Kick drum (cajon) - condenser damage?

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chconnor
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Kick drum (cajon) - condenser damage?

Post by chconnor » Sun Oct 14, 2007 12:33 am

Hi, sorry to ask the oldest question in the micing book, but a few searches on Google came up empty...

I have an AKG 535 EB and want to know if i can safely use it to mic my Cajon (marvelous instrument from Peru, basically a box with a circular bass port on the side that you can whack for a kick drum type sound. My feeling is that the SPL is roughly equivalent or perhaps a tad higher than the average kick... it's a thumping cajon).

The best spot for me is right in the port, the head of the mic just protruding into the box (i.e. at the max SPL...). I think the upper limit on the 535 is like 145 dB SPL, but I'm not even sure about that... that's obviously an important piece of info I lack (a query is outstanding with AKG at the moment) but maybe someone knows...

I have a very cheap dynamic that produces a usable, less-satisfying result, which I can use if I have to, but I'm hoping that occasional use of the 535 for this won't hurt it...

Any thoughts?

Much obliged!
-casey
Last edited by chconnor on Tue Oct 16, 2007 12:22 pm, edited 1 time in total.

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Post by A.David.MacKinnon » Sun Oct 14, 2007 7:21 am

It's blasts of moving air more than SPL that will damage your mic. Hold a match where you want to put the mic and then bang away on the drum. If the match blows out or flickers drasticly you know you shouldn't put a condensor there.

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Well hmmm....

Post by chconnor » Mon Oct 15, 2007 12:57 pm

Ok, sounds like perhaps it's out of the question then... Without even doing it I think the match would most certainly flicker at the very least, and probably it would go out. If it matters, it is a small diaphragm condenser, the 535, a hand-held "rugged" stage microphone in many cases, and lots of people use it on snare drums... ?

Thanks for the input.

-c

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Post by JohnDavisNYC » Mon Oct 15, 2007 1:01 pm

that match thing is retarded... any singer talking would blow out a match. please don't spread mis-information. maybe it is a good rule of thumb for a ribbon mic, but i've never heard of that 'test', and i actually record music....

a cajon doesn't put out very much SPL or air, so don't worry about it. if it sounds distorted, and the mic has a pad, try engaging the pad... but i wouldn't worry about putting any mic in front of a cajon... kick drums put out WAY more air and volume, and probably all engineers have at some point put a condenser mic in front of or inside of one.

use the mic. if it sounds good, awesome. especially since it is a stage condenser, it will have a built in pop filter, anyway.

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Post by directaction » Mon Oct 15, 2007 1:46 pm

a pop filter will also help. It really cuts down on air movement, but not SPL, so if it's the air movement you're worried about, then you might give that a shot. You could also try putting the dynamic inside, and the condensor outside, and out of the direct path off the air (off-axis).

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Post by A.David.MacKinnon » Mon Oct 15, 2007 5:48 pm

toaster3000 wrote:that match thing is retarded...
Maybe I shouldn't have said don't put the mic there but the match trick will at least give you a good indication of how much air the drum is pushing. If it's a cheap mic then go for it. If it's a vintage U87 I'd be more careful.

Many engineers (including myself) have pointed a condensor at a kick drum, or even put one inside, but putting it directly in front of the hole (or any vent in a drum) can be bad news if you haven't checked it out first. I'm not saying it will damage the mic. I'm just saying it can damage the mic.
As long as you know the risks do what feels good.

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Post by chconnor » Mon Oct 15, 2007 6:13 pm

Thanks for the ideas.

I'll go for it, pending feedback on the AKG forum or any last words of wisdom...

For the record, this is a cajon I made myself, and it's bigger and burlier than your average cajon (by design.) When I play it in a corner it does make a thumping big bass hit...

The reason I want to use the condenser inside, or at least direct in the path, is that it has much better bass response than the dynamic, but thanks for the dual-mic idea. I may do that anyway. I'll I'll experiment with the pop filter...

What I really need are a few new mics, but you go to record with the mics you have, not the mics you want. :-)

Appreciated,
-c

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Post by chconnor » Mon Oct 15, 2007 7:13 pm

junkshop wrote: Maybe I shouldn't have said don't put the mic there but the match trick will at least give you a good indication of how much air the drum is pushing. If it's a cheap mic then go for it. If it's a vintage U87 I'd be more careful.

Many engineers (including myself) have pointed a condensor at a kick drum, or even put one inside, but putting it directly in front of the hole (or any vent in a drum) can be bad news if you haven't checked it out first. I'm not saying it will damage the mic. I'm just saying it can damage the mic.
As long as you know the risks do what feels good.
Yeah... a cheap mic, but dear to me, if you know what i mean (it's ~$250-300, after all.) I am sticking it right in the highest intensity place (on purpose). I guess there's only one way to find out for sure. :-)

I just don't have much of a grasp on the seriousness of the be-careful-with-your-condenser advice... on the spectrum from "over-reactive gear-obsessed engineer nit picking" to "a genuine, common risk that has damaged or degraded many a microphone in the hands of the unexperienced", where the truth falls. My feeling is that it's a pretty tough stage condenser and so I'm willing to try it, but it does make me nervous. I'll check out a kick drum and compare before doing the deed... Experience, here I come.

Any thoughts on the utility of an SPL meter in these kinds of situations? They all seem to not be able to measure past ~130 dB SPL...

-c

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Post by Professor » Mon Oct 15, 2007 7:37 pm

The easiest way to protect against damage from a strong rush of air is with a pop-screen. Simple and effective, I use them when I place any mics (dyn, cond, ribbon) in front of sources that might be a little too explosive.
Of course, that said, I place ribbons in front of trombones in our big band without pop screens, and I stick them an inch over toms as well. Last week I had a C-414 hanging an inch over a snare drum head for two different sessions, although I do pad that down -10dB with the switch on the mic.

Here's a good 'rule of thumb' for dangerous levels at the mic...
If the instrument sounds clean acoustically, and the levels on the preamp are well below the red line (like -10dB peaks or lower), but you are hearing distortion, then you're probably pushing the mic too hard.
It's not a great rule, because those air rushes can be at such a low frequency that you might not hear it, or it might not distort quite the same way.

Either way, as hardcore as your cajon might seem, I can't imagine it's pumping out 135dB. If you pushed it that hard, you'd probably put your fist through the box.

-Jeremy

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Post by JohnDavisNYC » Tue Oct 16, 2007 5:15 am

there is no reason to be afraid of putting a vintage 87 in front of something moving air... i don't understand where this fear is coming from... it isn't a ribbon mic... it will be fine.

i have never heard of a condenser mic being damaged from volume... EVER...

i'm not trying to be a jerk, but spreading the fear of using microphones to record stuff that is loud is crazy... i put a late 60's/early 70's U77 (87 prototype for Danish Radio) a few inches from the hole on a kick drum all the time... if the air is too much for it, i angle it a tiny bit off axis... i put an AT4047 there all the time... sometimes right in the hole, flush with the head...

it is good for people to be cautious, but there is way too much trepidation on the interwebs about actually mic'ing things... a handheld condenser is designed to be screamed into every night on stage... a wooden box with a hole in it being hit with hands isn't gonna be too tough on it.

so, like professor said, if the mic is unhappy, it will let you know, and the only thing you will probably be hearing if there is distortion is the electronics overloading, not the capsule xploding...

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Hmmm...

Post by chconnor » Tue Oct 16, 2007 12:06 pm

I have heard a lot of caution (on this forum, even) about, for example, beat boxing into mics like the 535... which of course is probably a lot higher SPL, but the basic point being that deformation of the diaphragm can happen...

Thanks for the feedback. It helps me get a realistic picture going in my head... Be aware, be careful, but don't freak out. Good advice in general. :-)

-c

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Pads...

Post by chconnor » Tue Oct 16, 2007 12:09 pm

Oh, one other thing. The pads... the only pad on the 535 has a bass roll off, so it would defeat the point of using it in this case, but in general, this is more about signal overload than mic protection... the pad I assume has no affect on the physics of the membrane... yeah? When I did the test run, the mic was flat and there was no clipping or distortion, so I'm feeling pretty good about it. I'll try it with the screen just for fun.

Thanks again, -c

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Post by Professor » Tue Oct 16, 2007 7:34 pm

The low cut is a little different as it's an EQ circuit designed to drop off some of the low frequency. It doesn't remove it by any stretch, it simply starts dropping off the volume below a particular corner frequency... like say 12dB per octave below 100Hz. It also comes into play after the capsule anyway, so it would keep the electronics from overloading and have little to do with the physical air movement at the capsule.
On some Neumann & AKG condenser mics (and others too I'm sure) the -10dB pad switch actually reduces the phantom power voltage so the electrical characteristic of the capsule changes and the tone and timbre of the mic change. I don't recall all the models that use this method and if the 535 is among them. If the diaphragm were hit with enough force to short against the back plate (that's a lot of force) it would still short and sound ugly, but I seem to recall this method makes the capsule a lot less sensitive overall.

There's some good material about that on the Neumann info center at their website, though it takes some digging.

Blowing directly into a mic can actually produce much more force at the capsule than loud sounds in some case because the air isn't vibrating, it's like 'direct current' air flow. You can scream into a mic 1" away and generat maybe 110-120dB, but you can purse your lips and blow and push the equivalent of 130-140dB at a constant pressure. That's why some people have difficulty with beat-boxing... that and the poss? hanging in the control room. :D

-Jeremy

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Post by chconnor » Tue Oct 16, 2007 8:49 pm

Professor wrote:The low cut is a little different as it's an EQ circuit designed to drop off some of the low frequency.
Right, I forgot the 535 had a flat pad... I was thinking the only pad option was the one that also had the bass roll off... Only ever used the other settings. Thanks for the reminder. :-)
On some Neumann & AKG condenser mics (and others too I'm sure) the -10dB pad switch actually reduces the phantom power voltage ..(snip).. I seem to recall this method makes the capsule a lot less sensitive overall.
Wild. I suppose the logical next question is whether the lower sensitivity (if it's also true for the 535) results in higher tolerance of SPL... if the two main sources of potential damage are the smacking-against-the-capsule-boundaries and more general high-SPL-distorting-the-diaphragm, are these risks lessened (or even enhanced) by such a change...

Thanks!
-c

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FYI

Post by chconnor » Thu Oct 18, 2007 11:57 am

For the record, excerpts from replies from AKG:
My service technician is playing the Cajon as well and it will not create a
SPL that could destroy the mic.
What is the maximum recommend dB SPL for both short-term and sustained use of the 535?

130/144 dB = SPL max for 1% dist. 130 sustained, 144 peak.
Not sure if we communicated perfectly on the attenuation-affecting-SPL-limit issue, but got this response:
As the C 535 has a permanent loaded type of capsule, the voltage
of the phantom power (varied from 9-52V) does not affect the max SPL.
-c

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