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[Guybrush]

I have a home-built subwoofer with a home-built amp. Last night I attempted to watch LOTR and in the first 10mins the subwoofer started clicking. No bass track at all, just the loud clicking or clunking like the driver was trying to move but couldn't. I freaked out and turned the movie off. I played some music and ran a few other movie scenes to check it and all was normal - no clicking, just explosive bass. Then I went back to LOTR and the clicking was back.

Has anyone seen this before? When I first built the sub/amp, I had a faulty amp and it gave out after a few days and the clicking happened. I haven't heard it on this amp anywhere until now. All DSP is done by JRiver, including low pass filtering.

[mwillems]

A few theories:

1) Many plate amps will flip a relay as a failsafe when they get an input signal that's so "hot" that it would drive them into clipping.  Often those relays make a clicking sound when engaging or disengaging, which would mean that your amp is entering "protect" mode.  I would verify the maximum electrical output of your line source and the recommended input of the plate amp. 

In that vein, all "line level" sources are not created equal; "pro audio" DACs can often have outputs that are 10V (or more) hotter than "consumer" line level outputs like from a CD or DVD player. This can be a problem if your amp is expecting (i.e. is fully driven) with a 2VRMS input.  A 12V line input might trip the protection circuit.  The fact that your previous amp failed similarly points to this as something worth investigating.

2) Is your sub a ported design?  Where is the port tuned?  If you're trying to reproduce tones below the port tuning, the driver is essentially unloaded down there and will just flap around wildly not making any sound except for a soft chuffing and unfortunate clacking noises as the driver reaches it's excursion limit and crashes into the spider or pole piece.  If that's what's happening, you may need a new driver before too long.  The way to protect against this is to include a high pass filter at or just below your port tuning.   

3) You may just have another faulty amp.

[Guybrush]

The clicking does sound just like a relay tripping. I know the amp has a DC protection circuit, but after more testing, it is only happening on the one blu-ray, and not during bass-heavy stuff, but during dialogue. Almost as if there is a low amplitude dc signal on the sub channel as background. Thanks for your input.

[Guybrush]

I just realized the only time I have issues with the subwoofer clicking is on a bluray that is encoded with a 6.1 surround track. How does MC handle this? I don't have a physical low pass filter on my sub, have been relying on MC for xover. I'm thinking now that some of the extra channel is getting fed to the sub and the frequencies are too high for it to play. It used to do that with some mono sources until I set up a specific zone for it.

Next question, should I install a low pass filter? Has anyone used the inline RCA low pass filters? My biggest concern would be signal attenuation. Will any filter attenuate the signal?