Microphone suggestion for speaker testing - Thank You in Advance

Hello fellow DIYers.

I have the electrical set up
- SoundBlaster Extigy (to my laptop)
- good cassete player for a microphone Pre-amp if needed
- Amplifier - My old NAD2050
- Software [http://www.sumuller.de/audiotester/maine.htm] - cheap and highly recommended!

The Anechoic chamber
- O.K., it is an elevated platform on my outside deck


Now, all I need is a microphone that won't set me back an arm and a leg. Would prefer a studio mike with a good 20-20 response, but I would live with just about any good microphone that has a well calibrated response that I can then compensate the speaker response with.

? If my outdoor response is somewhat anechoic, does it matter if the microphone is unidirection or omnidirectional [responses from experience preferred].


Looking forward to your suggestions and thank you in advance.

Alvaius!
 

tomcat

Member
2001-09-30 10:36 pm
Sth. Oz
Try "Old Colony Sound Labs" (or something like that) Mitey Mike...
These are quite cheap and they offer a caliberation service (extra) that comes on a floppy that you can load into your pc. For ultimate accuracy I recomend the caliberation it is well worth it. I use one with my "Imp" audio analyzer and it works a treat...
tomcat
 

CHRIS8

Disabled Account
2001-12-12 8:47 am
VA, USA
Cheapest mic of accuracy is to make your own using a panasonic capsule. You can get capsules with a calibration file, that are rather accurate for $32 + shipping from Kim Giardin. These are the same capsules used in the mitey mike, which in addition is only a tube added to hold the mic capsule. He can be reached at:

[email protected]

If you use a preamp, please insure it has a linear frequency response, or obtain one that does. You can make your own, or partsexpress.com offers an ok priced, accurate mic preamp also. part number: 245-032 or they also have a velleman kit unit, for about $12, you need to add jacks, case and regulated power supply to use it though. Probably $45-$50 plus labor for that unit in the end.

-Chris
 
I am going to get a couple of each of the following:

WM-60AY and WM-61A. The WM-61 is a bit less sensitive but has better signal to noise. If you look above there is a link to some modifications.

If you go to the Panasonic Web-Site and look at the specs, these things are extremely flat (we are talking less that $5 each!).

http://www.panasonic.com/industrial/components/rec_mic.htm

Look at the response curves, they are no more than a few db off from 20-20 and where I am likely to have cross-over frequencies, i.e. 2K, they are very good!

Jack
 
low distortion measuremente mike?

Anybody got any suggestion as to what type of microphone has very low distortion so it could be used to characterize the distortion of a high-quality driver?

The link to Linkwitz labs had a description on how to change the FET in Panasonic electrets from common source to source follower to lower distortion. But I guess one could do better by replacing the FET with an op-amp or maybe by using something other than an electret...

Eric
 
Hi Eric,

Instrumentation mics tend to be high polarisation voltage condenser capsules of relatively small diameter. The best manufacturer of these would be B&K who make stunningly good quality and beautiful kit that is a joy to use, as is all their instrumentation kit, but you pay for it. Unless you are willing to remortgage your house, stick with the modified WM-60AY and WM-61A.
 
Info for Europeans:

I have also been looking for a cheap and decent measurement microphone.
One electronics dealer suggested the Monacor MCE-2000 capsule. It's data sheet is looking suspiciously similar to the Panasonic WM 61 one.
On the following link you find a FR - measurement diagram that was taken form the Elektor magazine and it looks quite interesting:
tkhifi.homepage.dk/simpelspeakermes/speaker-mes-simpel.html

I think within Europe this one might be easier to obtain than the Panasonic one.

Regards

Charles
 
MCE 2000

Charles,

you may be right:

www.reichelt.de has MCE 2000 (2.75€), MCE 2500 (4€) and MCE 201 (2.10€) capsules in the catalog. They say these are Panasonic back electrets but they do not give the Panasonic part number. Wonder who generated these new number.

Back to my disto question:
Would true condenser capsules have lower distortion?
Is there a way to get rid of the FET in a Panasonic capsule?

Eric
 
decent measurement microphone

Though I don`t know what You guys consider to be a "cheap" mic capsule I can recommend a Sennheiser KE 4-211-2 electret mic. capsule. I bought one some years ago from ELV (Germany)for about 30 Euros (now maybe 50) and it came with specified relative (to nominal specification) output sensivity.
It also has an integrated FET-buffer.
This is probably the next best (affordable) thing after big $$$ pro mic. capsules.

The two graphs below are measurements of the KE 4-211-2 (upper graph) and the Monacor MCE-2000 (lower graph) compared to a Brüel & Kjaer 4155 reference capsule. Hence the graphs show the deviations in dB (note y-scaling) over frequency from the B&K.
I took the graphs from the Elektor magazine (2/93).
The Sennheiser frequency response looks pretty damn good (though it does not show that there is some deviatian from linearity below about 40Hz).
Also the phase response (and pulse, for some of You Mangerists around here :D ) of the Sennheiser is supposed to be better than the Monacor due to the flatter response.
If somebody is interested in the Sennheiser data-sheet, feel free to email me for a copy.
 

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FYI - Working with my Panasonic WM-60 and WM-61 and they work fine un-modified. I am not doing distortion test as of yet, but they are working fine for frequency measurements. Just make sure you put them in a long tube, i.e. 12 inches or so, so the reflections from your holder do not interfere with the measurement.
 
I built the microphone like you alvaius . . .

I built a mic from the WM-60AY panasonic capsole, I put it inside a tube or straw and connected it to my sound card. I'm not sure if this is right.

My main problem is finding a program that I can use. Loudspeaker LAB 2 (demo) is a very good and user frieldly progra, but I cannot make measurements under 100 Hz and Speaker Workshop is a very confusing program which I have not been able to even design a box with.

Can some one suggest a good program for frequency measurements? Or how do you use the Speaker Workshop program? I'm usually not bad with computers (I built my own) and computer software, but this program absolutely confuses me, but I here it's good. Why can't it just say "measure frequency response?" I can't even get the theoretic frequency response for an enclosure and driver after I punch in the T/S specs. Last thing did I build the mic right?
 
More suggestions

I'm also on the lookout for a microphone to use with Speaker Workshop. In the US you can get a Behringer ECM8000 measurement microphone for $40, and the response on this looks very good - better than the panasonic capsules. True Audio recommend these for their measurement program. I'm trying to check availability in Australia at the moment.

Another option is the measurement microphone kit from Rod Elliot (ESP), which can use a capsule of your choice, but Rod mentions the Panasonic.

Jimmy, if you are using a capsule at the end of a tube, you will probably need a preamp as well, unless your soundcard is suitable for connection to an electret capsule directly, which is unlikely.
I also find speaker workshop a bit confusing, but I haven't spent enought time to figure it out yet.

Mick
 
I had a microphone like the panasonic capsole, that connected to my computer. I took the plastic outside off (it looks like the panasonic capsole except bigger), then soldered the wires that went to that capsole to my panasonic capsole.

Now I get it the microphone goes at the end of the tube.:xeye: I thought it went inside the tube facing the other way. Now the picture at this link http://www.linkwitzlab.com/sys_test.htm makes sense.

Does anybody know of any programs that measure frequency response? I think I've tried a lot of them, but there might be some out there that I haven't heard of and can figure out how to use.
 
I use AudioAnalyzer for most of my measurements. It is well worth the small registration fee. I tend to use the 2.0 BETA as opposed to the older version. It is easy to use and works.

While it will do impulse based frequency measurements, I prefer slow sweeps to see if any resonances develop, something also highlighted by Floyd Toole a respected expert in the field.

Once you set up SpeakerWorkshop, it is pretty good, but for basic testing, I prefer AudioAnalyzer.

In terms of microphones, some sound cards provide termination and phantom power for electret microphones. I just wire a 2K resistor and 4AA batteries to power mine. Look on the Panasonic web site for information.