Piezos. Is bigger better?

[Pbassred]

I'm going to investegate this anyway but...............

I'm going ahead with mounting a pair of piezo sounders under the bridge of my Yamaha TRB1005 bass as pickups. Now, they vary in size and resonant frequencies 9KHz at 12mm down to 2.8Khz at 35mm.

Do you think it matters as long as I don't mix them ( or should I mix them? does bigger make more out put?

I'll do a proper write up with sound clips when its done.

[ToneRanger]

What are 'piezo sounders'? Do you mean like the piezo buzzers that Radio Shack sell? If so, the resonant frequency doesn't seem to make any difference when used as a pickup. Using two or more in parallel gives more output and also helps reduce the impedance.
When I tried the buzzers on my EUB they sounded good but were fragile - I had trouble making the solder connections durable enough. I had much better success with MSI piezos I bought for $2 from here: http://www.windworld.com/products/catalog.htm
The pickup design I developed is here: www.fittell.id.au/piezo

[Pbassred]

Tried it. 3X 27mm piezos connected in parallel, between the bridge and body(with some packing to make sure it was flat).

Result:- ugly! ourput is low but ok. Not sufficiently sparkling or different to warrent doing it. The by-product was worse. It has turned the whole bass into a microphone. Every movement - finger noise, brushing the back of the neck, is obtrousivly amplified.

Need to think again.

Are factory made P bridges like this?

[ogrossman]

I don't know anything specifically about piezo bridges but I do know a fair amount about structural dynamics. You said you put them under the bridge? I think the problem might be that you've got the whole mass of the bridge between the strings and the pickup. I believe you'd want the piezos as close, structurally, to the strings as possible. Can you put one of the piezos under one of the saddles to test that theory? Maybe you would need a thin metal plate (aluminum for less mass?) between the piezo and the saddle to distribute the pressure evenly.

[Passinwind]

Originally Posted by ToneRanger

When I tried the buzzers on my EUB they sounded good but were fragile - I had trouble making the solder connections durable enough.

Don't solder 'em! Either use a mechanical solution (spring clips or something similar), or conductive epoxy (pricey, but works great).

[PilbaraBass]

Originally Posted by Pbassred

Tried it. 3X 27mm piezos connected in parallel, between the bridge and body(with some packing to make sure it was flat).

Result:- ugly! ourput is low but ok. Not sufficiently sparkling or different to warrent doing it. The by-product was worse. It has turned the whole bass into a microphone. Every movement - finger noise, brushing the back of the neck, is obtrousivly amplified.

Need to think again.

Are factory made P bridges like this?

piezo bridges, as opposed to piezos under a solid bridge develop more string sound than the "entire bass" sound because they predominately pick up what is happening on the bridge saddles, as opposed to the entire bass.

For this same reason, this is why accoustic guitars (and basses) with acoustic bridges use a piezo element under the saddle and not under the bridge.

My Carvin AC-40 bass uses a piezo element like an acoustic guitar, and while it is a tad microphonic, it is completely useable and is the only pickup on the bass.

Another very important thing about piezos...1) use a shielded cable for the first 2 inches or so from the pickup...2) make sure that you isolate this section as much as possible from pressure and vibration, as it will automatically have a fair amount of piezo quality, too, just by it being coupled to the piezo element.

for an "under the bridge" type setup, this means a properly located disc, and a sufficient channel for the shielded cable to pass through.

[ToneRanger]

Originally Posted by PilbaraBass

Another very important thing about piezos...1) use a shielded cable for the first 2 inches or so from the pickup...2) make sure that you isolate this section as much as possible from pressure and vibration, as it will automatically have a fair amount of piezo quality, too, just by it being coupled to the piezo element.

I learnt this the hard way. Especially the shilding - any gap in the shielding between pickup & preamp will make a big difference. The entire piezo needs to be shielded in my experience.

My next project is to remove the saddles from my Jazz and replace them with a wooden bridge that sits on a couple of piezos. Hopefully will give a better balabce between string sound & body sound than either (a) string saddle piezos or (b) piezo under bridge plate.