I normally set low pass on the amp to just let the low frequencies going to the rear speakers.

The D3 has the option to turn on/off the sub-woofer. If you turn on the sub-woofer, it will does something similar.

What should I do? both or just the amps?

If you have a sub/amp, turn it on

I have amps, but not sub. I select speakers with low frequency response for rear speakers to fill with bass.

You meant just turn the low pass on the amp? not the D3?

Why would you only want low frequency from your rear speakers? Seems like a waste to me. I would let the whole frequency range through and just turn up the amp's bass boost a bit if it has it.

Because I want it act as a sub.

Amps doesn't have bass boost.

It just seems kinda stupid to use full range stereo speakers as subs if they weren't designed to work that way. But if you must... It doesn't matter if you use the amp's frequency cutoff or the D3's. It has the same effect.

I run my rears as subs, fronts on high pass, sounds great. Left and right stagging is much better, instead of have vocals comming from front and rear. The front doors produce great mid range and highs, horrible enclosure for bass. Rears with a trunk has great bass, because the trunk is the enclosure. Why have mids and highs in the rear when it's right there at the doors?

Having all the speakers running full range is like listening to music on your home stereo in surround sound. Sorry, but there are no audiophile guys listeng to music in full surround.

Pioneer even had a feature on all the decks called "FIE", front image enhancer. The name confused people so they just changed it to rears as subs.

You don't get what I'm saying... Using a full range speaker as a sub when it wasn't designed to operate that way is probably going to shorten it's lifespan.

That makes no sense. How can you shorten the lifespan of a speaker by taking out frequencies?

By pushing high levels of bass out of them.

I think your a little confused on what sub frequencies are. A full range speaker is just that, full range of frequencies. Depending on the speaker, it is usually 45-22khz. It has nothing to do with "pushing high levels of bass through them". Of course you will damage a speaker by doing that, loud on with bass all the way up. You can also damage a speaker in full range the same exact way.

By setting the rears to "Sub", all your doing is cutting off the frequencies above 80, 100, or 120 hz. It is not adding those lower frequencies, the speaker was already playing them in full range.

I give up...

what Hfi is trying to say is,Sub spkrs of made to play low range from 40 -120..Ful range play from 120 up depending on the size..If you push 80h into a full range spkr alone it will blow before its time..Why dont you take the full range spkrs out and replace them with subs?

I think your a little confused on what sub frequencies are. A full range speaker is just that, full range of frequencies. Depending on the speaker, it is usually 45-22khz. It has nothing to do with "pushing high levels of bass through them". Of course you will damage a speaker by doing that, loud on with bass all the way up. You can also damage a speaker in full range the same exact way.

By setting the rears to "Sub", all your doing is cutting off the frequencies above 80, 100, or 120 hz. It is not adding those lower frequencies, the speaker was already playing them in full range.

I agree with superjet. The speaker I got reponses to frequency 25Hz-25,000Hz. I just want to play 25Hz-250Hz on this speaker. There is nothing wrong with this.

Pushing "unsupported" frequencies to the speaker is really bad. Just like send full spectrum to tweeter is bad since tweeter is designed for high frequencies only. But this is not a case in my scenario.

Why I don't try sub instead of this speaker? I am not a fan of bass. Having a sub gives me too much bass. This speaker gives me enough bass I am looking for.

Anyway, I think you guys are way off the topic.

Just need to know whether I should control from D3 or amps or both.

I answer myself by saying both with good reasons.

It doesn't matter if you use the amp's frequency cutoff or the D3's. It has the same effect.

Using the D3 gives you the convenience of changing the level and cutoff frequency of the sub output from the driver's seat, but only to one of 3 different frequencies. And Using the amp's low pass crossover, if it's the type with the frequency knob, gives you the ability to fine tune the cutoff frequency to exactly where you want it, but you have to go to the amp to do it. There's ups and downs of doing either, so it's basically up to personal preference, really.