Planar speakers in middle of room

[grawk]

big boxes stuffed with blankets or newspapers in the corners

[Dusty Chalk]

That's true too -- I rearranged my room so that the corners were actually taken up by large, heavy objects (bookshelves and dressers and record shelves and whatnot), that actually will help some. If you make the corners into more, lesser corners, that's a good thing.

But in my case, I'm also a bass-head, so that helped, too. You could try hitting yourself in the back of the head with a shovel.

[grawk]

Outlaw ICBM-1 ICBM Bass Management Active Crossover - eBay (item 200349178954 end time Jun-10-09 19:44:20 PDT)

That's how I'd deal with integrating a sub into your setup

[Fitz]

Another finding: depending on how I have the closet open (two sliding doors), I can get a significant increase in decay of the standing wave, although still far from ideal (instead of being 10dB down at a given point, it's up to 20dB down). It's actually two waves somewhere between 30Hz and 40Hz, because I remember I found some configurations where I got the massive peak to collapse into two narrow peaks (as measured on the waterfall plot, frequency response still has a big hump in that range); I'll make note of what they are on the next round of experimenting, I think one matched up to the axial mode in the direction the speakers fire, the other didn't have any obvious correlation (note to self: measure the distance of the short passage leading to the hall and factor it into the width of the room).

Unfortunately the effect of the "closet bass trap" was strongest with the speakers further back beside the TV, which doesn't image as well (it works like a massive baffle blocking reflections, rather than with the speakers forward where they can reflect off the stuff behind them and the TV itself), but I'm not giving up yet. I might try taking both doors off and seeing how that effects it. I wonder if the cavity is working like a helmholtz resonator, or just altering the room dimensions enough to attenuate the standing wave. Taking both doors off should provide some insight into that, hopefully it's the latter and I can just leave it that way with my AKG banner serving to hide the messy contents.

Edited June 9, 2009 by Fitz

[Dusty Chalk]

According to Ethan Winer's site, your resonances are at ~43Hz & ~40Hz (based on 13x14), which seems to be at least close to your findings. You ought to measure your room more carefully. If there's a mode at 565/(width of room + depth of closet) with the doors closed, then you'll know that the closet doors are acoustically transparent.

[Fitz]

Doing further experimenting and looking more carefully at the waterfall plots, it looks to be several closely spaced peaks and dips in the ~30-40Hz range, usually with 3 or 4 fairly evenly spaced peaks, but occasionally one larger peak or dip. The biggest one seems to always be between 36-38Hz. I do get one showing up sometimes at 40-41Hz, and occasionally a very minor one at 43Hz. Haven't gotten to making additional length measurements yet to see how these match up to the room shape, but the size I quoted before was a rough estimate which I now think is probably off.

I actually haven't been able to reproduce the same results I was getting before wrt to opening the closet door though, so perhaps I was getting a bit loopy after messing with it so long and misreading something. That's not to say I'm not getting any results, actually quite the opposite. I've loosened the hinges enough that I can take them on and off in just a couple minutes, and tested two speaker positions with no doors, both doors closed, left side open, and right side open. So far having no closet doors up gives the quickest decay and more spread out, narrower peaks. Having the right one open performed the worst in both positions, and the left one open or both closed ranked differently between the two. Happily, the position with the speakers closer to a more normal spot gives the best result of the two I've tested.

For reference, the bass frequencies in the 30-40Hz range hit between 75-84dB with the fullrange pink noise being set at 75dB, with the average level higher in the first test position. With no doors and the second test position, the highest peak in that range after 400ms is at 56.1dB, compared to 65.7dB with both doors closed. The frequency response is damn near identical regardless of the doors' presence except for a couple dB rise or dip in the midbass and treble (less than what happens from moving the speakers an inch or changing toe-in), so there appears to be no real negative effects of removing the doors, just the more rapid bass decay.

Gonna save these measurements this time in case I want to reference them again, and proceed with changing speaker placement with the closet doors off. Since I'm getting much better results from this position than I did before even with the doors closed, I suspect I may have hit a good spot by chance, so I'm going to mark it and work from there. It looks like I'll still need a bit of eq to smooth out the rest of the spectrum in this arrangement though, at least until I have the time/money to make or buy some bass traps to do it the right way.

[Dusty Chalk]

Well, 37Hz correlates to 15.27 ft (The same formula works both ways: freq == 565/feet; feet == 565/freq.), for whatever that's worth.

If the closet doors are acoustically transparent, then you should get two peaks, one at (width of room), the other at (width of room + depth of closet). That'd be my theory, anyway. In reality, there's probably a bit of "both" going on -- some acoustic transparency, some reflection. Maybe even some absorption.

The theory behind Ethan Winer's bass traps is that it absorbs some of the frequency on the way through, but then a significant amount more on the way back out (after reflecting on the wall behind it) -- which is where the tuning is. I'm almost wondering if there is an optimal place in your room to put something large, heavy, and solid (like at the halfway point?) that might help? Or is that where your speakers are? Maybe you should try putting them off center? Or at least angling them, perhaps? If nothing else, you'll learn something, even if it's an arrangement that you can't live with.

PS You also want to measure the height, there's another mode there. It's usually taken care of by carpeting, but sometimes it's an issue. Heck, you may have just indirectly measured your room, if you find three primary modes.

Edited June 10, 2009 by Dusty Chalk

[Fitz]

Heh, yeah, now that you mention it since they are interior doors it's just two thin wood panels with an air gap between them, so it could be doing all kinds of crazy stuff at low frequencies. I think I'm gonna try them out with how I have it now, as I applied the bass cut to 25Hz and below which gave another small improvement to the decay, and used the good old sledgehammer that is EQ to smooth out some of the smaller frequency imbalances caused by this placement. Oddly enough, tuning both separately to be relatively flat does not cause them to suddenly become very irregular when played simultaneously (e.g. centered sounds), as is usually been the case when I've played around like this with box speakers in this room before.

I'm gonna give it a listen and see if I can control myself long enough to listen to it for a few days before messing with things. Thanks for the input though, all this talk of basstraps got me to look at the room shape again and mess with the closet doors like that. If this sounds good, then I can start looking at more reasonably sized traps to deal with the other issues.

[Dusty Chalk]

Yeah, definitely give yourself a few days if you can.

And sorry if I totally dominated this thread -- I am by no means an expert, and hope I didn't drive anyone else off who may know more than I. It's just that the topic material interests me.

[Fitz]

Oh fuck me this sounds good. I mean like, it's not a subtle or incremental improvement, it sounds completely different now. These speakers have absolutely no right to sound this good being in a nearly square room and too close to the listening position. Initially I wasn't impressed, but as I continued to listen it became apparent all that fuzzy background mush was gone. Soundstage is much smaller, essentially that of the middle of my room, but I think the resonance was just creating the illusion of it being bigger before. Imaging is vastly better; electric instruments have a kind of ambiguity to their precise location, but acoustic instruments and vocals are right fuckin there. I had to make myself turn it off because it's getting late and I don't wanna wake the dead, so I didn't get to test it much with rock except one song. It might be a little more unforgiving on a lot of rock or metal with the lack of any bass boost now, but these things are definitely not bass light even with the stuff done. I was listening to some of a Rachael Yamagata CD I found laying around, and I was in a tranquil state as a fairly slow and gentle song faded out, then when the kick drum started off the next track I damn near jumped out of my seat. No lack of impact for sure.

[Fitz]

Yeah, definitely give yourself a few days if you can.

And sorry if I totally dominated this thread -- I am by no means an expert, and hope I didn't drive anyone else off who may know more than I. It's just that the topic material interests me.

Yeah dude, it's fine, I'd rather have someone dominate the thread than it wither and die with me being the only one posting. I talk to myself enough as it is.

[Fitz]

And just so everybody can laugh at my ridiculous nearfield speaker placement situation:

To give some idea of scale, that's as far away from the speakers as I possibly could get to take the pictures (check out the craptacular barrel distortion!). It's an absolute disaster on the other side of the speakers right now too. I still haven't even gotten my headphone rig hooked back up, or taken down the old shelves I put above where I used to have the workbench.

[swt61]

I have the same syndrome, TMSTLR.

Too much shit, too little room.

[Fitz]

Yeah no kidding. Especially once you start moving furniture around like this, you wonder where the hell all this shit came from.