Project:  Computer Speakers using Parts Express buyout Bravox 3.5” Drivers and Tang Band 1" Shielded Neodymium Dome Tweeter (P/N: 264-804).

Parts Express Description of the Bravox Speakers:  Shielded 3-1/2" woofer originally manufactured for use in a high-end home theatre speaker system. It boasts many special features that are perfect for your next speaker project. A polypropylene cone, rubber surround, ventilated cloth dustcap, flat spider, and large shielded magnet structure give this woofer good performance in a small package. The motor contains a copper shorting ring as well as an extra neodymium magnet on top of the pole piece to help maintain a strong, linear magnetic field. Cosmetically, the pincushion-style polymer chassis gives a very sleek and professional look. The 12 ohm and 6 ohm varieties can be combined in varying configurations to ensure a constant load to your amplifier.

Parts Express Description of the Tang Band Tweeters:  This small tweeter utilizes a soft fabric dome and slightly horn-loaded flange, resulting in an extremely flat and extended frequency response. Despite the small size, it has good power handling thanks to its  ferrofluid-cooled shielded neodymium motor structure. The truncated flange allows for close spacing of drivers, especially important in MTM designs.

Crossover:  The crossover was design by Vance Dickason for a MTM configuration; I used a TMM configuration. I choose the TMM config because I wanted the tweeter at my wife’s ear level and an MTM would make the cabinet too tall for my taste. For their purpose, the TMM still works. There was a small measurment error. The tweeter is way too high. The proper location for the tweeter actually is right between the woofers, so with this size cabinet, an MTM would have been indeal. Measure twice ... build once.

Starting with the 3.5” Bravox drivers, the 0.9 mH inductor and the 20uF capacitor forms a 2nd-order low-pass filter.  The 400 uF capacitor is a high-pass filter at approx. 60-Hz according to my calculations. I did try running the speakers without the high-pass (bass-blocker) and the Bravoxes do need it. I am actually thinking of raising that high-pass capacitor to be closer to 100-Hz. I think the Bravox could stand some additional bass releif.

The Tang Band tweeter has a 3rd-order high-pass filter with “amp-side" resistor for padding. The 3uF capacitor and the 3 ohm resistor in parallel with the tweeter is for impedance correction.

Simulated Frequency Response Curve:


Testing the Assembled Crossover:

Enclosure:  The enclosures are 1/2” MDF with a center brace. The veneer is curly maple. The front baffle is 1/2” solid maple. The finish is 7 coats of hand-rubbed Danish Oil. The enclosure’s size is approx. 24” tall, 5” wide and 8” deep, resulting in approx. 10-Liters of internal volume. The tweeter is positioned at my wife’s ear height when she is sitting at the computer table (she works from home). The chair must have not been adjusted correctly because the tweeter height off the table is way too high.


Back painted black (and bottom). Curly Maple veneer applied. Veneer was ordered fom  Veneer Supplies.
 
 


The top half is heavily stuffed and the bottom half is lightly stuffed with pillow stuffing from the local craft store. In the above picture, the danish oil is still wet.
 
 


Veneering method was the "cold press" method using yellow glue (Tilebond II).

Listening impressions: I have only listened in my larger living room connected to the B-Channel of my receiver. They do image very well and blend together. Right now they seem a little bright for my taste and I haven’t listened for prolonged periods of time so I can’t tell if they will be fatiguing or not. They can play clean at loud (for me) volume. I was listening to Diana Krall and did not hear the phone ring! With my subwoofer turned on and adjusted to the Bravox speakers (crossover over set at 40-Hz and volume turned way down), they have a huge sound and sound like much larger speakers. With the sub off, they are lacking they very low end and some of the warmth. Without the sub, they do sound like “smaller” speakers to me.  They are now on the computer desk and at close range, they are louder, plenty loud.

On to the next project, which is a passive sub for these guys using one Dayton 8" DVC Subwoofer using a 2" Precision Port Flared Port. They will have a built-in 2nd-order low-pass filter at 100-Hz (reuse of Kicker low-pass X-Overs).

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