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In Reply to: RE: David Aiken posted by Jolida on June 27, 2009 at 00:40:49
The tube traps should ideally go floor to ceiling, or as close to that as possible, in your room's 4 corners. You could stack the 13" ones in the front corners and the 9" ones in the back corners or simply stack a 9" on top of a 13" in each corner. I have no idea which approach would be the most effective but the corners are where you'll get the most effective bass trapping results.
You could consider using some of them to absorb first reflections but ideally you'd use panels at least 2' wide for that kind of purpose. Because of their width, the 13" tube traps would be the best option if you were going to use traps for early reflections but they are also the traps that will give you the best bass absorption and you'll get that from them in the corners. Basically I'd use tube traps in the corners only since that's where they'll make the biggest effect.
As for speaker placement there's lot's of different approaches and they can yield very different presentations of the sound. In addition, some work better in rooms with different proportions and some result in placements that are fine in a dedicated room but likely to result in relationship problems in a living room. Finally some speakers are designed with particular sorts of placement in mind so one should always pay some attention to the speaker manufacturer's recommendations, especially when those indicate things like minimum or maximum distances from walls. You can often get good results closer to a wall than recommended if there is some absorption at the first reflection points but placing them further from walls than recommended may result in the bass rolling off early if the placement recommendations are based on the speaker getting bass reinforcement from one or more walls.
Take a look at the Asylum's FAQ for info on a range of approaches to speaker placement. In general near field or similar setups such as the Audio Physic method which have listening positions relatively close to the speakers and the speakers placed significant distances from the walls resulting in reflection path lengths 2 or more times the length of the direct path will tend to minimise room influences which can be very useful, but will also result in more of a "front row" perspective which some people don't like. These approaches are also more likely to cause problems with insufficient bass.
So I'd suggest a bit of reading on the various placement methods and some consideration of how well each of them matches up with any recommendations your speaker's manufacturer makes and how well the placement will physically work in your room. Make a shortlist of the methods that will work best in your room and do a bit of experimentation to find out which one gives you the kind of presentation you prefer most.
David Aiken
Hi David.
Thanks for the reply. One thing i would like to ask.
I have bought an SPL meter & the Rives Test Cd 2. I have plotted the room response & found some peaks & nulls. My main concern is, HOW DO I FIND THE AREA thats causing these peaks & nulls. Only when i find the Area of Problem, can i treat it right??? For eg. my plot shows a 7db boost at 800Hz. How do i treat this frequency boost & where???
If im able to locate the area in the room thats causing a peak, its makes everything so simple thereafter. Please help...
Room modes are mostly caused by sound reflecting and resonating between 2 opposite surfaces like the front and back walls, left and right walls, and floor and ceiling. They are at their strongest wherever 2 surfaces intersect which is why it's recommended that you put bass trapping in the corners of the room—that's where the walls intersect and by treating the corner from floor to ceiling you also treat the places where 3 surfaces intersect, the 2 walls and either the floor or the ceiling.
800 Hz is probably too high to be a room mode. Room modes are usually only a problem up to 300 or 400 Hz or so and if you've got a 7 dB room mode at 800 Hz then I'd expect there to be stronger resonances at other frequencies such as 400, 200, 100, 50 and 25 Hz which are in octave relationships to 800 Hz.
Another reason why I doubt it's a room mode is because the wavelength of an 800 Hz tone is only 1.4', around 17", which is far too small to be a normal room dimension. If you've got 2 parallel surfaces that far apart—say a cupboard that far from a wall—you may be triggering a resonance between them, especially if one of the surfaces is prone to vibration, in which case moving one of the surfaces should solve the problem but you won't have 2 actual room surfaces that far apart. You may have a cupboard that deep or wide in which case either sealing it so sound can't get in, leaving it open, or filling it with some kind of absorbent material like cushions or clothes, may solve the problem.
Alternatively the cause could be some object in the room which resonates at 800 Hz. If you can find an 800 Hz test tone you can try walking the room and listening for the point where the sound is loudest and see what objects are there and removing them from the room one at a time. The resonance should disappear when the object causing it is removed. Once you know what it is you may be able to find some way to damp its resonance and return it to the room if you want it there, otherwise simply place it somewhere else in the house.
On the other hand it could be a fault somewhere in your system. If you have a portable music system of some sort, I'd put that in your room and try playing your test signal on it. If you still get the problem when the tone is being played on a completely different system and speakers then it's something in the room. If the problem goes away then it's something in your system.
David Aiken
I cant thank u enough. You have always been of great help to all of us. I will surely follow your procedure tonoght when i return home & post a follow-up. So u mean i must play the offending tone on 'repeat' & walk around the room to see where it is the loudest?
Thaks a million for the time you take to help us..
God Bless
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