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How Flat is Flat?

I have been trying to optimize speaker placement in my small, dedicated room for the past couple of weeks. I started out by calculating all the theoretical "best" positions following the advice on the Cardas Webstie, the Rule of Thirds (and fifths, and ninths) AND multiple iterations with the RPG Acoustics software. For each possible speaker/listener location, I measured Frequency Response using the Radio Shack meter and several test CD's, and conducted extended listening tests with a variety of music. Leaving questions of soundstagingf aside, I can't get very flat response regardless of where I place the speakers/seat. Response is flat (+/- 3 dB) above 100 HZ and from ~ 40-45 Hz, but plagued with problems in the 50-80 Hz range. The "dip" is in the range of 6 to 15 dB, with the worst frequency being ~ 60 Hz. I have used the SGHT Excel spreadhseet to calculate the room peaks/nodes, and there shouldn't be any nodes at this frequency at any of the seating positions I have tried. I am pretty certain it's not the speakers (SF Guarneri Homage), since they measure flat in an anechoic environment. The room is 14 ft long, by 12.75 ft wide by 7ft9inches long (dimensions chosen using the SGHT spreadsheet based on the fixed height of my basement ceiling). I have minimal sound treatment at this stage (RPG foam at the reflections points, RPG Diffusers behind the listening position, Corner Tunes at the top and bottom corners behind the speakers). My questions is...is it desirable to do better, or am I just being REALLY anal? If desirable, is it possible to do better? How (short of getting a Sigtech or similar)? Would also appreciate any comments on the best scheme for speaker positioning you've tried. Anyone have experienve with the RPG software? The Cardas-based set-ups sound good..but the bect sounding one is VERY awkward even in a dedicated room! AlexC
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bagwell
20 posts
 
Read the most recent TAS and you will find 3 or more references to the Sigtech. My experience suggests that you will not be able to reach a flat response without the Sigtech. Its a remarkable component that I would not be without. No system is complete without a room correction device. And I say...it's the room man, it's the room...and the Sigtech will do the trick.
greysquirrel
62 posts
 
I think Carl is right. Just moving the speaker/listening position and absorbing/diffusing first reflection points will not smooth out the low frequency response. For a given room dimension there are optimal locations to reduce the peaks and valleys, but you'll still have peaks and valleys. You smooth out those peaks and valleys by absorbing low frequency standing waves (most effective in the corners of the rooms since this is a common node for all frequencies and foam won't absorb deep enough nor flat enough). This really doesn't get rid of standing waves, it just reduces the amplitude/decay of those waves, hence smoothing out the peaks and valleys you measured. Tube traps are excellent, though a little salty. I'm building my own, based on F. Alton Everest book, "Master Handbook of Acoustics". I'll let you all know if they are effective when I'm finished. Good luck, Greysquirrel
sol322
426 posts
 
Real world rooms get into our audiophile ways of getting the best sound for us to enjoy. The closer you are to ideal ratios in room dimensions the better !!! Depending on cost (and if you are allowed depending on where you live) or how skilled you are you can modify one of the dimensions with sheetrock to get better ratios according to accoustics (using closer supports than normally recommended for added rigidity). This way you won´t need that much accoustic treatment and in the end if you need to add it, the task will be simpler, this is best if you own the dwelling. Regards
onhwy61's avatar
onhwy61
5,217 posts
 
Yes you're being anal, but hey, who visiting this site isn't. A suggestion for you -- place your speakers/listening chair asymetrically. Most text will preach a symetric setup. Without it tonal balance and imaging will suffer. However, sometimes an off center setup will actually improve the tonal balance by eliminating overlapping standing waves. One word of caution, don't overdamp your room. The first (and maybe the second) reflection point(s) are critical, but in general live rooms sound more natural than damped down rooms. Good Luck!
carl_eber
1,425 posts
 
Personally, if I had to use no room treatments, I wouldn't set up asymetrically, but would diagonally (going from a 45 degree angle out from a corner in the room). I've done that many times in different rooms, and it always works pretty well (with the necessary experimenting with placement). Both imaging and bass are terrific this way, especially in a setup that is closer to "nearfield". In the end, the symetrical arrangement with first reflections damped, and bass traps in the corners, is always best, however. And the second best way is in the nearfield, out in the middle of the room, with no walls near the listening seat, or the speakers.
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