# Need advise on room acoustics. Graphs and Video



## Guest (Feb 13, 2007)

First some background. My room is 16'x11'x8' and can be seen in http://www.youtube.com/watch?v=I-XlAJjzOgs. I have read all the stuff I can from Ethan's site and most of the post by bryan and other smart individuals on this site and AVS. I have read Bob Golds site and others on diy bass traps and absorption panels. In the video you will notice two spots on the side walls where there is tape on the wall and some GOM fabric samples. They are 2'x2' each and are my first reflection points. I will placing 2" thick 703 panels in those spots framed in pine and covered with GOM. Also I am building 2 2'x4'x4" thick bass traps with pine framed 703 covered in GOM and place them straddled against the two back corner where you see the dvd racks on the tape which the racks will be moved. And one in the corner where the lamp is in the back of the room. Also the boxes on the back wall are even with the front speaker which was not intended just lucked out that way. My seating position is 4 feet off the back wall not 6 feet which would be the 38% rule (WAF factor on seating spot). The main reason I have become obsessed with this is I love music of all kind but most of all classical. Second of all I love movies and want to play them close to reference with out listening fatigue of the high screeching and get the most detail and pinpoint accuracy of all 5 speakers. In other words Increase the gain reduce the pain. (Stolen from something I read) I have learned so much reading these forums you all do such a great service for all us amateurs who want a pleasant listening experience. Also I used the radio shack sound meter for my mic and understand it might not be as accurate above 4000 hz
Questions.
1. Based on the video and graph info do you think I am on the right track with this plan
2. Will I notice a difference in sound quality IE tighter bass and most importantly to my ears tame some of the high end stuff.
3. Is there anything I am missing or need to add. I am planning on more bass traps if the wife notices a difference in sound quality she really is behind this if she can hear the difference.
4. Can I still keep the lamp behind the bass trap that straddles or should it just be air.


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## bpape (Sep 14, 2006)

A couple of things...

- Your main speakers are high so your reflection points will be high too - plan accordingly.
- You refer to a reflection point in your video. Understand that with 3 speakers and 3 seats, you'll have 9 reflection points on each wall.
- If the graph you show is currecnt and at 1Hz resolution with no smoothing, you're the luckiest guy in the world! But, you'll still need some decay time control.
- The boxes on the rear wall will do nothing for diffusion, you need absorbtion back there due to the sheer size of the front cabinet vs the wall size.

Plan on moving the stuff out of the rear corners and tucking the bass control in there - as well as horizontally on the floor behind the couch.

Cover as much of the front wall as possible and tolerable.

Bryan


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## brucek (Apr 11, 2006)

It's quite difficult to interpret a frequency response graph that isn't presented in logarithmic scale.
Could you repost the upper graph (with a horizontal scale from 15Hz-200Hz LOG).

brucek


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## Guest (Feb 13, 2007)

The hight of the speaker is noted and the panels will go higher up. I used the mirror test and the math equation on ethans site and i can see both center and front side speakers. I would love to due the front wall just not feasible at this time due to budget. Thanks for the clarification on the back wall.
As far as the graphs go the upper is done from 15 to 200hz the 17 you see is were my mouse was when the screenshot was taken. the second one is done with no 1/3 octave scaling just default settings after of course I load the cal file and calibrated my sound meter


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## bpape (Sep 14, 2006)

We need to see the first one with the Log scale and with NO smoothing on. As it is now, you have basically hit a 4db window from 40Hz to about 190Hz. That's just almost unheard of with no treatment and no EQ.

Bryan


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## brucek (Apr 11, 2006)

> As far as the graphs go the upper is done from 15 to 200hz the 17 you see is were my mouse was when the screenshot was taken.


Yep, I realize that. The problem is that the graph is LINEAR and not LOGARITHMIC. It's not that meaningful if shown in linear scaling. Post graphs in LOG.

Also note that with a Radio Shack meter, the upper limit of accuracy is considered about 5KHz. After that there is too much variance between units to be useful. You require an accurate microphone if full range to 20KHz is used..

brucek


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## Guest (Feb 13, 2007)

Here is measurement I just took moments ago with the correct format. Also non of the graphs have smoothing.


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## bpape (Sep 14, 2006)

As I said, you're either the luckiest guy in the world or something else is going on. You're within a TOTAL of 6=7db from about 25Hz to almost 200Hz. All you really need to address if this is really correct is the decay times.

Bryan


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## Guest (Feb 14, 2007)

I took a look at the graphs and the video, and I noticed that this is a logarithmic plot. By definition, using a dB scale is a log scale. Just because it is not 6dB per division doesn’t mean it’s not a log scale.

The second thing I noticed is the large amount of absorption that this room possesses. The open window and doorway to the adjacent room/s, are acting as huge low frequency Helmholtz resonators with very low Q due to the large size of the opening in proportion to the adjacent room’s volume. In addition there is a very large about 6 foot wide by 4 foot tall window that even though it is closed, is a huge acoustic leak at low frequencies. The bass that goes out does not return. Absorption at 20Hz probably about 0.96

I am curious what method was used to achieve the graphs. Swept sinewave?


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## Guest (Feb 14, 2007)

I forgot to mention that thick plush seating helps too.

I agree that you need to treat the rear wall. The reflection off that rear wall is only 4 feet away, that’s about 4 milliseconds, and probably only ½ dB lower in level than the direct sound from your front speakers


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## Guest (Feb 14, 2007)

Yes it was a sine wave sweep I used for the measurement. I will post a older graph when my sub was out of phase. Also I rearranged furniture and have moved my sub around the room to get the best response. The graph will not be in the correct format but it still gives you a look of how bad my room can be.


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## Guest (Feb 16, 2007)

Real fast. I picked up 6, 2" panels of 703 today. I put them 1 at the early reflection points on the side walls and stacked two thick in two corners. In short OH MY F**king Goodness. Sorry for the language but what a difference these make. The sound is very pinpoint now and the Bass is TIGHT(BTW wasn't sure what that sounded like until now). I have not framed or covered them yet. I am going to treat the front wall with 2'x2' panel behind the center and 1'x2 ft behind my small bookshelf speakers. And now my wife want to treat the back wall but want it removable for movie watching only. It really made a impression on my wife and on me. I admit I was skeptical that it would make as much difference as it did. Thank for the advise. I will shoot new video and maybe graphs if my wife have time to help me by holding the mic. Also when I re-calabrated my system again my sub level had to be lowered down a few db's. I normal would run my sub 8 db's hot but now I keep it even with the other speakers because the bass just sounds so much better.


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## bpape (Sep 14, 2006)

Congrats. 

Your graphs of the sub out of phase and furniture/speaker/sub movements compared to the final result are an excellent example of what can be done with some time, persistance, and willingness to compromise on positioning. ....and those things are all free.

This is something I always try to stress to my clients. Before putting up any treatments, do everything you can to get everything as smooth as possible first. Once you start putting up treatments, they do their job and start smoothing things so finding that perfect place is much tougher. 

Most people would kill to get the response curve you have in your room AFTER treatment and even a bit of EQ.

Bryan


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## Ethan Winer (Jul 21, 2006)

stlfdemt said:


> OH MY F**king Goodness


Great, we got another convert! :jump:

--Ethan


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## Guest (Feb 26, 2007)

Here is a link to photos of my finished panels. I framed the O.C. 703 in pine lumber and the back is covered in gardening fabric and the front and sides covered in Guilford of Maine Cloth.


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