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Old 2nd October 2012, 04:18 PM   #1
diyAudio Member
Join Date: Oct 2012
Default putting an amp and speaker inside an acoustic bass

I'm trying to get enough power to bring an acoustic bass guitar to be heard with acoustic guitars. I'm thinking of the Smokey amp plugged into a 10" speaker mounted to the inside back of the guitar and maybe opening up a port hole or even an f hole on the front. Just enough to raise the db level from unamped at around 60db to 100db. Any thoughts?
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Old 2nd October 2012, 04:59 PM   #2
Struth is offline Struth  Canada
Join Date: Aug 2012
Location: books at londonpower.com
Hi Guys

You are asking for a lot of trouble with feedback.

Most acoustic instruments fitted with pickups use a peizo type mounted under the bridge. The compression of the crystal pickup generates a current output with the string and body vibrations, which must then be buffered using a high-impedance input stage like a jfet or jfet-input opamp. Buffering this way captures the full signal and gain here is not a requirement, so most acoustic preamps that are simple are just a single jfet.

Unless you fit your bass with metal strings, a peizo pickup or conventional microphone are the only options. Because both respond to vibrations of the entire instrument body, placing a speaker inside the body will just cause feedback. Better to have an outboard amp and speaker.

There is no acoustic guitar that produces 100db of sound - maybe 70-80db.

For your reference, 100db of sound requires that you stand shoulder-to-shoulder and shout to your buddy to be heard.

There is an acoustic preamp project in 'Tonnes of Tone'. See my site for details. We also published a similar project in 'Guitar' magazine a few years ago.

Have fun
Kevin O'Connor
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Old 2nd October 2012, 07:21 PM   #3
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Join Date: Jun 2011
Acoustic bass guitars are heard in mariachi bands. See guitarrón.

I've heard a fretless bass played with an acoustic (piezo) pickup through a bass amp, it sounded like a plucked double bass.

Your big problem is getting enough bass extension but also range with a smaller speaker and not having it feed back. I think it's so problematic I wouldn't try. I'd go for an electric bass and a customised amp/speaker with a shoulder strap. It's not a one-piece solution, but you could make it work.
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Old 2nd October 2012, 07:25 PM   #4
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Join Date: May 2002
Location: Switzerland
If you still want the acoustic bass amplified but less stuff to drag around then build yourself an instrument case with built-in amp and speaker.


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Old 2nd October 2012, 08:43 PM   #5
sreten is offline sreten  United Kingdom
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Join Date: Nov 2003
Location: Brighton UK

A small decent bass amplifier used for practicing electric bass is
enough for an small acoustic bass fitted with a piezo pick up.

i.e. for this sort of acoustic bass :

Click the image to open in full size.

Just use your electric bass practice amp.

rgds, sreten.

Last edited by sreten; 2nd October 2012 at 08:49 PM.
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Old 4th October 2012, 08:11 PM   #6
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Join Date: Oct 2012
I like the idea of an amp in the case...like the sears sivertone in the 60's... I'm simply attempting to be portable and unplugged to sit around the proverbial camp fire with the guitar players and be heard. Any thoughts of where the speaker would go, size type? I've tried using the Vox headphone bass plug and the little peaker that you can attach to it, it's a joke, it pushes no air...thoughts?
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Old 4th October 2012, 10:12 PM   #7
sreten is offline sreten  United Kingdom
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Join Date: Nov 2003
Location: Brighton UK

Another option is to plug a bass similar to the above into a portable
rock/boom box, ideally you need to go through a bass effects pedal
for compression, a bit of reverb, etc, but its not strictly necessary,
as a lot of them have biult in bass management / compression.

Just make up the right lead. You can't build it into the guitar.

rgds, sreten.
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Old 5th October 2012, 02:16 PM   #8
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Join Date: Oct 2012
So...I bought the smokey amp for $20 and put it inside the bass with velcro, took the 1/4" plug out of the back strap lock and connected the pre amp to it via a double male 1/4". i then connected the external speaker jack to a boston accoustics 6" subwoofer just to see how it sounded..well it was good, just enough extra to be heard over my very hard strumming friends Martin...the battery however only lasted about 15 min. I suspect a better battery may get me more time. Tonight I'll crack the sub woofer plastic cab open and experiment with mounting it in the bass. I've got three crappy dean basses to play with. I think if i surround the speaker with foam I may controll the feed back issue...
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Old 5th October 2012, 03:13 PM   #9
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Join Date: Feb 2010
Location: in half space
I was wondering what on earth you were on about....

Martin guitar, Dean bass....

I get it now.
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Old 29th August 2013, 01:39 AM   #10
diyAudio Member
Join Date: Aug 2013
Rich784, did you ever solve your problem? I'm in a similar situation, I have a Rogue acoustic/electric bass and I play a couple of places in bluegrass jams where they say "No Electric Allowed", but the bass doesn't put out enough sound acoustically to be heard over something like 3 or 4 guitars, a banjo, a fiddle and a mandolin. I figured if I could mount a speaker on the inside just to give it that extra push that maybe it would help. I don't need much. The last time I played with this bunch, after about 3 hours of playing, my index and middle fingers on my right hand both had HUGE water blisters from pulling on the strings so hard to try to be heard.
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