Double Bass help design a double bass amplification system, your input much appreciated!

[Silversorcerer]

One area that I think that has been underresearched is the use oif accelerometers for pickups- particularly multi-axisl accelerometers. I think an XYZ system in which you could vary the balance of the three inputs would be interesting.

Building source followers into pickups is another area to look at. FRAP did it back in the 70s, yet most acoustic pickups today are passive in design.

I think the Trance Acoustic Lens for acoustic guitars is a multi-axis accelerometer type system. Great Idea! And no one is doing that one for the DB.

 

[bloodyjack]

If a piezo produces a signal that is equal to that coming from a mag pick-up without a pre-amp and battery, why won't a rheostat/potentiometer volume knob work? If either signal can be fed into an amp, I can't see why putting a potentiometer between them is any different. For example if I have a Bassmax signal running into a volume pedal (not a powered pedal) and then out to the amp, what will the negative consequences be??? Please explain fully.

I don't get the "impedance match" statement either. Perhaps I'm an idiot, but the Bassmax I use does quite well when used as a high impedance signal source. It produces a signal of equal strength to that coming from my standard equipment Fender P, at full volume (open potentiometer). I can't see why a potentiometer in the path wouldn't work the same way it does with the magnetic pick-up. Are your statements based on experience? I haven't tried putting a potentiometer in the path, but I'm tempted to just try it out with an unpowered pedal to see if what you claim is true. Where's that old spare volume pot I used to have .....

Electrically, you can treat a piezo as a voltage source in series with a capacitor. The resistance of your input then forms a high-pass filter. The cut-off frequency of this filter (-3 dB point) is given by f(c) = 1/(2*pi*R*C) where C is the piezo,s capacitance, and R is the input resistance.
This is why a piezo needs a very high impedance input only available from an active impedance matching pre-amp.
If you don’t understand this stuff and need to be convinced listen to the difference
Bass max with impedance matching pre-amp
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bass max without impedance matching preamp
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[quee]

What about something similar to a dynamic mic capsule mounted in the bridge?
It would be possible to have an suspended coil in the circular part of an adjuster surrounded by a magnet.

For an amp how about the bass hat? A hat with a small amp and speaker mounted in it. It won't cover your ears like headphones but you will always be able to hear yourself above the rest of the band.

Another not so crazy idea would be to have an amp and speaker buit in to a carbon fibre bass case with the speaker in a space behind the neck. Great protection for your bass and just the one large heavy object to drag around!

cheers Quee

 

[stz]

accelerometer? my understanding was that piezo elements are a form of one of those. Multi axis stuff sounds intresting to say the least but I don't think I can even start to think of the maths involved!

An unscientific view on the volume/pot question. I'm sure there are some elemental maths involved that can prove that using a variable resistor a passive volume control isn't that good an idea as far as purity of tone. I'd have to go get a book, but my understanding is that a resistor dealing with AC has a frequency that it is happy/unhappy with. Though it could very well be in the MHz range and inaudible. I'm sure it isn't that great though.

FWTW I used to use a passive volume pedal which for its weight seemed to be a pot in a box with a footswitch and 2in2out jacks. On bass guitar I was using it to do volume swells during fast vibrato stuff as an effect for electronica. I will say my tone stunk in those days, though I can't pin it to the volume pedal as it was in a chain of 25-30 pedals.

Someone else has done a great job of describing impedence matching, it is totally needed. I've seen passive circuits to handle it, along the lines of a couple of resistors and caps. Don't know how well they'd sound but the theory seems solid.

I'll stick some together in the next couple of weeks and try them out. I've a very basic prototype for a pickup done, I'll try and get some sound samples and pictures. The whole gain part of the preamp is still very much work in process I'm afraid!

 

[Silversorcerer]

Thanks for the details BloodyJack. I've never understood exactly how piezo's did their trick. Your explanation makes perfect sense, and I don't doubt for a minute what you are saying, but I probably would need to get an impedance matching pre and hear it with my set-up to really hear what's happening. I get decent results using mine with a flat EQ, but you certainly gave me some food for thought on my amped up sound.