The effort of making an electric bass sound like a double bass is pretty much an exercise in futility. I've been trying to find a solution to that problem for about 25 years. And although my present solution sounds half-way decent in the mix for a trio or quintet, it still sounds like a poor excuse for a double bass when trying to do a solo.
Most of the suggestions to roll back the mid controls and increase the bass I think are not the best solution. Tdvt's suggestion to not dial out all your mids is a good one. A double bass actually has a wide range of tones, its just that in a mix, those are somewhat overcome by the ensemble and volume level and the technician controlling the mixing board, if that's involved. This is true of the steel strings used on double basses today, but when gut strings were the norm, there was a less distinctive overtone structure and a shorter decay rate which I think many are trying to mimic by using a piece of rubber/foam mute under the strings near the bridge. There's also a varied degree of note decay depending on the bass and strings. I've never used a piece of rubber/foam to shorten the decay time on my fretless, but I can see its use if the tune were a slow ballad, but on medium and up tempo tunes, I don't see the need for it.
I've played double bass for 46 years and I took up electric bass 25 years ago. So I come from a little different perspective. As far as thinking like a double bassist, hmmm, even though I'm coming from the other direction, I don't think I've been able to translate entirely what I do on double bass completely to fretless. I guess my take on that would be that if you really want to think like a double bassist, then you really need to pick up the instrument at least a little to more fully understand that concept. They may play the same notes, but they're entirely different instruments in approach and execution. One younger player I met a few years ago who is equally competent on both is Brian Bromberg. A very interesting player to hear.
My current setup on electric bass to simulate a double bass is a fretless I built 26 years ago from scratch.
I've tried a number of different pickups, starting with ceramic Dimarzio's (P-bass style) to what I'm using today which is an EMG active pickup. I've used various types of strings, flat and round wound, and have been using LaBella Deep Talkin' Jamerson's for the last couple years. I currently use a EA Micro 300 amp, an older SansAmp Acoustic DI preamp (
Invalid Link Removed ) and an EA CxL110 cab with an Eminence 10 in Basslite driver (the original coaxial driver had the bass driver's voice coil leads come loose and rattle and EA no longer carried the driver and so I went hunting for a suitable replacement). The amp's tone controls, bass, mids and highs are at 12 o'clock. The SansAmp is about 11 o'clock for the bass (maybe 12 depending on the room), mids 12 o'clock and about 9 o'clock for the highs. I also have the blend (tube enhancer) at about 1 o'clock and the mid shift at 160Hz. I use a Fishman Platinum Pro-Eq for double bass.
Contrary to the beliefs of many, a double bass does not have a substantial amount of fundamental in the lowest octave or so (listening not miked or with a pickup) as compared to an electric bass, but does have a tremendously varied tonal response through out its range and results in some basses have a brighter tone while some others have a darker tone inherent from their design. The cabinet can also over accentuate the lowest octave so it sounds bass heavy and un-natural as most cabs are meant for electric bass, not double bass. Many that hear my fretless setup comment that it is as close as they've heard an electric bass sound to a double bass. I also play fretted instruments, 4 ond 5 string depending on the group and style of music with other amps/cabs. You may ask why do I play a fretless bass when I already play double bass. Its just that there are a number of places I would never take a double bass. Also, if the volume level is going to be excessive (and I try to avoid those types of gigs), why use a double bass?
Sorry for the long post. I hope this gives you some food for thought.
Lloyd Howard