Room treatment prior to sub EQ & integration with mains

[HMenke]

As some of you know, not too long ago I got a Behringer DSP1124A Feedback Destroyer Pro to EQ my Paradigm PS-1000 10", 150W sub. The result was that I ended up (with the help of the folks on this forum) replacing the Paradigm with a high-performance DIY ported sub.

Now I am in the process of dialing the new sub into the room and integrating it with the rest of my system. This is the first time I have tried this, so I don't know the best approach. The trouble I am having is upper bass room modes that I can EQ for the sub but not for the mains. I end up having to fudge the sub EQ to compensate for excess gain from the mains at certain frequencies. It is possible to do but awkward (measure, adjust, measure). The last attachment is the best I was able to acheive for a combined sub/mains EQ. The sub level is higher because that is my preference.

I read Thomas' new introduction to subwoofers regarding the need to treat the room before attempting to EQ. To that end, the first thing I have done is to calculate the room modes. I find strong axial modes at 38 Hz and and two close together at 77 and 78 Hz. These manifest themselves as listening position peaks in the measured sub response. There is also an axial mode at 52 Hz, which seems to manifest itself as a null at 26 Hz at the listening position. A tangential mode at 94 Hz seems to be the source of a sharp listening position null at that frequency for the sub.

I am ready to attempt DIY bass traps to alleviate these conditions as much as possible, but I am seeking guidance as to how many / what size / where to place them.

In reading through several posts, I also gather that is is harder to integrate ported mains with a sub, than to integrate sealed mains with a sub. My L-R mains are early (soft-dome) Paradigm Mini-Mk III ported monitors and a soft-dome ported Paradigm CC-300 center. These have extension down to 40-50 Hz. I have been closely studying the Natalie P as an upgrade to this system, but I am wondering - if I build them - can they be made sealed and is this advisable with respect to sub integration?

Henry

[---k---]

Check out this website, I find it to be the most helpful:

http://bobgolds.com/

You will want to build something to straddle a corner out of rigid fibreglass, such as Owens Corning 703. Thickness is your friend. The more thickness you have, the more effective your absorber will be - both in terms of amount absorbed and the depth of frenquecies absorbed.

The more you can put across the corners the better. Wall to ceiling also counts as a corner, but not as effective as the wall-wall-ceiling corner.

The best suggestion I can give you, is buy a box of OC703 for <$100 and experiment with placing the raw peices around your room and see what effect it has.

Also, check out: www.readytraps.com . Very simple solution that is cheap.

[ThomasW]

I don't think the subwoofer alignment makes much difference with regard to integrating with the mains.

When possible centered between the mains or as Bosso pointed out, stereo on axis with the mains makes for the easiest integration. Obviously that's not an option for most people.

You can certainly build any of the ported designs (NatP, Modula MTM, etc.) as sealed boxes. Doing so doesn't buy you anything, since the XO point is always much higher than the port tuning.

The way to test for bass traps is start by putting the meter in the corners and measure the peaks there. Building traps to kill those peaks will help even out the in-room response.

The deal with traps is of course the bigger (taller and deeper) the better. Might look for a supplier of the preformed fiberglass duct insulation and whip up a few column traps using those for experimentation.

[Valorum]

I'm very interested in doing this as well. I tried to reserve some room in my budget to try the Owens Corning stuff. I'll be watching this thread!

Henry - What software did you use to generate those diagrams of the room modes?

[HMenke]

Valorum, it is called Room EQ Wizard. It is freeware, designed by a genius in England named John Mulcahy. It is extremely well-documented but there is a bit of a learning curve. Mostly you need to learn in what order to perform what operations.

https://www.roomeqwizard.com/

You'll need, at a minimum, a full-duplex sound card (in/out simultaneously) and the Radio Shack SPL meter. It seems most laptops (like mine) don't have the right sound card installed, so I bought this external USB model for very reasonable cost: http://www.soundblaster.com/products/mp3+/

[Valorum]

Ah, cool. I did read about RoomEQ Wizard and want to use it (to help with my BFD once i get my stuff going). Didn't realize the room modes stuff was built in

[ThomasW]

Didn't realize the room modes stuff was built in

Those are from a room mode calc website. They're not a part of Room EQ Wizard.

http://www.mcsquared.com/metricmodes.htm

[Valorum]

Ah, thanks. Now i gotta learn how to interpret the results and what to do about 'm. Which is what Henry is asking about, right?

[ThomasW]

The various modes are interesting to know, but making actual measurements with EQ Wizard is going to provide a usable frequency response plot.

[dyazdani]

The various modes are interesting to know, but making actual measurements with EQ Wizard is going to provide a usable frequency response plot.

And if you're planning on making the panel type absorbers with 703, etc - they work in more of a broadband sense - i.e. not attacking any particular peak frequency.

[HMenke]

Those are from a room mode calc website.

Oh yes, sorry I misinterpreted the question. The diagrams come from the source Thomas referenced; they're static pictures and only the data is dynamic depending on your dimensional input.