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Author Topic: Capacitor necessary in a sub enclosure?  (Read 4043 times)

Tim Perry

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Re: Capacitor necessary in a sub enclosure?
« Reply #10 on: April 05, 2014, 11:03:45 am »

In a perfect world the polyfuse is an extra part in the audio path and adds a small cold series resistance. In the real world (we live in) if you don't abuse the speaker you will never know the polyfuse is there, if you do overdrive your speaker, it will start working again after it cools down.

JR

As we can see by this chart http://www.littelfuse.com/~/media/electronics/datasheets/resettable_ptcs/littelfuse_ptc_lorho_datasheet.pdf.pdf the series resistance for the device could be as low as .001 ohm.

This link shows how closely they can resemble capacitors http://www.littelfuse.com/~/media/electronics_technical/application_notes/resettable_ptcs/littelfuse_polyfuse_ptc_selection_guide_application_note.pdf

For detailed explanation (with charts) see http://www.te.com/content/dam/te/global/english/products/Circuit-Protection/knowledge-center/documents/circuit-protection-psw-fundamentals.pdf
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John Roberts {JR}

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Re: Capacitor necessary in a sub enclosure?
« Reply #11 on: April 05, 2014, 12:36:15 pm »

The poly fuse cold series resistance is how it makes heat to sense the current flow. The actual resistance will vary with the current trip rating, and as it heats up the resistance will increase some. Any negative effect during this transition region, before going high impedance, is preferable to the damage caused by it not being in circuit.

=====

Peavey made one interesting speaker protection circuit where a poly switch was used in parallel with a series lamp. This effectively shunted the changing impedance of the lamp to remove that distortion, until the poly switch opened and the lamp started limiting the current to the driver. 

Apparently customers like distorted audio and flashing lamps, more than no audio during protect mode. Lamp protection circuits can add distortion even when cold or only warm.

JR
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Listen to what a properly "cleared" drum sounds like.   http://circularscience.com/
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