[youngho]

I asked this question on AVS forum but thought I'd also ask here:

Given the price of real estate in the Boston area, my wife and I have idly discussed buying an inexpensive suburban lot and a prefabricated home, like the LVL house linked here. Page 9 of the brochure (linked here) shows a possible configuration for the basement, which would allow for easy Dolby-suggested speaker placement and the use of a front projector, as the ambient light level would be easy to control. I don't think that I would be able to use room 2 due to anticipated uses for that space, but room 1 would be available. However, the square shape of room 1 and the concrete walls would present many challenges. I was wondering what people thought about the following ideas to address the problems related to the shape and concrete, assuming that the front of the room 1 would be the bottom on the floorplan, the door would located about 2/3 of the way back with walls extended to meet it, and the walls would be constructed with fiberglass behind the drywall:

1. Speaker setup to approximate the Dolby-recommended angles, take some advantage of mode cancellation, but not be too awkward:
   A. The front three speakers in a line located 1/8 of the distance from the rear wall to the front wall, with the L and R speakers 1/4 of the distance in from the side walls.
   B. The side surrounds located midway from the front and rear walls and moved in about 1/8 of the room width.
   C. The rear surrounds located about 1/8 of the distance from the rear wall and 1/4 of the distance from the side walls
   D. Two subwoofers located at the midpoint of the front and rear walls, as suggested by the Harman paper.

2. Listener setup with two couches, one in front of and the other behind the center of the room in order to avoid locating listeners in certain nodes and antinodes so that the peaks and nulls wouldn't be so bad.

3. Front- and sidewall first-reflection treatment with 6-8 of Ethan's Mondo Traps (www.realtraps.com, or an approximate DIY product), which would be turned sideways, so that each is now 2' tall and 4'9" wide, and mounted at the listening height. Actually, would there be any disadvantage from making an almost continuous layer of sideways Mondo Traps running at listener height around the periphery of the room, budget permitting?
   A. Two placed adjacent to each other at the middle of the front wall
   B. Two placed adjacent to each other at the middle of the real wall
   C. Two or three placed adjacent to each other on the front and rear walls

4. Floor and ceiling reflections with carpeting as the first stage, then later making a fiberglass "cloud" on the ceiling by suspending a layer of cloth-wrapped fiberglass panels

5. Bass treatment in two stages, depending on budget
   A. Four stand-mounted Mondo Traps located in each corner or
   B. Soffit Traps around the periphery of the ceiling, though this would probably have to wait

6. Parametric equalization for bass

Would these ideas be anticipated to make a reasonable-sounding room, or would everyone still expect it to sound pretty horrendous, anyway? Thanks!

Young-Ho

[ScottMayo]

23'x22.1' (x 8' I presume) is a nightmare. Build a false wall in so that it's 23'x19.5', and it's a less of a horror show. You'll still need traps and carefully planned positioning, but putting up a 3/8th" plaster wall will be cheaper than the massive number of traps you'd need to tame the huge modes at 50Hz, 100, 150, etc. You'll still need traps, but it will be less of a problem.

[youngho]

Thanks for your reply.

Will a 3/8th" plaster wall really reflect bass well? Wouldn't a significant amount of the low frequency energy will pass through and reflect off the concrete?

In terms of the problems with the modes, I had wondered whether the dual subwoofer positioning suggested in the Harman paper would help address many of the problems related to all bass modes related to the length of the room and odd-order ones related to the width of the room. I had hoped that mode cancellation related to the multiple loudspeakers would help with the modes above the low bass region (for example, wouldn't having the mains and rear surrounds at 1/4 wavelength distance from the side walls mean that they wouldn't excite the 100 Hz modes and up?). That would leave the 50 Hz peak, which might be amenable to parametric equalization, meaning that listeners off center might experience a relative null in this region, but that would be acceptable.

I know theory and practice are two different things. Is it almost impossible in reality to get a square room to sound reasonably good?

Young-Ho

[bpape]

The Mondo's are very nice for bass control.  They'll work best when mounted in the corners.  For the front wall and reflection points, you want something soft and fully broadband.  You can DIY something from cotton, fiberglass or mineral wool, purchase Ethan's Mini-Traps specifying mid-high, etc.

[ScottMayo]

Thanks for your reply.

Will a 3/8th" plaster wall really reflect bass well? Wouldn't a significant amount of the low frequency energy will pass through and reflect off the concrete?

Some will - but if you insulate in there - and it often makes sense to insulate basements - a good part of the energy is eaten. You want that to happen; putting up thicker walls will hold more bass in, but then you have to dissipate more energy inside the room, where it's uglier and harder.

In terms of the problems with the modes, I had wondered whether the dual subwoofer positioning suggested in the Harman paper would help...

It depends on your goal. If you're goal is to have things sound good at one position and one position only, then you can get good results with one sub and better results with two, though it takes work in both cases.

If you want things to sound good for several listeners, though, then the number of subs is less important than how the room deals with the bass. Two subs are still better than one, but if the room just echoes the bass from wall to wall, any positioning trick you do to improve things at one position, makes another worse. That's not less true as you add more subs - in fact you can get wilder modes with multiple sources.

I say it all the time: if the room is well behaved, adding gear can do wonderful things. If the room is badly behaved, throwing more gear at a problem can only succeed in making things better at a single position, and worse everywhere else. And that's if you're lucky. Develop a room treatment plan, and *then* decide if you want to bulk up on extra drivers.

I can draw up a plan for you, but I charge. See my website for details.

[youngho]

Thanks for the replies! I thought that ten (!) Mondotraps, careful placement and planning to take advantage of mode cancellation, and parametric might make even a square room with concrete walls sound okay. Floyd Toole's example of a 8x16x24 room in the third Harman white paper on rooms and loudspeakers had suggested that it was possible to do so with a dimensionally challenged one. I'll wait and see how the real estate market looks in a little more than a year.

Young-Ho

[ctviggen]

If you can wait, I'd wait.  They're calling for decreases in housing prices in some markets for the first time in a long time.