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In Reply to: Polarity posted by Peter Gunn on March 30, 2004 at 16:37:00:
square rooms will always be tough. check out this room mode calculator. my guess is if you plug in the room measurements you'll get 3 modes at very close to the same frequency. (ouch) the corner treatments will help with the Tangential and Oblique modes but the axial modes are the hard ones. even worse when you "stack" the modes decay time gets worse. i've found a narrow cut at the exact resonant frequency with a parametric eq does the job. you don't have to move the speakers and the chair around (much) so you can fine tune for imaging.
I really appreciate your post but....
We all have an achillies heel, and even though I have a rather high IQ, math and I have never seen eye to eye, especially in regards to anything to do with electricity, amplitude, wavelengths, trig or calculus etc..... I could learn it for a test, but forgot it a week later, entirely .
I plugged my dimensions into that thing, hit enter and sat there mystified. What's worse, I cannot even understand your post. I don't even know what the difference is between a tangential and oblique mode frankly, let alone how to stack them. (Wow, you can stack them?)
I've always relied on common sense and my senses, and will have to keep doing so. I always swore I'd get a book one day and really try to learn the "guts" of this hobby better, but the problem is, I really don't want to. I'd rather be listening, not crunching numbers. Even if the room is not 100%, I've always managed to get it pretty good and ignorance is bliss in this regard for me at least. I have observed that engineers are never happy people. (or rather, should I say satisfied people? : )
I'm already dreading having to do the crossover upgrades to my new maggies. One look at the jargon, the scribbling diagrams electricians call "schematics" with all the crytpic numbers, values and signs, and I don't have a damn clue where to begin. I don't even know what to buy.
Thanks for trying!
i don't enjoy the math either. what drives me crazy is the things you can't see. sometimes math helps me understand what i'm after at least, and sometimes the solution is more evedent. when you plug the dimmensions into the room mode calculator look first for frquencies under 100hz that match pretty close (within 3hz) in the axial mode. these are thre most powerful modes and are the frequency that resonate on the height, width, and length of the room. for example if your room is 8 feet tall take the speed of sound (1130 feet per second) / height (8 feet)= frequency of resonant wave (141.25hz).if you have two axial modes very close to the same resonant frequncy (stacked) the resonance will be reinforced. since we can't move the walls around we move the point of origin of the wave (speaker) and the point of reception (chair) to get an "inbetween" spot that is acceptable. with 2 or 3 stacked axial modes it is almost impossible. cancellation or equalization are about the only two options. running a sub out of phase and positioning it so that the offending mode is out of phase at the listening position. this can be accomplished with time delay and actual placement. here's a graph of a measurement taken in my listening room that used to have serious bass issues. notice the quick decay and even response. i used a combination of all these tricks - parametric eq, cancellation with sub, active bass absorbers and foam corner treatments - to obtain these results.
Maybe you don't like it but you have the fundamental knowledge of it's use. I could learn math in school long enough to pass a test, but it was gone in a month. I got an A in advanced algebra in 11th grade but I got a 57 on the final. Forgot it entirely.
The picture you posted didn't come thru, but I doubt it would have helped me get this post any more than the last one.
I do understand cancellation, but apply it with my ears and common sense. If parametric eq means creating a sound to negate a sound, I get the concept, but will never take that route to solve this problem. In any case, it's my friends problem : )
What really confuses me is how people throw out frequencies like they do. "Yeah, I have a problem at 400 hrz" How the hell do they know that? Not everyone can own test gear. I have no idea what 400 hrz sounds like. If there's a suck out at that frequency I'll hear it, but I won't be able to identify it, and frankly, I don't see the need to to solve the problem. Would I be better served by getting a clue? If so, how? Do you listen to test signal discs all day? The pic above is really how I feel about all this.
you can produce a graph like the one i tried to post and mart helped me out with for close to nothing (except for time which you will save later)if you already own the following equipment: a computer (i assume you have one since you are posting here)with a 16 bit sound card, a radio shack spl meter (used as an amplified mic), and the demo version of etf5. the demo version is fully fuctional except you can't save anything. it's kind of a pain to keep restarting the program if you're taking alot of measurements. i found it useful enough to buy the license. you can see the huge difference a small adjustment makes without listening to your entire collection. even if you end up listening to your entire collection anyways, you'll know why each adjustment made this or that sound better or worse. it will at least help the decision making process and keep you going in the right direction.
those room modes are a tough nut to crack. sometimes you get lucky, but in my experience if you want extended bass in a room that's not perfect more equipment and lots of head scratching is needed.
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