As for handling noise, it might be worth trying to use a "dummy" capsule wired in parallel but facing the opposite direction with the sound blocked.
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Dr. Paralogic, I think Dr. Dent has your answer.
You don't even need an Unobtainium supa WM61A capsule as most of the 6mm capsules are good to at least 2kHz.??? as recommended by Henry Spragens is probably a good start.
You can wire it for Plug-in-Power to feed most recorders with 3.5mm mike i/p or simpleP48 for P48 XLRs on the better recorders
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This is a very interesting thread for me, a micbuilder and a physician (geriatrician). I have tried building a couple of electronic stethoscopes over the years. In the first attempt, I built a kit from Silicon Chip magazine, August 2011. It used a piezo transducer as the "mic", being amplified and low pass filtered? by a TL074 quad op amp. I found this to work but there was too much handling noise and room noise. The circuit contained some interesting filtering, including a "gyrator" which the EE gurus here would understand better than me.? But I think the slope of the filter curve was probably not steep enough. It seems to me that considering the apparent simplicity of an acoustic stethoscope, it does an amazing job as a low pass filter and whatever else it does to get the sound waves directly to your ears. Then years later I read a website in which a covid ward doctor was wanting to transmit the sounds of lungs from one (isolation) room to another, and came up with squeezing an (internal FET) electret capsule into the tubing of a stethoscope resulting in a sort of electronic stethoscope transducer. Then they very cleverly created an Android app that did digital signal processing to create a very steep low pass filter, which you could hear the output of on your headset to the phone. However perhaps due to limitations of sampling rate etc it was quite noisy. Maybe with a really amazing filter (digital or analog) it could have been better.? But one thing I have observed here: whilst I love the sound of my littmann cardiology III stethoscope, I did find that a cheapie $10 stethoscope chest-piece, with the tubing cut off a few cm from the bell/diaphragm assembly (the bit that sits on the chest), with a (omni electret) WM-61A? type of electret squeezed into the tubing, then wired to a plug-in-power type of input, it sounds remarkably good. I think the stethoscope diaphragm itself acts as a very effective low pass filter, without ridiculous amounts of handling noise. No need to cut into your expensive littmann stethoscope in my opinion!
By the way, I think that whilst an electronic stethoscope is hard to make better than an acoustic one, it may be useful for telemedicine applications, teaching medical students and good for amplifying heart sounds for doctors who are hard of hearing.
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And Sennheiser had a mic back in the 1960s with a frequency response extending to 0.1 Hz. It was an omnidirectional condenser mic using low-voltage RF bias on the capsule. Using RF bias, there is much less restriction on how low a frequency can be measured. ? Sennheiser MKH 110: Frequency response 1-20,000 Hz Sennheiser MKH 110/1: Frequency response 0.1-20,000 Hz ? (I believe there was also a MKH 110/2; I do not know its frequency response limits) ?
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Thank you for all the explanations. I have a littmann core stethoscope, it is actually quite successful, but it stores the recorded sounds on its own server, so I cannot create a dataset for signal processing. Also, my goal is to record ECG simultaneously with heart sounds, there are devices that can do this, but the recording issue is still the same. I wonder if I can design a design that can record the heart sound simultaneously with the ECG in acceptable quality. I have taken care of the ECG issue, Bluetooth connections and the Android application for recording, and I can even record the sound from the audio output of the smartphone. But I have reservations about potential lags and compressed format of the sound.
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If the aim is to make a 'better' stethescope, could you tell us
- what is?bad about present ones
- annoying stuff
- important stuff that could result in misdiagnosis
If it's just a fun thing, I agree with Eric that finding headphones that have the required LF response may be the problem.
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I made several stethoscope mics. Just a Omni electret capsule glued into a st¨¦thoscope. About 10Hz- >20000 kHz. You hear the same as with a stethoscope thus with body noises. No need to adjust the sensitivity of the mic. The Hollywood heartbeat is an ankerchief, plied in 4 recorded rhythmically with a dynamic mic and light EQ. No body noise...
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That sounds like an interesting project.? I'm still amazed that doctors get so much information from such primitive passive technology, and wonder how much better they'd do with something better designed.
-Scott
toggle quoted message
Show quoted text
On 12/18/23 18:51, eric benjamin wrote: -- I am working on my own electronic sthethoscope design.
Great project. If you were?going to look at the waveform then you might need to go down to 1 Hz or lower. But if you are going to just listen, then the lowest?audible frequency is seven Hz. But most headphones do a poor job of that. Primo used to make several?capsules designed for very low frequencies. One of them is the EM246 which has a specified sensitivity of -44 dBV at 0.5 Hz. That may be overkill. Ordinary omnis may be fine.
I did a project a number of years ago where many Panasonic wm61?were installed into a rigid spherical body. All of the capsules were measured? and a few of them were deficient in their LF response. It seemed to have to do with the seal between the capsule body and the tiny internal PCB. So you might want to seal the back after soldering the wires on. On Mon, Dec 18, 2023 at 2:33?PM Jerry Lee Marcel <jerryleemarcel@...> wrote:
Transducers used in body exploration require a certain amount of
filtering and dynamic processing. Amplification in itself is
generally not too difficult, but the frequency response must be
tailoed to eliminate a smuch as possible parasitics, in particular
very low frequency due to moves and 50/60Hz due to mains voltage.
Some kind of dynamic processing is necessary in order to avoid
large surges that could be damaging for the person who listens in
case the transducer is hit.
Electret capsules of the omni type have a very good response down
to a few Hertz.
The actual circuits are not terrily complicated; what makes the
equipment so expensive is the safety implements and the ensuing
certifications. You don't want your electronic stethoscope turning
into an electric chair.
Le 18/12/2023 ¨¤ 22:26, Paralogic a ¨¦crit?:
Hi everyone,
I am a cardiologist. For a fun activity, I am working on my own
electronic sthethoscope design.
Heart sounds are low frequency and low intense sounds. (About 20
to 1200 Hz). Are listened to by touching the skin surface, that
makes them susceptible to motion artifacts.
I am looking forward to the suggestions of the audio experts in
this group on the following topics:
Which mic capsule, amplifier circuit and ext. should I prefer?
Is it better to make a diy circuit or are there commercial ones
to handle my needs?
I guess that mic sensitivity and frequency range is important,
are there ways to electronically modify mic sensitivity?
Which solutions can be made about motion artifacts?
And what about noise cancelling?
Thank you in advance?
--
---- Scott Helmke ---- scott@... ---- (734) 604-9340 ----
"I have ceased distinguishing between the religious and the secular,
for everything is holy" - Joe Henry
|
Far be it for me to rain on your parade, but if you're interested in seeing what the state of the art is, I recommend a little excursion down patent lane. You'll easily find modern patents with noise cancelling (for example, lung sounds) along with other DSP algorithms.
As a for instance, check out US Patent 10,765,399 issued to Johns Hopkins.
In the meanwhile, have fun!
Transducers used in body exploration require a certain amount of
filtering and dynamic processing. Amplification in itself is
generally not too difficult, but the frequency response must be
tailoed to eliminate a smuch as possible parasitics, in particular
very low frequency due to moves and 50/60Hz due to mains voltage.
Some kind of dynamic processing is necessary in order to avoid
large surges that could be damaging for the person who listens in
case the transducer is hit.
Electret capsules of the omni type have a very good response down
to a few Hertz.
The actual circuits are not terrily complicated; what makes the
equipment so expensive is the safety implements and the ensuing
certifications. You don't want your electronic stethoscope turning
into an electric chair.
Le 18/12/2023 ¨¤ 22:26, Paralogic a
¨¦crit?:
Hi
everyone,
I
am a cardiologist. For a fun activity, I am working on my own
electronic sthethoscope design.?
Heart
sounds are low frequency and low intense sounds. (About 20 to
1200 Hz). Are listened to by touching the skin surface, that
makes them susceptible to motion artifacts.
I
am looking forward to the suggestions of the audio experts in
this group on the following topics:
Which
mic capsule, amplifier circuit and ext. should I prefer?
Is
it better to make a diy circuit or are there commercial ones
to handle my needs?
I
guess that mic sensitivity and frequency range is important,
are there ways to electronically modify mic sensitivity??
Which
solutions can be made about motion artifacts?
And
what about noise cancelling?
Thank you in advance?
|
-- I am working on my own electronic sthethoscope design.? Great project. If you were?going to look at the waveform then you might need to go down to 1 Hz or lower. But if you are going to just listen, then the lowest?audible frequency is seven Hz. But most headphones do a poor job of that. Primo used to make several?capsules designed for very low frequencies. One of them is the EM246 which has a specified sensitivity of -44 dBV at 0.5 Hz. That may be overkill. Ordinary omnis may be fine.
I did a project a number of years?ago where many Panasonic wm61?were installed into a rigid spherical body. All of the capsules were measured? and a few of them were deficient in their LF response. It seemed to have to do with the seal between the capsule body and the tiny internal PCB. So you might want to seal the back after soldering the wires on.
Transducers used in body exploration require a certain amount of
filtering and dynamic processing. Amplification in itself is
generally not too difficult, but the frequency response must be
tailoed to eliminate a smuch as possible parasitics, in particular
very low frequency due to moves and 50/60Hz due to mains voltage.
Some kind of dynamic processing is necessary in order to avoid
large surges that could be damaging for the person who listens in
case the transducer is hit.
Electret capsules of the omni type have a very good response down
to a few Hertz.
The actual circuits are not terrily complicated; what makes the
equipment so expensive is the safety implements and the ensuing
certifications. You don't want your electronic stethoscope turning
into an electric chair.
Le 18/12/2023 ¨¤ 22:26, Paralogic a
¨¦crit?:
Hi
everyone,
I
am a cardiologist. For a fun activity, I am working on my own
electronic sthethoscope design.?
Heart
sounds are low frequency and low intense sounds. (About 20 to
1200 Hz). Are listened to by touching the skin surface, that
makes them susceptible to motion artifacts.
I
am looking forward to the suggestions of the audio experts in
this group on the following topics:
Which
mic capsule, amplifier circuit and ext. should I prefer?
Is
it better to make a diy circuit or are there commercial ones
to handle my needs?
I
guess that mic sensitivity and frequency range is important,
are there ways to electronically modify mic sensitivity??
Which
solutions can be made about motion artifacts?
And
what about noise cancelling?
Thank you in advance?
|
Transducers used in body exploration require a certain amount of
filtering and dynamic processing. Amplification in itself is
generally not too difficult, but the frequency response must be
tailoed to eliminate a smuch as possible parasitics, in particular
very low frequency due to moves and 50/60Hz due to mains voltage.
Some kind of dynamic processing is necessary in order to avoid
large surges that could be damaging for the person who listens in
case the transducer is hit.
Electret capsules of the omni type have a very good response down
to a few Hertz.
The actual circuits are not terrily complicated; what makes the
equipment so expensive is the safety implements and the ensuing
certifications. You don't want your electronic stethoscope turning
into an electric chair.
Le 18/12/2023 ¨¤ 22:26, Paralogic a
¨¦crit?:
toggle quoted message
Show quoted text
Hi
everyone,
I
am a cardiologist. For a fun activity, I am working on my own
electronic sthethoscope design.?
Heart
sounds are low frequency and low intense sounds. (About 20 to
1200 Hz). Are listened to by touching the skin surface, that
makes them susceptible to motion artifacts.
I
am looking forward to the suggestions of the audio experts in
this group on the following topics:
Which
mic capsule, amplifier circuit and ext. should I prefer?
Is
it better to make a diy circuit or are there commercial ones
to handle my needs?
I
guess that mic sensitivity and frequency range is important,
are there ways to electronically modify mic sensitivity??
Which
solutions can be made about motion artifacts?
And
what about noise cancelling?
Thank you in advance?
|
Hi everyone,
I am a cardiologist. For a fun activity, I am working on my own electronic sthethoscope design.?
Heart sounds are low frequency and low intense sounds. (About 20 to 1200 Hz). Are listened to by touching the skin surface, that makes them susceptible to motion artifacts.
I am looking forward to the suggestions of the audio experts in this group on the following topics:
Which mic capsule, amplifier circuit and ext. should I prefer?
Is it better to make a diy circuit or are there commercial ones to handle my needs?
I guess that mic sensitivity and frequency range is important, are there ways to electronically modify mic sensitivity??
Which solutions can be made about motion artifacts?
And what about noise cancelling?
Thank you in advance?
|
Re: SimpleP48 -- Polarity
Somewhat off topic¡
I'm not sure whether absolute polarity is audible. I¡¯m willing to believe that a trained listener can hear it. I don¡¯t think I can. I can tell when polarity is switched, but I can¡¯t say which is correct, except sometimes for a particular recording on a particular listening system.
I have been present when speakers were being critically listened to to determine whether they were ¡°in phase¡±. (Sorry) Sometimes a test was done to determine which was the correct polarity of the whole system. The problem is, some things sound better in one polarity, some in the opposite polarity. Some don¡¯t matter.
My personal take is speakers are non-linear. A paper cone is stiffer ¡°pushing¡± air than ¡°sucking¡±. The surround is nearly always stiffer in one direction. Take a battery and listen to a step transient in both polarities. So I blame the speakers for most polarity audibilty.
More common and bothersome are things like one big studio where the main monitors had fuzzy localization. It turned out that the midrange horn on one side was wired out of phase with the rest. (Sorry, I have never heard anyone say ¡°Out of polarity.¡±) It had been that way for years, and the house engineer liked the ¡°air". As long as the resulting mixes sounded good, who is to say he was wrong? Maybe that was the studio¡¯s secret sauce.
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Re: SimpleP48 -- Polarity
I didn¡¯t emphasize enough that if you are using stereo pair mic techniques, then polarity match matters.
_______________________________________________
One technique for achieving "noise cancellation" is to place two similar or (best) identical microphones back to back so as to cancel common mode sound activating each capsule - sorta, kinda like the way noise is cancelled on balanced transmission lines for microphones, radios, and other applications. Of course, in stereo recording, one does not typically place both microphones 180 degrees in different directions ... still my question:
Question > How does this relate to phase and polarity discussed in this thread?
Thanks - James / K8JHR
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Re: SimpleP48 -- Polarity
have multiple mics out there wired with "+" to Pin 3. It
works but the absolute phase is obviously reversed. Hmmmm....
________________________________________
No problem, JR. Just hold it upside down, or speak backwards . . . (Anonymous) :-)
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Re: SimpleP48 -- Polarity
I forgot to mention that the kick drum was recorded on tape, so there was no comparison with an acoustic source.
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Show quoted text
Le 18/12/2023 ¨¤ 14:21, Scott Helmke a ¨¦crit?: Indeed for live sound polarity matters very much - whether what comes out of the speakers is in the same acoustic polarity can make a big difference.
-Scott
On 12/18/23 02:19, Jerry Lee Marcel wrote:
On Mon, Dec 18, 2023 at 07:11 AM, Henry Spragens wrote:
??? For a single mic located away from the main pair, or isolated in a
??? studio setting, switching polarity can be heard, but usually
??? neither way sounds especially better.
There have been a number of studies regarding teh audibility of phase and polarity.
Regarding phase audibility, it's been shown that phase distorion could be heard when it changed significantly the crest factor of a complex signal.
Regarding polarity, I witnessed myself a case where two sound engineers diagnosed polarity reversal in loudspeakers, listening to a kick drum. They said "it sucks air, instead of pushing air". Thet were right, when correct polarity was restablished, the sound was better. I never had the possibility to investigate the issue.
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Re: SimpleP48 -- Polarity
Indeed for live sound polarity matters very much - whether what comes out of the speakers is in the same acoustic polarity can make a big difference.
-Scott
toggle quoted message
Show quoted text
On 12/18/23 02:19, Jerry Lee Marcel wrote: On Mon, Dec 18, 2023 at 07:11 AM, Henry Spragens wrote:
For a single mic located away from the main pair, or isolated in a
studio setting, switching polarity can be heard, but usually
neither way sounds especially better.
There have been a number of studies regarding teh audibility of phase and polarity.
Regarding phase audibility, it's been shown that phase distorion could be heard when it changed significantly the crest factor of a complex signal.
Regarding polarity, I witnessed myself a case where two sound engineers diagnosed polarity reversal in loudspeakers, listening to a kick drum. They said "it sucks air, instead of pushing air". Thet were right, when correct polarity was restablished, the sound was better. I never had the possibility to investigate the issue.
--
---- Scott Helmke ---- scott@... ---- (734) 604-9340 ----
"I have ceased distinguishing between the religious and the secular,
for everything is holy" - Joe Henry
|
Re: SimpleP48 -- Polarity
On Mon, Dec 18, 2023 at 07:11 AM, Henry Spragens wrote:
For a single mic located away from the main pair, or isolated in a studio setting, switching polarity can be heard, but usually neither way sounds especially better.
There have been a number of studies regarding teh audibility of phase and polarity. Regarding phase audibility, it's been shown that phase distorion could be heard when it changed significantly the crest factor of a complex signal. Regarding polarity, I witnessed myself a case where two sound engineers diagnosed polarity reversal in loudspeakers, listening to a kick drum. They said "it sucks air, instead of pushing air". Thet were right, when correct polarity was restablished, the sound was better. I never had the possibility to investigate the issue.
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Re: SimpleP48 -- Polarity
Goran: Appologies for using phase and polarity interchangeably. That is the way engineers I know carelessly use the terms.
"So I would hazard to claim that the + sign should indicate to be connected via a resistor
to a positive + voltage and has nothing to do with polarity.¡± I agree. Nonetheless, the + teminal of the capsule goes positive, and connects to pin 2 of the XLR for the basic Simple P48 mic. The resistor to pin 1 and the capacitor to pin 3 connect to the ¡ª terminal of the capsule. ¡°Linkwitz¡¯d¡± capsules and other circuits may differ.
I didn¡¯t emphasize enough that if you are using stereo pair mic techniques, then polarity match matters. Very much so. That would be X-Y, ORTF, crossed Fig-8s, Decca Tree, drum overheads, etc. However, if the polarity of BOTH mics is ¡°wrong¡±, they will work OK. As long as your pairs of mics match, absolute polarity doesn¡¯t matter. The positive signal on pin 2 with rising air pressure standard ensures that mics from Neumann, AKG, Shure, and others work together.
For a single mic located away from the main pair, or isolated in a studio setting, switching polarity can be heard, but usually neither way sounds especially better. Bleed from other mics makes for complex comb filter effects, and switching polarity makes dips into peaks and vice-versa, rather like moving the mic around a few inches.
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Re: SimpleP48 -- Polarity
I would think the upper and lower heads of a snare drum would be? pretty good test but with the opposite expectation. The summed sound would be thicker if the two mics have opposite polarity.
Regards,
On Sun, Dec 17, 2023 at 12:49 PM, Goran Finnberg via groups.io <mastering@...> wrote: Henry Spragens,
>So what happens if I have a mic with polarity reversed?
>
>Usually, nothing.
>
>If the mic is not paired with another one, for instance a soloist or individual drum mic,
>acoustic phasing is more or less random and varies with frequency (wavelength) in a
>way too complicated to figure out. If you have a ¡°PHASE¡± switch on your mic preamp,
> try it both ways. Chances are neither setting is vastly better.
If I were to believe in the above gospel then there should not be any standard at all as
regards polarity and stereo as we know it today would sound very weird indeed.
Henry Spragens:
>So what happens if I have a mic with polarity reversed?
>
>Usually, nothing.
Polarity, if hot is pin 2 or 3, you check by putting one reference mic from any reputable
manufacturer, Neumann, AKG, Schoeps, R?de, etc as CLOSE AS POSSIBLE TOGETHER
such as to remove the ACOUSTIC TIME DELAYS between capsules then and only then
you use the mono button while listening over headphones and/or looking at a VU meter.
The right polarity comes when the audio is as full sounding, in polarity, compared to the
thin sounding version, out of polarity sounding when pushing the mono button over
HEADPHONES.
As soon as you moves mic apart THEN and ONLY THEN, do I agree with your version
above Henry Spragens but as this is WAVELENGHT dependent then even the 16 feet
pipe on the church organ can be heard to diminish as the mics in a two mic recording
is monitored in mono as mics are moved apart.
YOU decide if that matters to you.
POLARITY do matter as soon as you use any INTENSITY recording techniques also called
XY, that excludes timing differences among microphone PAIRS.
Timing differences occur due to path length differences that is minimized in XY or Stereo
microphone techniques.
WHERE POLARITY REALLY MATTERS:
Using any of the INTENSITY Stereo recording methods that DO excists:
Schoeps CMC301/501, Neumann SM69 etc etc etc.
No wonder that in the age of CD that the old button on Neumann cutters
could be switched to mono everything below 70 Hz, 150 Hz & 300 Hz by rolling off the
difference channel using an inductor between the stereo feed and series resistors in each leg.
The above to avoid having the cutting head sapphire not lift out of the lacquer. so as the final
LP disc unplayable.
-------------
Best regards,
Goran Finnberg
The Mastering Room AB
Goteborg
Sweden
Learn from the mistakes of others, you can never live long enough to
make them all yourself.??? -?? John Luther
(\__/)
(='.'=)
(")_(") Pyret, Ranglet, Aron, VovVov, Nero, Smurfen & Pussin:RIP
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Paralogic
John Thaden