Lowering Fb - how much extra port length?
Posted 29 June 2012 - 09:57 PM
I have recently built a just over 5 cu.ft enclosure (net) for 2 x subs,when I had it tested on term lab it peaked at 52 Hz, I had intended to tune it to 40 Hz. The port area is 80 sq.in , it is a slotted type of port.
When I checked the port length tonight, I realised that I failed to "measure twice cut once" rule, the port was 16 in long, but should have been 18 in long as per the manufactures specs for a 5 cubic foot box for their subs.
My question is, by making the port 18 inch long, will this tune the box to 40 Hz - or should I go longer?
I had thought about adding 2 inches to the port, then having it tested when we meet again here in WA, then if that's not quite right, add another 2 inches etc etc till it's around 40 Hz?
Anyone got a quicker way to calculate the port length rather than trial and error?
Posted 29 June 2012 - 10:01 PM
Posted 29 June 2012 - 10:31 PM
As Sam mentioned, you're probably finding your cabin frequency, not enclosure frequency.
Posted 30 June 2012 - 05:52 AM
How are you deciding on a tuning frequency of 40Hz? I agree with the others, your cabin is probably peaking at 52Hz. If it's purely an SPL box, tune it up a bit.
I'd guesstimate that if you tune for 48Hz~ it'll fit in nicely with your cabin peak around 52Hz. That results in a port length of 10in.
Edited by TMM, 30 June 2012 - 06:07 AM.
Posted 07 July 2012 - 10:34 PM
today I got to run my 2 x Alpine subs in my car on termlab, they peaked at 42 Hz.
My 2 x AQ subs peaked at 52 Hz.
Sam amp, same car , same sensor location for the term lab..............what does this tell me about my cabin frequency ?
I will trying a 3 sub combination in the coming weeks.