Topic: Beyer CK930's with 15dB attenuator - what is the dBu output level??

[yates7592]

I am taking delivery of a pair of Beyerdynamic CK930's with a rated sensitivity of about 30mV/PA (max SPL 125dB) and will be using the -15dB switch on the mic as a matter of course.

If I use Table 1 on this great reference:

http://www.rane.com/note148.html

Does the mic -15dB switch alter the 'sensitivity' (so moves upwards in the table from 30mV/PA (-28dBu) to about 6mV/PA (-43dBu), or the sensitivity stays the same and the -15dB switch just increases the max SPL from 125dB to 140dB ?

I am inclined to think it is the latter, so that with the 15dB switch engaged and for example taping really loud stuff (at say 140dB) the mic output to the preamp will be a whopping +18dBu. Is this correct?

If so, and my recorder nominal input level was say +4dBu, I would need a further attenuator between the CV900 power unit and the recorder XLR inputs? Is this possible (something like the niant) ??

Very grateful for any help or advice.

[aaronji]

As I understand it, the pad on the microphone reduces the voltage between the capsule and the FET.  Functionally, it will reduce the sensitivity as you mentioned.  As for max SPL, I think you will get an increase, at least up until the point where the capsule itself is clipping. 

[yates7592]

Thanks.

So are you are saying is that in Table 1 BOTH the sensitivty and the max SPL change (to 6mV/Pa and 140dB respectively), so that my output level would in fact be closer to +4dBu for 140dB, in which case I probably wouldn't need another attenuator?

[page]

Does the mic -15dB switch alter the 'sensitivity' (so moves upwards in the table from 30mV/PA (-28dBu) to about 6mV/PA (-43dBu), or the sensitivity stays the same and the -15dB switch just increases the max SPL from 125dB to 140dB ?

I am inclined to think it is the latter, so that with the 15dB switch engaged and for example taping really loud stuff (at say 140dB) the mic output to the preamp will be a whopping +18dBu. Is this correct?

See the bolded for the correct answer. as aaronji notes, it tinkers with the sensitivity which gives you more headroom.

For what it's worth, I almost never ran the pads when I had the 930s; stage lip or onstage was the exception where I've found stuff to creep into the 130spl range. For normal room taping though, I never hit 125spl (came close a couple times, but didn't hit it) and I saw some small club rock/metal-ish acts with them. As long as you have a recorder which can accept above a +4dbu signal then you're good to go. Throwing a preamp in front of it though can be troublesome if you have one that has a minimum or fixed gain.

[yates7592]

Thanks for the advice guys. My recorder has nominal input level of +4dBu at half way (max +24dBu) so I will just back the level off a bit and I should be fine.

[DSatz]

Just curious: What kind of recording are you doing where the SPLs reach 140 dB? And how do you protect yourself from those levels?

--best regards

[yates7592]

Just curious: What kind of recording are you doing where the SPLs reach 140 dB? And how do you protect yourself from those levels?

--best regards

Yeah i know, not likely to happen, just working on a worst case scenario as it's the mics max SPL.

[page]

Just curious: What kind of recording are you doing where the SPLs reach 140 dB? And how do you protect yourself from those levels?

--best regards

Yeah i kniw, not likely to happen, just working on a worst case scenario as it's the mics max SPL.

I wouldn't worry about it. Unless you're spot micing or recording on stage, you won't encounter anything that loud. If your recorder will accept up to +24dbu before clipping, then the only remaining question (as the mics will max out at +4dbu) is does your preamp/powering module have a minimum gain on it? If not, then you're safe to run upwards of 18db of gain on it easily, otherwise figure out the minimum gain on the preamp and go from there.

The only reason to use the pad on the mics to get the increased headroom for room taping is if you're recorder won't tolerate a signal around +4dbu. It's specific recorders with these mics, the most everything else (the m10, d50, any of the SD 7 series, etc) will easily handle that.

[DSatz]

Actually, I'd say that the only good reason to use a pad switch on a microphone is if the sound pressure levels are so high that they overload (or threaten to overload) the microphone itself. If the microphone is operating in its "comfort zone" but the signals it's putting out are so strong that they threaten to cause distortion at the input of the recorder, then a resistive pad should be used at the input of the recorder.

The basis for this distinction is the inherent noise of the microphone's circuitry, which (on a voltage basis) remains essentially the same whether you use the pad switch or not. So if you use the pad switch unnecessarily, when the microphone could very well handle the sound levels without the pad, you're reducing the useful signal by 15 dB relative to the noise level. That's a considerable loss of signal-to-noise performance.

If on the other hand you use a resistive pad at the input to the recorder, the useful signal and the noise are both reduced by the same amount at the same time, so there's no decrease in your signal-to-noise ratio. You also get the advantage of a stronger signal in the cables, which is that much less vulnerable to interference.

In other words, pad switches aren't for matching a microphone to a recorder; they're for matching a microphone to the sound levels that it's picking up.

--best regards

[yates7592]

Actually, I'd say that the only good reason to use a pad switch on a microphone is if the sound pressure levels are so high that they overload (or threaten to overload) the microphone itself. If the microphone is operating in its "comfort zone" but the signals it's putting out are so strong that they threaten to cause distortion at the input of the recorder, then a resistive pad should be used at the input of the recorder.

The basis for this distinction is the inherent noise of the microphone's circuitry, which (on a voltage basis) remains essentially the same whether you use the pad switch or not. So if you use the pad switch unnecessarily, when the microphone could very well handle the sound levels without the pad, you're reducing the useful signal by 15 dB relative to the noise level. That's a considerable loss of signal-to-noise performance.

If on the other hand you use a resistive pad at the input to the recorder, the useful signal and the noise are both reduced by the same amount at the same time, so there's no decrease in your signal-to-noise ratio. You also get the advantage of a stronger signal in the cables, which is that much less vulnerable to interference.

In other words, pad switches aren't for matching a microphone to a recorder; they're for matching a microphone to the sound levels that it's picking up.

--best regards

Yes, I see a lot of good sense in what you have said. I will try it without the switch the first time and see how it goes, but I'm a 'set and forget' kind of guy, so the less to worry about the better for me.

[yates7592]

Well, I finally tried them first time last week with the -15dB switch ON - yeah I know I bottled out and took the easy route, but I needed to be safe rather than sorry, and it worked (I love these mics), but not in the way I was expecting.

Taping at front stage, fairly loud amplified post-punk band (drums, bass, guitar, pretty standard), but PA stacks were hanging above and behind me, so I was not getting much of that. Recorded on R-26, P48 XLR's in, lowest sensitivity setting (+4dBu), levels set at 50 which is half way. Very much ste@lth situation, couldn't check my levels even once, and no support band, so I just set the recorder rolling, put it away, and hoped for the best, hence the -15dB pad ON.

Result? Peak levels of -28dB!!!  I was amazed it was so low as I had previously taped half a dozen shows from stage front with Nevaton MCE400's with the same recorder sensitivity and level settings and always peaked at about -10dB. I was also taping with a pair of B3's and got exactly the same result I had expected for them (peak at -9dB), so it wasn't a quiet show by any means.

MCE400 sensitivity is about 10mV/PA, so the 15dB switch must change the CK930 rated 32mV/PA to something less than 5mV/PA??

So, Page and DSatz were both right (of course....), I didn't need to use the -15dB switch.  Luckily I was taping in 24 bit, and it was a fairly noisy show, so upping the levels and then slapping a limiter on at the end did not appear to induce any noise, not that I noticed anyway. So worked out well considering first attempt, better that than bricking IMO. No doubt I would have got a better pull (in this show at least) with that switch OFF.

But, next time, what do I do?? (bearing in mind next show I might well be catching the PA stacks as well as the stage):
(1) Turn the -15dB switch OFF;
(2) As (1), and lower levels on R-26 to 30 or 40 (5 to 10dB level drop)
(2) Leave it ON, but increase the sensitivity on the R-26 by 12dBu (or 18dBu?, or more?)
(3) Keep all the settings the same and up the levels on the R-26 - up to 70 would add about 10dB gain. Don't know how high is safe.

My inclination is to knock the -15dB to OFF, but just worried about hitting a loud PA-driven situation.

Any more advice will be gratefully received.

[Fatah Ruark (aka MIKE B)]

I have NEVER even come close to having to put the 15db pad on. Either with the Tinybox or my DR-680.

[yates7592]

Thanks. What kind of music are you taping? I ask because there are several users on the Beyer Team Thread that say they always use the 15db pad. The discrepancy might be down to the recorder differences rather than the mics?

[page]

Yeah, if your taping a PA, its a recorder issue, not a mic overload issue. The pmd 661 is one example cause the mic in is just too low ofa ceiling.

[ninjadave]

not to bring up an old subject, but i have a related question and since i've owned the Beyers CK930 at one point, i think its relevant.

background....
when i ran the CK930s into the PMD661 (no pre), i used the -15db pad and i had the 661 MODDED that the -18db setting was actually -30db (oade CM mode with the -30db mod on top). at those settings, at pretty loud rock shows (heart, yes, RUSH, Def leppard), i was able to set recorder at just OVER 5 on the 661. not running with the -15db pad and the recorder mod, i would think for sure, i'd have to run the recorder well under 4 which means clipping...is this an issue with the recorder then? my peaks where around -12db to -9db.

i'm currently running my milab vm-44 links with NO pad on the mic and at the -30db setting, and i can run the 661 at over 6 mic in and no issues of clipping with db peaks sometimes in the -6db range (like say at Black Sabbath i recently taped). however i did notice my wav forms are REALLY fat, very few peaks of the fat form, and most of the fat is about -12db....with few peaks into -6db. the sound seems compressed, its not very open air, etc. doesnt' sound right for these mics....could be my mounts. i don't have much air around the mics, very close to side of hat.....etc. so this could be issues with mic position, stealth in kangol and angled IN almost as i'm having issues with my hat mount...

does the wave seem right? i really need advise on stealth mounting my mics but another subject (pm please if any advise is to be had). but my question is, are these settings screwing up my sound.....?

the sabbath show i was back and little off center but 2/3 back in venue. sounded great and loud......

i've listened to other milab recordings and i know something is off.....i was told the -30db is no issue, can just increase the level on teh 661 to compensate, no loss of signal db, etc. is that right? I THINK SO based upon the commments in this thread about reducing signal at recorder vs mic.........thanks for any help. i wish i knew more about recording and setup....i know i've missed out on some good pulls.....