There is an excellent thread on using TrueRTA for audio measurement over on AVS - http://www.avsforum.com/avs-vb/showthread.php?t=572477

I highly recommend it if you’re looking to try out measurement for fun.

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The past four days have been a bit of a blur and I’m paying the price (now home sick). This year’s AV123 Colorado GTG was great. There were a lot of great folks there: Danny Ritchie (GR Research), Ron Stimpson (SV Subwoofers), Keith Allsop (Perpetual Technologies, etc.), Phil Bamberg (BESL), Rich Hollis (Hollis Audio Labs), Dave Tremblay (RDES developer), the AV123 crew (Mark, Suzanne, Steve, Sean, Greg, Kyle, John, Wendy), Chris Cahill and lots of enthusiasts. I’m glad to have had the chance to hang out with these folks, even if some of the conversations were half (or more) over my head.

There was a lot of good discussion on many topics and some work done on measurement and number crunching. It was great to get a variety of perspectives and input on some topics.

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Before I get around to posting measurements, here’s a quick breakdown of the equipment that I am measuring with. It’s nothing too fancy, but it seems to do a pretty good job:

Behringer ECM8000 mic
M-Audio MobilePre as both the mic pre-amp and the soundcard
Dell Inspiron D600 laptop on battery power
ETF 5.98x software

RadioShack SPL meter for setting the SPL calibration level in ETF

I have some additional software installed to play with like the free Room EQ Wizard and trial versions of various programs to try out (TruRTA, Spectra Plus, etc.).

I highly recommend the Room EQ Wizard if you have a soundcard with a stereo line-in (many notebooks only have a ‘mic’ in and not a stereo line in) and want to measure your in-room response. It’s an excellent program and can be used with just a Radio Shack SPL meter as the mic.

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I’m going to spend some time talking about working on low frequency response in room. I’m just learning this stuff, so feel free to point out information of note (references would be great, I’ll be picking up some books on the topic soon).

The room itself in in a fully finished basement with pad and carpet on concrete and 7.5′ ceilings. Here is a diagram of the room, click to enlarge (pink - speakers, purple - sub, green - treatments):

The numbers along the sofa are reference points for the measurements I’ll be posting later. Each time I do measurements, I measure at all six points for each test. It takes some time, but gives a much more complete picture of how things sound for various positions. The sofa back and mic stand are also marked to try and keep measurement positions consistent between runs. I also run a new baseline for each test and the baselines have remained consistent.

The room dimensions noted here aren’t exactly correct. I remeasured and the length is just under 22′. That would give an axial mode of about 25Hz (I tend to use this page for calculating modes - >http://www.marktaw.com/recording/Acoustics/RoomModeStandingWaveCalcu.html ). Since the main sofa is right about the half way point in the room, that places it in prime first axial mode location.

Since the room is open to another area and a staircase, it’s more difficult to predict behavior. My measurements show that the expected 25Hz mode is closer to 22Hz, but that’s for another post. I’m hoping to pick up CARA sometime and model the full space.

Measurements to come soon.

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I’m contemplating putting some of my audio postings/ponderings into a blog instead of forums. Might happen, might not.

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