DIY Acoustic Guitar Speakers Selection and Cabinet Design

[Jayz]

I have a 20watt RMS @8ohm powered mixer that I'd like to use to amplify acoustic guitar. I also have a LR Baggs Para DI preamp for tone so the mixer doesn't need to color the sound in any way. The lowest note on guitar is about 80hz. The decent off the shelf acoustic amps all seem to have 2 - 8" coaxial speakers and many also have a tweeter. I don't want to spend a fortune on the speakers and cabinet. Ideally I'd mount the mixer/amp in the cabinet for portable convenience. Weight is important.
Does anyone have experience with Goldwood GW-8004's? I know very little about speakers and cabinet designs so would appreciate some suggestions regarding the size of the speaker compartment, closed or open, port size, tweeter type, crossover (I assume is necessary). I'm a decent carpenter so actual construction shouldn't be a major challenge once I know what to build.
Thanks all.

[J M Fahey]

That's a Hi Fi speaker, good at home or car but unefficient (87dB) ; buy a Jensen Mod 8 which is a guitar speaker and has 4X the sensitivity (93dB).
For sparkle add a cheap generic Piezo tweeter.
Jensen MOD Series speakers - Jensen MOD8-20 8" speaker. 4 or 8 ohms. Great choice for lead guitar cabinets.

[Jayz]

Thanks Juan! You say; "great choice for lead guitar". Should I assume that they are also a great choice for an acoustic guitar amplifier?

[Leo_Gnardo]

Just because there are a lot of commercial designs using a pair of 8 inch speakers, don't think you have to limit yourself to the twee speaker format. Try your mix/amp through a PA speaker, 12" plus horn or 15" plus horn (I'm thinkin' Community CS-series or similar) and see if you get some appreciable low end. I've always thought it was a mistake to try to force 8" speakers to woof, and it eats up a lot of power to get 'em to do so. With only 20 watts at your disposal, I'd make the most of it with a larger, efficient speaker.

[Jayz]

Thanks. I tried a 12" Yamaha full range and got lots of volume but too much "woof" even with bass rolled off. Could be the characteristic of my amp I know. Its just a simple IC based PA amp.

[Leo_Gnardo]

Thanks. I tried a 12" Yamaha full range and got lots of volume but too much "woof" even with bass rolled off. Could be the characteristic of my amp I know. Its just a simple IC based PA amp.

With both the PA and Baggs EQ's, still too much woof? I know you wrote you didn't plan to use the PA amp to "color" the sound, but I'd consider too much low end a blessing in disguise. The less power you have to put to work on the low frequencies, the more there is for mids & highs. There's only 20W to do all of it. Grab the low eq and dial down as necessary.

For a portable kit I'd have a look at the old EV plans for Thiele aligned speakers, I'm sure you'll find on ElectroVoice website. Simple to build. Add a horn and a "shelf" for the PA amp. If you're convinced 12" is too much, go for 10". If you want to get out the slide rule and reverse polish notation calculator, you could get the specs on your speaker and go thru all the math to decide what size port is best. Or experiment, put a rectangular port in the baffle, and try covering it up partially until your ears get happy.

[Steve Conner]

Nowadays you can use WinISD instead of a slide rule and RPN calculator.

[Jayz]

Terrific! Thanks. I'll experiment with your suggestions until I find something I like.

[Jayz]

Thanks for the tip in WINISD. Nice little program. To try it out I used the specs on the Jensen MOD 8-20. Not all the specs that WINISD has fields for are provided by Jensen. Are there some that aren't absolutely necessary? And of course, those that are mandatory to get meaning results fom WINISD?
Mod 8-20 | Jensen Loudspeakers

[Steve Conner]

Looks like all the important Thiele-Small parameters are there on the Jensen website. Which ones are you missing?

[Jayz]

I guess just "Pe"

[Steve Conner]

Pe is the power handling capacity of the driver in watts, so just enter 20 I guess.

[J M Fahey]

And of course, if you can go for a little larger diameter, a 10"" would be a step up the ladder, while still being light and relatively inexpensive.
Jensen MOD 1035 would roughly be MOD 820 on steroids, although if you can "graduate" to 10", in your case I'd choose MOD 1050, much better bass, and smoother treble, more even balanced tone, just what the Doctor ordered.

And worst case, simply build a cabinet with size "inspired" in some similar good sounding Acoustic amp (think Fishman and such) , add some internal damping to kill "boxyness" and call it a day.

You definitely won't sound *bad*, that's for sure.