All about bass (or lack thereof)

Since I only have an under-seat sub, which does NOT produce deep bass like a "real" sub (and I'm really not interested in a "real" sub - at least not at this point), I want to do everything I can to "maximize" by bass output using what I have.

Since I have 6x9 speakers in the doors, they are actually capable of producing some decent bass. However, right now, I have them crossed over at 80hz with the sub. Would it be "problematic" if I let the door speakers run down to 40hz or 50hz in order to "combine" their output with the under-seat sub - just to produce the "best" bass I can, using what I have? Or would having such an overlap between the under-seat sub and door 6x9's cause more issues than it's worth?

Obviously, I can just try it and see what happens - but I'm kind of interested in the technical side - the "whys"...

Just FYI - I have 75W per channel RMS, by the way (6-channel amp - 2 channels to 3.5" dash coaxials, 2 channels to door 6x9's and 2 channels to rear speakers). I need my rear speakers though - so I'm not willing to use 4 channels for my 6x9 midbass drivers.

Thanks in advance!

What kind of 6x9's are they?
I doubt you'd get them down much lower than 70Hz... even if they were high-end ones.

Which underseat subwoofer do you have? If anything, you may want to lower the crossover on the sub, and keep those at 6x9 at 80Hz

I guess details like what speakers/sub I have might help... :-)

The 6x9 door speakers are the 6x9's included with the Kenwood Excelon KFC-XP6903C component set (6x9's midbass for doors and 3.5" coaxials for dash). According to my REW measurements when I first got the speakers (before I even had ANY "break-in" time on them), they actually go all of the way down to below 40hz! Believe it or not, 38hz is actually the frequency that has the highest dB over the entire frequency range (at least in my car, at my seating position). Here the REW graphs for them without any crossovers or EQ applied:

https://uploads.tapatalk-cdn.com/201...1047c3f831.jpg

The under-seat sub is a JBL BassPro SL. Its freq response as listed as 35hz-120hz - don't have a REW graph of it off-hand though. It's a 135W RMS 8" under-seat sub. It seems that the 6x9's may actually go a tiny bit lower than the 8" under-seat sub! :-) But the under-seat sub definitely seems to produce more bass volume-wise overall.

It just seems such a waste to cross those 6x9's over at 80hz considering they output bass down to 38hz. Was just thinking that combining both the 6x9 speakers and the under-seat sub would help with the lower-end bass. I just wasn't sure if it would cause any "phase" issues or something like that (still don't have phase figured out!). :-)

In my other car, which has older Pioneer D-series speakers (6.5" in doors and 6x9" in rear deck), I *definitely* get "better" bass when I don't cross them over at all and just let them roll off naturally - combined with a Pioneer under-seat sub. I always see people say that 6.5" or 6x9" speakers don't play bass below 80hz well, but that doesn't seem to be the case, at least not with these two inexpensive speakers (the Kenwood Excelons in my Challenger and older Pioneer D-Series in my other car)?

Yeah no doubt, 6x9's can definitely drop down and boogie like no other 6.5" midbass I've heard - but you also want to keep them clean (low distortion). You could try lowering the crossover on them a bit more, but also drop the sub down even further and see if you like that better. I believe if the midbass and subwoofer meet, then you will have localization, phase issues, and even cancellation.

Those Kenwoods were designed to be true mid bass speakers which might explain the performance on the lows. It's also why I've been wanting to try them in my 4runner. Question is, how well they go that low and at what level. I would imagine some distortion starting pretty early at 40Hz. If not, I really need to try a set.
They can be run with the sub but I would imagine phasing may be a problem. Also, without an adjustable high pass for the sub, the sub's roll off could be difficult to match and you may get some strange goings on as the sub no longer has the 6x9's helping out.
Basically, you may get an unnatural sounding boost beginning at 80Hz when the sub kicks all the way to where the 6x9's begin to drop. This will require some eq, phasing and maybe a little luck. I like chithead's suggestion but if you decide to experiment I'm curious to know the results.

Is the JBL on the driver's side, or the passenger's? While discussing my install with Steve Cook, be recommended I put the sub on the passenger side, because having it on the driver's side would cause a bass-trap effect.

The JBL sub is under the passenger seat. While I'd like to claim that I put it there because I knew it would work out better there sonically, like mentioned above, the honest truth is that is just fit better there, so that is where I put it. :-) The drivers seat is a power seat - and at it's lower settings, it would physically hit into the sub if it were under the drivers seat. I didn't want to risk someone lowering the seat too far and damaging something. The passenger seat is a manual seat with no up/down adjustment, so there is no way the seat can physically contact the sub on the passenger side. There is not much room under the seats in the Challenger, so my choices for an under-seat sub were VERY limited. The JBL seemed like the best I could do - and it actually fits perfectly under there - and even works out perfectly for the wiring (with where the power/ground connections are, etc).

I would have preferred a 10" under-seat sub, but just didn't see it happening with the physical constraints.

I'll do a little experimenting. So far, I've only been doing pink-noise tuning, so I have no idea what phase looks like. I need to start getting some REW "Measure" measurements to see more data (such as phase) at this point, I guess.

Thank you all for taking the time to reply - I really do appreciate it. I'm learning what I can, when I can. :-)

Get some test tones and play them.
Sub only (turn off other speakers) 30Hz, 40Hz, 50Hz, 63Hz, 80Hz, 100Hz
Now play with your sub amplifier's crossover and lower it
Play the tones again do that over and over again so that 30Hz sounds slightly less powerful than 40Hz and 50Hz
Now if you have a gentle slope going from 30Hz and up, use your head-unit's crossver now with a 24dB slope @ 80Hz and listen.
Now try 70Hz (or 63Hz) and listen
Choose the one you prefer.
You can revisit your gain for the subwoofer in the process coz you might be losing some output that way

Did the above when I had an under passenger seat subwoofer and I choose 40Hz 12dB/oct on the amplifier and 70Hz 24dB/oct on the HU

Kelvin

Just to follow-up on the under-seat sub talk from above... Here I found that my under-seat sub crossover was actually set to 80hz, NOT 120hz like I had thought! So the sub had a 80hz 12dB LP filter and I was defining an 80hz, 24dB LP filter for the sub in my DSP - so obviously, I was ending up with a 36dB LP filter at 80hz!

I've adjusted the DSP to use a 80hz 12dB LP filter, so that I end up with a 24dB LP filter and it seems much better! I actually had to turn the sub down a little once I had the correct settings. :-)

Mystery solved. Thanks everyone!