[Tyson]

OK, as some may know, I've been building my own speakers (the elsinores, detailed elsewhere here in the lab). 

My problem is I don't have a calibrated mic, or the software that would be needed for doing really precise speaker setup.  Basically I have a spreadsheet, a radioshack SPL meter, and some 1/3 octave test tones. 

By chance (luck) I've stumbled across a MUCH better set of tools, and it cost less than the Radio Shack SPL meter. 

Two tools, actually.  The first is called RTA, and it does real time signal generation, measurement, and graphing, and allows several options to get the data you are looking for with regard to your speaker's frequency response. 

The second is called FFT and it lets you do Fast Fourier Transform, with a LOT more granularity, precision, and options. 

One of the drawbacks of the RS SPL meter is that it's actually not very accurate when compared to a calibrated mic, but the RTA and FFT here are much, much closer.  That's because the developers actually went out and measured a bunch of the internal Iphone mic's and built in automatic compensation into the software.  Soooo, you might end up with a "slight" deviation based on variations between individual microphones, but on the whole, specs are pretty tight.

Anyway, for $30 total for both programs, you get a pretty well calibrated mic system, a tone generator, graphing, storing, averaging, min/max tracking, and a bunch of other stuff, it's pretty much a steal and a quantum leap over the RS SPL dinosaur. 

I thought it was very useful, so I wanted to share:

http://www.studiosixdigital.com/products_2.html

If you have an iphone, just search for RTA or FFT or for Digital Six in the app store.


Demo of RTA:

http://www.studiosixdigital.com/rta_demo_video.html

Demo of FFT:

http://www.studiosixdigital.com/fft_demo_part_one.html

[Levi]

Thanks. I will try it in my 3Gs. I have one installed for free but only measures fir the quality of noise.

[brj]

Tyson, if you'd like to compare with a different setup, you can borrow my measurement rig.  I have a Nady CM100 mic calibrated by Kim Girardin and a Edirol UA-25 USB pre-amp for it, along with the needed cables.  I don't remember exactly what part of town you're in, but I don't think you're too far away...

[Tyson]

Heck yeah!  I'm just south of downtown proper, near the new Denver Art Museum.

[Pez]

Interesting, just when I think iPhone couldn't be more useful, one more overpriced specialty app comes along and changes everything. Question, If you had to pick just one... 

[Tyson]

FFT, no doubt.  Has all the capabilities of the RTA, with finer detail and more control.  Plus it has a signal generate that can do white noise, pink noise, sine waves, and square waves.  Crazy.....

Another interesting app is the "Speaker Pop", which generates a burst tone through your speakers and measures the polarity of the driver.  Cool stuff

[brj]

Ok, that's roughly 20-25 minutes Northeast of my office, so I'm sure we can make that work.  I think I'm due for a trip to the flagship REI soon (maybe Friday?), so we can probably arrange a transfer then.  Shoot me your contact info via PM and we'll work something out.

[Pez]

I'll look into FFT later, right now I feel like it'd be pointless for me to buy it because A. I don't have an EQ to correct abberations that I find and B. My wife's idea of room treatment is a fern. 

Speaker Pop on the other hand seems like it could be extraordinarily useful to my particular situation.  Downloading now.

[Tyson]

Haha, I have to say that after using it a bit more, I'm even more impressed with it.  Combining it with a 3 way digital crossover in my main system, and the ability to do real time crossover adjustments and real time EQ, I have been able to make more progress today dialing in my speakers than I've been able to make in 2 months with the RS meter and a spreadsheet.

It's pretty crazy to be able to sit there, dialing various parameters on my EQ and see the immediate affect on the readout.  What's even more interesting is how a couple of humps in the bass (which didn't show up w/the RS SPL meter) were really affecting my perception of the midrange and highs.  I kept turning up the mids to compensate, and just ended up having a very midrange-forward sound.  Dealing with the bass humps directly has allowed me properly dial in the mids.

Once that was done, I also realized that there is a peak at 1.35khz that was making the speakers sound a bit bright.  But it wasn't showing up w/the RS SPL meter at all, and so I kept turning the tweeters down to make it less "bright", which didn't fix anything, and just make them sound a bit dull and muffled.  Now, I've got the peak dialed out, which let me bring the tweeter levels back up.  Net result, MUCH better clarity and transparency in the mids/highs. 

One other thing I noticed the mic in the iphone is MUCH less directional than the one in the RS SPL meter.  With the RS SPL meter, if I moved it around a bit, or "pointed" it anywhere except straight at the speaker, it would dramatically affect any reading at 1khz or higher.  With the iphone, I can move it around, point it different directions, etc... and very little change in the readings occur.  This makes room corrections MUCH easier to do. 

Anyway, for $30 it blows away the RS SPL meter.  brj and I are going to hook up next week and see how it compares to a more absolute standard of proper equipment.

[Tyson]

One other cool/fun thing - if you want to see what frequency range different sounds occur, just turn on the RTA or FFT and make SSSSSS or SSSHHHH or AAAAA or TTTHHHHH sounds and you'll see a spike at the frequencies that they dominate.

For example, if I do a hard SSSS sound, it spikes at 8-10kzh.  If I do a SSSHHHH sound, its 5-7khz, and a hard AAA sound, like in "Jack" is 1.2khz.  Cool stuff

[Pez]

What frequency is it if you turn your head and cough?