MCM Tower Project

This is my design for the DIY 2001 budget category.   I figured the competition would be stiff and the only way I could compete is if I came up with something out of the mainstream.  My original thinking was to build an 8" two way using MCM components.  I figured I could get the bottom octave out of the 8" 55-1550 with the light carbon woofer would get me to 3000Hz and I could use a cheaper tweeter.  I ordered a $10 tweeter (same one as in the Bang! kit) from MCM and found it was a piece of junk.  So I had to rethink and find a better tweeter.  The next tweeter level was in the $20 range and that put me over the $150 limit with the 8" woofer.  So I selected the MCM 55-1545 6.5" carbon fiber woofer and the Peerless 811815 tweeter.  I wanted to try this tweeter because it does not have ferro fluid and I wanted to see how different it sounds. 

Testing the woofer on a 18 liter box sounded pretty good.  I was on my way.  I tried to measure the woofers using Speakerworks and got within 15% of specs.  I figured that was the limit of my measurement capability for now.  The unibox model gave a nice low response in a 38 liter box.  So I built a thin and tall tower.  Once the drivers were in the 38 liter box I started getting weird responses.  I had a lot trouble with the xo and it took a lot of work.  The tweeter did not behave with anything short of a 4th order so that is what I used.  But with a 4th order it measured perfectly.   The woofer just would not dial in.  I fudzed with it for a couple of weeks and finally gave in with a third order XO around 3400Hz. 

The measurements confirmed the audible coloration.  The tweeter is great.  The woofer has a peak around 1,000Hz followed by a valley at 2,000hz.  There is also a pretty marked baffle step.  While the overall measurements are almost totally within +-4db, there is a fair amount of variation.   So that must be the coloration I can hear.  I am debating weather to give these away or try to retrofit a new woofer into the box.  If I give them away I can rip all the good xo parts out ;) 

So this was a learning experience.  What I learned: 

1. Stick to mainstream drivers.  But the tweeter is a good find. 

2. You are not going to get the bottom octave out of a 6.5" speaker either. 

3. Don't cut your finger off.  I spent the last week of finish with with a chunk of finger missing.   

4. Leave enough room for the port.  I built a narrow cabinet and used 3" PVC with a 90 elbow.  The elbow took up so much room in the box it restricted cut off air to the bottom half of the box.  I had to cut out the elbow and put in a normal port tube.  (The box was acting like a sealed box).  

5. Don't work with contact cement all day and then sand.  That stuff is potent.  I sanded the veneer through in two places and made some bad veneer cuts.  This is why I am leaning toward giving them away. 

 

MLS at about 1m 1/6 ocatave smoothing. You can see the tweeter is doing a great job. The woofer, well, lets say I will make you a special deal. The drop after 10k is my mic.


This is Dennis's MLS of the same speaker in the same room. General shapes are the same. My room hump at 150Hz shows more than Dennis. I think the smoothing is different also.

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Copyright Peter Jay Smith 2005 Return to helarc.com