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Building A Speaker
Cabinet For The Firefly
Last Updated 02/16/04
By Paul J. Marossy
After building
my FireFly amp, I felt that it needed a speaker cabinet that was its very own.
With this little amp, an open back cabinet seems to lack punch and bass response. I intuitively thought that a closed back 2x8 speaker configuration might sound good with this amp.
So, I decided to build a speaker cabinet for it. Building this speaker cabinet
had much in common with the first cabinet I built. Below is some pictures of
this speaker cab project.
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I didn't take any pictures
of it during construction, but the cabinet was built out of pieces of
a cheap bookcase that were cut down to the sizes I needed to build the
enclosure. The back and sides were made with these pieces and are made
of 3/4" particle board. To make the rounded corners, I used a jigsaw
to remove most of the material. I finished the edges with a file and an
orbital sander. It was a pain in the neck doing it this way, but I don't
own a router or have easy access to one. I guess it turned out pretty
well for such primitive woodworking techniques.
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Here is the rear of the speaker baffle. The baffle is made out of 1/2"
plywood. The speakers are some thrift store treasures, $8.00 for the pair.
They are from some ceiling mounted speakers that were apparently removed
from a building. They are 8" Atlas "Soundoliers", which have an aluminum spider, are rated
for 15 watts, are 8 ohms and have a frequency response of 50Hz to 18kHz. Believe it
or not, they sound really good in this cabinet with the FireFly! I wired
the speakers in parallel for a 4 ohm load. In order not to fry the output
transformer, I installed a switch in my FireFly to enable use with a 4
ohm or 8 ohm speaker cabinet, which is easy to do with the Hammond 125A
transformer.
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Here is a view of the front of the cabinet, minus the speaker grille
which has yet to be manufactured. The cabinet dimensions are as follows:
19.5" wide, 18" high and 9.5" deep. I didn't do any calculations of Qtc and all that stuff
since I do not have the full specs on the speakers I used. Instead,
I used an intuitive approach for the cabinet size. It worked out pretty
well, all things considered. After a few days, I was just too curious about where this cab peaks. So, I fed this cabinet with a sine wave from a function generator set at 10dB attenutation, and the resonant frequency occurs at about 100Hz. That seems to account for the cabinet's seemingly rather flat frequency response with an electric guitar. I made these measurements after I drilled a 3/8" hole in the baffle, directly above the lower left speaker, which definitely improved the bass response. It really is amazing how a tiny hole can affect the bass response.
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The covering I used matches the covering on my FireFly. I had just enough
material to cover this cabinet. The speaker jack plate comes from the
unused portion of a small RadioShack project enclosure. At this point,
I am trying to find some grille cloth and some plastic amp corners that
match what I used on my FireFly. I found out that www.PartsExpress.com has the strap handles and corners, which is where I ordered those parts from. Finding grille cloth to match what I used on my Firefly is a little more problematic, though...
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Here is the finished cabinet. All in all, it didn't turn out too bad. It looks and sounds good and the cost was very minimal. Overall weight of this cab is about 20 lbs. |
My FireFly Page
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