squeal, but one overdrive alone, cranked way up, isn't quite enough to get the feedback. This was never in question though, its rather easy to demonstrate that unpotted pickups will feedback (in a bad way) more easily. Note that this type of feedback isn't the "good" kind, the good kind being the sounds Hendrix got, or what you get when you have potted pickups and you face your speaker stack, this "bad" kind of feedback is the pickup making a high pitched, ear piercing sound that is immediately painful to the ear drums. Earlier in the week I jammed with a drummer friend for about an hour, and I had the MIJ with the unpotted pickups at fairly high volumes and overdrive, but no stacked overdrive, and it neither fed back, nor did it sound remarkable in any particular way. We play a lot of covers for fun, some clean, some dirty, loud enough for me to be heard over his drums, and we have everything mic'd with a PA system and pumped back at us through loud speakers, still, no feedback. I forgot that I was using unpotted pickups, it was thje same old Strat sound I've always come to expect. The guy who made the pickups, a member on TDPRI named Kingvox, did a video demo of his potted versus unpotted Strat pickups, and in his video the unpotted pickups seemed a little brighter, but I don't attribute that to the pickups being unpotted necessarily, because in such a demo there are a thousand things that can make the test imperfect and result in a brighter sound, even plucking the strings closer to the bridge will give you a brighter sound, and that's why I don't do video comparisons and favor meticulously data plots instead. But suppose for the sake of argument that the unpotted pickups were brighter, then in situ I would have just been rolling the tone back a little farther than normal, because I jockey the tone control as I'm playing. A part of me was hoping the magic adjectives would come true; that the guitar would somehow sound "like it had built in reverb" or "sound more alive", but I don't think any of that was there, and though the sound was pretty awesome, I'd attribute all of that the cranked up Fender Super Reverb and the Caline Pure Sky pedal I have in between. |
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