I'm trying to make a resistive port cardioid woofer similar to a D&D 8c. The frequency response of the woofer will be limited to 150-400Hz. There will be a rear facing subwoofer operating below and mid-range horn above. I'm using a Hypex DLCP digital crossover and N-core amps.
I've read the many relevant threads here and have built and tested one cabinet. I used a Beyma 12BR70 woofer (it's what I had). The port area is 40% of the driver SD and I used Melamine foam and Acoustistuff to fill the cabinet. So far I've reached a 12dB front to back difference. With EQ to boost below 150Hz it doesn't look to bad.
To get more attenuation of the rearward wave do I need more output from the vents or less? Or, do I need to slowdown (delay) the sound going out of the vents with a different ratio of foam/stuffing?
I'm going to build a second test cabinet tomorrow with a larger port volume and with the ports located closer to the back wall of the cabinet. I'll post the results.
The attached ground plane measurements were taken at 0 and 180 degrees with the mic 2M from the box.
I've read the many relevant threads here and have built and tested one cabinet. I used a Beyma 12BR70 woofer (it's what I had). The port area is 40% of the driver SD and I used Melamine foam and Acoustistuff to fill the cabinet. So far I've reached a 12dB front to back difference. With EQ to boost below 150Hz it doesn't look to bad.
To get more attenuation of the rearward wave do I need more output from the vents or less? Or, do I need to slowdown (delay) the sound going out of the vents with a different ratio of foam/stuffing?
I'm going to build a second test cabinet tomorrow with a larger port volume and with the ports located closer to the back wall of the cabinet. I'll post the results.
The attached ground plane measurements were taken at 0 and 180 degrees with the mic 2M from the box.
Attachments
^Resistance could be quite okay already and nothing needs to be done. 180 deg alone should not be used for evaluating directivity because it's quite insignificant in theory and practice. For example hyper-cardioid has just 6 dB attenuation to 180 deg though is has the highest directivity index in group of basic gradients.
Your design looks super-cardioid having about 10 dB attenuation to 180 deg, but it's not sure until you verify total directivity by measuring e.g. 0, 30, 60, 90, 120, 150 and 180 deg and calculating directivity index. VituixCAD can do calc. Super-cardioid is the best target imo. Targeting maximum attenuation to 180 deg probably leads to worse result.
Your design looks super-cardioid having about 10 dB attenuation to 180 deg, but it's not sure until you verify total directivity by measuring e.g. 0, 30, 60, 90, 120, 150 and 180 deg and calculating directivity index. VituixCAD can do calc. Super-cardioid is the best target imo. Targeting maximum attenuation to 180 deg probably leads to worse result.