In the first part i presented some of the woodwork on the satellite speakers and a first schematic of the crossover. These days i had time to finish the front baffles, made the edges round, cover the speaker with dark colored carpet and install the drivers and crossover for testing and voicing.
The rounding of the baffle’s edges is done using a 8mm round-over bit on the router. Make sure you get the board fixed so that u can push the router in the edge.
Once this is done i applied the first layers of black paint and glued the baffle on the rest of the cabinet. While i was waiting for it to dry i carpeted the back plate. When you chose to use carpet it’s a good idea to install the back plate a little inside the cabinet and this way to leave an edge. This will allow you to glue the carpet and not leave any visible marks at the joints. After the back plate the sides, top and bottom will be carpeted in one piece.
The front baffle was cut with 3mm more on each side so that the carpet would go right at the same level
The satellite speakers are almost done at this point, it is time to install everything inside for the first tests. I chose to fill the cabinet about 70 to 80 % with wool and this way lower the total Q of the speaker to somewhere around 0.8. This can be a high value but since i will use active filter on the subwoofer matching will be easier. The first version of the crossover network was done in air just for testing. It seems the waveguide gain was slightly higher than expected so the initial L-pad had to be changed. Also the cut frequency was little too high for the tweeter. Since i wanted the option of bi-amping i decided to add a tweeter protection circuit i had in my schematics notebook which I’ve seen used in some professional speakers. After these changes in crossover came another session of listening tests. There was still a part in the upper midrange (voice sibilance) i found to be too emphasized. Adding a resistor of about 1.5ohms in series with the inductor in the high pass filter lowered the Q and smooth the sound.
In the last picture you can see the Zobel network which is an impedance equalization
These are 2nd order filters so you need to reverse polarity of the tweeter, connect the plus of the tweeter to the minus of the filter and vice versa. Otherwise you will have a big dip in the frequency response caused by the phase shift of the filters. Another thing to be careful about is not to connect ground of the high pass and low pass filters if you’re using bi-amp connector. The strap at the connector takes care of that. The radiator i used on the TIP transistors may be an overkill but better safe than sorry.
I did an experiment with a baffle step circuit. From a certain frequency the directivity of the speaker becomes focused and this may appear as an increase in sound pressure level. A baffle step attenuates the response a little from that frequency up. Usually i don’t use it for i didn’t find it necessary. In this case however i got better response on bass at the expense of overall efficiency. However once i will add the subwoofer to the system this circuit might not be necessary. In this case the circuit is made of a 2.7mH inductor in parallel with a 8 ohm resistor connected before the crossover. Baffle step circuit is impractical when using bi-amping though.
Here is simulated baffle step responses using Edge software:
To be continued:
– Measurement of on-axis and off-axis frequency response
– Building the subwoofer