Alpine Head Unit question


New member
Username: Wmzzz

Post Number: 1
Registered: Oct-05
I've been searching my way through countless helpful posts but couldn't find anything pertaining to my issue (did find some good info though on tweaking my setup).

I've got an Alpine CDE-7870 head unit, 2 MTX 12" subs, Alpine 6x9s, soon to have Alpine 5.25s for the doors. Subs are powered by a Kenwood 800W amp.

Upon checking some settings on my head unit, I found that if I toggle the Alpine's "Sub On/Off" option to OFF, my subs hit about twice as hard as when the sub option is ON. I'd assume that the subs should quit playing. Comments? Anything to check?

Additionally, my Kenwood amp has a HPF/Off/LPF switch. Just to make sure, I have the amp set on LPF, and the freq. set at around 80hz. My head unit's "bass center frequency" is set at either 60Hz or 80Hz. Is this correct? Any changes/recommendations?

Thanks a ton in advance!

Platinum Member
Username: Glasswolf

Wisteria, Lane USA

Post Number: 10788
Registered: Dec-03
your sub amp isn't connected to the sub RCA outs of the alpine. its connected to front or rear RCA outs.
the sub on/off switch affects the sub out RCAs, and when you turn it off, you're allowing full range to go to your front/rear RCAs as if there's no sub present. otherwise with sub turned on, you're sending low frequencies to the sub RCAs, which you don't have connected to the sub amp.

easy fix.
connect the sub amp to the right preouts

New member
Username: Wmzzz

Post Number: 3
Registered: Oct-05
My CDE-7870 only has one set of RCA connections in the back, labeled "Rear/Subwoofer RCA Connectors (CDE-7870 only)". The 7872/7874 has 2 sets of RCA connectors - Front RCA and Rear/Subwoofer RCA connections. This info is found in my owner's manual for the head unit.

Basically I'm assuming with my HU, when I turn the sub OFF, i'm putting full range to the subs, and ON allows low frequencies to the subs? Basically there is no way on my HU to turn the subs off, other than by the switch I installed in-line w/the Remote On wire, due to the setup of the RCA connectors?

Also, any advice on my frequency setting questions?

Gold Member
Username: Illuminator


Post Number: 2008
Registered: Apr-05


Basically I'm assuming with my HU, when I turn the sub OFF, i'm putting full range to the subs, and ON allows low frequencies to the subs?

Yeah, you're toggling between full range and sub out.

I guess a switch hooked up to the remote wire is, in fact, the only way to turn it off.

New member
Username: Lukewarm12

Bedford, PA USA

Post Number: 4
Registered: Oct-05
I may have a suggestion....
I also have an ALPINE HU and when I first got it I had the same problem.
When SUB is ON, my subs played lower than when it was OFF.
The reason for this was because of a hidden feature. There is a sub level control setting on mine (you have to hold in the tuner knob to get to it) that is used to toggle the sub volume. the factory default was on 1. The level control went to 15. It is probably set this way so you do not blow your subs when first hooking them up. So basically unless you find it and turn it up, you are playing your subs at the lowest volume when the SUB level control is ON. When you turn it to OFF, there is no level control, and basically you are pushing out the full power of the RCA wires.
This may be your case, but was the case with mine.

New member
Username: Lukewarm12

Bedford, PA USA

Post Number: 5
Registered: Oct-05
One thing I forgot in my last post....
When you are turning the SUB feature to are not turning the "SUBS" or your RCA signal "OFF" you are turning that SUB level control I mentioned off. Basically, with it off, your RCA's send the full power signal through. You cannot toggle the RCA signal. With the SUB level control on, you have the option to turn the RCA level from 1 up to 15.
Until you find that feature within your settings, I bet it will be on 1, (the default), which is why it sounds shitty.

New member
Username: Lukewarm12

Bedford, PA USA

Post Number: 6
Registered: Oct-05
And Jexx is right, the only way to REALLY turn off your SUBS when playing your stereo is by installing a toggle switch onto your remote Wire. (although I do not know why you would want to turn your subs off). If you find the SUB control feature, you can turn it down to 1, which does not shut them off, but does cut out most of the bass. I use it when someone is riding with me who would not appreciate by subs blowing them through the front windshield (like my Grandma!!!)

New member
Username: Wmzzz

Post Number: 4
Registered: Oct-05
Thanks a bunch. I've already adjusted the sub volume feature. Very easy to find on my Alpine - it's in the same menu as the fader, balance, etc. I re-adjusted LPF frequencies on the amp, amp gain, and hu settings (as well as finally put in my Alpine 5.25" door speakers. Now everything is balanced.

I used to have the subs set to really kick hard. That was my reasoning for installing the amp kill switch. But now my tastes have changed, and it's all Sound Quality. Now I really DON'T need to turn the amp off. Still nice however if I want to listen to music w/o the car running and don't feel like draining my battery.

Thanks for the detailed info though everyone.

New settings on headunit:
Sub: +5 (out of 15)
Bass: +1 or +2 (out of 7)
Trebel: 0 (out of 7)
Fader: Neutral
Balance: Neutral
Bass Center Freq.: 80Hz
Trebel Center Freq.: 15kHz
No "Loudness" control enabled

LPF Freq.: 80Hz
Gain: approx. midway
No bass boost

Everything sound like it's set correctly for least distortion and for maximum sound quality?

New member
Username: Lukewarm12

Bedford, PA USA

Post Number: 9
Registered: Oct-05
This sounds almost exactly how I have my settings set. I am also all about the SQ. The only thing I have different set is the trebel at about 5 instead of 0. However, this is because I amped my internals, and they can handle the hire settings. If you are running straight deck, it may get to tinty and annoying.

Unregistered guest
I used to have 6x9's as a rear fill and a sub. When I took the 6x9's out, the bass was much better, I don;t know why. A lot of audiophiles don't have a rear fill at all, but I do.

Have any of you experienced this?
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