Room treatment options

[Anthony]

I have some plots from Room EQ wizard showing my sub + magnepans. I'm getting good center imaging and some tighter midbass, but there's some work to do. Before I build any speakers, tear down walls, or move things around, I would like to fix some room modes first.

The first plot is the full range and sub. The levels were matched using the receiver pink noise. As you can see, with a sweep the sub looks much higher, but it sounds okay. A little heavy on the bass, but for movies, I like it.

The second shows the same thing, but with the sub level lower. Notice how the hump at 130 Hz stays the same even with the sub level about 8 dB lower. That one item to fix.

Another item of note is the big dip at 33 Hz. This is not sub rolloff, the room is taking this away. Other dips at 105 and 260 also need attention.

So one hump at 130 hz and dips at 33, 105, and 260 Hz.

Those plots are four sweep average, 1/3 octave filtering. Slight EQ on the sub for local peaks. Room is L-shaped and "existing" (no drywall tearouts please). I have an entire back wall I can put an absorber on and there's room to fit 1' cylinders behind the magnepans (including one corner). Other than that, selling treatment changes will be difficult.

All advice appreciated. I am not afraid to DIY something.

Thanks,
Anthony

[Anthony]

Followup info:
30 Hz corresponds with the 1/2 wavelength of the long axis of the room (18.8 ft)

105 Hz corrensponds with the full wavelength of the width of the listening area of the L, or 10.75' So that may just be a microphone null in the listening position. I'll verify that tomorrow with another location.

I have no idea what the 260 Hz (4.3') is about, although that is about the height of the magnepans

Also the peak at 130 Hz corresponds to 8.6', which isn't anything special in this room, except that it's double the frequency of the 260Hz dip. Might be related to the magnepan size.

[BoomieMCT]

First off, because I know you have it, I'd read chapter 9 in the Master Handbook of Acoustics. Then I'd play test tones at those trouble frequencies and go around the room and see where they seem strongest. Mark those areas for treatment.

I think thick panels of OC703 attached to frames, wrapped in fabric and put in corners and edges is a good start and are easy to move around and experiment with.

I'd be worried about cylinders behind your maggies as they could mess up your rear wave. I have some leftover sonotube (a few feet of 16", not enough for a final project) if you want to experiment. It could be good for a helmholtz resonator test too.

[bpape]

What is the distance from the rear of the maggies to the wall behind them? What is the distance from the front wall to your seated ear position? Where are you sitting in the room side to side?

Bryan

[Anthony]

2' from the back wall and 10' to the listening position are the mains.

40" off ground listening height (7' 8" ceiling), 55" from the side wall.

There is no "center" seat. We have 2 rows of oversized loveseats, so everyone is offset.

Room layout from CARA coming in my next post.

[Anthony]

Here are some plots from CARA showing the room layout.

The 3D view is from the riser looking out from the corner. You can see the step down, window and sliding glass door on the right. Half wall on the left leading into a bar and the soffit hanging down over there.

The Magnepans are way too tall, but the best they had was an MG12 model, which are wider and slightly taller (still this model has them almost 6' tall, which they aren't).

But it gives a good relative relation for the room.

[Anthony]

And here's the Sabine / Ambience / Reverb calculation done in CARA:

Their automated help suggests that the reverb time is too long in the middle.

Here's a quote:

Analysis and Suggestions for Improvements:
Midrange frequencies contain the basic tones of the human voice and of most musical instruments.

This room probably contains large material surfaces such as thin, hard wall-to-wall carpeting, roughly woven curtains, and tapestries.

To increase the midrange frequency sound absorption without increasing the high frequency sound absorption, use slotted wood surfaces such as blinds, shutters, or pegboard, placing them a few centimeters from the wall, and adding a sound absorbant material between that and the wall.

Their analysis is spot on (thin carpeting -- rugs over linoleum, cloth vertical blinds, etc). There is some padding on the rug, which helped immensely with the bass a while back. Full carpeting or floating floor are probably out of the question.

And I can't move the speakers much farther forward without the Wrath of Wife, or WoW factor.

Again, all help appreciated. I've been meaning to delve into this for years and have used CARA for speaker placement a lot, but never for treatments.

[Anthony]

Okay, more self posting, but here are some pics.

First, the front soundstage.

Notice the space on wall behind the left speaker and space in the corner. Sub is not finished yet, it will be a satin black when I'm done.

[Anthony]

Next we have the back wall and behind the couch. Both wide open for use, although anything up high on that back wall will need to be semi-decorative.

Finally, I have the DVD rack in another corner. There is a lot of empty space behind the DVDs that I was thinking of making corner triangles for. They would be hidden, even if they weren't the optimum depth. Any problems with this approach?

[Anthony]

Okay, I just finished some runs (two hours) of CARA on the room design with some Magnepan MG12s and a dipole sub that I made myself. Not exactly my sub in the room or the MG10.1's, but probably close enough.

The sub results were very interesting. See the three attachments.

The measured nulls around 35 Hz (wide) and 105 Hz (narrow) show up in the modeling perfectly. Now the question is: what to do about it? The 101 Hz can be "moved" around, but when you look at other frequencies, you don't need to move much before you are in a null at 105 or 110 Hz.

The lower null is more worrisome. It's pretty wide in bandwidth and location, so I can't move out of it with seating location.

Thoughts and comments appreciated. Thanks.

Anthony

Attachments are 34 Hz, 43 Hz, and 101 Hz, respectively. Pins at listening location and sub location.