Basics of crossover points & slopes

[SQ SUBARU]

As requested... Hopefully helps a few of u guys setting crossovers and if u are running active.

Crossovers & frequencies:

Just something quick I wrote about the basics of crossover points & slopes:

Let's start simple with crossover filters, high pass (HPF), low pass (LPF) and bandpass.

High Pass means only frequencies above the crossover point, or sometimes referred to as the cutoff frequency, are played. For example, a 3000 hz high pass will only play frequencies above 3000 hz. Low Pass means only frequencies below the crossover point are played. For example, a 80 hz low pass means only frequencies below 80 hz will be played. BandPass plays frequencies between two points by utilizing both a high pass and low pass in the same filter network. So, for example you could have a midrange driver only playing 80 hz to 3000 hz.

Next are slopes.

Slopes refer to the numbers, 6 decibel (db),12db, 16db and 24db, are the most common. What they actually mean is "X" decibel drop off after the cutoff frequency PER OCTAVE. An octave is half or double a frequency. So for example let's take a 3000 hertz high pass filter. (Which is common for tweeters) the frequencies do not just stop playing below the 3000hz point, they roll of at a certain db ( attenuated ).

So a 12 db slope, it will mean a 12 decibel dropoff of output (sound) at 1500 hz (one octave lower) (half) and 24 dbs by 750 hz, etc. The higher your slope number determines how sharp your cutoff is. 48 db is like a cliff and 12db is a gradual slope. Now understand that a 3 db gain is double the output, and 3 db loss is half the output.

Now an example for a sub.

Let's say the low pass filter is set at 80 hertz for a sub. Which means only frequencies below 80hz get played. But the frequencies ABOVE 80hz don't just stop being played, they will "rolloff" at a certain db slope. So say u put a 6db slope on the sub, (crossed over at 80hz) This means all frequencies above 80hz will gradually roll off. So one octave above 80hz is 160hz (double) will be 6 decibels DROP of output in sound. So basically 6 decibels less as loud. A 3db drop of output is usually heard as only 2 or 3 clicks less on the volume dial on the headunit. And 10db drop of output is around half as loud.

Hopefully that all made sense lol.

[afrakes]

Thanks!

[scooter99]

So I'm trying to understand, and this is a perfect write up for me thank you.

I'm trying to understand the "drop-off" and the "roll-off". Does this mean, as you said the frequencies don't just stop being played, that it would essentially be like having a tone, say 80hz, and you just turned the volume down, to act as the "roll-off"? Essentially the tone over 80hz just fades away so to speak, instead of just stopping.

Same thing with the high point. When it get's below, 3000 hz in this case, it just fades off instead of stopping.

Are the slopes allowing for better blending with the frequencies in between, or how does a slop work. Better question, what is it specifically for?

Thanks for posting this! I hope to learn some more.

[SQ SUBARU]

Yes essentially having a slope helps "blend" drivers together, so the frequencies pretty much "fade" or rolloff a certain db. They don't just stop, the frequencies gradually roll of at the certain rate, 12,24 db etc. If u didn't have it "rolloff", it wouldn't sound right. So say take a sub and a mid bass driver. If u have them say crossed at 80hz, and u didn't have a slope on the frequencies to "rolloff" then the frequencies would just stop, and any frequency above the 80hz would move onto the next driver up (the midbass). By having a certain db of rolloff slope, helps blend the sound to make it sound more natural. A better way if saying it could be, the slope is the rate of the audio level (sound) increases or decreases, but remember it's per octave!! If u look at a crossovers graph or look at a rta u can see the difference between 6,12,24 db etc, This way u can c the difference in slopes and how they be effected.

[SQ SUBARU]

Bump. STICKY ? anyone feel free to add to it/feedback?

[White Lightning]

Impressive ... Welcome to SMD

Bump. STICKY ? anyone feel free to add to it/feedback?

I'm not sure about Sticky ... But this thread should be moved to the Sound Quality section for future viewing and discussion ...

[Skullz]

Good write up, just would like to add that every 6db slope is a 90 degree shift in phase which is mainly why you see 12db and 24db used the most as they are the easiest to get back in phase.

[rockFord_Expedition]

Yes essentially having a slope helps "blend" drivers together, so the frequencies pretty much "fade" or rolloff a certain db. They don't just stop, the frequencies gradually roll of at the certain rate, 12,24 db etc. If u didn't have it "rolloff", it wouldn't sound right. So say take a sub and a mid bass driver. If u have them say crossed at 80hz, and u didn't have a slope on the frequencies to "rolloff" then the frequencies would just stop, and any frequency above the 80hz would move onto the next driver up (the midbass). By having a certain db of rolloff slope, helps blend the sound to make it sound more natural. A better way if saying it could be, the slope is the rate of the audio level (sound) increases or decreases, but remember it's per octave!! If u look at a crossovers graph or look at a rta u can see the difference between 6,12,24 db etc, This way u can c the difference in slopes and how they be effected.

Most people don't "like" their own posts.

[SQ SUBARU]

Yes essentially having a slope helps "blend" drivers together, so the frequencies pretty much "fade" or rolloff a certain db. They don't just stop, the frequencies gradually roll of at the certain rate, 12,24 db etc. If u didn't have it "rolloff", it wouldn't sound right. So say take a sub and a mid bass driver. If u have them say crossed at 80hz, and u didn't have a slope on the frequencies to "rolloff" then the frequencies would just stop, and any frequency above the 80hz would move onto the next driver up (the midbass). By having a certain db of rolloff slope, helps blend the sound to make it sound more natural. A better way if saying it could be, the slope is the rate of the audio level (sound) increases or decreases, but remember it's per octave!! If u look at a crossovers graph or look at a rta u can see the difference between 6,12,24 db etc, This way u can c the difference in slopes and how they be effected.

Most people don't "like" their own posts.

So?? I'm new to this forum didn't know I hit the like button. I can like my own post if I want too haha