Calibrating a mic

[Sceadwian]

How would I go about calibrating a home audio system without breaking the bank? I'm not looking for scientifically flat audio just as close as I can practically get with the EQ on my PC. I have good hearing but my brain just isn't up to the task.
I guess the hard part is that microphones aren't flat in their response so if I'm doing it with a spectrum analyzer and a mic I don't know how to calibrate out the mics curves so I know if I'm getting even close to a flat response, especially in the low range. If I could characterize the curves of the mic first then I'd have a start? Any other suggestions?

 

[Nigel Goodwin]

You just need a cheap electret microphone, with a bit of work these are amazingly good, check out:

**broken link removed**

 

[Sceadwian]

I had no idea their frequency responce was so flat, I have at least two of those floating around.

 

[Nigel Goodwin]

I had no idea their frequency responce was so flat, I have at least two of those floating around.

Impressive aren't they?

 

[Sceadwian]

Stupid question. I thought electrets were polarized devices because of the internal FET? The reason I ask is no matter which way I hook it up to my mic in on my PC it works. What am I missing?

 

[audioguru]

Your home sound system has low frequency standing waves that add and subtract to the sound pressure at certain distances and certain frequencies.
The midrange and high frequencies are affected by reflections from the floor, ceiling, walls and things.

I tested speakers and EQ by placing the speaker outside pointing straight up and the mic hanging over it on a long rod. Then there were no standing waves and no reflections.

 

[Hero999]

Stupid question. I thought electrets were polarized devices because of the internal FET? The reason I ask is no matter which way I hook it up to my mic in on my PC it works. What am I missing?

I thought they were too, wtf?

 

[Sceadwian]

I know audioguru, I probably have the worst audio setup in the known universe. I have a 'hutch' for my computer that allows me to close it all up when I'm not using it (very very limited space) The speakers are at the back of a 19x28x21 inch deep 'box' with the side facing me obviously open. They're Creative cheapie speakers. They're nice enough, pretty compact but they're basically just a pair of 1.5 inch 'woofers' stacked vertically that are ported to increase the low end response a little, I don't have room for anything else right now. Even worse (and I wish I'd known this before I bought them) the headphone out jack is a passive bypass to the audio card, which BLOWS because the audio out on my PC isn't enough to drive headphones. It's been seriously bothering me lately, I can hear the phase shift from the reflections just moving my head a few inches, and the headphone output makes my ears 'squint' Even worse is the speakers are on either side of my LCD monitor which is only 4 inches from the back of the hutch which acts as a secondary air column which the bass port on the speakers happens to empty into. So the audio is to say the least, not flat, and I doubt it's fixable.
It's the only thing I hate about being married =) When I lived alone I had a studio that was virtually acoustically perfect for the 5.1 system I had. The standard stereo output was even phase shifted slightly from the front/rear speakers to avoid peaky areas. Sadly I gave it to a friend in need (poor DJs are much more in need than me) and I wouldn't dream of asking for it back, I should have just put it in storage.
My analog skills are lacking but I may just find a decent op amp from my junk box and make a headphone amp for my crappy open air headphones.

 

[audioguru]

My computer speakers have 3" drivers with big magnets. They are driven with 3.4W per channel and sound alright but are not Hi-fi.

 

[Sceadwian]

At any rate, after that rant I thought this needed a new post =O

So what's up with my electret mics? The headphone jack on my card has a stereo connector, but it's only mono in. When I check the base to tip voltage I get 2.32 volts DC and .1mv AC on my meter. Oddly enough I get 0VDC and 50mv AC on the center conductor, but I'm guessing this is noise from a floating center conductor inside the machine. So how am I getting output from my eletrets regardless of which polarity I hook them up?

 

[Sceadwian]

Yeah, the Creative set does 2 1.5inch drivers per speaker, keeps audio power up but they just can't produce mid range the porting helps the low and some of the mids but the output is just all over the place.

 

[Sceadwian]

Anyone with any clue about the electret 'problem' this post is about?

 

[mneary]

The drain and source on many JFETs are interchangeable.