Stereo upgrade - Subwoofer connections...

[BarneyB]

OK this one is for the audio enthusiasts...

I recently upgraded the stereo in my 2008 STX D40.
I ditched all the factory stuff and fitted a new head unit, tweeters with a dedicated crossover, and front and rear speakers. Nothing crazy about it - just a cheap & cheerful upgrade.
Currently there is no external amplifier - just the HU driving everything.
I'm quite happy with the sound quality, clarity, imaging etc. The rear doors are not amazing but that's more about their location methinks.
But the only bummer is the lack of bass. The lower frequencies are OK on some tracks where the recording was loaded with bass, but many other, more balanced, recordings don't quite have enough.

So enter the small, self-powered under-seat subwoofer....
I have narrowed down a short list based on dimensions and price.

As far as I can see I can connect the sub a number of ways - and I'm wondering which way is best....?

1. Use the dedicated HU output for subwoofer.
This is a SINGLE RCA output....and I don't know if it's low level (pre-amp) or high level? (more on that later)
Presumably this would need an Y-splitter RCA connector to run to the 2 x RCA inputs at the sub?
This method has the advantage of being linked to the software options in the HU. So I would go into the system settings and select subwoofer "ON/Connected" and then adjust all the sub controls from the HU, including cross-over frequency, slope, gain, auto on/off etc. This functionality is designed to control a sub straight from the HU.
BUT.... don't know what I would set the gain, BB, cross-over Hz etc etc on the sub to? Would the HU settings confuse or conflict with the sub's amp? I guess the subs amp would just amplify whatever it was fed? (remembering the sub's amp is integrated).
The sub also has a wired remote control for volume (and in some cases gain, phase etc).

2. Use the L/R low level (pre-amp) outputs on the HU and run them to the low level input at the sub.
I believe this is the "traditional" way, but is falling out of favour more recently as high level inputs to amps are becoming the better SQ option?
I would then tune the gain, BB, phase, and x-over settings on the subs amplifier. I think the HU sub controls are redundant with this method...which is a bummer because any adjustment must be done down at the sub under the drivers seat. Most of them do have a wired remote for simple volume adjustment at the dash however...

3. Tap the speaker level signal from either the HU or the rear speaker wires, and connect to the subs' high level inputs.
I have reached out to Kicker Australia and they recommended using high level (speaker voltage) inputs to their active subs for better SQ, all else being equal. This is also confirmed by other audio guru's around the web. It seems high level inputs to an amp started as an option to facilitate retention of the factory head unit with aftermarket speakers....but has become a better option for overall SQ and sound "cohesion".
This method would probably also render the HU subwoofer control screen redundant because the HU wouldn't be able to apply the dedicated slope and gain settings via the full-range high level outputs??
I'm also not sure whether I would tap one left channel and one right channel?... or both channels from both sides...?

So what's the best way to connect and control the sub?
Maybe I should contact Kenwood (HU brand) and ask them for more details....

 

[exomoons]

I don't know if you've done this or not but maybe it'll help someone.

Don't tap speaker signal. Firstly wiring will be a mess. Secondly you are going to lower the impedance of the speaker (s) which will put stress on the amplifier, depending on how low the impedance is, you might cook the internal amp sooner then you'd think.

Average pre-out are 2V, some are 4V and some are 8V. Unless you're running for competition I wouldn't worry too much about it.

For 1: Use your HU to control the sub setting, you don't need to use y splitter as the HU is already filtered and combine both channels low frequencies into that single out put. Plug it in R or L of the sub yields the same result. Turn every setting in the sub amp off if you can, or by pass all.
For 2: Use your amp to control the settings, this is pretty straight forward.