Last month, we began discussing ideas on how to get a great electric bass sound onstage. If you missed it, you can check it out here: fohonline.me/1laHdMc. We examined how the sound of an electric bass can be seriously influenced by the phase relationship between the DI and the bass amp, and we looked at possible solutions.
Before we get into a different aspect of bass sound, I’ll mention another dirty issue regarding phase and bottom-end. Similar to the relationship between the mic and the DI, the P.A. may be fighting the sound of the bass coming from the bass amp on stage. Think about this: when standing at the mix position, you’ll probably hear bass from two different locations: the P.A. and the stage.
You (and the entire audience) are almost certainly closer to the P.A. speakers than you are to the instrument backline. As a result, sound from the P.A. arrives at your ears before sound coming from the bass amp. Depending upon the distance between the P.A. and the backline, this time-misalignment causes (at best) smearing and comb filtering, or (at worst) destructive interference between the bass rig and the P.A. system. The audibility of the problem depends upon the venue: it tends to be more noticeable in smaller venues where the audience hears a lot of sound from the stage— as opposed to larger venues where the audience gets the majority of the bass sound from the P.A., not the stage. If there’s no bass amp on the stage, the issue disappears. [This time alignment issue persists across the frequency range but is most pronounced at low frequencies —ed.]
The solution is to delay the entire house P.A. to the backline. Not delay as one might apply to a lead vocal or a guitar solo. It’s more like “let’s hold back that P.A. system just enough so that sound from the backline can catch up to it and reach the listener at the same time as sound from the P.A.”
Every modern P.A. processor (and most digital mixing consoles) incorporates a signal delay that can be applied to the main outputs. We measure this delay in milliseconds, but most processors allow you to view and adjust it in feet or meters. Measure the distance from the acoustic center of the P.A. to the backline, and then dial in the number of feet as the delay time. I’ve had experiences working in smaller venues where adding this delay made a profound improvement in the bottom end, due to the fact that you hear significant amounts of sound from both the P.A. and the bass rig. But in larger venues where the P.A. is responsible for the majority of bass sound heard by the audience, the difference may be minor or insignificant.
Sound To DI For
Now that we have that mess out of the way, let’s discuss the bass sound coming through your P.A. system. We’ll start with the DI.
I’ve worked with at least one player who (though he was always willing to try) typically shied away from placing a DI between his bass and amp. He felt that anything in the path compromised the sound of the instrument. Judging from the excellent tone he got, I would not argue with him. Theoretically, the DI shouldn’t influence the amp tone of an electric bass, but there’s a reason this column is called Theory and Practice — in practice, theory often goes out the window! We can’t discount the possibility that an inferior DI could negatively impact the sound of an electric bass. If I recall correctly, he did not shudder at the thought of plugging into an Avalon U5 or a Radial Engineering JDV — both of which are premium-quality DI’s employing Class-A circuitry.
That being the case, it’s very helpful if the bass amplifier/head has some sort of a direct output. This guy’s amp of choice was an Ampeg SVT Classic or SVT Vintage Reisssue, both of which have a balanced XLR output as well as a 1/4-inch TS line-level preamp out. Given the age, crankiness and modifications that some of these heads suffered (we used rental gear much of the time), we didn’t have a formula for his bass sound, other than the bass always went directly into the amp. Whenever possible, we’d take the XLR output from the head straight to the P.A. Usually, it worked like a charm, but occasionally we’d get a ground loop. Often, it could be cured using the SVT’s ground lift switch, but other times not — in which case we’d patch the preamp out to a DI, take the DI to the house P.A. and use the DI’s ground lift switch to cure the ground loop. [Lifting/removing the ground pin on the amp’s AC cable is a strict no-no, as it removes the safety factor of grounding an electric appliance].
Mic Selection, Placement
In almost all cases I use a mic on the speaker cabinet in addition to the DI for two reasons: the first is contingency — if one source goes down, we still have the other. Losing the bass in the mix is not an option. The second reason is that the DI produces a tone very different from that of a mic on the amp. You can view this in Fig. 1 and Fig. 2, which show RTA for the same note played on a bass through the DI and a mic on the amp.
Where do you place that mic? In an ideal world, we’d place the mic several feet from the front baffle — after all, that’s how the player hears the amp and adjusts his or her tone. Most 4-by-10 or 8-by-10 cabinets are designed to (pardon the artsy-fartsy description) “bloom” several feet away, where the individual drivers combine to produce a whole that’s “greater than the sum of the parts.” Onstage, you can’t mic a bass cabinet from several feet away because it captures too much spill from the other instruments and monitors, so we end up placing a mic fairly close to one of the many speakers in the cabinet.
First order of business: make sure all of the speakers actually work. During sound check, move the mic from speaker to speaker and find out which one sounds best (trust me — they will sound different). A flashlight helps locate the speakers behind a dark grill.
In terms of mic choices, kick drum mics are obvious suspects for bass amp: Shure Beta 52, AKG D112, Audix D6, Sennheiser e602 (II).
Not-so-obvious suspects include the Sennheiser MD441, Sennheiser MD421, beyerdynamic M88, Electro-Voice RE20 and RE320, and — for bass players who growl (through the amp, that is), the ol’ trusty Shure SM57 or Audix i5. I sometimes see people jam the mic up against the grill cloth, but that spooks me because once the amp is cranked up, the grill cloth is going to move back and forth against the mic, so I usually back off an inch or two. If I’m looking for snap and growl, the mic is aimed at the dust cap. If I want a round tone with more bottom, I’ll shoot for the paper between the dust cap and the surround.
Compression Suggestions
Back at the mixing console, this channel gets a bit of compression to help even out the volume of the instrument across its range: 2:1 or 3:1 ratio, medium attack and release, threshold set low enough that there’s always a few dB of gain reduction. Feel free to compress the DI more aggressively than the amp: 4:1 or 5:1 ratio, fast attack and a threshold low enough to maintain 6 to 10 dB of gain reduction. Over-compressing the DI usually produces an ugly snap that will actually stick out of the mix and be self-defeating. If you can hear it working, you’re probably using too much.
Equalization Advice
Both channels (miked and direct) get a high-pass filter dialed in anywhere between 20 Hz and 120 Hz, depending upon whether I want the amp or the DI to contribute more of the low-end. The low E string on a bass has a frequency of approximately 41 Hz, so boosting frequencies lower than this will probably give you some thump but may not be particularly musical.
While I can’t tell you precisely how to EQ the bass (that’d be like telling you how much hot sauce to put on your food), here are some general ideas:
• A shelf boost between 50 and 100 Hz will give you more size, but don’t overdo it or you’ll kill the kick drum. A peak around 70 Hz will produce more thump and rumble, but again — mind the kick drum.
• A peak between 600 and 700 Hz adds presence. If the amp sounds nasally, try a dip in this region.
• Add 1 kHz for more growl.
• If the sound of the strings on the fretboard is too pronounced, try a shelf cut between 7k to 8k Hz or a low-pass filter with a corner frequency around 4k Hz.
• If the bass is generally dull, an HF shelf boost set between 4k-5k Hz may help if the strings aren’t dead. If the bass is too woody (!) try a dip around 400 Hz.
In the future, we’ll look at speaker simulators and modeling DIs.
