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Junior Varsity
Dim tweeter
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<blockquote data-quote="Art Welter" data-source="post: 216726" data-attributes="member: 52"><p>Ben,</p><p></p><p>The ferrofluid itself, not the diaphragm could be the cause of lower output, if it has partially dried out, its viscosity increases. Think of running your hand through a bucket of syrup compared to water, and you get the idea of the difference the coil experiences.</p><p></p><p>As well as aftermarket diaphragms seldom being equal to the original, ferrofluid has dozens of different types. </p><p>If you bought the cabinets used, very possible some crap generic ferrofluid was put in, or contaminated old stuff left in place.</p><p>Even the wrong amount of the right stuff will affect the response.</p><p>If you want original performance, the old ferrofluid must be cleaned out, gap completely cleaned, Roys suggestion of Pec-Pads, followed with masking or artist's tape until the tape shows no sign of debris is needed.</p><p></p><p>Then, after putting in the measured quantity of ferrofluid, the diaphragm must be aligned.</p><p>Alignment pins or rings on the JBL diaphragms generally will center the diaphragm adequately to prevent rubbing and buzzing, but they do not guarantee it.</p><p></p><p>A narrow frequency band, sometimes only a few Hz wide, may trigger a “buzz” distortion. For that reason, misalignment distortion may not be at all evident except with certain musical passages, making music, pink noise, or even specifically spaced sine wave tones near useless for alignment.</p><p></p><p>In most cases, low frequencies of several octaves below the usual pass band will make the harmonic distortion most audible. After determining a reasonable mid pass band output level, slowly sweep from 200 Hz up, listening for "buzz". Most times the range between 200 Hz to 800 Hz will reveal the "buzzing", but I have found a few diaphragms that only buzzed when driven at anywhere from 800 Hz to 5kHz or so.</p><p></p><p>The horn, or even the long throats of "old school" drivers like Altec, JBL, or TAD makes the diaphragm output much louder, which will mask a dragging voice coil distortion component. Removing the driver from the horn, or stuffing the horn with rags, or laying it mouth down on a rug or carpet makes the buzz easier to hear.</p><p></p><p>To align the diaphragm, re-install the diaphragm with it's screws just loose enough to not rattle, but tight enough to allow one to tap a portion of the screw ring in the direction that eliminates the buzz, then re-sweep to determine this did not cause a buzz at a different frequency, then tighten the screws fully, and test again. Lather, rinse, repeat ;^).</p><p></p><p>Art</p></blockquote><p></p>
[QUOTE="Art Welter, post: 216726, member: 52"] Ben, The ferrofluid itself, not the diaphragm could be the cause of lower output, if it has partially dried out, its viscosity increases. Think of running your hand through a bucket of syrup compared to water, and you get the idea of the difference the coil experiences. As well as aftermarket diaphragms seldom being equal to the original, ferrofluid has dozens of different types. If you bought the cabinets used, very possible some crap generic ferrofluid was put in, or contaminated old stuff left in place. Even the wrong amount of the right stuff will affect the response. If you want original performance, the old ferrofluid must be cleaned out, gap completely cleaned, Roys suggestion of Pec-Pads, followed with masking or artist's tape until the tape shows no sign of debris is needed. Then, after putting in the measured quantity of ferrofluid, the diaphragm must be aligned. Alignment pins or rings on the JBL diaphragms generally will center the diaphragm adequately to prevent rubbing and buzzing, but they do not guarantee it. A narrow frequency band, sometimes only a few Hz wide, may trigger a “buzz” distortion. For that reason, misalignment distortion may not be at all evident except with certain musical passages, making music, pink noise, or even specifically spaced sine wave tones near useless for alignment. In most cases, low frequencies of several octaves below the usual pass band will make the harmonic distortion most audible. After determining a reasonable mid pass band output level, slowly sweep from 200 Hz up, listening for "buzz". Most times the range between 200 Hz to 800 Hz will reveal the "buzzing", but I have found a few diaphragms that only buzzed when driven at anywhere from 800 Hz to 5kHz or so. The horn, or even the long throats of "old school" drivers like Altec, JBL, or TAD makes the diaphragm output much louder, which will mask a dragging voice coil distortion component. Removing the driver from the horn, or stuffing the horn with rags, or laying it mouth down on a rug or carpet makes the buzz easier to hear. To align the diaphragm, re-install the diaphragm with it's screws just loose enough to not rattle, but tight enough to allow one to tap a portion of the screw ring in the direction that eliminates the buzz, then re-sweep to determine this did not cause a buzz at a different frequency, then tighten the screws fully, and test again. Lather, rinse, repeat ;^). Art [/QUOTE]
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