Mic/preamp for test measurement system

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Silent Mike

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HI Everyone, I am newbie from a group with a peripheral interest -- Silent Computing. I run the website www.silentpcreview.com.

What I am looking for is info & advice on mics & mic preamps, not exaclty for home recording, but more for measurement.

I have a Terratec DMX6fire 24/96 that I wish to run with this software: RAL / Realtime Analyzer Light http://www.freewareseek.com/audio/1535/ (or similar) and combine it with a high quality mic & preamp (which seems necessary) to use as a SLM/sound analysis system for PC and PC component noise. When you get quiet stuff, you're often looking at sub-25 dBA/1m, so high sensitivity, low noise and linearity at low volume are very important. (My several systems all run under 20 dBA, and one is at 15 dBA/1m.)

A secondary use is to actually record the noises and convert them into high quality MP3s for download on my website. All recordings would be at the same level & conditions, with a reference key provided so people could actually get a sense of relative levels and the quality of noise just listening to these through their PC systems.

This was done in one article with a couple of fans -- look for the files in the table entitled "Recordings of PC Noise (MP3)" towards the bottom of this page: http://www.silentpcreview.com/goto.php?t=s&id=71&a=3

Anyway, I have reduced my choices for mic preamps to 2:
1. Behringer MIC2200 Ultragain Pro ~$99
2. MAudio DMP3 ~$199

Anyone have knowledge about these 2 or can you point me to a good review site for this? Other choices I should consider? ($200 is around the top of my budget BTW). Naturally, it is not features I seek but the lowest noise and best linearity (transparency?).

For a mic, I saw a few on sale for under $100 (again my budget) --
1. Marshall Electronics V57M Studio Condenser Microphone $60 http://www.zzounds.com/a--2676837/item--MSEV57M
2. Behringer ECM8000 Measurement Microphone - $39 - http://www.zzounds.com/a--2676837/item--BEHECM8000
3. Nady SCM900 Studio Condenser Mic - $59
http://www.zzounds.com/a--2676837/item--NDYSCM900

But the choices seem endless, and my experience is limited, so any suggestions & comments are welcome. My key criteria in all of this is #1 - accuracy (especially midband & lows) & low noise. I see many have a noise spec of "equivalent of 20 dBA" or similar. 20 seems too high to me if I am trying to pick up on stuff that's like 14 dBA. Close miking is an option but not ideal because of the proximity boost effect on bass; maybe 1ft is the min distance i can use -- probably more like 1/2 meter -- which brings the quiestest stuff up to around 16 dBA...

Oh, and do you think the Terratec is good enough for my application?

Part of me wonders if I am already aiming too high with the mic/preamp... maybe I should just use the built-in mic input on the Terratec and a mic that doen't need phantom voltage? Please educate me!

Thanks for reading through the long post. I look forward to your suggestions.

Mike Chin
Editor / Publisher
www.silentpcreview.com

PS -- If you have never checked out my site, it's probably worth a look for anyone who is doing computer recording. SPCR is the #1 silent computing hardware site around. There really isn't any other site like it. A low noise or silent PC is almost mandatory, isn't it? Save on enclosing a noisy one (with all the attendent drawbacks of that method). Many regular visitors are hifi/music/recording/htpc enthusiasts...
 
Of the three mics you suggested, get the ECM8000. The Behringer is known for a very transparent, clean sound.

That being said, try before testing or buy from a place with a good return policy. The mics vary in self-noise, so maybe even buy a couple, do some diagnostics at home, return the loud ones and keep the quietest one.

As for preamps: I'm guessing that the DMP3 is much superior to the Behringer in terms of self-noise. The DMP3 is regarded much more highly on this board.
 
There are a number of microphones and preamps made for the express purpose of testing & recording environmental and industrial sound and noise. None of the products you mention are among them, and I doubt if they would be up to the task. Earthworks and DPA are 2 of the better known makers of measurement mics and preamps. They cost a lot more than the pieces you are considering - primarily because they are much more linear, cleaner, and have faster impulse response.

Scott
 
DigitMus said:
There are a number of microphones and preamps made for the express purpose of testing & recording environmental and industrial sound and noise. None of the products you mention are among them, and I doubt if they would be up to the task. Earthworks and DPA are 2 of the better known makers of measurement mics and preamps. They cost a lot more than the pieces you are considering - primarily because they are much more linear, cleaner, and have faster impulse response.

Scott
Click to expand...
Yes, they certainly do cost more!

While I don't doubt the products you mention are indeed better, their pricing makes them completely out of reach. This is why I specified my budget -- the best I can do with the resources available. From an engineering PoV, this is far more challenging than having an unlimited budget. So you don't think they would be "up to the task..." Which aspect of the task -- the low noise & high sensitivity? Dynamic linearity and low levels? Anything cheaper that you would consider more suitable?
 
I think the ECM8000 is the best you can do in your budget (i.e. really cheap)...but I don't know how valuable your test results are going to be.
 
It seems to me that as you said, a low noise, high sensitivity mic would be the primary consideration. At the lower price end, you might want to put the compromise on the other quality issues of frequency and transient response.
As a generality, the small diaphragm condensers mentioned can be flat and fast but will have higher noise. (Compare the similar Earthworks tc-30 to the qtc-1, and the mics in the DPA line.)
There are some very low noise high output large or medium diaphragm mics for just a few hundred $ from AT and Rode for example. Frequency response is largely relative as long as you use the same mic/setup, and a higher output mic might make it easier to find a low cost pre that cuts it too.
Just food for thought.:)
Wayne

edit:rolleyes:
Hmm. Maybe it's not AT. Who else makes those -7dba LD's?
 
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mixsit --

Thanks for your thoughts. :)

I did some hunting and found a Rode NT1-A which has the incredible "self noise" spec of 5 dBA. http://www.rodemic.com/specsnt1a/index.html The price of ~$200 is higher than what I budgeted, but perhaps it is worth the investment. There's a bit of a question about what this self-noise spec means -- I've seen references on some sites that state (for this mic): "Equivalent Noise: <13 dB SPL (A-weighted per IEC268-15)"

There are a number of *much* cheaper mics from CAD that have similar Equivalent Noise specs. The GXL1200, for example, for $60: "Equivalent Noise Level: +14dB (A-weighted)" -- http://www.zzounds.com/a--2676837/item--GLOGXL1200

The CAD M177, which I found for as little as $129, is said to have a "10 dB Equivalent SPL, A weighted" http://www.cadmics.com/m177.htm

As is so often the case, tech specs appear to be obsfucating rather than illuminating; I expect many of the members here will be able to plough through the mess & make sense of it all...

Any thoughts on the items above?

And suggestions about best places to buy?

What of the MAudio DMP3 mic preamp? Will it be good enough for the mics above?
 
It's not just about self-noise. It's also about as flat a response as you can get across the spectrum of the mic. And the preamp. The kind of testing you're describing isn't done on the cheap.

Plus, you're really gonna need something approaching an anechoic chamber to really do definitive testing in. Maybe a small one big enough for the computers/appliances you're testing. But a soundproof space with measureable, repeatable, plottable characteristics.
 
c7sus said:
It's not just about self-noise. It's also about as flat a response as you can get across the spectrum of the mic. And the preamp. The kind of testing you're describing isn't done on the cheap.

Plus, you're really gonna need something approaching an anechoic chamber to really do definitive testing in. Maybe a small one big enough for the computers/appliances you're testing. But a soundproof space with measureable, repeatable, plottable characteristics.
Click to expand...

All good points except I don't now if transient response or a few db +/- in a noise spectrum in a relative way might mater. But again, once you get into the better mics, you'd get both anyway.
 
The GXL 1200 MIGHT do the job. It's a pretty good mic, and CAD does offer stereo matching of mics for 20% charge. I use a stereo pair myself. If you want to record the same source from disparate positions, properly matched mics are a must.

If you just want to use a single mic and record in multiple positions, nothing wrong with an ECM8000. (Thouh personally I did return an ECM8000 recently for bad buzzing...)

A DMP3 would probably do a decent job as well...

So what are you planning on doing? Recording computer cases? Fan configurations? Heatsinks?

The NT1-A is a nice mic and it was quiet, but it didn't seem to be that much more quiet than my CAD M179...
 
On second thought, c7sus might indeed be on the better track. One thing I had completely forgot about for one thing was proximity effect in the LD condensors we were looking at. With cardoid, any notion of 'flat' goes right out the window at close ranges. You might be forced right back to the likes of the DPA omni's and such.
And the test box might also have it's own resonances that come in to play.
This happens when we throw around gereralities without thinking through all the details. Oops. My bad.:)
Just curious Mike, are you going for 'absolute' numbers, or just more general comparisons?
 
Hey thanks for the feedback everyone!

Sklathill -- so you feel I am ok with the DMP3? Well that's good to know. It seemed OK judging from reviews & sepcs. If others are in agreement with you that the GXL 1200 could do the job, well, that price is tough to ignore. Could get 3 of those for the price of one NT1-A.

Chances are I only need one mic, but 2 might be convenient. Never knwo -- maybe I'll get back into music again (used to be a total audio/music fanatic for decades...)

I will mostly be measuring/recording from 1m or closer distance from the source in a room ~15 X 12 x 8', fairly well damped for reflections, and ~14 dBA during test time (after midnight). My plan is to keep the sound source in the middle of the room away from room boundaries, and to prop up some sound absobtion/diffusion panels as seems necessary during testing. I occasionally have access to an anechoic chamber. (At the Univ of BC in Vancouver)

I AM looking for absolute numbers. I currently use a 30 yr old B&K SLM that is still very accurate and can measure down to 0 dBA. Of course my ambient is too high for that but... Here's a description of the beast:
http://www.silentpcreview.com/modul...ns&file=index&req=viewarticle&artid=97&page=3 (bottom of page)

I am fairly sure the software I mentioned in the first post will actually allow me to calbrate absolute SPL levels with a good mic, and this will give me not just a SLM, but a full spectrum analyzer, etc. Plus I mentioned already, I want to record the sounds and post them as MP3s for people to make their own assessments about the noise. This is only doable if all the recordings are done under identical controlled conditions -- levels being one of the absolute keys.

The noise sources are fans, hard drives, and aggregrate noises from a PC. As I've mentioned, mine are sub-20 dBA/1m. One of them is ~14 dBA / 1 meter. 99% of people can't tell it's until until they get on their hands and knees on the floor with their ear a foot away. And then the look on their faces -- I should take pics next time. :)

So is the DMX6fire 24/96 sound card I plan to use good enough for this? Well, it's what I have... will use it for now anyway.

Right now, the short list seems to me:

1. CAD GXL1200 mic
2. MAudio DMP3 mic preamp

Pricewise, it's great, actually UNDER my budget, which is always amazing. Any further comments on this?
 
Silent Mike,

If you need a measurement mic, the only choice here is the ECM8000 for one simple reason--it is an omni. I just looked at the 'real' measured curve of the mic, and it looks pretty linear. I will try to attach the curve. The reason for omni--since it is a pressure type of the mic, it does not have a 'proximity effect'. Also, due to simplicity of the capsule construction, usually omnis exhibit flatter response. With any pressure-gradient type ones (which CAD is), you will get a bass boost at close distances.
 

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Oh yeah, and smaller diameter of the capsule suggests flatter response on the top of the range, but it seems that you don't need it. If ECM8000 is too noisy for you, I would suggest also looking at Oktava MK012, Behringer B5, Rode NT5, Studio Projects C4, but with omni capsules. Watch for true omnies (i.e, not dual diaphragm, with variable patterns).
 
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Marik, thanks for the info. :)

So how close before the proximity bass boost begins? any idea?

This Audix is probably a better mic? http://www.zzounds.com/a--2676837/item--AUDTR40 (3x the $ so...) rated for 17 dBA self noise.

The Behringer ECM8000 cites no noise figures -- not reassuring... Their B5 model looks like it's just $80 with both omni & cardoid elements!? Seems too cheap to be true! NOt sure what the noise apec is -- if equiv SPL is it, seems to be 18 dBA for the omni capsule. A bit high maybe.

None of the Rodes seem to be available with omni capsules, and the Studio Projects C4, tho nice, is at $370/pr, beyond my budget. Also seems the omni version is hard to find. I guess if I could buy just one, this would be close to ideal...

But the most interesting one from a noise PoV is the CAD M179, which seems to be the 177 with cardoid/omni built-in for ~$200: Its noise is rated at 11 dba (if this is to be believed...) Only downside seems to be a bit of peakiness beyond 10kHz, which I can probably equalize with software.

What do you think Marik (and anyone else)?
 
Yeah, thats the tough one.

<So how close before the proximity bass boost begins? any idea?>

At 98" the boost starts at 100Hz with +3db at 20Hz. At 19" the boost starts at 500Hz with 14db at 20Hz, and at 3" the boost startsat 2KHz with 28(!)db at 20Hz. Not much fun.

The CAD 179 is a pressure-gradient type, which I was already talking about.

<Their B5 model looks like it's just $80 with both omni & cardoid elements!? Seems too cheap to be true!>

I wouldn't dismiss it for that very reason. After all, ECM8000 is also cheap. Don't forget, all of them are made in China, so it comes to the labor cost. All you need is a linear and low noise mic. The linearity determined mostly by the capsule, if electonics are not completely screwed up. I would not be surprised that all the capsules (except of Oktava) for the mics I was talking above, came from the same batch from China.
 
Marik said:
At 98" the boost starts at 100Hz with +3db at 20Hz. At 19" the boost starts at 500Hz with 14db at 20Hz, and at 3" the boost startsat 2KHz with 28(!)db at 20Hz. Not much fun.

The CAD 179 is a pressure-gradient type, which I was already talking about.

<Their B5 model looks like it's just $80 with both omni & cardoid elements!? Seems too cheap to be true!>

I wouldn't dismiss it for that very reason. After all, ECM8000 is also cheap. Don't forget, all of them are made in China, so it comes to the labor cost. All you need is a linear and low noise mic. The linearity determined mostly by the capsule, if electonics are not completely screwed up. I would not be surprised that all the capsules (except of Oktava) for the mics I was talking above, came from the same batch from China.
Click to expand...
OK, so all I am lloking for is a "linear and low noise mic". That I understand.

I still don't understand this:

What's the difference between an omni and a mic that is switchable from omni to cardoid?

The CAD179 is exactly that -- switchable. You warned about this type but I don't understand why. If it is switched into omni mode, does it not then exihibit all the charateristics of any omni -- like no close proximity effect?
 
<OK, so all I am lloking for is a "linear and low noise mic". That I understand.

I still don't understand this:

What's the difference between an omni and a mic that is switchable from omni to cardoid?

The CAD179 is exactly that -- switchable. You warned about this type but I don't understand why. If it is switched into omni mode, does it not then exihibit all the charateristics of any omni -- like no close proximity effect?>

Yes and no. It is a very broad topic, but I will try to explain it in short. The construction of the mic is full of trade offs and compromises. The small diaphragm mics (SD) are usually much more accurate than large diaphragm (LD) ones, but have lower output. So for your purposes you might need a SD one, but here you lose noise performance. All directional mics have proximity effect. Because of wave cancelation, the "dual switchable" capsules help to eliminate it, but because of parts tolerances, such as diaphragm tension, spacing between plates and diaphragms, in reality it never works presisely.
Once again, because of capsules' construction, this phenomen
does not exist in 'true omni' ones. So you need to fugure out a compromise between price, accuracy and noise performance.

I would try to contact Behringer first, and ask them exact noise figure in ECM8000, and of course, let us know.
 
<I would try to contact Behringer first, and ask them exact noise figure in ECM8000, and of course, let us know>

If you do, please also ask if it has a BACK electret capsule.
 
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