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Junior Varsity
Subwoofer "Throw", Facebook... huh?
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<blockquote data-quote="Tom Danley" data-source="post: 91199" data-attributes="member: 259"><p>Re: Subwoofer "Throw", Facebook... huh?</p><p></p><p>Hi</p><p>I think I can put a sharper point on this. To be sure, I have heard what sounds like horns having more throw or being stronger at distance than the direct radiators.</p><p>The reason is the rate of change in the loudness gradient up close. An optical analogy, lets say you had two light sources, each of which put out 1W of light energy.</p><p>One radiated from a half inch diameter and the other from a 2 by 4 foot panel. Into the room, they each provide the same candle power BUT up close, the tiny aperture is too bright to look at. </p><p>A 15 inch cone and port producing the same distant SPL as a 2 by 4 foot horn mouth, which one sounds louder up close next to it? In either case, a light meter or sound meter shows the larger source radiating the same total power must have the lower surface intensity.</p><p>As Art mentioned too, there is a minimum distance one needs to be before the size of the object is small compared to the distance because up close, a solid object is not the same as that meter airspace would be. This space distortion extends to the radiation pattern too;</p><p><a href="http://www.synaudcon.com/site/author/pat-brown/far-field-criteria-for-loudspeaker-balloon-data/" target="_blank">Far-field Criteria for Loudspeaker Balloon Data « Synergetic Audio Concepts</a></p><p></p><p> For Ivan and I at work, what matters is a 1W1M equivalent so that contractors can figure out how loud and at what Voltage it will be at say 100Meters or whatever. </p><p>To make it easy, the large stuff is measured at 10 meters (-20dB from 1M) and then driven at 10X the normal Voltage (+20dB) so that the result is a 1W 1M equivalent. </p><p>Other than that, nothing magic about the distance.</p><p>Another reason to measure at a greater distance vs up close is that up close if loud, ones pressure microphone can also pick up “psudo-sound” which is an non-radiating erroneously high SPL reading caused by the kinetic impact of air molecules with the diaphragm (but is a not radiating pressure). John and i ran into this with several loud noise makers like a loud siren thing in the old days. If it's loud enough to move or blow out a flame, it's loud enough to potentially cause this effect too (if the reading is the same with the mic turned 90 degrees, that' a good sign).</p><p>Best,</p><p>Tom Danley</p></blockquote><p></p>
[QUOTE="Tom Danley, post: 91199, member: 259"] Re: Subwoofer "Throw", Facebook... huh? Hi I think I can put a sharper point on this. To be sure, I have heard what sounds like horns having more throw or being stronger at distance than the direct radiators. The reason is the rate of change in the loudness gradient up close. An optical analogy, lets say you had two light sources, each of which put out 1W of light energy. One radiated from a half inch diameter and the other from a 2 by 4 foot panel. Into the room, they each provide the same candle power BUT up close, the tiny aperture is too bright to look at. A 15 inch cone and port producing the same distant SPL as a 2 by 4 foot horn mouth, which one sounds louder up close next to it? In either case, a light meter or sound meter shows the larger source radiating the same total power must have the lower surface intensity. As Art mentioned too, there is a minimum distance one needs to be before the size of the object is small compared to the distance because up close, a solid object is not the same as that meter airspace would be. This space distortion extends to the radiation pattern too; [url=http://www.synaudcon.com/site/author/pat-brown/far-field-criteria-for-loudspeaker-balloon-data/]Far-field Criteria for Loudspeaker Balloon Data « Synergetic Audio Concepts[/url] For Ivan and I at work, what matters is a 1W1M equivalent so that contractors can figure out how loud and at what Voltage it will be at say 100Meters or whatever. To make it easy, the large stuff is measured at 10 meters (-20dB from 1M) and then driven at 10X the normal Voltage (+20dB) so that the result is a 1W 1M equivalent. Other than that, nothing magic about the distance. Another reason to measure at a greater distance vs up close is that up close if loud, ones pressure microphone can also pick up “psudo-sound” which is an non-radiating erroneously high SPL reading caused by the kinetic impact of air molecules with the diaphragm (but is a not radiating pressure). John and i ran into this with several loud noise makers like a loud siren thing in the old days. If it's loud enough to move or blow out a flame, it's loud enough to potentially cause this effect too (if the reading is the same with the mic turned 90 degrees, that' a good sign). Best, Tom Danley [/QUOTE]
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Subwoofer "Throw", Facebook... huh?
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