# RT60 graph



## ddgtr (Nov 1, 2009)

Hi,

Here is my RT60 graph generated with REW. I need a bit of help interpreting it. Prior to installing acoustic panels, I had calculated my room's RT60 with an online calculator and it came up to be around 1.40s which I know it's bad because it was really obvious.

I found out about REW after I installed my panels which address the first and second reflection points.

Thanks


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## bpape (Sep 14, 2006)

First of all remember that RT60 is really only for larger spaces. We are looking to address the time domain but in a different way than a large space.

Can you post more info about your room? Seating location? Speaker location? Sub xover point? Room dimensions? What you treated and where?

Response looks pretty good from 70 and below which is good. A few anomalies above that but no way to tell what is what without knowing the above.

Bryan


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## ddgtr (Nov 1, 2009)

Bryan,

Thank you for the help!!

Ok, here it is:

- Room is 19'6" long by 15'5" wide by 9'6" tall.
- Speakers are 3 feet from back and side walls
- My chair is about 13 feet from front wall and centered between side walls
- It's a 2 channel system with a sub, sub is crossed at 70hz
- I am attaching some pics. OC703, 2" thick, 2 x 4 feet for panels and 4 corners are OC705 6"thick.
- 14 OC703 2" thick 2 x 4 feet panels (4 are on the ceiling, only the back ones show in the pics below. The front ones are at the first reflection points).
- 4 OC705 6" thick 2 x 4 feet panels in corners
- Cylindrical polys on the upper half of the room have helped tremendously with flutter echoes.
- I placed the panels following both the first reflection points (mirror method) and the calculations I found on a web site. The placement coincided.

I am attaching pictures of the room, panels and so on. 

Thanks!!


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## Drudge (Sep 1, 2008)

Wow!
Very nice set-up.The room treatment looks very professional.:T


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## bpape (Sep 14, 2006)

Looking good. Sorry for missing this earlier.

The first things I would try:

Play with the sub phase

Pull the seats forward to about 12' from front wall to seated ear position

Offset the speakers in the front so it's not the same distance from baffle to front wall and center to side wall.

Bryan


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## ddgtr (Nov 1, 2009)

Thanks, Drudge and Bryan!

Bryan,

- When I offset the fronts, should I do it like an inch or more? The reason I am asking is that I obsessed about following the equilateral triangle rule.

- Also, to get the waterfall graph response I posted above I had to move the sub around the room quite a bit. I found that the flattest graph was with the sub located in the back of the room, right corner as I face the front speakers, up against the bass trap, with the driver pointing 45 degrees towards the right wall (side of subwoofer is almost touching the bass trap).

- I know this violates the "no sub in the corner rule", so what do you think? Also, because it is in the corner the bass is "louder" in the four corners of the room as opposed to say when I placed the sub 2/3 between front and back walls. So do I keep it there since the waterfall at the listening position looks best with least EQ, or do I move it back and apply more EQ while getting a bit more uneven graph and get rid of some of the standing bass in the corners?

Thanks!!


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## bpape (Sep 14, 2006)

Use what works best for you in terms of position. Normally, we'd look at the frequency response graph, not the waterfall when doing sub positioning.

Don't get hung up on the equilateral triangle thing. It's just a starting point and more for borderline nearfield listening rather than home theater.

You can move the speakers however you want. 1" difference between those 2 measurements isn't going to really do much. However, you may find that moving closer to front wall vs closer to side wall (or opposite way around) addresses different things.

Bryan


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## bjmsam (Sep 12, 2010)

I am preparing to tackle my room and am inspired by your approach! Are the polycylindrical absorbers filled? Does your carpet have much of an underlay? Is there any airspace behind the panels? How did you determine thickness? It would be interesting to see measurements of your room with 4" panels considering the significantly higher absorption coefficient below 250 Hz.


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## ddgtr (Nov 1, 2009)

Hi bjmsam,

The polys are filled. They are made of 2lb density foam, (I think it's called expanded polystyrene) the kind they use for custom stucco projects.

I had them cut at the correct radius for best diffusion, I got that from a scientific white paper on the subject.

A 1/8" coat of cement was applied on top of the foam, then another coat of 1/16" of drywall mud. Sanded and painted it to match the rest of the room. The polys are attached to the wall with caulk, they are very light.

Since I did everything myself, I found this to be the cheapest and easiest way. I just had the polys custom cut and the first rough coat of cement applied. It cost roughly $50 per poly on average in my area. I drywalled them myself...

Let me tell you, they did wonders. I had a super-nasty flutter echo in that room that was horrible. The absorbtion panels were installed first, but did not completely eliminate the echo. Polys totally did the job for me.

The panels are indeed spaced from the wall, about 2 inches. This was recommended on most specialized sites I visited.

In retrospect, perhaps going to a 6lb density all panel might have worked better for below 250hz, like you say. Now only the bass traps are 6lb, 6" thick. But bass is all right, actually the overall sound is very pleasant. 

I am planning to build 3 qrd diffusers on the back wall behind the listening position to replace the 2 panels to see if or how they would change the sound...

Checked out your room and it looks really cool. I think the tile ceiling you have will help tremendously with reflections...


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