# A little feedback



## chewie (Oct 26, 2011)

Hey guys, first post here! I found this site yesterday as I was looking for some software to take some readings from my room which I am in the process of acoustically treating. This is also my first foray into acoustic treatments, although I have some reasonably nice HT gear.

My HT system currently consists of an NAD receiver, Linn Ninka and Trikan front and center and Linn Unik rears and s-rears along with a Vandersteen powered subwoofer. I have done the old school SPL balancing on the system before and read quite a bit on speaker placement, but I never got quite the quality sound I wanted out of my system.

I figured out why. This is in a perfectly rectangular room that is 20X 16, carpeted floors and drywall walls and ceiling along with a couple of doors and windows. Reflections galore! So I started reading about acoustic treatments, modal issues of rooms and such and realized what my major issue most likely is.

Here is what I have done to date: I have a large bookshelf that was against one wall, so I slid it to the rear wall and randomized the items on it to vary the depth of them as much as possible to use this as a large poor mans diffuser. 

I then built 6 acoustic panels in order to hang 3 down each wall. The panels are about 30X48 and are made from a 1X4 frame and 2" OC703 board. This allows for an almost 2" air gap behind the insulation. I placed there so that the panels start at about tweeter height and go up from there and they are placed at my first reflection points as discovered using the mirror method.

Finally I built 2 floor to ceiling bass traps for the front corners of the room that are 15" out from each corner and give me a front width of about 22". I filled them with the OC703 because I did not feel that I had enough depth in the area I was putting them to use pink fluffy stuff and still make them look decent.

I am going to pick up an external sound card this weekend and do a little Room EQ reading, but I can say that what I have done so far has made such an amazing difference I feel like I am listening to a totally different set of equipment and a different room.

My biggest area of concern right now is bass. I am thinking that I may need to put 2 more traps in the rear corners, but I do not want to over damp the mid to highs in the room. As of now I have about 25-30% absorption coverage on the side walls and none on the rear (I put the diffuser there).

Can you guys provide me some feedback on what you think are the areas that I may want to re visit, add more or should I just live with it a bit and then see how it all looks? 

Thanks in advance and sorry for the wall of text as a fist post!


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## bpape (Sep 14, 2006)

Before you do anything else. optimize your seating location and subwoofer location. We can treat til we're blue in the face but if your head is in a really bad place, you'll never get it really right.

While there is some debate on this, my personal opinion in the HT world is to do the bass control first and bring decay times in line. This may spread to having reflection panels being 4-6" thick but not usually. Having to concern yourself on minimizing high frequency control is backward - sorry.

Again, for HT, the front wall should be 100% dead to stop reflections from the surround channels from contaminating the front soundstage. The rear of the room should be more sparse.

Don't put too much faith in the bookshelf. That's purely an audio myth. The books will be relatively absorbent which disqualifies them from being portions of a diffuser, which by definition, must reflect the frequencies it's designed to diffuse. Also, just randomizing things does not provide diffusion. While it's different than a flat wall, it may actually be worse rather than better.

Welcome to the craziness...

Bryan


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## chewie (Oct 26, 2011)

Can you give me some information or links on sub positioning? That is one thing I was noticing last night while doing some listening. While sitting near the center of the room everything sound tight and very clean, but as I slide into the seats closer, especially, the left wall the bass gets muddy and seems to overpower some of the low mids.

There is not really much I can do with my seating. I have a large sectional that runs up the left wall and extends out into the room. I am planning to put a bar along the back of it and have the second row of seating as bar stools there. Eventually I may put another coach along the right wall. I know that the wall seats are far from optimal, but I have to make do a little with what I have and putting the bar in allows me to get more people into the sweet spot of the room before I have to spread them to the sides.

I agree with what you are saying, most of the movies that I tend to watch are action type movies and I am not trying to get recording studio sound. I just want to get it to where my movies, and the music that I listen to, sounds as good as possible.


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## bpape (Sep 14, 2006)

With sub placemet, it's really more trial and error. I personally like to use fractions of room dimensions with prime number for denominators. So, it might be 2/11 from the front wall and 1/7 from the side wall.

The left seats by the wall will never be right. Sitting against a boundary puts your head where the bass builds up.

Adding a bar right behind the front row is going to now cause the same problem with the main seating in the middle of the width since you're effectively adding a boundary again right behind the heads - not to mention absolutely killing the surround field for that area.

Bryan


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## chewie (Oct 26, 2011)

I get what you are saying about the bar and seating so let me elaborate a bit because I had actually thought of that a little. The bar will not be up to head level, it will be just slightly over the top of the back of the coach as in order to make it work even remotely in this room it will have to come off of the windowsill. It will also not be a solid bar, but something like a few metal tubes anchored to the floor to hold a sheet of wood or granite in place. This should allow it to not interfere too much with surround fields or the front row of seating.

I will move my sub around some and see how it sounds by doing so. I may also look into putting some additional bass traps in my rear corners. Are the types of traps that I put in my front corners (Described in initial post) solid? Or should I look at re working them or using a different type?

Thanks a lot for the feedback and help! I certainly do not mind critiques on what I am planning, getting the additional sets of eyes on it are what forums like these are all about!


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## chewie (Oct 26, 2011)

Wow, moving the sub around makes a lot of difference. It is amazing how little I find that I actually know about acoustics and such, even after as much time as I have spent reading!

Moving my sub out away from the wall and corner really helped the muddiness that I was hearing along the left side of the room (Possibly being further out lets my bass traps work more efficiently?) but it has left my sweet spot with a little weaker bass response than I like. 

Looks like experimenting is in order!


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## bpape (Sep 14, 2006)

What you're getting now is more direct sub output and much less room gain and mode excitement.


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