Setting a subwoofer's crossover

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coppellstereo

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Posted: January 30, 2006 at 12:49 AM / IP Logged

Where do you guys have your sub's crossover set? What is the equation again that shows you how power declines after the cutoff point? I may have phrased that wrong - I lost my CA&E magazine that talks about it.

Thanks!

coppellstereo

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Posted: January 30, 2006 at 2:25 PM / IP Logged

Anyone have any suggestions?

DYohn

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Posted: January 30, 2006 at 2:27 PM / IP Logged

Subs are usually low-passed anywhere between 70Hz and 200Hz, depending on the setup and what you're trying to accomplish. What "equation" are you talking about?

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coppellstereo

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Posted: January 30, 2006 at 5:16 PM / IP Logged

something to do with the efficiency below the crossover point. I'll research

DYohn

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Posted: January 31, 2006 at 12:01 AM / IP Logged

A crossover filter reduces the signal strength above (for a low-pass) or below (for a high-pass) the cut-off frequency depending on the slope. Crossovers can have several slopes, generally in multiples of 6db per octave. (6, 12, 18, 24, 36 being the most common.) An octave is a doubling of frequency. So, a 12db/oct low pass filter set at, say, 100Hz will reduce the incoming signal strength so it is down by 12db at 200Hz, and by 24db at 400Hz, etc. A 10db reduction in signal strength is 10 times less amplifier power. 20db is 100 times less. You could take this data and create an equation if you like. Here's a page with simple xover curves illustrated for you.

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coppellstereo

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Posted: January 31, 2006 at 12:48 AM / IP Logged

Thats right!

In most music what is the frequency of most of the bass. On this CD I have it starts at 320Hz and goes down to 10Hz and my bass seems to be the strongest at about 100 - 120 Hz. Would changing the x-over frequency help with the low end bass reproduction?

DYohn

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Posted: January 31, 2006 at 8:33 AM / IP Logged

Yes, the first four octaves (20-40Hz, 40-80Hz, 80-160Hz, 160-320Hz) are generally called the "bass" region. The purpose of a sub-woofer is to reinforce the first two octaves (and a little higher sometimes, plus the lower sub-20Hz tones that we cannot really hear but that we can most certainly feel.) Where is your subwoofer low-pass set now, and where is your main speaker high-pass set? Whatever crossover frequency you use, these settings should be the same.

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coppellstereo

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Posted: January 31, 2006 at 11:16 AM / IP Logged

I've been playing with it, it is at about 80 right now - is that what you recommend?

DYohn

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Posted: January 31, 2006 at 11:19 AM / IP Logged

coppellstereo wrote:

I've been playing with it, it is at about 80 right now - is that what you recommend?

That's where I recomend.

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coppellstereo

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Posted: January 31, 2006 at 8:40 PM / IP Logged

Are there any disadvantages to turning my subwoofers lpf to the upper extent of the range and using my HU's subwoofer crossover? This is much easier to set. I can adjust between 50, 80, and 135

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