x over points

ok, i'm playing around with my crossover points on my amp, trying to get a better balance between when the LPF on the sub kicks in and the HPF on the speakers kick in. here's what i have, suggestions on where to start would be greatly appreciated.

DC Audio 12" XL on a Fosgate T-1500bdcp crossover set at 85 and it is 24dB/octave box is tuned to 33hz

Fosgate T3652-s components, Fosgate crossover is 12dB/octave and amp is a Fosgate T-600 which has a 24dB/octave crossover

JL C5-650x (can't find the specs for the crossover) on the same Fosgate T-600 as the T3s


T-1500

T-600

T3652-s

JL C5-650x

DC 12" XL

other than keeping harmful frequencies out of your highs the crossover point is presonal preference. no one can tell you anything about where to start without actually being there to hear your system. if you think certain frequencies sound better coming out of the sub than the mid then set your lpf higher.

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Ideally, still... WHEREVER you set your LPF for your subs, THAT is where you set your HPF for your highs. If you don't, you'll end up with a hole (if you set the LPF at 80Hz, and the HPF at 100Hz - an "underlap") or a bump (if you set the LPF at 100Hz, and the HPF at 80Hz - an "overlap") in your frequency response, and at those frequencies, it's generally not good at all.

Additionally, a "crossover frequency" is where the high- and low- pass frequencies meet - they are both set at the same frequency, with the "knee" at 3dB below reference, bringing the SPL of the crossover frequency (for example, 85Hz) to "flat". A HPF by itself is not a crossover, nor is a LPF. In a standalone configuration, or when referred to individually, they are "filters", not "crossovers".

Below I have drawn up what happens when you "overlap" filters, "underlap" filters, and an ideal crossover slope.



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It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

Thank you for the replies. I understand the HPF and LPF being filters, not crossovers, and you want to have them set the same (lpf at 80, hpf at 80), what throws me off is the slope. Having your LPF set at 80, your speaker still plays frequencies above 80hz because of the slope of the filter (or crossover). Is slope normally taken into account, or do you just typically go off of the raw 80hz?

Just go off the 80Hz. The slopes and frequencies SHOULD be the same, so the sound power from the array is flat. Using different slopes will cause the output CURVES shown above (the green lines) to be pulled one way or the other. That's even worse sounding than the nice, uniform humps that are shown. Either way, it's just not OFTEN good. There are exceptions to this blanket statement, but it takes VERY careful planning and placement to make sure that non-symmetrical slopes or filter frequencies applied in a given system sound good. Just generally, DON'T DO IT.

Every filter is specified at the half-power point, or -3dB, so at 3dB per octave, the knee is one octave above the frequency specified... Odd the way I typed that...

Examples:

1: A 100Hz filter, at 3dB per octave, would still be flat at 200Hz, but -6dB at 50Hz (this type of filter doesn't exist, as far as I know, it's only for example of mathematics. If it DOES exist, it's a Class D filter, and can't be achieved with passive components)

2: A 100Hz filter, at 6dB per octave, would still be flat at 150Hz, but -9dB at 50Hz (this is a first-order crossover, and is as simple as a cap on a tweeter and a coil on a woofer)

3: A 100Hz filter, at 12dB per octave, would still be flat at 125Hz, but is -15dB at 50Hz (this is a second-order crossover, and is a cap/coil on a tweeter, and a coil/cap on a woofer)

The "100Hz" is the filter frequency. The filter frequency is always -3dB from "reference", or the 0dB line. The order of the crossover simply tells you how fast it filters the frequencies above or below the specified point, in dB per octave. It's how steep the red lines in my example above are. The higher the order, the steeper those lines become, and the closer the "knee" frequencies get.

An octave is a halving or a doubling of frequency from a given frequency, or the "fundamental". A fundamental of 100Hz will have 50Hz, 25Hz, 12.5Hz as octaves 1, 2, and 3, BELOW it, and 200Hz, 400Hz, 800Hz, etc., as octaves 1, 2, and 3, ABOVE it.

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It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

@haemphyst

thank you

^^^ dido...that was the clearest and most concise I have seen that info stated.

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Dodge Magnum in progress:
Pioneer DEH-80PRS - PPI Amps - Dayton Subwoofer(s) - Exodus Anarchy's - Vifa Tweeters - Kinetik Battery

not to dig up an old thread, but i found this on the PAC website, and it is really good. PAC Crossover Calculator and Guide

SWEETNESS!!!

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Dodge Magnum in progress:
Pioneer DEH-80PRS - PPI Amps - Dayton Subwoofer(s) - Exodus Anarchy's - Vifa Tweeters - Kinetik Battery