March 31, 2014

AV8 8" home theatre speaker

 AV8 is a home theatre speaker based on a 1" compression driver, 8" waveguide and 8" midbass driver. Shown here on my measurement turntable where the dispersion performance is tested. The MDF enclosure is rubber lined for vibration damping and it's also sealed with fibreglass resin to resist moisture changes, hence providing a good substrate for the textured paint finish that will be applied. 

AV8 is a 93 dB speaker designed to reach THX reference levels with an ordinary AV receiver. It has an 8 ohm load, 70 Hz extension and a small box. Being an AV speaker, it's anticipated that it will be placed near the wall. This particular pair is designed for a client where it will be placed on a pro audio bracket.

The midwoofer has a clear coating which helps to damp cone breakup. When testing the raw driver with no filters in place, this is audible in comparison to lighter untreated cones. 

This is an alternative driver that was tested, without the treated cone. It has higher sensitivity in the upper midrange, but cone breakup is clearly audible. Although a cheaper driver, the savings are likely lost in a more expensive crossover.

Woofer baffle. Neo magnets are hidden in the baffle for grille attachment of woofers. These are machined manually, not via CNC, since they are machined from the rear of the baffle and this doesn't easily suit the CNC process, where all work is done from the top side. This is done with a drill press manually, then what remains is filled with bog. A straight cut bit is used, since a drill bit would not let the magnet get close enough to the surface without breaking through. 

The baffle above is for the surround (AV8S).

CNC panels laid out:

Rubber sheets line the box for vibration damping. 

Front baffle:

AV8S construction. Damping rubber and some of the lining is attached during assembly, as access is limited after.

Woofer baffle is double thickness.

Keyhole brackets allow the box to be installed to the wall. You can also see a recessed section around the speaker terminal cut out. This allows a speaker wall plate to be located here, so all cabling is hidden, and installation is simple, with no need to offset the speaker from the wall.

Top and back of the surround (AV8S). Dual ports fire up out of sight.

Sometimes you just can't have too many clamps!

The compression driver/waveguide for the surround is angled down 15 degrees. 


AV8S (surround) rear sitting upside down. Here I've used a neo driver to keep the weight down.

AV8 rear:

Dayton Titanic ported sub

The new Dayton Titanic Mk 4 15" sub driver is very appealing. This is a custom sub for a client as part of a home theatre system. In this design, I've used a down firing design to keep things simple in terms of grilles, high driver excursion and little fingers. A key feature of this design is a large slot port with a generous flare at the end.

Good aerodynamics here is the key to ensuring the port does not limit the LFE potential. 

The internals of the port are pre sprayed as there is no chance once fully assembled.

Solid timber feet avoid the weight of this heavy sub bearing down upon the MDF feet. The feet near the port are angled to avoid interference. 

Polyurethane glue is used here for extra strength, along with screws into each solid timber insert.

After complete assembly, the edges were all rounded over with the router and the box is sealed with fibreglass resin to provide a more stable substrate. Often prior to finishing, raw MDF expands and absorbs moisture, resulting in a seam appearing, which then requires more sanding.