Questions about EUB feedback

There are several reasons why people decide to play an electric upright bass. Some have lots of children and do not have the space for a large doghouse bass in their crowded houses…Others have weak spines and refuse to carry heaps of wood on their backs. Taking a double bass with you in trans-continental flights costs as much as inviting your girlfriend for a trip (which is mostly more rewarding as she is able to walk, as opposed to the large block of wood that is waiting to be transported). Some think the sound of EUBs is more versatile and prefer the growl some basses offer. Taking your eighty-year old Hungarian bass to a hot dance club is also not favourable. The look of the wooden eub-sticks mostly appeals the audience.

I could continue for ages summing up reasons for buying an eub, but a very common reason for buying an eub is because acoustic double basses can be rather sensitive for feedback, especially in places where the sound-pressure level is required to be quite high.

Bass feedback

As an owner of two acoustic basses, I find the sensitivity to feedback amongst acoustic basses to be very diverse. My most-used acoustic bass, which has a beautiful and loud tone when played acoustically can become a nightmare when played on large stages. The amplified kick drum of the drummer triggers the body of the bass and it easily starts resonating. Feedback is accomplished easily.
The other acoustic bass, a fourty year old plywood bass, has a more quiet character. It’s OK when played acoustically, but when amplified, it becomes the growling groover I like! It just does not feedback, whatever I do.

This made me realize, there is this thing called construction. Regular double basses are still built to fit in acoustical settings. Most basses sound great in ‘timid’ jazzy settings and there of course, there are basses who never suffer from feedback. But to me, it seems that the better the bass performs when played acoustically, the weaker it performs in louder sound levels.

Motivation

I got to this topic because Dominic Peters sent me the following message:
Hi there great site! I wanted to ask you advice – I am or have been) the owner of a Yamaha SLB 200, an Eminence removable neck bass, the Aria custom shop EUB and a electric upright bass made here in Cape Town, South Africa (which is where I am based). I am looking for a solution to a problem I am having with amplification-I play in a Nu-Jazz outfit called Goldfish [www.goldfishlive.com] and although I am very happy with the Eminence as the bass of choice (it travels well although is a bit of a mission to re-assemble each time I fly,3 times a week on ave) but for the style of music I am doing, the pick up doesn’t handle the spl and levels on stage, feeding back easily. I have seen a Steinberger which uses the magnetic option but sounds nothing like a double bass. Have you got any ideas that might help? are there magnetic kits suitable for fitting to the Eminence?

Look forward to any feedback (from you and your readers… not my bass!)

A groovy video

First of all, you definitely should check this movie of Dominic performing live with Goldfish, playing a Yamaha Silent (SLB-200), as this video has this great vibe, and shows some great bass playing. Furthermore, it helps us to understand the setting in which the bass is played: a place with screaming audience and loud beats. Keyword is excitement!

I like that tone of the Yamaha Silent. Although it misses some of the character of acoustic basses, it seems to stand out well in rooms with lots of noise.

Back to the problem: feeeeeedback!

But back to the problem of Dominic…now there we are. Feedback…the Eminence bass is a hollow body eub (in fact, it could be seen a small body double bass, or a semi acoustic) and it can’t be altered that hollow bodies are more sensitive than most solid body instruments.

When I built ebass, I wanted to have a more portable instrument (which is not really solved because ebass is quite heavy) which would not suffer from feedback. The latter has worked out well, because I never have feedback loop, unless I rest the bass to my amp when taking a pause, without muting the sound.

The magnetic solution?

The problem of the Eminence is that it has a hollow body, which makes it more susceptible to feedback. I doubt that adding a magnetic pickup will be the perfect solution, because magnetic pickups eliminate part of the work of the body (as you’re picking up the strings more directly). If you buy a beautiful hollow body instrument, why would you not use the resonance of the body?

Furthermore, I find magnetic pickups on double basses only suitable for specific styles of playing, for instance rockabilly. Placing a magnetic pickup (such as the Schaller magnetic bass pickup) on the Eminence might solve some of the feedback issues, but I doubt that it will provide the same tonal quality on this bass.

But or course, feel free to try this yourself! Mixing a magnetic with the original piezo signal is also an option to consider.

Other solutions?

Sub-frequencies

There are some things to keep in mind here. EUBs can on one hand solve feedback issues at loud SPLs. But the downside, is that the player misses acoustical feedback though his body, because most EUBs are practically silent. This can makes the player insecure about his playing (after all fretless players need some instrumental feedback for correct intonation), which is mostly solved by cranking up the volume and adding lots of bass, in order to feel the bass in the stomach. A downside of adding bass with EQ is that this is mostly a low shelving EQ, which means that you are adding lots of sub-frequencies as well. And in my experience, those are responsible for many problems: you lose definition, the bass is more susceptible for feedback, the bass amp puts lots of energy in those subs, the bass sound can cause listener-fatigue and in some cases, lots of sub can lead to speaker failure, if you’re very unlucky.

In a sense, this is a monitoring issue which can be solved. A solution would be to use a high pass filter (which mutes all sound below a specific frequency) and attenuate this in such a way that it leaves the regular bass frequencies intact, while filtering the sub-harmonics (so 38 Hz for a four string bass would be safe, 28 for a five string). Or course, you can try if a 31 band EQ works for you to eliminate the most prominent feedback tone(s) as well.

The idea that a double bass needs lots of extra added bass and sub harmonics can be a fallacy. It sure was for me. You can get bass-addicted, which eventually makes your bass sound like a massive muffled nuclear explosion. Question yourself on a regular base: isn’t there to much bass in my sound now? 🙂

OK, just be careful with adding lots of bass. For you – the player – basses are difficult to hear, while others are perfectly capable of hearing your bass tones. Bass frequencies need some distance, so stepping away from your amp actually might help you hearing and feeling the bass better. In my experience, this works better with larger speakers (15″ or 18″) while the ‘horizontal reach’ of an array of 10 inchers often is more limited. But one speaker cab is not the other, so this again requires some searching and experimenting.

Hollow floors

Another thing I found is that feedback can occur through the floor. Many gig floors are hollow, so if you place your amp and bass on the same floor panel, you can have a problem. Experiment with placing the amp onto blocks, rubber pads or whatever that prevents the floor from vibrating. Try to place the amp on a different panel than the one you’re standing on. If you’re not sure how the floor reacts to bass, just jump on it and you’ll probably hear what it does.

Experiment with your position in relation to monitors and drum sidekicks. Other low frequencies can also ‘trigger’ the bass.

Now if there are PA-subs placed under the stage, you have a real problem. : )

Use a preamp

Be careful with adding lots of bass. EQ amplification can phaseshift your signal, which might lead to other problems. If your signal lacks proper low frequency balance, look for a preamp or amp with a piezo input. The signal of most piezos is not always optimised for all amps. If your bass has an internal preamp, adding another preamp probably not very useful.

Experiment with the placement of the piezo

This small heading says it all…I found that moving the piezo about 1 mm can hugely alter the sound and dynamics of your instrument. If the pickup has moved during transport, your bass sounds differently. When you use and Underwood-style of pickup, leaving one of the transducers out or sticking it half-way in the bridge might make your tone better.

Fishman phase switch

Now please notice that I’m not getting paid for recommending Fishman material. What has helped me with feedback on my acoustic bass is the Fishman Pro-EQ Platinum Bass. This long-named device has a phase switch which can really help you out. On my problematic double bass, turning this switch to the right makes the bass about half as sensitive to feedback, so the volume can be louder before feedback occurs!

Tweak your instrument

You can experiment – at your own risk – with placing pieces of foam on your bass to eliminate some extra resonance. Do not expect miracles, but placing some foam underneath the tailpiece might work. It has eased my pain a little…

In conclusion

As you’ve read, it’s all about experimenting. If you want to get rid of the problem, buy a solid body and feedback will likely become a rare phenomenon. If you just need that hollow body, experiment with SPL, your place on the stage, monitors, EQ, other pickups or piezo’s, etc.

All basses are different and some are more suitable for high sound levels than others. I hope some of these tips might help you. A final note: although I have some experience and know something about sound, this is not the only truth. Bass playing is a very personal experience, so a good tone for me could be not that useful for others. Make sure to experiment in order to find what works for you.

Please let us know if there are other tricks that worked for you in the comments section!

Double bass picture by Mark Lorch

Does your double bass feedback… at AnswerGarden.ch.

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