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I'm finally about to start working on my music room in the new house, and am thinking about the acoustical treatment for the wall directly behind my head. My speakers are all planars (QUAD ESL, Tympani, and Eminent Technology), and the wall 5' behind them will have diffusion (racks of LP's, CD's, and books, plus perhaps some GIK panels). The opposite wall 13' away will have the listening couch right up against it, so my head will be only a foot from the wall. I'm thinking that for such a close distance, absorption (like Owens Corning 703 panels covered in fabric) on that wall would be preferable to diffusion. Agree or disagree?
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Sofa cushions and upholstered throw pillows. Works well and you can probably find some laying about the house to start with. At least for experimentation.
Note that sofas and futons are bass traps/absorbers so you don't really want that right where you listen - put those in a more strategic location in the room where they do the acoustic job if you need it.
Great, thanks guys. I'll look into those products. Here's another question, regarding the wall behind the speakers: there is a 4' x 4' window dead center on the wall, inset 5", with curtains covering it. I'm thinking of installing a flat screen in the window sill, closing the curtains when not using it. I'm also thinking of making new curtains out of acoustically appropriate material, to minimize any sound quality penalty of such an arrangement. Are there materials available specifically for such a purpose? A material that will block sound from reaching the screen, and from reflecting off it. In other words, acoustically non-transparent, and either absorptive or randomly reflective. That sounds like a tall order!
Edits: 01/28/17
This is not so much of an issue as the seating location is. It doesn't sound like a problem since it's centered, and more importantly not a deep space. Some people have problems with cavity resonances due to a fireplace or, less likely, a deep bay window on the front wall behind the speakers. If the flat screen is at listening height and set flat against the front wall in the window space with some curtains drawn in front of it, don't worry about it.You don't say, but if you have any asymmetrical door openings on one side and/or behind the speakers, you've got a bigger problem, as that will significantly shift the sound stage to the opposite of the opening unless you can close it.
If you think you're going to spend time with speaker placement, I'd advise buying a cheap USB mic and downloading a copy of REW to a laptop and measuring things. If you're limited by room layout, don't bother and enjoy.
Good luck!
Edits: 01/28/17
Thanks Barry. Nope, no doors in the wall behind the speakers (or in the side walls, except for the room's entrance door, located at the back right corner), and I have 9", 11", and 15" ASC Tube Traps (13 in all) for the rooms corners. The wall space behind the listening position is 5' wide, with a 28" door on either side (one to a bathroom, the other a closet), and then 2' more on the other side of each door. The 5' space absolutely, as you said, needs absorption (I'll be mounting 4" thick 703 there, two 24" x 48" pieces. I'll space then 2" from the wall, for more low frequency absorption. Thanks for the tip!). I wonder if I should mount a 703 panel on each door on the back wall as well, or the 2' wall expanses on either side of them?
I'd listen first or you'll end up like me. A lot of extra traps. I've been thinking about putting some of the extras in the bathrooms. I like it quiet in there....
Barry---I have that many Tube Traps only because years ago (the late 90's) a guy advertised them in the L.A. weekly newspaper The Recycler for ten bucks apiece. I got over to his place, an empty house, and there they were---two 15", four 11", and seven 9". In three different colors---black, charcoal, and oatmeal. How could I not buy them all?!Watts---Six feet from the listening position seems awfully close for a six foot tall, four foot wide speaker, but maybe I WILL try it. Thanks for the suggestion! The two bass panels of my Tympani T-IV's will be separated from the m/t one, and the m/t may end up being the only one that close.
Edits: 01/29/17 01/29/17 01/29/17
Look at Josh's experiments with placing his TIVa in his small room.. It is what we refer to as the reverse split configuration where the bass panels are ahead of the M/T panels. It is also the current setup I am experimenting with. That alignment provides time alignment to the mids with the bass as the bass low pass has a group delay equivalent to about 2ft of offset. It works very well for imaging but is not great for bass consistency since the crossover is not designed for it, it is designed to be in phase when there is further delay with the M/T ahead or at about the equidistant placement.
The IV-A woofer network has a two foot electrical delay???
Dave.
I calculated that out for my xo where the delays are different, but the OEM XO is 3rd and 1st or 4th and 2nd depending on which model and spaced by a bit so the bandpass delay difference is roughly on that order - perhaps more like 18", worth.
Yeah Satie, 3rd order LP @ 250Hz, 1st order HP @ 500Hz. 18" will be great, and I assume that is true whether the bass panels are in front of the m/t or visa versa? Should I reverse the polarity of one or the other? I figure on trying the bass panels behind the m/t ones first, so they don't block the sound from the m/t as they would if they were in front. The bass panels will be very close to the side walls, as I have only 14' 4". I will then position the m/t panels for best imaging. I will also try your equidistant panel positioning, the three panels in a concave shape. Didn't you state you use 1st order filters for all panels in that arrangement?
Edits: 02/01/17
That equidistant only works for symmetrical crossovers - and best with 1st order. I also tried 3rd and 4th (LR).
With OEM XO the equidistant arc works well but does not produce quite the same image precision and the bass is just in phase.
In the normal split config taking the bass back requires flipping its polarity to regain in phase (but not time alignment), And with the reverse split with the bass forwards you flip phase (IIRC, if that does not work then flip back) and you should be in time alignment in the pass band - but not in all of the crossover region - you can fine tune a bit to get better imaging or more uniform upper bass/lower mids..
My Tympani's are T-IV's, not T-IVa's. The a and non-a crossovers are different, therefore I believe requiring different distances between staggered bass and m/t panels. But then I will be bi-amping with an outboard x/o, so the relative panel locations will have to be matched to the frequencies and slopes used. I will be retaining the Magnepan x/o characteristics, trying the split panel set-up pictured in the T-IV manual.
Edits: 01/31/17
As usual, Satie's comments are confusing.
The IV-A and IV crossover are different in that a delay network is used in the high-pass section of one.....but not in the low-pass.
However, he mentioned the low-pass section (apparently on his speakers only) adding a 2ft electrical delay.
Dave.
I'm confused alright, but I attribute that to my lack of technical knowledge. Like they say, a little bit of knowledge is dangerous thing! Another apropos expression is "I know enough to get me into trouble, but not enough to get me out". I'll be doing some reading (going back years here on PSA) as I try different set-ups and x/o settings.
You can take the delay figures from Neo's spreadsheets it is inside the calculation portion - aim at matching the relative delays of the mid an octave above the HP and bass an octave below the LP to the driver offsets.
Or you can use the magnepan suggested offsets for the staggered configuration as the guide and use the same offset when putting the bass panels ahead of the mids.
Thanks Satie. Above you differentiate between reversing the phase and reversing the polarity, in regards to bass panels in front versus in back. Reversing polarity I understand (swapping red and black speaker cable leads to both subs), but not phase. Could you explain for me?
I am talking about aligning phase vs. aligning the drivers for time coherence. and I don't remember what the OEM polarity should be so I suggested to flip it so that you hear it in both polarities. IIRC the staggered positioning from the maggie manual requires flipping the polarity to compensate for some 60-120 deg phase difference turning into 180 deg at some portion of the XO range between 250hz and 400 hz and thus a big dip in FR at a critical portion of the F spectrum. That since the 2'ish ft offset of the bass in back introduces another 1/4 wave of phase.
That as opposed to time alignment (bass ahead) where you are reducing phase by that same 1/4 wave. In this case you risk having a lump in the FR at the lower mids or a suckout when polarity is reversed.
Thanks Satie, I know just enough to now understand! I'll be trying every configuration possible---the standard Magnepan panel alignment and x/o settings; your equidistant panel/1st order filter arrangement; bass panels behind m/t and visa versa, with the Magnepan x/o settings. The T-IV manual does not include related info for split panel operation, but the T-IVa manual does, I believe.
This is why I got myself a First Watt B4 crossover, which will do pretty much any textbook filter you need (in 25Hz increments). Fun awaits me!
Absorption is the only way to go if your seating position is that close to the back wall. It's a major improvement.I like GIK and Real Traps panels with Guilford of Maine fabric options.
Also, Real Traps makes a Post Base panel wall mounting system that places the panels 4" out from the walls substantially increasing their lower frequency effectiveness and their WAF. If that's too far out, or too unsightly, you can cut the bracket in half, mounting them 2" out from the wall. These brackets should work with either company's panels as long as there's an RT mounting bar attached to the panels.
Here's a link to the RT site showing what I'm talking about:
http://realtraps.com/mini_door.htm
Edits: 01/28/17
mounted with 2" spacing (these are 2" thick panels, (you'd ideally want 4" and 2'x2' not as large as these), mounted at least 2" out from walls if you can. This shows side walls, but works exceptionally well behind your head.
You absolutely need thick damping there. No pillows necessary to determine this. It'll sound like crap otherwise. You're sitting in a wall boundary mode with lots of bass gain, so the thicker the panel and farther the wall mounting distance, the better.
The usual recommendation is really thick absorption behind your head. It's too close for a phase grating diffusor. A polycylindrical diffusor might work, and it could be be combined with absorption . . .
I'm in the same boat, BTW, but haven't experimented yet.
Thick to lower the effective frequency range, right Josh? OC 703 comes in 2", 4", and 6" thicknesses, and I was thinking of using 4". Perhaps 6" would be better---bass frequencies really build up along floor/wall/ceiling intersections.
Exactly. Which is important because depending on how far you are from the wall you can get some bad midbass nulls.
Why do you need to be right against the back wall? surely you could pull the seat out 2' or so and be 6' from the speaker plane?
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