Where Analog Beats Digital, Fun Stories - Page 1
Forum section: electronics / general

author: mawyatt
author_rank: Super Contributor
timestamp: July 25, 2025, 11:07:09 pm
content: We'll start off with one that dates back to the 60~70s, others chime in please!!Honeywell had developed a new type cable called MILES along with a signal processor called MAID (discussed later), this was utilized for perimeter security around critical US government facilities and assets throughout the world. Originally the cable was designed to concentrate the earths natural magnetic field around the cable by means of a special complex metal cable core with Cu windings around the core alternating every so often for far field rejection.The cable was optimized to concentrate the earths field which when disturbed by some means (intruder) would produce a small voltage across the Cu windings detectable and processed by MAID. The intruder needed to be magnetically active it was thought to distort the concentrated cable field and produce a signal voltage proportion to the rate of change of the cable localized magnetic field detectable by MAID.During early MILES cable testing it was discovered that magnetically "clean" intruders could be detected under certain circumstances, even intruders without any metallic objects could be detected!! After some investigation it was discovered the cable was also responsive to "Magnetostrictive Effects" where the core effective permeability changes with stress, and such stress was induced into the ground as a pressure change across the MILES cable. This effect was optimized within the cable core without degrading the overall cable magnetic sensitivity and went into full production along with the companion MAID signal processor.The Perimeter Security MILES/MAID system was deployed around the world and performed admirably, except in certain locations where false alarms and/or ""blind spots were discovered. These drawbacks created an opportunity to developed a new "System" and it was decided to just improve MAID the cable signal processor since the MILES cables were already buried and worked well.A contract was awarded to improve the MAID performance in false alarm rate and reduced "blind spots" while improving or maintaining MAID detectability. This was a tall order since MAID was already pretty darn good in most parameters!!MAIDs design was well done (most early Honeywell stuff was well done!!) and employed a traditional design with a low-noise preamp with post filtering and amplitude comparisons.It was discovered that the orgin of the signal from the MILES cable was caused by a change in the concentrated Earths magnetic field around the cable or a change in the cable core permability due to the Magnetostrictive effect, both caused by local cable intrusion. Since these were Rate Sensitive results (change in magnetic field and/or core permeability) we decided to develop a unique preamp where the signal directly from the MILES cable would be integrated by the preamp and never appear within the signal processing chain without prior integration.This preamp concept wasn't simple tho, as the noise levels needed to be extremely low at very low frequencies while maintaining a high dynamic range as "seen" from the input. For those low-noise gurus we utilized a custom discrete direct coupled preamp based around select pairs of multiple differential bipolar transistors configured with an op-amp utilizing a large wet-slug tantalum as the feedback integration capacitor. The second stage was AC coupled at 0.1Hz to a pair of T-Notch Mains filters followed by additional gain and high pole active lowpass filtering and more T-Notch filters at the mains harmonics.There was quite a bit of additional analog signal processing after the unique Rate Compensated Preamp where band select filtering and band energy ratios with adaptive gain (forms a unique type AGC) and so on, most of which additional details can't be discussed or simply forgotten!!While we were developing this effort unknown to us was that 2 major well known West Coast Institutions and Sandia Labs were teamed given all our reports and design details, they were working on a new type Digital Signal Processing algorithm called Adaptive Recursive Filtering (ARF) to address the MAID shortcomings.So we were being "setup" for an eventual "fly off" so the Sandia and University efforts would win and go on into production. We didn't find out about any of this until the first field test at Eglin AFB where we had adhered to the requirements of a container no larger than 150mm cube, and a power budget of 50mw total, self contained battery backup, full Mil Spec temp range and EMI/EMC compliance. Sandia shows up with a Grumman Truck (same as UPS), a diesel generator, VAX 11780 Minicomputer and a large ~1000mm by 800mm by 600mm container with a bunch of electronics and the most advanced high resolution ADC available implementing the ARF solution. When asked about this they said, "don't worry we'll integrate all this into a couple chips"!!!We equaled or outperformed the ARF in every category including the most important PD (Probability of Detection) and FAR (False Alarm Rate). After that, later another test with Frozen Ground was conducted at Rome AFB in the winter, same result.Our design went on into full production after an initial low rate production (another fun story) replacing all the MAID processors around the world.This is a case of Analog Signal Processing outperforming the best DSP at the time and one could consider the fundamental reason was the Rate Compensated Preamp which integrated the signal at the front end before anything and produced the large dynamic range required.This result begs the question, what if the Sandia and Co ARF had employed the Rate Compensated Preamp instead of a conventional preamp?? That question remains to be answered as far as we know as we moved on to other projects around 1980!!Anyway, hopefully others can tell stories of how/when analog defeated digitalBest

author: tggzzz
author_rank: Super Contributor
timestamp: July 26, 2025, 07:24:23 am
content: It is always pleasing to hear of stories where skill and imagination beats a brute force design.Back then ADCs and DSPwerecrude brute force by today's standards; the astounding improvements in ADCs and DACs is one of the few revolutionary advances over the past 30/40 years.

author: nfmax
author_rank: Super Contributor
timestamp: July 26, 2025, 08:41:23 am
content: The concept of (time) integrating signals from magnetic sensors deserves to be more widely appreciated. Such sensors will generally provide a signal that depends on the rate of change of magnetic flux, so rises with frequency. Integrating removes this trend, exposing the underlying problem to be solved 😊. I’ve used this method for getting accurate timing pulses from magnetic shaft rotation sensors.

author: SteveThackery
author_rank: Super Contributor
timestamp: July 26, 2025, 10:50:03 am
content: That's a fascinating account, @mawyatt!

author: RJSV
author_rank: Super Contributor
timestamp: July 26, 2025, 10:03:09 pm
content: Member nfmax: Thanks for mention of the use of integration, when monitoring magnetic flux. I have an audio application; sensing magnetic flux in a Spring Reverb for my (acoustic) guitar. Figured on first trying a typical electric guitar pickup, placed near to the spring.

author: RoGeorge
author_rank: Super Contributor
timestamp: July 26, 2025, 10:09:00 pm
content: Quote from: nfmax on July 26, 2025, 08:41:23 amOnce I've pulled away a few turns out of a magnet's field, and integrated V to measure the permanent magnet's B.https://www.eevblog.com/forum/projects/measure-a-magnets-b-field-with-a-rigol-ds1054z-oscilloscope-and-a-piece-of-wire/

author: John Coloccia
author_rank: Super Contributor
timestamp: July 27, 2025, 01:24:06 am
content: Quote from: RJSV on July 26, 2025, 10:03:09 pmWhat's the application?

author: Analog Kid
author_rank: Super Contributor
timestamp: July 27, 2025, 01:36:19 am
content: Quote from: John Coloccia on July 27, 2025, 01:24:06 amNot RJSV, but it's covered inthis thread here.Interesting li'l project.

author: basinstreetdesign
author_rank: Frequent Contributor
timestamp: July 27, 2025, 02:12:10 am
content: Awhile ago I decided to build, by hand, the best audio oscillator I could to see what I could achieve. Using analog techniques only (balanced Wien Bridge)I got one with 0.00018% distortion. That's about -115 dB down from the fundamental. I measured it on a HP 3580A spectrum analyzer that I calibrated myself using HPs tech manual. It has a noise floor at about -150 dBV (32 nV rms) so I felt confident in the results.I have read of many other sources with distortion in that ballpark. They were all of the same analog technology. Mine covered the entire audio spectrum but the others were single-frequency efforts. I have never heard or read of any digitally-generated signal source to match.

author: John Coloccia
author_rank: Super Contributor
timestamp: July 27, 2025, 02:30:56 am
content: Quote from: Analog Kid on July 27, 2025, 01:36:19 amI believe, if I'm not being stupid, that the whole character of the spring Reverb is essentially looking at the tension at one end. Ie, it's like a strain gauge.I feel like I should know this given my background, but I don't. All I know is if I bop my amp, it makes a racket. A magnetic pickup feels wrong.

author: Analog Kid
author_rank: Super Contributor
timestamp: July 27, 2025, 02:48:55 am
content: Quote from: John Coloccia on July 27, 2025, 02:30:56 amHeh;this page about spring reverb unitssays:QuoteThat's right, "lamentations".If you put your earrealclose to them you can hear them sighing, sometimes outright crying and sobbing (and rending their garments) on a good day.

author: BrianHG
author_rank: Super Contributor
timestamp: July 27, 2025, 02:56:22 am
content: Without any 'UNDO', or infinite & precise on and off again splicing and mixing, musicians had to actually perform to lay down a track.

author: John Coloccia
author_rank: Super Contributor
timestamp: July 27, 2025, 03:12:55 am
content: That's what I thought. It's not the spring so much as the tension.But anyhow, I'll just mention, and it was slightly before my time, that a company I worked for implemented an analog wavefront correction computer because there was no processor that could do it fast enough at the time.It's hard for me to imagine what that looked like, but I'm sure it was impressive.

author: RJSV
author_rank: Super Contributor
timestamp: July 27, 2025, 05:12:17 am
content: (newest lame smartphone isn't able to post photos ! Sorry).The TOY I bought is housed like a big microphone, and it has a hard plastic 'cup' for bringing the (air) oscillations down to a point, or focus. There, one end of a spring coil is attached, while the spring stretches the length of the housing, and I think has another smaller cup, this time for acting as a reverb 'output', (all this mechanical).The kid playing with the TOY $3 microphone, (ages 2 and up), can place an ear near, and get sound resembling what Frantone's plate reverb sounds like; a big cave-like room or auditorium.

author: Smokey
author_rank: Super Contributor
timestamp: July 27, 2025, 06:43:26 am
content: Quote from: mawyatt on July 25, 2025, 11:07:09 pmAN/GSS-26Ahttps://apps.dtic.mil/sti/citations/ADA056703https://apps.dtic.mil/sti/pdfs/ADA056703.pdfhttps://digital.library.unt.edu/ark%3A/67531/metadc1071251/m2/1/high_res_d/5358916.pdfhttps://inis.iaea.org/collection/NCLCollectionStore/_Public/08/348/8348508.pdfhttps://www.prc68.com/I/GSS26.html

author: mawyatt
author_rank: Super Contributor
timestamp: July 27, 2025, 02:47:28 pm
content: Quote from: Smokey on July 27, 2025, 06:43:26 amYes those are the systems!! Good find!!We setup a field test site on our campus with various full length 100m MILES cables. Then for the MSP development created a dedicated cable interface with a conventional design low noise preamp (LNA) to monitor and record signatures from the cables, later after we developed the Rate Compensated Preamp we recorded signatures from this as well as the LNA. Data was recorded on a Honeywell FM Dual Channel Tape recorder as the signals were often well below 1Hz and below a conventional tape recorders ability.During the algorithm development for the MSP a group was send around the US to various facilities which had MILES cables installed to record various "events" such as different terrains, aircraft overhead, sonic booms, parallel trains passing, storms, local fencing, and so on. This provide a good signature data base from which the algorithm emerged. We also hired some local high school kids and had them try and defeat the cable detection by crawling, walking, jumping and even using a pole to try and jump over the cable, and we made the cable location easy by painting the grass. All this was recorded and used for algorithm development and improvement.After the initial algorithm and circuit development we were conducting long term background noise and false alarm rate tests on site. False alarms were showing up around 6am almost every morning in one of the test cables, so we recorded the event and this didn't appear the signal was a False Alarm but more an Intruder detection. After setting up a Polaroid Camera triggered by the "event" we captured a man walking his dog across the cable, even tho the area was roped off and labeled "Restricted Do Not Enter".He was taking a short-cut across the large open field rather than walking around the perimeter of the Restricted Zone.After the development of MSP, the commercial version of the MILES/MAID system called BLS 1000 was redesigned with the MSP Rate Compensated Preamp and algorithms. These were used in commercial applications and prison perimeter security.Anyway, thanks for the links, those were fun times back then and we have fond memories of suchBest

author: RJSV
author_rank: Super Contributor
timestamp: July 27, 2025, 08:45:59 pm
content: I liked reading about how you were taking good care of stray items, while developing the system. (In contrast I've observed other projects where the ones in charge were pretty LAZY on following up).You needed a fairly astute perception, and common sense, when confronted with mysteries, like that innocent dog walker causing a system response.Now, I am more curious, about that 'rate sensitive ' preamp that was developed !

author: coppercone2
author_rank: Super Contributor
timestamp: July 27, 2025, 08:50:01 pm
content: when the complex digital emergency stop button does nothing so you flip a switch to turn it off

author: KE5FX
author_rank: Super Contributor
timestamp: July 28, 2025, 12:35:35 am
content: I wonder if a simple rubber hose full of water would do as well as the MILES cable, if you're going to rely on microphonic effects rather than magnetic ones.I'd have to assume that idea was considered and rejected at a very early stage.

author: mawyatt
author_rank: Super Contributor
timestamp: July 28, 2025, 12:56:40 am
content: Quote from: RJSV on July 27, 2025, 08:45:59 pmThe previous MAID signal processor which utilized a conventional LNA design, could be saturated (or post amplification saturated) with large input signals that were not intruder based. Since we had the MAID (and MILES cables) we studied the MAID response in the presence of the signals we had available (recorded and real time from our own campus test field, our area is the Lightning/Storm capital it seems and massive thunder storms/lightning are common here).After many hours/days/months of study/experimentation we began to understand the limitations of MAID and knew exactly what caused the blind spots in certain field locations (obviously not open to discussion!!) and also created false alarms. We also realized that the MILES cable response was a signal directly proportional rate of change in time, either from the earths concentrated natural magnetic field due to the cable core, or from the small pressure changes in the ground causing a small change in the core permeability (Magnetostrictive effect), each inducing a small signal from the cable.At some point early in MSP development/investigation we realized that removing the Rate Sensitivity from the Cable would allow a higher dynamic range in the system and also realized thatIFthis could be implemented right at the MILES cable output before any gain circuitry we could dramatically improve the MSP performance. This is where we began to investigate signal integration right at the input, which wasn't an easy task considering we needed an equivalent input noise density level in sub-nanovolt/rtHz well below 10Hz, right smack in the 1/f^n region!! Our approach was to employ a differential bipolar transistor pairs which were selected for no popcorn and very low 1/f noise, and low offset. These pairs were configured in an optimal bias and gain setup for low frequency noise, followed by a op-amp which then completed a closed loop (the transistor pairs were inside the loop) inverting integrator utilizing a wet-slug tantalum feedback capacitor. The time constant of integration was set by the MILES cable and the large feedback capacitor (many detailed parameters of the MSP design are not open for discussion). The supply voltage for the Rate Compensated Preamp was formed by a discrete low noise +-15V from a +-18V internal rail system derived by an ultra-low noise switcher operating well out of band.Later in the project the customer requested the ability to detect a MILES cable tamper and provide an alarm for such. We thought about this for awhile and realized we could use the natural base bias current from the NPN input transistors as the sense element without any noise penalty. Here the small base current flows thru the MILES cable (the preamp was DC coupled to the MILES cable) and if the cable is cut or disconnected the input amplifier will ramp up and saturate causing the output of the preamp to rail. We simply integrated the preamp output with a very long time constant RC filter into an RCA CD4000 CMOS Schmidt Trigger with VDD at 18 Volts (all the internal logic was based upon RCA CD4000 CMOS operating from 18 Volts VDD). Don't recall if Sandia and Co were able to implement this feature in their ARF system, but we had it from the get go!!We build a few of these Rate Compensated Preamps for recording data in field tests along with conventional Preamps to allow post signal capture comparisons.Turns out that probably the best one can do in the presence of large interference is performing signal integration right at the input before anything else!! This was much later discovered to have a similar impact on RF/MW/MMW signals with the unique PolyPhase Mixer (aka N-Path) which defied conventional physics and produced measured noise figures well below theoretical, but that's another story.Best

author: mawyatt
author_rank: Super Contributor
timestamp: July 28, 2025, 01:01:22 am
content: Quote from: KE5FX on July 28, 2025, 12:35:35 amInteresting idea!!The MILES cable had the Cu windings around the core reversed every so often for far-field rejection. Each section of the cable acted as a transformer and having the windings reversed allowed the transformer sections voltages to cancel, thus improving the cable far-field response.Best

author: RJSV
author_rank: Super Contributor
timestamp: July 28, 2025, 01:33:25 am
content: Myawatt: (hope I remembered the correct spelling):Could you mention, please, on that MAID project, what kind of ratios of personnel were involved ? Assuming you are an EE, but that sounding like also a heavy physics oriented project ? So, were there other specialists needed ? Audio processing MATH specialist ?Of course I keep thinking here in terms of digital algorithms !!

author: mawyatt
author_rank: Super Contributor
timestamp: July 28, 2025, 02:17:33 am
content: Quote from: RJSV on July 28, 2025, 01:33:25 amDon't know how many or of what kind of engineers/scientists were involved in the early MILES cable or MAID signal processor development, we were hired as a consultant after these were developed. Honeywell had a large number of material, physics and math specialist as well as the usual EE and ME types back then. We did discuss things with a few engineers that had worked on the MILES/MAID earlier.For the MSP processor we had 3 EEs (myself included), one was dedicated as Program Manger (no technical contributions), one part time ME (packaging), and 2 technicians. Don't know what Sandia had dedicated or the two Universities, but suspect it was a much larger group overall than we had. The Adaptive Recursive Filter had gathered some interest in the DSP research community at the time, almost like AI in that it learned from its past experiences and adapted to changing conditions, fascinating subject once we were allowed to know about it!!Best

author: tggzzz
author_rank: Super Contributor
timestamp: July 28, 2025, 08:30:08 am
content: Quote from: mawyatt on July 28, 2025, 01:01:22 amHmmm. What does that mean?Or maybe that is something to apply to the next generation of audiophool products?

author: mawyatt
author_rank: Super Contributor
timestamp: July 28, 2025, 03:14:57 pm
content: Quote from: tggzzz on July 28, 2025, 08:30:08 amThe MILES cable core was composed of multiple strands of a special "wire" created for high permeability and Magnetostrictive effects. This core was covered with an insulating wrap, then Copper wire wound around the core similar in fashion like winding a wire around a linear shaft core to create a long inductor. The core served as the return to the connector for the windings end. Multiple braided shields (recall the outer was thick stainlesss steel for physical protection while the inner was tinned copper braid for E-Field shielding) covered the windings after additional insulated wraps and a thick silicone rubber as the final covering.BTW recall that Honeywell didn't produce the MILES cable but licensed and sub-contracted this to Teledyne.This Copper winding would induce a voltage when the local magnetic field changed due to external disturbances. If just a long winding was utilized then the results would be a response to everything localized to the cable as well as everything far removed. The windings were reversed from CW to CCW around the cable core every so often to create equal and opposite induced voltages in the winding sections from far field disturbances and thus the net result was they canceled when summed up across the entire cable. Where local disturbances would create induced effects localized to a few winding sections and not cancel and produce a cable output voltage.The signal levels from the cable could be very small (nanovolt region) with a slow crawling magnetically clean intruder too much larger with a vehicle, and everything in between. The MSP algorithm classified the intruder type based upon various signal parameters and signatures.Yes we're sure that a version of the MILES cable could out perform any of the specialized audio speaker cablesBest

author: tggzzz
author_rank: Super Contributor
timestamp: July 28, 2025, 03:50:16 pm
content: Ah, interesting. Not something you could buy in a local store - or even DigikeyAudiophools would only be interested if it was oxygen free. (Or is that only mandatory for the mains power cable?)

author: RJSV
author_rank: Super Contributor
timestamp: July 28, 2025, 06:59:10 pm
content: Thinking about US Patents regarding that periodically reversing winding, I do wonder how that applies, to commercial AUDIO, and various IP (Intellectual Property). I think that military or security related PATENTS have certain rules, and priority status.

author: John Coloccia
author_rank: Super Contributor
timestamp: July 28, 2025, 08:45:37 pm
content: Quote from: tggzzz on July 28, 2025, 03:50:16 pmI strongly suspect the entire listening room is oxygen free.

author: RJSV
author_rank: Super Contributor
timestamp: July 28, 2025, 08:57:23 pm
content: John; A neighbor a while back used to insist that we 'DONT TOUCH!' anything near the HIFI stereo tables. Even he would use an empty toilet tissue roll (core) when fiddling with knobs. Oil on the skin was the culprit to avoid.But he has some other quirks, besides the AUDIO perfectionism:Public Nudity......the otherwise reasonable neighbor apparently liked, also, recycling his containers. BUT, we thought it humourous that he (the neighbor) did BOTH together; going through and sorting the empty cans and bottles,...in the nude.Nice guy, but a little quirky !

author: John Coloccia
author_rank: Super Contributor
timestamp: July 28, 2025, 09:15:19 pm
content: Quote from: RJSV on July 28, 2025, 08:57:23 pmI can pretty much guarantee I wouldn't touch anything in his house.I don't want to turn this into an audiophool thread, as there are plenty of those. But I'm always reminded of this (RIP, seems like a nice guy):

author: Analog Kid
author_rank: Super Contributor
timestamp: July 28, 2025, 09:44:33 pm
content: To paraphrase that famous saying, when I hear "soundstage" I reach for my revolver.

author: themadhippy
author_rank: Super Contributor
timestamp: July 28, 2025, 09:58:52 pm
content: Quotei thinks great decent catering

author: EEVblog
author_rank: Unknown
timestamp: July 29, 2025, 01:33:39 am
content: Quote from: mawyatt on July 25, 2025, 11:07:09 pmI really do need to get you on The Amp Hour!

author: tggzzz
author_rank: Super Contributor
timestamp: July 29, 2025, 07:42:21 am
content: Quote from: EEVblog on July 29, 2025, 01:33:39 amBackground prep would include his articles in EDNhttps://www.edn.com/author/mike-wyatt/

author: Echo88
author_rank: Frequent Contributor
timestamp: July 29, 2025, 10:39:57 am
content: The cable reminds me of the Wiegand effect.Vaguely similar in construction, but using pulses:https://en.wikipedia.org/wiki/Wiegand_effectIt was discovered 1972, so around the same time as the MAID/MILES system.Can you remember if this effect was also considered during the design stage of MAID/MILES mawyatt?

author: mawyatt
author_rank: Super Contributor
timestamp: July 29, 2025, 01:52:34 pm
content: Quote from: Echo88 on July 29, 2025, 10:39:57 amBelieve the early MILES cable was developed before the Wiegand discovery in 1972. Recall we started as a consultant in 1977, so well after the MILES cable and MAID signal processor development. By then the MILES/MAID had been extensively deployed, so our baseline was from talking with a few other Honeywell scientist/engineers that had been part of the earlier developments.Best

author: mawyatt
author_rank: Super Contributor
timestamp: July 29, 2025, 02:02:25 pm
content: Quote from: EEVblog on July 29, 2025, 01:33:39 amDave, wish this could happen but our situation prevents such at this time.....sorrySo for now we'll just keep posting things that folks might find interesting until our memory fades away, if that's OK!!Best

author: mawyatt
author_rank: Super Contributor
timestamp: July 29, 2025, 03:17:29 pm
content: One thing we hope folks glean from these discussions about MILES/MAID, MSP (MILES Signal Processor), and the Rate Compensated Preamp (RCP), is the importance of pure analog integration in the signal processing chain, and doing so early in the processing chain. The earlier the better and the RCP pushing this right upon the input signal before any signal processing or gain.The signals from the MILES cable ranged from nanovolts to almost volts imposing an enormous dynamic range on the preamp. Had Sandia and Co incorporated the RCP with their Adaptive Recursive Filter, the results might have surpassed MSP but don't think that ever happened, as we moved on to another project (XM-21) after the initial development of MSP.This isn't restricted to low frequency use but can benefit even microwave signals by imposing an integration right at the antenna input as mentioned above with the PolyPhase N-Path Mixer. Here the effect (in multiple integration samples) allows a Bi-Phase Mixer tobreak the theoretical noise figure barrierpassively without any amplification!!! Of course you can't dothat, but in fact it doeshttps://www.eevblog.com/forum/rf-microwave/polyphase-or-n-path-mixer/Anyway, folks are encouraged to investigate the effects of analog integration with all sorts of signals and frequencies, as results may benefit from such.Best

author: mawyatt
author_rank: Super Contributor
timestamp: August 01, 2025, 02:24:26 am
content: Quote from: John Coloccia on July 27, 2025, 02:30:56 amWay back a band called the Safaris had an instrumental hit called Wipe Out, they kicked the Fender Twin Reverb Guitar Amp to create the uniqueSoundat the start (along with laughter). This kick caused the reverb spring to bounce off the housing walls and create the Crashing Sound!!Best

author: coppercone2
author_rank: Super Contributor
timestamp: August 01, 2025, 02:34:54 am
content: can you make a high power weigand wire?I always wondered about that. I imagined some guy in like a 'broom closet' filled with spools of wire came up with it. Like with a single light bulb using the window sill a a bench. It seems like something a building superintendant would think of. Crazy things with wire.

author: RJSV
author_rank: Super Contributor
timestamp: August 01, 2025, 03:53:06 am
content: Like I mentioned before, regarding Amusement park sounds, (cavern echo along with loud crashing or explosion-like bursts of sound). It's simply the high amplification, and the sonic persistence that makes the startling crash impact sounds.Likely that little audio device got used, sometimes in late 1950's cheapo scifi shows and movies.

author: RJSV
author_rank: Super Contributor
timestamp: August 01, 2025, 04:09:56 am
content: Anyway, (John), actually a single pole magnetic pickup is the natural sensing, using a wound bobbin coil, very similar to a guitar pickup, but with only the one bobbin and magnetic pole piece.The other music-instrument sensing is purely audio vibrations, and THAT is possible in the TOY CONVERSION case, but just allows too much extraneous sound to influence the piezo-sensor.Optical sensing, is another option, while having your light beam travel through the spring volume, getting alternately blocked and passing to a photo-diode, or CdS photo-resistor, for audio as was done in classic film projector play back.I don't see a problem, (in theory) using magnetic effects, on that steel coiled spring, same as a vibrating metal string on an electric guitar. I believe a guitar pickup utilizes a nearby magnet, to get some flux residing in the wire (musical string), for the sensing action to work.

author: John Coloccia
author_rank: Super Contributor
timestamp: August 01, 2025, 05:30:23 am
content: Quote from: RJSV on August 01, 2025, 04:09:56 amI finally looked up how spring reverbs work. I can't believe I didn't know this. LOL.The coil isn't picking up the springs directly. It's interacting with magnets that the springs are attached to. So I was close that you're sensing at the end of the spring, not along it's length. I didn't think a pickup sensing along the length wouldn't work at all. I'm just imagining that the spring doesn't move very much along it's length. But only one way to know...

author: Thomas Ballantine
author_rank: Contributor
timestamp: August 01, 2025, 04:40:13 pm
content: Other than special wires for detection like this, are there any normal types of spiral-core wire? It would be cool to have it so that xcm is yuH

author: coppercone2
author_rank: Super Contributor
timestamp: August 01, 2025, 08:34:18 pm
content: appliance wire is spiral core sometimes for the thin stuff

author: Ground_Loop
author_rank: Frequent Contributor
timestamp: August 02, 2025, 02:14:19 am
content: Quote from: mawyatt on July 25, 2025, 11:07:09 pmI worked in a military installation out in the woods in upstate NY in the mid eighties. The facility had an approach sensing system around the perimeter, among many other things, that may have been what you are describing. I was always curious how that system worked. Great story.

author: RJSV
author_rank: Super Contributor
timestamp: August 02, 2025, 04:31:38 am
content: John: Thanks for comments, on the REVERB MICROPHONE TOY, and efforts for sensing the magnetic fluctuations, of the audio vibrations.From now, that idea will be split off, into a new thread. I did purchase a stand,-alone guitar pickup...used on any acoustic guitar, having steel strings of course.Thanks again.Rick B.