A Better Explanation of Impedance for Audio Signals
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- เผยแพร่เมื่อ 21 มิ.ย. 2022
- This video is conceptual summary intended to help those trying to understand the output impedance of sources like microphones or instrument pickups and how they interact with the input impedance of preamps, interfaces, buffers, and amplifiers.
#microphones #impedance
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I have one update/correction I'd like to add to this video that has come up since I put it out. I mention in the video that impedance tends to go up as frequency goes down. This is true for ribbon and dynamic microphones as well as piezo based pickups, however it is not true for traditional electromagnetic guitar pickups. Wound pickups have an impedance that peaks usually somewhere from 2kHz - 8kHz or so. The same general principles from the video apply, however impedance mismatch will lead to loss of voltage more at the resonant peak of the pickup rather than in the low end.
I have continued to learn more about impedance while designing products for audio, and may post an updated video in the future. If that would be of interest to you, please let me know here in the comments section if you would like.
This sent me down a deep rabbit hole! It seems that the changed frequency response when the load impedance is too low could also be due to the varied voltage transfer efficiency of the divider that records the voltage. I got this from the Wikipedia article for "Impedance bridging" and I wonder what you think of it. Although your explanation about the load impedance restricting the circuit seems intuitive too. In any case, thank you for the video and the whole transformer series!
I am also a fan of rabbit holes :) Yes, I believe the description you share there is correct, if I understand correctly what you mean. Though I took a look at their pros and cons list in that article and disagree with it because they do not take into account the effects of a source that has an output impedance that varies with frequency, which is basically the main point of this video.
I'll also say, the language I use in the video is more of a model of understanding than completely proper EE. The language of talking about a "reflected" signal comes from some previous work I did in designing cables for digital data transfer. All that work falls under "transmission line theory" and thinking about it in those terms is kind of a different perspective. If you want another rabbit hole good that one!@@felixhilden2782
@@alderaudio Thanks for the response! Yeah it's odd that they don't mention it although there is something about DIs later on, but I do think this is what's happening on the electrical level. Your model though is, as I said, very intuitive 👌 I'm not sure what you meant with reflections. But as it was mentioned in the same article incidentally, audio cables are not transmission lines due to their comparatively short length. Perhaps the "reflection" physically *is* the attenuation in signal on peak impedance wavelenghts even in shorter cables just applied essentially instantly to the whole cable, but this is just hand waving.
You are right, transmission line theory applies when the wavelength of the signal is shorter than the cable run, which doesn't really ever happen in the studio. It does happen on both telephone lines running over miles, and in a short ethernet cable passing signal in the GHz region, and I just find all that fascinating. I appreciate the comment though, it makes me wonder whether it would be more accurate to reserve the term "reflection" for transmission lines. At some point, I will do an update to this video, as I would do it better today than when it was recorded. Discussions like this help me know what to clarify, so I appreciate the comments. Thanks!@@felixhilden2782
@@alderaudio I agree! It's very useful to bounce ideas off others, so thank you too 👌Looking forward to all of your new vids!
Another good analogy is acoustic impedance. Sound travels well through air (which has low acoustic impedance) and sound also travels well through concrete (which has high acoustic impedance). But it doesn't easily transition between the two mediums, because there's an impedance mismatch.
When a sound-wave in air hits a concrete wall, most of it will bounce back rather than continue through.
And the reverse is also true. A sound-wave in a solid-body guitar doesn't propagate out into the surrounding air much.
I have been working in sound for about 30 years and this is the clearest and most useful explanation in a practical sense that I have seen. 👍
Thanks!
Do you want speak french😊
The explanation given is also wrong and misleading... Impedance is a vector that consists of two values: resistance and reactance.
It's a concept that layman has difficulties to understand because it's a sum of complex numbers and is in itself a complex number.
But because it's a value that tries to tell you how system reacts in both voltage, current AND frequency, it has to be.
This explanation completely ignores the most important thing why impedance exists, the FREQUENCY dependency.
You definitely shouldn't think you now understand much about impedance based on this explanation.
It took me a few repeats but I got there in the end. It explains why plugging upright pickups into non-specific audio inputs can be hit or miss...
Thanks for the explanation.
Fantastic explanation. Leaving out the wild math and just using relative values really helped illustrate the basic principle. Suddenly, the “high-z” jack makes sense lol. Thank you!
I'm a guitarist researching DI and line isolator boxes for the first time and you're right, useful/informative explanations are hard to come by. Strong work here. Great vid.
Thank you! A lot of audio videos on this don't explain the physics, and a lot of physics videos on this don't explain how it applies to audio.
Ahhhhh. I make a living from audio and just follow the rules of thumb on impedance. NOW I finally understand the logic to some degree. THANK YOU for this excellent content and delivery.
Thank you so much for this video. I was going through a lot of videos with so much math, but I just wanted to understand how this applied to audio signals, but I've been building tube amps and everyone is always talking about impedance, but no one is gonna tell what it really is. The fact phase shifting doesn't actually apply to audio was veeery enlightening. Thank you again.
Thanks Edson. Yes, when you try to look this up the first time it gets overwhelming, and it's hard to separate the information that is more applicable to digital signals in the MHz range from what is applicable to audio. In digital world phase shift is a much bigger topic since the wavelength is so short, but in audio it's usually not something you have to consider in the vast majority of situations.
One thing you should remember is that the concepts here in this video are mainly directed at audio signals rather than power, so the concept of plugging in something with a small signal like a pickup or microphone into a preamp or interface. In amps, as I'm sure you know, there is also impedance to consider with the output electrical power supplied to the speakers. While I don't talk about that in this video, in that situation the ideal is to have the output impedance match the speaker impedance for most efficient power transfer. This is quite different from signals where having the output impedance of the device be much lower than the input impedance of preamp is preferred
@@alderaudio Sure! But my bias towards this topic was more about understanding things I always hear but no one actually explains or justify. For example, you send your signal through a cathode follower to lower the impedance before going to the tone stack (so the gain loss is lower). Ok, but what does that mean? Now I understand this trick must change the current while keeping the voltage, or something like this.
To quote Einstein "If you can't explain it simply, you don't understand it well enough." Well, you obviously understand what you´re talking about! :-) Thank you for this video!
I wish I could give this video an infinite number of thumbs up.
Really really helpful! thank you kindly.
Genius! Absolutely bloody brilliant that (as we say in Yorkshire (England) - what a fantastic explanation. Won’t go over my background or areas of knowledge, but that was a real ‘light bulb moment’ for me, and I can’t believe I didn’t see it that way before. In fact, just the simple point of explaining that the impedance is the ratio of where a signal sits in terms of voltage to current was such an obvious, but devastatingly useful way of looking at it, it was worth watching the whole video for that. However, it totally makes sense from that starting point how the signal is affected when it hit an input with a difference impedance. Now I properly understand the rule of thumb of x10’s input impedance to output impedance I feel rather pleased with myself. Thank you so much 🙌 🙌 🙌
Thanks for the comment, this absolutely made me smile. Appreciate you saying hello, glad it was helpful.
Thank you. I am going to have to watch this video a few times to let the concept of impedence really sink in, and also how it applies to headphones. It looks like I was lucky to find this video early on in my search to understand impedence, so you saved me a lot of time. Thank you for generously sharing
Thank you so much for this video! Sharing with my Berklee Critical Listening class since this is the best "impedance matching" description I have ever heard.
Thanks for the comment! It's quite an encouragement to me, I am glad to hear that it is useful.
Great explanation, just what I was looking for. Thank you so much!
Fantastic video - thanks.
This was very comprehensive, I salute you!
Thank you very much for your video! I’m in my way to understand more and more about this topic. I’m subscribed and ready to learn more from you
Very well explained. Thank you!
Well explained!! thanks 👏🏻
This is hugely helpful for a basic understanding of impedance. THANK YOU!
It's not. Impedance isn't ANYTHING like explained here...
Great lesson!
This is the best explanation I've seen . Great color coding and use of language; it is appreciated. I subscribed in hopes of you doing the video about how to measure impedance. There are no videos about it on TH-cam for audiophiles incapable of reading, and I am wanting to measure the impedance of a headphone jack on an old keyboard. So please do it. At least one person is interested.
Job well done, Sir!!
Very well done indeed.
😎👍👍
Thanks so much for those explanations. I knew about impedances matching but I didn't know why and how it could affect the sound. Congratulations for the time and energy you spent sharing those precious infos for musicians.
Thanks for this. I'm a guitarist and I've gotten into the rabbit hole... Best explanation I've had
Thank you so much for this video, I'm in my final year of a university degree and building a piezo based noise box / effects pedal sound device using a daisy seed and some basic circuitry inspired by guitar effects. I also had zero electronics experience before starting this. From being a musician into hardware for quite a few years I sort of knew the rule of thumb and negative consequences of not considering it when connecting certain devices, however when designing one my lack of knowledge really became a barrier. This is the video I randomly stumbled across whilst not intending to research the matter that just switched on a huge lightbulb of basic understanding. I am going to check out the rest of your channel in the morning plus the website etc and look into your products as one of my case studies 🙂 you have just had a hugely positive impact, a final Christmas present of 2023!
I am excited to dive into the above first thing tomorrow.
Thanks Tyler, great explanation! : )
That was very good! Thanks. I subscribed. Looking forward to the next video.
I agree, this is a better explanation.
It can also be used when impedance is not related to audio signals.
Thank you.
THANKS, A LOT, now I get (at least conceptually) why everyone talks about the impedance of a device driving the signal at the same time they talk about the impedance of an input, why I would like a Hi-Z input if I want to directly record a guitar or a base, why isn't necessary when it goes through a effects / amplification / SIGNAL chain and how it changes the frequencies and shape of the sound instead of the intensity only.
Hey thanks for taking the time to reply. It's rewarding to get to hear this is helping people. I appreciate it.
Thank you!
Great video! :)
Ok, I'm gonna buy one of those MICs right here and right now 😅. Thx man, great explanation!
well done
Thank you, this is a really excellent explanation! I have a question. If the input impedance was to increase to a very large number, say Z=10,000, does that mean the current in the 100Hz and 1,000Hz examples would decrease to achieve a ratio of 10,000 (voltage presumably cannot increase because that's a function of acoustic pressure on the mic capsule)? If so, does that reduction in current have any negative side effects? Said another way, for input impedance higher is better, but up to a certain limit?
Good video
Great video, really helped a lot!
Just curious, does adding a 1:1 ratio input transformer between the mic and amplifier gives any significance? I have seen such transformers with various impedance ratios, always curious if it helps since it is not a step up or step down type..
This is an interesting and surprisingly complex question. I'll admit, while I do have experience designing transformers for ribbon mics, I do not have direct experience with a situation where you would want a 1:1 transformer, so I might not foresee all the factors going on there. However, one thing that is certain about any 1:1 transformer is that it physically separates the circuit from DC voltage transfer. Transformers transmit changes in electricity - so waves. AC passes through, but with DC, there will be just a little spike of signal with the DC is turned on or off, but otherwise it doesn't pass through the transformer. That is one benefit in some situations. Otherwise, the impedance does not change with a 1:1 transformer, but the sound will still be impacted. Each transformer imparts a bit of its own character to the signal. Two different transformers of the same ratio can sound quite different because they can have very different values of inductance in how they are designed. So I suppose a 1:1 transformer could also be added for the character or color it has. That's what I've got off the top of my head, hope it helps!
@@alderaudio Appreciate for taking time to write the reply, it does help! But gotta spend some afternoon to further digest the concept, along with coffee. Cheers!
We are out there:) Thanks so much for clearing this up! This is definitely something I'll be sharing with my students. I'd love to hear the H44 or H44S in real life. Do you have any dealers in europe/the Netherlands?
Hey, thanks for saying hello. As far as international sales, for the time being what we are trying to do is offer the best service we are able to while still selling and shipping direct to consumer around the world. This helps keep prices reasonable even with all the import taxes. So while the prices are listed in dollars, anyone in the world can order direct from alderaudio.com, and we are always getting better and faster at handling shipping and fulfillment.
Damn bro thank you 🙏🏽
nice video, although we do care about phase since the capacitance and inductance are still a problem to phase unless we digitalize the interconnection of endpoints, (I did my research in college about CI and DI)
Thanks for the comment. I know I didn't go into that part in depth. The argument for not worrying about phase here is that the effects are negligible, not that there aren't any going on. I believe this is the case because we are talking about a single signal in the audio range, so no higher than 20-30kHz or so. Are you saying that phase effects can cause an audible difference in this case? If I'm wrong feel free to point me in the right direction. I learned most of this on the job designing data cable, so I'm sure I have holes. Also, what do you mean by CI and DI in this case?
@@alderaudio anyway, you are doing a good job, I enjoy the video
Great Video! Question, I'm thinking about buying an AEA R44C ribbon mic for vocals. I have a Universal Audio LA-610 pre-amp/compressor that I love and want to keep using. Can I run the R44C through the LA-610? If yes, what settings would dial it to? If not, can I add a ribbon mic pre-amp in-between the mic and the LA-610 without damaging anything or ruining the signal? If not, can I put a DI box between the mic and the LA-610?
Thank you!! ~mike
Hey Mike, great question. You can absolutely use your LA-610 no problem at all. The R44C has an output impedance of 270ohms, and it looks like AEA recommends plugging it into something 1.2K or higher. The LA-610 appears to have a selector for an input impedance of either 2K or 500. On the 2K setting you are solidly in the bounds recommended by AEA, so that will work great. You can also use the 500 ohm setting, and it will give you a very natural sort of low end cut you may find useful in certain situations.
Also, AEA is great, and you should get that mic. You will love it. However, if a vocal oriented ribbon handmade by yours truly for one tenth the price makes you at all curious, you could always check of this demo: th-cam.com/video/WXOqO8UuK8Q/w-d-xo.html
Happy recording!
you are a godsend
About 7:40m you mention impedance goes up in a microphone circuit;
I am only an electronic student since the 80s, but it sounds to me that it is exactly backwards: if the frequency induced in a dynamic microphone decreases, the impedance also decreases. Why? Because in the microphone you have a diaphragm attached to a moving coil. This coil is an inductor, and inductive reactance decreases as frequency decreases. As a matter of fact, if your frequency approaches zero HZ (DC) the coil becomes a short. The opposite would occur if instead of a coil, you had a capacitor. As the frequency lowers, capacitance reactance increases. If you approach Zero Hz the Impedance would approach maximum (an open circuit) because the capacitor has time to fully charge, and no longer passes any current. So you should specify what type of microphones you are referring to.
Thanks for the question, I can understand where your points come from. Perhaps in the future I will make a longer video with less hand-wavy explanations of some technical details. Both ribbon mics and dynamic mics have a large impedance peak in the low end that is caused by the resonant frequency of the element. The same thing applies to a loudspeaker, which is very much like a dynamic mic. (Google "loudspeaker impedance" and you will see the graphs with the hump in the low end, often accompanied by poor explanations) Because that peak is often somewhere from 20-100Hz, I generalized that impedance goes up as frequency goes down. In reality, it goes up, reaches a max at resonance, and then goes back down again below the range of human hearing. Here is a stack exchange that has a good discussion on the subject:
electronics.stackexchange.com/questions/341595/understanding-loudspeaker-impedance
Condensers are a different matter, as they have a powered circuit, they were not my focus for this video, which I could have pointed out. I build ribbons and my experience is mainly rooted there.
Thanks a lot for this brillant explaination.
In the end, does it means that the higher input impedance is the better (assuming I'm not deliberately trying to reduce the low end)?
I faced the question yesterday when having to choose among différent DI boxes.
Well, if you have the exact same input with switchable impedance, than in general I'd say you are not going to perceive any difference as long as the input impedance is at least 5x the output impedance of the device you are using. So really just equal above that point, not better. However, sometimes the high impedance input is designed with a different circuit which is not as well suited. For example, it will sound worse rather than better if you attempt to use an adaptor to plug an xlr mic into a high impedance 1/4" input. In your case, if you were choosing between DIs, I'd guess the other parts of the DI (the tranny or circuit) is going to dominate any noticeable difference in sound.
I have flown around the sun on this rock 38 times but I've never seen a beard this red.
Finally I understood 😅🙏🙏
Excellent explanation! I saw one time in a video that impedance changes different in the case of inductors. The lower the frequency the lower the impedance. Is that truth? Does it mean impedance works in direct proportion in the case of inductors (dynamic mics) and inverse proportion in the case of capacitors (condenser) or the behavior is equal in both? This is inverse proportion
Thank you for giving some great information here. I have a question. trying to record my Korg synth by bringing the output left and right to my Usb Audio device Steinburg ur22mkii at 24bit 192k . It is so obvious that the sound now in the DAW coming out of the Audio device is not as rich and full compared to the sound coming of the headphones from the synth directly :( I feel as if I got robbed along the way.
This goes also for the condensed Mic, great quality mic but I don't feel with the sound coming from the audio device into which the mic is plugged.
So, my question is what is the solution for this ? I just guess that it may have to do with impedance I really would like to hear things recorded i the DAW the way they really are originally and nothing quality taken away.
I would really appreciate if you can shade some light on this and propose the cheapest solution possible to solve this problem. Thanks
Ah, well, what you have here is something I think is very common to anyone who starts getting into recording. It never sounds as good as you expect, and you find yourself asking why. The truth is, there is usually just a lot to it. I don't know if I can solve the problem with the information you have here, but I doubt very much it has anything to do with impedance. The microphone not sounding good is unsurprising. If you are comparing it to how the mic sounds through headphones while using it, hearing the live sound in the room while at the same time hearing it through headphones can vastly change the sound. The synth on the other hand is confusing, something feels wrong there. I would think you should be able to plug into your interface, listen to the synth on headphones through the interface, and that should sound very similar to the headphone out on the synth. If it does not sound the same, I believe something has gone wrong, but I'm afraid I wouldn't know what that is without looking at it in person. But best of luck with it! You are in good company as you work through trying to get it sound right!
@@alderaudio from the keyboard , it sounds wider and bigger and you can immediately tell that you can increase the volume without getting distortion, but hearing it through the Daw like I said doesn't sound as good.
why does current change to make the ratio work at 1000hz, but voltage changes to make the ratio work at 100hz in your example?
Do you mean attenuate or reduce in the use of the word "reflect"? I think that's it.....
Makes sense
So is it fair to say the 100hz then gets compressed by a ratio or is it more of a hard limit, or is it more like a static eq cut like a low shelf
Great question. My first response is that it is not like compression, the effect is even over varying volume range. However, this is still a concept video rather than a detailed analysis of exact electrical behavior. Effects in real life are going to have some finer points involved, but in general, I'd say it is not a bad to think of it as a sloped low shelf.
It is a good explanation. I just don't really understand the term "reflect" as you are using it herein. Maybe I'll get it after a few more views.
Thanks
Voltage is just a potential. No Voltage nor current can be reflected. Your home electrical outlet has 110V AC and Zero current in Amps (Open Circuit) Xl and Xc are reactive components of impedance: Condenser Microphone=~variable capacitor. At lower frequencies, C reactance is larger, impeding current flow. Dynamic Microphone=~ coil changing its inductive reactance . When reactances XL = XC impedance Z=0 and you are in resonance . * It is a signal that is reflected if mismatch of impedance accrue .* Phase is very important in music from classical physics stand point too.
I have a ART TPS2 and it has an impedance knob. Where do I set it & why?
It looks like the TPS2 is variable from 3K down to 150 ohms on input impedance. You should mostly leave it maxed out at 3k because that is going to get you the best flat input of just about any normal mic. Then pretend it is a fancy complicated low cut and turn it down to taste if you want cut out some low end and get a different more focused sound.
@@alderaudio Thank you so much that helped me more than the 20 videos I watched trying to figure it out.
What happens in the OPPOSITE situation. Most modern interfaces have line output inpedances of 30ohms-75ohms. What happens when you plug this output into a color preamp with an input impedance of 1200ohms-2kohms?
Well, you won't have impedance matching problems, so that part is sort of fine, but you will have level problems and possibly ground problems. Because both devices are referenced separately to ground you may get a hum. The input level will also be really loud. But you can turn down the level in your daw and give it a try if you like. It may work. If you have hum, you can probably solve it with a reamp box, which will also bring down the level.
@@alderaudio no ground problems here, but about the level, would the pad button on the preamp help, or is that not enough or at a different point in the circuit?
@@alvincornistamusic8754 the pad could help and is probably a good idea but really if you have no hum it's just a gain staging thing. All you need is to not distort the input on your preamp, so whether you want to use the pad, turn down the output on your interface, or turn down the source right inside the DAW, you can get it to the right level using any combination.
I do not understand what is reflect current or reflected voltage.
"In audio we are not worried about phase" it's a misleading statement talking about impedance or audio in general, am I wrong?
Good question, yes I am only referring to phase shift as related to the topic of audio signal impedance. In audio in general, like when recording, phase is absolutely important, but that is not the topic I am referring to in the video.
The longer context to the comment is that phase shifts related to the topic of impedance are incredibly important in the world of digital signals, so if you happen to be someone trying to learn about impedance on the internet it can be really confusing reading through all kinds of detailed information that is not significant for audio devices. The big difference is that we are dealing with the audio frequency spectrum, so only up to 20 or 30 kHz. When it comes to digital data transfer, signals can be operating in the GHz range, where the wavelength is WAY smaller. When the wavelength gets that small, any kind of phase shift can really mess with things, but the same sort of shift on a signal under 1MHz has a completely negligible impact. I hope that helps!
speakers are inductive load,frequencies are matter
You clearly missed the lesson "Microphone Drawing 101" - the rest of the video is great!
Comment je peut transformer mes speakers 6homs en 8 homs
Even I understood this! Haha
Voltage or current gets reflected. Which one when?
This is one of the stickier points that I am glossing over a bit in the video to make a point. Technically, you cannot have a voltage without a current or vice versa, so reflection isn't so simple. However, the big point is that you have a particular voltage to current ratio natural to the signal output, and when it goes into an input, it will get squeezed into the ratio of the input impedance number. Looking at it broadly, you can see that that either voltage or current needs to be reduced to achieve the new ratio, and the difference in impedance defines which needs to be reduced. Now, because you can't reflect ONLY voltage or ONLY current, the detailed reality is more complex. However, the overall point is still helpful and describes 95% of what is going on.
@@alderaudio Ahhh !!! That was the bit that had me puzzled ... brilliant explanation - thanks 🤪
@grahamh7041 actually; or officially in German electronics, impedance it's the addition of capacitive and inductive resistances. Depending on the circuit (ac) the voltage could be faster than the current or vice-versa. They cancel each other resulting in a "impedance curve" if you measure lots of frecuencys. It's all pitagoras, Best example: imagine a German bier. The whole glass it's power in watts, the white part ist the blind power and the yellow one it's the effective liquid. The yellow make you drunk while the white gas make you fart...
Still a bit confusing. I always saw impedance as more of a requirement for what a signal needs, not what it physically has. Someone said that was incorrect, but it seems correct to me.
Impedance is the relationship between a primary variable and a secondary ditto. Electrical this is voltage and current. Acoustics is pressure and volume velocity. Structural mechanics is force and velocity. If your electrical source is a voltage source, the current then has to comply with that voltage and the impedance loading the source.
@@Rene_ChristensenSo basically what I just said then
thats a hell of a microphone putting out 10 volts at 5 amps. /s
😅
I have mixed feelings about this video,since the formula for capacitive reactance shows why the IMPEDANCE INCREASES WITH A DECREASE IN FREQUECY.XC=1/2πFC,WHERE XC IS THE CAPACITIVE REACTANCE AT THE FREQUENCY "F".THE WORD IMPEDANCE MEANS THE TOTAL OPPOSITION TO AC DUE TO REACTANCE AND RESISTANCE OF A CIRCUIT.
Z=√XC^2+R^2 FOR AN RC CIRCUIT.Z=√XL^2 + R^2 FOR AN RL CIRCUIT. Z=√(XL -XC)^2(WHICHEVER IS LARGER)+R^2 FOR AN RLC CIRCUIT.
FOR COILS,INDUCTIVE REACTANCE WHICH IS THE OPPOSITION OF AN INDUCTOR TO AC CURRENT THE FORMULA IS XL=2πFL,THIS TIME A DECEASE IN FREQUENCY CAUSES A DECREASE IN REACTANCE AND THEREFORE A DECREASE IN IMPEDANCE " Z".
Your comment is very informative but do you know why this happens ,the actual cause of the rise? Answer is you got a conductor coil ,and a magnet that's producing electrical power by the physical movement. Even when being move with electrical power higher frequency less movement
Now wait... I think you're confusing impedance matching with filtering. If you have a mic with say output impedance of 1K Ohm... and you load is a 100 Ohm resistor... you're right... you will not get Maximum power transfer from mic to resistor... but the frequency response will not change. However, if your load is capacitive or inductive... then the frequency response will be affected.
Thanks for the comment. This is definitely a thing though, and pretty widely accepted in audio as a factor that effects frequency response. It leads a common adage that a preamp input impedance should be 5-10 times the output impedance of the input device. This is in contrast to something like, say an old telephone line, where you want to match impedance to maximize power transfer because you are actually driving the receiver with the signal. In that case you are worried about power but if you just running into a FET circuit you are only worried about signal voltage. Check out my follow up video if you are curious, the impedance mismatch example with the piezo pickup displays how significant the audio effects can be.
Yes, in the case of a mic driving a preamp... impedance matching is really something that you don't want. As you say, the load (in this case the preamp) would want to be much higher impedance than the mic you're driving it with... to avoid any unnecessary loading on the mic. But again... any two resistive impedances (matched or otherwise) one driving another... are NOT frequency dependent. Only when there is some capacitance or inductance introduced will there be frequency effects. That said, most (if not all) preamp inputs are capacitively coupled. By doing this, they immediately introduce some level of RC filtering which will impact the frequency response of the system. But by carefully choosing the value of the R and the C on the input... you can set the filter "pole" for a desired frequency location... perhaps even out of the band of desired frequencies.
Why don't preamp manufacturers just build extra high input impedance devices that any instrument or mic could plug into? Why does it have to be around 10 times higher and not more? The current would reduce but the voltage pickup at the input should remain unchanged, no?
Also what about cable impedance? Does it add to the input impedance or to the output impedance? Or neither?
Big questions here, hard to answer quickly. First, unless you are running miles of cable the capacitance is going to be the biggest thing that that has an effect on the input. There's been a lot written about this and it's interaction with pickups that you can find and read online if you like. And as far as input stages, manufactures don't get to just set it wherever they want, the input impedance that is appropriate is linked to the design choices of the first stage. So if you have an op amp vs a FET vs a tube, things change. The input impedance options are limited by the overall design.
I'm just learning to be a nerd
In the real world inductive and capacitive resistance will never be the same... you are explaining dc current, not Ac... U= R x I x cos phi. Thats why eco energy its so difficult, cos you need to retain the 50hz or 60hz net frecuency.
If you watch the video, his explanation say that impedance change by frequency. He didn't want it to be super technical so he didn't convey inductive and capacitive reactance.
"In audio we aren't worried about phase".... This isn't true at all. Phase is really important with crossovers, summing, filters and especially in room acoustics
I have realized over time that my statement in the video isn't clear enough to some people. I'm talking about phase in this specific context of electrical impedance, as in the phase angle difference between the voltage and the current waves. I am not at all talking about all the effects of phase cancelation that can happen with sound waves. That is very important.
For me as a electronics designer it's immediately weird that you start by defining impedance wrong... impedance is a complex number and you COMPLETELY ignore it.
This is very misleading and completely useless... yeah, impedance isn't simple to understand, but then you should just explain it better.
Impedance rises as frequency increases. The resonant frequency of a driver has the lowest impedance and either side of that point the impedance increases.
So, I'm with you on the second bit, but then whether the impedance goes up or down as frequency goes down kind of all depends on where the peak is yeah? And whether going down in frequency is moving toward the peak or away from it? So I simplified this in the video, but if you take a guitar pickup of a few henries and winding plus cable capacitance of a few hundred pF, then you land on resonant LCR network peak somewhere around 5 to 10kHz. That's where your min impedance is as well, as you've said. So as you are moving down from that peak to 1k and then from 1k to 100Hz like my example in the vid, you are going up in impedance. Yes, it is more complicated than get into in the vid and varies by source but I still think the generalization I am making here from 1k moving lower is generally true for mics and pickups.
@@alderaudio Yes I agree that short videocasts do not contain all the of the details. I am not trying to be flippant as it may seam, I just added a little more food for thought for others to read, and you so maybe a bit more interest on the topic may spark questions and statements so we can all learn a bit more. The information you share here is helpful to me as I am working on tweeter diaphragms and crossovers where I am shimming the diaphragm coils to a point where the response as at the flattest level. I welcome more of your knowledge.
Thank you!