# Odd room, with modes < 20Hz whose harmonics are showing up as well



## woody77 (Aug 21, 2008)

All,

I swept our system with REW, and ended up getting a really ugly response. I did a near-field sweep of the sub as well, and it's pretty clear that the problems are almost entirely the house resonating (not just room, but house). See the waterfall at the end. The pink is the near-field response, and the blue is the 2 meter response, from the couch.

Now, a couple sins have been committed that I need to deal with, but I'll be working with my wife as to whether or not I can do them. She (rightly) expects the living room to look nice. If it was a theater room, that would be different (and it wouldn't have nearly so much stuff in it.

Anyway, here are the current problems:

1) Sub's in the corner, a corner with a slanted ceiling above it (and it slants up away from the sub).
2) Our main listening/watching couch is against the wall (same as the sub)

I'm building a new, smaller cabinet for the sub (an active linkwitz transform will handle a fair bit of EQ and make it sound "bigger" as I have plenty of headroom at our listening levels). That will be far easier to reposition.

Here, I'm looking for guidance on repositioning the sub and maybe moving the couch out from the wall a couple inches.

Our listening room is our living room, at one end of the open "half" of the house. The house is 36x24 (roughly), and the front half (36x14) is one long open space. I'll get a floor plan together later and post it. To complicate things, the ceiling is heavily vaulted (~42 degree pitch). It's 9' at the short end and ~16-20 at the other (it's not peaked, but a single angle). There are openings everywhere into other rooms (both upstairs and on the same floor).

The house's construction is late 70s california wooden frame, with open beam floors and ceiling. The beams are on 4' centers.

I'm a big fan of treating room first and getting the placement right, then EQ'ing. It sounds so much better than trying to force a bad room into behavior via EQ.

So...

How far out of a corner is enough? 3 feet? 6 feet?


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## bpape (Sep 14, 2006)

Any chance you can extend the db range or scroll down so we can see the frequency response too - both nearfield and at the seating position. Realistically, only at the seating position matters but the others may be useful in diagnosis.

There unfortunately isn't a rule of thumb for how far out of a corner. It's just wherever you get the smoothest response and best blend to the mains. One thing you can try is to have the driver face/center being a prime fraction of the room length and width (maybe 1/7 of length and 1/13 of width) Doesn't always work out to be the best but it would likely help with response - though not ringing a ton.

Bryan


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## woody77 (Aug 21, 2008)

What range do you want? I lost the nearfield measurement (somehow managed to not record them). But I saved the listening position measurements (I have 4 locations, and their average).

30dB and 5Hz? I'm on a mac, and if I try to do the full 15-200, the display goes all wonky. I can do 5-100 or so (I think).


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## bpape (Sep 14, 2006)

ideally, 20-300. You can adjust the range in REW for all 3 axes to make it all fit. You can also shorten the depth of the window down to 400ms or so which will make it a lot easier to fit. Right now, I just can't see the top of the seating position measurement to see what the FR looks like. You could also just attach the FR plot if that's easier.

Bryan


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## woody77 (Aug 21, 2008)

Ok, these are a lot clearer (I wasn't paying attention to the FR, as I already had that, but you guys don't).

Here's a 300ms and 600ms waterfall, showing 11-200 Hz (the generated data from my sweep is only 10-200 Hz).

This room mode calculator:
http://www.bobgolds.com/Mode/RoomModes.htm
using 36,15,15 shows some of the peaks that are sustaining in these graphs.

The final graph is an average from 4 different places in the room (all 6 feet apart or more, two on opposite sides of the room from the sub) vs the frequency response of the single listening position in the waterfalls. (red is the single position, green is the average).


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## bpape (Sep 14, 2006)

What are the subs? Looks like an overall loss of energy starting about 35Hz except for a hump at 20Hz. BIG dep at just under 30. Try playing with the prime fraction thing and see what you can do. Realistically, in a room that large, I'd want 2 subs, 1 front and 1 rear but not sure that's going to happen. 

As for decay times, you'll find that while they're likely still long, they'll be much more tolerable the farther you can get from that wall behind you.

Bryan


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## woody77 (Aug 21, 2008)

The sub is an Image Dynamics IDQ15 d4 v2 in a ~ 6cu ft enclusore, fully stuffed with fiberglass. It measures out via impedance as a Fsc = 34.5Hz and a Q of .567. A nearfield measurement with both a radioshack spl meter (accounting for the curve of the meter) and the ECM8000 both agree with that assessment.

I think it's less of a falloff in output than it is that much resonance from the corner loading of the room. The ~40Hz tones (synth bass hits, for instance) make the entire house resonate with it (kitchen, upstairs bathroom shower, hall that's alongside the living room and open to it in two places, etc).

I'll move stuff around tonight and see what I can find with the sub position and the couch.


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## woody77 (Aug 21, 2008)

This is from about a year ago, with it in a very different location in the room. The driver was about 3' out from the wall, facing into the room, and it was near the boundary between the living area and the dining area.

I can't put the sub there now (exactly), due to a re-arrangement of the furniture in the room.


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## bpape (Sep 14, 2006)

The curve there is very similar to what you're getting now. A broad dip around 30 and a hump around 20.

Looks like either the 48 or the 65 is what you used to have around 58 but different interference pattern now - and you've picked up the other null.

Bryan


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