Speaker Inside a guitar: reccomendations

[Peter Pan]

I have a small "Applecreek" travel guitar that I've made playable through a lot of work. I've put a magnetic pickup in it and have actually used it in shows. But some of my intended use is outdoors at things like Renaissance fairs, where all I need is a little battery powered amp so it could be heard at or slightly above the level of ordinary sized acoustic guitars. I've done that and its worked out well. See where I'm going? I'd like to try to build a whole little amp, maybe an efficient class 'D' circuit, right inside the guitar. So.. knowing that I can't expect GREAT sound doing something like that, I'd still like a fighting chance and making it as good as it can be. Can anyone recommend a small (like 3" or less" full range speaker that might work decently?

links come and go on line, but here's a link showing the guitar I started with...
Applecreek Acoustic Travel Guitar | Best Travel Guitars

[Pano]

Where would you put the speaker? The amp is easy, it can be small.

[weltersys]

A full sized acoustic guitar can hit some rather surprising levels, over 100 dB at one meter is easy without really playing hard.
Smaller speakers are less efficient than larger speakers, requiring lots more power (and more battery) to achieve that level.
A speaker rated 80 dB 1watt 1 meter requires 100 watts to make 100 dB.

I'd suggest a Galaxy Audio Hot spot speaker, they are 5" nominally. The Neo magnet version (about $50) is lightweight, gets loud, sounds pretty good, and at 95 dB 1w 1m is far more efficient than any 3" driver I know of.

Art

[Peter Pan]

Originally Posted by Pano

Where would you put the speaker? The amp is easy, it can be small.

I'm thinking of the lower part of the face, midway between the the sound hole and bridge, as close to the lower edge as possible.

[Peter Pan]

Originally Posted by weltersys

A full sized acoustic guitar can hit some rather surprising levels, over 100 dB at one meter is easy without really playing hard.
Smaller speakers are less efficient than larger speakers, requiring lots more power (and more battery) to achieve that level.
A speaker rated 80 dB 1watt 1 meter requires 100 watts to make 100 dB.

I'd suggest a Galaxy Audio Hot spot speaker, they are 5" nominally. The Neo magnet version (about $50) is lightweight, gets loud, sounds pretty good, and at 95 dB 1w 1m is far more efficient than any 3" driver I know of.

Art

Well its hard to tell this from the picture I linked, but go back and look at it, and then consider that looking at its face, the widest part of the body , measured from about an inch off the bridge (toward the sound hole) is barely 8 inches! There's no possible way to get anything bigger than 3" inside this thing without encroaching on the sound hole, and 2-1/2 would be even better.

I realize this is a long shot, and its only some of the modern speaker technology I see making small radios sound pretty good, that I even think its worth trying.

[Johno]

I'm not a muso' but knowing a little about the physics of string instruments suggests the speaker driver should be mounted deep inside the resonant cavity and be used to augment the resonating air column, rather than replace it like an electric guitar. With a carefully chosen amplifier frequency response I suspect you could give the acoustic appearance of a normally sized cavity, or even a chelo.

However, because it is the strings resonating with the air column there is a high risk of positive feedback through the pickup with even moderate gain. I am trying to visualise the electrical equivalent of the mechanical system and its inter-action with the electrical add-on, but alas I lack the wit.

Alternatively, do away with the resonance entirely and mount your speaker over the hole and design your electrics and acoustic output around a sealed enclosure.

[Pano]

I do wonder about the possibility of feedback. Only one way to tell!

[eyoung]

I think that a small full ranger suspended inside the body and venting the backside of the driver through a port to the rear might be the ticket to augment the guitar while sending rear pressure out the back so as not to cancel the forward facing sound pressure....hi-Vi makes some small impressive drivers.

regards E

[Peter Pan]

Originally Posted by Johno

I'm not a muso' but knowing a little about the physics of string instruments suggests the speaker driver should be mounted deep inside the resonant cavity and be used to augment the resonating air column, rather than replace it like an electric guitar. With a carefully chosen amplifier frequency response I suspect you could give the acoustic appearance of a normally sized cavity, or even a chelo.

However, because it is the strings resonating with the air column there is a high risk of positive feedback through the pickup with even moderate gain. I am trying to visualise the electrical equivalent of the mechanical system and its inter-action with the electrical add-on, but alas I lack the wit.

Alternatively, do away with the resonance entirely and mount your speaker over the hole and design your electrics and acoustic output around a sealed enclosure.

Yes... I've thought of these things. As another responder (Pano) mentioned, the feedback problem is obviously one I'd have to contend with, and I suspect that putting a speaker where the existing sound hole is could be the worst thing for feedback. then again maybe not at reasonable low levels. And I guess a paper cone speaker over the sound hole would act as a passive radiator when the amplifier was off (provided its coil were not damped by a low impedance amplifier, doubtful is the power is off).

But whatever I do, the fact remains that my best chance of success will require the best possible small speaker, so I'd still appreciate links to possible sources. Maybe if I pose my question to the right speaker company they will have some recommendations. I'm sure though if I just go to Radio Shack, i won't get any intelligent recommendations. :-)

[Peter Pan]

Originally Posted by eyoung

I think that a small full ranger suspended inside the body and venting the backside of the driver through a port to the rear might be the ticket to augment the guitar while sending rear pressure out the back so as not to cancel the forward facing sound pressure....hi-Vi makes some small impressive drivers.

regards E

Thanks Eyoung! I'll check into Vi today. Never heard of them though... do you have a link?

If venting to the back might be a good idea, then its possible I suppose that I could just mount the speaker facing the back, with a hole and grill cut out on the rear. I'd then be using the revers side of the speaker as the main part of the driver, and let the back radiated sound come out the guitar's sound hole. Would that be a bad idea? On such a low scale, would the back of the speaker be all that different from the front? Of course I might have to play with the pickup and polarity to get the phasing right. Theoretically I'd have to have a whole CPU driven A/D->D/A with buffering to really get the phasing right. Hopefully one or the the other setting of s simple revers switch on the input or speaker connection will be close enough. The good news, I guess, is that this is a fairly inexpensive guitar and can be easilly replaced. So if I have to make a lot of holes before I figure out the best way to do this, I could start over with another one when I'm sure of what works best.