Optimal Tune & Port Frequency/Velocity for UXL-18?
I’m planning to get four UXL-18’s with the pending AVS group-buy to build four slot port Marty type subs for a 10,000 cf room. While I wait for drivers, I’m trying to find the optimum Port Resonance and Port Velocity at the lowest efficient Tuning Frequency for my build. As I play around with WinISD and try to get a feel for different tuning and port options, I’m finding it hard to meet all the various member recommendations that appear in AVS.
SUGGESTIONS
Most people have said to push port resonance above 150 Hz to keep it out of the pass band. They have also recommended keeping the port velocity below 25 m/s to minimize chuffing. However, if I keep resonance above 150 Hz, the velocity rises above 31 m/s or more. If I push the velocity below 25 m/s, the resonance drops below 100 Hz or more. Each of these values change slightly when I adjust internal volume.
I have also read that the slot port design I’m planning to use (like the Marty subs) are much more forgiving than round ports; that a BFD or notch filter can attenuate a port resonance in the audible range without affecting the sound; and that a port velocity around 32 m/s is usually masked by the rest of the LFE in movie soundtracks. Lastly, people recommend flaring the port openings inside and outside to reduce turbulence, but this mostly relates to round ports and I don’t see how this can be applied to a Marty-style slot-port other than routing out a radius in the ¾ plywood at either end.
PARAMETERS
The theater area is open on two sides to a 10,000 cf open floor plan, so I can’t expect much room gain until about 6 Hz. Therefore, all four subs will sit behind the LP for maximum near field response. To fit my space limitations, the four UXL’s are going into two right/left rear subs at approximately 32"h 27"w 24"d and two center rear subs at approximately 32"h 32"w 21"d.
I know the UXL-18 likes between 9-12 cf to really perform, but space limitations keep me around 8 cu ft . Although the UXL-18 is rated at 1200w RMS, most people feed it 2000w RMS and using a HPF to keep cone excursion below the UXL-18’s Xmax of 45mm. LTD02 has recommended that I build all four subs at the identical tune. He also wrote that as long as the port area, port length and box internal volume remain the same, different cabinet configurations will match at the same tuning frequency.
I’m planning to get four UXL-18’s with the pending AVS group-buy to build four slot port Marty type subs for a 10,000 cf room. While I wait for drivers, I’m trying to find the optimum Port Resonance and Port Velocity at the lowest efficient Tuning Frequency for my build. As I play around with WinISD and try to get a feel for different tuning and port options, I’m finding it hard to meet all the various member recommendations that appear in AVS.
SUGGESTIONS
Most people have said to push port resonance above 150 Hz to keep it out of the pass band. They have also recommended keeping the port velocity below 25 m/s to minimize chuffing. However, if I keep resonance above 150 Hz, the velocity rises above 31 m/s or more. If I push the velocity below 25 m/s, the resonance drops below 100 Hz or more. Each of these values change slightly when I adjust internal volume.
I have also read that the slot port design I’m planning to use (like the Marty subs) are much more forgiving than round ports; that a BFD or notch filter can attenuate a port resonance in the audible range without affecting the sound; and that a port velocity around 32 m/s is usually masked by the rest of the LFE in movie soundtracks. Lastly, people recommend flaring the port openings inside and outside to reduce turbulence, but this mostly relates to round ports and I don’t see how this can be applied to a Marty-style slot-port other than routing out a radius in the ¾ plywood at either end.
PARAMETERS
The theater area is open on two sides to a 10,000 cf open floor plan, so I can’t expect much room gain until about 6 Hz. Therefore, all four subs will sit behind the LP for maximum near field response. To fit my space limitations, the four UXL’s are going into two right/left rear subs at approximately 32"h 27"w 24"d and two center rear subs at approximately 32"h 32"w 21"d.
I know the UXL-18 likes between 9-12 cf to really perform, but space limitations keep me around 8 cu ft . Although the UXL-18 is rated at 1200w RMS, most people feed it 2000w RMS and using a HPF to keep cone excursion below the UXL-18’s Xmax of 45mm. LTD02 has recommended that I build all four subs at the identical tune. He also wrote that as long as the port area, port length and box internal volume remain the same, different cabinet configurations will match at the same tuning frequency.
Granted you'd probably hear the coil slamming against the backplate first, but why chance it?
