Question about Ebay's ELECTRET MIC

[Jam]

I was wondering if anyone has used one of these stereo elctret mics which are on Ebay all the time:

Ebay Link

the specs are as follows:

Response: Stereo, Omni-directional

Connection: 3.5mm Miniature Stereo jack plug

Frequency response: 20Hz to 20kHz

Sensitivity: –60dB ±3dB (0dB = 1V/µbar at 1kHz) Vcc = 4·5V, Rl = 1k Ohms) . . very sensitive!

Impedance: 1k Ohms maximum

S/N ratio: >58dB

Sound pressure level: 120dB maximum

Power supply: 1·5V to 10Vdc

Recommended voltage: 4·5V (optimum performance)

Current drain: 1.0mA

I was wondering how these compare to GreenMachines Mics or those made with his plans (couldn't fins much detailed specs on them)?

cheers

[raintheory]

The main thing with these type of microphones is that they are much more liable to pick up mechanical noise of the MiniDisc unit itself operating (since they sit so close to the unit, if not directly on the unit). One way around this however, is to use a headphone extension cable to hold the mics away from the unit. Though this somewhat defeats the purpose of the design I suppose...

Also you are limited as far as your stereo separation since they are fixed-point.

Edited April 7, 2007 by raintheory

[Jam]

Thanks for the quick and informative reply.

I need a quick fix for some Electroacoustic work I'm doing so I'll probably buy one of these and couple it with the extension cable as you recommend.

I'm also building my own as per GreenMachines instructions but can't see me getting it finished anytime soon so this'll do nicely in the meantime!

Once this arrives I'll post up samples/review.

[Strungup]

With a S/N of 58 db I dont think it will be a quiet mic . when you get a S/N of -70 or better then you have a good quiet mic.

The AT822 is S/N -78 db but you pay for that . one of the things you want to watch for . that Number tells you how far above th NOISE floor that the signal will be . So if you have a mic that is S/N 40 db the signal is onlt 40 db above the noise (Hiss)

when you crank it up to get a loud recording , you will be cranking up the noise along with it .

[A440]

The AT822 is S/N -78 db but you pay for that

Actually, its's -70dB. And you pay $249. It's not really comparable to the mic being considered at one-tenth the price.

http://www.audio-technica.com/cms/resource...822_english.pdf

Many home mic builders use Panasonic WM61a cartridges, which have a S/N ratio of 62 dB. The decibel scale is not linear. 58 decibels is 800 to 1. 62 would be considerably better, as would 70, but assuming you're not recording utra-quiet sounds, you should be OK with those mics.

http://www.micworks.com/freeinfo/decibel.htm

As you understand, you can't plug them directly in to the MD unit or you'll get very high-fidelity motor noise. But they are separated somewhat, so you should get a decent stereo image.

Unless you are completely in love with that design, for cheap mics on Ebay you might also look at micro-sound, which has similar specs.

[Strungup]

Actually, its's -70dB. And you pay $249. It's not really comparable to the mic being considered at one-tenth the price.

http://www.audio-technica.com/cms/resource...822_english.pdf

Many home mic builders use Panasonic WM61a cartridges, which have a S/N ratio of 62 dB. The decibel scale is not linear. 58 decibels is 800 to 1. 62 would be considerably better, as would 70, but assuming you're not recording utra-quiet sounds, you should be OK with those mics.

http://www.micworks.com/freeinfo/decibel.htm

As you understand, you can't plug them directly in to the MD unit or you'll get very high-fidelity motor noise. But they are separated somewhat, so you should get a decent stereo image.

Unless you are completely in love with that design, for cheap mics on Ebay you might also look at micro-sound, which has similar specs.

Interesting , mine quotes 78 , it is an older model that was Japan only marked on the package ,

A good Idea with those Panasonics , is find a Brad point Drill bit , exactly the diameter of the capsules. or Just a hair bigger . and a pretty peice of Hardwood , Rosewood , Purple Heart ,Curly Maple , Sycamore , etc.

Make the Block Long enough , to hold comfortably , with a slightly larger portion at the end. Drill two holes at an angle to each other ;(Like a Y) but just the angle you want it instead of 45 . or 90 degrees. Also with a long narrow bit , drill from end to end a Hole just big enough for the cable . The two hole for the capsule should be drilled so they meet in the middle , and the Wire hole goes right between the two , out the end that you hold. Run the wire and solder evrything , then epoxy the mic capsules into the holes that you drilled for them just pushing them slightly below the edge of the hole ( use very little epoxy you dont want to get it into the mic capsule or on the wires, just the sides of the capsules.) 1/8 of an inch below the edge of the hole will let you glue in a peice of black

acoustic foam . Also If you plan on Laquering the wood or some other finish , do it before you installe the mics, and just do the outside of the wood , dont get finish in the holes , ( the epoxy wont hold if you do)

Tools : A dremel with a bit to shape

: Saw( japanese saw cut smoother , Woodcraft if there is one near you , or Lowes hardware,)

Files If you want to get fancy with the shaping ,

: A drill and the appropriate bit 's

: A vice to hold the wood.

: Sandpaper to smooth it all out and make it look good.

I have done this several times with the capsule from radio shack , But I used two halfs and shaped the inside of the handle with the dremel , so that the Capacitors , and stuff would fit in the handle , then glue the two halves together with everything in place.

An example of my work .

Edited April 9, 2007 by Guitarfxr

[greenmachine]

The relatively high self-noise figure of most small diaphragm mics can be an issue for recording very quiet sounds that require a lot of pre-amplification. In this case you would amplify the self-noise along with the signal. For concert recording or any other higher SPL applications which require little pre-amplification, small diaphragm mics have many advantages over their larger brothers, see here.

In fact, I think the self-noise figure is the only weak point of small diaphragm mics, which is really none for recording in louder regions. They're also most of the time way more affordable than their larger brothers, which are mainly used for recording relatively quiet sounds, where self-noise would be an issue. But they have drawbacks as well, see the above link.

[Jam]

A lot of useful information there thanks!

I took a look at the microsound microphones as suggested and foudn this one MicroSound T-Mic

It would cost ~£20 and here are the specs given on the description (waiting for an answer on the exact capsules used):

frequency response 20 to 20,000 Hz

-44 dB +/- 5 dB sensitivity

sound to noise ratio > 58 dB

Is this worth the extra £4 over the 1st one posted?

I'm looking at these T designs as I only need a single point stereo source really as i will be using the mic with my Sharp MT-190 to close-mic sounds (such as house-hold items) which I will then use to make sound FX for games and also as sound material for ElectroAcoustic compositions.

At the moment I'm using a Yoga Em-278:

Frequency Response: 100Hz~16KHz

Sensitivity: -68 dB 3 dB at 1KHz (0dB=1V/£gbar)

So as long as I can notice a performance increase over this then I'll be happy until I can find time to build my own!

thanks

[A440]

Just remember you won't be able to plug the T-mic in without an extension cord either. My guess is that it's the same capsules, so choose based on the design.