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Microphone Month 5


Live Sound / Studio / Control Room tips Subwoofer placement and the characteristics of low frequencies

Is low end really omnidirectional? “I purchased a powered sub for my studio monitors recently and I have been struggling to place it in my control room. The guy who sold it to me said that low frequencies are omnidirectional so I could place it anywhere in the room and it would do the job. I am not finding this to be the case. Things sound quite a bit different when I move it around. What am I doing wrong?” You’re not doing anything wrong. The information you are working with is only partially correct. Low frequencies themselves are not more or less directional than high frequencies. They’ll all radiate in an omnidirectional way given the chance. Low frequency wavelengths are longer and so they tend to be able to more easily move around (or through) large objects. Consider a speaker cabinet. Higher frequencies will tend to be projected out of the front of the cabinet, or out of the front of the speakers. Low frequencies will tend to radiate from the front, sides, top and bottom. The lower the frequency the more omnidirectional the cabinet’s characteristics become. Simple proof of this is to stand behind any full range speaker system and listen. There is no point at which the sound emanating from your sub becomes omnidirectional. It simply tends to become more omnidirectional as the wavelengths get longer (frequencies get lower). How much change occurs at what frequencies will depend on the design and size of the cabinet enclosure.Another factor you are experiencing is that even though very low frequencies may be radiating from your sub in more or less of an omnidirectional pattern this still does not mean your ears can’t tell where the sound is coming from. This is a mistake many people who use subs make. Your ears (and brain) are very sensitive to all sorts of little cues that give away the location of sounds (most likely a key factor in man’s survival back in prehistoric times). Low frequency sounds tend to be harder to locate due to those long wavelengths, but we can still do it pretty accurately most of the time, depending of course on how low a frequency we are talking about.There are other factors such as harmonic distortion, intermodulation distortion, cabinet resonances, room modes and reflections that can give away the location of a sub or make it sound different depending on placement. You are already doing what must be done, which is to move it around and listen to the results. When possible, it is best to position a sub close to your main listening speakers. This minimizes time arrival delays and makes for a more coherent soundstage, but the acid test is to move it around and listen until you find the sweet spot. An individual’s judgement of the sweet spot may vary depending upon your concern. Some simply want to place it where things sound the most aesthetically pleasing while others should concern themselves more with accuracy and placing where it causes them to create the best mixes.

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