Cross over filter level question

[dieseltwitch]

So I'm new to car audio. I've done my best to learn as much as I can but one thing that still confuses me is dB. For example on my amp a 900/5 JL there is a High Pass filter on the speaker channels. there are 3 settings; off, 12 dB, 24 dB. and a dial for selecting frequency. I understand how the dial is should to work. But maybe Im missing something. The speakers I have (JL C2-650) are said to handle 59Hz and up, so I set the cross over on the amp to 60Hz. However, when I play a test tone of 50 and even 40 Hz I can still get a response from the speakers? I tried adjusting the filter but the only thing that seams to work is by is moving the cross over setting to 70-75 Hz but then I feel it doesn't sound as good as it should.

What am I missing?

Also my speakers have external cross overs that also have a filter setting of +2dB, REF and -3dB... Help here would be great!

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[Side Show 10+ year member]

set hpf (high pass filter) to 80hz (so speakers and tweeters will play 80hz and above)

the external crossovers have adjustments on the tweeter output or on the crossover itself. I usually set them to 0 or ref to start with, then if they seem too harsh/bright I set them to -3db.

 

[TheMayer 10+ year member]

The 12db and 24db settings are referring to the slope of the filter. The higher the number, the steeper the slope. If you use a steeper slope you will hear less of the frequencies below where you set the filter, the shallower the slope the more you will hear.

This is the interface for the Audison Bit processors. The red line on the graph above the EQ bands shows the slope. This person is using a 12db slope so it is shallow and extends far past his set crossover frequency, if set to a 18db or 24db slope, the line would be much steeper and cutoff closer to the set frequency.

Also, if you look close at that graph you can see a scale for db on the left side (12, 0, -12). That tells you what frequencies will be allowed to pass through the filter depending on what volume the processor is set at.