@g-dude
Sorry this may seem TLDR, but I have tried to give you some useful info. Try to read through and don't hesitate to ask questions.
A good mic will capture a more authentic representation of your bass's sound. But using a mic live tends to be rather problematic. There are two major problems with using a mic: 1. Bleed from other instruments and 2. Feedback between the bass and various speakers the bass is running through. These problems become progressively worse as volume requirements go up. So a mic may work if the volume is low, but as the volume increases it becomes more and more difficult to get a good sound with a mic.
A big part of both problem is the upright bass is not a very loud instrument to begin with. If other sound sources are louder at the mic than your bass, then it tends to be a problem. To compensate you need to place the mic really close to the bass, which narrows the area of the bass that the mic is actually sensing. Unfortunately focusing on a small area may prevent the mic from picking up an accurate representation of what the bass sounds like.
Also, the sound from higher frequency instruments like cymbals will tend to hit the hard wood surface of the bass and reflect back into the mic. This can result in the cymbals being way louder in your mic signal than the bass. Worse yet, since the front of the bass is curved, the sound coming from the cymbals can be take multiple paths to the mic, which results in a nasty phasing/flanging effect. If the audio tech turns down the treble to try and mitigate the flanging, you no longer have a nice authentic bass sound. At this point IMHO, you might as well use a pickup.
Even worse if the sound of your bass coming back from your amp, the stage monitors, or the main PA cabs is louder at the mic than the direct sound coming from your bass. The bass, pickup, amp, speaker, and room acoustics form a feedback loop. If the gain is high enough, this feedback loop will start to modify the frequency response. In effect you get comb filtering where some frequencies add and other frequencies cancel. If the gain is high enough the resonant peaks will break over into feedback.
While a pickup may not sound as good as a mic, it typically will be way better at rejecting bleed from other instruments, and also have way higher gain before feedback. So IMHO mics are ideal in recording situations where the bass is isolated from other sound sources and you monitor on headphones instead of using a speaker of some sort. Then the mic only hears the sound of your bass and small amount of indirect reflections coming from the space you are in.
As has been mentioned, piezos pickups must be terminated with a relatively high impedance to sound their best. 1Meg is generally considered the minimum. The optimum impedance varies by pickup design. Many are best with an impedance somewhere between 4-5Meg, but even higher impedances can be optimum.
Most DIs put the amp's input impedance in parallel with the DI's input impedance. So if both have 1meg input impedance, the combined load on the pickup drops to 500K. The Countryman Type 85 has a 10Meg input impedance. So if the amp's input impedance is 1Meg, the combined load is 909K. I.E still almost 1Meg. The Countryman Type 85 is very common:
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Another option is the Radial PZDI. The PZDI input impedance can be switched between 220K, 1Meg, and 10Meg. Additionally the "Thru" can be switched from parallel to buffered. If the Thru is buffered, the pickup is isolated from the input impedance of your amp and only sees the impedance of the DI. PZDI also has a switchable 3khz Low Pass Filter and a variable High Pass Filter. Although this is a very good option, I would expect the PZDI to be fairly rare:
View attachment 4644412
Some modern pickups actually sound really good. Older pickups tend to require quite a bit of corrective EQ to smooth out the high-mids and treble response. They can actually sound surprisingly good with some corrective EQ to smooth out the frequency response. I used to run a Fishman BP100 or Underwood. I thought the Underwood was marginally better, but neither was pleasant without a lot of corrective EQ.
IMHO you will probably have the best results running your bass through your amp and applying a bit of corrective EQ to get the best possible sound. You can try sending the mic to the audio tech, but the mic signal should not be used for stage monitors. If it's necessary to put the bass in the stage monitors, use a signal that comes from your pickup. Regardless, the audio tech should avoid putting the bass in monitors that are close to you.
I have had good luck elevating my cab to about waist level and tilting it back to aim at my head. When used this way, the cab is intended as my personal monitor and the PA delivers the bass to other players and the audience. This approach results in more clarity and the ability to hear with your amp running at a lower level. This reduces volume and aiming the mids away from the bass's body improves gain before feedback, but you won't hear a deep thumpy tone on stage. If that is what you want, you should put the amp on the floor. But you need to understand that you will probably have more problems with low frequency feedback with the amp on the floor. Choose the preferred compromise.
Working all of this out in a rehearsal is really a good idea. It's very likely that the audio tech will not know how to deal effectively with an acoustic upright bass. Upright bass tends to be rather difficult to amp well, so the audio tech really needs the right skills and knowledge. Attention to how the ensemble and monitors are laid out are important considerations.
Even if you get everything perfect in rehearsal, it's likely that considerable rework will be required on gig day unless everything remains exactly the same. Make sure the audio tech sets aside time on gig day to ensure everything is still dialed in.
Thankfully I wasn’t very good at German grip…
