| the toobzAL5 Mk 1 |
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This speaker was not designed but evolved into a design. I needed to build a set
of small speakers to complete a gear swap.
What kind of box? It would be nice to get better bass than the 95 Hz F3
of a 0.7 Q sealed box. I had some 6" plastic pipe and had wanted to make some
of this into a speaker. So we build a toob TL. |
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Many hours of filing (those top plates have ALOT of file equity in them) and some routing & gluing and more filing. The terminus shape is dictated by the tools I have to make the hole. With the complex radius of the shape maybe we spread the Q of any across-the-port resonances. The mid-woofer cutout placement was done so that the magnet would wedge against the back of the tube -- i got close, I only had to shave away a millimeter or 2 to make them fit.
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Then some flat black paint -- wow that brings out the elegance of the shape of
these things -- and the resemblence to a big cigarette has gone away.
1" of low-density foam lining the walls of the last 18" of the tube. 30
g of well-teased polyester fluff, then 40 g, then 50 g. Happy. Bass down to 75 Hz?
They are playing music and even with just a 3.3 uF cap on the tweeter they show potential.
Add an inductor to the woof and that cleans up some ringing in the top. These things
are gonna work out.
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Some measuring. Coat the mid-bass -- that cleans up the ringing and we can toss the inductor. Better. Still a bit of a dip near the XO. Evolve the XO to a lower cutoff 2nd order (~4.5 kHz vrs 6k) on the tweeter complementing the (now) smooth roll-off of the woofer. |
Add a solid Garry Oak (endangered & from a Heritage Tree -- it was a windfall)
base. This is spaced 1.25" from the bottom of the tube with pieces of copper
pipe with a lag bolt thru the base into the medite on the bottom of the tube. Afix
the XO and add some terminals. They are going on carpet so I made some spikes by
grinding pointy bits to some bolts.
With my SO's help I (she did the sewing -- check out her web
site) made up some grill socks recycled from my old Accoustat frames (suffering
a bit from kittens using them for climbing practice) and they are ready to go.
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Chart 1: in-room pink noise response curve (red-- 1/3 octave RTA, green -- Spectrum Analyzer)
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Cost of Bits (in USD) |
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| MCM 55-1855 5" Aluminun cone mid-bass |
$ 13.50 |
less in quantity | |
| ApexJr Ribbon Tweeter |
5.00 |
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| 3.3 uF cap + 0.1 uF cap + wire |
2.50 |
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| Nuts & Bolts |
2.00 |
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| 0.4 mH inductor | salvaged | ||
| terminals / 6" PVC tube / Medite for bases & baffle / gary oak / grill cloth | salvaged | ||
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Total |
$ 44.00 |
for the pair | |
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Pictures of a similar project (added 25_09_06)
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