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New DIY Mid High (90deg) - AKA PM90
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<blockquote data-quote="Peter Morris" data-source="post: 133521" data-attributes="member: 652"><p>Re: New DIY Mid High</p><p></p><p></p><p></p><p>The short answer is no I don't think it will work. You have to remember that any correction you apply by preconditioning the signal will be applied to both the mid and hi through the crossover region. If they are not time aligned and a fighting each other, preconditioning the signal will not be a good solution. If you can get good smooth summation through the crossover even if the amplitude response is not flat it will work. This is what Nexo do with the PS15 in passive mode. In this case my best guess is that the time offset is too much to get this to work ... I may be wrong. </p><p></p><p>You use APL WORKSHOP software to generate a file (coefficients) for the ALP1’s FIR chip. The file can be exported to other FIR processors instead of the APL1, but the file format Lake uses will not allow this to happen. (not easily ... )</p><p></p><p>What’s interesting about this approach is that the correction curve is based on a power response.</p><p></p><p>“Measurement of the emitted sound power occurs in many (about one hundred or two hundred) points in space, arranged on an imaginary spherical surface (or its segment in the most important direction of radiation) around the speaker in which information is collected. In simpler terms: a measurer with a microphone in his hand draws an imaginary vertical lattice for about a minute (1 min=180 points). A specially developed program fixes the value of the sound pressure at separate points and later calculates sound (acoustic) power frequency characteristics (SPFR) where the factors of interference are eliminated. On the basis of these characteristics the correction curve is then synthesized. It is created to mirror the radiated sound power frequency response curve; one can now follow this curve at a level of precision unavailable in traditional equalizers. The fact is that a FIR, a filter with finite impulse response, is used as an equalizer in SPFR correction technology. This is nothing new for radio and communication engineering, but in sound engineering it has been used quite rarely.”</p><p></p><p>What I did was use FIR crossovers and all pass filters in the Lake to partially correct the phase response. The problem is if you flatten the phase response too much, especially if you are using any reflex load speakers you will end up with a lot of latency. I selected an FIR time of only 2.5ms and used an IIR crossover between the Mid/Hi.</p><p></p><p>I also tried a full FIR 4 way crossover; there is 180 degrees less of phase rap with this approach and it requires 2 x LM26’s for a stereo system. A minimum FIR time of 12.5ms is required to process the sub crossover. The FIR time required is proportional to the crossover frequency and filter slope. </p><p></p><p>To my ear, all thing being equal except phase, speakers with a flat phase response sound more real than those that do not. I think the critical region for this between about 500 – 6000Hz; accordingly I designed / processed this design to achieve that.</p><p></p><p>I also tried the double 10 and horn speaker that I posted a picture of above 2 way with a passive HF/VHF crossover and 3 way. It sounds a little bit better 3 way.</p></blockquote><p></p>
[QUOTE="Peter Morris, post: 133521, member: 652"] Re: New DIY Mid High The short answer is no I don't think it will work. You have to remember that any correction you apply by preconditioning the signal will be applied to both the mid and hi through the crossover region. If they are not time aligned and a fighting each other, preconditioning the signal will not be a good solution. If you can get good smooth summation through the crossover even if the amplitude response is not flat it will work. This is what Nexo do with the PS15 in passive mode. In this case my best guess is that the time offset is too much to get this to work ... I may be wrong. You use APL WORKSHOP software to generate a file (coefficients) for the ALP1’s FIR chip. The file can be exported to other FIR processors instead of the APL1, but the file format Lake uses will not allow this to happen. (not easily ... ) What’s interesting about this approach is that the correction curve is based on a power response. “Measurement of the emitted sound power occurs in many (about one hundred or two hundred) points in space, arranged on an imaginary spherical surface (or its segment in the most important direction of radiation) around the speaker in which information is collected. In simpler terms: a measurer with a microphone in his hand draws an imaginary vertical lattice for about a minute (1 min=180 points). A specially developed program fixes the value of the sound pressure at separate points and later calculates sound (acoustic) power frequency characteristics (SPFR) where the factors of interference are eliminated. On the basis of these characteristics the correction curve is then synthesized. It is created to mirror the radiated sound power frequency response curve; one can now follow this curve at a level of precision unavailable in traditional equalizers. The fact is that a FIR, a filter with finite impulse response, is used as an equalizer in SPFR correction technology. This is nothing new for radio and communication engineering, but in sound engineering it has been used quite rarely.” What I did was use FIR crossovers and all pass filters in the Lake to partially correct the phase response. The problem is if you flatten the phase response too much, especially if you are using any reflex load speakers you will end up with a lot of latency. I selected an FIR time of only 2.5ms and used an IIR crossover between the Mid/Hi. I also tried a full FIR 4 way crossover; there is 180 degrees less of phase rap with this approach and it requires 2 x LM26’s for a stereo system. A minimum FIR time of 12.5ms is required to process the sub crossover. The FIR time required is proportional to the crossover frequency and filter slope. To my ear, all thing being equal except phase, speakers with a flat phase response sound more real than those that do not. I think the critical region for this between about 500 – 6000Hz; accordingly I designed / processed this design to achieve that. I also tried the double 10 and horn speaker that I posted a picture of above 2 way with a passive HF/VHF crossover and 3 way. It sounds a little bit better 3 way. [/QUOTE]
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