Tuning assistance for LPF and HPF on amplifier (subwoofer and 2 way component)


CarAudio.com Newbie
was hoping to get some help tuning the amplifier that is powering the speakers.


- alpine 10 inch sub (swt-10s4. Manufacture list frequency from 30-200hz) currently set on LPF 80-100hz

- alpine 2 way 6.5 component speaker. it has its seperate tweeter and crossover box (xs65c. manufacture list frequency from 50-50,000hz) currently set at HPF 100hz

- amp: xa70f

I’m getting confused as to what settings I should have the amplifier settings set to.

current settings are:
sub is at 80-100hz LPF
2 way at 100 hz HPF

Should I have the settings at 30hz LPF (sub) and 50 hz HPF (2 way component)? or is above preferable?

the head unit has LPF and HPF settings… should I turn use thoses values on to correlate the values selected on amp or do not use them at all. to reiterate all speaker wires are wired directly to the amplifier and not the headunit

please school me, thank you!


CarAudio.com VIP
does one set the LPF and HPF values on the headunit as well, or is the amplifier sufficient? thank you
I would use the ones in the head unit instead of the amp personally, but either would work. One doesn’t need the other to work. The knobs on the amps aren’t very accurate sometimes and hard to tell if you actually have it set at exactly where you want it. I have my sub LPF at 70 and my midbass woofer at 65 HPF.
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Barry Schanz
5,000+ posts
10+ year member
St Cloud, MN
What's the vehicle?
What's the brand and model of your head unit?
Where is the subwoofer placed?


CarAudio.com Newbie
I would use the ones in the head unit instead of the amp personally, but either would work. One doesn’t need the other to work. The knobs on the amps aren’t very accurate sometimes and hard to tell if you actually have it set at exactly where you want it. I have my sub LPF at 70 and my midbass woofer at 65 HPF.

I’d like to use the digital feed off deck but I cant
control the slope so the amp will have to do. one benefit I have using the amp is when i disconnect the battery the settings should be fixed 👍


CarAudio.com Newbie
I'm an audio engineer. I haven't read other answers but I would say that this depends entirely on preference, however, it would be nice to know either the -3dB and -10dB drop off frequencies for both speakers, this can influence your decision.

Personally, 100Hz is a little high if you enjoy bass heavy genres of music like EDM and Hip-hop, but it's perfect for rock, country and alternative music.

There are two types of bass: you have your bass and then you have your sub-bass which is an entire octave lower than your traditional bass levels.

The bass region includes most bass guitars, toms, some brass instruments like the tuba and trombone, but it especially includes the kick drum.

Your sub-bass region is hard to hit with natural instruments, but it can be reached by large enough toms and kick drums, and also the piano, which includes bass guitars fitted with large piano gauge strings (like Korn, Slipknot and other heavy metal bands), but the sub-region is mainly incorporated into songs with the use of synthesizers, so if you aren't listening to rap, trap, edm, dubstep, house, future bass, etc, etc... then it's not really advisable to focus on cleaning up this region of the sound spectrum.

Above your bass comes the mids and the highs. How you set your crossovers is basically deciding the balance of your music. If you prefer a cleaner high-end, then you want to send less low-end and mids to your main speakers, but this will muddy up your low-end and actually make your sub-bass region weaker to nearly non-existant...

You can do this by setting the low pass as high as it goes (preferably no higher than 100hz) and matching that with your low pass. As it sits right now, this is going to be your setup.

If you want the cleanest "sub" bass frequencies then you'll want to set your low pass at either 50 or 63Hz and no higher than 80hz. This will take away from your high end since you are now sending more of the audio spectrum to your main speakers, but this can be easily offset with EQ. If you can, just boost anything above 8kHz and you should be good.

EQ works well for high end, but this same technique cannot be applied to the low-end. Boosting low-end with EQ is not really advisable... any form of EQ ALWAYS adds distortion to both sound but more importantly to phasing, which can actually add to your high-end but it can muddy up your low-end and actually make it sound weaker.

If you really want to know why, then study additive synthesis, or better yet, look up the frequency of a pure sine wave, then look up a sine wave + a sine wave with a ratio of two. The amplitude of the original sine wave is diminished by the addition of a sine wave one octave up (meaning its muddy). This happens with all distortion because distortion always adds higher harmonics to your fundamental frequency.... to sum this up in lamens terms, option 2 is usually better (but again it comes to preference).

Also, you don't want any overlap in your crossovers. You might think "the more speakers playing the bass frequencies, the louder it is", but this is not true at all... it introduces phasing and "phase modes", which are notorious bass killers, so never let the crossovers overlap, and if your high pass gives you a range (like 80 to 100hz) this is because filters taper off, usually at -12dB per octave, so if you set your filter to 100hz, you are beginning your filtering at 100hz, but it is still audible down to 80hz and beyond (but only to a negligible degree after 80hz), Personally, I'd set your low pass to match the lower end of that high pass range (80Hz), and if you don't care for it then try 90hz, then 100hz.

One last thing, the frequency response of your speakers is not as accurate as the spec sheets claim. If your speakers claim to go all the way down to 50Hz, then this is either their -10dB cutoff point or their -3dB cutoff. Knowing which it is- is very helpful, because if they are advertising their -10dB benchmark (meaning that at 50Hz, the sound dropped by -10dB, which is significantly quieter than -3dB) then this isn't accurate.

If the rating is referring to its -3dB cutoff point, then you can say that it is truly capped at 50Hz, but if it is referring to its -10dB point, then it's cap is much higher than this. The -10dB cutoff is the point where the frequencies start to become entirely inaudible, and the -3dB cutoff is where the audio first becomes noticeably quieter but still audible (it gradually decreases after this until it's inaudible) but companies will market their speakers using the -10dB cutoff, in order to trick people into believing their speakers go lower than they actually do, when in reality the speakers are incapable of reaching that frequency to effect.

Hope this helps, and if you want me to possibly elaborate more or want pics, or have other questions just let me know.


CarAudio.com Veteran
10+ year member
id use the deck settings, 80 for sub and mids. good starting point

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