Alpair7/Scanspeak 18WU/8741 Fast

markre

Member
2012-01-01 7:23 pm
Some time ago I built my first speakers based on alpair 7 and modified pensils. They sounded very good but after a while a started to want a little improvement in the bas region and it also seemed that it missed a lot of detail when there was music with more bas. However there was a lot that I liked with the alpairs so I decided to give them a little help with some woofers.

With the kind help by Dave Dlugos we decided on scanspeak 18WU/8741-T00 in a push-push configuration and a 46L vented enclosure with the alpair in a aperiodic transmission-line about 5-6L.
I built it from inside out. After constructing the t-l for the alpair I made the bracing and a frame. Over that I laminated two layers of 4mm birch-plywood (vhv), after that a 8mm board used to damp floors, after that plywood (hvh) and last mdf. It turned out to be a very stiff construction without any vibrations even when playing very loud.

[IMGDEAD]http://i43.tinypic.com/33tkufa.jpg[/IMGDEAD] [IMGDEAD]http://i39.tinypic.com/xddti.jpg[/IMGDEAD] [IMGDEAD]http://i41.tinypic.com/zxjz1j.jpg[/IMGDEAD] [IMGDEAD]http://i44.tinypic.com/b3rf5g.jpg[/IMGDEAD]

One technical challenge was how to fix the elements to each other to get the most of the push-push configuration. Obviously it has to be done when the elements are in place and a hole would not be a satisfying solution. I decided to do aluminum pieces that I could attach to the elements and that would click into each other. It turned out to work very well.

[IMGDEAD]http://i42.tinypic.com/219aix.jpg[/IMGDEAD][IMGDEAD]http://i39.tinypic.com/2j4poqx.jpg[/IMGDEAD]

A big thank to Dave for all his valuable help,
Markus
 

markre

Member
2012-01-01 7:23 pm
Cross-over point 213 Hz/second order (happened to fit with the values). In the future I may bi-amp it.
Well my goal was that a symphony orchestra should sound like a symphony orchestra and a funk band like funk band without giving up details. I must confess that I’m satisfied. The alpairs also seems a bit happier without struggling with the bas.
 
Very nice build. The curves are incredible. 200hz seems like a good spot. Where is the box tuned to?

Edit - is that a passive or active cross over?


"in the future I may bi-amp it" sounds to me like currently passive XO
Markus - gorgeous freaking work on the machining of interlocking aluminum coupling parts - glued to drivers' magnets , I guess?
 

markre

Member
2012-01-01 7:23 pm
The scanspeaks has the magnet attached to the frame by screws. I just extended them to go through the aluminum parts. I would not trust glue in the long run. There was some work with the aluminum parts, guess 3d-printing would be the easy way out.


If I understand Dave’s calculations right the box is tuned to 41Hz.