Usable port velocity with large ports?

[mathiasb]

Hi all,

After having enjoyed my dual sealed 24"'s from Harbottle Audio for about a year now, I am toying with the idea of building ported boxes for them. For example;

• 17Hz tune, 300L (10.6 cu ft) box
• Two ports - ~150mm (6in), ~1090mm (3" 7in), pipe resonance around 90Hz
• Xmax is 38mm 1-way per mfg
• Amplifier Sinbosen FP14k - 4400W RMS / 4 ohm, per channel - 133 volts (195V peak)

I would have to add a flare (40mm / 1.6" radius or so) to the ports. It appears the max port velocity in this setup would be ~30m/s which for 6" ports does NOT work according to https://www.subwoofer-builder.com/port-flares.htm :

 

 

 

My thoughts are:

1. Increase port diameter to 170mm to get port velocity down to 25m/s - but then we have a pipe resonance around 71Hz which is getting close to audible territory - but might be OK if the subs are low passed at 60Hz (and at this SPL is it audible?...)
2. The amp has 195V peak capability apparently, that is going to blow the ports out of the box. I assume the "correct / better" approach would be to design the box and port around 160V, a bigger port which means a bigger box...

Am I on the right track? Thank you