Members sibyrnes Posted February 29, 2012 Members Share Posted February 29, 2012 Makes sense. Link to comment Share on other sites More sharing options...
Members W. M. Hellinger Posted February 29, 2012 Members Share Posted February 29, 2012 Interesting! Is it possible for the reflected sound to ever be "equal to or greater than the direct sound". Yes. In-fact, it's oftentimes likely. The myth #42 I posted touches on this. For a quick explanation, pages 50 - 53 here cuts to the chase: http://www.jblpro.com/catalog/support/getfile.aspx?docid=275&doctype=3 Link to comment Share on other sites More sharing options...
Members jasps Posted February 29, 2012 Members Share Posted February 29, 2012 Doesn't matter whether or not a horn is involved. In fact it doesn't even matter if a speaker is involved. You DO until you reach the critical distance line. From that point since the reflected sound is equal to or greater that the direct sound it basically remains constant from there. Now if you take that outdoors you will basically lose 6 dB per each doubling of distance if you are in an open field. It can change depending on reflections. Don,You are preaching 'theory' that is much different from practice, IMO. Of course you are correct...My point is that people get so worked up about crap that doesn't even matter with a properly deployed rig. Yes, if one were to measure free field on axis, you are correct in that one will lose 6 dB until critical distance. However, MOST professionals do not aim a speaker in a straight line (parallel to a floor), but angle the speaker so that the on axis portion of the horn is pointed to the furthest listener. In doing so, front to back coverage is much improved. Link to comment Share on other sites More sharing options...
Members agedhorse Posted February 29, 2012 Members Share Posted February 29, 2012 Directivity of information Link to comment Share on other sites More sharing options...
Members jasps Posted February 29, 2012 Members Share Posted February 29, 2012 Directivity of information Yes, the loss of directivity v. freq. depends on the speaker, but the dispersion characteristics of a speaker all change to omni as the wavelengths get longer. I'm not even trying to dispute reflections and critical distance.Yes, the speaker will lose 6dB per doubling of distance, but it isn't like a person can't angle the speaker within the listening area at the proper height so that front to back coverage doesn't fall 6dB within that defined coverage area where the speaker still has pattern control. Guess I could've been more clear. Link to comment Share on other sites More sharing options...
Members stunningbabe Posted February 29, 2012 Author Members Share Posted February 29, 2012 You must ALWAYS have a power amp double or more watts than your speakers. Myth ya? Link to comment Share on other sites More sharing options...
Members Coaster Posted February 29, 2012 Members Share Posted February 29, 2012 You must ALWAYS have a power amp double or more watts than your speakers.Myth ya? not a myth. more of an untruthitude; a falsity if you will. perhaps even a total misunderstanding of the facts. Link to comment Share on other sites More sharing options...
Members agedhorse Posted February 29, 2012 Members Share Posted February 29, 2012 Yes, the speaker will lose 6dB per doubling of distance, but it isn't like a person can't angle the speaker within the listening area at the proper height so that front to back coverage doesn't fall 6dB within that defined coverage area where the speaker still has pattern control. Guess I could've been more clear. Unless using a line array with a cylindrical (ie. not spherical) type dispersion pattern, you will always encounter a 6dB falloff of SPL versus distance (less reflective gain) because the radiating pattern of even a horn is a spherical section and this is what is responsable for the invers square law... the area of a spherical section increases as the square of the distance. This applies no matter what the angles of the spherical section (horn pattern) are. Link to comment Share on other sites More sharing options...
Members stunningbabe Posted February 29, 2012 Author Members Share Posted February 29, 2012 not a myth. more of an untruthitude; a falsity if you will. perhaps even a total misunderstanding of the facts. Care to elaborate so that this will not be a myth then? Link to comment Share on other sites More sharing options...
Members jasps Posted February 29, 2012 Members Share Posted February 29, 2012 Unless using a line array with a cylindrical (ie. not spherical) type dispersion pattern, you will always encounter a 6dB falloff of SPL versus distance (less reflective gain) because the radiating pattern of even a horn is a spherical section and this is what is responsable for the invers square law... the area of a spherical section increases as the square of the distance. This applies no matter what the angles of the spherical section (horn pattern) are. Again, I'm not arguing against the inverse square law. I am trying to say that one can take advantage and use the dispersion characteristics of the speaker to obtain even coverage from front to back. Within the audience plane, one is not losing 6 dB for a doubling of distance. That is because the audience is usually not in the same plane as the speaker in a professional application. I know this is rudimentary, but it is worthwhile to say for those who don't know. Link to comment Share on other sites More sharing options...
Members dboomer Posted February 29, 2012 Members Share Posted February 29, 2012 Guess I could've been more clear. You lost me. It doesn't matter how or where you point a speaker (or like I said above that a speaker is even involved), Inverse square applies until you cross critical distance. Where exactly that line is does depend on how you aim a speaker (or your voice) within a room, so yes a well aimed speaker works better than a non well aimed speaker ... but inverse square still applies. Lets add one more myth ... speaker are omni directional at low frequencies. They are not! They are omni within a 6 dB window which is not exactly the same thing ... so like Andy says above "essentially omni". It depends on box size and frequency Link to comment Share on other sites More sharing options...
Members dboomer Posted February 29, 2012 Members Share Posted February 29, 2012 You must ALWAYS have a power amp double or more watts than your speakers.Myth ya? The important part you left out is ... "to do what". By itself, it is correct but it's nearly useless Link to comment Share on other sites More sharing options...
Members dboomer Posted February 29, 2012 Members Share Posted February 29, 2012 ce. That is because the audience is usually not in the same plane as the speaker in a professional application. Doesn't matter ... on a per frequency basis Link to comment Share on other sites More sharing options...
Members agedhorse Posted February 29, 2012 Members Share Posted February 29, 2012 Care to elaborate so that this will not be a myth then? Because the marketing folks do not understand the cost/benefit ratio that engineers design the products to. I have explained this exact topic in agonizing detail. Link to comment Share on other sites More sharing options...
Members jasps Posted February 29, 2012 Members Share Posted February 29, 2012 You lost me.It doesn't matter how or where you point a speaker (or like I said above that a speaker is even involved), Inverse square applies until you cross critical distance. Where exactly that line is does depend on how you aim a speaker (or your voice) within a room, so yes a well aimed speaker works better than a non well aimed speaker ... but inverse square still applies. Don,The inverse square law holds no matter what. I agree with what you are saying. BUT, If a sound at 4 kHz is 100 dB SPL at a listener a 10' away, it is not necessarily 94 dB SPL at listener b 20' away, unless somehow both listeners are in the same plane wrt the source, which doesn't really happen. At 5' away from listener a, the sound will be 106 dB SPL, sure, no argument. Link to comment Share on other sites More sharing options...
Members agedhorse Posted February 29, 2012 Members Share Posted February 29, 2012 Don,BUT, If a sound at 4 kHz is 100 dB SPL at a listener a 10' away, it is not necessarily 94 dB SPL at listener b 20' away, unless somehow both listeners are in the same plane wrt the source, which doesn't really happen. At 5' away from listener a, the sound will be 106 dB SPL, sure, no argument. If there are no reflective contributions AND the listener is doub;e the distance from the SOURCE, the SPL will indeed be -6dB at the second listeners position. Link to comment Share on other sites More sharing options...
Members dboomer Posted February 29, 2012 Members Share Posted February 29, 2012 It only matters that they are in the same line. It will be 94 dB SPL unless that distance (20') is beyond the critical distance ... That's the definition. So make a measurement. If you start with your example and you get 100 dB SPL at 10' (which is a big IF) just keep moving back. At the point it stops changing you will have discovered the critical distance line. Now beyond that line it won't change (well not much depending on a million things) I found a pretty easy to visualize example ... http://www.lenardaudio.com/education/04_acoustics_2.html If the room in the example is 60' long by 40' wide with a ceiling height of 12' and a reverb time of 1 second ... the critical distance will be aprox 13 feet ... damn short. So in that case a listener away (using your example) at 13 feet and at 50 feet will both hear about 99 dBSPL Link to comment Share on other sites More sharing options...
Members Mutha Goose Posted February 29, 2012 Members Share Posted February 29, 2012 What you are describing as a "critical distance" is nothing more than the distance at which reflections become your dominate source (if I'm not mistaken). Or more accurately, where the reflections = the direct source (in SPL) Link to comment Share on other sites More sharing options...
Members dboomer Posted February 29, 2012 Members Share Posted February 29, 2012 Bingo! It's just much closer than most realize. bonus points ... it's also the point where your EQ likely stops being effective (in big general terms) Link to comment Share on other sites More sharing options...
Members Mutha Goose Posted February 29, 2012 Members Share Posted February 29, 2012 And double bonus points: This is also the exact point of least intelligability. Link to comment Share on other sites More sharing options...
Members Axisplayer Posted February 29, 2012 Members Share Posted February 29, 2012 This is also the exact point of least intelligability. My wife also knows this as whatever place I am standing. Link to comment Share on other sites More sharing options...
Members dboomer Posted February 29, 2012 Members Share Posted February 29, 2012 And double bonus points: This is also the exact point of least intelligability. Not really. "Intelligibility" continues to decline at inverse square at least another 12 dB or so. Link to comment Share on other sites More sharing options...
Members Mutha Goose Posted February 29, 2012 Members Share Posted February 29, 2012 At this point you have maximum disruptive convergence. This is what causes the intelligiblity issues. Link to comment Share on other sites More sharing options...
Members agedhorse Posted February 29, 2012 Members Share Posted February 29, 2012 My wife also knows this as whatever place I am standing.... a time and place sensitive function Link to comment Share on other sites More sharing options...
Members dboomer Posted February 29, 2012 Members Share Posted February 29, 2012 At this point you have maximum disruptive convergence. This is what causes the intelligiblity issues. Issues, yes ... but you still have equal direct sound. As you add distance that ratio slants more towards the reflected sound and away from direct, hence intelligibility continues to get worse. Take a look at the chart I posted the link to in post #120 Link to comment Share on other sites More sharing options...
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