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Old 26th February 2007, 05:16 PM   #1
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Default Inexpensive mike?

I have an RTA program called SpectraPlus on my laptop. I did some messing around, using a Radio Shack digital SPL meter and a Stereophile test CD. Now I'd like to get a better pickup.

What inexpensive microphone (under $40.00?) could I buy that would plug directly into the laptop's internal sound card (mini-jack), and does not require calibration for reasonable results? I'll also need some good test tones. I did a search but I didn't find exactly what I want. Thanks.
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Old 26th February 2007, 05:36 PM   #2
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You have a few options here.

If you want something fairly cheap then a Behringer ECM8000 is a good choice - a friend used to use one for room corrections to good effect. You can pick one up for under £40, here's a link to the Behringer website:
Behringer - ECM8000

Unfortunately you'll need phantom power and a preamp to use this with your laptop/PC.

I've just bought some Panasonic electret capsule inserts that I hope to make a measurement mic. from and if you're technically minded I suggest you invest some time and (not much) money and do the same. If you do a google search for "Panasonic wm-61a" you'll get plenty of info on the capsule, how to modify it to get lower distortion (conversion from common source to source follower) and circuit diagrams for an amplifier.

I'm no expert on microphones, however I think the only type that you can plug directly into you laptop/PC are dynamic types that don't require power - I think these typically have much poorer frequency response than electret.

I hope this helps!?


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Old 26th February 2007, 05:36 PM   #3
Svein_B is offline Svein_B  Norway
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The virtually no cost microphone solution is a Panasonic WM-61A electret capsule at $2 a piece. The mic needs a battery and a couple of resistors for power feeding, as described here: Powering Microphones

The Behringer ECM-8000 is an equivalent performance ready-made mic at around $40-50. Itis normally used with a pre-amp with 48V phantom power. I do not know if a simple passive power feed of this one is possible.

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Old 26th February 2007, 05:37 PM   #4
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I'd listen to this guy - he clearly knows what he's talking about
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Old 26th February 2007, 05:41 PM   #5
qwad is offline qwad  Australia
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regretably you will not get far without a caliberated mike, it is a must if you want accurate results, as for cheap try the mitey mike... which is a panasonic mike capsule.... cheapn cheerfull cheers and good luck T.J.
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Old 26th February 2007, 06:23 PM   #6
Svein_B is offline Svein_B  Norway
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If you want to make precise measurements you obviously need a calibrated mic, preferably a B&K $$$.

For DIY purpose you can probably get close enough without calibration. Both the Panasonic and the Behringer usually have a small hump of a couple of dB above 10KHz. Below 10K the errors in amplitude seem to be negligible. Generic calibration files can be found which may compensate [most of] the small errors.

The mounting of the mike i a narrow neck is important to maintain its frequency response.

The picture below shows a canibalized 3$ mike which has been rebuilt with a VM-61A capsule and battery power.
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Old 27th February 2007, 06:38 AM   #7
akunec is offline akunec  Canada
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I highly recommend getting a Panasonic capsule thats been calibrated. I got it done for about $35. You can build a preamp for it for another $30. With this setup you can get very accurate response curve down to ~300hz in an average room.
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Old 27th February 2007, 07:07 AM   #8
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Quote:
What inexpensive microphone (under $40.00?) could I buy that would plug directly into the laptop's internal sound card (mini-jack), and does not require calibration for reasonable results? I'll also need some good test tones. I did a search but I didn't find exactly what I want.
laptop soundcards usually need calibration themselves. They have poor low and high frequency properties at their mic input.
I once build a microphone after a Klang+Ton article. It uses a relatively cheap capsule with good linearity.
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Old 27th February 2007, 07:22 AM   #9
Svein_B is offline Svein_B  Norway
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Quote:
Originally posted by juergenk
laptop soundcards usually need calibration themselves. They have poor low and high frequency properties at their mic input.
Agreed, but if it is not to bad, it is easily done.
Connect a minijack-to-minijack cable from PC output to mic input, and set low volume and low mic gain.
Run an FR curve, and prepare the necessary calibration file to make it flat from 20-20K.
You probably only need to do this to the nearest dB for indicative measurements, and ignore phase correction.

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Old 27th February 2007, 07:35 AM   #10
fotios is offline fotios  Greece
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Default Re: Inexpensive mike?

Quote:
Originally posted by audiobomber
I have an RTA program called SpectraPlus on my laptop. I did some messing around, using a Radio Shack digital SPL meter and a Stereophile test CD. Now I'd like to get a better pickup.

What inexpensive microphone (under $40.00?) could I buy that would plug directly into the laptop's internal sound card (mini-jack), and does not require calibration for reasonable results? I'll also need some good test tones. I did a search but I didn't find exactly what I want. Thanks.
Suitable microphones for measurements are only those of electret condenser type due to flat response that they have in all audio spectrum compared with dynamic microphones. Laptops they offer only one input that it is permanently under a supply voltage of 2,5 to 3 Volts and marked as mic. Thus she is not suitable for connection of a device with line level output. The microphone of Panasonic that proposed to you is the more suitable that it exists. If you throw a glance in the site www.Audua.com you will find a compensation file for this microphone as for Behringer ECM8000. I suppose that this file will work only with the application Speaker Workshop which is offered free to download in this site and this is also a P.C. based RTA. Because i began precisely as you before one year (with other RTA), finally i led to the Speaker Workshop due to this compensation file who gives reliable results in measurements. At this time of course, i use the Behringer that is better than Panasonic with small difference in cost. From then you pass in necessity in other add-ons, as a preamplifier for the Behringer with Phantom Power and a USB external sound card. Do not deal with the microphone of B&K, that proposes to you somebody here (be serious please!), because his cost is disproportionate concerning the equipment that you have.What to you i propose, based on my knowledge, spend some money (if you cannot make now left it for some moment in the future) to get additional equipment so that you make reliable measurements. These all with Laptop sound cards and cheap microphones are only to make training on how to use the RTA that you have this moment. In such level do not spend aimlessly your money. If now you decide to be equipped better, the cost is:
1) One external USB sound card with separate line input (not with only one input shared between mic and line). There are two inexpensive of Creative. One is the “Sound Blaster Live! 24bit” about 50$ and the other (recommended from me) is the new “Sound Blaster Connect” about 57€. Avoid PCMCIA cards because they have same inputs as your Laptop and are expensive.
2) One Behringer ECM8000 electret condenser mic about 55€.
3) One inexpensive mic preamplifier with a supply at least of 15Volts for this microphone about 60€. Or a DIY single channel microphone preamplifier such that i have made from my own (i enclose one photo of this, but take a look and in the thread “Speaker Workshop?” in this forum where you will find one relative reply from me) cost of 50€ but with unsurpassed sound quality from every inexpensive mixer on the market.
The sum is about 160 - 170€ for all these above, and it should spend him if you really want your measurements to be compared with those that give luxury instruments on the market. The cheapest such that i could find was a USB data acquisition 12bit device of National Instruments about 600€.
Regards
Fotios Anagnostou
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