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Corner Basstraps (Chunk Traps) - build and outcomes

1953 Views 7 Replies 5 Participants Last post by  jim1961
I have a dedicated listening room in my home measuring approximately 7m L x 5m W x 2.8m H. The room has a carpeted concrete floor, painted brick and plaster walls and a gypsum ceiling. When I initially set up my hi-fi in the room the acoustic response was terrible - the room was loud, boomy and an incoherent mess that dictated listening at very low levels to avoid listening fatigue and a headache. At some point I had some acoustic treatment done to dampen the room a little - basically four panels containing PET on the front wall and two on either of the side walls, covering first reflection points. On top of that I also had the same PET panels (2 of) installed in the room corners. Overall the room showed significant improvement and listening was a lot more enjoyable. I could begin to appreciate my kit and my music collection. Whilst it was a large improvement over what I initially had, I wasn't satisfied that things were as good as they should be - this was confirmed every time I found myself in a listening space that had been properly treated. Bass was either absent or boomy, midrange wasn't as detailed as it should be and occasionally I found myself thinking things were missing from some songs I knew well - had I listened to different releases as a kid? I added an in ceiling IB subwoofer comprising 4 x 15" woofers powered by a Crown XTi 1000 amp and the bass response and soundstage definitely improved, but to my mind the midrange still lacked detail and bass was occasionally boomy and wasn't articulate - kind of what people refer to as "one note bass".

In any event, I resolved to look into additional treatments, but this time to take things into my own hands rather than just hand over cash to someone. After much reading, confusion and contradiction I decided that the best thing to do was to build and install chunk traps using high density mineral wool boards. The boards came in 1200mm x 600mm dimensions so I sized the chunk traps by cutting the board in half and then halving each resulting board diagonally, yielding 4 triangular mineral wool sheets per board. Dimensions of the triangles were 600mm x 600mm x 848.53mm (see Right Triangle Angle And Side Calculator). I used 19mm 2.4m x 1.2m plywood sheets cut along the "grain" into 75mm widths to build 8 triangular enclosures in which to place the mineral wool triangles. These were sized approx 615mm x 615mm x 870mm (ensuring that the triangular mineral wool sheets could be easily placed). I chose to make 8 stackable enclosures rather than four very tall enclosures so that it would be possible for one person to place/ move the traps if necessary. I'll let the pictures do the talking where the build is concerned. That green stuff is PET - lined the frames to keep the mineral wool inert.

More to follow...
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Before installing the chunk traps I ran a sweep:

After installing the chunk traps I ran another:

End result: detailed, articulate bass, much improved midrange clarity.

To deal with the suckout around 100Hz I placed a 1200mm W x600 H x 100mm D mineral wool panel diagonally against the bookshelf and floor directly behind the listening position. The outome? A 5dB decrease in the extent of the suckout and a slightly flatter overall response.

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Looks good! It reminds me of some old corner traps I made years ago... Mine were round but same basic principles.
Great solution egd. Sounds like you got exactly the results you were looking for. Have you had an extended listening session in the new room and been able to avoid the fatigue and headaches? Oh, and any pics of the finished panels in the room?
I'm very happy with the sound in the room now. Overall soundstage is deep and wide, midrange is very clear, instrument placement is easy and bass is very tight and articulate. I'm sure further improvements can be made, but this is the best it's been in my listening space.

I'll post some pics of the room with traps and other panels in-situ as soon as I've had the traps properly upholstered.
What's up with the waterfall showing nothing at and around 40hz? Does your system not reach that low or is it just missing completely.

That is what I would work on finding out more on maybe I am just to tired as I have been up way to long but I would think it should show more energy there. If not that would be a enlarge hole in your response. But I am not a pro so maybe someone else can comment on this.
There is a suckout there, but there's not much music down there so I'm not overly concerned at this point. I will seek to address it in time, however, there are bigger gains to be had elsewhere, e.g. ~ 72-120Hz.
There is a suckout there, but there's not much music down there so I'm not overly concerned at this point. I will seek to address it in time, however, there are bigger gains to be had elsewhere, e.g. ~ 72-120Hz.
My system used to start dropping off after 42hz. Now my extension (-3db point) reaches 16.5hz. Believe me, there is more there than you think. Not saying its the most critical element, but I am saying it will be worth fixing the dropout.

The lowest note on a organ / piano is about 27hz and on a 5 or 6 string bass guitar about 31hz :T

Text Line Plot Slope Pattern

This shows where I was, and where I am at in graph form.
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