Why did my speaker blow?

[Rochambeau 10+ year member]

This is borderline whether this should be in Amps forum or Speaker forum but since I was setting gains, i'll post it in the Amps section.

I recently purchased a set of Boston Z6 speakers and one blew while I was attempting to set the gains on the amplifier. The source(s) is an Alpine IVA-W200 with a PXA-H701 processor between the head unit and amp.

The amp is an Alpine PDX 4.150 bridged to 318W RMS per side. When the speaker blew, the gains were set all the way to minimum and I was turning the volume up on the head unit trying to find where the source would clip (Alpine's recommended method). All processing was turned off, the EQ was set to flat, the channel was high-passed at 80hz with a 24db slope. I had the channel isolated by having the balance and fader turned all to that one speaker.

When it blew, I was using a 1kZ/0db sine wave from a disc in the head unit and heard no distortion until it blew. Admittedly, it was pretty close to full HU volume when it blew.

Aren't these speakers rated for 400w RMS? If so, why would it blow like that when the gains were set all the way down? Maybe my ear is so bad that I didn't hear that the distortion was so bad and it blew simply from the distortion in the HU?

Thank you for your time.

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[sundownz Pro Seller]

Any idea what a large amount of power will do to a coil at a higher frequency? Since the coil is moving very little the cooling properties are greatly diminished. If you were playing a sine wave at max HU volume you probably sent a good bit of power, even at 1 kHz, to that speaker and simply fried the coil. On actual music the speaker would be seeing a mix of frequencies and would be moving significantly more, thus helping to cool it's coil.