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#81
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Speaker sensitivity and fs in multiples.
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#83
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Speaker sensitivity and fs in multiples.
(Bob-Stanton) wrote in message . com...
(Svante) wrote in message You cannot sum the powers. You have to sum the sound pressures. The sum of four 1/2 pressures is 2. So, sound pressure will double (+6.02 dB) for the same input power. ... No, again you cannot sum the individual powers. To say: "You cannot sum individual powers", is a violation of the law of conservation of energy. Assuming that there is no change in the acoustic power from each speaker... You are going in circles, you say that efficiency does not change, because efficiency does not change. Another fundamental law a physics is Energy = Force * Distance. If each of four drivers in an array is pushing the air with half the force, for half the distance, each puts out 1/4 the energy. The total power output of four will be only the same as a single driver. The distance is halved, but the force is not. Each driver sees the pressure created by itself, but also the pressure from three more drivers. Thus the pressure is four times half the original pressure (= two times the original pressure), and thus the force is doubled. So if energy = force * distance, and the force is doubled, the distance is halved, and the number of drivers is four, the net energy will be four times the single driver. For the system, total displacement will be x*2. This is acheived with the the same input power. This corresponds to an increased efficiency of +6.02 dB. Thats right. BUT the force exerted by the drivers in the array is only 1/2 that of a single driver, that corresponds to a decreased efficiency: -6.02 dB. Nope, see above. 6.02 dB -6.02 dB = 0 dB change. P = F/2 * x*2 is the same pressure as: F * x. That means NO increase in pressure, No incease in effiency and no increase in power. This reasoning holds for low frequencies, ie when the drivers are mounted close to each other compared to the wavelength. For higher frequencies it holds straight in front of the speaker (anechoic conditions) but to the sides, interference will decrease the sound pressure. So for higher frequencies, on average (over frequencies and directions) your statement ends up correct (ie the efficiency/sensitivity is the same) No. Given an ideal piston driven to an acceleration corresponding to the signal, the level EXACTLY straight in front of and far away from the piston does NOT vary with frequency. To the sides it does. To the sides the level will vary towards higher frequencies due to interference from the different parts of the piston. This will cause on-axis level to be constant (vs frequency), but efficiency to drop towards higher frequencies. Thus, the efficiency gain I have described in this thread is only acheived in the low-frequency region. At higher frequencies, as the polar pattern narrows, the energy will be concentrated toward the front. The sound pressure level will increase. Bob Stanton |
#84
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Speaker sensitivity and fs in multiples.
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#86
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Speaker sensitivity and fs in multiples.
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#87
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Speaker sensitivity and fs in multiples.
(Bob-Stanton) wrote in message . com...
(Svante) wrote in message Nope, see above. I set up a test. I had an array of four drivers. I wired them such that I could switch from a single driver to an array of four. I measure the sound power levels at: 60 Hz 70 Hz 80 Hz 90 Hz 100 Hz 120 Hz 140 Hz Switching from a single driver to an array of four, I measured an increase in sound power level of 5.5 to 6.5 dB. Even varying the distance of the sound power level meter from 3 ft to 6 ft, I still got a consistant +6 dB change, just as you perdicted. Bob Stanton Great! This proves that the best way to settle things when one runs out of theoretical arguments is to examine the real world. Which you did, and I should have. My compliments. Just a small question here, were you outdoors or indoors? Big room/small room? Was the level increase consistent in different directions? |
#88
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Speaker sensitivity and fs in multiples.
(Bob-Stanton) wrote in message . com...
(Svante) wrote in message Nope, see above. I set up a test. I had an array of four drivers. I wired them such that I could switch from a single driver to an array of four. I measure the sound power levels at: 60 Hz 70 Hz 80 Hz 90 Hz 100 Hz 120 Hz 140 Hz Switching from a single driver to an array of four, I measured an increase in sound power level of 5.5 to 6.5 dB. Even varying the distance of the sound power level meter from 3 ft to 6 ft, I still got a consistant +6 dB change, just as you perdicted. Bob Stanton Great! This proves that the best way to settle things when one runs out of theoretical arguments is to examine the real world. Which you did, and I should have. My compliments. Just a small question here, were you outdoors or indoors? Big room/small room? Was the level increase consistent in different directions? |
#89
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Speaker sensitivity and fs in multiples.
(Bob-Stanton) wrote in message . com...
(Svante) wrote in message Nope, see above. I set up a test. I had an array of four drivers. I wired them such that I could switch from a single driver to an array of four. I measure the sound power levels at: 60 Hz 70 Hz 80 Hz 90 Hz 100 Hz 120 Hz 140 Hz Switching from a single driver to an array of four, I measured an increase in sound power level of 5.5 to 6.5 dB. Even varying the distance of the sound power level meter from 3 ft to 6 ft, I still got a consistant +6 dB change, just as you perdicted. Bob Stanton Great! This proves that the best way to settle things when one runs out of theoretical arguments is to examine the real world. Which you did, and I should have. My compliments. Just a small question here, were you outdoors or indoors? Big room/small room? Was the level increase consistent in different directions? |
#91
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Speaker sensitivity and fs in multiples.
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#92
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Speaker sensitivity and fs in multiples.
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#93
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Speaker sensitivity and fs in multiples.
Bob-Stanton wrote:
... Switching from a single driver to an array of four, I measured an increase in sound power level of 5.5 to 6.5 dB. Even varying the distance of the sound power level meter from 3 ft to 6 ft, I still got a consistant +6 dB change, just as you predicted. Bob Stanton Thanks, Bob. I was just getting ready to buy a dartboard. That makes sense. I put a matching pair of speaker cabinets, each with a four-speaker cluster, on a stereo amp, mono in, outputs matched. These were the Audax PR-17 mids, with the signal filtered to 300-8K through a TDM stereo 24 dB/octave electronic crossover. I ran noise from a Gold-Line pink noise generator. A picture of these cabinets is in a previous post. When I disconected three of the drivers from one side, the the quad array was definitely much louder. I didn't measure the actual output but there was a marked difference. And thank you all for your responses. ________________ Marc Stager |
#94
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Speaker sensitivity and fs in multiples.
Bob-Stanton wrote:
... Switching from a single driver to an array of four, I measured an increase in sound power level of 5.5 to 6.5 dB. Even varying the distance of the sound power level meter from 3 ft to 6 ft, I still got a consistant +6 dB change, just as you predicted. Bob Stanton Thanks, Bob. I was just getting ready to buy a dartboard. That makes sense. I put a matching pair of speaker cabinets, each with a four-speaker cluster, on a stereo amp, mono in, outputs matched. These were the Audax PR-17 mids, with the signal filtered to 300-8K through a TDM stereo 24 dB/octave electronic crossover. I ran noise from a Gold-Line pink noise generator. A picture of these cabinets is in a previous post. When I disconected three of the drivers from one side, the the quad array was definitely much louder. I didn't measure the actual output but there was a marked difference. And thank you all for your responses. ________________ Marc Stager |
#95
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Speaker sensitivity and fs in multiples.
Bob-Stanton wrote:
... Switching from a single driver to an array of four, I measured an increase in sound power level of 5.5 to 6.5 dB. Even varying the distance of the sound power level meter from 3 ft to 6 ft, I still got a consistant +6 dB change, just as you predicted. Bob Stanton Thanks, Bob. I was just getting ready to buy a dartboard. That makes sense. I put a matching pair of speaker cabinets, each with a four-speaker cluster, on a stereo amp, mono in, outputs matched. These were the Audax PR-17 mids, with the signal filtered to 300-8K through a TDM stereo 24 dB/octave electronic crossover. I ran noise from a Gold-Line pink noise generator. A picture of these cabinets is in a previous post. When I disconected three of the drivers from one side, the the quad array was definitely much louder. I didn't measure the actual output but there was a marked difference. And thank you all for your responses. ________________ Marc Stager |
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