spectrum analyzers

[Dave Jones]

Okay, this is not about loudspeakers per se, but I'll bet you guys know all about this stuff.

I've read ads for software that can be used to analyze loudspeaker frequency response, using a sound card. Those ads say you will need a "calibrated microphone." I wrote to one such software company asking where I could get such a thing, but no one returned my email. (If they had any business sense, they would be _selling_ the required microphones, and not letting emails from prospective customers go unanswered.)

So, what's the deal with "calibrated" microphones?

Is a calibrated microphone an ordinary microphone that's been calibrated somehow? And if so, how? Does one adjust the microphone itself... or what?

There are always ads on ebay for spectrum analyzers like this one: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3042678525. Notice that the ad says there is a microphone input, but says nothing about a mike. So, what kind of mike would it take?

Are those spectrum analyzers any good?

 

[leadbelly]

http://www.speakerbuilder.net/web_files/Articles/diymic/diymicmain.htm

 

[Dave Jones]

http://www.speakerbuilder.net/web_files/Articles/diymic/diymicmain.htm

Are you sure of that link? I get "430 Not found
Unable to resolve name: www.speakerbuilder.net"

 

[Ken L]

Are you sure of that link?

Try it again


It worked for me

regards

Ken L

 

[r0cket-]

Are you sure of that link? I get "430 Not found
Unable to resolve name: www.speakerbuilder.net"

For whatever reason, that domain seems to have pretty frequent problems. Try it again later and see if it resolves. I've had a lot of problems with it myself, but the information there is worth the effort.

 

[Dave Jones]

The software I was looking at is from "True Audio". In their FAQ, it says you need both a calibrated mike and a mike preamp. Yes?

It also gives an address for a fellow who can calibrate a microphone. I'm still wondering what that entails. If you send a microphone off to be calibrated, do you get back a microphone that's been modified somehow? Or do you get back a datasheet that has to be fed to the software by some means? What if you are using it with a garden variety "EQ/Spectrum analyzer"?

Here's the link: http://www.trueaudio.com/rta_faq1.htm

 

[jleaman]

i wish i could find a audio control one. i miss those. it was a "eq" and a spectrum analyzer in one. you could use a mic too. i've looked on Ebay a lot but still yet to find one. DAM..

ever seen the movie ferris Bulers day off. he had one on top of his carver amp OHHH i so want one now.

 

[kelticwizard]

Damn, Dave, whenever I read your posts, your computer can't get to a URL or download a program. Maybe you should switch back to Win 98SE, LOL.

Anyway, try this for that link.
http://www.speakerbuilder.net/web_files/Articles/diymic/diymicmain.htm

 

[jleaman]

Like this..

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3042604004&category=3271


does any one know where to either buy a kit or a schematic to build such a display.. i like all the lights and stuff. Ive looked and looked every where but cant see a schematic for one i don't want the eq par just the graphical display.

 

[kelticwizard]

Dave:

For testing speakers, there is always the freeware Speaker Workshop. Apparently takes some time to set up, but the people who do it are well satisfied.
http://www.speakerworkshop.com/


A "calibrated microphone", to my understanding, is merely a mic with flat response. This is as opposed to many microphones which have up-and-down response.

The WM 60AY available at Digi-Key is cheap, ($2.20) and Siegfried Linkwitz recommends them. I am sending away for mine this week. Even without the mod, they give flat response.
http://www.linkwitzlab.com/sys_test.htm#Mic

 

[cocolino]

So, what's the deal with "calibrated" microphones?

Is a calibrated microphone an ordinary microphone that's been calibrated somehow? And if so, how? Does one adjust the microphone itself... or what?

Hi Dave,

"Calibrated microphone" usually means that it`s sensivity versus frequency is measured against a known reference microphone (hence no, the mic itself is not adjusted).

Sometimes, in case of PC-based measurement systems the deviations in performance of the two mics can be recorded, stored on disk and fed into the software for automatic compensation. In regard to frequency response, the measurement system now shows results as it would work together with the reference mic.

Reference microphones are highly costly (up to a couple of k$) and very precise devices and their linearity of frequency response and sensivity (among other things) have to meet strict calibration standards . Search the web for Brüel&Kjaer, ACO Pacific, Larson Davis to name a few.

There are other ways to investigate the calibration of a mic. element (also usually not over the entire frequency response but at one or several discret frequencies). One is a so called "Sound-Level-Calibrator", the other is a "Pistonphone" (actually there are even more methods). Somewhat simplified both are some sort of speakers basically which are adapted to the microphone and which put out a precise "calibrated" sound level.

 

[sfdoddsy]

If you're using TrueRTA, just get a Behringer ECM 8000 measurement mic. It costs around $30 from www.americanmusical.com.

The Nehriner mic is remarkably accurate for such a cheapie anyway, but TrueRTA includes a calibration file for it in any case.

Cheers

Steve

 

[Dave Jones]

i wish i could find a audio control one. i miss those. it was a "eq" and a spectrum analyzer in one

http://shop.store.yahoo.com/avshopper/243.html

 

[jleaman]

Do you or any one have a schematic for just the display part..? i want to build just the display part. if not ill have to buy the whole thing heh.

 

[Dave Jones]

If you're using TrueRTA, just get a Behringer ECM 8000 measurement mic. It costs around $30 from www.americanmusical.com.

The Nehriner mic is remarkably accurate for such a cheapie anyway, but TrueRTA includes a calibration file for it in any case.

Cheers

Steve

Will I need a microphone preamp with it? My soundcard is a SoundBlaster Audigy II, if that matters. (I am totally ignorant about this stuff, but I guess you figured that out.)

 

[jackinnj]

this will work

these HP 3581 "wave analyzers" will really fit the bill -- they are very sensitive, have excellent resolution and have been pretty cheap on EBay of late -- anywhere from $50 to $120. The unit has a built in sweep generator and very fine resolution. You can also get a companion plotter which accepts the 0 to 5 VDC out and graph the results.

Here's the link to the HP3581 manual I put on my website:http://www.tech-diy.com/hp3581.htm

 

[Dave Jones]

Like this..

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3042604004&category=3271

Yeah, I started to bid on that one, but then I saw 10 negative feebacks. I've gotten stuck for about two grand worth of stuff buying from ebay. I don't know why I even bother looking at something that costs more than 50 bucks or so.

 

[Hisatugo]

Really good stuff...

Hey, guys... I had to comment, sorry for my entrance without invitation. I have that combo, True RTA and Behringer ECM8000 in use... I made a small preamplifier to the mic and all is working very, very good. The level 4 with 1/24 oct RTA works perfect to our application,(to build speakers) and my curves got under a mat are very close to driver's factory measured response. The overall cost is very low, I recomend it.
Just my drop in the ocean.

Regards.
Hisatugo

 

[sfdoddsy]

I use it straight into a Soundblaster MP3+ external card (I have a laptop) so you won't necessarily need a preamp.

You will need to supply it with phantom power though. I use a Behringer 602 mixer, which is $50 or so and has volume controls so it acts like a preamp if needed. The Behringer Shark is also cheap and good.

Cheers

Steve