Normal
You don't want it as close as 1-2cm from the back wall, that will likely throw the tuning off and possibly cause it to choke up at higher volume. The rough rule of thumb is to keep the end of the port at least one diameter away from any other surface in the box to avoid problems like that.Shortening the port would raise its tuning frequency. That would raise the frequency at which you have minimum excursion (& cooling), possibly putting it further into the band of frequencies you're using this sub for, so not a good idea.Also, all ports tend to unload below the tuning frequency - this means they allow much more excursion, without providing any acoustic gain - we definitely don't want this occurring within the operating band of the sub as distortion will rise at the very least, with damage to the driver being a real risk too.
You don't want it as close as 1-2cm from the back wall, that will likely throw the tuning off and possibly cause it to choke up at higher volume. The rough rule of thumb is to keep the end of the port at least one diameter away from any other surface in the box to avoid problems like that.
Shortening the port would raise its tuning frequency. That would raise the frequency at which you have minimum excursion (& cooling), possibly putting it further into the band of frequencies you're using this sub for, so not a good idea.
Also, all ports tend to unload below the tuning frequency - this means they allow much more excursion, without providing any acoustic gain - we definitely don't want this occurring within the operating band of the sub as distortion will rise at the very least, with damage to the driver being a real risk too.
