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We used in in our studio. While it helped with sub placement, we got the most value from sizing and positioning the acoustic treatment, and also fine tuning the listening position. It was striking how much changed with a 10 inch move in the listening position. Particularly before the bass traps, but even after adding them.

At the best, it helps you get better sound from your mixes, and at the least it makes you aware of the sensitivity of resonances and interferences to listening position. I can't count the number of times I've played a mix for someone else and their analysis differed from mine. After I ran REW, I understood that they were listening to a whole different sound due to different acoustics at different locations. Now we have identified the best spots for listeners to stand as well.
 

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Not a problem. Just paying back for all the help I've been given online.

As for guidance, you summed up everything I learned online, with one clarification...treat the ceiling too. We started without doing enough research and used foam Lenrd bass traps in the triple corners and along all of the double corners, and 2" sawtooth on portions of the walls. Looked pretty, but when we tested with REW, the room was a mess. So we added 4" x 2' x 4' of the higher density Owens Corning fiberglass panels in each vertical corner, 6" x 2' x 4' of the medium density OCF in the horizontal corners, 2" x 2' x 4' panels of the higher density OCF hanging from the ceiling. The corner panels bridged across the corners and we left the original foam bass traps behind them. The ceiling panels were hung from hooks in the ceiling and were angled slightly so each panel hangs between 6" and about 10" from the ceiling (space between the panel and the room surface is supposed to help provide some bass attenuation even from a thin panel).

Next, we hung two more 2" x 2' x 4' higher density OCF panels from vertical mic stands and positioned them about 8" from the back wall at the first reflection points. Because of the room geometry, the side reflection points should not be an issue, and they were already treated with the foam that seemed to be taming higher frequencies that are the issue from the first reflections.

For trap construction, we simply used the bags sold by Ready Acoustics online. They provide a clean look, hanging straps and hooks, and plastic corners to protect the fiberglass. The only difference from their directions is that we left the foil facing on one OCF sheet in each panel facing into the room (as recommended by Ethan Winer).

These changes resulted in a substantial improvement in the sound and in the REW results. We might have gotten better results using more massive corner traps made up of a stack of OCF triangles filling the corners, but this is a home studio and I was not prepared to either live with "rustic" look, or invest the additional effort to camouflage them. We did not do this incrementally with testing. We decided what we were going to do, were prepared to live with the result, and were pleased when we measured with REW at the end. As a result, we have no measure of the effects of each component.

We did use REW to position our subwoofer, and to adjust the positioning of the mains. Moving the sub had a large effect on bass. With the mains, the benefit was in their positioning off of the front wall (behind the monitors).

What I meant about "played a mix for someone else and their analysis differed from mine" comes from having recorded others, mixing their (usually bass-heavy) music, and having the musician tell me that the bass was too weak...or that it was inconsistent. Turns out that about 1-2 ft behind my chair was a terrible null at around 50-70 Hz. There was one spot where, if I set that frequency on the signal generator, you could barely hear a tone that was at 75 dB only about 2 ft away. Well that was where people would naturally stand when listening to the music while I was operating the panel from my chair. If they moved around a little, they might leave the null and and then say that the bass was ok for that passage...but the mix was all the same. Now, we have spots marked on the floor, and we let listeners know of the situation so that what they hear is as close to what I do as possible. If it is critical, they get the chair position.

As for the hardware, we are just using the digital radio shack SPL meter with its built-in mic and signal output. For mic/meter calibration/correction we use the file available on this website. We're running REW on an old Compaq laptop (use the battery if you get AC hum when plugged in). We actually got some useful results using the built-in sound card, but I bought a cheap external soundcard on eBay. Mine came from Hong Kong, but there are now ones sold from the US. Here is an example:

http://cgi.ebay.com/USB-6-Channel-5...14&_trkparms=72:1234|66:2|65:12|39:1|240:1318

Our signal path goes thru the subwoofer then to the mains. So we just fed the sub and turned the mains on or off if we wanted bass only or bass and mids. We took the advice and never went above 2500 Hz with the Radio Shack meter. If you have no sub, then go directly to the mains. With our setup we get a soundcard calibration in REW that is flat down to about 22 Hz. We really didn't do much above 250 Hz, so I don't recall how flat it was at the high end, but just recall that it was similar to other calibration graphs I had seen here.

We chose not to use an equalizer. I am not an expert, and please if someone disagrees with my analysis, consider their points. Our problem is spatially variable. We already have a spot where the response is satisfactorily flat (the operator's chair). But other locations in the room are bad. We could add a parametric equalizer and boost the frequencies that are quiet there, and cut those that are resonant. Unfortunately, that would boost the quiet and cut the softer frequencies everywhere...including the operator's chair where they would become too loud/quiet. A little like audio Wack-A-Mole. Correct a problem in one spot and one rises up in another. We decided that we were better off with a simpler signal path and marks on the floor indicating the best listening points.

The biggest expense was the OCF and the trap bags. I found that a local insulation supplier sold the OCF panels for about 60% of the cost online...plus it save the substantial shipping cost. The bags are about $30 ea. but they are attractive and easy to build/install (you just slide them over the panels, zip the zipper, and vacuum the exterior, and hang from hooks on the wall). Using the bags also limited us to using fiberglass vs. mineral wool. The glass panels seemed more rigid and could take being free standing (the Ready Acoustics bags alone have no frame). This was also the reason why we only used the thicker, medium density traps along the horizontal ceiling corners where it couldn't be damaged by contact. We used the more rigid higher density OCF where it might be bumped in the vertical corners between walls, and on the ceiling where they would have to stay rigid while hanging horizontally.

Hope this helps. Good luck whatever you decide to do.
 

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Ethan Winer recommends that the single layer of foil be left on the face directed towards the center of the room. Claims that in his experiments it resulted in a material improvement in attenuation which he attributes to it being a "limp membrane". I'm not sure what that means, but I am impressed enough with the detail of his postings and the level of actual data he references that I accepted his recommendation even though I can't do the measurements to test it on my own.

Translating the mix to other systems is always an challenge. One that REW doesn't really address. It isn't feasible, I think, to set up your listening space to mimic the sound of Cars...or an iPod...or a home sound system. To me, it is the performer's call as to how to adjust the mix to get the sound that they want.
 
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