The Sunshine

By Holger Kraft
09 Aug 1997

Construction of the cabinet

Pictures of the speaker:

• Fig. 6. Cabinet cross section 1
  
• Fig. 7. Cabinet cross section 2
  
• Fig. 8. Speaker in room
  
• Fig. 9. Speaker pair in room
  

Like you have seen on the pictures above the cabinet is constructed of birch multiplie. I chose it because of the great sound I expected from this kind of wood. It is very stiff and I did not want to use many internal bracings inside the cabinet because they do not kill the wall vibrations at all. As you know a bracing only kills one mode of wall vibrations. Another reason for this choice is the look of the speaker. I didn't like to spend many money on colour or veneer. It is better to spend some money on the structure of the wood than on the surface. Here in Germany the price for veneered MDF is the same as for birch multiplie. Yet remember out of what kind of wood pianos are made. There are surely not made out of MDF! As you can see in the picture below the cabinet is divided into two chambers. The upper chamber, nearly triangular shaped, is the effective volume for the woofer. The lower chamber, also triangular shaped, is for sand filling Fig. 10. Cross section explained. This sand filling damps the whole sidewalls and the free area of the front panel. The filling will provide that the speaker is very stable positioned in the room. This is true for two facts: The first is, the whole thing weights around 75 Kg and you will be very glad when you have found the right listening position for it in your listening room. The second is, there is only a very small impulse transfere from the driver to the cabinet. The most important reason why to use sand filling for a part of the cabinet is, that the sand filling acts as a trap for all the resonances in the cabinet. Its similar to for example damping a tonearm with silicone fluid. As you can imagine from the pictures, the cabinet gets softer from the front panel to the rear end. It is very important to make the front panel as stiff as you can and mount the drivers as fixed as possible. Do not use any softener between the tweeter and the cabinet. Look also at the bracing in the upper chamber. Later on the cabinet plans, you will see that this part is U-shaped. It is not only a bracing for the front panel and the sidewalls. The second important task of that piece of wood is, to prevent a direct sight from the woofer to the bass reflex port. Although the port is placed on the rear, you should try to minimize the ammount of midrange that disappears out of the bass reflex port, especially when you use as less damping material as I used in this design. I only covered the top part of the upper chamber with self adhesive roofing felt and covered all walls of the upper chamber with 15 mm felt lining, also over the roofing felt. (You can see the coverage of roofing felt in the top part of the effective volume in the picture above.) There are many additional design features in the enclosure, I will not discuss in details here like the off-axis tweeter, that reduces the standing waves between the tweeter and the edges of the front panel and the positioning of the tweeter under the woofer which provides a runtime correction and proper phase aligment between the tweeter and the woofer ( partly covered in the chapter: Crossover construction ). If you are interested in this design you can contact me and we can discuss some further details. But now lets stop talking and have a look at the nasty plans. Again you can click on the thumbnails to get a bigger image. (Please excuse the poor handdrawing quality of the schematics)

Cabinet drawings:

• Fig. 11. Front and side
  
• Fig. 12. Back wall
  
• Fig. 13. Brace shelf
  
• Fig. 14. Back inner wall
  

Of course, if you are interested in this speaker project and you have some additional questions that I did not cover with my pages, feel free to contact me.

About the
author

Print this
article

Email this
article