the toobzAL5 Mk 1

comments on the Mk 2s

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 drivers did I have on the shelf? The
MCM 55-1855 mated to an ApexJr ribbon were my best bet.

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.

Other details? Lets mount the drivers on an angled top plate (need room for the tweeter after all). 45 degrees is fairly easy to cut so lets start there.

How long? As long as i could get from my piece of pipe ~ 25". Fb = 135 Hz before stuffing. With stuffing and end correction it will be in the ballpark of what is required.

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.

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.

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.

Chart 1: in-room pink noise response curve

(red-- 1/3 octave RTA, green -- Spectrum Analyzer)

Line Configuration

  Physical length 25 inches
  Physical fs at 1/4 wl 135 Hz
  Sd 11.6 in2
  Tube cross section 26 in2
  Terminus area ~12 in2
  Stuffing foam & polyester stuffing

Cost of Bits (in USD)

MCM 55-1855 5" Aluminun cone mid-bass

$ 13.50

  less in quantity
ApexJr Ribbon Tweeter


3.3 uF cap + 0.1 uF cap + wire


Nuts & Bolts


0.4 mH inductor     salvaged
terminals / 6" PVC tube / Medite for bases & baffle / gary oak / grill cloth     salvaged


$ 44.00

  for the pair

Pictures of a similar project (added 25_09_06)

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