garyrc Posted March 12, 2012 Share Posted March 12, 2012 I entered my room dimentions in the Dan Siefert/Flloyd O'Toole Standing Wave Calculator at http://www.harman.com/EN-US/OurCompany/Technologyleadership/Pages/Calculators.aspx?CategoryID=Calculators , and I'm confused. The instructions say that the table and graphs show where the standing waves occur, but, If I look at the "Length" graph there is a dip in the line that touches the bottom of the graph at 12 1/2 feet (exactly 1/2 room length), labeled 23 Hz. Since that is a dip, I would think that the standing wave would be at minimum SPL there (at minimum amplitude) and that there would be a dip in the bass it I were to sit right there, 12 1/2 feet from both the front and back wall. BUT, that 23Hz is listed in the table above and to the right as one of the first axial standing waves. Normally if somebody said "there is a standing wave at 23 Hz" and I didn't have any graphs to look at I would think that 23 Hz would be a point of maximum loudness, a bass peak, rather than a dip. Can someone help me interpret the graphs? Quote Link to comment Share on other sites More sharing options...
Greg Oshiro Posted March 13, 2012 Share Posted March 13, 2012 Gary-- Standing waves produce peaks *and* nulls. Anywhere the graph amplitude is zero is a null. Anywhere the graph amplitude is maximum is a peak. So, the software predicts that there will be a 23 Hz null in the center of the 12-1/2 foot dimension *for a standing wave in the direction of that dimension*. Since there can be standing wave in 3 dimensions (as well as oblique and tangential), in order for a frequency to "disappear", your head would have to be in a location where all the possible standing waves have a null at one frequency. Toole's book http://www.alibris.com/booksearch?qwork=10813619&matches=22&cm_sp=works*listing*title, Chapter 13 explains this much better than I can. I can't recommend this book enough. Quote Link to comment Share on other sites More sharing options...
artto Posted March 13, 2012 Share Posted March 13, 2012 Yes, as Greg mentioned above, standing waves can be peaks or nulls ~ constructive or destructive. And it helps to keep in mind that the room is a three dimensional *system*. All of this primarily has to do with phase ~ displacement and pressure. If you really want to challenge yourself, use a sine wave generator (NCH Tone Generator - downloadable) and test one speaker at a time. Turn your head just a few degrees in any direction and you will hear dramatic differences in loudness.Want some more fun? Do the same thing except vary your elevation. The same thing happens. And then for some real peculiar observations, stay in one place while listening to the lowest frequencies. Play a tone continuously for 60 seconds or more. You'll hear the sound level change even if you remain perfectly still! [8-|] Quote Link to comment Share on other sites More sharing options...
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