Is there a way to tell if the x-max rating is one way or peak to peak?

[Umbra]

I'm trying to figure out the minimum port diameter needed for some subs (as per this thread: http://www.caraudio.com/forums/advanced-sql-spl-discussion/617972-geting-proper-port-area.html) and I'm not sure if the ratings on the datasheets define x-max as one way or peak to peak. Is there a way to tell? Do you just have to be familiar with how the brand defines it?

The particular subs I'm working with are as follows:

http://www.rockfordfosgate.com/support/knowledge.aspx?kbsrc=http://rftech.custhelp.com/cgi-bin/rftech.cfg/php/enduser/std_adp.php?p_faqid=273&p_li=&p_topview=1 (there's a data sheet once you click through)

and

15PRX12D4 - Memphis Car Audio

On a completely unrelated note: how do you account for port displacement? Is it just the physical space the port material takes up? i.e. the MDF or wood you add for a slot port, or the thin PVC or other material used in an aero.

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[UMWDawg92 10+ year member]

Most manufacturers use one way linear travel as xmax, there a few that use P-P excursion but it is usually labeled as total excursion or something similar. The one variable that is not very consistent is how the linear xmax was derived. That can make comparing xmax between manufacturers difficult unless they list which method that they use. There are only a few that do.

 

[Umbra]

Most manufacturers use one way linear travel as xmax, there a few that use P-P excursion but it is usually labeled as total excursion or something similar. The one variable that is not very consistent is how the linear xmax was derived. That can make comparing xmax between manufacturers difficult unless they list which method that they use. There are only a few that do.

Thanks.

The manual for the RF subs has a recommended box design with a 3" aero. Using the formula in the aforementioned thread the recommended minimum was about 3.6" (assuming the x-max was one way) and 5.1" (assuming it was both). So it looks like their listing is probably one way as the formula gave me a diameter closer to the one they recommend.

 

[trumpet 5,000+ posts]

Port displacement is the volume of the port material that takes away from the enclosure, plus the internal volume of the port.

 

[Umbra]

Port displacement is the volume of the port material that takes away from the enclosure, plus the internal volume of the port.

So just to double check: the volume inside the port is not part of the volume of the box and for all intents and purposes should be treated like a solid object occupying space?

 

[trumpet 5,000+ posts]

So just to double check: the volume inside the port is not part of the volume of the box and for all intents and purposes should be treated like a solid object occupying space?

yes

A port holds a column of air. The air moves back and forth as music plays. The width or area of the port depends on how much air the subwoofer can move, power applied, etc. Adding to port length reduces the tuning frequency. There's a lot more to it but that's the gist of it.

 

[big scott]

do you account for the fs of the sub when picking the box port tuning ?

do you have to keep the # close ?

 

[Umbra]

do you account for the fs of the sub when picking the box port tuning ?do you have to keep the # close ?

That's what I'm reading up on now. Take a look at this: Useful Formulas