Can someone explain the concept behind LOC/Equalizers?

Context:

1. 2017 Tundra SR5 crewmax non-jbl
2. Alpine Speakers (Front Doors: S2-S69C, Rear Doors: S2-S65C, Dash: 3" Component, Tweeter: 1" Component)
3. NVX 5-channel amp (1500W peak 750W rms)
4. $220 Rockford Fosgate r2s-1x12 Single R2S Slim 12” Shallow Subwoofer Loaded in a Wedge Enclosure with 250 Watts RMS / 500 Watts Max
   Rockford Fosgate r2s-1x12
5. Amazon Sound Deadening in the doors
6. Stock HU (with an aftermarket Carplay "software"; Audio isn't affected and can be thought of as stock)
   1. Note: I usually plug in via the USB cable, so there's no issue with Bluetooth lossy audio

The truck sounds great for the most part, however, I'm noticing that there is definitely a frequency that the truck is not playing correctly or even at all. It's somewhere in the mid-range. I notice it the most in pop music where there's a good amount of midrange, especially mid-range bass. I know, as a general fact, that the stock HU only sends low-ish frequencies to the doors and so im assuming that there is some mid-range frequency that is being filtered out and not played by either the doors (and subwoofer as it comes from that sound) and the dash/tweeters due to their high-pass filter.

So my quesiton is, how do you add that frequency back in? Ive read about LOC or Equalizers, but how do they add sound back in that has been removed? And, what is the difference between the 2?

Thanks for any input!

 

For example: https://www.skaraudio.com/products/ska7eq-7-band-half-din-car-audio-pre-amp-graphic-equalizer vs

$83 AudioControl LC2i 2 Channel Line Out Converter with AccuBASS and Subwoofer Control

https://www.amazon.com/AudioControl-Channel-Converter-Accubass-Subwoofer/dp/B00IIL0LW0?gQT=2&th=1

 

You aren't going to be able to "add sound back" without replacing the head unit with a quality aftermarket unit. I was in the "i wanna keep the stock head unit" boat for a long time. Ultimately, i should have listened to everyone that was saying "just replace the head unit"....i eventually did and went with a 10" kenwood, and should have done it from the start.

LOC's just convert high level speaker output to a RCA output, makes it easier to connect an amp to. Ones with adjustment (stay away from skar) will use amplification or suppression to adjust what signal is coming out of the head unit...if the factory head unit isn't giving out a certain frequency due to its filters/crossovers, you aren't going to be able to magically add it back in. Audiocontrol does have a nice feature that corrects bass-roll-off (more volume less bass) from the factory head unit.

Real midbass is a bitch to get right....

 

Did you bypass the OEM amp?
I'm pretty sure that is what sends mids and lows to the front doors, not the HU.

If you didn't bypass, and remove, the OEM underseat amp, you need to.
I'd guess you removed it when you installed your amp..

 

You can absolutely keep the stock head unit. Look at audio control equalizers like a DQS or a 4.1. That will help the signal and boost output.
The radio should always be passive/flat going to an amp or eq.

 

Have you tried running the HU EQ flat and using amp crossovers to adjust the sound?

Did you run new speaker wire from the new amp to the dash speakers?
The OEM wiring has the dash speakers powered straight from the HU and then the signal is split to the OEM amp for the doors.
The rear door tweeters are the same straight from the HU, then split to the amp for the rear doors...
That signal should already be full range.



As @Tundra1D6 stated, a decent Audio Control LOC/EQ will flatten the signal and also help prevent the bass roll off of the Entune as you turn up the volume.


Line Output Converters - AudioControl