|27th July 2010, 09:28 AM||#11|
Join Date: Apr 2010
Once again, it is more than a speaker mic or a regular mic with top end EQd out of it. The resonator-sub-mic is not for amplifying the didge, it is for amplifying the resonance created by the sympathetically-tuned drumhead and volume of the drum. I have two separate mics in front of the sub-mic-resonator to pick up all the frequencies of the didge itself, including a little bit of the 45hz fundamental.
As far as I could tell, the Yamaha subkick and other DIY projects out there do not calculate the volume of the resonance chamber to cause a pronounced impedance peak at a frequency that is an exact match to the instrument being played. A resonance system is not hit and miss when you have the instrument and resonator precisely matched in frequency. It is hit, hit, hit and I dare say it is probably a better set up (ok, except for size) than the Yamaha $400 waste of money (so easy to DIY for a fraction of the price) which can capture a range of frequencies but is not designed to hone in on one particular frequency. You couldn't design an output subwoofer enclosure haphazardly without calculations of volume and such and expect a good outcome. This is the same deal in reverse, how could you expect it not to be hit and miss if you are not taking into account volume/impedance matching considerations?
Again, this thing works beautifully, the only problem is the feedback. When you say "a mic can't add frequencies that aren't there", you're missing two points: 1) as I stated, the total set up of the drum and subwoofer is not the same thing as a mic (yes, the sub on its own is just a mic) and 2) the frequency is there--the fundamental tone of the didge is 45hz and is plenty audible but very weak on the beef. There is no missing fundamental, the fundamental is strong as far as a didgeridoo is concerned. The resonator-sub-mic adds more of that exact frequency with a robustness created by the volume of the chamber and the large circumference of the speaker.
I'm sure y'all have more experience than I do with these smaller mics you're talking about. But both from what I've read elsewhere and from my own tinkering I think the large circumference gives the subwoofer an ability to capture the low frequencies better than any of the suggested smaller mics. And then when you take into account the sympathetically tuned chamber/drumhead...it's even better. I've used some pretty decent mics for my budget (Rode NT1A and Shure Beta whatever number) in every position relative to the end opening of the didge and applied compression, equalization and what not, and most definitely nothing comes close to the resonator-sub-mic.
Maybe it's the wrong forum. When I asked for suggestions of alternatives, I was thinking of alternative clever organic means, not more expensive equipment. (Not organic like granola or birkenstocks and dreads; I'm all for genetically modified organisms--as long as someone else tests them out first.) So far, all I've gotten is convention from everyone except Ferrit. I'm looking to complete the process of pulling off something spectacular here (the only thing left to complete being the feedback problem) artfully bypassing these electronics in favor of a somewhat more organic hybrid instrument just for the art of it. Geez, these devices y'all are talking about are probably well out of my budget anyway. It's the art. (a sub harmonic synthesizer could be fun though).
And as of yet, no one here has addressed my specific questions (I'm not really complaining; it's free advice after all. Thank you.) Being obstinately attached to completing a most successful project, I am looking for knowledge on specific aspects of the project.
Those questions were:
If I attempt a Helmoltz style resonator, how to calculate volume of chamber and port in terms of impedance matching? Would the Helmholtz resonance created in the port make it back to the speaker in a way that would add bass to the input without causing phasing issues? I know that sub enclosures are designed to eliminate bounce back of waves that are generated from the backside of the speaker cone; so this causes me to question whether my proposed djembe-mic set up would work properly. In this case I would want the sound waves passing through the speaker to bounce back, and with added amplitude. But the time delay of passing through the chamber to the port and back makes it seem a questionable idea. In any case, I've got a 10 inch sub and an 11 inch djembe to experiment on.
The other questions came after looking into Ferrit's link on the Yamaha Subkick. No one has addressed these either. So, really not meaning to be rude, i'm just wondering if there is a more appropriate forum for this that someone knows about.
|27th July 2010, 10:44 AM||#12|
Join Date: Nov 2005
I think you might be in the right enough forum but I don't think the speaker mic angle is so appropriate for these instruments, In the case of trying to pick up a kick drum, you're dealing with extremely high sound pressure levels at low frequencies where mic dynamic range is an issue, and of course using a speaker as a mic is a great solution for that, even on the cheap, which is how I think the whole thing got started. Good kick drum mics are quite expensive, but not necessarily 400 dollars. I think a 400 dollar commercially offered speaker mic is therefore truly a joke.
The output peaks of a djembe can get very high, but not so much at very low frequencies. A conventional dynamic mic with fairly limited diaphram excursion capability would work well enough. In the didge scenario I don't think you're dealing with very high sound pressures at all, leading to the necessity of a high sensitivity and/or gain arrangement for a good mix, and lots of feedback problems if a resonant system is used on the mic.
In the usual kick drum mic case I think the woofer resonance is selected quite a bit below drum fundamental for good sound. The heads are often fairly heavy and the drum still large in relation to the mic speaker, and the instrument is able to fairly dominate the output signal.
My opinion is that you should be more interested in electronic EQ using good microphones selected to preserve the natural envelope of the insturment even if you want to alter the frequency response for some effect. The port of a djembe already introduces some delay and softening of attack for the fundamental tuning and adding yet another resonant system to that would likely sap the life out of the sound and make it comparitively boingy. On the other hand there is practically no attack to smear from the sound of a didge but the sensitivity issue is severe enough. For the didje fundamental pickup I might try placing a small condenser element in the center of the mouth of the open end and sharply filtering off everything but the instrument fundamental frequency. You'll probably need to build a custom filter for best results but you could experiement with a run of the mill EQ. Just pull everything down around the fundamental.
|27th July 2010, 12:38 PM||#13|
Join Date: Apr 2003
sounds like what you are wanting to do, is put your sub/mic in a 'one note wonder' 6th order bandpass box, that has a huge peak at 45hz. right? Sounds like a quick pass with winisd or some other design program could give you what you are looking for.
|27th July 2010, 03:29 PM||#14|
Join Date: Jul 2010
Thanks for posing such a good question. I am the owner of audiogabriel, and the author of the DIY subkick article posted in this thread and have had some experience dealing with this problem in the past. I feel as though there are a couple of things I can offer directly in response:
I understand completely where you are coming from in your project, and you are definitely thinking along the right path when it comes to resonance. The didgeridoo is an instrument I have had experience recording and understand clearly what the problem is when it comes to fundamental frequencies. Just don't forget the overtones! A lot of what makes Bass sound deep is the energy that exists above in its upper-harmonics.
What I think you are looking for is a microphone that specializes in low frequency capture. There have been some replies suggesting use of dynamic mics such as the EV RE20 combined with the use of a dramatic eq filter. This is where I would start if I were you. To echo Andrew Eckhardt's response: while the subkick is a good tool, it depends on high SPL source to really get the cone moving. What's more, you'll probably have to use some EQ on the subkick signal anyway to eliminate some less-than-desireable low-mid to mid-range muck. I'm not sure how loud you are performing the dig, and this may not be a problem, but I just thought I'd mention it. If you do decide to go this route and build your own, look for a cheapo computer subwoofer with a mylar gasket. These generally are easier to push in or out with your finger and will lead to better response at lower SPL levels.
Impedance matching has to do with the output impedance of the microphone in conjunction with the input impedance of the microphone preamp. What I think you are proposing (and correct me if I'm wrong about this supposition) is to intentionally design a microphone with a mis-matched impedance to a particular mic pre so that there is a phase shift that produces and electrical resonance at the fundamental frequency of your dig. While theoretically possible, this still might not give the results you're looking for. Remember, with a fundamental comes a series of overtones. If you emphasize one Harmonic, you will be altering the perception of the surrounding frequencies resulting in a weird comb-filtered signal that might sound neat in an effects kind of way, but definitely not natural. While this effect is less noticeable in the extreme lower octaves, it would be better if you can get a clear picture across all frequencies as low as possible. Remember, the clearer the upper harmonics of a bass frequency, the deeper the perceived bass energy.
Assuming an ideal situation: The right way to go about this is to have a very good acoustically treated room that has some natural resonance from 20Hz up, a condenser microphone that is carefully placed and is matched to an appropriate microphone preamp with a very high amount of headroom, connected to a DA converter clocking at very high sample rate and monitor the outcome on properly calibrated studio monitors that are capable of reproducing detail at low frequencies.
I realize that this solution is not what we want to hear, because it's ideal = expensive. If you're a DIY, then you're going to have to sacrifice in one or all of these areas. This might be why you have seen so many different posts addressing your problem in so many creative ways. Let's face it, it takes creativity.
I would encourage you to go the DIY subkick route for experimentation. It's super cheap and it'll force you to think outside of the box, which is what it will take. But be careful not to over-think the elements too much. My personal suggestion would be to try to solve the problem at ONE point along the ideal signal path. ie: point 1- acoustically treated room: Q: What can I do to acoustically modify the room I'm in to enhance bass response? A: Put the mic in a corner, build a resonant acoustic amplification box.... Just be aware that when you change one point in the path, you indirectly change any point thereafter. This holds true for the acoustic environment as well. If you build an acoustic resonance box to play in, it will help your sub mic, but it might throw off your picture in the higher frequencies.
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|27th July 2010, 06:02 PM||#15|
Join Date: Apr 2010
Reply to Andrew
Thanks for the responses. This is some good information. Since I’m so verbose and full of questions, I’ll split up my responses into separate posts.
“In the didge scenario I don't think you're dealing with very high sound pressures at all, leading to the necessity of a high sensitivity and/or gain arrangement for a good mix, and lots of feedback problems if a resonant system is used on the mic.”
True. In fact, the 45hz didge I am dealing with here is one I modeled on software before actually building it. (didgmo.sourceforge.net) Didgmo’s predictions are fairly accurate as far as the arrangement of impedances relative to harmonic spectrum, so I think it is pretty accurate as far as its predictions regarding the levels of the various impedances. I can spectrum analyze the impedance frequencies relative to harmonics, but have no way to measure the actual amount of impedances. (The analysis is a pretty neat trick: you play the didge with mouth to establish the frequency of the fundamental and its harmonics—integer multiples. Then, to establish the frequencies of the intrinsic resonances/impedances you slap the mouthpiece with your hand and hold it down, encouraging all the intrinsic resonances/impedance maxima to sound at once. If you slap it and quickly release your hand, it reveals all the impedance minima, which are the notes that would occur if the instrument were played as a double-open-ended instrument such as a flute. But I digress…) Anyway, according to the prediction in this case, and in general, a didge is in the range of about 15 to 20 Mohms, which, yes is a tiny fraction of a kick drum’s impedance level (what, something like 50+ Ohms?) But to me, the comparatively low impedance is all the more reason to use a resonant system with the didge.
So, to be sure, are you saying that the reason the sub-mics applied to kick drums don’t have feedback problems is that the mic input level relative to gain is much lower than I need for the didge?
As far as feedback problems, there is not too much feedback when I use just the subwoofer alone, and I continue to believe that it is possible to get my gain levels where I want them with some revisions of the resonant system. I’m going to start by replacing the drum head with a mesh head as in the Subkick. Another possibility is to scrap the idea of a drumhead at all and just mount the subwoofer at the front of the drum (where the drumhead would be) and take advantage of simply the volume of the chamber alone. Which reminds me of another question: I currently only have one drumhead with the subwoofer mounted in the back. If I had a drumhead on each end, with subwoofer either inside or outside, do you think the different behavior of having two drumheads (which I don’t understand, doesn’t it double the fundamental up an octave? ) would add to the feedback or reduce it? My guess is it would add to it.
By the way, there are other reasons I want to perfect this thing. I am also a drummer and have experimented with the sub-mic in that fashion as well. For example, I have a recording with amazing bass created by banging merely a small shaman’s drum in front of the sub mic. I’m guessing the impedance level of the shaman’s drum is well below that of a kick drum. The shaman’s drum I used in fact had just a flat cardboard sound—most of the tonal qualities and impedance came from the sub-mic-resonator alone. So I would still need a high sensitivity/gain mix resulting in feedback if I tried out the shaman’s drum live.
More digression… skip this paragraph if you want. One thing I really want to do in the long run is to use the resonator-sub-mic in such a way that the feedback is not a problem, but rather a way to create a new instrument. At 45 hz, the feedback loop feels really good on the ears and body. When the drumhead is not tuned precisely, it is fairly easy to change the feedback loop to restabilize at a different frequency just by tapping on different parts of the drumhead and triggering various harmonics. . Imagine changing the note by either using a head which allows the tension to quickly be changed (like a talking drum) or, more easily, using an adjustable sliding chamber to quickly change the chamber’s volume, like an overgrown trombone—this would allow me to adjust the feedback loop and create a nice bass track.
Back to the feedback problem… Perhaps tuning the drum to 45hz helped to create the feedback loop. If I increased the volume of the drum and brought it to a very low fundamental, maybe below 30hz, perhaps the feedback would be reduced/eliminated and I could still get the boost I wanted. Plus, this would be more like the kick drum sub-mics which you said are tuned to below the fundamental of the kick (But how could the Yamaha Subkick, as small as it is, be tuned that low?) If I tuned it to an octave below my didge fundamental (a subsonic 22 to 23 hz) maybe it would boost the subharmonic at that frequency—wouldn’t be audible but would be felt physically.
Also you said:
“My opinion is that you should be more interested in electronic EQ using good microphones selected to preserve the natural envelope of the insturment even if you want to alter the frequency response for some effect.”
I can see that, but again, it’s about the art/fun of it. Plus, I’m really not convinced the bass would be as nice with the electronic EQ/good microphones arrangement. Maybe I’ll have to upload the recording with and without the sub-mic to give an idea. True, you could say I just need to adjust the mics or use better mics. I really like the combo of the Shure Beta and Rode mics, the shure tends to excel at higher frequencies and the Rode fills in the midrange to lower frequencies. Yes, Rode is lower budget, but it really does a nice job. I have experimented with every position and found that the optimal arrangement is to have the Shure mic about 4 to 5 inches away from the bell of the didge and the Rode at about 15 inches from the bell (1:3,no phasing) The Rode, if placed closer, gets too bassy, not a punchy low bass at the desired frequency, but a saturated kind of bass at a large range of frequencies. I suppose I could take the suggestions and apply clever equalization to the Rode input, but then I would lose my nice combo of the two mics and can’t afford a third one. Anyway, I’m still not convinced that the clever arrangement and equalization, or some similar variation, would result in as satisfying and robust bass as produced by the sub mic. It wouldn’t just be a matter of stripping down all frequencies except for 45hz. Surely the sub-mic resonator has other effects occurring which would be difficult to duplicate with mic placement and equalization. For one thing, it would require isolating all the frequencies coming from the resonator-sub-mic (easy enough) and then attempting to duplicate the robustness by adjusting the equalizer at the same frequencies and maybe add compression and whatever other effect I still haven’t heard of. (Digression: I think it would be fun to apply sidechaining and “ducking” as in some House music so that with a drum and didge track, the didge would duck every time the kick drum sounds. Still haven’t tinkered enough with Ableton to set this up, but the software definitely has the capability for it.)
“The port of a djembe already introduces some delay and softening of attack for the fundamental tuning and adding yet another resonant system to that would likely sap the life out of the sound and make it comparitively boingy.”
Thank you, this is the kind of understanding I’m searching for. Let me make sure I understand what you said here. A standard djembe, with drumhead and port is one resonant system. But a didge, subwoofer and port introduces one more resonant system? So the delay could saturate the sound too much? Also, I guess this statement implies an affirmative answer to my question about whether the Helmholtz effect in the port would significantly affect the amplitude of the speaker movement.
“On the other hand there is practically no attack to smear from the sound of a didge but the sensitivity issue is severe enough.”
Actually, attack depends on the playing style. Traditional playing techniques involve a more continuous, soft flow of sound. But didges are kind of a hybrid wind/percussion instrument—especially didges with a modern tuning. My style involves a lot of percussion and attack, so maybe as you said, it would end up smearing the attack. I guess the only way is to experiment and see what I get. Boingy and smearing might sound nice on a didge.
“For the didge fundamental pickup I might try placing a small condenser element in the center of the mouth of the open end and sharply filtering off everything but the instrument fundamental frequency. You'll probably need to build a custom filter for best results but you could experiement with a run of the mill EQ. Just pull everything down around the fundamental.”
Pardon my ignorance, but are you talking about a condenser mic? The first mic I tried when I started recording didges was a Shure Beta 98H clip-on cardiod condenser mic, marketed for brass and percussion and more expensive than either the Shure Beta 58A or Rode mics. Shure Americas | BETA 98H/C Instrument Microphone | Precision, Sensitivity, Vocal, Instrument
The 98H would be perfect for what you are suggesting—that is, if it didn’t absolutely suck balls. This mic was a let-down for both percussion and wind and I should have returned it. It is tinny with virtually no low frequency response. I really don’t understand why it sounds so bad. For one thing, the mic cable on the 98H is very thin. How can it be so thin and be expected to sound nice? This expensive (for my budget) mic was a huge disappointment. Maybe it is because it has such a small diaphragm. This would lend support to my opinion that a subwoofer is the best way to go, having such a large diaphragm.
Last question: As I said before, I’ve mostly experimented with Ableton’s EQ and compression and don’t know about the filter to which you refer. Is it likely to be an effect that is included in Live? What other title might it be under? I’d like to try out all the suggestions and see what I get.
If you made it this far, thank you. If you can answer all the questions, thanks even more.
|27th July 2010, 07:49 PM||#16|
Join Date: Apr 2010
Thanks for chiming in. I was wanting to ask, after reading your site, how you liked the set up of having the sub mounted at the front of a tube. I was thinking of trying it this way.
“Just don't forget the overtones! A lot of what makes Bass sound deep is the energy that exists above in its upper-harmonics.”
Yes, and that is why in an earlier post I said that, in addition to the resonator-sub-mic I also have two regular mics and the result is a well balanced spectrum. Having gone deep into the science and playing techniques of the didge, I am very familiar with the harmonic effects. Check out this website: Computer Animated Didge Sound Design (CADSD) - Die Methode
Frank, the pioneer of Computer Aided Didge Sound Design, has been kind enough to share several different acoustic formulas with me over the last few years. Recently, he confirmed my hypothesis regarding what it is that makes it possible to coax out of the instrument various “trumpet notes” (also called “toots” among didgers) at frequencies that actually have no impedance. What makes it possible to coax and stabilize an unofficial trumpet note or phantom note is that one or more of the harmonics of that phantom note are boosted by impedance peaks. The more harmonics of a phantom note that are boosted, the easier it is to play and stabilize the phantom note as if it had its own impedance peak. Don’t know if this makes any sense to you. I calculated all the frequencies that would need an impedance peak to result in a didge that has an optimally playable phantom trumpet note between the fundamental/drone and the first official impedance peak/first trumpet or toot (1-drone, 2-phantom at perfect fifth, 3-first official trumpet at one octave above drone) Frank responded with that exact formula (and one he came up with designed to have three phantom notes) using his recently implemented evolutionary algorithm to “evolve” the shape necessary to get the desired impedance frequencies. Anyway, yes, I’m all about the harmonics at all ends of the spectrum; not just the harmonics but special effects that occur as a function of the placement of impedances relative to the harmonics. For example, you can get a didge that is a “wobbler”, a didge that is a “singing didge” (a harmonic is louder than the drone itself), a didge with specific “heterodyne amplification effects”, and more. A lot of this is on his website. Amazing stuff! Maybe too much detail, but you mentioned having experience with the didge, so I thought you might like it.
“To echo Andrew Eckhardt's response: while the subkick is a good tool, it depends on high SPL source to really get the cone moving. What's more, you'll probably have to use some EQ on the subkick signal anyway to eliminate some less-than-desireable low-mid to mid-range muck.”
The SPL is plenty to get the cone moving. It is very “hot” and I end up padding it with the built in pad in my MOTU Traveler (one of the few times I could afford something nice). The cone is a pretty thin material (15” sub). I’ve experimented with EQ on the subkick signal and found that it really makes no difference—the sound is very clean and the sub just doesn’t put out much mid-range at all. In any case, applying equalizer in this case is a very simple matter compared to other suggestions.
“Impedance matching has to do with the output impedance of the microphone in conjunction with the input impedance of the microphone preamp. What I think you are proposing (and correct me if I'm wrong about this supposition) is to intentionally design a microphone with a mis-matched impedance to a particular mic pre so that there is a phase shift that produces and electrical resonance at the fundamental frequency of your dig.”
This is not what I’m talking about and I hadn’t heard of it until I read the material on your site yesterday. What I mean is matching the impedance frequency of the didge fundamental (45hz) with the impedance frequency of the resonator-sub-mic (a function of volume and head tension, but mainly volume). Like jBell said: “sounds like what you are wanting to do, is put your sub/mic in a 'one note wonder' 6th order bandpass box, that has a huge peak at 45hz. right?” Right. Though I don’t know what a 6th order bandpass box is; but the point is that the drum tuning results in a huge peak at 45hz.
“Remember, with a fundamental comes a series of overtones. If you emphasize one Harmonic, you will be altering the perception of the surrounding frequencies resulting in a weird comb-filtered signal that might sound neat in an effects kind of way, but definitely not natural. While this effect is less noticeable in the extreme lower octaves, it would be better if you can get a clear picture across all frequencies as low as possible. Remember, the clearer the upper harmonics of a bass frequency, the deeper the perceived bass energy.”
Yep. But again, the full spectrum is well-balanced.
“My personal suggestion would be to try to solve the problem at ONE point along the ideal signal path. ie: point 1- acoustically treated room: Q: What can I do to acoustically modify the room I'm in to enhance bass response? A: Put the mic in a corner, build a resonant acoustic amplification box....”
Remember, I’m quite satisfied with the sound results obtained while recording—the mp3 I wanted to upload (but just found out that it is not a valid file extension for uploading. I could email it to you.) was recorded in a large, reverberating dining hall, with people talking in the background. I like the sound effects that resulted from the people talking and making noise. In the version that I tried to upload, I’ve got the sub-mic track EQd to eliminate all frequencies above 50hz and also to give a little boost at 45hz (neither of which are really necessary, I couldn’t decide which version I liked best). No compression on the bass track.
I could email another version of the same song without the submic, a version with the submic but with no EQ, and a version with just the sub-mic track.
I don’t believe in studios when it comes to recording didges. My studio is mostly in my backpack (except of course for the giant unwieldy sub-mic. If I can make something the size of the Yamaha subkick work as well as the sub-mic I made, it would make things a lot easier as far as traveling/performing live goes.) Why not hone in on making the sound great in any situation or environment, recorded or live?
The answer I’m looking for is how to take what I’ve got to a live situation without the feedback problem (and wind on the drumhead interfering with the input--a couple thoughts are to use a blanket canopy over the set up when performing live to eliminate wind interference and to shock mount the subwoofer instead of the way I currently have it mounted.) In any case, I’m going to start experimenting with a ten inch woofer mounted inside a 10 to 12 inch tom with mesh heads and see what I get. My impedance matching (didge to drum) might not have been necessary. Again, I am still confused about how the Yamaha Subkick, being as small as it is, can have such a low frequency range. Surely it has its own particular fundamental impedance frequency and it must be a relatively high frequency judging by the volume of the drum. So maybe size and impedance matching doesn’t matter so much. Or maybe it does and the Yamaha version doesn’t add as robust bass as mine does. More experimentation necessary.
Thanks for the response.
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