154 lines
6.1 KiB
PHP
154 lines
6.1 KiB
PHP
<?php
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const FORM_METHOD = 'GET'; // or 'POST'
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const FALLBACK_DRIVER_IMPEDANCE = 4.;
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const TWO_PI = 2. * 3.1415926535;
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const FREQ_MIN = 500.;
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const FREQ_MAX = 16000.;
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$form = FORM_METHOD === 'POST' ? $_POST : $_GET;
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$form_submitted = !empty($form);
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$tweeter_impedance = $woofer_impedance = FALLBACK_DRIVER_IMPEDANCE;
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if ($form_submitted) {
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$tweeter_impedance = @(float)($form['tweeter_impedance']) ?: FALLBACK_DRIVER_IMPEDANCE;
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$woofer_impedance = @(float)($form['woofer_impedance']) ?: FALLBACK_DRIVER_IMPEDANCE;
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}
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?>
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<!DOCTYPE html>
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<html lang="en">
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<head>
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<meta charset="UTF-8">
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<meta http-equiv="X-UA-Compatible" content="IE=edge">
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<meta name="viewport" content="width=device-width, initial-scale=1.0">
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<title>First-order crossover component calculator</title>
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<style>
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* {
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font-size: 12pt;
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font-family: sans-serif;
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line-height: 1.5;
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color: #EED;
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background-color: #22222A;
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max-width: 1024px;
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}
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.narrow {
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width: 80%;
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}
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.with-breating-room {
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margin: 1.5em 1em;
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}
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.right-aligned {
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text-align: right;
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}
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.explaining {
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margin-top: 2rem;
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margin-bottom: 1rem;
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font-style: italic;
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}
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.source {
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margin-top: 1rem;
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margin-left: 1rem;
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}
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.monospace {
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font-family: monospace;
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}
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.bordered {
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border: 1px solid;
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border-color: #666674;
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border-collapse: collapse;
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}
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.height-padded {
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padding-top: 0.45rem;
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padding-bottom: 0.45rem;
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}
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.left-padded {
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padding-left: 1rem;
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}
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.right-padded {
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padding-right: 1rem;
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}
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.width-padded {
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padding-left: 1rem;
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padding-right: 1rem;
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}
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.underlined {
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border-bottom: 1px solid #888;
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}
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</style>
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</head>
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<body>
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<div class="with-breating-room">
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This is a simple component calculator for a first-order crossover.
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Component values are calculated with the following formulae:
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<div class="with-breating-room height-padded">
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<span class="monospace">C = 1 / (2 * π * f * R)</span><br/>
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<span class="monospace">L = R / (2 * π * f)</span>
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</div>
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</div>
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<div class="with-breating-room explaining underlined">
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First-order filters have a 20 dB/decade (or 6 dB/octave) slope.
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All first-order filters have a Butterworth filter characteristic.
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[...]
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First-order filters are considered by many audiophiles to be ideal for crossovers.
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This is because this filter type is 'transient perfect',
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meaning it passes both amplitude and phase unchanged across the range of interest.
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[...]
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In practice, speaker systems with true first-order acoustic slopes are difficult to design
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because they require large overlapping driver bandwidth,
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and the shallow slopes mean that non-coincident drivers interfere
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over a wide frequency range and cause large response shifts off-axis.
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<br/>
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<div class="with-breating-room source">
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From Wikipedia: <a href="https://en.wikipedia.org/wiki/Audio_crossover">Audio Crossover</a>
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</div>
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</div>
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<div class="with-breating-room underlined height-padded">
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<form class="height-padded" action="" method="<?php echo FORM_METHOD; ?>">
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<table>
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<tr>
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<td class="height-padded right-padded">Tweeter impedance (Ω):</td>
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<td class="height-padded">
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<input class="monospace left-padded" type="number" min="0.5" step="0.5"
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name="tweeter_impedance" placeholder="Tweeter Ω" value="<?php echo $tweeter_impedance; ?>">
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</td>
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</tr>
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<tr>
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<td class="height-padded right-padded">Woofer impedance (Ω):</td>
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<td class="height-padded">
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<input class="monospace left-padded" type="number" min="0.5" step="0.5"
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name="woofer_impedance" placeholder="Woofer Ω" value="<?php echo $woofer_impedance; ?>">
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</td>
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</tr>
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<tr>
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<td class="height-padded" colspan="2"><input type="submit" value="Calculate"></td>
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</tr>
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</table>
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</form>
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</div>
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<?php if ($form_submitted): ?>
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<div class="with-breathing-room height-padded width-padded">
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<table class="bordered narrow">
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<tr><th class="width-padded height-padded bordered" colspan="100%">
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Component table for <?php printf("%.3g Ω ", $tweeter_impedance) ?> tweeter
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and <?php printf("%.3g Ω", $woofer_impedance) ?> woofer
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</th></tr>
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<tr>
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<th class="width-padded height-padded bordered">Crossover Frequency (Hz)</th>
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<th class="width-padded height-padded bordered">Tweeter Capacitor (μF)</th>
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<th class="width-padded height-padded bordered">Woofer Inductor (mH)</th>
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</tr>
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<?php for ($f = FREQ_MIN; $f <= FREQ_MAX; $f += FREQ_MIN): ?>
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<tr>
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<td class="width-padded height-padded bordered monospace">
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<?php printf("%g", $f); ?>
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</td>
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<td class="width-padded height-padded bordered monospace">
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<?php printf("%.4g", 1000_000. * (1. / (TWO_PI * $f * $tweeter_impedance))); ?>
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</td>
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<td class="width-padded height-padded bordered monospace">
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<?php printf("%.4g", 1000. * ($woofer_impedance / (TWO_PI * $f))); ?>
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</td>
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</tr>
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<?php endfor ?>
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</table>
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</div>
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<?php endif ?>
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</body>
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</html>
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