sizing a port properly.

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People, i'm getting a bit confused. I have a 0.17cuft enclosure and hoping to tune my Tectonic Driver TEBM65 down to 59Hz, which i dont quite understand what is happening.

WiniSD is telling me that i need a 1inch port 2.8inches long, but a smaller diameter gives a shorter length. Not quite understanding, does this sound right and if there any improvement on this?

I currently have some electrical conduit which measures 19.5mm hence the question. My boom box was suggested to have a 3.5inch long port with a slightly smaller (0.150cuft) box, so not sure if i'm actually reading this correctly.
 

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GM

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Joined 2003
WiniSD is telling me that i need a 1inch port 2.8inches long, but a smaller diameter gives a shorter length. Not quite understanding, does this sound right and if there any improvement on this?

That's correct, the smaller diameter vibrates at a higher frequency, so doesn't need to be as long to tune the cab to the same frequency.

The downside is that the speaker system can't handle as much power down around/at tuning [Fb], so ideally the vent should be sized based on the system's power handling.

As a general rule, the vent area needs to be at least 1/3 Sd, though WinISD can calculate vent mach, which ideally needs to be < ~17 m/sec., but I no longer remember how to do it.

GM
 
I spoke to someone on a different forum and they mentioned something similar, but aired caution on using a smaller port on it's own as it was floating around chuffing territory. The suggestion was two use twins and at 4inches in length if I wanted to up cycle that conduit. Like all time I jumped in with both feet and did one last night....fingers crossed it works lol
 
As a general rule, the vent area needs to be at least 1/3 Sd, though WinISD can calculate vent mach, which ideally needs to be < ~17 m/sec., but I no longer remember how to do it.

GM

WinISD Pro just has a tab on the drop-down menu labelled "rear port - air velocity", which gives you a graph of air velocity vs frequency.

You can adjust power input, and the graph will change accordingly.

Chris
 
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