EEVblog - 2014-04-25
Part 3 of microphone technology with Doug Ford, former head designer at Rode Microphones. This video discusses both regular condenser and electret condenser microphone construction and physical properties. All videos in this series are here: https://www.youtube.com/playlist?list=PLvOlSehNtuHv98KUcud260yJBRQngBKiw Forum: http://www.eevblog.com/forum/blog/eevblog-608-condenser-electret-microphone-construction/ EEVblog Main Web Site: http://www.eevblog.com EEVblog Amazon Store: http://astore.amazon.com/eevblogstore-20 Donations: http://www.eevblog.com/donations/ Projects: http://www.eevblog.com/projects/ Electronics Info Wiki: http://www.eevblog.com/wiki/
It is amazing the detail these videos get into.
Dave, thanks for doing these videos, I'm sure they don't get as many views as say mailbag Monday but they have a value in their own right. Just as your videos on Op-map theory.
Thanks for getting Doug in Dave, Might be a 101, but I'm gonna feel like I have a degree on mics by the end of this series. Great stuff.
ya :D
Wonderful lectures. Doug reminds me of my old very much admired lecture. Old but very knowledgeable. Step by step and enthused into the topic. wonderful! Valve old analogue still rules. Thanks Dave.
You say old as if that is a bad thing!! Where do you think experience comes from? Old is good it doesn't need a "but" after it, thanks!
So in love with this videos! Thank youuuuu. I just miss the dynamic design
Curious as to if there were other materials used for the diaphragm before the age of plastics, or did this design arise only after? If so, were the only designs preceding it of the ribbon and carbon-impregnated capsule variety that Doug mentioned in the introductory video #602? @EEVblog
Please show more things like this!
How about Noise, I just got a mic in and it humms like hell. Its a Electret SE1000A, had the same problem with the older version SE1000. I thought I could bias it with a 10k Trim Pott? Any one have a cure for this?
What kind of microphone would you need to record elephants who are known to communicate with infra-sound (sub 10 Hz )? Every microphone I've ever heard of dies a horrible death at low frequencies. Would you be in pressure transducer range and would you need multiple microphones to get a high fidelity wide range recording?
@TrickyNekro No. That was contradicted in their first video. Small diaphragm condensers have better bass response than large diaphragm condensers.
To answer OP's question You could easily use a reference microphone on the level of an Earthworks QTC40 which has the following (copy/pasted) specs of:
Frequency Response: 4Hz to 40kHz ±1dB
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Read this for more info: http://www.thomann.de/gb/onlineexpert_84_3.html
@TrickyNekro A critical point here is that we do not want the diaphragm to oscillate. We want it to track the pressure waves impinging on the diaphragm with the least harmonic distortion possible. If at any frequency, in the range of interest, the diaphragm begins to oscillate, then it will begin to generate harmonic content that does not allow tracking the pressure waves from the sound source accurately. We want the diaphragm mass to be as small as possible, and as pliable(and elastic) as possible, without it experiencing collisions with the plate structure(s), or tearing, or self-oscillation. All of this favors a very small and thin diaphragm rather than a large one, up to the limits of practical materials science. This is why I like hearing from engineers like Doug Ford. They offer great insight into the theory and practice, and can also do a passable job of dumbing it down a bit for those of us who have less exposure to their chosen expertise.
Take a close look at the specs for those pressure transducers. They have very poor response to near-infrasonic pressure waves, because they want to measure pressure, not sound. It might be possible to do it with a differential pressure transducer with one port connected to a carefully designed pressure cell, and the other side hooked up to a carefully designed horn. This would handle the case of listening to elephants. As for e-quakes... a 3DOF accelerometer with large dynamic range would be the best way to go. Maybe a few accelerometers with different G-force ranges? Not sure... I'd have to do some careful research to see what can be done with COTS (read cheap) devices.
Most of the pressure tansducers from Freescale Semi, et al, have very small diaphragms, but they are fairly thick to protect them from (mild) over-pressure, and chemical erosion. It would take a fair amount of research to find one in the catalogs that will have the desired frequency characteristics, dynamic range, etc. Many of them have built in amps that may or may not be beneficial for your use case(s). Heck, even recording infrasonic signals is going to be kind of tricky. It might require some kind of frequency modulation to use standard recording gear, and then some custom software to demodulate the FM into a sonogram and waterfall(frequency domain plot)
@metaforest There are off-the shelf mics ~$1000 that have a frequency response of 4Hz to 40kHz ±1dB. That doesn't leave much room at the lower end of the spectrum, but there are general use products out there that don't require a complicated setup.
hey really trying hard to study sound technology very passionate about it but some of the anagrams e.g puffs and a couple others I didnt understand maths I get circuitry I get powersource etc but puffs etc I don't is there a video to explain them or could u reply please to explain some thanks very much great video very funny love when education is made with humour and is intresting
+traitle87 puff = pF = picofarad.
+Scott Drake thankyou
great video but the end is creepy.
I own an NT1000, did Doug design that one? Can he tell me stories about it?
Creepy Crawlers !!
first
Ronald Lijs - 2014-04-25
Dave, these series of videos are GREAT. Better than reading from a book, much more informative, so anyway great stuff and keep them coming!