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Your tube mic is upside down

Friday, February 22nd, 2013 | by


You’ve probably seen engineers hang tube condenser microphones upside down. Do you know why they do it?

Frank Sinatra with U47, upside downMaybe it’s just because of old studio photos of Frank Sinatra.

The explanation I’ve heard, probably from some totally reliable source like one of the audio forums, is that microphone capsules will last longer if they’re not continually baked by the heat rising from the tube. Hang the mic capsule-end-down, and the capsule won’t be in the in the proverbial line of fire. It’s an easy thing to do, and if it was good enough for Sinatra’s U47, it ought to be good enough for all of the cheap tube mics I own that “sound just like the U47.”

The problem is, this explanation doesn’t really make any sense. The capsule deck in every tube mic I’ve seen is sealed off from the chamber where the tube is. Plus, the headbasket is vented to the outside air. Does the capsule really get any warmer due to tube heat?

I don’t believe so, but as they used to say in Chicago, that and a dollar will get you on the “L.”

There’s one other factor worth considering: the electrolytic capacitors found in most audio gear have a useful life span that is inversely proportional to operating temperature. The hotter they run, the sooner they die. So, maybe we shouldn’t be asking so much about the capsule temperature as the PCB temperature.

(Who am I kidding? Of course we’re going to ask about both. But jump to the TL;DR (summary) if you’re not up for a nerdy elaboration on microphone component temperature.)

Tube Mic Temperature Test

I hung a temperature probe in an Apex Electronics 460Apex 460. The sensor was laying alongside the PCB. I let the mic warm up for several hours in each position.

PCB Temperature – with mic inverted (tube above PCB)

Ambient temperature: 72.5° F
PCB temperature:     90.0° F
Delta:               17.5° F

PCB Temperature – with capsule at top (tube below PCB)

Ambient temperature: 70.9° F
PCB temperature:     96.1° F
Delta:               25.2° F

tube mic PCB temperaturesThis answers one question: Inverting the Apex 460 keeps the PCB ~8° F cooler. Does it matter? More on that shortly.

What about the capsule? I didn’t expect much of a delta, for the reasons stated previously. The capsule deck has small holes drilled into it to allow passage of the capsule leads to the PCB. Otherwise, the deck seems like a pretty effective firewall. Nonetheless, let’s test and see:

Capsule Temperature – with mic inverted

Ambient temperature: 68° F
Capsule temperature: 78.4° F
Delta:               10.4° F

Capsule Temperature – with capsule at top

Ambient temperature: 67.3° F
Capsule temperature: 82.4° F
Delta:               15.1° F

Inverting the Apex 460 keeps the capsule ~5°F cooler.

Will these results be consistent for every tube mic? No, of course not — it depends on the heat output of the tube, the presence of ventilation ports, and the interior structure of the mic’s circuitry and chassis.

Regarding the last point: some mics put the tube between the capsule and the PCB. With such mics you have to choose whether to cook the circuit or the capsule.

The experts weigh in

I asked some microphone designers for their thoughts on whether tube mics should be used upside down.

David Royer

With the Mojave microphones, I don’t favor one position over the other… the 5840 tube runs relatively cool and because of the way it is installed in the microphone, heat related problems are reduced.

Dave went on to analyze the power output of various tube models — and to suggest a much more practical explanation for why Frank’s U47 is usually pictured upside-down:

With the Mojave microphones, the power being dissipated inside the microphone is just under a watt.

With a microphone using a 12AX7 or similar dual triode, with both halves of it in operation, the power dissipation would be just under two watts.

As for the Neumann U 47Neumann U 47, the VF 14’s heater and its dropping resistor … dissipated 4 watts between them. With the U-47, it made sense to have them upside down.

But I think that an even more important reason for U-47’s being used upside down was to keep them out of the way, and well out of range of a singer turning the pages of a score.

I also asked Dr. Charles Chen, the lead microphone designer at Lauten Audio.

Charles Chen

The tube will heat the air; as the hot air rises, it will increase the temperature of the air [surrounding] the capsule if the capsule is above the tube. Theoretically this will change the tension of the diaphragm a little bit, and therefore its frequency response. But the slight frequency change due to the temperature change might not be detected, and even if it is noticeable, we cannot say whether it is good or bad.

Dr. Chen noted that inverting the mic will change the recorded signal due to changes in reflection and refraction of the incoming audio waves. But, as with the diaphragm tension, we can’t predict whether this would generally be perceived as a beneficial or detrimental change.

As if reading my mind, he also mentioned the issue of capacitor temperature:

The life of electrolytic capacitors, compared to the other components on the PCB, is most sensitive to high temperatures.

But how sensitive?

The lifespan of electrolytic capacitors

We’ve come this far. We might as well get our geek fully on. We already know that the lifespan of electrolytic capacitors is determined significantly by operating temperature. Arrhenius’ Law of Chemical Activity suggests that the lifespan of a capacitor doubles for every 10 degree Celsius decrease in temperature.

For the Apex 460 specifically: the PCB measures 8°F cooler when the mic is inverted. According to the capacitor lifespan calculator linked above, there is a nontrivial extension of usable life due to this 8°F drop when the mic is inverted — something like 20,000 hours more, given a 4°C drop in operating temperature.

That said, even at a higher temperature, the capacitor for which I ran the equation will live 60,000 hours. That gives you more than 20 years of daily 8-hour sessions before you have to find a replacement capacitor.


TL;DR

Should you worry about the orientation of your tube mic?

As in so many cases, the answer is: it depends. But in general, probably not.

If your mic uses a subminiature tube, as found in the Mojave mics, orientation probably makes no difference to lifespan, because the tube isn’t putting out enough heat to matter.

If your mic uses a hotter tube, and the tube is not isolated from the PCB or capsule, then orientation might help the mic last longer. But you won’t live long enough to notice.

Unless you keep your mics powered up 24×7, I think the mic’s orientation makes no practical difference to lifespan.

Regarding the capsule, I think it is even less likely to be affected by tube heat. The test results show a ~5°F delta depending on the mic’s orientation. I can’t prove it, but I suspect one “spitty” singer does more damage to your mic’s capsule than a 5°F temperature change.

In summary: although your mic’s components might theoretically live longer if you orient them so the tube heat goes in the other direction, those same components will probably already outlive your recording career. Therefore, you should mount the microphone so that the artist is unimpeded in delivering an inspired, energetic performance. This outweighs technical considerations.

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Posted in Interviews, Microphones | 37 Comments »




37 Responses to “Your tube mic is upside down”

  1. Peter Morgan

    February 22nd, 2013 at 9:48 am

    …or it’s just a way to get the mic out of the way of Mr Sinatra’s music stand in front of him?

  2. Ryan

    February 22nd, 2013 at 10:06 am

    I’ve always wondered why, too, I’ve seen mics rigged upside down. And the technical explanation does seem to hold water. But when Mr Royer mentioned the score pages explanation, that immediately made the most sens to me.
    I wonder, too, about the actual sound of a mic hanging upside down, or more specifically, the room. It seems to me the relationship between the floor and ceiling being inverted may have a fairy noticeable impact on the signal. Perhaps some studios find the inverted mic to sound better in their rooms and some not.
    In any case, very cool question.

  3. matthew mcglynn

    February 22nd, 2013 at 10:16 am

    @Peter, yes, that’s sort of the point of the article.

  4. Darren J. Morton

    February 22nd, 2013 at 10:29 am

    Any chance that the fulcrum on the stand balances better with the boom elevated? (Ya, I know its a stretch…)
    -Darren

  5. Vinx

    February 22nd, 2013 at 10:48 am

    Perhaps by flipping the mic upside down, Frank had more room and freedom to make hand movement as he sang? If he hand held his lyric this too would make sense. This is why I flip my u87. Vinx

  6. Adam

    February 22nd, 2013 at 2:07 pm

    In the case of many mics, including Elam251s, the polar pattern of the mic extends far out above the top of the headbasket. I choose my orientation based on:
    1. What surface is above or below the mic (or to its side if horizontal), and
    2. What makes the performer more comfy.
    3. Would be what looks cool, of course!

    Often I tilt my vocal mics at a bit less than 45 degrees, with the capsule looking at the singer’s mouth from an inch or two above. This reduces plosive pops and some sibilance. It also gives the singer a sense of more space from the mic….

  7. Steve Faul

    February 23rd, 2013 at 2:37 am

    Fascinating stuff. My FET condenser is inverted simply to keep the mic connector and cable out of the way. I’ve heard some old school engineers say things like “saves the tube” when asked about inverting a tube condenser. At NPR you see a lot of U87’s mounted sideways for the convenience of the the talent. Wonder what kind of temperature data you would get from that.

    In days gone by I used to hear the following: “When recording a vocalist, place the mic on an overhead boom and position the capsule at forehead level, aiming slightly down towards the nose. This will encourage the performer to raise her head, thus opening the throat and creating a fuller, more open tone.”

  8. Justin Colletti

    February 23rd, 2013 at 11:37 am

    Interesting piece.

    I was always under the impression that they were hung upside down more to deal with the change in capsule tension due to the heat, and less to deal with life expectancy of parts. That’s the explanation I’ve heard most frequently anyway.

    It would be interesting to see if in older designs, like the Neumann U47, the temperature differences are even greater. I wouldn’t be surprised if they were.

    Measuring the difference in frequency response between the two orientations wouldn’t be very difficult. You’d just need a fairly well-controlled room and some pink noise. (An anechoic chamber would be nice and all, but for our purposes, you could do useful test of a U47 without one.)

    Any volunteers?

  9. randall

    February 23rd, 2013 at 12:42 pm

    They hang down a lot easier than they stand up.

  10. ninja

    February 23rd, 2013 at 8:24 pm

    In finland this is known as “läpällä”.

  11. Przemek

    February 24th, 2013 at 2:04 am

    Tube or FET, don’t forget about one thing – spitting. When mic is uspide-down, it’s much cleaner after recording session, and pop-filter helps only a bit ;)

  12. DC Patterson

    February 24th, 2013 at 1:15 pm

    I hang it because of the photo – it looks cooler to Noob vocalists. I used to try and explain that an SM58 into a good pre would be great on their vocals (particularly in a poor acoustic space) but they get all excited when I hang anything (eg. solid state LD condenser) off the ‘big boom’ and stick a pop filter in front.

    I think being able to read the music easier with the mic out of the eyeline is the only real reason to go inverted. All other reasons, see Goose’s explanation in Top Gun :)

  13. RTF

    February 25th, 2013 at 2:17 pm

    This whole discussion is very funny to me. They are big mics, we hung them because they are more stable that way and it gets them out of the way.

  14. Unai

    February 26th, 2013 at 11:29 am

    Is there any chance that the heat emanating from the tube may be translated to added noise floor in the signal, if the microphone is not hung upside down?

  15. Luciano Muratori

    February 26th, 2013 at 12:12 pm

    Ho lavorato con l’U47 e ancora ne ho uno,il fatto di tenerlo capovolto e’ dovuto all’uso della giraffa che come si sa’ puo’ lavorare solo dall’alto ed e’ preferibile al microfono tenuto sull’asta,perche’ percerirebbe, per effetto stetoscopio, il rumore del pavimento.

    [Google translation: "I worked with the U47 and still have one, keep it upside down and the fact that 'due to the use of the giraffe as we know' can only work from the top and is 'preferable to the rod-held microphone,' cause percerirebbe, to effect stethoscope, the noise floor."]

  16. berl

    February 27th, 2013 at 3:29 pm

    Well, the best electolitics caps has a 10000 hours life. Best and big, also ! never seen a 60000 h :-D

    Another explanation for the upside-down position : most of the tube microphones has their valve connection near the capsule to shorten the hi-impedance wires… so the valve is upside-down in the microphone body. A valve should be positioned with the getter-flash at the top, especially with a valve that heats not a lot : the job of the getter-flash is to maintain the vacuum at its best, and to do this it needs to heat…

    So hanging your mike upside-down keeps the tube in good condition and the noise at a low level (noise increases as the valve gets old and also when the vacuum deteriorate)

  17. Mark Fouxman

    March 1st, 2013 at 10:45 pm

    Indeed, often we can see upside down not only tube mics but also ribbons. The explanation is simple–this way it is easier to see lyrics (or text for VO talents) on the stand.

  18. Richard Patterson

    March 2nd, 2013 at 5:16 am

    I have always hung my LDC microphones upside down. Two main reasons:
    1. As mentioned to get it out of the way of the music stand with the words or music.
    2. if perchance any spit goes on the capsule it will drain downwards because of gravity towards the ground and away from the other electronics of the microphone.

    rsp

  19. DonM

    March 17th, 2013 at 3:48 pm

    Great article. During some vocal tracking and overdubbing sessions, I have been inclined to turn the talent upside down.

  20. Pedro Van der Eecken

    March 17th, 2013 at 5:36 pm

    With a large boom stand, most common in studios those day’s, it is much easier to hang a microphone instead of trying to get it upright in the desired position for vocal recording.

    I used upright the stand wil be cluttering all the space where normally the music stand is (or in Franks case his hands are)

    I personally think it has nothing to do with the kind of microphone. Tube/Ribbon is seen most hanging on old footage or fotos but that is also because they where the common mics for a while…

  21. Evan

    March 21st, 2013 at 7:58 pm

    I would bet that the microphone would be far more affected by the cigarettes that Sinatra and everyone else smoked during the sessions, than the mic orientation.

    I’ve just always assumed that they hung it upside down to keep the giant Atlas stands out of the way.

  22. Richard

    March 31st, 2013 at 1:08 am

    I just tried it. It doesn’t make sense that you could see a score sheet easier, as the mic body would be in your line of sight rather than seeing over the top. May be it’s an old practice (and perhaps urban myth) about the heat factor, but it makes sense if you’ve got a singer passionately waving their arms around……

  23. Juan Franco Picasso

    April 17th, 2013 at 8:41 am

    Excellent article, great analysis. Posted it on my facebook and twitter accounts at http://www.ingenierodesonido.com.

  24. Francois

    May 2nd, 2013 at 11:14 am

    Wow that’s the kind of articles i like!

  25. Owen buck

    May 13th, 2013 at 4:11 pm

    During an internship there, the folks over at blackbird recording studio swear its more about the sound quality.

    The mic hanging upside down has an orientation the aims more at the chest and not up the nose which can lead to deeper and richer tones from the recording. They did this for all vocal mics, tube or not. Of course it’s probably only one factor but its one to consider.

  26. Henk van den Haak

    May 17th, 2013 at 6:43 am

    For the direct sound there is no difference between the 2 orientations, as the capsule has rotational symmetry. However, for the indirect sound (i.e. the reflections from the walls, the ceiling and the floor) there is a difference. My microphone is 5 dB less sensitive for sound coming from below (where the house blocks the sound) than for sound coming from above. Now if you hang it upside down you will get less reflections from the ceiling (which is usually hard) but more reflections from the floor (which can easily be killed with a carpet). So hanging your microphone upside down can give you a dryer recording, especially if the ceiling is low. Of course it is a matter of taste which one you prefer.

  27. Cody Jarrett

    June 9th, 2013 at 8:04 pm

    The previous two posts are onto the correct answer. Several well-studied engineers explained this one to me a while ago. When using a large-bodied side-address mic (like a U47) there is a lot of surface area on the body of the mic to create reflections. A singer’s chest is also a source of their sound, and to place a large object directly in front of their chest (such as a huge mic body) would cause reflections. Some of those reflections end up arriving at the capsule after bouncing back off the singer (delayed) causing acoustic phase issues, etc, that you can actually hear in the recording. Hanging the mic upside down positions the large reflective mic body out of the direct path of their chest. (although if you wear a huge hat, like Sinatra, that’s a different issue altogether)

  28. adam

    June 22nd, 2013 at 8:04 pm

    I like the idea of reflections of the singer’s bodies, but how about reflections off the floor or ceiling? The pattern of the mic is not only front and back, but also above the basket and, to a lesser extent, below the body of the mic. In a low ceiling room, point the mic away from the ceiling, for a short singer, point away from the floor. More importantly, for a seated guitarist, point the mic away from the floor, which may be almost the same distance to the mic as is the guitar. How about the mic pointing sideways? You really have to try the mic in each room configuration and with each vocalist to see what sounds best on any given day.

    In practicality, I like to hang my mics to that the singer has a clearer view of the music stand. If there are other players in the same room, or within view, I’ll position the mic for best sight lines. Remember, a comfortable performer will always create a better performance.

  29. Baron

    July 5th, 2013 at 12:32 am

    The easiest explanation to why the upside-down mic for Frank is simply that it’s a recording studio. Some recordings are of vocals, some of musicians playing instruments. Not having a mic stand will get it out of the way if you’re playing a horn (trumpet, trombone, saxophone, etc) and bring it down into a more resting position.

    You also don’t have the mic cord on the floor to be stepped on (damaged) and get in the way along with the mic stand. Plus there’s no mic stand to knock over and damage an expensive studio mic.

  30. benni

    July 10th, 2013 at 12:11 am

    Yeah, same as Baron.

    It’s practical to get the stand right out of the way for easy access to sheet music, lyrics without having to look around a chunk of tubing. Singers can’t tap on the leg of the stand or trip over the cable and send an expensive mic nosediving into the floor, making me very p*ssed off!

    I have big olde speaker stand with a 2.5 metre boom which keeps it as far away from the action as possible. Can stash headphones on it and/or hang a curved acoustic shell from the boom at exactly the right place. It’s saved heaps of problems from ever arising.

    BTW Hi from Sydney Aus

  31. Bill Ruys

    July 22nd, 2013 at 2:20 pm

    I think in the case of the Frank Sinatra illustration accompanying this story, it is simply a case of getting the mic stand/boom out of the way. That said, my observation regarding mic placement is that plosives travel straight out or downward, never upward. Positioning a mic from slightly above facial mid-line or even higher and pointing downward toward the vocalist will completely eliminate plosives, negating the need for a pop filter. If you’re going to mic that way, the inverted method works the best.

  32. Gabor

    July 27th, 2013 at 9:42 pm

    Even elcos that are specified to live for 2000h can live up to 60000, it all depends on how fast the electrolyte dries out. This depends on ambient temperature, ripple current and its frequency (heats up from inside), and the ventilation around it (if it’s hermetically covered with resin potting, it will hardly ever dry out, for instance). The aging is not like one day 100%, and the next day dead. It will develop unwanted effects. You’d better keep your electronics cool. Arrhenius’ law apply here big time and the elcos of that era had poor performance compared to one today.
    The heating up of the capsule and membrane: how exactly did you measure it? Only with a radioshack room thermometer?? The temperature of these metal plates are relatively difficult to measure, I would possibly use thermocouples, and measure their ambience temperature like in 1mm vicinity. There are a number of parameters that make a LDC sound differently if the capsule is 20degC warmer. The expansion of the plates, the slight sound diffraction of the hot air, but I’m just guessing here. One thing is sure, that the modern LDC all come with the instruction not to expose it to more than 40degC ambient temperature.
    Above these two reasons there are number of good ideas in the other posts. And in the end it can be that they did it only cause it looked cool and gave more freedom of movement to the singer :) .

  33. Dan Ortego

    August 14th, 2013 at 1:38 pm

    Dang, for even a certified geek as myself, I found this particular review a bit dry. My guess is that Frank’s microphone most likely outlived himself. Still, it did give me pause as to some of the gear I’m buying at my age. My kids will most certainly inherit it, so the lifespan of products just doesn’t have the same ring to it as it used to.

  34. bern21

    August 31st, 2013 at 10:13 am

    Come on, you know it’s because it looks better!

  35. steve

    September 3rd, 2013 at 12:36 pm

    I’ve just bitten the bullet and purchased an overhead stand for my cherished U47. Having run studios for bands, actors and small classical groups, the main issue is wire tangle and artist freedom of movement. The rest is really just fun talk (which as a committed mic-nerd, I just love).

    I recall an engineer colleague who spent many years recording large orchestras and live events, and when asked which was the best mic for solo instruments her replied: “The ones that can fall over as musicians arrive – and still work when tape starts rolling..” The other thing he said was: “All mics over about £300 will do the job; it’s the one that keeps working I use the most!”

    I think that artist comfort and engineer security (ie no breakdowns) accounts for 99% of the reason for choosing particular ‘positions’ and ‘brands’ of mic. The rest is down to your religion and how much you enjoyed your breakfast.

    Thanks for the great comments up to this point.

  36. Ryan

    September 16th, 2013 at 11:58 am

    I think the mics in those days were hung upside down because those were the most heavy duty mic stands. It it only until recently we have mechanics that can safely hold those tube beasts, like a U-47 or C-12. It also put the mic in the right area without the stand getting in the way.

    So I think it is a question of physics and mechanics over electronic capacitance and heat. I bet most of those places did not even have air conditioning.

  37. Trayse Cook

    April 12th, 2014 at 4:59 am

    I hang them upside down so I can put another mic directly under it and blend the sounds.

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