02-13-2020, 09:56 PM
Bonsoir Michel
Pour le décalage tu peux lire l'article de Troels Gravesen: http://www.troelsgravesen.dk/The-Loudspeaker.htm
Il a le même problème que moi pour aligner sa compression avec le médium. Il a trouvé une solution avec le filtre qu'il explique très bien. On voit bien sur ses courbes que çà ne s'additionne pas très bien malgré tout vers 2000/4000 Hz.
C'est ici ans son article:
To time-align - or not time-align
Do we need to time-align the midrange and horn with steep slopes and a point of crossover around 1.2-1.5 kHz? Some will say yes, some may say it all depends. Fact is that these old monsters deliver an astonishing midrange/lower treble, regardless of the compression driver acoustically being some 10-15 cm behind the midrange driver. Doing dZ on the two drivers reveals the compression driver being 112 mm behind the midrange driver from mounted on a flat panel. With these date put into the simulation software, we can manage a flat frequency response from connecting the horn with opposite polarity relative to the midrange, where a 4th order filter would normally require same polarity.
There's the thing about frequencies in this range having a wavelength around 25-30 cm, close to the distance between our ears, thus making it hard for us the locate sound. Pay attention next time you hear a 1 kHz sine wave alarm tone - and you may experience how difficult it can be to locate the source. Thus, we may not notice the phase issues going on here. Now, the only thing to do is to set up the drivers on suitable baffles and make a crossover with a flat frequency response. Pulling the horn forward some 12 cm (about half the wavelength of the point of crossover) and connecting with the same polarity also made a flat response. Which one sounded the best? That was really, really hard to decide, because the horn to some extent would jeopardize the dispersion of the midrange driver unless they were wide apart. As always, any speaker is full of compromises. Numerous simulations were done, more than twenty, and some of them were set up for actual testing.
Jean-Paul
Pour le décalage tu peux lire l'article de Troels Gravesen: http://www.troelsgravesen.dk/The-Loudspeaker.htm
Il a le même problème que moi pour aligner sa compression avec le médium. Il a trouvé une solution avec le filtre qu'il explique très bien. On voit bien sur ses courbes que çà ne s'additionne pas très bien malgré tout vers 2000/4000 Hz.
C'est ici ans son article:
To time-align - or not time-align
Do we need to time-align the midrange and horn with steep slopes and a point of crossover around 1.2-1.5 kHz? Some will say yes, some may say it all depends. Fact is that these old monsters deliver an astonishing midrange/lower treble, regardless of the compression driver acoustically being some 10-15 cm behind the midrange driver. Doing dZ on the two drivers reveals the compression driver being 112 mm behind the midrange driver from mounted on a flat panel. With these date put into the simulation software, we can manage a flat frequency response from connecting the horn with opposite polarity relative to the midrange, where a 4th order filter would normally require same polarity.
There's the thing about frequencies in this range having a wavelength around 25-30 cm, close to the distance between our ears, thus making it hard for us the locate sound. Pay attention next time you hear a 1 kHz sine wave alarm tone - and you may experience how difficult it can be to locate the source. Thus, we may not notice the phase issues going on here. Now, the only thing to do is to set up the drivers on suitable baffles and make a crossover with a flat frequency response. Pulling the horn forward some 12 cm (about half the wavelength of the point of crossover) and connecting with the same polarity also made a flat response. Which one sounded the best? That was really, really hard to decide, because the horn to some extent would jeopardize the dispersion of the midrange driver unless they were wide apart. As always, any speaker is full of compromises. Numerous simulations were done, more than twenty, and some of them were set up for actual testing.
Jean-Paul
Atoll CD400SE/ Atoll IN400SE/ Thechnics 1200GR/ Lehman black cube SE/ Enceintes DIY, et d'autres trucs.
