Newbie, after eight hours of trying...

Folks,

Here's my first REW graph. I don't have a clue what it means, but it looks ugly. I was actually just trying to get REW to work. Took about six hours to calibrate the soundcard. Thanks brucek for an earlier post.

Does this actually represent anything, or have I made an error somewhere in setting up REW? Using an RS 33-2050. Onkyo 805. Audyssey off. Stereo. No BFD in the loop. Hsu VTF2 Mk3. Mains crossover at 80Hz. LPF at 120Hz. No room treatments. 14'7 X 14'9' X 7'11" room.

Any recommendations?

deadhead

[Wayne A. Pflughaupt]

Well, that big hole at 60 Hz is certainly a problem. Can you try the sub in other locations?

Regards,
Wayne

Wayne,

I've read your posts with awe and envy.

Here's that same setup with two DIY bass traps I made (put together) today.



I bought four of those R-13, 3.5" X 15" wide rolls of insulation and two 24" X 36" gray jersey material laundry bags from Linens and Things. Each laundry bag just holds two rolls. It's a tight enough fit the rolls don't even need to be taped together. Draw string at the top doesn't quite close completely. Believe it or not, they don't look that bad, and they only cost me about $55. There's quite an improvement in the overall sound. I have already exchanged emails with Bryan from GIK. I'm sure now treatments are the right thing to do.

I obviously have some work to do with sub placement, but it is honestly the best sound I've been able to get so far...

When I got the sub, I plunked it down in the corner, hooked it up and ran Audyssey. The bass was lacking, which I compensated for by turning up the gain on the sub. I lived with it for a while, but the more I read, the more I knew it wasn't right.

I had some time, so I did start moving the sub around. I don't have much room to play with--the sub has to be in the left front corner area of the room. Since the room is square, I don't really see the other corners making much of a difference, at least theoretically. I currently have it 32" (measured from the back of the sub) from the front wall and 5" from the side. I had it 9" from the side, but I got some nasty ringing (if that's the right term). At the primary listening position, a 40Hz tone had the RS SPL (no REW then) dancing from less than 78dB to over 84, and the 80Hz tone banged the needle around between 76 and 80dB. With the sub closer to the side wall, those volume changes were much reduced. On paper, the curve didn't look as bad as REW makes it out to be. Was I correcting the wrong thing?

What is really perplexing, however, is in the current position (but without the DIY traps), the volume was drastically different in different parts of the room. Astonishingly different. I don't remember it being that way with the sub stuffed in the corner. The traps tamed some of that. I have one in the front left corner behind the sub, and the other in the right rear. The entryway is in the front left corner, but now I wish I'd put together three of those things.

I still have a little room to play with as far as sub placement goes, but not much. Are there any rules of thumb I might try, or is this strictly a hit or miss game now, down to the fraction of an inch, I'm playing? My plan is to try to find a smoother curve since I have REW running while I wait for some GIK 244s, and run Audyssey. I probably won't play with the BFD till after the treatments arrive. If I didn't already have the BFD, I might skip it. I won a Xenyx 502 and an ECM8000 on eBay a day or two ago. My wife's gonna kill me.

Thanks,

deadhead

[Wayne A. Pflughaupt]

deadhead wrote:

Wayne,

I've read your posts with awe and envy.

Thanks for the kind words, deadhead! (Wow, it seems strange calling someone "deadhead" who just said something nice about you. )


Waterfall graphs will show you what improvement you're getting from your bass traps. If it's not too hard to move them back out of the room, you'll for sure want "before" and "after" waterfalls. Traps typically improve the sound by reducing ringing (aka decay i.e., the time it takes for the signal to fade to nothing), making the bass sound "tighter." You can find some info here on how to decipher and get the most from your waterfall graphs.

Even with bass traps, you'll probably need the equalizer to finish off the peaks and other rough areas of response. Now that you have REW you can take readings at all those different locations you mentioned, but I expect you'll get the best results with it in the corner, or down the wall a few feet from the corner. Seems to work best for most people, as far as getting response that's easy to equalize.

Regards,
Wayne

I spent some time moving the sub around. I did two inches at a time forward or back while holding the same distance from the side wall. When I got as far as I could, I moved it over an inch and started going back the other way. There's still lots to do, but I need some advice.

Which of the following is a better graph? The top one is 5 inches from the side and 27 from the back wall. The bottom is 8 inches from the side and 41 from the back.





I have others that look similar, but I don't know if I should be worrying more about the spikes on the right side near the crossover region or keeping the 60Hz dip as small as possible. I can't seem to get both.

Thanks,

deadhead

[brucek]

A couple tips:

1. Maintain the same standard graph axis when you evaluate your responses. Always use a vertical axis of 45dB-105dB and a horizontal axis of 15Hz-200Hz.

2. When making comparisons, use the Measured tab in REW. It allows you to overlay measurements for easier evaluation.

3. Uncheck the Mic/Meter cal box to remove the meter calibrate file from your graphs. It just adds distraction.

brucek

brucek,

I read about the graph limits a dozen times. If I click on the Graph tab, it shows the values you mentioned. Not sure what else I'm supposed to do when I create the jpg.

I wasn't really looking for a specific comparison between the two. I'm more interested in your insight as to what is more important in general, keeping the valleys small, or smoothing the crossover area. I can't seem to do both with sub placement.

Does this mean I'm in the penalty box?

Thanks,

deadhead

[brucek]

If I click on the Graph tab, it shows the values you mentioned. Not sure what else I'm supposed to do when I create the jpg

After you take a measurement, if the graph doesn't show the limits of vertical 45dB-105, horizontal 15Hz-200Hz, then click the Graph Limits Icon in the top right corner of REW, and enter those values into the form-fills and hit Apply Settings. The graph will change to those limits and the jpg will save with those limits. Takes only a second.

We're sticklers on consistent axis because a lot of people look at these graphs and it is extremely easy to be fooled when an incorrect axis is used. We have lots of people with exaggerated axis worried how terrible their response is and many more who are proud of their perfect response when they've used a huge axis spread. The conclusion we reached was to demand the same axis for every graph posted.

Anyway, there isn't a whole lot of difference in those graphs. They both have a few peaks that could be equalized out with a BFD. Dips are hard to deal with, so I would use positioning and sub phase to get the least dips and apply some EQ to the few peaks and I think it would be fine...

brucek

[acoustat6]

Hi Deadhead, Can we see two graphs out to 1250hz, with mains and subs. One graph with no smoothing and another with one octave smoothing?

Thanks,
Bob

[Wayne A. Pflughaupt]

deadhead wrote:

Which of the following is a better graph? The top one is 5 inches from the side and 27 from the back wall. The bottom is 8 inches from the side and 41 from the back.

The lower graph looks a little better, as the 60 Hz depression is reduced by something like 5-6 dB.

Did you every try a corner like I suggested?

Regards,
Wayne

Bob,

I have only a small idea about what you asked. Not quite there yet as far as my understanding of REW.
I have only been playing with the sub placement. I need to run through it again and this time switch phase at each position as well. Then I'll add the mains.

Wayne,

Thanks. Will the spikeyness in the crossover area go away when the mains are added?

I have a DIY bass trap in the corner the sub is near. I have purchased, but not yet received, some 244 bass trap panels from GIK Acoustics and plan to put one in that same corner (one in all the corners). I originally had the sub tucked in that corner, but was unimpressed with the bass at the listening position. I did not have REW then, but I also did not have the DIY traps in place. The rear port on my Hsu VTF2 Mk3 would be firing into the 244 when I get them set up. Any reason not to do that?

Now the big question... Should I wait to get all the traps in place before messing around further with sub placement and phase?

Thanks again,

deadhead

[acoustat6]

Hi Deadhead, No problem, take your time. What is interesting for me to see is a non-smoothed freq response graph. This should show your freq response out to at least 1250hz (or 3000hz, its just what I use) this will show comb filtering which is another important aspect of room acoustics and treatment.

A freq response graph out to the same freq (1250 or 3000hz) with one octave smoothing shows the balance between mains and subs. It also shows broad freq response abberations such as an overall reduction in levels where there are a number of nulls within a freq range, or just the opposite such as an overall rise in levels in the lower freq that would show, the bottom end is nicely boosted.

Bob